Preventive Technologies, Research Toward a Cure, and Immune-Based and Gene Therapies

January 2014 Update

Research Toward a Cure

At the close of 2013 there was another update from Timothy Henrich about the Boston area stem cell transplant cases, revealing that the respite from HIV replication was relatively short-lived. Henrich reported in a statement that HIV viral load ultimately became detectable again in both individuals, after 12 and 32 weeks respectively.

For ongoing, regularly updated links to cure-related research information, including newly opened clinical trials, see the cure resource page at TAG’s website.

July 2013 Updates

Research Toward a Cure

Timothy Henrich has presented updated informaton on the two HIV-positive individuals from the Boston area who received stem cell transplants for cancers and have since shown a lack of detectable HIV reservoirs. At the IAS 2013 conference, Henrich reported that they have been off antiretroviral therapy (ART) for 7 and 15 weeks, respectively, and have not yet shown any sign of HIV rebound. Longer-term follow-up is needed, but it is hoped that these individuals may have been cured of HIV infection.

Sadly, there is very bad news regarding the 12-year old boy with HIV and leukemia who received a CCR5-Δ32 homozygous cord blood stem cell transplant at the University of Minnesota in Aprll of this year. On July 12, it was announced that he had died as a result of severe graft-versus host disease (resulting from his immune system attacking the transplanted cells), which is a known and significant risk associated with stem cell transplantation.

Preventive Technologies

Results from the CDC-sponsored trial of tenofovir as pre-exposure prophyalxis (PrEP) among individuals with a history of injection drug use in Thailand were published in The Lancet on June 13, 2013. TAG issued a statement in response to the publication. The CDC has also issued an updated interim guidance document regarding the use of PrEP for individuals at risk for HIV infection due to injection drug use.

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June 2013

By Richard Jefferys

Until last year, no product inching through the pipelines covered in this chapter had ever emerged into the marketplace. That changed on July 16, 2012, with the approval in the United States of the antiretroviral drug combination pill Truvada (tenofovir/emtricitabine) for preexposure prophylaxis (PrEP).¹ The labeling for the drug now notes that, in addition to its longstanding indication for HIV treatment, it is “indicated in combination with safer sex practices for preexposure prophylaxis (PrEP) to reduce the risk of sexually acquired HIV-1 in adults at high risk.”²

Consistent with the complexity that attends the topic of biomedical HIV prevention, Truvada PrEP exited the pipeline into a sea of questions and uncertainty. The overall message from the trial data is that Truvada offers a high degree of protection against HIV acquisition if taken daily as prescribed. The acceptability of the approach is less clear, and has varied in different populations. In trials where adherence was low, efficacy was not observed. The challenges associated with daily administration have led both the PrEP and microbicide fields to pursue potentially simpler strategies, such as long-acting antiretrovirals that might be given once-monthly (or less) and vaginal rings that deliver microbicides continuously for several weeks at a time.

For the HIV vaccine field, achieving the levels of efficacy observed in the most successful PrEP trials (>70% reduction in HIV acquisition risk) remains a distant dream. In 2013, the storm clouds that have lingered over the use of adenoviruses as vaccine vectors rained bad news, first with the failure of a DNA-plus-adenovirus serotype 5 (Ad5) prime-boost regimen in the only ongoing HIV vaccine efficacy trial, HVTN 505,³ and second with extended follow-up from a prior study in South Africa showing a significant enhancement of HIV risk associated with receipt of Merck’s discontinued Ad5-based HIV vaccine.⁴ Researchers and funders are now scrambling to assess whether the many other earlier-phase trials of adenovirus-based HIV vaccine vectors can safely continue.

All is not lost, however. The multi-stakeholder collaboration named the Pox-Protein Public-Private Partnership (P5) continues to work toward launching efficacy trials that will attempt to improve on the slender but significant protection against HIV infection documented in the RV144 trial in Thailand in 2009.⁵ In the sphere of basic research, evidence is emerging that it may be possible to design vaccines capable of cajoling B cells into producing broadly neutralizing antibodies against HIV, a challenge that once seemed insurmountable. Scientists are also pursuing a potential alternative, more radical strategy using an approach akin to gene therapy to deliver genes for making broadly neutralizing antibodies into muscle tissue.

The research effort to cure HIV infection achieved its highest-ever profile over the past year, garnering extensive—though not always accurate—media coverage. The ascendancy began in July 2012, just ahead of the International AIDS Conference in Washington, D.C., with the launch of the International AIDS Society’s global scientific strategy, Towards an HIV Cure.⁶ The document is essentially a lengthy scientific review describing the current understanding of the issues that will need to be addressed in order for a globally accessible cure to be developed.

An assemblage of case reports provided encouragement that a cure is possible, with the most widely publicized being that of an HIV-infected child from Mississippi said to be devoid of active virus after receiving very early antiretroviral therapy (ART) that was stopped after around 18 months.⁷ Timothy Ray Brown remains the lone adult considered cured of HIV, but two other men who received stem cell transplants for concomitant cancers have been reported to show no evidence of viral reservoirs; ART interruptions are planned in both cases to assess whether the virus returns.⁸

Researchers in France described 14 individuals treated with ART during acute infection exhibiting “post-treatment control” of viral load after lengthy periods off treatment (an average of 7.4 years).⁹ Known as the VISCONTI cohort, these individuals are not considered cured but rather in virological remission, and follow-up is continuing.

While these case reports offer hope, they all involve circumstances that are relatively unusual. When it comes to curing the vast majority of HIV-positive people—those with chronic infection, and lacking cancers requiring stem cell transplants—progress is painstaking, and significant scientific obstacles remain. Currently there are only a few preliminary trials of potential interventions ongoing, none of which is expected to cure anyone.

To a large extent, the immune-based and gene-therapy pipelines have become intertwined with the cure research agenda. Therapeutic vaccines in particular have multiple possible roles: enhancing HIV-specific immunity with the aim of improving control of HIV replication,¹⁰ stimulating the release of virus from latently infected resting CD4 T cells that are specific for HIV antigens,¹¹ and increasing the ability of HIV-specific CD8 T cells to kill latently infected CD4 T cells (after they are prompted to produce virus by latency-reversing strategies).¹² Several ongoing and planned trials intend to evaluate the ability of therapeutic vaccines to perform these tasks.

Gene therapies converge on the goal of creating CD4 T cells that are resistant to HIV, using a variety of mechanisms including disrupting expression of the HIV coreceptor CCR5. The key challenge faced by these approaches is the modification of enough cells to confer measurable benefits.

The effectiveness of ART has narrowed the pipeline of immune-based therapies (IBTs) for potential disease-management indications. There are two main areas where there might still be opportunity for adjunctive IBTs to offer benefits:

• For the subset of HIV-positive people who experience limited CD4 T-cell recovery despite viral suppression by ART (referred to as immunologic nonresponders, or INRs). The main risk factors are low CD4 T cells at the time of ART initiation and older age.¹³ INRs face a significantly increased risk of morbidity and mortality,¹⁴ which an effective IBT might conceivably be able to lessen.
• To address the subtler, residual dysregulation of the immune system that can persist in individuals on ART. Most concerning are elevated levels of inflammation, and features resembling the aging-related immunologic wear and tear seen in the elderly, such as inverted CD4:CD8 ratios and increased numbers of senescent immune cells.¹⁵

Table 1. HIV Vaccines Pipeline 2013

Agent	Class/Type	Manufacturer/Sponsor(s)	Status
ALVAC-HIV vCP1521	Canarypox vector including HIV-1 CRF01_AE Env, clade B Gag, the protease-encoding portion of the Pol gene, and a synthetic polypeptide encompassing several known CD8 T-cell epitopes from the Nef and Pol proteins	Sanofi Pasteur/U.S. HIV Military HIV Research Program (USMHRP)/National Institute of Allergy and Infectious Diseases (NIAID)	Phase IIb
pGA2/JS7 DNA + MVA/HIV62	Prime: DNA vaccine Boost: MVA vector Both including Gag, Pol, and Env genes from HIV-1 clade B	GeoVax/NIAID	Phase IIa
HIVIS 03 DNA + MVA-CMDR	Prime: HIVIS DNA including Env (A, B, C), Gag (A, B), reverse transcriptase (B), and Rev (B) genes Boost: MVA-CMDR including Env (E), Gag (A), and Pol (E) genes	Vecura/Karolinska Institutet/Swedish Institute for Infectious Disease Control (SMI)/USMHRP	Phase II
LIPO-5	Five lipopeptides comprised of CTL epitopes from Gag, Pol, and Nef proteins	Agence Nationale de Recherches sur le Sida et les Hépatites Virales (ANRS)	Phase II
VICHREPOL	Chimeric recombinant protein comprised of C-terminal p17, full p24, and immunoreactive fragment of gp41 with polyoxidonium adjuvant	Moscow Institute of Immunology/Russian Federation Ministry of Education and Science	Phase II
DNA-C + NYVAC-C	Prime: DNA vaccine including clade C Env, Gag, Pol, and Nef genes Boost: NYVAC-C attenuated vaccinia vector including clade C Env, Gag, Pol, and Nef genes	GENEART/Sanofi Pasteur/Collaboration for AIDS VaccineDiscovery (CAVD)	Phase I/II
MYM-V101	Virosome-based vaccine designed to induce mucosal IgA antibody responses to HIV-1 Env	Mymetics Corporation	Phase I/II
Ad26.ENVA.01	Prototype adenovirus serotype 26 vector including the HIV-1 subtype A Env gene	Crucell/IAVI/NIAID/Beth Israel Deaconess Medical Center/Ragon Institute of MGH, MIT and Harvard	Phase I Prime-boost phase I w/Ad35-ENVA
Ad35-ENVA	Prototype adenovirus serotype 35 vector including the HIV-1 subtype A Env gene	Crucell/IAVI/NIAID/Beth Israel Deaconess Medical Center/Ragon Institute of MGH, MIT and Harvard	Phase I Prime-boost phase I w/ Ad26.ENVA.01
Ad35-GRIN/ENV	Two adenovirus serotype 35 vectors, one including HIV-1 subtype A Gag, reverse transcriptase, integrase, and Nef genes, and the other including HIV-1 subtype A Env (gp140)	International AIDS Vaccine Initiative (IAVI)/University of Rochester	Phase I Prime-boost phase I w/GSK HIV vaccine 732461
Ad5HVR48.ENVA.01	Prototype hybrid adenovirus vector consisting of a backbone of serotype 5 with the hexon protein from serotype 48; includes HIV-1 subtype A Env gene	Crucell/NIAID	Phase I
Cervicovaginal CN54gp140-hsp70 conjugate (TL01)	HIV-1 clade C gp140 protein with heat shock protein 70 (Hsp70) adjvant, delivered intravaginally	St George’s, University of London/European Union	Phase I
DCVax + poly ICLC	Recombinant protein vaccine including a fusion protein comprising a human monoclonal antibody specific for the dendritic cell receptor, DEC-205, and the HIV Gag p24 protein, plus poly ICLC (Hiltonol) adjuvant	Rockefeller University	Phase I
DNA-HIV-PT123, NYVAC-HIV-PT1, NYVAC-HIV-PT4, AIDSVAX B/E	DNA and NYVAC vectors encoding HIV-1 clade C Gag, gp140, and Pol-Nef AIDSVAX B/E recombinant protein vaccine containing gp120 from HIV-1 clades B and CRF01_AE	IPPOX/EuroVacc/HVTN	Phase I
DNA + Tiantian vaccinia vector	DNA and recombinant Tiantian vaccinia strain vectors encoding Gag, Pol, and Env genes from HIV-1 CN54	Chinese Center for Disease Control and Prevention/National Vaccine and Serum Institute/Peking Union Medical College	Phase I
EN41-FPA2	Gp41-based vaccine delivered intranasally and intramuscularly	PX’Therapeutics/ European Commission	Phase I
GEO-D03 DNA + MVA/HIV62B	Prime: DNA vaccine with GM-CSF adjuvant Boost: MVA vector Both vaccines include Gag, Pol, and Env genes from HIV-1 clade B and produce virus-like particles (VLPs)	GeoVax/NIAID	Phase I
GSK HIV vaccine 732461	Gag, Pol, and Nef proteins in proprietary adjuvant	GlaxoSmithKline	Phase I Prime-boost phase I w/Ad35-GRIN
HIV-1 Tat/delta-V2 Env	Tat and oligomeric ΔV2 Env proteins	Istituto Superiore di Sanità/ Novartis Vaccines	Phase I
MAG-pDNA, Ad35-GRIN/ENV	Multi-antigen DNA vaccine comprising the Env, Gag, Pol, Nef, Tat, and Vif proteins of HIV-1 and GENEVAX, interleukin-12 (IL-12) pDNA adjuvant, delivered using the electroporation-based TriGrid delivery system, two adenovirus serotype 35 vectors, one including HIV-1 subtype A Gag, reverse transcriptase, integrase, and Nef genes, and the other including HIV-1 subtype A Env (gp140)	IAVI/Profectus Biosciences/ Ichor Medical Systems Incorporated	Phase I
MAG-pDNA, rVSVIN HIV-1 Gag	Multiantigen DNA vaccine comprising the Env, Gag, Pol, Nef, Tat, and Vif proteins of HIV-1 and GENEVAX, interleukin-12 (IL-12) pDNA adjuvant, attenuated replication-competent recombinant vesicular stomatitis virus (rVSV) vector including HIV-1 Gag protein	Profectus Biosciences/HVTN	Phase I
MV1-F4-CT1	Recombinant measles vaccine vector including HIV-1 clade B Gag, Pol, and Nef	Institut Pasteur	Phase I
MVA.HIVA	MVA vector including a synthetic copy of a major part of HIV’s Gag gene and 25 CD8 T-cell epitopes	Impfstoffwerk Dessau-Tornau (IDT)/ University of Oxford/Medical ResearchCouncil/ University of Nairobi/ Kenya AIDS Vaccine Initiative	Phase I in infants born to HIV-positive (PedVacc002) and HIV-negative mothers (PedVacc001)
MVA HIV-B	MVA vector including HIV-1 Bx08 gp120 and HIV-1 IIIB Gag, Pol, and Nef	Hospital Clinic of Barcelona	Phase I
PENNVAX-G DNA + MVA-CMDR	Prime: DNA vaccine including HIV-1 clade A, C, and D Env proteins and consensus Gag protein Boost: MVA-CMDR live attenuated MVA vector including HIV-1 clade CRF_AE-01 Env and Gag/Pol proteins DNA component administered intramuscularly via either Biojector 2000 or CELLECTRA electroporation device	NIAID/USMHRP/ Walter Reed ArmyInstitute of Research	Phase I
PolyEnv1 EnvDNA	Vaccinia viruses including 23 different Env genes and DNA vaccine with multiple Env genes	St. Jude Children’s Research Hospital	Phase I
pSG2.HIVconsv DNA + ChAdV63.HIVconsv, or MVA.HIVconsv	Prime: DNA vaccine pSG2 Boost: chimpanzee adenovirus vector ChAdV63 or MVA vector All contain the HIVconsv immunogen, designed to induce cross-clade T-cell responses by focusing on conserved parts of HIV-1	University of Oxford	Phase I
rAd35 VRC-HIVADV027-00-VP	Adenovirus serotype 35 vector	Vaccine Research Center, NIAID	Phase I
rVSVIN HIV-1 Gag	Attenuated replication-competent recombinantvesicular stomatitis virus (rVSV) vector including HIV-1 Gag protein	Profectus Biosciences/ HIV Vaccine Trials Network (HVTN)	Phase I
SAAVI DNA-C2, SAAVI MVA-C, subtypeC gp140/MF59	SAAVI DNA and MVA vectors encoding an HIV-1 subtype C polyprotein including Gag-reverse transcriptase-Tat-Nef and an HIV-1 subtype C truncated Env Novartis protein subunit vaccine comprising a subtype C oligomeric V2 loop-deleted gp140 given with MF59 adjuvant	South Africa AIDS Vaccine Initiative/ HVTN/Novartis	Phase I
SeV-G(NP), Ad35-GRIN	Sendai virus vector encoding HIV-1 Gag protein delivered intramuscularly or intranasally, adenovirus serotype 35 vector including HIV-1 subtype A Gag, reverse transcriptase, integrase, and Nef genes	IAVI/DNAVEC	Phase I

More Bad News for Adenovirus Vectors

In the early 2000s, there was a great deal of excitement regarding prospects for adenovirus-based vaccine vectors. Adenoviruses are common in nature, causing severe colds, and are categorized into different serotypes dependent on the types of antibody response they induce. Adenovirus serotype 5 (Ad5) was attenuated and modified for use as an HIV vaccine by Merck, and early trials showed that it effectively addressed a problem that scientists had been trying to solve for more than a decade: the reliable induction of virus-specific CD8 T-cell (also known as killer T-cell) responses in the majority of recipients. Prior to Ad5, the best results had been achieved with the ALVAC canarypox vector, which created low-level but detectable HIV-specific CD8 T cells in around 10 to 20 percent of immunized individuals.¹⁶ In stark contrast, more than 70 percent of individuals given Merck’s Ad5 candidate developed HIV-specific CD8 T-cell responses, sometimes of high magnitude.¹⁷ These immune responses were not expected to protect against HIV infection, but there was hope that they might be able to suppress the virus in vaccinated individuals who became infected.

An efficacy trial named the Step study was conducted by the HIV Vaccine Trials Network (HVTN), but had to be stopped early after a review by the Data Safety Monitoring Board (DSMB) concluded that there was no possibility of the vaccine’s proving efficacious. Further dissection of the data revealed an unwelcome surprise: a subset of vaccine recipients (those with preexisting antibody responses to Ad5) had experienced a statistically significant increase in risk of HIV infection compared with placebo recipients. Extended follow-up ultimately showed that the increase in risk was statistically significant in the overall vaccine group (hazard ratio of 1.40 for vaccine vs. placebo; P = .03), but a subset of men who have sex with men (MSM) who were circumcised and lacked preexisting antibody responses to Ad5 did not appear to be affected (hazard ratio 0.97; P = 1.0).¹⁸ Receipt of the vaccine did not alter viral-load levels or CD4 counts in Step study participants who acquired HIV.

Two other HIV vaccine efficacy trials were directly and immediately affected by the cessation of Step. HVTN 503 (also known as the Phambili trial) was a placebo-controlled assessment of the same vaccine in heterosexuals in South Africa that had only partially enrolled; immunizations were discontinued and the study arms were unblinded, with counseling provided to participants regarding the Step results. Although the study was not completed, data from the trial were published in 2011, and were consistent with the lack of efficacy observed in Step; at that juncture, however, there was no evidence that the Ad5 vaccine had enhanced the risk of HIV infection.¹⁹ A separate trial named PAVE 100 was days away from beginning at the time of the Step DSMB review, aiming to evaluate a prime-boost vaccine regimen comprising a DNA construct followed by an Ad5 vector similar to Merck’s (designed by the National Institutes of Health’s Vaccine Research Center in collaboration with GenVec, Inc.). PAVE 100 was stopped, extensively redesigned in light of the Step findings, and rechristened HVTN 505, finally getting under way in the spring of 2009.

On April 25, 2013, any hopes of Ad5’s being rehabilitated were dashed when it was announced that vaccinations in HVTN 505 were ending due to an interim DSMB review, which found that the trial would be unable to demonstrate efficacy, either in terms of preventing HIV infection or lowering viral load in participants who acquired HIV. A total of 2,494 participants were included in the efficacy analysis: 1,250 in the vaccine arm and 1,244 in the placebo group. To try to address the safety concerns raised by Step, HVTN 505 limited enrollment to Ad5 antibody-negative circumcised men and male-to-female transgender persons who have sex with men. Despite this restriction, there was a noticeable—but not statistically significant—imbalance in the number of HIV infections: a total of 41 in the vaccine group and 30 in the placebo group after a median of 15 months of follow-up. The primary efficacy analysis focused on infections that occurred after the full immunization series (week 28 onward), but this didn’t favor the vaccine either: there were 27 infections among vaccinees and 21 in placebo recipients. As with Step, vaccination had no significant effect on viral loads and CD4 T-cell counts in study participants who became infected.

On the heels of the HVTN 505 denouement came more grim tidings: during extended follow-up of participants in the Phambili trial, significantly more HIV infections occurred in vaccine compared with placebo recipients (63 vs. 37). Although the differential has to be interpreted with caution because the study was no longer blinded, and drop-out rates may have had some influence, when summed with the concerning outcomes of Step and HVTN 505, the findings bode a bleak future for adenovirus vaccine vectors. Because the mechanism for the apparent increase in HIV acquisition risk remains unclear, it is not yet certain if studies of serotypes other than Ad5 might still move forward. Sponsors of ongoing trials are currently convening meetings to discuss the issue.

Pox-Protein Public-Private Partnership (P5)

The early termination of HVTN 505 means that there are no ongoing HIV vaccine efficacy trials, and none are anticipated before 2015 at the earliest. Next in line are a suite of studies that will be conducted under the aegis of the Pox-Protein Public-Private Partnership (P5), a coalition consisting of the U.S. National Institute of Allergy and Infectious Diseases (NIAID) Division of AIDS, the Bill & Melinda Gates Foundation, the HIV Vaccine Trials Network, the U.S. Military HIV Research Program, Sanofi Pasteur, and Novartis Vaccines and Diagnostics.²⁰ The goal of P5 is to improve upon the modest protection documented in the RV144 ALVAC-HIV vCP1521/AIDSVAX B/E prime-boost trial in Thailand. Current plans include two efficacy trials to be conducted in South Africa: a traditional evaluation of a poxvirus vector/protein boost combination and a novel “adaptive” design²¹ that will allow multiple different prime-boost tandems to be assessed in a single trial. An additional efficacy trial in Thailand, in a population of MSM at high risk of HIV infection, is in the early planning stages.

The Future

Outside of the efforts of P5, it is not clear where the next candidate for an HIV vaccine efficacy trial might come from. In early-phase trials are relative newcomers to the vector armamentarium: recombinant vesicular stomatitis virus (VSV) from Profectus BioSciences,²² and recombinant Sendai virus (SeV) from DNAVEC,²³ but it remains to be seen if the immune responses induced by these candidates offer any advantages over those created by previous approaches. Also in the first phase of testing are two protein-based vaccines that aim to induce antibodies against HIV at mucosal surfaces CN54gp140 and EN41-FPA2; both have been reported to be immunogenic in animal models, but human trial data are pending.^24,25

Much of the progress that has occurred in HIV vaccine research over the past year has been in basic rather than clinical territory. Most notably, an ever-increasing number of antibodies have been identified that can neutralize a broad array of different primary HIV isolates from around the globe, and there is intense scientific focus on solving the problem of inducing similarly effective antibodies with vaccines.²⁶ Substantial support for this research comes from the Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery (CHAVI-ID) grant awarded to Duke University and the Scripps Research Institute by NIAID in July 2012.²⁷

A common feature of the broadly neutralizing antibodies (bNAbs) identified to date is that the B cells that produce them have undergone unusually extensive somatic hypermutation. Somatic hypermutation is the process by which the B cell’s antibody-producing genetic code is progressively revised as the cell undergoes repeated rounds of proliferation, leading to an increase in the affinity of the antibody for its target. The genetic code that the B cell starts out with is known as the germline sequence, and it is typically altered by around 5–15 percent to produce antibodies against common infections, whereas the range is 19–46 percent for the bNAbs against HIV. This requirement for extensive mutation appears to be connected to the unusual shapes the bNAbs must form to access hard-to-reach conserved areas of the HIV envelope (Env) protein, which are shielded by highly variable decoy targets. The key challenge for vaccine design is to stimulate a B cell with the appropriate germline sequence to start making antibodies, and then provide additional stimulation that guides the B cell along a somatic hypermutation pathway that ultimately generates a bNAb. Recent progress has included a detailed tracing of the evolution of this process in an HIV-infected individual, from the starting B cell to the somatically hypermutated bNAb-producing B cell,²⁸ and the publication of several studies identifying antigens capable of activating B cells with germline sequences that can ultimately give rise to bNAbs.^29,30,31

Two research teams are working on a more radical approach to delivering bNAbs. Both projects involve the use of adeno-associated viruses (AAVs), not as vaccine vectors but as gene-delivery vehicles that take up residence in the episome of cells and serve as long-lived bNAb-making factories. Rather than traditional vaccination, this approach resembles gene therapy, similar to the current experimental use of AAV vectors to deliver factor IX as a treatment for hemophilia B.³² The International AIDS Vaccine Initiative (IAVI) is collaborating with Phillip Johnson at the Children’s Hospital of Philadelphia on plans to launch a phase I trial of an AAV vector that encodes the bNAb PG9, while David Baltimore’s laboratory at the California Institute for Technology has published encouraging preclinical results using AAV to deliver multiple bNAbs in humanized mice³³ and also hopes to ultimately translate the approach to humans.

A far less technological method for delivering bNAbs is passive immunization, wherein the antibodies are manufactured on a large scale and given intermittently via infusion. Plans are afoot to assess whether passive immunization with bNAbs can help protect against mother-to-child transmission (MTCT) of HIV, primarily as a “test-of-concept” to ensure that the antibodies are as protective as they appear to be in laboratory and animal studies. However, the efficacy of antiretroviral therapy in preventing MTCT has led to questions about the ethics of this type of study,³⁴ and an editorial in the journal Nature Medicine has called for a rigorous
independent assessment of the issue by the Institute of Medicine prior to initiation of any trial.³⁵ TAG supports this recommendation.

On the T-cell front, macaque studies of a CMV-based vaccine vector conducted by Louis Picker’s research group at Oregon Health & Science University continue to suggest that, under some circumstances, virus-specific T-cell responses can offer a high degree of protection. Picker’s published work has shown that the vaccine consistently leads to strict control of a highly pathogenic SIV challenge virus in 50 percent of immunized macaques.³⁶ At the 2013 Conference on Retroviruses and Opportunistic Infections (CROI), Picker presented evidence that these animals actually clear the SIV infection over time—an unprecedented finding.³⁷ Analysis of the SIV-specific CD8 T-cell responses in the protected macaques has revealed two unusual and potentially important features: they target a far larger number of virus epitopes than has been seen with other vaccines, and in many cases recognize their targets via a pathway that was thought to only be used by CD4 T cells (the major histocompatibility complex class II pathway).³⁸ Although there are some concerns as to whether CMV can be rendered safe enough to use as an HIV vaccine vector in humans, this research is shedding new light on the type of T-cell response vaccines need to induce in order to be effective.

Table 2. PrEP and Microbicides Pipeline 2013

Agent	Class/Type	Manufacturer/Sponsor(s)	Status
dapivirine vaginal ring	Reverse transcriptase inhibitor	International Partnership for Microbicides/ Microbicide Trials Network	Phase III
Viread (tenofovir)	Nucleotide reverse transcriptase inhibitor	Gilead Sciences/NIAID/CDC	Phase III
tenofovir gel	Nucleotide reverse transcriptase inhibitor	CONRAD/CAPRISA/South Africa Department of Science Technology/South Africa National Department of Health/USAID/Bill & Melinda Gates Foundation	Phase III Phase II
Truvada (tenofovir/emtricitabine) (intermittent dosing)	Combined nucleoside and nucleotide reverse transcriptase inhibitors	ANRS/HIV Prevention Trials Network	Phase III Phase II
maraviroc, maraviroc + emtricitabine, maraviroc + emtricitabine and tenofovir	CCR5 inhibitor	HIV Prevention Trials Network	Phase II
dapivirine (TMC120) gel	Reverse transcriptase inhibitor	International Partnership for Microbicides	Phase I/II
maraviroc (standard or reduced-dose in women)	CCR5 inhibitor	Emory University	Phase I
maraviroc + dapivirine vaginal ring	CCR5 inhibitor, reverse transcriptase inhibitor	International Partnership for Microbicides/Microbicides Trials Network/NIAID/NIMH	Phase I
maraviroc vaginal ring	CCR5 inhibitor	International Partnership for Microbicides/Microbicides Trials Network/NIAID/National Institutes of Mental Health (NIMH)	Phase I
rilpivirine long-acting (RPV-LA)	Non-nucleoside reverse transcriptase inhibitor, long-acting injectable formulation	St Stephens AIDS Trust/ Janssen Pharmaceuticals	Phase I
tenofovir gel (rectal formulation)	Nucleotide reverse transcriptase inhibitor	Microbicides Trials Network	Phase I
UC-781 (vaginal and rectal gels)	Reverse transcriptase inhibitor	Biosyn	Phase I
Vaginal tablets containing tenofovir and/or emtricitabine	Nucleoside and nucleotide reverse transcriptase inhibitors	CONRAD	Phase I

Preexposure Prophylaxis (PrEP)

The approval of Truvada for PrEP in the United States has largely shifted the drug out of the pipeline and into the realm of implementation or operational research. A number of demonstration projects are getting under way to evaluate Truvada PrEP in the real world (described in detail in the 2012 AVAC report Achieving the End: One Year and Counting³⁹), and there are community-based educational efforts such as the AIDS Foundation of Chicago’s “My PrEP Experience” project.⁴⁰ A formal guidance document for clinicians is due to be released by the U.S. Centers for Disease Control and Prevention later this year.

Truvada’s approval was based on positive results from three large trials: iPrEx, conducted among 2,470 MSM and 29 transgender women at high risk of HIV infection (primarily in Peru and Ecuador, with some participants from Brazil, the United States, South Africa, and Thailand);⁴¹ Partners PrEP, which recruited 4,758 serodiscordant heterosexual couples in Uganda and Kenya;⁴² and CDC TDF2, involving 1,219 men and women in Botswana.⁴³ But the FEM-PrEP trial, which enrolled 2,120 women in Kenya, Malawi, South Africa, and Tanzania, did not show efficacy.⁴⁴ Additionally, in March 2013, it was announced that the VOICE study—a multi-arm randomized comparison of Truvada, tenofovir, or tenofovir gel versus placebo that recruited 5,029 women in South Africa, Uganda, and Zimbabwe—found no significant reduction in HIV incidence in participants assigned to Truvada PrEP.⁴⁵

The major factor that has emerged to account for the conflicting results is adherence; analyses of the iPrEx and Partners PrEP trials indicate that among Truvada recipients with detectable levels of tenofovir, protective efficacy was 92% and 90%, respectively (higher than the reported Truvada efficacy results in the overall trial populations: 44% and 75%).⁴⁶ In the FEM-PrEP and VOICE trials, drug-level testing indicated that less than 40% of participants were taking the drug regularly. Another suggested contributor to differential efficacy in men and women is lower drug penetration into vaginal tissues;⁴⁷ however, an analysis of women in the Partners PrEP trial at the highest risk of HIV infection found that protection was equivalent to that observed in the study as a whole.⁴⁸

The varying adherence to Truvada PrEP has highlighted the need for approaches that are more broadly acceptable among populations at risk for HIV infection. Particular focus is now being placed on next-generation PrEP candidates that can be dosed intermittently or as needed, rather than daily, in the hope of providing more convenient and user-friendly means of achieving protection. A phase I study of a long-acting formulation of the non-nucleoside reverse transcriptase inhibitor rilpivirine (RPV-LA), which may allow for monthly or quarterly dosing, has offered encouragement that such approaches might be feasible.⁴⁹ More recently, a macaque study of a long-acting injectable version of an integrase inhibitor, GSK744LAP, has demonstrated protective efficacy against intrarectal virus challenges; the investigators believe that, like RPV-LA, the drug might be given as infrequently as four times a year.⁵⁰ A phase I study involving HIV-negative volunteers is exploring the pharmacokinetics and safety of RPV-LA combined with GSK744LAP, though it is unclear if this regimen will be explored in PrEP efficacy studies.⁵¹  

The CCR5 inhibitor maraviroc, an approved HIV treatment, is being evaluated as a possible novel PrEP agent in an ongoing phase II trial conducted by the HIV Prevention Trials Network (HPTN).⁵² But the potential of the drug for this indication has been called into question by a study in macaques, which found that it failed to protect against intrarectal SHIV162p3 challenges despite high concentrations in rectal tissue.⁵³ Administration of maraviroc also caused an unanticipated increase in the percentage of CCR5-expressing T cells in the blood, leading the researchers to note that “the implications of these immunological effects on PrEP with MVC [maraviroc] require further evaluation.”

Microbicides

As with PrEP, the acceptability of microbicides has been affected by the downsides of frequent product administration, leading to the prioritization of approaches amenable to intermittent application. The International Partnership for Microbicides (IPM) is leading the way with a vaginal ring that delivers the antiretroviral dapivirine for four weeks before it needs replacing. The dapivirine ring is now being tested in two efficacy trials: the IPM-sponsored Ring Study, involving 1,650 women at sites in South Africa, Rwanda, and Malawi, and ASPIRE, led by the Microbicide Trials Network (MTN), which aims to recruit 3,476 women in Malawi, South Africa, Uganda, Zambia, and Zimbabwe.

Tenofovir gel—which reduced risk of HIV acquisition by 39 percent in the CAPRISA 004 study,⁵⁴ but did not prove efficacious in the VOICE trial⁵⁵—is the subject of two ongoing trials in South Africa: FACTS 001, a confirmatory efficacy trial in 2,200 women, and CAPRISA 008, a randomized study of the feasibility of delivering tenofovir gel to women who participated in CAPRISA 004 via family planning clinics compared with research clinics.⁵⁶

Analyses of tissue drug levels in CAPRISA 004 have echoed results from PrEP trials, revealing a correlation between the presence of drug and protective efficacy.⁵⁷ But follow-up studies have also highlighted another contributor to diminished microbicide activity: inflammation, measured both in the genital tract⁵⁸ and systemically.⁵⁹ These findings add to the evidence that immunomodulators capable of dampening inflammation—such as glycerol monolaurate, which has already shown potential in the macaque model⁶⁰—deserve evaluation in human trials, and may be able to play a valuable adjunctive role combined with antiretroviral approaches.

A rectal formulation of tenofovir gel is making progress through the pipeline; safety results from a phase I trial have been published,⁶¹ and the MTN is now planning to launch a larger phase II evaluation.

CONRAD has developed vaginal tablet formulations of tenofovir, emtricitabine, and tenofovir/emtricitabine (the combination contained in Truvada); a phase I study is under way to assess the safety, pharmacokinetics, pharmacodynamics, and disintegration time of the tablets.⁶²

Table 3. Research Toward a Cure 2013

Clinical Trial	ClinicalTrials.gov Identifier(s)	Manufacturer/Sponsor(s)
ACE inhibitors	NCT01535235	University of California, San Francisco/amfAR
Allogeneic transplant in individuals with chemotherapy-sensitive hematologic malignancies and coincident HIV infection (BMT CTN 0903)	NCT01410344	National Heart, Lung, and Blood Institute (NHLBI)/National CancerInstitute (NCI)/Blood and MarrowTransplant Clinical Trials Network
Alpha interferon intensification	NCT01295515	NIAID
ChAdV63.HIVcons, MVA.HIVconsv vaccines	NCT01712425	IrsiCaixa/Fundació Lluita contra la SIDA/Hospital Clinic of Barcelona/ HIVACAT/University of Oxford
disulfiram (Antabuse)	NCT01286259 (closed to enrollment)	University of California, San Francisco/the Johns Hopkins University
DNA/Ad5 HIV vaccine, ART intensification	NCT00976404 (closed to enrollment)	Vical/GenVec/U.S. National Institutes of Health (NIH) Vaccine Research Center/Objectif Recherche VACcin Sida (ORVACS)
Dual anti-HIV gene transfer construct	NCT01734850	Calimmune
Genetically modified peripheral blood stem cell transplant in treating patients with HIV- associated non-Hodgkin’s or Hodgkin’s lymphoma	NCT01769911	Fred Hutchinson Cancer Research Center
Intravenous Ig in primary HIV infection	No ID yet. Study name: CHERUB 001	CHERUB (Collaborative HIV Eradication of viral Reservoirs: UK BRC)
panobinostat	NCT01680094 (closed to enrollment)	University of Aarhus/Massachusetts General Hospital/Monash University/Karolinska Institutet/Novartis
Prime-boost therapeutic vaccine (MAG-pDNA, rVSVIN HIV-1 Gag)	NCT01859325	NIAID/Profectus Biosciences
Redirected MazF-CD4 autologous T cells for HIV gene therapy (MazF-T)	NCT01787994	Takara Bio/University of Pennsylvania
SB-728-T, autologous CD4 T cells genetically modified at the CCR5 gene by zinc finger nucleases	NCT01543152 (with cyclophosphamide) NCT01044654 NCT00842634 (closed to enrollment) NCT01252641 (closed to enrollment)	Sangamo BioSciences
Tat Oyi vaccine	NCT01793818	Biosantech
vorinostat (SAHA)	NCT01319383 NCT01365065 (closed to enrollment)	Merck/University of North Carolina at Chapel Hill/NIAID/Bayside Health

Defining what constitutes the cure-research pipeline inevitably involves some subjective judgments; for the purposes of this report, we have included trials evaluating the impact of interventions on the latent HIV reservoir, as well as new studies looking to create HIV-resistant immune cells or induce immunologic control of viral replication. The latter two goals have historically been pursued by gene therapies and therapeutic vaccines, respectively, before the term “cure research” came into widespread usage, so there is some overlap with those pipelines (listed in tables 4 and 5).

The Mississippi Child

The most widely publicized scientific developments in the field over the past year have related to evidence from case reports that a cure is possible. Chief among them is the case of a child in Mississippi who may have been functionally cured of HIV infection, presented at the 2013 CROI by Deborah Persaud from the John Hopkins University.⁶³ The context is unusual in that the child’s mother was not diagnosed with HIV until in labor, precluding the use of prophylaxis against mother-to-child transmission. Separate HIV DNA and RNA tests at 30 and 31 hours after birth indicated that the baby had acquired infection in utero. Prior to the test results’ becoming available, the treating clinician—Hannah Gay from the University of Mississippi Medical Center—initiated a combination ART regimen at treatment rather than prophylactic doses due to the high risk of infection.

This judgment call was shown to be correct when the diagnostic results came in, and subsequent sequential viral-load tests documented the stepwise decline typical of the response to ART (the initial reading was 19,812 copies/mL, followed by 2,617 copies/mL, 516 copies/mL, 265 copies/mL, and then below the limit of detection of 48 copies/mL).

ART was continued for around 18 months, but the mother and child were then lost to care. Upon their return five months later, it transpired that ART had been discontinued. Gay performed new viral-load tests, expecting to observe the typical rebound, but surprisingly HIV RNA remained undetectable. This prompted Gay to contact Katherine Luzuriaga at Massachusetts General Hospital, an expert in pediatric HIV research, who in turn contacted Persaud (who was lead author on the first paper to describe the latent HIV reservoir in children⁶⁴). In collaboration with several other laboratories, the researchers searched for HIV DNA and RNA in samples taken at 24 and 26 months of age. Only a minority of the samples showed trace amounts of viral genetic material, at the borderline of the limit of detection of the assays. Persaud looked for replication-competent virus in 22 million resting CD4 T cells using a viral outgrowth technique—the gold-standard approach for measuring the latent HIV reservoir—but the results were negative. HIV-specific antibody and T-cell responses were also not detected.

Based on these results, the research team concluded that the case is best defined—at least tentatively—as a functional cure: some trace amounts of HIV may be present, but no active virus is evident, and the child has remained off ART for over 10 months and counting. A number of scientists not involved in the studies expressed skepticism and tried to offer alternative interpretations of the data. Among the suggested possibilities were that the viral RNA and DNA detected in the infant came from maternal cells that would have been cleared anyway, or that HIV infection had not been established and ART acted as prophylaxis rather than treatment, or that the infant might have spontaneously cleared the virus without treatment (a phenomenon that several studies published in the 1990s claimed to have documented, albeit rarely^65,66,67).

None of these scenarios seem likely based on the evidence in the scientific literature: the number of HIV-infected maternal cells that would have to have been transferred in order to account for the viral-load readings would be physiologically implausible, and there are no published data supporting the idea that HIV DNA and RNA from maternal cells are detectable in exposed infants who turn out to be uninfected. Similarly, studies of large numbers of infants receiving ART prophylaxis after birth—including those born to HIV-positive mothers who did not receive prophylaxis themselves—do not offer evidence of detectable HIV DNA and RNA readings followed by an absence of infection.^68,69 Lastly, the reports of transient HIV infection in infants that were published in the 1990s were questioned by a paper published by Lisa Frenkel and colleagues in Science in 1998,⁷⁰ which evaluated several cases and showed that they were explained by problems such as PCR contamination and sample misattribution. Frenkel’s study laid out criteria for formally proving transient HIV infection in infants, and it is notable that no cases have since been reported.

The implications of Persaud’s report for the broader field are still being discussed. The most commonly mentioned hypotheses to explain the outcome are that very early ART prevented the establishment of a latent HIV reservoir, or that the reservoir is shorter-lived in a person so young and was eliminated before treatment was interrupted. The pediatric HIV trials network IMPAACT is planning trials to assess whether the apparent cure can be duplicated in other HIV-infected neonates by providing immediate ART. Another avenue of research suggested by the case is the study of HIV reservoirs in perinatally infected individuals who were treated early with ART and have remained on therapy long-term. Katherine Luzuriaga presented a poster at CROI showing that, in five such individuals, replication-competent HIV could not be detected, viral DNA levels were low, and viral RNA was below the limit of detection of a sensitive assay (<2 copies/mL) in four out of the five.⁷¹ Based on these results, Luzuriaga noted that, “perinatally infected youth with marked curtailment of HIV reservoirs following early therapy are prime candidates for interventions to achieve functional cure or eradication.”⁷² That statement perhaps also captures the clearest message from the Mississippi case: pediatric and adolescent HIV-infected populations, who face the greatest burden of lifelong ART, must be included in the cure research agenda.

Duplicating the Case of Timothy Brown

At the current time, Timothy Ray Brown remains the only adult considered cured of HIV infection. Last year, the presentation of results from an intensive search for HIV in his body generated some controversy when three of the laboratories involved detected trace amounts of viral genetic material in a minority of samples. The study has since been published in the open-access journal PLoS Pathogens and, while the authors highlight the difficulty of formally proving a cure using assays that are operating at the limits of their sensitivity, they also state unequivocally that “the absence of recrudescent HIV replication and waning HIV-specific immune responses five years after withdrawal of treatment provide proof of a clinical cure.”⁷³ Further evidence to support this conclusion was presented at the 2013 CROI by Joyce Sanchez from the University of Minnesota, who showed that the amount of fibrosis—scarring damage caused by immune activation in HIV infection—in Brown’s gut-associated lymphoid tissue was comparable to a group of HIV-negative controls (6.8% vs. 7%), and far lower than that observed in infected individuals, even those controlling viral load in the absence of ART (15.9%).⁷⁴

Efforts to duplicate the outcome achieved in Brown in other people with HIV in similar circumstances—a diagnosis of concomitant cancer requiring stem cell transplantation as part of the treatment—are continuing. Gero Hütter, the hematologist responsible for treating Brown with adult stem cells from a donor homozygous for the CCR5-Δ32 mutation (which abrogates expression of the HIV coreceptor CCR5), has identified other potential candidates, but so far has not been able to attempt the same procedure (largely due to difficulties identifying an appropriate stem cell donor).⁷⁵ A trial in the United States that will attempt to identify CCR5-Δ32 homozygous adult stem cell donors for HIV-positive people with hematologic malignancies (BMT CTN 0903; see table 3) remains ongoing.

Cord Blood Stem Cell Transplantation

Researchers are also pursuing the possibility of using cord blood stem cells from CCR5-Δ32 homozygous donors; a company called StemCyte has led an effort to screen banked cord blood units for the mutation in order to facilitate this work.⁷⁶ At the 2013 CROI, a poster presentation described the outcome of two cases in which the aim was to employ these cells:⁷⁷ one individual in the Netherlands with progressive myelodysplastic syndrome received the CCR5-Δ32 homozygous cord blood stem cell transplant but died shortly afterward from severe pneumonia and a relapse of the cancer. In a second case in Madrid involving an individual with Burkitt’s lymphoma, there was concern about the viability of the CCR5-Δ32 homozygous cord blood stem cells,⁷⁸ and cells from a donor lacking the mutation were used instead. The cancer is in remission, but the individual remains on ART and still has a low-level but detectable HIV reservoir.

The newly formed European HIV Cure and Transplant Consortium (EHCTC) plans to continue seeking opportunities to provide CCR5-Δ32 homozygous cord blood stem cells to HIV-positive people requiring transplants. In the United States, a team led by John Wagner at the University of Minnesota has recently administered a CCR5-Δ32 homozygous cord blood stem cell transplant to a 12-year-old boy with leukemia and HIV, in the hope of curing both diseases. The procedure took place on April 23, 2013, and information regarding the outcome is not likely to be available for several months.⁷⁹

Two cases involving stem cell transplantation that drew media attention last year were presented by Timothy Henrich from Massachusetts General Hospital at the International AIDS Society (IAS) “Towards an HIV Cure” symposium in Washington, D.C., in July 2012,⁸⁰ and subsequently published in the Journal of Infectious Diseases.⁸ Henrich studied two people with HIV and cancer diagnoses who were originally heterozygous for CCR5-Δ32, but received successful stem transplants from donors lacking the mutation. ART was maintained throughout the procedures and continued afterward. Both individuals experienced periods of graft-versus-host disease (GVHD) that resolved with treatment. After 21 and 42 months of follow-up, respectively, neither has detectable levels of HIV DNA, RNA, or replication-competent virus in peripheral blood mononuclear cells, CD4 T cells, or plasma. Henrich and colleagues are planning careful ART interruptions to assess if HIV levels rebound. The outcome of these studies may help shed light on which factors were important in achieving a cure in Timothy Ray Brown.

The VISCONTI Cohort

Another widely discussed presentation at the IAS symposium—given by Asier Sáez-Cirión from the Institut Pasteur—described the VISCONTI cohort, a group of 14 HIV-positive individuals in France who received ART soon after acquiring infection, but later stopped (after a median time on treatment of three years) and have maintained undetectable or extremely low viral loads ever since (currently, a median of 7.4 years). Although some media stories have characterized members of the cohort as examples of a functional cure, Sáez-Cirión and colleagues are more circumspect, and refer to the outcome as “long-term virological remission.”⁸¹ Analyses to date suggest a number of potential contributing factors: low levels of HIV infection in long-lived central memory CD4 T cells, low levels of T-cell activation and, possibly, the extended duration of ART compared with some other studies of acute HIV infection treatment. HIV-specific CD8 T-cell responses in the VISCONTI cohort are generally weak, and participants lack the favorable HLA alleles that have been associated with control of viral replication in elite controllers. In fact, HLA alleles that have been associated with more rapid progression in untreated HIV infection appear to be overrepresented. Additional studies are ongoing, with the goal of extracting lessons to guide the development of therapies capable of promoting control of HIV in the absence of ART.

HDAC Inhibitors and Toll-Like Receptor Agonists

HDAC inhibitors remain the lead compounds for awakening long-lived latent HIV reservoirs. Results from a phase I trial of the HDAC inhibitor vorinostat were presented at the 2013 CROI by Sharon Lewin from Monash University in Australia.⁸² A total of 20 participants on ART received 14 days of the drug, and a significant increase in cell-associated HIV RNA expression of close to threefold was documented (consistent with the drug prompting at least some latently infected cells to start actively transcribing viral RNA). These results appear congruent with those in the single-dose trial of vorinostat published by David Margolis’s research group in 2012.⁸³ HIV DNA levels did not change, however, indicating that additional approaches will likely be needed to kill latently infected cells even if HIV RNA expression is successfully stimulated.

In Denmark, Ole Søgaard and colleagues at Arhus University Hospital are conducting a phase I evaluation of the effects of the HDAC inhibitor panobinostat on latent HIV,⁸⁴ after finding it to be highly active in vitro.⁸⁵ Preliminary results are due to be presented at the June 2013 “Towards an HIV Cure” symposium in Kuala Lumpur. Unfortunately, the trial became the subject of intense and extremely misleading media hype after a journalist for the U.K. newspaper the Daily Telegraph wrote that the scientists were “on brink of HIV cure.”⁸⁶ The article was eventually corrected after considerable outcry from activists and the issuance of a correction by Arhus University Hospital.⁸⁷

The same group of researchers has identified a potential complementary immune-modulating strategy that may help prompt elimination of latently infected cells: a compound that stimulates Toll-like receptor 9 (referred to as a TLR9 agonist). TLRs are a family of cell receptors involved in the recognition of pathogenic organisms, and the TLR9 agonist CPG 7909 has been studied in people with HIV as an adjuvant to improve immune responses to a pneumococcal vaccine.⁸⁸ The Danish researchers used samples from this trial to conduct an unplanned, exploratory analysis of the effects of CPG 7909 on the latent HIV reservoir, finding that it was associated with a significant reduction in HIV DNA that correlated with increases in markers of improved CD8 T-cell function.⁸⁹ Further studies are now in the works.

Gilead Sciences is considering a similar dual approach against HIV latency: the HDAC inhibitor romidepsin, which has shown potency in vitro,⁹⁰ and a TLR7 agonist (GS-9620), which is already being studied in humans as a candidate hepatitis B therapeutic.⁹¹ The AIDS Clinical Trials Group (ACTG) is currently collaborating with Gilead to plan a phase I trial of romidepsin.

There are, however, some clouds on the HDAC inhibitor horizon. At the 2013 CROI, Anthony Cillo from the laboratory of John Mellors at the University of Pittsburgh presented evidence that vorinostat only induces HIV expression by a small fraction of latently infected CD4 T cells,⁹² raising the possibility that the approach may leave a significant proportion of the viral reservoir unperturbed. The data suggest that a variety of mechanisms may be involved in HIV latency, not all of which can be reversed by HDAC inhibition—underscoring the importance of pursuing combination approaches to address the problem.

SB-728-T

Trials of Sangamo BioSciences’ SB-728-T gene therapy—which uses zinc finger nucleases to disrupt the CCR5 gene and prevent expression of the CCR5 coreceptor on modified CD4 T cells—remain ongoing. Limited news of progress has trickled out in the past few months: at the 2013 CROI, Rafick-Pierre Sékaly presented data showing that increases in central memory CD4 T cells are the main component of the immune reconstitution that has previously been described in a study of nine immunologic nonresponders (INRs), but also that the magnitude of the reconstitution was negatively affected by baseline levels of inflammation.⁹³ At the 16th Annual Meeting of the American Society of Gene and Cell Therapy in May 2013, Dale Ando from Sangamo BioSciences revealed the interesting finding that seven of nine participants in the INR trial showed significant decreases in HIV DNA levels over 12 months of follow-up, which correlated with the proportion of detectable gene-modified CD4 T cells (the higher the number of cells, the lower the HIV DNA).⁹⁴

Ando also offered a glimpse at some data from an ongoing study in individuals heterozygous for the CCR5-Δ32 mutation. The rationale behind this work is that one of the pair of CCR5 genes that exists in cells is already nonfunctional in CCR5-Δ32 heterozygotes, leaving less work for SB-728-T to do, and potentially increasing the number of CCR5-negative CD4 T cells created by the therapy. Ando described four study participants, two of whom experienced a decline in viral load during an ART interruption and two who did not. The viral-load declines were associated with increased polyfunctional HIV-specific CD8 T-cell responses, hinting that the protection of CD4 T cells by SB-728-T may, in some cases, be able to have positive effects on other important components of the immune response. Furthermore, when looking at all SB-728-T recipients to date who have undergone an ART interruption, there was a statistically significant correlation between the estimated proportion of gene-modified CD4 T cells and reductions in viral load. Lastly, Ando reported preliminary data from a trial investigating whether transient immune suppression with the drug cyclophosphamide (Cytoxan) can improve the uptake and survival of gene-modified CD4 T cells; so far no significant impact has been observed, but results from participants receiving the highest cyclophosphamide dose are not yet available.

Emerging Gene Therapies

Two new clinical trials involving gene therapies have opened over the past year. Calimmune, a company founded by David Baltimore, has developed a dual gene therapy dubbed LVsh5/C46 (also known as Cal-1) that comprises a lentiviral vector encoding a short hairpin RNA that inhibits expression of CCR5, and a fusion inhibitor, C46 (a peptide with a mechanism of action similar to the approved fusion-inhibitor drug Fuzeon). The trial will explore the modification of both CD4 T cells and hematopoietic stem cells with LVsh5/C46; cells are harvested from study participants, modified in the laboratory, and then reinfused. Some participants will receive transient immune suppression with the chemotherapy drug busulfan to assess if this enhances the uptake of gene-modified cells.⁹⁵

Drexel University is collaborating with the Japanese company Takara Bio to conduct a trial⁹⁶ in which autologous CD4 T cells are modified with a retroviral vector encoding the MazF endoribonuclease gene.⁹⁷ The gene has been shown to strongly inhibit HIV replication in CD4 T cells in vitro.⁹⁸ A team at the Fred Hutchinson Cancer Center led by Anne Woolfrey is also employing C46 to modify hematopoietic stem cells in a pending study for individuals with HIV and non-Hodgkin’s or Hodgkin’s lymphoma requiring autologous peripheral blood stem cell (PBSC) transplants.⁹⁹

Therapeutic Vaccines

Therapeutic vaccines are the subject of separate studies in Bethesda and Barcelona. In the former, a prime-boost combination of DNA and recombinant vesicular stomatitis virus constructs developed by Profectus Biosciences will be administered to individuals treated with ART soon after acquiring HIV infection.¹⁰⁰ The protocol has generated some concern due to the inclusion of a placebo control and an ART interruption after 56 weeks; these issues are due to be discussed by the NIH’s Recombinant DNA Advisory Committee (RAC) at a meeting on June 12, 2013. The trial in Barcelona involves chimpanzee adenovirus and modified vaccinia Ankara strain (MVA) vectors, and also aims to recruit HIV-positive people treated with ART early after infection.¹⁰¹ The primary endpoint is safety, but secondary analyses will evaluate changes in HIV-specific CD8 T-cell responses—including measuring the ability of CD8 T cells to suppress viral replication in vitro—and levels of both integrated and unintegrated HIV DNA in peripheral blood. Although adenovirus-based vectors are under review in the preventive context due to the potential for enhanced acquisition risk, a study of Merck’s Ad5 HIV vaccine as a therapy did not uncover any safety issues. On the contrary, receipt of the vaccine was associated with a strong trend toward lower viral load during an ART interruption.¹⁰²

Intravenous Immunoglobulin

The National Institute for Health Research in the United Kingdom has funded a new collaborative cure research endeavor named CHERUB (Collaborative HIV Eradication of viral Reservoirs: UK BRC). The first clinical trial, CHERUB 001, is evaluating the effects of a combination of ART and intravenous immunoglobulin (IVIG) on virus reservoirs in ten people with primary HIV infection. A prior “proof of concept” study conducted at the Karolinska Institutet in Sweden reported that the addition of high-dose IVIG to ART for seven days led to a transient decline in HIV reservoirs (as measured by the viral outgrowth assay).^103,104

ART Intensification Plus IL-7

One cure-related clinical study has exited the pipeline since last year. The Eramune 01 trial investigated ART intensification with maraviroc and raltegravir, either with or without the addition of the cytokine IL-7. A total of 29 HIV-positive individuals were enrolled. No decrease in the HIV reservoir was observed in any participant. IL-7 significantly improved CD4 and CD8 T-cell numbers, consistent with previous reports, but also increased the amount of HIV DNA, likely by inducing the proliferation of latently infected CD4 T cells.¹⁰⁵ The results do not mean that IL-7 cannot benefit INRs—in whom the need to reconstitute CD4 T cells in order to prevent excess morbidity and mortality is more important than small changes in HIV DNA levels—but indicate that the cytokine is unlikely to have a role as an anti-latency agent (as was once proposed¹⁰⁶).

An overarching question for all cure research is how best to measure the HIV reservoir. Sobering results from a comprehensive, multilaboratory effort to compare currently available assays were published in February 2013.¹⁰⁷ The different techniques studied showed little to no correlation with each other or the gold-standard (but cumbersome) viral-outgrowth assay for replication-competent HIV. The explanation likely pertains to the large number of defective HIV proviruses that can be detected by PCR methods but cannot generate replication-competent viruses. The findings indicate that more work is needed to develop tests that can accurately quantify the number of latently infected cells capable of releasing infectious virus. A step in this direction has been reported by the laboratory of Robert Siliciano at the Johns Hopkins University; his team has streamlined the viral outgrowth assay to increase the speed with which it can be performed and reduce associated labor and costs.¹⁰⁸

Table 4. Immune-Based and Gene Therapies Pipeline 2013

Agent	Class/Type	Manufacturer/Sponsor(s)	Status
mesalamine (5-aminosalicylic acid)	Oral anti-inflammatory drug approved for the treatment of inflammatory bowel disease	University of California, San Francisco/ Salix Pharmaceuticals	Phase IV
Chloroquine phosphate	Antimalarial, anti-inflammatory	NIAID/ACTG	Phase II
etoricoxib	Cox-2 inhibitor, anti-inflammatory	Oslo University Hospital	Phase II
Interleukin-7 (CYT 107)	Cytokine	Cytheris	Phase II
lubiprostone	Apical lumen ClC-2 chloride channel activator	Ruth M. Rothstein CORE Center/ Chicago Developmental Center for AIDS Research	Phase II
LVsh5/C46	Dual anti-HIV gene transfer construct	Calimmune	Phase I/II
Prebiotics + glutamine	Gut microbiota modifiers	Fundación para la Investigación Biomédica del Hospital Universitario Ramón y Cajal	Phase I/II
Umbilical cord mesenchymal stem cells (UC-MSC)	Adult stem cells originating from the mesenchymal and connective tissues	Beijing 302 Hospital	Phase I//II
Gene transfer for HIV using autologous T cells	Infusions of autologous CD4 T cells modified with by a lentivirus vector encoding three forms of anti-HIV RNA:pHIV7-shI-TAR-CCR5RZ	City of Hope Medical Center/Benitec	Phase I
HLA-B*57 cell transfer	Cell infusion	NIH Clinical Center	Phase I
hydroxychloroquine	Antimalarial, antirheumatic, anti-inflammatory	St Stephens Aids Trust	Phase I
M87o	Entry inhibitor gene encoded by a lentiviral vector, introduced into CD4 T cells ex vivo	EUFETS AG	Phase I
Redirected high affinity Gag-specific autologous T cells for HIV gene therapy	Gene therapy that introduces an HIV-specific T-cell receptor into CD8 T cells and reinfuses them	University of Pennsylvania	Phase I
Redirected MazF-CD4 autologous T cells for HIV gene therapy (MazF-T)	Autologous CD4+ T cells genetically modified with a retroviral vector expressing the MazF endoribonuclease gene (MazF-T), given via intravenous infusion.	University of Pennsylvania	Phase I
SB-728-T	Autologous T-cells genetically modified at the CCR5 gene by zinc finger nucleases	University of Pennsylvania/Sangamo BioSciences	Phase I

Table 5. Therapeutic Vaccines Pipeline 2013

Agent	Class/Type	Manufacturer/Sponsor(s)	Status
Vacc-4x	Synthetic peptides from the HIV-1 Gag p24 protein + adjuvant	Bionor Immuno	Phase IIb
AGS-004	Mature dendritic cells electroporated with autologous HIV-1 RNA and CD40L RNA	Argos Therapeutics	Phase II
DCV-2	Autologous myeloid dendritic cells pulsed ex vivo with high doses of inactivated autologous HIV-1	University of Barcelona	Phase II
DermaVir patch (LC002)	DNA expressing all HIV proteins except integrase formulated to a mannosylated particle to target antigen-presenting cells	Genetic Immunity	Phase II
FIT-06, GTU-MultiHIV vaccine	DNA vaccine encoding complete sequences of HIV-1 clade B Rev, Nef, Tat, and p17/p24 proteins, and T-cell epitopes from Pol and Env proteins	FIT Biotech	Phase II
GSK HIV vaccine 732462	p24-RT-Nef-p17 fusion protein in proprietary adjuvant AS01B	GlaxoSmithKline	Phase II
HIV-1 Tat vaccine	Tat protein vaccine	National AIDS Center at the Istituto Superiore di Sanità, Rome	Phase II
VAC-3S	3S peptide from gp41	InnaVirVax	Phase I/IIa
Autologous HIV-1 ApB DC vaccine	Autologous dendritic cells pulsed with autologous, inactivated HIV-infected apoptotic cells	University of Pittsburgh	Phase I/II
DNA/MVA	DNA vaccine and an MVA vector encoding HIV-1 Gag and multiple CTL epitopes	Cobra Pharmaceuticals/Impfstoffwerk Dessau-Tornau/University of Oxford/U.K. Medical Research Council	Phase I/II
Tat Oyi vaccine	Synthetic Tat protein vaccine	Biosantech	Phase I/II
TUTI-16	Synthetic HIV-1 Tat epitope vaccine	Thymon	Phase I/II
Vacc-C5	Peptides from the C5 region of gp120	Bionor Pharma	Phase I/II
AFO-18	18 peptides representing 15 CD8 T-cell epitopes and 3 CD4 T-cell epitopes from HIV-1 in an adjuvant (CAF01)	Statens Serum Institut/Ministry of the Interior and Health, Denmark/European and Developing Countries Clinical Trials Partnership	Phase I
Autologous dendritic cell HIV vaccine	Autologous dendritic cells pulsed with conserved HIV-derived peptide	University of Pittsburgh	Phase I
ChAdV63.HIVconsv, MVA.HIVconsv	Chimpanzee adenovirus vector and MVA vector containing the HIVconsv immunogen	IrsiCaixa/Fundació Lluita contra la Sida/Hospital Clinic of Barcelona, HIVACAT/University of Oxford	Phase I
DC vaccine	Autologous dendritic cells generated using GM-CSF and interferon alpha, loaded with lipopeptides and activated with lipopolysaccharide	Baylor University/ANRS	Phase I
HIVAX	Replication-defective HIV-1 vector pseudotyped with VSV-G envelope	GeneCure Biotechnologies	Phase I
HIV-v	Lyophilized mixture of polypeptide T-cell epitope sequences	Seek	Phase I
MAG-pDNA vaccine, GENEVAX, TriGrid	Multiantigen DNA vaccine comprising the Env, Gag, Pol, Nef, Tat, and Vif proteins ofHIV-1 and GENEVAX,interleukin-12 (IL-12) pDNA adjuvant, delivered using the electroporation-based TriGrid delivery system	ACTG/NIAID/Profectus BioSciences/Ichor Medical Systems	Phase I
MAG-pDNA vaccine, rVSVIN HIV-1 Gag	Multiantigen DNA vaccine comprising the Env, Gag, Pol, Nef, Tat, and Vif proteins ofHIV-1 and GENEVAX,interleukin-12 (IL-12) pDNA adjuvant, attenuated replication-competent recombinant vesicular stomatitis virus (rVSV) vector including HIV-1 Gag protein	Profectus Biosciences/NIAID	Phase I
mRNA-transfected autologous dendritic cells	Dendritic cells transfected with vectors encoding consensus HIV-1 Gag and Nef sequences	Massachusetts General Hospital	Phase I
MVA HIV-B	MVA vector including HIV-1 Bx08 gp120 and HIV-1 IIIB Gag, Pol, and Nef	Hospital Clinic of Barcelona	Phase I
MVA.HIVconsv	MVA vector	University of Oxford/U.K. Medical Research Council	Phase I
PENNVAX-B biological: GENEVAX IL-12-4532, pIL15EAM	DNA vaccine including HIV-1 Env, Gag, and Pol, with GENEVAX IL-12 and IL-15 adjuvants	University of Pennsylvania/Drexel University	Phase I
PENNVAX-B (Gag, Pol, Env) + electroporation	DNA vaccine encoding Gag, Pol, and Env genes of HIV-1 + electroporation	Inovio Pharmaceuticals/University of Pennsylvania	Phase I
pGA2/JS7 DNA MVA/HIV62B	Prime: DNA vaccine Boost: MVA vector Both including Gag, Pol, and Env genes from HIV-1 clade B	GeoVax/AIDS Research Consortium of Atlanta/University of Alabama at Birmingham/AIDS Research Alliance	Phase I
SAV001-H	Whole-killed HIV-1 vaccine	Sumagen	Phase I

Immune-Based and Gene Therapies, and Therapeutic Vaccines

In the area of adjunctive therapies for ART, pickings are relatively slim. Several years of accumulated data—covered in past TAG pipeline reports—support the potential for IL-7 to benefit INRs, but plans to evaluate clinical efficacy in this population have yet to come to fruition.

During the past year, researchers from China have published promising-looking data regarding the ability of umbilical cord mesenchymal stem cells (UC-MSC) to promote immune reconstitution in INRs.¹⁰⁹ In a small placebo-controlled phase I trial, significant increases in naive- and central memory CD4 T cells were documented, along with declines in markers of immune activation and inflammation. Expanded studies are under way to further explore the efficacy and mechanism of the approach.¹¹⁰ However, because UC-MSC are obtained from donated fresh human umbilical cords, it is uncertain if the therapy can be made practical for large-scale use.

Concern about residual immune activation and inflammation in people on ART has prompted interest in therapies that might address one of the contributing factors: microbial translocation (the leakage of normally friendly digestive bacteria from the GI tract into the systemic circulation). A trial in Spain is investigating whether a combination of prebiotics and glutamine can improve markers of microbial translocation, inflammation, immune activation, and endothelial dysfunction—both in HIV-positive individuals on ART and those who have yet to start treatment.¹¹¹ Researchers in Chicago are planning a similar evaluation of lubiprostone, a drug that is FDA-approved for the treatment of chronic idiopathic constipation and irritable bowel syndrome with constipation.¹¹² Additional impetus for these types of studies has come from recent research in the SIV/macaque model, demonstrating that a probiotic/prebiotic combination improved gut CD4 T-cell levels and reduced inflammatory damage to GI tract lymphoid tissue.¹¹³

On the therapeutic vaccine front, salutary results were published from a study of a dendritic cell-based strategy that has been lurking in the pipeline for several years, DCV2.¹¹⁴ Immunization was associated with a statistically significant decline in viral load compared with placebo at the 24-week time point after ART interruption (−0.80 vs. −0.19 log; P = .01). While relatively meager compared with ART-mediated viral-load reductions, this rates as one of the largest effects seen with therapeutic vaccination in a controlled study. However, the impact was transient: after 48 weeks of follow-up, the viral-load difference between groups was no longer significant. Despite this limitation, the researchers suggest their findings support the idea that beneficial modulation of HIV-specific immunity is possible.

Scientists from the Statens Serum Institut in Denmark published results from a small phase I trial of their AFO-18 peptide-based vaccine, conducted in Guinea-Bissau with HIV-positive participants naive to ART. The construct was safe but induced new T-cell responses in only 6 of 14 participants.¹¹⁵

Although vaccines based on the HIV Tat protein have a checkered history,¹¹⁶ a new candidate named the Tat Oyi vaccine has entered human testing in France.¹¹⁷ The researchers developing the vaccine have reported positive results from studies in the SHIV/macaque model.¹¹⁸

Conclusion

Despite the many setbacks, the development of an HIV vaccine remains an urgent priority—an effective product would make a vast and vital contribution to ending the epidemic. New opportunities for progress are being opened up by technological advances, such as those that have allowed the detailed dissection of bNAb-producing B-cell responses, and the advent of systems biology as a means of analyzing and understanding the dauntingly large sets of data that can now be generated. A group of respected vaccine researchers, led by Wayne Koff from IAVI, have proposed the creation of a “Human Vaccines Project” to capitalize on the availability of these tools and focus on identifying and generating effective immune responses against the most intractable pathogens, including HIV, TB, and malaria.¹¹⁹

Demonstration projects will be crucial to understanding the acceptability and effectiveness of PrEP in different settings and populations, as well as how to integrate the intervention into a comprehensive package of situation-appropriate prevention options. Now that Truvada PrEP is approved in the U.S., there are unresolved questions about how the drug should be incorporated into control groups in biomedical prevention trials (particularly whether PrEP should be optional or mandatory) that need to be addressed.¹²⁰ For both PrEP and microbicides, results from trials of long-acting approaches will be central to determining the future directions of the fields.

The spotlight on HIV cure research continues to intensify, but challenging problems persist. Among them is how exactly a cure should be defined: as has been learned from the cases of both Timothy Brown and the child in Mississippi, formally proving the complete absence of virus—a sterilizing cure—is essentially impossible. The term “functional cure,” to indicate an end to the requirement for ongoing treatment despite the possible presence of HIV, is increasingly invoked, but is still somewhat loosely defined since long-term follow-up is needed to prove that an individual with controlled virus is not still burdened by elevated immune activation and inflammation (and facing the risk of adverse clinical consequences that can result over the long haul). Solving the conundrum of an HIV cure continues to require a multidisciplinary scientific effort. For this work to bear fruit, it will need not only significant contributions from laboratory science, but substantial additional investments of financial capital and sustained political will.

The achievements of ART have to some extent cast into shadow the areas where additional therapeutic options are required for HIV-positive people. Clinical efficacy trials for immunologic nonresponders are long overdue, and candidate therapies need to be pushed through the pipeline faster than at the current glacial pace. As the population on ART ages, the possibility arises that approaches similar to those being evaluated in the HIV-negative elderly (such as anti-inflammatories or even basic interventions like diet modification and exercise) could offer benefit, but this research portfolio is still nascent at the current time and demands expansion.

Success in all the spheres outlined in this chapter is critically dependent on funding support, and the looming specters that threaten the pipelines are the global economic downturn and U.S. budget sequestration. Advocacy continues to be crucial to ensure that shortsighted spending cuts are reversed, and scientific breakthroughs occur on the near—not distant—horizon.

Sources

ClinicalTrials.gov: http://clinicaltrials.gov

AVAC HIV Prevention Research and Development Database: http://data.avac.org

IAVI Report Trials Database: http://www.iavireport.org/Trials-Database/Pages/default.aspx

 

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Endnotes

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