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CROI 2012: The Long and Winding Road to a Cure for HIV

No one ever thought finding a cure for AIDS would be easy. Medical research is rarely clear-cut, and an HIV cure breakthrough will be a monumental achievement. Yet at this year's Conference on Retroviruses and Opportunistic Infections (CROI 2012), there were significant signs that AIDS cure research is on its way up a long and winding road at the foot of a very big hill. While a functional cure (ability to control HIV without antiretroviral treatment) or total HIV eradication (known as sterilizing cure) may be a steep climb, advances in this field may improve the current state of HIV treatment.

At CROI it was clear that the proverbial foot is getting in the door, with promising findings from early proof-of-concept trials and significant pre-clinical research. HIV cure research took center stage in several sessions, with a popularity not seen since last year's positive news about pre-exposure prophylaxis (PrEP). One symposium -- HIV Latency and Eradication: Clinical Perspectives -- was so packed that 2 overflow rooms were ordered.

Major cure-related topics discussed at the conference included mechanisms of viral latency, discovery of compounds with the potential to reactivate latent virus, clinical trials of potential latency-breaking drugs, and strategies to prevent the spread of reactivated HIV. This report offers a review of the cure studies that appear most promising.

Attempts to "Redux" the Berlin Patient

After the kick-start of the phenomenal first HIV cure in Timothy Brown, known as the "Berlin patient," attempts to decipher the reasons why he was cured are an integral part of this new field of research. Brown shows no signs of HIV 5 years after receiving bone marrow transplants to treat leukemia, from a donor with a natural mutation (CCR5-delta-32) that makes T-cells resistant to viral entry. But it is not clear whether this is due to the CCR5-delta-32 stem cell transplants, strong chemotherapy to treat the cancer, a graft-vs-host reaction, or other factors.

In an attempt to shed more light Brown’s case, researchers studied 10 people with AIDS-related lymphoma who received autologous (self) hematopoietic stem cell transplants (abstract 154). Brown was transplanted with donor cells, so this procedure was less risky. Essentially, the transplanted stem cells reconstitute the patient's immune system after chemotherapy kills existing immune cells. Participants were on antiretroviral therapy (ART) with plasma HIV RNA < 50 copies/mL.

After their transplants, 9 of the 10 participants still had persistent low-level viremia with a median viral load of 1.5 copies/mL and a median HIV pro-viral DNA level of 554 copies/million PBMCs. In addition, 2-LTR circles, a marker of unintegrated pro-viral HIV DNA, were detectable in only 2 of 10 patients.

While this study indicates that stem cell transplantation itself does not eradicate HIV, questions remain because participants in this study -- unlike Brown -- did not undergo total body irradiation, did not have graft-vs-host disease, and most likely carried over HIV from their own transplanted cells.

Other attempts to reproduce Timothy Brown’s success with stem cell transplantation in leukemia and lymphoma patients with HIV are now underway at multiple centers in the U.S. One currently enrolling study is seeking HLA-matched donors with the CCR5-delta-32 mutation (clinicaltrials.gov BMT CTN 0903)

CCR5 Gene Therapy

Another group of researchers has tried a variation on the Berlin Patient approach, using gene therapy to make immune cells resistant to HIV (abstract 155). Years ago HIV gene therapy was only a dream. But this area of cure research has presented an opportunity to use zinc finger nuclease technology developed by Sangamo Biosciences in Richmond, Calif., to create resistant T-cells by knocking out the CCR5 gene. Other approaches for modifying the CCR5 gene are also being tested.

The first cohorts using autologous T-cells modified with the zinc finger technique -- known as SB-728-T -- at the University of Pennsylvania and Quest Research in San Francisco were presented at CROI and at ICAAC last year. Pablo Tebas presented additional data at this year's CROI.

Study participants included both immunological responders to ART with CD4 cell counts > 450 cells/mm³ and immunological non-responders with < 500 cells/mm³. They all received 1 infusion of modified SB-728-T cells.There have been no serious adverse events except 1 transfusion reaction that resolved after a few days.

After about 1 year, dramatic CD4 cell increases were seen in both groups, which investigators think was related to increases in levels of IL-2, IL-7, and IL-15 -- cytokines associated with CD4 cell expansion.CD4/CD8 T-cell ratios normalized in the majority of participants. After infusion, SB-728-T cells were detected in peripheral blood from 90 through 700 days thus far.The modified cells also traffic to the rectal mucosa, proving that they are reaching important gut-associated lymphoid tissue.

A critical question was whether SB-728-T cells would have an effect on HIV RNA, but in order to show this, participants had to interrupt antiretroviral treatment during the trial.After an initial increase in viral load, all experienced significant drops in plasma HIV levels before resuming ART. One man who dropped to an undetectable level while off antiretrovirals was found to be heterozygous for the CCR5-delta-32 mutation, meaning he naturally had 1 copy of the HIV-resistant version.A study has started to look at this population to confirm the finding.Another study is using a single infusion of a chemotherapy drug to make room for more expansion of the modified CD4 cells.

Unraveling Viral Persistence and HIV Latency

Much cure research is focused on finding agents that can break HIV out of its latent state in resting cells. Encouragingly, Sharon Lewin from Alfred Hospital in Melbourne presented a substantial list of drug classes that have the potential to activate latent HIV and are currently in laboratory trials (abstract 106).

Several of these drugs are attractive to start studying in clinical trials for HIV since they have already been used for other indications in people, such as histone deacetylase (HDAC) inhibitors, the cytokines IL-7 and IL-15, and a methylation inhibitor, 5-aza-dC. HDAC enzymes keep viral DNA tightly bound and unusable. HDAC inhibitors and methylation inhibitors release the DNA so it can be used to produce new virus.

Other compounds that have potential for activating latent HIV include NF-kB activators such as prostratin and PMA, and Akt/HEXIM-1 modulators such as HMBA. It has been shown that combining these drugs enhances their potency.

Sifei Xing from Johns Hopkins and colleagues found a whole new group of compounds that are derivatives of quinolin-8-ol (abstract 156). These compounds, discovered via high-throughput screening, not only induce latent HIV in a primary cell model, but do not cause dangerous global T-cell activation.

A proof-of-concept trial showing that HIV can be purged from resting cells using a single dose of vorinistat (aka Zolinza or SAHA), an HDAC inhibitor used as an anti-cancer drug, was presented by David Margolis and his team from the University of North Carolina (abstract 157LB).

Margolis presented data from 6 HIV positive men who had been on stable antiretroviral regimens with viral load < 50 copies/mL and CD4 cell counts > 500 cells/mm³. First, CD4 cells were removed and tested to establish baseline virus levels inside the cell. The cells were then exposed to a single dose of vorinostat, and HIV RNA levels were compared before and after to show whether HDAC was inhibited.

There was a 2-fold increase in histone deacetylation 8 hours after the dose. All 6 participants had HIV RNA increases inside their cells ranging from 1.5- to 10-fold, showing that 1 dose of the study drug could activate sleeping virus. There were no drug-related adverse events or toxicities. "This proves for the first time that there are ways to specifically treat viral latency, the first step towards curing HIV infection," Margolis stated.

Lewin also presented a talk about the challenges of doing cure-related clinical trials. Her clinic is conducting a small study in which 9 participants, who had been virally suppressed for 7.4 years on average, completed 14 days of vorinostat. There were no changes in CD4 counts after 83 days of follow-up. Most adverse events were mild (grade 1) and resolved after a few days of treatment. Although viral load data was not presented, T-cell activation in rectal biopsies was not seen at day 0 or day 14. This study is ongoing.

Preliminary results from a study looking at disulfiram (Antabuse, a drug used to manage alcoholism) -- another compound that specifically reactivates gene transcription -- were presented by Adam Spivak from the University of Utah (abstract 369).

This 14-day single-arm pilot trial of 14 participants with suppressed HIV showed that there was a slight rise in viral load in all participants after receiving disulfiram, but the increase did not reach statistical significance. However, 1 participant achieved a 4.5 log increase in HIV RNA in a surprisingly short period of a few hours. There was a 14% decline in the latent HIV reservoir that was within the dynamic range of the assay used.

Since disulfiram is used to treat alcohol abuse, all participants abstained from alcohol during the study. The drug was found to be safe and well tolerated. Real-world use of the drug for activating the latent reservoir would only be short-term. While the benefits of this drug were not proven in this pilot study, it is being further evaluated in ongoing trials.

The Missing Pathway -- Therapeutic Vaccines

Most scientists agree that therapeutic vaccines that play a role in boosting the immune response, used in addition to activating drugs and perhaps gene therapy, will most likely provide the best chances for a cure.

Liang Shan from Johns Hopkins presented a critical message at CROI that may end up being a key to a cure (abstract 153). His team showed that latent HIV is still measurable even after introducing vorinostat to PBMCs, meaning some infected resting CD4 T-cells survive after reversal of latency. The host immune response to these cells is defective and the cytopathic effect of the reactivated virus is also incomplete.

According to Richard Jefferys, who reported on Shan’s study for Tagline, "…simply rousing HIV is not sufficient; CD8 T-cells are needed to deliver the coup de graceand kill the infected cells." Boosting the cytotoxic CD8 T-cell response through a vaccine will likely be necessary.

Jefferys concluded, "Despite the history of controversy and uncertainty, the ascendancy of cure research has provided a strong and scientifically sound rationale for further studies of therapeutic HIV vaccines. The goals are now far clearer: to achieve containment of HIV replication and prevention of disease in the absence of ongoing treatment (now described as a 'functional cure'), or complete elimination of the virus (a 'sterilizing cure')."

Looking Up the Big Hill

Critical to achieving a cure is a smart research strategy. Many lessons were learned with development of antiretrovirals in the early days of AIDS, and activists have already played a crucial role in HIV cure research. A collaborative strategy involving all stakeholders will be needed. A single big mistake could set back the whole concept of a cure.

Community advocates held a Cure Workshop prior to CROI with leading cure researchers, regulators from the Food and Drug Administration, and well-known activists from across the globe, focusing on strategies to move the field ahead. The meeting was sponsored by the AIDS Treatment Activists Coalition (ATAC), Project Inform, and the Treatment Action Group (TAG), with support from Bionor Pharma, Bristol-Myers Squibb, Gilead Sciences, and Janssen.

Some, but not all, of the most important cure research is part of the Martin Delaney Collaboratory, which is providing the first dedicated National Institutes of Health funding for cure-related programs. The 3 current funded projects described their research programs at the pre-CROI meeting.

Five critical messages that need to be addressed emerged from the workshop: funding for ongoing cure research is crucial, non-human primate models continue to be difficult to study, validation and standardization of assays to test HIV latency and reservoirs is needed, the risk/benefit balance of cure research for patients is a challenge in the era of effective ART, and coordination of research will be a critical component.

This summer the International AIDS Society will introduce a global collaborative cure strategy at the International AIDS Conference in Washington, DC. This may be a make-or-break moment when cure research will spread its wings. While CROI provided an important first look at new areas of cure research, the future appears hopeful with new concepts, new drugs, new trials, and growing activist support.

4/13/12

References

A Cillo, A Krishnan, R Mitsuyasu, et al. Plasma Viremia and Cellular HIV-1 DNA Persist Despite Autologous Hematopoietic Stem Cell Transplantation for AIDS-related Lymphoma. 19th Conference on Retroviruses and Opportunistic Infections (CROI 2012). Seattle, WA. March 5-8, 2012. Abstract 154.

C June, P Tebas, D Stein, et al. Induction of Acquired CCR5 Deficiency with Zinc Finger Nuclease-modified Autologous CD4 T Cells (SB-728-T) Correlates with Increases in CD4 Count and Effects on Viral Load in HIV-infected Subjects.19th Conference on Retroviruses and Opportunistic Infections. Seattle, March 5-8, 2012. Abstract 155.

S Lewin. HIV Latency and Eradication: Clinical Perspectives. 19th Conference on Retroviruses and Opportunistic Infections (CROI 2012). Seattle, WA. March 5-8, 2012. Abstract 106.

S Xing, S Bhat, H Zhang, et al. Novel Structurally Related Compounds Reactivate Latent HIV-1 in a Bcl-2 Transduced Primary CD4⁺ T Cell Model without Inducing Global T Cell Activation. 19th Conference on Retroviruses and Opportunistic Infections (CROI 2012). Seattle, WA. March 5-8, 2012. Abstract 156.

D Margolis, N Archin, A Liberty, et al. Administration of Vorinistat Disrupts HIV-1 latency in Patients on ART. 19th Conference on Retroviruses and Opportunistic Infections (CROI 2012). Seattle, WA. March 5-8, 2012. Abstract 157LB.

A Spivak, A Andrade, R Hoh, et al. Safety and Feasibility of Using Disulfiram to Enhance HIV Transcription among Long-term ARV-treated Adults: Preliminary Results from a Pilot Study. 19th Conference on Retroviruses and Opportunistic Infections (CROI 2012). Seattle, WA. March 5-8, 2012. Abstract 369.

D Evans, K Fisher, J Taylor, et al. Community Cure Report. Seattle, WA. March 4, 2012 (not yet released).