In the global response to HIV/AIDS to date, development and implementation of effective antiretroviral therapy (ART) have been the premier accomplishments. Not only has ART transformed a once near-universally fatal disease into a manageable infection, it now shows great promise as an approach to preventing infection in those at greatest risk. Mother-to-child transmission of HIV has been nearly eliminated in resource-rich settings,1 and recent studies suggest that sexual transmission among discordant couples can be prevented by treating the infected partner.2
Progress in ART was the result of years of laboratory and clinical investigations, including large carefully controlled clinical trials. No single drug or class of drugs was instrumental to the advances; rather, it was the study and use of combination regimens employed over the past 20 years that yielded the progress that is now evident.3
Although we can rightfully take pride in this progress, many important challenges remain as follows: Can we eradicate virus from HIV-infected individuals, eliminating the need for a lifetime of expensive, potentially toxic drugs? Are there problems with the pipeline leading to new and more effective antiretroviral drugs? If so, how can the pipeline be repaired? How can we improve access and adherence to life-saving ART in at-risk populations? These are some of the questions we will address in this report.
SEARCH FOR A CURE
A few years ago, the concept of ridding an infected individual of HIV was considered highly unlikely, if not impossible. However, one improbable medical experiment has changed our attitude and once again raised the possibility of cure.4,5 In a remarkable series of events, one infected individual seems to have been cured by a stem-cell transplantation procedure involving the use of donor cells homozygous for the Δ32 deletion in the chemokine receptor 5 (CCR5) gene, making these cells resistant to HIV infection. The individual had acute myeloid leukemia and now, several years after transplantation, shows no evidence of HIV or HIV RNA in plasma or organs despite discontinuation of ART. Moreover, he has shown successful reconstitution of CD4 T cells in blood and gut.
The procedure utilized in this patient—justified by the need for bone marrow transplantation to treat his relapsed acute myeloid leukemia—would be too risky and expensive to translate into routine clinical practice. However, this anecdotal case has inspired researchers to consider less arduous approaches directed toward eradicating HIV from latent virus reservoirs.6 Several experimental approaches are being studied, including activation of HIV in latently infected cells by reversing the epigenetic silencing of HIV transcription7; the use of immune-based therapies to boost HIV-specific immunity or dampen HIV-associated immune activation8; and the use of genetically modified CD4+ T cells or bone marrow–derived stem cells that are rendered resistant to HIV infection.9 The National Institute for Allergy and Infectious Disease has launched an initiative involving pharmaceutical, academic, and governmental partners in an effort to stimulate the search for a cure.
Designing clinical trials to test experimental approaches for HIV eradication poses special challenges as follows: selecting appropriate participants for study; defining end points for proof-of-concept studies; and balancing the potential benefits of novel treatments with unknown risks. Several virological and immunological markers may serve as appropriate end points for proof-of-concept trials, but tests of cure or functional cure eventually will require analytical treatment interruptions. Criteria for advancing from proof-of-concept trials to analytical treatment interruption trials require careful consideration, with particular attention to the informed consent process to ensure that potential participants are fully aware of potential risks and not unduly influenced by the chances for a cure which remain hypothetical.
THE ANTIRETROVIRAL DRUG PIPELINE
Over the past 25 years, more than 30 antiretroviral drugs and coformulated drug combinations have been approved in the United States, leaving little doubt that when the history of HIV/AIDS is written, this quarter century will be seen as the “golden age” of HIV therapeutics. However, the momentum in HIV drug development seems to be slowing, and fewer drugs are in an advanced stage of development than in years past. Paradoxically, the availability of many convenient, highly effective, and generally well-tolerated antiretroviral regimens has raised the bar for demonstrating the potential advantages of new drugs in an already crowded market—thereby increasing the risks for pharmaceutical companies and reducing potential profit margins. Moreover, pending competition from low-price combination regimens as current first-line agents go off patent over the next few years means that to justify premium pricing, newer drugs will need to show superiority to established regimens, not just equivalence. In addition, the focus of several pharmaceutical companies has turned to other infectious agents (eg, the hepatitis C virus, where many targets have proven accessible and virological cure seems attainable). Nevertheless, HIV/AIDS continues to be an enormous global problem, and current ART regimens remain costly, potentially toxic, and associated with the development of viral drug resistance.
What can be done to overcome obstacles to development of new ART regimens? One approach to repair the drug pipeline is to design less complex, less costly clinical trials of investigational agents, leading to faster and easier drug approval.10 The US Food and Drug Administration, pharmaceutical companies, physicians, and patients share the desire for trials to be less cumbersome without sacrificing the collection of essential safety and efficacy data. Simplifying clinical trials is particularly important for the development of new drugs needed to treat highly drug-resistant HIV infection. The activity of a novel agent against drug-resistant virus can generally be demonstrated by monitoring the drop in plasma HIV-1 RNA levels over 10–14 days; long-term virological response depends on the activity of the other drugs in the regimen and adherence. Thus, an approach advocated by many is to assess drug activity in a 14-day trial in which the new drug or placebo are added to a failing regimen. Thereafter, all participants are given access to the new drug; allowed to optimize the “background” ART regimen to include other drugs to which the virus remains susceptible; and followed for 24–48 weeks to determine the new regimen's long-term safety and durability. It will be important to evaluate such novel trial designs in a variety of populations, including children, pregnant women, and those with comorbid conditions, such as hepatitis C virus infection.
Improving the delivery of antiretroviral drugs through the development of depot formulations, being studied by several pharmaceutical companies, could have a dramatic impact on the challenge of sustaining high levels of treatment adherence and might significantly improve outcomes in difficult-to-treat populations. Local subcutaneous drug depots that require only infrequent replenishment are one such approach11 and intravaginal drug-containing rings to reduce transmission are another.12 Important biological safety and regulatory issues related to depot preparations need to be addressed before they are employed widely.
It has been encouraging to watch partnerships arise between pharmaceutical companies to coformulate antiretroviral drugs, reducing pill burdens for patients who require prolonged therapy. Partnerships among pharmaceutical companies, academic investigators, and both governmental and nongovernmental agencies have also facilitated access to lifesaving regimens in both resource-rich and resource-poor settings. Organized efforts such as the United States President's Emergency Plan for AIDS Relief and the Global Fund to Fight AIDS, Tuberculosis, and Malaria have made the promise of ART a reality for millions of infected persons in developing countries; concerted efforts by groups such as the Clinton Foundation have reduced the cost of treatment. International efforts must be expanded to build infrastructures that ensure treatment programs' sustainability, that make greater use of point-of-care diagnostics and that continuously monitor drug resistance and toxicity to anticipate problems before they emerge.
1. Perinatal HIV Guidelines Working Group, Public Health Service Task Force. Recommendations for Use of Antiretroviral Drugs in Pregnant HIV-Infected Women for Maternal Health and Interventions to Reduce Perinatal HIV Transmission in the United States. Washington, DC: US Public Health Service Task Force. Available at: http://aidsin-fo.nih.gov/ContentFiles/PerinatalGL.pdf
. Accessed February 20, 2012.
2. Cohen MS, Chen YQ, McCauley M, et al.. Prevention of HIV-1 infection with early antiretroviral therapy. N Engl J Med. 2011;365:493–505. E-pub: July 18, 2011.
3. HHS Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents. Department of Health and Human Services. Washington, DC: US Public Health Service Task Force. Available at: http://www.aidsinfo.nih.gov/ContentFiles/AdultandAdolescentGL.pdf
. Accessed February 20, 2012.
4. Hutter G, Dowak D, Mossner M, et al.. Long-term control of HIV by CCR5 Delta 32/Delta 32 stem-cell transplantation. N Engl J Med. 2009;360:692–698.
5. Allers K, Hutter G, Hoffman J, et al.. Evidence for the cure of HIV infection by CCRT delta 32/Delta 32 stem cell transplantation. Blood. 2011;117:2791–2799.
6. Richman DD, Margolis DM, Delaney M, et al.. The challenge of finding a cure for HIV infection. Science. 2009;323:1304–1307.
7. Margolis DM. Histone deacetylase inhibitors and HIV latency. Curr Opin HIV AIDS. 2011;6:25–29.
8. Shan L, Deng K, Shroff NS, et al.. Stimulation of HIV-1 specific cytolytic T lymphocytes facilitates elimination of latent viral reservoir after virus reactivation. Immunity. 2012;36:491–601.
9. DiGiusto DL, Krishnan A, Li L, et al.. RNA-based gene therapy for HIV with lentiviral vector-modified CD34(+) cells in patients undergoing transplantation for AIDS-related lymphoma. Sci Transl Med. 2010;2:36ra43.
10. Mani N, Murray J, Gulick RM, et al.. Novel clinical trial designs for the development of new antiretroviral agents. AIDS. 2012;26:899–907.
11. Van't Klooster G, Hoeben E, Borghys H, et al.. Pharmacokinetics and disposition of rilpivirine (TMC278) nanosuspension as a long-acting injectable antiretroviral formulation. Antimicrob Agents Chemother. 2010;54:2042–2050.
12. Moss JA, Malone AM, Smith TJ, et al.. Simultaneous delivery of tenofovir and acyclovir via an intravaginal ring. Antimicrob Agents Chemother. 2012;56:875–882.