TAG HIV Basic Science, Vaccines, and Cure Project Blog

Humanized Mouse Models of HIV Latency

A major obstacle in the pursuit of a cure for HIV infection is the existence of long-lived cells containing viral DNA integrated into the cellular genome. These latently infected cells spark renewed rounds of viral replication when suppressive antiretroviral therapy (ART) is interrupted. Researchers are now aiming to develop strategies to purge latently infected cells, and these efforts would be greatly aided by animal models that recapitulate—at least to some extent—what occurs in humans.

Two new papers in the Journal of Virology describe the creation of mice with human immune systems that support HIV infection and develop a reservoir of latently infected, resting CD4 T cells similar to those observed in HIV-positive people. The researchers express hope that these models will facilitate the preclinical evaluation of approaches to depleting the latent reservoir, thereby reducing the need to conduct potentially risky human trials.

There are some potential limitations, however. The small size of mice limits the blood volume that can be sampled, so the degree of HIV viral load suppression by ART can only be assessed down to around 500-800 copies/mL. The extent of engraftment of the human immune system is also not complete, so for example some tissues in the Rag2-/-{gamma}c-/- mice such as the gut and female reproductive tract show a minimal presence of human cells whereas these locations may represent important HIV reservoirs in humans. The short lifespan of the mice also constrains the ability of the model to fully mirror ART treatment of HIV in people. Despite these caveats, humanized mice add to the range of options available to researchers pursuing a cure, and will likely be complimented by the further development of non-human primate models (which are also in the early stages, as previously reported on the blog).

J Virol. 2011 Oct 19. [Epub ahead of print]

Latent HIV-1 Infection of Resting CD4+ T Cells in the Humanized Rag2-/-{gamma}c-/- Mouse.

Choudhary S, Archin N, Cheema M, Dahl N, Garcia JV, Margolis D.

Abstract

Persistent HIV-1 infection of resting CD4(+) T cells, unaffected by antiretroviral therapy (ART), provides a long-lived reservoir of HIV infection. Therapies that target this viral reservoir are needed to eradicate HIV-1 infection. A small animal model that recapitulates HIV-1 latency in resting CD4(+) T cells may accelerate drug discovery and allow the rational design of non-human primate (NHP) or human studies. We report that in humanized Rag2(-/-)γ(c)(-/-) mice, as in humans, following HIV-1 infection with CCR5 tropic JR-CSF and suppression of viremia by ART, resting CD4(+) T cell infection (RCI) can be quantitated in pooled samples of circulating cells and tissue reservoirs (e.g. lymph node, spleen, bone marrow). Replication competent virus was recovered from pooled resting CD4(+) T cells in seven of sixteen mice with a median frequency of 8 (range 2-12) infected cells per million, demonstrating that HIV-1 infection can persist despite ART in the resting CD4(+) T cell reservoir of hu-Rag2(-/-)γ(c)(-/-) mice. This model will allow rapid preliminary assessment of novel eradication approaches and combinatorial strategies that may be challenging to perform in the NHP model or in humans, as well as a rigorous analysis of the effect of these interventions in specific anatomical compartments.

J Virol. 2011 Oct 19. [Epub ahead of print]

Generation of HIV Latency in BLT Humanized Mice.

Denton PW, Olesen R, Choudhary SK, Archin NM, Wahl A, Swanson MD, Chateau M, Nochi T, Krisko JF, Spagnuola RA, Margolis DM, Garcia JV.

Source

Division of Infectious Diseases, Department of Internal Medicine, Center for AIDS Research.

Abstract

Here we demonstrate that a combination of tenofovir, emtricitabine and raltegravir effectively suppresses peripheral and systemic HIV replication in BLT humanized mice. We also demonstrate that antiretroviral therapy (ART) treated BLT humanized mice harbor latently infected resting human CD4(+) T cells that can be induced ex vivo to produce HIV. We observed that the levels of infected resting human CD4(+) T cells present in BLT mice are within the range of those observed circulating in patients undergoing suppressive ART. These results demonstrate the potential of BLT humanized mice as an attractive model for testing the in vivo efficacy of novel HIV eradication strategies.

Open Access Articles on HIV in Cold Spring Harbor Perspectives

The journal Cold Spring Harbor Perspectives is offering several free review articles on HIV research, see abstracts and links below.

doi: 10.1101/cshperspect.a007252

Vaccine Design for CD8 T Lymphocyte Responses

Richard A. Koup and Daniel C. Douek

Immunology Laboratory, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892

Abstract

Vaccines are arguably the most powerful medical intervention in the fight against infectious diseases. The enormity of the global human immunodeficiency virus type 1 (HIV)/acquired immunodeficiency syndrome (AIDS) pandemic makes the development of an AIDS vaccine a scientific and humanitarian priority. Research on vaccines that induce T-cell immunity has dominated much of the recent development effort, mostly because of disappointing efforts to induce neutralizing antibodies through vaccination. Whereas T cells are known to limit HIV and other virus infections after infection, their role in protection against initial infection is much less clear. In this article, we will review the rationale behind a T-cell-based vaccine approach, provide an overview of the methods and platforms that are being applied, and discuss the impact of recent vaccine trial results on the future direction of T-cell vaccine research.

doi: 10.1101/cshperspect.a007096

HIV Latency

Robert F. Siliciano1 and Warner C. Greene2

1Department of Medicine, Johns Hopkins University School of Medicine, Howard Hughes Medical Institute, Baltimore, Maryland 21205

2Gladstone Institute of Virology and Immunology, Department of Medicine, Microbiology and Immunology, University of California, San Francisco, California 94158

Abstract

HIV-1 can establish a state of latent infection at the level of individual T cells. Latently infected cells are rare in vivo and appear to arise when activated CD4+ T cells, the major targets cells for HIV-1, become infected and survive long enough to revert back to a resting memory state, which is nonpermissive for viral gene expression. Because latent virus resides in memory T cells, it persists indefinitely even in patients on potent antiretroviral therapy. This latent reservoir is recognized as a major barrier to curing HIV-1 infection. The molecular mechanisms of latency are complex and include the absence in resting CD4+ T cells of nuclear forms of key host transcription factors (e.g., NFκB and NFAT), the absence of Tat and associated host factors that promote efficient transcriptional elongation, epigenetic changes inhibiting HIV-1 gene expression, and transcriptional interference. The presence of a latent reservoir for HIV-1 helps explain the presence of very low levels of viremia in patients on antiretroviral therapy. These viruses are released from latently infected cells that have become activated and perhaps from other stable reservoirs but are blocked from additional rounds of replication by the drugs. Several approaches are under exploration for reactivating latent virus with the hope that this will allow elimination of the latent reservoir.

doi: 10.1101/cshperspect.a007278

Rational Design of Vaccines to Elicit Broadly Neutralizing Antibodies to HIV-1

Peter D. Kwong, John R. Mascola and Gary J. Nabel

Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892

Abstract

The development of a highly effective AIDS vaccine will likely depend on success in designing immunogens that elicit broadly neutralizing antibodies to naturally circulating strains of HIV-1. Although the antibodies induced after natural infection with HIV-1 are often directed to strain-specific or nonneutralizing determinants, it is now evident that 10%–25% of HIV-infected individuals generate neutralizing antibody responses of considerable breadth. In the past, only four broadly neutralizing monoclonal antibodies had been defined, but more than a dozen monoclonal antibodies of substantial breadth have more recently been isolated. An understanding of their recognition sites, the structural basis of their interaction with the HIV Env, and their development pathways provides new opportunities to design vaccine candidates that will elicit broadly protective antibodies against this virus.

doi: 10.1101/cshperspect.a006841

Origins of HIV and the AIDS Pandemic

Paul M. Sharp1 and Beatrice H. Hahn2

1Institute of Evolutionary Biology and Centre for Immunity, Infection and Evolution, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom

2Departments of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104

Abstract

Acquired immunodeficiency syndrome (AIDS) of humans is caused by two lentiviruses, human immunodeficiency viruses types 1 and 2 (HIV-1 and HIV-2). Here, we describe the origins and evolution of these viruses, and the circumstances that led to the AIDS pandemic. Both HIVs are the result of multiple cross-species transmissions of simian immunodeficiency viruses (SIVs) naturally infecting African primates. Most of these transfers resulted in viruses that spread in humans to only a limited extent. However, one transmission event, involving SIVcpz from chimpanzees in southeastern Cameroon, gave rise to HIV-1 group M—the principal cause of the AIDS pandemic. We discuss how host restriction factors have shaped the emergence of new SIV zoonoses by imposing adaptive hurdles to cross-species transmission and/or secondary spread. We also show that AIDS has likely afflicted chimpanzees long before the emergence of HIV. Tracing the genetic changes that occurred as SIVs crossed from monkeys to apes and from apes to humans provides a new framework to examine the requirements of successful host switches and to gauge future zoonotic risk.

Published in Advance September 14, 2011, doi: 10.1101/cshperspect.a007385

Microbicides: Topical Prevention against HIV

Robin J. Shattock1 and Zeda Rosenberg2

1Centre for Infection and Immunity, Division of Clinical Sciences, St George’s, University of London, Cranmer Terrace, London SW17 0RE, United Kingdom

2International Partnership for Microbicides, 8401 Colesville Road, Suite 200, Silver Spring, Maryland 20910

Abstract

Microbicides represent a potential intervention strategy for preventing HIV transmission. Vaginal microbicides would meet the need for a discreet method that women could use to protect themselves against HIV. Although early-generation microbicides failed to demonstrate efficacy, newer candidates are based on more potent antiretroviral (ARV) products. Positive data from the CAPRISA 004 trial of tenofovir gel support use in women and represent a turning point for the field. This article reviews current progress in development of ARV-based microbicides. We discuss the consensus on selection criteria, the potential for drug resistance, rationale for drug combinations, and the use of pharmacokinetic (PK)/pharmacodynamic (PD) assessment in product development. The urgent need for continued progress in development of formulations for sustained delivery is emphasized. Finally, as the boundaries between different prevention technologies become increasingly blurred, consideration is given to the potential synergy of diverse approaches across the prevention landscape.

Published in Advance September 7, 2011, doi: 10.1101/cshperspect.a007153

Nonpathogenic Simian Immunodeficiency Virus Infections

Nichole R. Klatt1, Guido Silvestri2 and Vanessa Hirsch1

1Laboratory of Molecular Microbiology, NIAID, NIH, Bethesda, Maryland 20892

2Department of Pathology and Laboratory Medicine, Emory University School of Medicine, and Yerkes National Primate Research Center, Atlanta, Georgia 30322

Abstract

The simian immunodeficiency viruses (SIVs) are a diverse group of viruses that naturally infect a wide range of African primates, including African green monkeys (AGMs) and sooty mangabey monkeys (SMs). Although natural infection is widespread in feral populations of AGMs and SMs, this infection generally does not result in immunodeficiency. However, experimental inoculation of Asian macaques results in an immunodeficiency syndrome remarkably similar to human AIDS. Thus, natural nonprogressive SIV infections appear to represent an evolutionary adaptation between these animals and their primate lentiviruses. Curiously, these animals maintain robust virus replication but have evolved strategies to avoid disease progression. Adaptations observed in these primates include phenotypic changes to CD4+ T cells, limited chronic immune activation, and altered mucosal immunity. It is probable that these animals have achieved a unique balance between T-cell renewal and proliferation and loss through activation-induced apoptosis, and virus-induced cell death. A clearer understanding of the mechanisms underlying the lack of disease progression in natural hosts for SIV infection should therefore yield insights into the pathogenesis of AIDS and may inform vaccine design.

Assessing the Role of Virus-Specific CD4 T Cells in Controlling SIV

One of the studies presented at the recent AIDS Vaccine 2011 conference has now been published in the Journal of Clinical Investigation. It addresses a longstanding uncertainty in HIV research regarding the role of virus-specific CD4 T cells in controlling viral replication. On the one hand, basic immunology research conducted over the last two decades has made it increasingly clear that CD4 T cell responses play a vital role in sustaining functional CD8 T cell and B cell responses in most settings. In HIV infection, however, it is known that HIV-specific CD4 T cells are preferentially infected by the virus, raising the concern that these responses may enhance rather than limit viral replication. Although the issue is still debated, the preponderance of evidence now suggests that functional, broadly targeted—and particularly Gag-specific—HIV-specific CD4 T cells are vital for sustaining effective HIV-specific CD8 T cell responses and are therefore typically beneficial rather than harmful. 

The new study by Guido Silvestri and colleagues adds to this evidence by demonstrating that depletion of CD4 T cells from rhesus macaques profoundly impairs their ability to reduce SIV viral load after it peaks during acute infection. In discussing the results the authors note that, to inform vaccine development, it will be important to better define the elements that constitute a protective CD4 T cell response:

“The current study suggests that, in addition to humoral and/or CD8+ T cell–mediated immune responses, the antiviral CD4+ T cell response may play an important role in limiting HIV replication, a finding that could be exploited in the design of candidate AIDS vaccines. As CD4+ T cell activation induced by an AIDS vaccine has the intrinsic potential of generating more targets for HIV (and SIV) infection, it will be essential to investigate at the phenotypic and functional level what type of CD4+ T cell responses mediate the protective antiviral effect revealed in this study.”

J Clin Invest. 2011 Oct 17. pii: 46023. doi: 10.1172/JCI46023. [Epub ahead of print]

Depletion of CD4+ T cells abrogates post-peak decline of viremia in SIV-infected rhesus macaques.

Ortiz AM, Klatt NR, Li B, Yi Y, Tabb B, Hao XP, Sternberg L, Lawson B, Carnathan PM, Cramer EM, Engram JC, Little DM, Ryzhova E, Gonzalez-Scarano F, Paiardini M, Ansari AA, Ratcliffe S, Else JG, Brenchley JM, Collman RG, Estes JD, Derdeyn CA, Silvestri G.

Abstract

CD4+ T cells play a central role in the immunopathogenesis of HIV/AIDS, and their depletion during chronic HIV infection is a hallmark of disease progression. However, the relative contribution of CD4+ T cells as mediators of antiviral immune responses and targets for virus replication is still unclear. Here, we have generated data in SIV-infected rhesus macaques (RMs) that suggest that CD4+ T cells are essential in establishing control of virus replication during acute infection. To directly assess the role of CD4+ T cells during primary SIV infection, we in vivo depleted these cells from RMs prior to infecting the primates with a pathogenic strain of SIV. Compared with undepleted animals, CD4+ lymphocyte-depleted RMs showed a similar peak of viremia, but did not manifest any post-peak decline of virus replication despite CD8+ T cell- and B cell-mediated SIV-specific immune responses comparable to those observed in control animals. Interestingly, depleted animals displayed rapid disease progression, which was associated with increased virus replication in non-T cells as well as the emergence of CD4-independent SIV-envelopes. Our results suggest that the antiviral CD4+ T cell response may play an important role in limiting SIV replication, which has implications for the design of HIV vaccines.