J. Shawn Justement

Relationship between pre-existing viral reservoirs and the re-emergenceof plasma viremia after discontinuation of highly active anti-retroviral therapy

We examined the pathogenic significance of the latent viral reservoir in the resting CD4+ T cell compartment of HIV-1-infected individuals as well as its involvement in the rebound of plasma viremia after discontinuation of highly active anti-retroviral therapy (HAART). Using heteroduplex mobility and tracking assays, we show that the detectable pool of latently infected, resting CD4+ T cells does not account entirely for the early rebounding plasma HIV in infected individuals in whom HAART has been discontinued. In the majority of patients examined, the rebounding plasma virus was genetically distinct from both the cell-associated HIV RNA and the replication-competent virus within the detectable pool of latently infected, resting CD4+ T cells. These results indicate the existence of other persistent HIV reservoirs that could prompt rapid emergence of plasma viremia after cessation of HAART and underscore the necessity to develop therapies directed toward such populations of infected cells.

HIV-infected individuals receiving effective antiviral therapy for extended periods of time continually replenish their viral reservoir

The persistence of latently infected, resting CD4+ T cells is considered to be a major obstacle in preventing the eradication of HIV-1 even in patients who have received effective antiviral therapy for an average duration of 5 years. Although previous studies have suggested that the latent HIV reservoir in the resting CD4+ T cell compartment is virologically quiescent in the absence of activating stimuli, evidence has been mounting to suggest that low levels of ongoing viral replication persist and in turn, prolong the overall half-life of HIV in patients receiving antiviral therapy. Here, we demonstrate the persistence of replication-competent virus in CD4+ T cells in a cohort of patients who had received uninterrupted antiviral therapy for up to 9.1 years that rendered them consistently aviremic throughout that time. Surprisingly, substantially higher levels of HIV proviral DNA were found in activated CD4+ T cells when compared with resting CD4+ T cells in the majority of patients we studied. Phylogenetic analyses revealed evidence for cross infection between the resting and activated CD4+ T cell compartments, suggesting that ongoing reactivation of latently infected, resting CD4+ T cells and spread of virus by activated CD4+ T cells may occur in these patients. Such events may allow continual replenishment of the CD4+ T cell reservoir and resetting of the half-life of the latently infected, resting CD4+ T cells despite prolonged periods of aviremia.

Decreased Survival of B Cells of HIV-viremic Patients Mediated by Altered Expression of Receptors of the TNF Superfamily

Human immunodeficiency virus (HIV) infection leads to numerous perturbations of B cells through mechanisms that remain elusive. We performed DNA microarray, phenotypic, and functional analyses in an effort to elucidate mechanisms of B cell perturbation associated with ongoing HIV replication. 42 genes were up-regulated in B cells of HIV-viremic patients when compared with HIV-aviremic and HIV-negative patients, the majority of which were interferon (IFN)-stimulated or associated with terminal differentiation. Flow cytometry confirmed these increases and indicated that CD21low B cells, enhanced in HIV-viremic patients, were largely responsible for the changes. Increased expression of the tumor necrosis factor (TNF) superfamily (TNFSF) receptor CD95 correlated with increased susceptibility to CD95-mediated apoptosis of CD21low B cells, which, in turn, correlated with HIV plasma viremia. Increased expression of BCMA, a weak TNFSF receptor for B lymphocyte stimulator (BLyS), on CD21low B cells was associated with a concomitant reduction in the expression of the more potent BLyS receptor, BAFF-R, that resulted in reduced BLyS binding and BLyS-mediated survival. These findings demonstrate that altered expression of genes associated with IFN stimulation and terminal differentiation in B cells of HIV-viremic patients lead to an increased propensity to cell death, which may have substantial deleterious effects on B cell responsiveness to antigenic stimulation.

Gene expression and viral prodution in latently infected, resting CD4+ T cells in viremic versus aviremic HIV-infected individuals

The presence of HIV-1 in latently infected, resting CD4+ T cells has been clearly demonstrated in infected individuals; however, the extent of viral expression and the underlying mechanisms of the persistence of HIV-1 in this viral reservoir have not been fully delineated. Here, we show that resting CD4+ T cells from the majority of viremic patients are capable of producing cell-free HIV-1 spontaneously ex vivo. The levels of HIV-1 released by resting CD4+ T cells were not significantly reduced in the presence of inhibitors of cellular proliferation and viral replication. However, resting CD4+ T cells from the majority of aviremic patients failed to produce virions, despite levels of HIV-1 proviral DNA and cell-associated HIV-1 RNA comparable to viremic patients. The DNA microarray analysis demonstrated that a number of genes involving transcription regulation, RNA processing and modification, and protein trafficking and vesicle transport were significantly upregulated in resting CD4+ T cells of viremic patients compared to those of aviremic patients. These results suggest that active viral replication has a significant impact on the physiologic state of resting CD4+ T cells in infected viremic patients and, in turn, allows release of HIV-1 without exogenous activation stimuli. In addition, given that no quantifiable virions were produced by the latent viral reservoir in the majority of aviremic patients despite the presence of cell-associated HIV-1 RNA, evidence for transcription of HIV-1 RNA in resting CD4+ T cells of aviremic patients should not necessarily be taken as direct evidence for ongoing viral replication during effective therapy.

Challenges in Detecting HIV Persistence during Potentially Curative Interventions: A Study of the Berlin Patient

There is intense interest in developing curative interventions for HIV. How such a cure will be quantified and defined is not known. We applied a series of measurements of HIV persistence to the study of an HIV-infected adult who has exhibited evidence of cure after allogeneic hematopoietic stem cell transplant from a homozygous CCR5Δ32 donor. Samples from blood, spinal fluid, lymph node, and gut were analyzed in multiple laboratories using different approaches. No HIV DNA or RNA was detected in peripheral blood mononuclear cells (PBMC), spinal fluid, lymph node, or terminal ileum, and no replication-competent virus could be cultured from PBMCs. However, HIV RNA was detected in plasma (2 laboratories) and HIV DNA was detected in the rectum (1 laboratory) at levels considerably lower than those expected in ART-suppressed patients. It was not possible to obtain sequence data from plasma or gut, while an X4 sequence from PBMC did not match the pre-transplant sequence. HIV antibody levels were readily detectable but declined over time; T cell responses were largely absent. The occasional, low-level PCR signals raise the possibility that some HIV nucleic acid might persist, although they could also be false positives. Since HIV levels in well-treated individuals are near the limits of detection of current assays, more sensitive assays need to be developed and validated. The absence of recrudescent HIV replication and waning HIV-specific immune responses five years after withdrawal of treatment provide proof of a clinical cure.

Rebound of plasma viremia following cessation of antiretroviral therapy despite profoundly low levels of HIV reservoir: implications for eradication.

Objectives:Sustained suppression of plasma viremia in HIV-infected individuals is attainable with antiretroviral therapy (ART); however, eradication of virus that would allow discontinuation of ART has been hampered by the persistence of HIV reservoirs. It is of great interest to identify individuals who had received ART for prolonged periods of time with extremely low or undetectable HIV reservoirs and monitor plasma viremia following discontinuation of therapy. Methods:We measured the size of HIV reservoirs in CD4+ T cells of individuals on long-term ART and monitored plasma viremia following cessation of ART in one individual with an exceptionally low viral burden after a decade of therapy. Results:We demonstrated undetectable levels of HIV DNA in the blood of eight of 45 infected individuals on long-term ART. Among those eight individuals, the frequency of cells carrying infectious virus was significantly lower in those who initiated ART during the early versus the chronic phase of infection. One individual with undetectable HIV DNA in both blood and tissue and a profoundly low level of infectious virus experienced plasma viral rebound 50 days following discontinuation of ART. Conclusions:Our data suggest that a significant reduction in the size of viral reservoirs may be achievable in selected individuals who initiate standard ART early in infection. However, given re-emergence of plasma viremia in an individual with an extraordinarily low viral burden, therapeutic strategies aimed at specifically targeting these extremely rare HIV-infected cells with novel interventions may be necessary in order to achieve eradication of virus.

Decay of the HIV Reservoir in Patients Receiving Antiretroviral Therapy for Extended Periods: Implications for Eradication of Virus

The persistence of latently infected resting CD4+ T cells has been clearly demonstrated in human immunodeficiency virus (HIV)-infected individuals receiving effective antiviral therapy. However, estimates of the half-life of this viral reservoir have been quite divergent. We demonstrate clear evidence for decay of this HIV reservoir in patients who initiated antiviral therapy early in infection. The half-life of this latent viral reservoir was estimated to be 4.6 months. It is projected that it will take up to 7.7 years of continuous therapy to completely eliminate latently infected resting CD4+ T cells in infected individuals who initiate antiviral therapy early in HIV infection.

Short-cycle structured intermittent treatment of chronic HIV infection with highly active antiretroviral therapy: Effects on virologic, immunologic, and toxicity parameters

Although continuous highly active antiretroviral therapy (HAART) is effective for many HIV-infected patients, it can be toxic and prohibitive in cost. By decreasing the total amount of time patients receive medications, intermittent HAART could reduce toxicity and cost. Therefore, we initiated a pilot study in which 10 HIV-infected individuals receiving effective therapy that resulted in levels of HIV RNA <50 copies per ml of plasma and CD4+ T cell counts >300 cells per mm3 of whole blood received repeated cycles of 7 days on HAART followed by 7 days off of HAART. Patients maintained suppression of plasma viremia for 32–68 weeks. There was no significant increase in HIV proviral DNA or replication-competent HIV in peripheral CD4+ T cells or HIV RNA in peripheral blood or lymph node mononuclear cells. There was no significant change in CD4+ T cell counts, no significant increase in CD4+ or CD8+ T cells expressing activation markers or producing IFN-γ in response to HIV, no increase in CD4+ T cell proliferation to p24 antigen, and no evidence for the development of resistance to HAART medications. There was a significant decrease in serum cholesterol and triglyceride levels. Thus, in this proof-of-concept study, short-cycle intermittent HAART maintained suppression of plasma viremia as well as HIV replication in reservoir sites while preserving CD4+ T cell counts. In addition, there was a decrease in serum cholesterol and triglyceride levels. Intermittent therapy may be an important strategy to reduce cost and toxicity for HIV-infected individuals.

Relationship Between Residual Plasma Viremia and the Size of HIV Proviral DNA Reservoirs in Infected Individuals Receiving Effective Antiretroviral Therapy

Residual plasma viremia (<50 copies/mL) persists in certain human immunodeficiency virus (HIV)-infected individuals receiving antiretroviral therapy (ART); however, the relationship between the degree of residual plasma viremia, the size of HIV reservoirs, and the level of immune activation has not been delineated. Here, we demonstrate that residual plasma viremia correlates with the size of the CD4(+) T cell viral reservoir, but not with markers of immune activation, suggesting that reactivation of the latent viral reservoir may not be the sole source of residual plasma viremia. Novel therapeutic strategies aimed at targeting the source of residual viremia may be necessary to achieve viral eradication.

Impact of HIV on Cell Survival and Antiviral Activity of Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDCs) are important mediators of innate immunity that act mainly through secretion of interferon (IFN)-α. Previous studies have found that these cells can suppress HIV in vitro; additionally, pDCs have been shown to be severely reduced in the peripheral blood of HIV-infected individuals. In the present study, we sought to determine the ability of pDCs to directly suppress viral replication ex vivo and to delineate the potential mechanisms whereby pDCs are depleted in HIV-infected individuals. We demonstrate that activated pDCs strongly suppress HIV replication in autologous CD4+ T cells via a mechanism involving IFN-α as well as other antiviral factors. Of note, unstimulated pDCs from infected individuals who maintain low levels of plasma viremia without antiretroviral therapy were able to suppress HIV ex vivo via a mechanism requiring cell-to-cell contact. Our data also demonstrate that death of pDCs by both apoptosis and necrosis is induced by fusion of HIV with pDCs. Taken together, our data suggest that pDCs play an important role in the control of HIV replication and that high levels of viral replication in vivo are associated with pDC cell death via apoptosis and necrosis. Elucidation of the mechanism by which pDCs suppress HIV replication in vivo may have clinically relevant implications for future therapeutic strategies.