Evaluation of the pathogenesis of decreasing CD4(+) T cell counts in human immunodeficiency virus type 1-infected patients receiving successfully suppressive antiretroviral therapy.

Most human immunodeficiency virus (HIV)-infected individuals experience increases in peripheral CD4(+) T cell counts with suppressive antiretroviral therapy (ART) that achieves plasma HIV RNA levels that are less than the limit of detection. However, some individuals experience decreasing CD4(+) T cell counts despite suppression of plasma viremia. We evaluated 4 patients with a history of CD4(+) T cell decline despite successfully suppressive ART, from a median of 719 cells/mm(3) (range, 360-1141 cells/mm(3)) to 227 cells/mm(3) (range, 174-311 cells/mm(3)) over a period of 18-24 months; 3 of the patients were receiving tenofovir and didanosine, which may have contributed to this decrease. There was no evidence of HIV replication, nor of antiretroviral drug resistance in the blood or lymphoid tissue, or increased proliferation or decreased thymic production of naive CD4(+) T cells. All 4 patients had significant fibrosis of the T cell zone of lymphoid tissue, which appeared to be an important factor in the failure to reconstitute T cells.

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)-alpha. 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-alpha 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.

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.

Characterization of CD56-/CD16+ natural killer (NK) cells: a highly dysfunctional NK subset expanded in HIV-infected viremic individuals.

Natural killer (NK) cells are an important component of the innate immune response against viral infections. NK cell-mediated cytolytic activity is defective in HIV-infected individuals with high levels of viral replication. In the present study, we examined the phenotypic and functional characteristics of an unusual CD56(-)/CD16(+) (CD56(-)) NK subset that is greatly expanded in HIV-viremic individuals. The higher level of expression of inhibitory NK receptors and the lower level of expression of natural cytotoxicity receptors observed in the CD56(-) NK fraction compared with that of CD56(+) NK cells was associated with extremely poor in vitro cytotoxic function of this subset. In addition, the secretion of certain cytokines known to be important in initiating antiviral immune responses was markedly reduced in the CD56(-), as compared with the CD56(+) NK cell subset. These data suggest that the expansion of this highly dysfunctional CD56(-) NK cell subset in HIV-viremic individuals largely accounts for the impaired function of the total NK cell population.