HIV vaccines induce CD8+ T cells with low antigen receptor sensitivity.

Current HIV vaccines designed to stimulate CD8+ T cells have failed to induce immunologic control upon infection. The functions of vaccine-induced HIV-specific CD8+ T cells were investigated here in detail. Cytotoxic capacity was significantly lower than in HIV controllers and was not a consequence of low frequency or unaccumulated functional cytotoxic proteins. Low cytotoxic capacity was attributable to impaired degranulation in response to the low antigen levels present on HIV-infected targets. The vaccine-induced T cell receptor (TCR) repertoire was polyclonal and transduction of these TCRs conferred the same reduced functions. These results define a mechanism accounting for poor antiviral activity induced by these vaccines and suggest that an effective CD8+ T cell response may require a vaccination strategy that drives further TCR clonal selection.

CD8(+) T-cell Cytotoxic Capacity Associated with Human Immunodeficiency Virus-1 Control Can Be Mediated through Various Epitopes and Human Leukocyte Antigen Types.

Understanding natural immunologic control over Human Immunodeficiency Virus (HIV)-1 replication, as occurs in rare long-term nonprogressors/elite controllers (LTNP/EC), should inform the design of efficacious HIV vaccines and immunotherapies. Durable control in LTNP/EC is likely mediated by highly functional virus-specific CD8(+) T-cells. Protective Human Leukocyte Antigen (HLA) class I alleles, like B*27 and B*57, are present in most, but not all LTNP/EC, providing an opportunity to investigate features shared by their HIV-specific immune responses. To better understand the contribution of epitope targeting and conservation to immune control, we compared the CD8(+) T-cell specificity and function of B*27/57(neg) LTNP/EC (n = 23), B*27/57(pos) LTNP/EC (n = 23) and B*27/57(neg) progressors (n = 13). Fine mapping revealed 11 previously unreported immunodominant responses. Although B*27/57(neg) LTNP/EC did not target more highly conserved epitopes, their CD8(+) T-cell cytotoxic capacity was significantly higher than progressors. Similar to B*27/57(pos) LTNP/EC, this superior cytotoxicity was mediated by preferential expansion of immunodominant responses and lysis through the predicted HLA. These findings suggest that increased CD8(+) T-cell cytotoxic capacity is a common mechanism of control in most LTNP/EC regardless of HLA type. They also suggest that potent cytotoxicity can be mediated through various epitopes and HLA molecules and could, in theory, be induced in most people.

Broadly neutralizing antibodies suppress HIV in the persistent viral reservoir.

Several highly potent and broadly neutralizing monoclonal antibodies against HIV have recently been isolated from B cells of infected individuals. However, the effects of these antibodies on the persistent viral reservoirs in HIV-infected individuals receiving antiretroviral therapy (ART) are unknown. We show that several HIV-specific monoclonal antibodies--in particular, PGT121, VRC01, and VRC03--potently inhibited entry into CD4(+) T cells of HIV isolated from the latent viral reservoir of infected individuals whose plasma viremia was well controlled by ART. In addition, we demonstrate that HIV replication in autologous CD4(+) T cells derived from infected individuals receiving ART was profoundly suppressed by three aforementioned and other HIV-specific monoclonal antibodies. These findings have implications for passive immunotherapy as an approach toward controlling plasma viral rebound in patients whose ART is withdrawn.

Effect of antiretroviral therapy on HIV reservoirs in elite controllers.

Elite controllers suppress human immunodeficiency virus (HIV) viremia to below the limit of detection in the absence of antiretroviral therapy (ART). However, precise frequencies of CD4(+) T cells carrying replication-competent HIV and/or the dynamics of the infectious viral reservoirs in response to initiation and discontinuation of ART in elite controllers are unknown. We show that the size of the pool of CD4(+) T cells harboring infectious HIV diminished significantly after initiation of ART and rebounded to baseline upon cessation of therapy. Our data provide compelling evidence that persistent viral replication occurs in untreated elite controllers even in the absence of detectable plasma viremia.

Cytotoxic capacity of SIV-specific CD8(+) T cells against primary autologous targets correlates with immune control in SIV-infected rhesus macaques.

Although the study of non-human primates has resulted in important advances for understanding HIV-specific immunity, a clear correlate of immune control over simian immunodeficiency virus (SIV) replication has not been found to date. In this study, CD8(+) T-cell cytotoxic capacity was examined to determine whether this function is a correlate of immune control in the rhesus macaque (RM) SIV infection model as has been suggested in chronic HIV infection. SIVmac251-infected human reverse transcriptase (hTERT)-transduced CD4(+) T-cell clone targets were co-incubated with autologous macaque effector cells to measure infected CD4(+) T-cell elimination (ICE). Twenty-three SIV-infected rhesus macaques with widely varying plasma viral RNA levels were evaluated in a blinded fashion. Nineteen of 23 subjects (83%) were correctly classified as long-term nonprogressor/elite controller (LTNP/EC), slow progressor, progressor or SIV-negative rhesus macaques based on measurements of ICE (weighted Kappa 0.75). LTNP/EC had higher median ICE than progressors (67.3% [22.0-91.7%] vs. 23.7% [0.0-58.0%], p = 0.002). In addition, significant correlations between ICE and viral load (r = -0.57, p = 0.01), and between granzyme B delivery and ICE (r = 0.89, p<0.001) were observed. Furthermore, the CD8(+) T cells of LTNP/EC exhibited higher per-cell cytotoxic capacity than those of progressors (p = 0.004). These findings support that greater lytic granule loading of virus-specific CD8(+) T cells and efficient delivery of active granzyme B to SIV-infected targets are associated with superior control of SIV infection in rhesus macaques, consistent with observations of HIV infection in humans. Therefore, such measurements appear to represent a correlate of control of viral replication in chronic SIV infection and their role as predictors of immunologic control in the vaccine setting should be evaluated.

Effect of histone deacetylase inhibitors on HIV production in latently infected, resting CD4(+) T cells from infected individuals receiving effective antiretroviral therapy.

Persistence of the latent viral reservoir has been recognized as a major obstacle to eradicating human immunodeficiency virus (HIV) in infected individuals receiving antiretroviral therapy. It has been suggested that histone deacetylase inhibitors (HDACis) may purge HIV in the latent viral reservoir. However, the effect of HDACis on the degree and extent of HIV expression in the latent viral reservoir has not been fully delineated. Here we demonstrate that HDACis do not induce HIV production in the latent viral reservoir of aviremic individuals. Therefore, alternative therapeutic strategies may be necessary to eliminate HIV in the latent viral reservoir.

Antibody-dependent cellular cytotoxicity against primary HIV-infected CD4+ T cells is directly associated with the magnitude of surface IgG binding.

Antibody (Ab)-dependent cellular cytotoxicity (ADCC) is thought to potentially play a role in vaccine-induced protection from HIV-1. The characteristics of such antibodies remain incompletely understood. Furthermore, correlates between ADCC and HIV-1 immune status are not clearly defined. We screened the sera of 20 HIV-1-positive (HIV-1(+)) patients for ADCC. Normal human peripheral blood mononuclear cells were used to derive HIV-infected CD4(+) T cell targets and autologous, freshly isolated, natural killer (NK) cells in a novel assay that measures granzyme B (GrB) and HIV-1-infected CD4(+) T cell elimination (ICE) by flow cytometry. We observed that complex sera mediated greater levels of ADCC than anti-HIV-1 envelope glycoprotein (Env)-specific monoclonal antibodies and serum-mediated ADCC correlated with the amount of IgG and IgG1 bound to HIV-1-infected CD4(+) T cells. No correlation between ADCC and viral load, CD4(+) T cell count, or neutralization of HIV-1(SF162) or other primary viral isolates was detected. Sera pooled from clade B HIV-1(+) individuals exhibited breadth in killing targets infected with HIV-1 from clades A/E, B, and C. Taken together, these data suggest that the total amount of IgG bound to an HIV-1-infected cell is an important determinant of ADCC and that polyvalent antigen-specific Abs are required for a robust ADCC response. In addition, Abs elicited by a vaccine formulated with immunogens from a single clade may generate a protective ADCC response in vivo against a variety of HIV-1 species. Increased understanding of the parameters that dictate ADCC against HIV-1-infected cells will inform efforts to stimulate ADCC activity and improve its potency in vaccinees.

Comprehensive analysis of unique cases with extraordinary control over HIV replication.

True long-term nonprogressors (LTNPs)/elite controllers (ECs) maintain durable control over HIV replication without antiretroviral therapy. Herein we describe 4 unique persons who were distinct from conventional LTNPs/ECs in that they had extraordinarily low HIV burdens and comparatively weak immune responses. As a group, typical LTNPs/ECs have unequivocally reactive HIV-1 Western blots, viral loads below the lower threshold of clinical assays, low levels of persistent viral reservoirs, an over-representation of protective HLA alleles, and robust HIV-specific CD8(+) T-cell responses. The 4 unique cases were distinguished from typical LTNPs/ECs based on weakly reactive Western blots, undetectable plasma viremia by a single copy assay, extremely low to undetectable HIV DNA levels, and difficult to isolate replication-competent virus. All 4 had at least one protective HLA allele and CD8(+) T-cell responses that were disproportionately high for the low antigen levels but comparatively lower than those of typical LTNPs/ECs. These unique persons exhibit extraordinary suppression over HIV replication, therefore, higher-level control than has been demonstrated in previous studies of LTNPs/ECs. Additional insight into the full spectrum of immune-mediated suppression over HIV replication may enhance our understanding of the associated mechanisms, which should inform the design of efficacious HIV vaccines and immunotherapies.

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.

Trivalent adenovirus type 5 HIV recombinant vaccine primes for modest cytotoxic capacity that is greatest in humans with protective HLA class I alleles.

If future HIV vaccine design strategies are to succeed, improved understanding of the mechanisms underlying protection from infection or immune control over HIV replication remains essential. Increased cytotoxic capacity of HIV-specific CD8+ T-cells associated with efficient elimination of HIV-infected CD4+ T-cell targets has been shown to distinguish long-term nonprogressors (LTNP), patients with durable control over HIV replication, from those experiencing progressive disease. Here, measurements of granzyme B target cell activity and HIV-1-infected CD4+ T-cell elimination were applied for the first time to identify antiviral activities in recipients of a replication incompetent adenovirus serotype 5 (Ad5) HIV-1 recombinant vaccine and were compared with HIV-negative individuals and chronically infected patients, including a group of LTNP. We observed readily detectable HIV-specific CD8+ T-cell recall cytotoxic responses in vaccinees at a median of 331 days following the last immunization. The magnitude of these responses was not related to the number of vaccinations, nor did it correlate with the percentages of cytokine-secreting T-cells determined by ICS assays. Although the recall cytotoxic capacity of the CD8+ T-cells of the vaccinee group was significantly less than that of LTNP and overlapped with that of progressors, we observed significantly higher cytotoxic responses in vaccine recipients carrying the HLA class I alleles B*27, B*57 or B*58, which have been associated with immune control over HIV replication in chronic infection. These findings suggest protective HLA class I alleles might lead to better outcomes in both chronic infection and following immunization due to more efficient priming of HIV-specific CD8+ T-cell cytotoxic responses.

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.

A randomized, controlled, trial of short cycle intermittent compared to continuous antiretroviral therapy for the treatment of HIV infection in Uganda.

BACKGROUND: Short cycle treatment interruption could reduce toxicity and drug costs and contribute to further expansion of antiretroviral therapy (ART) programs. METHODS: A 72 week, non-inferiority trial enrolled one hundred forty six HIV positive persons receiving ART (CD4+ cell count > or =125 cells/mm(3) and HIV RNA plasma levels <50 copies/ml) in one of three arms: continuous, 7 days on/7 days off and 5 days on/2 days off treatment. Primary endpoint was ART treatment failure determined by plasma HIV RNA level, CD4+ cell count decrease, death attributed to study participation, or opportunistic infection. RESULTS: Following enrollment of 32 participants, the 7 days on/7 days off arm was closed because of a failure rate of 31%. Six of 52 (11.5%) participants in the 5 days on/2 days off arm failed. Five had virologic failure and one participant had immunologic failure. Eleven of 51 (21.6%) participants in the continuous treatment arm failed. Nine had virologic failure with 1 death (lactic acidosis) and 1 clinical failure (extra-pulmonary TB). The upper 97.5% confidence boundary for the difference between the percent of non-failures in the 5 days on/2 days off arm (88.5% non-failure) compared to continuous treatment (78.4% non failure) was 4.8% which is well within the preset non-inferiority margin of 15%. No significant difference was found in time to failure in the 2 study arms (p = 0.39). CONCLUSIONS: Short cycle 5 days on/2 days off intermittent ART was at least as effective as continuous therapy. TRIAL REGISTRATION: ClinicalTrials.gov NCT00339456.

Defective human immunodeficiency virus-specific CD8+ T-cell polyfunctionality, proliferation, and cytotoxicity are not restored by antiretroviral therapy.

Identifying the functions of human immunodeficiency virus (HIV)-specific CD8+ T cells that are not merely modulated by the level of virus but clearly distinguish patients with immune control from those without such control is of paramount importance. Features of the HIV-specific CD8+ T-cell response in antiretroviral-treated patients (designated Rx <50) and untreated patients (long-term nonprogressors [LTNP]) matched for very low HIV RNA levels were comprehensively examined. The proliferative capacity of HIV-specific CD8+ T cells was not restored in Rx <50 to the level observed in LTNP, even though HIV-specific CD4+ T-cell proliferation in the two patient groups was comparable. This diminished HIV-specific CD8+ T-cell proliferation in Rx <50 was primarily due to a smaller fraction of antigen-specific cells recruited to divide and not to the numbers of divisions that proliferating cells had undergone. Exogenous interleukin-2 (IL-2) induced proliferating cells to divide further but did not rescue the majority of antigen-specific cells with defective proliferation. In addition, differences in HIV-specific CD8+ T-cell proliferation could not be attributed to differences in cellular subsets bearing a memory phenotype, IL-2 production, or PD-1 expression. Although polyfunctionality of HIV-specific CD8+ T cells in Rx <50 was not restored to the levels observed in LTNP despite prolonged suppression of HIV RNA levels, per-cell cytotoxic capacity was the functional feature that most clearly distinguished the cells of LTNP from those of Rx <50. Taken together, these data suggest that there are selective qualitative abnormalities within the HIV-specific CD8+ T-cell compartment that persist under conditions of low levels of antigen.

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.

Comparisons of CD8+ T cells specific for human immunodeficiency virus, hepatitis C virus, and cytomegalovirus reveal differences in frequency, immunodominance, phenotype, and interleukin-2 responsiveness.

To better understand the components of an effective immune response to human immunodeficiency virus (HIV), the CD8(+) T-cell responses to HIV, hepatitis C virus (HCV), and cytomegalovirus (CMV) were compared with regard to frequency, immunodominance, phenotype, and interleukin-2 (IL-2) responsiveness. Responses were examined in rare patients exhibiting durable immune-mediated control over HIV, termed long-term nonprogressors (LTNP) or elite controllers, and patients with progressive HIV infection (progressors). The magnitude of the virus-specific CD8(+) T-cell response targeting HIV, CMV, and HCV was not significantly different between LTNP and progressors, even though their capacity to proliferate to HIV antigens was preserved only in LTNP. In contrast to HIV-specific CD8(+) T-cell responses of LTNP, HLA B5701-restricted responses within CMV pp65 were rare and did not dominate the total CMV-specific response. Virus-specific CD8(+) T cells were predominantly CD27(+)45RO(+) for HIV and CD27(-)45RA(+) for CMV; however, these phenotypes were highly variable and heavily influenced by the degree of viremia. Although IL-2 induced significant expansions of CMV-specific CD8(+) T cells in LTNP and progressors by increasing both the numbers of cells entering the proliferating pool and the number of divisions, the proliferative capacity of a significant proportion of HIV-specific CD8(+) T cells was not restored with exogenous IL-2. These results suggest that immunodominance by HLA B5701-restricted cells is specific to HIV infection in LTNP and is not a feature of responses to other chronic viral infections. They also suggest that poor responsiveness to IL-2 is a property of HIV-specific CD8(+) T cells of progressors that is not shared with responses to other viruses over which immunologic control is maintained.

Frequency and phenotype of human immunodeficiency virus envelope-specific B cells from patients with broadly cross-neutralizing antibodies.

Induction of broadly cross-reactive neutralizing antibodies (NAb) is an important goal for a prophylactic human immunodeficiency virus type 1 (HIV-1) vaccine. Some HIV-infected patients make a NAb response that reacts with diverse strains of HIV-1, but most candidate vaccines have induced NAb only against a subset of highly sensitive isolates. To better understand the nature of broad NAb responses that arise during natural infection, we screened patients for sera able to neutralize diverse HIV strains and explored the frequency and phenotype of their peripheral Envelope-specific B cells. We screened 113 HIV-infected patients of various clinical statuses for the prevalence of broad NAb. Sera able to neutralize at least four of five viral isolates were found in over one-third of progressors and slow progressors, but much less frequently in aviremic long-term nonprogressors. Most Env-specific antibody-secreting B cells were CD27(hi) CD38(hi) plasmablasts, and the total plasmablast frequency was higher in HIV-infected patients than in uninfected donors. We found that 0.0031% of B cells and 0.047% of plasmablasts secreted Env-specific immunoglobulin G (IgG) in an enzyme-linked immunospot (ELISPOT) assay. We developed a novel staining protocol to label HIV-specific B cells with Env gp140 protein. A total of 0.09% of B cells were found to be Env-specific by this method, a frequency far higher than that indicated by ELISPOT assay. gp140-labeled B cells were predominantly CD27(+) and surface IgG(+). These data describe the breadth and titer of serum NAb and the frequency and phenotype of HIV-specific B cells in a cohort of patients with broad cross-neutralizing antibody responses that are potential goals for vaccines for HIV.

Lytic granule loading of CD8+ T cells is required for HIV-infected cell elimination associated with immune control.

Virus-specific CD8+ T cells probably mediate control over HIV replication in rare individuals, termed long-term nonprogressors (LTNPs) or elite controllers. Despite extensive investigation, the mechanisms responsible for this control remain incompletely understood. We observed that HIV-specific CD8+ T cells of LTNPs persisted at higher frequencies than those of treated progressors with equally low amounts of HIV. Measured on a per-cell basis, HIV-specific CD8+ T cells of LTNPs efficiently eliminated primary autologous HIV-infected CD4+ T cells. This function required lytic granule loading of effectors and delivery of granzyme B to target cells. Defective cytotoxicity of progressor effectors could be restored after treatment with phorbol ester and calcium ionophore. These results establish an effector function and mechanism that clearly segregate with immunologic control of HIV. They also demonstrate that lytic granule contents of memory cells are a critical determinant of cytotoxicity that must be induced for maximal per-cell killing capacity.

Human immunodeficiency virus viremia induces plasmacytoid dendritic cell activation in vivo and diminished alpha interferon production in vitro.

Human immunodeficiency virus type 1 (HIV-1) infection has been associated with perturbations of plasmacytoid dendritic cells (PDC), including diminished frequencies in the peripheral blood and reduced production of type I interferons (IFNs) in response to in vitro stimulation. However, recent data suggest a paradoxical increase in production of type 1 interferons in vivo in HIV-infected patients compared to uninfected controls. Using a flow cytometric assay to detect IFN-alpha-producing cells within unseparated peripheral blood mononuclear cells, we observed that short-term interruptions of antiretroviral therapy are sufficient to result in significantly reduced IFN-alpha production by PDC in vitro in response to CpG A ligands or inactivated HIV particles. The primary cause of diminished IFN-alpha production was reduced responsiveness of PDC to de novo stimulation, not diminished per cell IFN-alpha production or migration of cells to lymphoid organs. Real-time PCR analysis of purified PDC from patients prior to and during treatment interruptions revealed that active HIV-1 replication is associated with upregulation of type I IFN-stimulated gene expression. Treatment of hepatitis C virus-infected patients with IFN-alpha2b and ribavirin for hepatitis C virus infection resulted in a profound suppression of de novo IFN-alpha production in response to CpG A or inactivated HIV particles, similar to the response observed in HIV-infected patients. Together, these results suggest that diminished production of type I interferons in vitro by PDC from HIV-1-infected patients may not represent diminished interferon production in vivo. Rather, diminished function in vitro is likely a consequence of prior activation via type I interferons or HIV virions in vivo.

Persistence of HIV in gut-associated lymphoid tissue despite long-term antiretroviral therapy.

Human immunodeficiency virus (HIV) persists in peripheral blood mononuclear cells despite sustained, undetectable plasma viremia resulting from long-term antiretroviral therapy. However, the source of persistent HIV in such infected individuals remains unclear. Given recent data suggesting high levels of viral replication and profound depletion of CD4(+) T cells in gut-associated lymphoid tissue (GALT) of animals infected with simian immunodeficiency virus and HIV-infected humans, we sought to determine the level of CD4(+) T cell depletion as well as the degree and extent of HIV persistence in the GALT of infected individuals who had been receiving effective antiviral therapy for prolonged periods of time. We demonstrate incomplete recoveries of CD4(+) T cells in the GALT of aviremic, HIV-infected individuals who had received up to 9.9 years of effective antiretroviral therapy. In addition, we demonstrate higher frequencies of HIV infection in GALT, compared with PBMCs, in these aviremic individuals and provide evidence for cross-infection between these 2 cellular compartments. Together, these data provide a possible mechanism for the maintenance of viral reservoirs revolving around the GALT of HIV-infected individuals despite long-term viral suppression and suggest that the GALT may play a major role in the persistence of HIV in such individuals.

Innate immunity in HIV infection: enhanced susceptibility to CD95-mediated natural killer cell death and turnover induced by HIV viremia.

In the present study, we performed DNA microarray analyses and phenotypic and functional analyses in an effort to elucidate the mechanisms by which ongoing HIV replication affects the physiologic function of natural killer (NK) cells. Functional assays confirmed an increased propensity of NK cells from HIV-infected viremic individuals to undergo Fas-mediated apoptosis but not CD16- or NKG2D-mediated apoptosis. Serum levels of sFasL and expression of Ki67 on NK cells were markedly elevated in HIV-infected viremic individuals when compared with those of HIV-infected aviremic and HIV-seronegative individuals. Our data demonstrate that ongoing HIV replication results in profound NK-cell abnormalities that are likely to be attributable to the effects of virus-induced immune activation. Of note is an increased susceptibility to cell death mediated by CD95-sFasL interactions. In addition, these NK cells, particularly the CD56(dim) CD16(bright) subset, undergo enhanced cell turnover in vivo, as demonstrated by intracellular Ki67 expression.