Polyfunctional T cell responses are a hallmark of HIV-2 infection

HIV-2 is distinguished clinically and immunologically from HIV-1 infection by delayed disease progression and maintenance of HIV-specific CD4(+) T cell help in most infected subjects. Thus, HIV-2 provides a unique natural human model in which to investigate correlates of immune protection against HIV disease progression. Here, we report a detailed assessment of the HIV-2-specific CD4(+) and CD8(+) T cell response compared to HIV-1, using polychromatic flow cytometry to assess the quality of the HIV-specific T cell response by measuring IFN-gamma, IL-2, TNF-alpha, MIP-1beta, and CD107a mobilization (degranulation) simultaneously following Gag peptide stimulation. We find that HIV-2-specific CD4(+) and CD8(+) T cells are more polyfunctional that those specific for HIV-1 and that polyfunctional HIV-2-specific T cells produce more IFN-gamma and TNF-alpha on a per-cell basis than monofunctional T cells. Polyfunctional HIV-2-specific CD4(+) T cells were generally more differentiated and expressed CD57, while there was no association between function and phenotype in the CD8(+) T cell fraction. Polyfunctional HIV-specific T cell responses are a hallmark of non-progressive HIV-2 infection and may be related to good clinical outcome in this setting.     

Combined Env- and Gag-specific T cell responses in relation to programmed death-1 receptor and CD4+ T cell loss rates in human immunodeficiency virus-1 infection

Additional progression markers for human immunodeficiency virus (HIV) infection are warranted. In this study we related antigen-specific responses in CD4⁺ and CD8⁺ T cells to CD38, reflecting chronic immune activation, and to CD4⁺ T cell loss rates. Clones transiently expressing CD107a (CD8⁺) or CD154 (CD4⁺) in response to Gag, Env and Nef overlapping peptide pools were identified, along with their expression of the inhibitory programmed death-1 receptor (PD-1) in fresh peripheral blood mononuclear cells (PBMC) from 31 patients off antiretroviral treatment (ART). HIV-specific CD8⁺ T cell responses dominated over CD4⁺ T cell responses, and among CD8⁺ responses, Gag and Nef responses were higher than Env-responses (P < 0·01). PD-1 on CD8⁺ HIV-specific subsets was higher than CMV-specific CD8⁺ cells (P < 0·01), whereas PD-1 on HIV-specific CD4⁺ cells was similar to PD-1 on CMV-specific CD4⁺ cells. Gag and Env CD8⁺ responses correlated oppositely to the CD4 loss rate. Env/Gag CD8⁺ response ratios, independently of PD-1 levels, correlated more strongly to CD4 change rates (r = −0·50 to −0·77, P < 0·01) than the total number of Gag-specific CD8⁺ cells (r = 0·44–0·85, P ≤ 0·02). The Env/Gag ratio performed better than CD38 and HIV-RNA in logistic regression analysis predicting CD4 change rate as a measure of progression. In conclusion, HIV-specific CD8⁺CD107a⁺ Env/Gag response ratio was a stronger predictor for progression than CD38 and HIV-RNA. The Env/Gag ratio may reflect the balance between possibly beneficial (Gag) and detrimental (Env) CD8⁺ T cell responses and should be explored further as a progression marker.     

CTL escape and increased viremia irrespective of HIV-specific CD4+ T-helper responses in two HIV-infected individuals

We investigated whether development of mutations leads to loss of CD8 T-cell recognition in HIV-1 infection and is possibly linked to alterations in HIV-1-specific CD4(+) T-cell responses in 2 HIV-infected individuals. In patient, H434 full genome sequencing of HIV-1 biological clones at early and late time points during disease progression showed development of fixed mutations in 16 predicted HIV-specific CTL epitopes. Loss of T-cell recognition and reactivity against wild-type and mutant epitopes was observed primarily for the HLA-B27-restricted KK10 epitope and HLA-A2-restricted SL9 epitope. Similarly, in patient H671, decreasing numbers of HLA-A3-restricted CD8(+) T cells specific for the wild-type RK9 epitope was observed after CTL escape. Only in patient H434 loss of CTL responses was paralleled by a decrease in HIV-specific IL-2(+) CD4(+) T-helper responses. This suggests that loss of T-cell reactivity may not be directly linked to HIV-specific CD4(+) T-cell responses but that increased viremia after CTL escape may influence CD4(+) T-helper responses.     

Human leucocyte antigen‐Bw4 and Gag‐specific T cell responses are associated with slow disease progression in HIV‐1B‐infected anti‐retroviral therapy‐naive Chinese

In China, the majority of human immunodeficiency virus (HIV) infections are predominately subtype B. It is important to characterize the HIV‐1 subtype B‐specific and its T cell response within the Chinese population, with the aim of identifying protective correlates of immunity to control HIV‐1 infections. In this study, we performed a comprehensive analysis looking into the magnitude/strength of T cell responses directed at the Gag protein of the HIV‐1 subtype B, one of the most conserved HIV‐1 proteins. The study group consisted of anti‐retroviral native and chronic HIV‐1 subtype B‐infected individuals. We used enzyme‐linked immunospot (ELISPOT) assay to quantify the total T cell responses to HIV‐1 Gag at the single peptide level. Twenty‐eight (38%) peptides were recognized in 24 (82·8%) individuals. The p24 was identified as the most frequently recognized subunit protein with the greatest T cell response in the test, which correlated positively with CD4⁺ T cell count and inversely with viral load (VL). At the level of the human leucocyte antigen (HLA) supertypes, we detected the highest levels and a significant correlation with both the CD4⁺ T cell count and the VL with Gag T cell responses in Bw4/Bw4. These findings demonstrate that (i) the HIV‐1B Gag p24‐specific immune responses play an important role in controlling viral replication and slowing clinical progression; and (ii) HLA‐Bw4/Bw4 allele has stronger T cell responses, which is associated with slow clinical progression in Chinese HIV patients.     

CD8 T cell effector maturation in HIV-1-infected children

HIV-1 infection generates maturational responses in overall CD4 and CD8 T cell populations in adults, with elevated expression of lytic effector molecules perforin and granzyme B, and reduced expression of CCR7 and CD45RA. Here, we have found that these marked effects were significantly less pronounced in children, both in terms of the skewed CCR7/CD45RA expression profile as well as the increased perforin expression. Similar to adults, HIV-specific CD8 cells in children were largely CD27+ CD45RA- and lacked perforin. However, one pediatric subject with late-stage infection displayed robust expansion of Gag 77-85-specific CD8 T cells which were perforin+ and lytic, but lacked expression of CD27 and IFNgamma. Our data indicate that the T cell effector maturation induced by HIV-1 infection is markedly weaker in children as compared to adults. The data also suggest, however, that the perforin-deficient state of HIV-specific CD8 T cells in children may be reversible.     

Variable fate of virus-specific CD4(+) T cells during primary HIV-1 infection.

Impairment of CD4(+) T lymphocyte responses to human immunodeficiency virus (HIV)-derived antigens is the classic immunological defect observed during the chronic phase of HIV-1 infection. Early intervention with potent antiretroviral therapy (ART) can preserve HIV-specific CD4(+) T lymphocyte reactivity, providing indirect evidence that such responses are mounted during primary infection and subsequently lost in the majority of infected individuals. Here, we demonstrate early and dramatic expansions of functional HIV-specific CD4(+) T lymphocyte frequencies directly ex vivo. These responses are initially of broad specificity, and can disappear rapidly during the natural course of primary infection. This process of loss is variable, such that the rapidity and extent of functional compromise differs between individuals. Institution of ART during these early phases of HIV-1 infection preserves patterns of functional reactivity within the HIV-specific CD4(+) T lymphocyte population. However, there was no evidence for the restoration of deleted responses. These findings indicate that, in some individuals at least, ART must be administered within a narrow window of opportunity during primary HIV-1 infection to effect substantial immune preservation.     

Comprehensive analyses of a unique HIV-1-infected nonprogressor reveal a complex association of immunobiological mechanisms in the context of replication-incompetent infection

We recently demonstrated that a unique HIV-1-infected nonprogressor was infected with a nonevolving replication-incompetent HIV-1 strain, showing a total absence of viral evolution in vivo. Potent immune responses against HIV-1 were observed in his PBMC, despite an apparent lack of viral replication for at least 8 years. His PBMC resisted superinfection with CCR5, CXCR4, and dual-tropic HIV-1 strains, although highly purified CD4+ T cells supported infection, but without any visible cytopathic effect. Potent noncytolytic CD8+ T cell antiviral activity was shown to protect his PBMC from productive infection. This activity was not mediated by several known chemokines or IFN-gamma, which were produced at high levels after PHA activation of his CD8+ T cells, indicating the action of other CAF-like CD8 factors. This antiviral activity was a memory response, induced by HIV-specific stimulation to similar levels observed by PHA stimulation, but absent in ex vivo resting T cells. Immunological mechanisms associated with this antiviral suppressive activity included vigorous Gag-specific helper T cell proliferative responses and high-level IFN-gamma release by both CD4 and CD8 T cells. These responses were broadly directed against multiple Gag epitopes, both previously reported and some novel epitopes. Strong HIV-specific helper T cell function was also associated with strong neutralizing antibodies. Understanding how to induce these protective immune responses in other individuals could provide a major step forward in the design of effective immunotherapies or vaccines against HIV infection.     

Host CCL3L1 gene copy number in relation to HIV-1-specific CD4+ and CD8+ T-cell responses and viral load in South African women

HIV-specific T-cell responses play an important role in control of infection. Because CCL3 has immune modulatory and antiviral activities, we hypothesized that host CCL3 genotype (CCL3L1 gene duplications) would influence the development of effective HIV-specific immune responses. Copy numbers of CCL3L1 were determined for 71 HIV-infected women, and HIV-specific CD4 and CD8 T-cell responses to overlapping peptide pools spanning the HIV-1 subtype C genome were simultaneously measured by an interferon-gamma and interleukin-2 whole-blood flow cytometric assay. Host CCL3L1 copy number correlated negatively with viral load (r=-0.239, P=0.045), as did magnitudes of Gag CD4 (r=-0.362, P=0.002) and CD8 (r=-0.261, P=0.028) T-cell responses. Patients with a Gag CD4 response (P=0.002) or dominant Gag CD8 (P=0.006) response had significantly lower viral loads than those whose dominant response targeted another region of the genome, whereas a dominant Nef-specific CD8 T-cell response was associated with higher HIV viral load. CCL3L1 copy number greater than or equal to the population median of 5 was significantly associated with increased magnitude of CD4 Gag responses (P=0.017), and women who had CD4 and CD8 Gag-specific responses had significantly lower viral loads (P=0.004) and higher CCL3L1 copy number (P=0.015) than those women with only CD8 Gag-specific responses.     

CD8+ T cell responses to human immunodeficiency viruses type 2 (HIV-2) and type 1 (HIV-1) gag proteins are distinguishable by magnitude and breadth but not cellular phenotype

The mechanisms underlying the relatively slow progression of human immunodeficiency virus type 2 (HIV-2) compared with HIV-1 infection are undefined and could be a result of more effective immune responses. We used HIV-2 and HIV-1 IFN-gamma enzyme-linked immunospot assays to evaluate CD8(+) T cell responses in antiretroviral-naive HIV-2- ('HIV-2(+)') and HIV-1-infected ('HIV-1(+)') individuals. Gag-specific responses were detected in the majority of HIV-2(+) and HIV-1(+) subjects. Overlapping gag peptide analysis indicated a significantly greater magnitude and breadth of responses in the HIV-1(+) cohort, and this difference was attributable to low responses in HIV-2(+) subjects with undetectable viral load (medians 2107 and 512 spot-forming units per 10(6) PBMC, respectively, p=0.007). We investigated the phenotype of viral epitope-specific CD8(+) T cells identified with HLA-B53- and HLA-B58-peptide tetramers (8 HIV-2(+), 11 HIV-1(+) subjects). HIV-2-specific CD8(+) T cells were predominantly CD27(+) CD45RA(-), and only a minority expressed perforin. The limited breadth and low frequency of CD8(+) T cell responses to HIV-2 gag in aviremic HIV-2(+) subjects suggests that these responses reflect antigen load in plasma, as is the case in HIV-1 infection. Immune control of HIV-2 does not appear to be related to the frequency of perforin-expressing virus-specific CD8(+) T cells.     

Frequency and function of HIV-specific CD8(+) T cells

The virus-specific CD8(+) T cell responses of 27 HIV-infected patients were studied, including a unique cohort of long term nonprogressors (LTNP) with normal CD4(+) T cell counts, low levels of plasma viral RNA, strong proliferative responses to HIV antigens and an over-representation of the HLA B*5701 class I allele. The frequencies of CD8(+) T cells specific to the majority of HIV gene products were measured by flow cytometric detection of intracellular interferon-gamma (IFN-gamma) in response to HIV-vaccinia recombinant infected autologous B cells. Very high frequencies (1.4-22%) of circulating CD8(+) T cells were found to be HIV-specific and were not only found in LTNP with reduced plasma virus. No correlation was evident between the frequency of HIV-specific CD8(+) T cells and levels of plasma viremia. In each case, the vast majority of cells (up to 17.2%) responded to Gag-Pol gene products. Although similar frequencies of Gag peptide-specific CD8(+) T cells were found in LTNP and progressors by either intracellular IFN-gamma or MHC class I tetramer staining, the breadth of these responses was greater in patients with progressive HIV infection compared with the LTNP group. The frequency of CD8(+) T cells specific for a single peptide was not representative of an individual patient's total HIV-specific CD8(+) T cell response. These data demonstrate that high numbers of HIV-specific CD8(+) T cells exist even in patients with high level viremia and progressive disease. Further, they suggest that other qualitative parameters of the CD8(+) T cell response may differentiate some patients with very low levels of plasma virus and nonprogressive infection.     

Development of a whole blood intracellular cytokine staining assay for mapping CD4(+) and CD8(+) T-cell responses across the HIV-1 genome

A whole blood peptide mapping intracellular cytokine staining (ICS) assay was developed that allows the direct comparison, at the individual peptide level, of CD4(+) and CD8(+) T-cell responses that span every encoded protein, in patients infected with HIV-1. Whole blood samples from HIV-1 infected patients were stimulated with overlapping synthetic peptides spanning nine subtype C HIV-1 gene regions (Gag, Pol, Nef, Env, Tat, Rev, Vif, Vpu, Vpr). Following stimulation and permeabilization, cells were stained with fluorochrome labelled antibodies to CD3, CD8 (CD4(+) cells were defined as CD8 negative cells), and IL-2 and IFN-gamma. A total of 396 overlapping peptides were arranged in pools with a matrix design which allowed the identification of individual peptide responses from multiple pool responses. HIV-1 infected patients screened using this method showed a broad range of peptide responses across the entire HIV-1 genome with CD8 T-cell responses being higher in frequency in magnitude than CD4(+) T-cell responses. The advantages of this whole blood ICS assay include the following: (1) the response to all potential HIV-1 epitopes across the genome can be examined, (2) the responding cell type can be monitored in the same reaction, and (3) considerably less blood is required than would be necessary if peripheral blood mononuclear cells (PBMC) were first isolated prior to peptide stimulation.     

Phenotypic and kinetic analysis of effective simian-human immunodeficiency virus-specific T cell responses in DNA--and fowlpox virus-vaccinated macaques

Although T cell immunity is important in the control of HIV-1 infection, the characteristics of effective HIV-specific T cell responses are unclear. We previously observed protection from virulent SHIV challenges in macaques administered priming with DNA vaccines and boosting with recombinant fowlpox viruses expressing shared SIV Gag antigens. We therefore performed a detailed kinetic and phenotypic study of the T cell immunity induced by these vaccines prior to and following SHIV challenge utilizing intracellular cytokine staining. Pigtail macaques vaccinated intramuscularly with DNA/recombinant fowlpox virus exhibited a coordinated induction of first Gag-specific CD4 T cell responses and then a week later Gag-specific CD8 T cell responses following the fowlpox virus boost. Overall, the magnitude and timing of the peak CD8 T cell responses following challenge was significantly associated with reductions in SHIV viremia following pathogenic challenge. After pathogenic lentiviral challenge, virus-specific effector memory T cells derived from animals controlling SHIV infection recognized a broad array of epitopes, expressed multiple effector cytokines and rapidly recognized virus-exposed cells ex vivo. These results shed light on some of the requirements for T cells in the control of pathogenic lentiviral infections.     

Expression of perforin on HIV-1-specific CD8+ lymphocytes after immunization with a gp120-depleted, whole-killed HIV-1 immunogen.

We examined HIV-1 antigen specific intracellular expression of perforin on CD4+ and CD8+ lymphocytes in subjects with chronic HIV-1 infection on antiviral drug therapy after immunization with a gp120-depleted, whole killed HIV-1 immunogen (inactivated, gp120-depleted HIV-1 in IFA, REMUNE). Based upon previous results, we hypothesized that the restoration of adequate T helper immune responses by vaccination against HIV-1 could result in the augmentation of CD8+ lymphocyte immune responses measured as perforin expression. In the current study we observed an increase in the frequency of perforin in CD8+ lymphocytes in HIV infected individuals immunized with a gp120-depleted HIV-1 immunogen while on antiviral drug therapy. Furthermore, the frequency of HIV-specific CD8+ perforin expressing cells correlated with the T helper immune response as measured by the lymphocyte proliferative response (LPR). The induction of such responses with immunization may have direct antiviral consequences and is being studied in ongoing clinical trials.     

HIV-specific cytolytic CD4 T cell responses during acute HIV infection predict disease outcome

Early immunological events during acute HIV infection are thought to fundamentally influence long-term disease outcome. Whereas the contribution of HIV-specific CD8 T cell responses to early viral control is well established, the role of HIV-specific CD4 T cell responses in the control of viral replication after acute infection is unknown. A growing body of evidence suggests that CD4 T cells-besides their helper function-have the capacity to directly recognize and kill virally infected cells. In a longitudinal study of a cohort of individuals acutely infected with HIV, we observed that subjects able to spontaneously control HIV replication in the absence of antiretroviral therapy showed a significant expansion of HIV-specific CD4 T cell responses-but not CD8 T cell responses-compared to subjects who progressed to a high viral set point (P = 0.038). Markedly, this expansion occurred before differences in viral load or CD4 T cell count and was characterized by robust cytolytic activity and expression of a distinct profile of perforin and granzymes at the earliest time point. Kaplan-Meier analysis revealed that the emergence of granzyme A(+) HIV-specific CD4 T cell responses at baseline was highly predictive of slower disease progression and clinical outcome (average days to CD4 T cell count <350/μl was 575 versus 306, P = 0.001). These data demonstrate that HIV-specific CD4 T cell responses can be used during the earliest phase of HIV infection as an immunological predictor of subsequent viral set point and disease outcome. Moreover, these data suggest that expansion of granzyme A(+) HIV-specific cytolytic CD4 T cell responses early during acute HIV infection contributes substantially to the control of viral replication.     

HIV-1B／C重组病毒感染者Gag特异性T淋巴细胞免疫应答的研究

目的研究中国主要流行的HIV-1B／C重组毒株感染者Gag特异性T淋巴细胞反应特征。方法本研究以10例感染时间〈1年和25例感染时间〉3年未接受抗病毒治疗的HIV-1B／C重组毒株感染者为研究对象,以10例HIV．1阴性健康人作为对照,用Elispot方法检测其针对HIV-1B／C同义BGag重叠多肽产生1干扰素的特异性T淋巴细胞反应。结果8例（8／10）感染时间〈1年的HIV-1B／C重组毒株感染者产生Gag特异性分泌Y干扰素的T淋巴细胞反应,主要识别散在分布的五条多肽;17例（68％）感染时间〉3年的感染者产生反应,主要识别p17区域内的-条和p24区域内六条多肽。感染时间〉3年组产生IFN-吖的特异性T淋巴细胞反应强度与病毒载量呈明显正相关（P=0．0318,r=0．519）,感染时间〈1年的感染者反应强度明显高于感染时间〉3年的感染者（P=0．021）。健康人对照组无阳性反应。结论HIV-1B／C重组病毒感染者在疾病进程不同阶段识别Gag的不同区域。     

HIV-1蛋白诱导T细胞产生IFN-γ反应特征及对HIV-1感染者病情进展的影响

目的 探讨HIV-1特异性T细胞反应特征及对HIV-1感染者病情进展的影响.方法 通过合成重叠肽技术及ELISPOT技术,采用队列研究方法对37名HIV-1感染者的病毒特异性T细胞免疫反应进行分析.结果 83.78%(31/37)的HIV-1感染者对1个或多个合成肽反应(反应强度大于50 SFU/106 PBMCs).HIV-1B型病毒不同蛋白均可激发HIV-1感染者的特异性T细胞反应,其中HIV-1 Gag蛋白被识别的频率最高,81%的HIV-1感染者识别HIV-1 Gag而且HIV-1 Gag蛋白诱导的T细胞反应强度最高,相对强度达到28.25%,明显高于其他蛋白,差异具有统计学意义(F=17.969,P<0.001);重叠肽诱导T细胞分泌IFN-γ反应频率、反应强度在HIV-1感染无症状期和艾滋病期无明显区别,但是HIV-1 Gag蛋白诱导的T细胞反应强度在无症状期明显高于艾滋病期.结论 HIV-1B型病毒不同基因编码蛋白激发T细胞分泌IFN-γ反应小同,其中HIV-1 Gag蛋白特异性T细胞在控制病情进展方面发挥了重要作用.     

Sequence variation occurs in CD4 epitopes during early HIV infection

OBJECTIVE: To determine whether viral sequence variation occurs in HIV-specific CD4 epitopes during early HIV infection. METHODS: Gag, Nef, and integrase (Int) sequences were obtained from the plasma of 7 subjects identified during acute HIV-1 infection. Changes in the viral sequence were determined based on comparison of sequences obtained at 2 time points during early infection. Peptide-specific CD4+ T-cell responses were measured at matched time points using interferon-gamma enzyme-linked immunosorbent spot assays to identify CD4 epitopes. RESULTS: An average of 4 mutations were identified per subject. The majority of the mutations were nonsynonymous and resulted in a total of 6 amino acid changes in Gag, 7 changes in Nef, and 6 changes and a deletion in Int. Half of the sequence changes were within recognized CD4 epitopes. Mutations within CD4 epitopes were coincident with changes in the peptide-specific CD4 response. CONCLUSION: These data indicate that sequence variation occurs within recognized CD4 epitopes during early HIV infection. Furthermore, it suggests that mutations within HIV-specific CD4 epitopes may affect T helper cell function.     

HIV-1B/C重组病毒感染者Gag特异性T淋巴细胞免疫应答的研究

目的 研究中国主要流行的HIV-1 B/C重组毒株感染者Gag特异性T淋巴细胞反应特征.方法 本研究以10例感染时间＜1年和25例感染时间＞3年未接受抗病毒治疗的HIV-1 B/C重组毒株感染者为研究对象,以10例HIV-1阴性健康人作为对照,用Elispot方法检测其针对HIV-1B/C同义B Gag重叠多肽产生γ干扰素的特异性T淋巴细胞反应.结果 8例(8/10)感染时间＜1年的HIV-1 B/C重组毒株感染者产生Gag特异性分泌γ干扰素的T淋巴细胞反应,主要识别散在分布的五条多肽;17例(68％)感染时间＞3年的感染者产生反应,主要识别p17区域内的一条和p24区域内六条多肽.感染时间＞3年组产生IFN-γ的特异性T淋巴细胞反应强度与病毒载量呈明显正相关(P =0.0318,r=0.519),感染时间＜1年的感染者反应强度明显高于感染时间＞3年的感染者(P=0.021).健康人对照组无阳性反应.结论 HIV-1 B/C重组病毒感染者在疾病进程不同阶段识别Gag的不同区域.     

HIV-1 Subtype C gag-specific T-cell responses in relation to human leukocyte antigens in a diverse population of HIV-infected Ethiopians

Knowledge of the most dominant T-cell epitopes in the context of the local human leukocyte antigen (HLA) background is a prerequisite for the development of an effective HIV vaccine. In 100 Ethiopian subjects, 16 different HLA-A, 23 HLA-B, and 12 HLA-C specificities were observed. Ninety-four percent of the population carried at least 1 of the 5 most common HLA-A and/or HLA-B specificities. HIV-specific T-cell responses were measured in 48 HIV-infected Ethiopian subjects representing a wide range of ethnicities in Ethiopia using the interferon (IFN)-gamma enzyme-linked immunospot (Elispot) assay and 49 clade C-specific synthetic Gag peptides. Fifty-eight percent of the HIV-positive study subjects showed T-cell responses directed to 1 or more HIV Gag peptides. Most Gag-specific responses were directed against the subset of peptides spanning Gag p24. The breadth of response ranged from 1 to 9 peptides, with most (78%) individuals showing detectable responses to <3 Gag peptides. The magnitude of HIV-specific T-cell responses was not associated with HIV viral load but correlated positively with CD4 T-cell counts. The most frequently targeted Gag peptides overlapped with those previously described for HIV-1 subtype C-infected southern Africans, and therefore can be used in a multiethnic vaccine.     

Immune Reconstitution and Viral Stimulation Are Required to Restore HIV-Specific CD8 T Cell Responses Following Advanced Infection

The extent to which highly active antiretroviral therapy (HAART) restores human immunodeficiency virus (HIV)-specific immunity in advanced infection is unknown. Therefore, we studied how effective therapy affected HIV-specific CD8(+) T cell responses in 4 individuals who had progressed to advanced infection. CD8(+) T cell responses were assessed by cytotoxicity and interferon-gamma (IFN-gamma) production. Proliferative CD4(+) T cell responses against HIV, Candida and mitogen were measured by (3)H-thymidine incorporation. Substantial immune reconstitution indicated by increased CD4(+) and CD8(+) T cell numbers followed suppression of viral replication. This was associated with emergence of HIV-specific cytotoxic T lymphocytes (CTL), but only concurrent with detectable viral replication. Emergent anti-HIV CTL were similar to those at earlier stages of infection in terms of their specificity, function, and CD28 phenotype. However, they were very short-lived in the absence of detectable HIV replication. Antigen-specific CD4(+) T cell responses remained severely compromised. Thus, effective antiretroviral therapy restores the capacity for HIV-specific CTL responses after advanced infection. However, the transient nature of these responses suggests failure to generate stable long-lived memory cells in the absence of HIV-specific helper T cell responses.