HIV-Specific Cytotoxic Cell Frequencies Measured Directly Ex Vivo by the Lysispot Assay Can Be Higher or Lower Than the Frequencies of IFN-γ-Secreting Cells: Anti-HIV Cytotoxicity Is Not Generally Impaired Relative to Other Chronic Virus Responses

Abstract

CD8+ T cells in HIV-infected patients are believed to contribute to the containment of the virus and the delay of disease progression. However, the frequencies of HIV-specific CD8+ T cells, as measured by IFN-γ secretion and tetramer binding, often do not correlate with a delay in disease progression during chronic infection. Using the Lysispot and ELISPOT assays, we measured the frequencies of cytotoxic and IFN-γ-secreting T cells responding to overlapping peptides from Gag, Nef, Env, and Pol consensus HIV-1 clade B sequences. PBMC from the majority of HIV-infected subjects have significant frequencies of HIV-specific cells that killed targets within 5 h directly ex vivo. The relative frequencies of IFN-γ-secreting and cytotoxic cells varied markedly between different HIV peptide pools within the same patient, and some T cells lysed targets without secreting IFN-γ. These results indicate that measurement of IFN-γ production alone may be insufficient to evaluate the breadth of the HIV-specific T cell response. Also, neither the CTL to IFN-γ ratios nor the ex vivo CTL frequencies specific for different HIV proteins were consistently lower than responses specific for two other chronic viral infections, human CMV and EBV, within the same subjects. Thus ex vivo cytotoxic T cell frequencies do not provide evidence for a model of “preterminal differentiation” of HIV-specific CD8+ T cells during chronic HIV infection. Analysis of the frequency of directly cytotoxic HIV-specific T cells may be of considerable value in the assessment of disease progression and the potential efficacy of HIV vaccines.

Emergence of Polyfunctional CD8+T Cells after Prolonged Suppression of Human Immunodeficiency Virus Replication by Antiretroviral Therapy

“…Taking these results together, we show here that a high level of HIV viremia causes a selective functional impairment of HIV-specific CD8 ϩ T cells with regard to cytokine secretion but not with respect to degranulation capacity and GrB expression (68). The fact that prolonged treatment with ART allowed the restoration of cytokine secretion capacity by CD8 ϩ T cells suggests that the level of antigen exposure in vivo is the main cause of CD8 ϩ T-cell dysfunction.…”

“…Recently, we have reported a similar dichotomy in CD8 ϩ T-cell effector functions in chronic murine lymphocytic choriomeningitis virus infection, where prolonged in vivo antigen exposure led to severely impaired cytokine production while degranulation and cytolytic activity were maintained at a cellular level (1,68). Furthermore, a detailed cross-sectional analysis of various CD8 ϩ T-cell functions in HIV-infected individuals showed that degranulation was a relatively robust effector function in most cases (13).…”

“…The overall improvement of CD8 ϩ T-cell function is not due to the presence of increased frequencies of naïve CD8 ϩ T cells after prolonged ART as naïve CD8 ϩ T cells are poor cytokine producers in 5-h stimulation assays (data not shown), and functional improvement was observed for both SEB-reactive and HIV-specific CD8 ϩ T cells. It has been reported previously that HIV-specific CD8 ϩ T cells from viremic patients are impaired in cytokine production (11,13,24,46,58,68), and it was proposed that this might be a consequence of persistent antigen exposure, which induces a state of functional exhaustion. Thus, only a fraction of HIVspecific CD8 ϩ T cells detectable by tetramer staining produced IFN-␥ upon stimulation (30,46,58,67), and this fraction increased with long-term ART (58).…”

Flow cytometric detection of degranulation reveals phenotypic heterogeneity of degranulating CMV-specific CD8+ T lymphocytes in rhesus macaques

“…It is noteworthy that studies that have used granzyme B or perforin ELISPOT, or the Lysispot assay to measure cytolytic function at the single-cell level, have shown a marked discordance between the frequencies of IFN-γ-secreting and cytolytic cells for SIV-, HIV-, and human CMV-specific CD8+ T lymphocytes (Snyder et al, 2003;Kleen et al, 2004;Calarota et al, 2006;Snyder-Cappione et al, 2006). In most instances, the frequency of IFN-γ-secreting cells has far exceeded the frequency of cytolytic cells.…”

HIV induced suppression of host immunity: relevance to <i>Mycobacterium tuberculosis</i> infections

“…These observations may have implications in vaccine development and protection from M. tuberculosis reactivation. Furthermore, out of 9 proteins of HIV available for vaccination, the early proteins Tat, Rev, and Nef may be better CD8+ T cell targets than the late-expressed structural proteins Gag, Pol, and Env [74][75][76][77]. It is also believed that CD8+ T cells directed against these early expressed proteins may be able to catch the infected cells prior to the establishment of disease.…”