Mohamed Elrefaei

Central Memory CD4 + T Cell Responses in Chronic HIV Infection Are Not Restored by Antiretroviral Therapy

A strong CD4+ T cell response has been correlated with better control of HIV infection. However, the effect of HIV on the maintenance of Ag-specific memory CD4+ T cells is not fully understood. We characterized the function and phenotype of memory CD4+ T cells generated by mumps and influenza A or B viruses in HIV-infected individuals receiving highly active antiretroviral therapy (n = 21), HIV-infected long-term nonprogressors (n = 10), and HIV-seronegative volunteers (n = 10). We observed significantly decreased proliferation of the Ag-specific central memory CD4+ T cell population (CD28+/CCR7+/CD45RA−) in the antiretroviral treated HIV-infected individuals compared with the seronegative controls. Restored CD4+ T cell count and decreased HIV viral load while on highly active antiretroviral therapy did not result in increased proliferation, whereas nadir CD4+ T cell count predicted the presence of Ag-specific proliferation. Our results indicate that HIV infection leads to impaired maintenance of virus-induced or vaccine-generated central memory CD4+ T cells that is not restored by HAART.

Coinfection with Schistosoma mansoni Is Associated with Decreased HIV-Specific Cytolysis and Increased IL-10 Production

Impaired virus-specific immune responses have previously been observed with Schistosoma mansoni coinfection. We characterized Gag-specific responses in HIV-1-positive Ugandans with and without S. mansoni coinfection. We observed no significant difference in the frequency of IFN-γ CD8+ T cells between the two groups. Interestingly, expression of CD107, a marker for cytolytic activity, was significantly lower in volunteers with S. mansoni coinfection compared with those with HIV-1 infection alone (p = 0.002). In contrast, the frequency of IL-10-positive Gag-specific CD8+ T cell responses was higher in volunteers with S. mansoni coinfection (p = 0.004). Analysis of human CMV-specific CD8+ T cell responses in the same individuals failed to reveal a similar pattern of altered CD107 and IL-10 expression. Our results suggest that S. mansoni coinfection is associated with decreased Gag-specific CD8+ cytolytic T cell responses and increased number of Gag-specific IL-10 positive CD8+ T cells. Our findings may have important implications toward the implementation of HIV preventive and therapeutic programs in Africa.

HIV-Specific IL-10-Positive CD8+ T Cells Suppress Cytolysis and IL-2 Production by CD8+ T Cells

IL-10 producing T cells inhibit Ag-specific CD8+ T cell responses and may play a role in the immune dysregulation observed in HIV infection. We have previously observed the presence of HIV-specific IL-10-positive CD8+ T cells in advanced HIV disease. In this study, we examined the suppressive function of the Gag-specific IL-10-positive CD8+ T cells. Removal of these IL-10-positive CD8+ T cells resulted in increased cytolysis and IL-2, but not IFN-γ, production by both HIV- and human CMV-specific CD8+ T cells. In addition, these IL-10-positive CD8+ T cells mediated suppression through direct cell-cell contact, and had a distinct immunophenotypic profile compared with other regulatory T cells. We describe a new suppressor CD8+ T cell population in advanced HIV infection that may contribute to the immune dysfunction observed in HIV infection.

HIV-Specific IL-10-Positive CD8+ T Cells Are Increased in Advanced Disease and Are Associated with Decreased HIV-Specific Cytolysis

IL-10-producing T cells have been shown to inhibit Ag-specific CD8+ T cell responses, and may play a role in the immune dysregulation observed in HIV-1 infection. We characterized the Gag-specific IL-10 responses by CD8+ T cells in HIV-1-positive volunteers from Uganda. HIV-specific IL-10 responses were detected in 32 of 61 (52.4%) antiretroviral naive and 2 of 15 (13.3%) volunteers with a complete virologic response on antiretroviral therapy (< 400 copies/ml). The frequency of HIV-specific IL-10-positive cells was significantly higher in volunteers with advanced disease (CD4+ T cell count <200 cells/mm3; p = 0.0004), and correlated positively with plasma HIV RNA (r = 0.43, p = 0.0004). Interestingly, the frequency of Gag-specific CD107a/b-, but not IFN-γ-, positive cells was significantly lower in individuals with detectable IL-10-positive CD8+ T cells (p = 0.004). Gag-specific IL-10-positive CD8+ T cells demonstrated a pattern of surface memory marker expression that is distinct compared with CD107a/b- and IFN-γ-positive CD8+ T cell populations (p < 0.0001). Our study describes a distinct population of IL-10-positive CD8+ T cells that may play a role in HIV-associated immune dysfunction.

Evaluation of antigen-specific responses using in vitro enriched T cells

Antigen-specific lymphocytes are important in the immune response to viral infection. Peripheral blood mononuclear cells (PBMC) are traditionally used as a source of effector cells in most immunological studies. We described here the use of the bispecific monoclonal antibodies (BSMAB) anti CD3:CD8 (CD3,8) and anti CD3:CD4 (CD3,4B) to expand and selectively enrich CD4+ and CD8+ T cells populations, respectively. The expanded cells demonstrated >90% CD3+CD4+ or CD3+CD8+ by 14 days. We measured HIV- and CMV-specific responses of these subset-enriched T cell and found that sensitivity and specificity is similar or higher when compared to PBMC in various cellular immunology assays (CMI). Vbeta analysis of BSMAB-enriched cells demonstrated comparable repertoire to the parent PBMC. Although both CD45RA(hi) and CD45RO(hi) cell populations were expanded with the BSMAB, selective subset depletion demonstrated that the antigen-specific T cell responses were restricted to the initial CD45RO(hi) memory effector subgroup. In conclusion, BSMAB in vitro enrichment of T cells allows significant expansion of the cell population without loss of specificity. This technique of cell expansion permits studies of T cell subset function in situations where the initial cell source is scarce, and presents an alternative for viable and functional T cells in immunological assays.

Presence of Suppressor HIV-Specific CD8+ T Cells Is Associated with Increased PD-1 Expression on Effector CD8+ T Cells

Mechanisms leading to the observed immune dysregulation in HIV-1 infection are not well understood. HIV-specific IL-10-positive CD8+ T cells are increased in advanced HIV disease. We have previously reported that Gag-specific IL-10-positive CD8+ T cells suppressed cytolysis. In this study we describe the suppressive effect of Nef-specific IL-10-positive CD8+ T cells. Interestingly, simultaneous removal of both Gag- and Nef-specific IL-10-positive CD8+ T cells led to higher HIV-specific cytolysis compared with the removal of Nef-specific IL-10-positive CD8+ T cells alone. We also examined the level of programmed cell death-1 (PD-1) as a measure of immune dysfunction in association with IL-10-positive suppressor CD8+ T cells. The level of PD-1 expression on CD107-positive effector CD8+ T cells was significantly increased when IL-10-positive suppressor CD8+ T cells were present (p < 0.05). Our results suggest that IL-10-positive suppressor CD8+ T cells contribute to the immune dysfunction observed in advanced HIV infection and that the concomitant presence of multiple IL-10-positive CD8+ T cell populations may have an additive suppressive effect.

Profile of T Cell Immune Responses in HIV-infected Children from Uganda

Human immunodeficiency virus (HIV) immunopathogenesis in children remains poorly understood. We assessed T cell immune activation in antiretroviral therapy-naive children in Uganda (n=154). Increased CD4+ and CD8+ T cell activation strongly correlated with decreased CD4+ T cell percentage. Interestingly, no correlation between plasma HIV RNA level and T cell activation was observed after controlling for CD4+ T cell count. In addition, the presence of Gag-specific CD4+ T helper responses was associated with increased HIV-specific CD8+ T cells. Understanding the balance between immune activation and T cell immunity in HIV-infected children may provide further insights into the mechanisms leading to effective immune control.

Human immunodeficiency virus-specific responses in adult Ugandans: patterns of cross-clade recognition.

ABSTRACT Human immunodeficiency virus (HIV) or AIDS is currently the leading cause of death in Uganda, with at least three HIV clades (subtypes) accounting for most new infections. Whether an effective vaccine formulated on viruses from a single clade will be able to protect against infection from other local clades remains unresolved. We examined the T-cell immune responses from a cohort of HIV-seropositive individuals in Uganda with predominantly clade A and D infections. Surprisingly, we observed similar frequencies of cross-clade T-cell responses to the gag, env, and nef regions. Our data suggest that the level of viral sequence variability between distinct HIV strains does not predict the degree of cross-clade responses. High sequence homologies were also observed between consensus peptides and sequences from viral isolates, supporting the use of consensus amino acid sequences to identify immunogenic regions in studies of large populations.

HCV-specific CD27− CD28− memory T cells are depleted in hepatitis C virus and Schistosoma mansoni co-infection

Factors that influence the generation and maintenance of memory CD8+ T cells are not fully understood. The homeostasis of memory T cells is highly dynamic and tightly regulated by various stimuli, including cytokines and antigen–major histocompatibility complex ligands. We characterized the hepatitis C virus (HCV)‐specific CD8+ T‐cell responses in a cohort of HCV‐infected individuals with or without Schistosoma mansoni co‐infection from Egypt. We observed a significantly decreased CD27− CD28− (late differentiated) memory T‐cell population in the HCV co‐infected individuals compared to those with HCV infection alone. In contrast, there was no significant difference in the CD27+ CD28+ (early differentiated) memory T cells between the two groups. Analysis of human cytomegalovirus‐specific CD8+ T‐cell responses in the same individuals failed to reveal a similar pattern of altered memory T‐cell differentiation. Thus, S. mansoni co‐infection targets a specific subset of memory CD8+ T cells in HCV infection.

TGF-β and IL-10 Production by HIV-Specific CD8+ T Cells Is Regulated by CTLA-4 Signaling on CD4+ T Cells

Immune dysregulation in HIV-1 infection is associated with increased expression of inhibitory molecules such as CTLA-4, TGF-β, and IL-10. In this study we examined one potential mechanism for regulating TGF-β and IL-10 expression by HIV-specific suppressor CD8+ T cells. No overlap between TGF-β, IL-10, and IFN-γ cytokine production by HIV-specific CD8+ T cells was observed. TGF-β positive and IL-10 positive cells were FOXP3 negative, CD25 negative, and displayed a heterogeneous surface expression of CD127. TGF-β and IL-10 positive CD8+ T cells did not express CTLA-4. Nevertheless, CTLA-4 blockade resulted in a significant decrease in HIV-specific TGF-β positive and IL-10 positive CD8+ T cell responses, and a concomitant increase in HIV-specific IFN-γ positive CD8+ T cell responses. Depletion of CD4+ T cells abrogated the impact of CTLA-4 on HIV-specific TGF-β positive and IL-10 positive CD8+ T cells. Our study suggests that CTLA-4 Signaling on CD4+ T cells regulates the inhibitory functions of the HIV-specific suppressor CD8+ T cells.