Background:  Hepatitis C virus (HCV)-specific responses are rarely detected in peripheral blood, especially in the presence of HIV, and we hypothesized that this was due to specific suppression by cytokines associated with regulatory T cells.

Methods:  We studied 3 groups of subjects:  10 HCV mono-infected, 10 HCV/HIV co-infected, and 8 healthy controls. Peripheral blood mononuclear cells (PBMC) were analyzed by ELISpot for the frequency of T-cells specific for 3 pools of overlapping peptides representing the HCV-1a core regions, 3 pools of  overlapping peptides representing the HIV-p24 region and 1 pool of cytomegalovirus, Epstein Barr, and influenza virus peptides (CEF). Blocking antibodies anti-TGF-β_1,2,3 and anti-IL-10 or the appropriate isotype antibody were added simultaneously to the assay. Results were expressed as numbers of IFN-γ secreting spot-forming-cells (SFC)/10⁶ PBMC after subtraction of background and as proportion of subjects who were above the threshold of 40 SFC/10⁶ PBMC for HCV and 53 SFC/10⁶ PBMC for HIV (respecting 2 criteria:  > maximum value and > mean + 2SD, observed in controls).

Results:  In subjects with chronic hepatitis, in the absence of blocking antibodies HCV-specific T-cell responses were very weak in both groups (median, range): HCV (29, 5 to 72) with 1 responder and HIV/HCV (7, 0 to 177) with 2 responders. Addition of blocking Abs increased the HCV-specific T-cell responses in both groups (median, range):  HCV (122, 11 to 333) (p = 0.013) and HCV/HIV (36, 0 to 271) (p = 0.056), that became detectable in 7 of 10 and 4 of 10 subjects, respectively. There was no significant difference between the 2 HCV and HCV/HIV groups, and enhancement was not observed with the isotype control antibodies. However when compared with the control group only the group with HCV alone has significantly higher HCV-specific responses (p = 0.002). In contrast CEF-specific T-cell responses, significantly higher than responses towards HCV (p = 0.002), were detected in 7 subjects of both HCV and HCV/HIV, before and after addition of blocking antibodies, and were similar to the control group. HIV-specific responses were detected only in HCV/HIV group:  in 3 of 5 tested subjects before and 5 of 5 after addition of blocking antibodies.

Conclusions:  These data demonstrate that blocking of Treg-associated immunoregulatory cytokines may significantly amplify the HCV specific T-cell responses in PBMC of chronic HCV infection even when co-infected with HIV. This may explain the low frequency of HCV-specific responses observed in PBMC.

Keywords: Hepatitis C; T-cell immune responses; T reg