E. Piriou

High responsiveness of HLA‐B57‐restricted Gag‐specific CD8+ T cells in vitro may contribute to the protective effect of HLA‐B57 in HIV‐infection

HLA‐B57 has been shown to be associated with long‐term asymptomatic HIV‐1 infection. To investigate the biological mechanism by which the HLA‐B57 allele could protect from HIV‐1 disease, we studied both the number of CD8+ T cells as well as CD8+ T cell responsiveness directed to different HIV‐1 Gag peptides presented by HLA‐A2, ‐B8 or ‐B57. T cells specific for the HLA‐B57 peptide KAFSPEVIPMF responded more readily and to a higher extend to antigenic stimulation in vitro than T cells specific for the HLA‐A2 peptide SLYNTVATL or the HLA‐B8 peptide EIYKRWII. This phenomenon was reproducible with T cells from individuals expressing HLA‐B57 in combination with one or both of the other alleles and was persistent during long‐term follow‐up. Lower reactivity of A2‐ and B8‐restricted T cells was not explained by mutations in the B8‐ or A2‐restricted Gag‐peptides. Moreover, no correlation between peptide mutation frequency and IFN‐γ production by the corresponding Gag‐specific T cells was observed. In conclusion, functional differences were observed between T cells specific for HIV epitopes derived from the same protein presented by different HLA molecules. B57‐restricted KAFSPEVIPMF‐specific CD8+ T cells have relatively high responsiveness, which could contribute to the protective effect of HLA‐B57 in HIV infection.

Detailed analysis of Epstein–Barr virus‐specific CD4+ and CD8+ T cell responses during infectious mononucleosis

We studied simultaneously Epstein–Barr virus (EBV)‐specific CD4+ and CD8+ T cell responses during and after infectious mononucleosis (IM), using a previously described 12‐day stimulation protocol with EBNA1 or BZLF1 peptide pools. Effector function of EBV‐specific T cells was determined after restimulation by measuring intracellular interferon‐γ production. During IM, BZLF1‐specifc CD4+ T cell responses were dominant compared with CD8+ T cell responses. EBNA1‐specific CD4+ and CD8+ T cell responses were low and remained similar for 6 months. However, 6 months after IM, BZLF1‐specific CD4+ T cell responses had declined, but CD8+ T cell responses had increased. At diagnosis, EBV‐specific CD8+ T cells as studied by human leucocyte antigen class I tetramer staining comprised a tetramerbrightCD8bright population consisting mainly of CD27+ memory T cells and a tetramerdimCD8dim population consisting primarily of CD27‐ effector T cells. The remaining EBV‐specific CD8+ T cell population 6 months after the diagnosis of IM consisted mainly of tetramerbrightCD8bright CD27+ T cells, suggesting preferential preservation of memory T cells after contraction of the EBV‐specific T cell pool.

Reconstitution of EBV Latent but Not Lytic Antigen-Specific CD4+ and CD8+ T Cells after HIV Treatment with Highly Active Antiretroviral Therapy

The incidence of (EBV-related) malignancies in HIV-infected subjects has declined since the introduction of highly active antiretroviral therapy (HAART). To investigate the effect of HAART on EBV infection, we performed a longitudinal analysis of the T cell response to both a latent and a lytic Ag and EBV viral load in 10 subjects from early in HIV infection up to 5 years after HAART. All individuals responded to HAART by a decline in HIV viral load, a restoration of total CD4+ T cell numbers, and a decline in T cell immune activation. Despite this, EBV load remained unaltered, even after 5 years of therapy, although a decline in both CD4+ and CD8+ T cells specific for the lytic EBV protein BZLF1 suggested a decreased EBV reactivation rate. In contrast, latent EBV Ag EBNA1-specific CD4+ and CD8+ T cell responses were restored after 5 years of treatment to levels comparable to healthy individuals. In two individuals who were treated by HAART late during HIV progression, a lymphoma developed shortly after initiation of HAART, despite restoration of EBV-specific CD4+ and CD8+ T cells. In conclusion, long-term HAART does not alter the EBV DNA load, but does lead to a restoration of EBNA1-specific T cell responses, which might allow better control of EBV-infected cells when applied early enough during HIV infection.

Novel method for detection of virus-specific CD4(+) T cells indicates a decreased EBV-specific CD4(+) T cell response in untreated HIV-infected subjects

A lower function of EBV‐specific CD8+ T cells in HIV‐infected subjects could be related to a lack of specific CD4+ T cell help. Therefore, we studied EBV‐specific CD4+ T cells in both healthy donors and untreated or highly active antiretroviral therapy (HAART)‐treated HIV‐seropositive homosexual men. To this end, PBMC were stimulated with overlapping peptide pools from a latent and a lytic EBV protein, EBV nuclear antigen (EBNA)1 and EBV lytic‐switch protein ZEBRA (BZLF1), respectively. EBV‐specific CD4+ T cell frequencies measured directly ex vivo were low. To measure EBV‐specific memory CD4+ T cells, capable of both expansion and IFN‐γ production upon antigenic challenge, we developed a specific and reproducible assay, combining ex vivo expansion of specific T cells with flow cytometric analysis of IFN‐γ production. Untreated HIV‐infected individuals had a lower CD4+ T cell response to both EBNA1 and BZLF1 as compared to healthy EBV carriers and HAART‐treated HIV‐positive subjects. This suggests loss of EBV‐specific CD4+ T cells due to HIV infection, while HAART might restore this response. In addition, we found an increase in the EBNA1‐specific CD8+ T cell response in HAART‐treated subjects. Interestingly, numbers of EBV‐specific CD4+ and CD8+ T cells were inversely correlated with EBV viral load, suggesting an important role also for EBV‐specific CD4+ T cells in the control of EBV infection.