The Yellow Fever Vaccine Immunity in HIV Infected Patients : Development of New Assays for Virological and Immunological Monitoring in HIV Infected Patient.

Main objective : To develop the tools for evaluation of humoral and cell-mediated immunity after Yellow Fever Vaccine (YFV) and compare virological and immune responses in HIV-positive and HIV-negative individuals who had not been given YFV before. Secondary objectives : * To develop and assess ELISPOT technology for yellow fever and to measure the response within 7, 14, 28, 90 and 365 days of administration of YFV in 30 HIV negative subjects and 40 HIV positive subjects (CD4 \> 350/mm3 under Highly Active Antiretroviral Therapy (HAART) for at least one year, with a viral load \< 50 copies/mL since at least 6 months) in terms of : (1) seroconversion by fluorescence, (2) cytotoxic response in ELISPOT, (3) neutralizing antibody levels in Plaque reduction neutralization test (PRNT:reference method) and a new pseudotype based method, (4) post-vaccination viremia and (5) diversity of viral quasi-species. * To assess the impact of YFV on the T-lymphocyte response against HIV by ELISPOT and viral load.