Human immune response to HIV-1-Nef. I. CD45RO− T lymphocytes of non-infected donors contain cytotoxic T lymphocyte precursors at high frequency

The immune response of peripheral blood lymphocytes (PBL) of non-exposed human individuals to the Net protein of HIV-1 was studied. Net is a regulatory protein of HIV which is immediately expressed after infection and which seems to be important in the pathogenicity of HIV. Nef may therefore serve as a potential target for effective immunity against HIV infection. Epstein-Barr (EBV)-transformed lymphoblastold B cell lines (LCL) were established from four healthy young seronegative adults and transfected with the Nef gene. These cells served as stimulator cells for autologous PBL in vitro and as target cells for CTL CTL responses were readily generated against Nef-transfected LCL, consisting of Nef-specific and putative EBV-specific CTL. Nef-specific CTL were generated exclusively from CD8+ cells and were MHC class I restricted. Since a vigorous Nef-specific CTL response in non-infeted individuals was unexpected, CTL precursor frequencies were determined by limiting dilution analyses in non-fractionated PBL and in PBL separated into the CD45RCT− (naive) and CD45RO+ (memory) T cell populations. As expected, the putative EBV-specific CTL precursors were predominantly found in the CD45RO+ subset at frequencies typical for memory T cells. Nef-specific CTL precursors, in contrast, were found predominantly in the CD45R0− population, at even higher frequencies of ∼1/1000–;1/3000. Nef may thus display either an unusually high number of immunogenic peptides or a limited number of peptktes presented in a very efficient way, so that many T cells including low affinity cells, would be triggered.