Differential cytotoxic T-lymphocyte (CTL) responses in HIV-1 immunised sibling chimpanzees with shared MHC haplotypes.

Cell mediated immune responses to HIV-1 and CTL responses in particular differ dramatically in infected individuals. This may largely be influenced by the immunogenetic differences of different individuals such as those encoded by the MHC. These differences may be difficult to dissect due to the immunosuppressive nature of HIV-1 infection itself. In order to reduce the variables associated with effects of the virus, one recombinant viral antigen was chosen from a particular HIV-1 variant (rgp120 of the clinical isolate HIV-1w6.1D). To minimise differences between outbred hosts, we chose two sibling chimpanzees from which the family pedigree and genetic segregation with respect to polymorphic MHC molecules was known. Immunisation induced strong antigen specific antibody and T-helper immune responses. The magnitude and persistence of the humoral and T-helper immune responses were comparable in both chimpanzees. However, CTL responses were only observed in one sibling. These responses were subsequently mapped to several distinct epitopes. The CTL response to the immunodominant epitope was found to be presented in the context of a MHC molecule which was shared by both siblings. The absence of a CTL response in the other sibling is not yet understood, but could not be attributed to MHC alleles that were not shared by these two chimpanzees. These findings suggest that other polymorphic immunoregulatory mechanisms such as those involved in antigen processing and presentation influence host CTL responses to HIV-1.

Conserved CTL epitopes shared between HIV-infected human long-term survivors and chimpanzees.

Certain HIV-1 infected humans that do not progress to AIDS have been documented to share particular MHC class I alleles that appear to correlate with long-term survival. HIV-1-infected chimpanzees are relatively resistant to progression to AIDS. Out of a group of 10 chimpanzees with CTL activity and nonprogressive HIV-1 infection, 2 animals with prominent cytolytic CD3+CD8+ T cell responses to HIV-1 Ags were studied in detail. Characterization of these CTL revealed that they contained the granzymes A and B, T cell intracellular Ag-1, and perforin and induced calcium-dependent cytolysis that correlated with the presence of apoptotic nuclei in target cells. These CTL responses were directed against two gagpeptides, which were found to be identical to previously described epitopes recognized in the context of HLA-B27 and HLA-B57 molecules. The latter two restriction elements occur with increased frequency in human long-term survivor cohorts. Phylogenetic comparisons revealed that the chimpanzee restriction elements, Patr-B*02and -B*03, described here do not show any obvious similarity with the HLA-B*27 and -B*57 alleles, suggesting that CTL responses to HIV-1 in distinct primate species may be controlled by different types of HLA-B-like molecules. The CTL responses in these two chimpanzees are directed, however, against highly conserved epitopes mapping across the majority of HIV-1 clades.

Plasmid rescue of an oncogenic sequence containing a mouse mammary tumor virus gene.

Plasmid rescue was performed on an oncogenically transformed cell line established by transfection of NIH/3T3 cells with normal mouse DNA and plasmids containing a murine leukemia virus long terminal repeat, and a selectable marker. One of the rescued plasmids contained newly acquired DNA 3,500 basepairs in length. This sequence was present in several extra copies in the parental cell line. It was also found to be transcribed. NIH/3T3 cells transfected with the rescued plasmid proved to be oncogenic in nude mice. The acquired sequence appeared to contain (part of) the long terminal repeat of mouse mammary tumor virus.