In a longitudinal study of HIV seropositive patients, there were fluctuations in the specificity of cytotoxic T cells for the virus. This was matched by variability in proviral gag DNA epitope sequences in the lymphocytes of these patients. Some of these viral variants are not recognized by autologous T cells. Accumulation of such mutations in T-cell antigenic targets would provide a mechanism for immune escape.

No abstract

Current candidate vaccines fail to protect primates against challenge with human immunodeficiency virus (HIV) in the presence of antibody responses; this underlines the importance of studying cell-mediated immunity to HIV and identifying specific epitopes that stimulate cytotoxic T lymphocytes (CTL). Using a recombinant vaccinia virus to express the gag protein of HIV-1 we found HLA class-I-restricted gag-specific CTL in thirteen out of fifteen healthy HIV seropositive patients. We then used short synthetic peptides in the lysis assay to screen for gag CTL epitopes. In one patient we have identified a peptide in p24 that is recognized by CTL in association with HLA-B27. This peptide, and further peptide sequences defined by these methods, could be incorporated in vaccines designed to induce cell-mediated immunity against HIV.

Haemophilia A is a mutationally heterogeneous disease caused by defects in the large and complex factor VIII gene. Recent studies examining the putative promoter, all exons and most intron/exon boundaries have failed to detect mutations in half the patients with severe disease leading to hypotheses such as mutations in remote controlling regions or even in genes other than factor VIII. We have amplified the factor VIII gene (putative promotor, coding region and polyadenylation/cleavage signal region) in 8 fragments from reverse transcribed mRNA and genomic DNA. Any mutation is then located by chemical mismatch detection and characterised by direct sequencing. This rapid and efficient method has been fully successful and has revealed an unusual cluster of mutations causing severe disease. Of the 28 patients we have reported, 5 had mild or moderate disease and all had a missense mutation. Twenty-three patients were severely affected and 13 of these had different detrimental mutations that were fully characterised at the genomic DNA level. The remaining 10 patients all had mRNA with exon 22 not contiguous to exon 23. Since all exons were normal and so were the splice sites of intron 22, the mutation in these patients should be in the regions of intron 22 that were not screened. These results prove that all haemophilia A cases are due to mutations of the factor VIII gene where, unexpectedly, intron 22 seems to be the target of approximately 40% of the mutations causing severe haemophilia A.