ANALYSIS OF THE HUMAN ENV-SPECIFIC CYTOTOXIC T-LYMPHOCYTE (CTL) RESPONSE IN NATURAL HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 INFECTION - LOW-PREVALENCE OF BROADLY CROSS-REACTIVE ENV-SPECIFIC CTL

Major histocompatibility complex-restricted cytotoxic T lymphocytes (C TL) are part of the cellular immune response to persistent virus infec tions, Candidate vaccines against human immunodeficiency virus type 1 (HIV-1) should elicit broad cross-reactive immunity to confer protecti on against different. strains of HIV-1, As it is likely that candidate vaccines will include the envelope gene product Env, we determined th e proportion of CTL clones which recognized variable and conserved det erminants in three env variants during natural infection, Limiting dil ution analysis was used to characterize numerous short-term CTL, clone s derived front peripheral blood of HIV-1-infected subjects, using spl it-well analysis to assay cytotoxicity against target cells expressing gp160(env) of HIV-1 strains IIIB, MN, and RF, In 9 of 12 HIV-1-infect ed subjects, at the clonal level most env-specific CTL recognized dete rminant(s) within one env variant but not in the other variants. In so me subjects, CTL recognized multiple nonconserved determinants in diff erent variants, The pattern of recognition of different env variants w as relatively stable over time. In most of the patients studied, the p roportion of CTL which showed cross-recognition of conserved determina nts shared among the three strains was low, Two novel CTL epitopes wit hin gp41 were identified by using 15-mer peptides of the HIV-SF2 seque nce, When specific peptide was used to stimulate CTL precursors in vit ro, the frequency of peptide-specific CTL precursors was very high, bu t the CTL elicited by this stimulation were highly strain specific, We conclude that the use of a single HIV env variant to detect CTL activ ity can underestimate the magnitude and complexity of the env-specific CTL response. The low prevalence of CTL clones which show cross-recog nition of conserved determinants may hare implications for immunizatio n strategies based solely on env; to elicit broadly cross-reactive CTL other, more conserved viral antigens are likely to be needed in addit ion to env, Because of its capacity to distinguish CTL responses again st different virus strains, limiting dilution analysis is particularly appropriate to quantitate the immune responses generated by candidate env-based vaccines.