STUDIES OF THE MECHANISM OF CYTOLYSIS BY HIV-1-SPECIFIC CD4+ HUMAN CTL CLONES INDUCED BY CANDIDATE AIDS VACCINES

Vaccine-induced, virus-specific CTLs may rapidly eliminate the host ce lls that first become infected after virus exposure, thereby preventin g disseminated infection. Thus, there is much interest in the ability of candidate AIDS vaccines to elicit CTLs. All HIV-1 envelope (env) pr otein-based vaccines tested to date in seronegative humans induce CTLs from the CD4(+) subset. Because the mechanism of cytolysis by CD4(+) CTLs is controversial, a detailed study of the cytolytic reactions med iated by vaccine-induced, HIV-1-specific human CD4(+) CTL clones was c onducted. CD4(+) CTL clones induced rapid destruction of Ag-pulsed tar get cells. Lysis was readily detectable within 15 min. Lysis was not a result of syncytium formation between CD4(+) effector cells and env-e xpressing targets. Target cell destruction was not dependent upon de n ovo RNA or protein synthesis in either the effector or the target cell . Expression of perforin mRNA was detected by Northern blotting and re verse-transcriptase-PCR in CD4(+) CTL clones but not in autologous B l ymphoblastoid cell lines. Immunohistochemical studies demonstrated per forin protein in cytoplasmic granules in CD4(+) CTL clones. Lysis by C D4(+) CTLs was strictly dependent upon extracellular Ca2+ and was high ly specific, with no lysis of innocent bystander cells. DNA fragmentat ion was detectable in target cells, but did not precede Cr-51 release. Taken together, these results provide a dramatically different view o f cytolysis by human CD4(+) CTLs. Target cells are lysed by a rapid an d efficient mechanism that involves a preformed mediator and that is f unctionally similar to the mechanism used by CD8(+) CTLs.