Ep. Miskovsky et al., STUDIES OF THE MECHANISM OF CYTOLYSIS BY HIV-1-SPECIFIC CD4+ HUMAN CTL CLONES INDUCED BY CANDIDATE AIDS VACCINES, The Journal of immunology, 153(6), 1994, pp. 2787-2799
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.