Ba. Pulaski et al., INTERLEUKIN-3 ENHANCES DEVELOPMENT OF TUMOR-REACTIVE CYTOTOXIC-CELLS BY A CD4-DEPENDENT MECHANISM, Cancer research, 53(9), 1993, pp. 2112-2117
We investigated the effects that mouse interleukin 3 (IL-3), in compar
ison to mouse IL-2, has on the generation of cytotoxic effectors capab
le of killing line 1 tumor cells. These potent immunological mediators
were delivered locally using gene transfection, rather than systemica
lly, to the tumor site. We created line 1 transfectants that express h
igh levels of IL-3 (3750 units/ml) or IL-2 (200 units/ml) by driving t
ranscription from the beta-actin promoter. These levels of expression
significantly enhanced tumor rejection in syngeneic mice. Tumor-infilt
rating lymphocytes purified from IL-3 or IL-2 transfected tumors showe
d a dramatically enhanced cytotoxic response to parental line 1 target
s. Also, IL-2, but not IL-3, expression enhanced the nonspecific lysis
of YAC-1 cells. In vivo depletion of CD8+ cells with monoclonal antib
ody 2.43 abrogated the generation of cytotoxic effectors in both cases
. Interestingly, depletion of CD4+ cells with monoclonal antibody GK1.
5 abrogated the IL-3-mediated cytotoxic response but not the IL-2-medi
ated response. In vivo depletion of CD4+ or CD8+ cells abrogated the e
ffect IL-3 had on reducing tumorigenicity. Reverse polymerase chain re
action analysis demonstrates that IL-3 transfected tumors, when compar
ed to untransfected tumors, express increased levels of IL-2 and IL-4
mRNA. These results strongly suggest that IL-3, unlike IL-2, works to
generate cytotoxic effectors by a mechanism that requires CD4+ cells.