THE INDUCTION OF CYTOTOXIC T-CELLS AND TUMOR-REGRESSION BY SOLUBLE-ANTIGEN FORMULATION

CTLs specific for tumor antigens play a major role in the immunity aga inst cancer. We have shown that class I-restricted CTLs can be induced by injecting soluble antigens mixed in an antigen formulation (AF) th at consists of squalane, Tween 80, and Pluronic L121 (S. Raychaudhuri et al., Proc. Natl. Acad, Sci, USA, 89: 8308-8312, 1992). In this stud y, using ovalbumin and the ovalbumin-expressing transfectoma (EG7) as a tumor model system, we examined the in vivo antitumor effect of anti gen-AF mixture. Vaccination of mice with ovalbumin in AF 2 or 3 days a fter EG7 tumor challenge showed significant inhibition of tumor growth compared to mice vaccinated with ovalbumin in alum or in saline. Depl etion of CD8(+) cells at the time of immunization completely abrogated the AF-induced tumor protection, indicating that CD8(+) T cells are t he major effecters in tumor protection in vivo. Depletion of CD4(+) ce lls led to a marginal loss of tumor protection, which may be the resul t of inhibition of ovalbumin-specific CTL response due to the lack of T-helper activity. Our results demonstrate that AF can be used in subu nit vaccines to stimulate CTLs and tumor regression in vivo.