Tumor cells genetically modified by transduction of B7 (B7-1/CD80), a
natural ligand for the T-cell costimulatory molecules CD28 and CTLA-4,
can elicit potent tumor immunity, and they can be effective for treat
ment of established cancers in animal models. In this study, three tum
or lines, the EL4 lymphoma, the P815 mastocytoma, and the MCA102 sarco
ma mere transduced with recombinant retrovirus containing the murine B
7 gene, and their potency to induce systemic immunity protective again
st challenge with wild-type tumor nas compared to that of the same tum
or cells admired with the commonly used adjuvant Corynebacterium parvu
m. While admixture of tumor cells with C. parvum resulted in complete
regression of tumors in syngeneic mice, it did not induce protective i
mmunity against a subsequent challenge of mild-type cells from any of
the 3 tumors tested. In contrast, B7-transduced EL4 and P815 tumors re
gressed locally and induced a potent systemic immunity to wild-type tu
mors and a higher level of cytotoxic T-cell activity than did tumor ce
lls admixed with C. parvum. No systemic immunity was induced by B7-tra
nsduced nonimmunogenic MCA102 sarcoma cells. Our results demonstrate t
hat immunogenic tumor cells transduced with the B7 gene are superior t
o tumor cells mixed with C. parvum for the induction of systemic tumor
immunity.