MINIMAL DETERMINANT EXPRESSED BY A RECOMBINANT VACCINIA VIRUS ELICITSTHERAPEUTIC ANTITUMOR CYTOLYTIC T-LYMPHOCYTE RESPONSES

Anticancer vaccine strategies can now target intracellular antigens th at are involved in the process of malignant transformation, such as on cogene products or mutated tumor suppressor genes. Fragments of these antigens, generally 8-10 amino acids in length and complexed with MHC class I molecules, can be recognized by CD8+ T lymphocytes (T-CD8+). T o explore the possibility of using a genetically encoded, minimally si zed fragment of an intracellular antigen as an immunogen, we construct ed a recombinant vaccinia virus encoding an 8-residue peptide derived from chicken ovalbumin that is known to associate with the mouse H-2K( b) molecule. Compared to standard methods of immunization, recombinant vaccinia virus expressing the minimal determinant as well as full len gth ovalbumin were the only approaches that elicited specific primary lytic responses in C57BL/6 mice against E.G7OVA, a transfectant of the murine thymoma EL4 containing the ovalbumin gene. Stimulating these e ffecters in vitro with OVA(257-264) peptide induced H-2K(b)-restricted T-CD8+ that not only lysed but also specifically secreted IFN-gamma i n response to an antigen. Furthermore, when transferred adoptively, th ese anti-OVA(257-264) T-CD8+ cells significantly reduced the growth of established ovalbumin-transfected tumors in a pulmonary metastasis mo del system. Synthetic oligonucleotides encoding minimal antigenic dete rminants within expression constructs may be a useful approach for tre atment of neoplastic disease, thus avoiding the potential hazards of i mmunizing with full-length cDNAs that are potentially oncogenic.