Immunogenicity of whole-cell tumor preparations infected with the ALVAC viral vector

The immunogenicity of recombinant canarypox (ALVAC) viral vectors within mu rine whole-cell tumor vaccines was evaluated using the T cell thymic lympho ma STF10 and the B16 melanoma. Tumor cells were modified with the recombina nt ALVAC vectors and injected into syngeneic mice. Control mice receiving c ells alone all developed tumors, while mice injected with tumor variants be aring parental and recombinant vectors either completely rejected their tum ors, or exhibited a significant delay in tumor formation. Rechallenge of mi ce receiving STF10-variant vaccines yielded a protective effect against par ental tumor cells only when a modified regimen incorporating two vaccinatio ns was utilized. Notably, the parental ALVAC virus was equivalent to all ot her recombinant ALVAC viruses in conferring antitumor immunity when using a prime-and-boost protocol. Tumorigenicity experiments in nude mice revealed that the effector mechanism mediating rejection of tumor cells bearing ALV AC vectors is multifactorial, in that the immunogenicity of STF10/ALVAC vac cines is reduced, but not completely abolished in these mice. Finally, in v itro experiments revealed that cytotoxic T cells specific for parental STF1 0 cells could be generated as a result of in vivo immunization with STF10/A LVAC vaccines.