2154

Angiogenesis has been shown to be a critical mechanism for tumor progression. Multiple studies have suggested that tumor growth can be suppressed if tumor angiogenesis can be inhibited using various types of agents. These include inhibitors to the molecules involved in angiogenesis and antibodies to the related molecules. Recent studies in mouse models showed tumor-angiogenesis can also be inhibited if cellular immune response could be induced against vascular endothelial growth factor receptor2 (VEGFR2), which has been shown to be a key factor in tumor angiogenesis. In this study, we examined the possibility of developing this novel immunotherapy using A2/Kb transgenic mouse model. At first, we identified the VEGFR2-derived epitope peptides restricted to HLA-A*0201 and A*2402 and showed that CTLs induced with these peptides had strong cytotoxicity against not only target cells pulsed with the peptides but also endothelial cells endogenously expressing VEGFR2 in HLA class I restricted fashion. Furthermore, these CTL clones showed strong cytotoxic activities against proliferative endothelial cells but little cytotoxic activities against non-proliferative or slowly proliferative endothelial cells. In vivo anti-tumor effects were also examined using the A2/Kb transgenic mouse which is considered to be a good model for evaluating immune responses in human system. Vaccination using the identified epitope peptides, which are present in both human and mouse VEGFR2 sequences, showed significant suppression of the tumor growth and prolongation of the survival in A2/Kb mouse model. This peptide-based vaccine was also effective for the established tumor setting as well. In anti-angiogenesis assay, tumor-induced angiogenesis was significantly suppressed with vaccination using these epitope peptides. Interestingly, our vaccination using these epitope peptides did not show any adverse effects in vivo. Homology analysis of these epitope peptides indicated that the sequences of these peptides were unique and there were little possibility, to our best knowledge, to raise immunological response to other molecules, whereas the sequence of VEGFR2 was very similar to other growth factor receptors. Furthermore, CTLs specific to the epitope peptides were successfully induced in cancer patients and confirmed their specificities using functional and HLA-tetramer analysis. These results, in vitro and in vivo, strongly suggest that VEGFR2 could be a promising target of cellular immunity in human and support the definitive rationale for the clinical application of this strategy as another form of anti-angiogenic therapy against cancer. Vaccination using epitope peptides derived from VEGFR2 is now in the process of clinical application in our institute.

[Proc Amer Assoc Cancer Res, Volume 45, 2004]