Vaccination with multiple antigen peptide as rejection antigen peptide in murine leukemia

pRL1a (IPGLPLSL) is the L(d)-binding tumor rejection antigen peptide recognized by CTLs on BALB/c radiation leukemia RL♂1. We demonstrated that in vivo and in vitro sensitization with pRL1a multiple antigen peptide (MAP), but not with the pRL1a peptide itself, generated pRL1a-specific CTLs in the spleen cells of BALB/c mice. No enhancement of cytotoxicity was observed by emulsifying pRL1a MAP in incomplete Freund's adjuvant or in complete Freund's adjuvant for in vivo sensitization. Selective depletion of CD4⁺ T cells in mice by treatment with anti-L3T4 (CD4) monoclonal antibody and that of macrophages by treatment with carrageenan on in vivo sensitization with pRL1a MAP abrogated CTL generation. The findings suggest that CD4⁺ T cells and antigen-presenting cells were necessary for the in vivo priming of CD8⁺ T cells with pRL1a MAP. Furthermore, we demonstrated that in vivo sensitization of BALB/c mice with pRL1a MAP, but not with pRL1a peptide, showed an inhibitory effect on RL♂1 tumor growth. No growth-inhibitory effect was observed on control RVA, RVD, or Meth A tumors.