Identification of a Unique Antigen Peptide pRL1 on BALB/c RL♂1 Leukemia Recognized by Cytotoxic T Lymphocytes and Its Relation to the Akt Oncogene

BALB/c radiation leukemia RLCel is an immunogenic tumor. We established bulk and cloned cytotoxic T lymphocyte (CTL) lines from regressor (BALB/c × C57BL/6)F₁ (CB6F₁) spleen cells that recognized RL♂1 specifically. We then obtained antigen peptide recognized by CTL from RL♂1 by acid extraction. Analysis of the acid extract by reversed-phase high performance liquid chromatography (HPLC) on a semipreparative C18 column revealed that fractions eluted in 23 min (peak a) and 26 min (peak b) showed sensitization activity on the P815 target for specific CTL. On further purification of these fractions by HPLC and direct sequencing by Edman degradation, we identified the CTL-recognizing RL♂1 peptide pRL1a (IPGLPLSL) in peak a and its possible precursor peptide pRL1b (SIIPGLPLSL) in peak b. Sequence homology indicated that these peptides were derived from the 5' untranslated region of c-akt oncogene.