A SINGLE RETROVIRAL GAG PRECURSOR SIGNAL PEPTIDE RECOGNIZED BY FBL-3 TUMOR-SPECIFIC CYTOTOXIC T-LYMPHOCYTES

Several dominant T-cell receptors of cytotoxic T-lymphocyte (CTL) clon es specific for FBL-3 tumor antigen were clonally amplified in mixed l ymphocyte tumor cell cultures derived from an individual immune mouse. Every CTL clone analyzed had a common specificity for a single epitop e in the precursor to cell membrane associated nonstructural gag-encod ed protein, pr75(gag), which can be minimally identified by nine amino acid residues, SIVLCCLCL. This epitope is located within the hydropho bic signal sequence motif that mediates translocation of the protein i nto the endoplasmic reticulum. These novel observations suggest that e xpression of Pr75(gag) in FBL-3 tumor cells led to the amplification o f CTLs which recognize the signal sequence of the nonstructural gag-en coded glycoprotein precursor.