UP-REGULATION OF SPECIFIC TYROSINASE MESSENGER-RNAS IN MOUSE MELANOMAS WITH THE C(2J) GENE SUBSTITUTED FOR THE WILD-TYPE TYROSINASE ALLELE - UTILIZATION IN DESIGN OF SYNGENEIC IMMUNOTHERAPY MODELS

The expression of cell-specialization genes is likely to be changing i n tumor cells as their differentiation declines. Functional changes in these genes might yield unusual peptide epitopes with anti-tumor pote ntial and could occur without modification in the DNA sequence of the gene. Melanomas undergo a characteristic decline in melanization that may reflect altered contributions of key melanocytic genes such as tyr osinase. Quantitative reverse transcriptase-PCR of the wild-type (C) t yrosinase gene in transgenic (C57BL/6 strain) mouse melanomas has reve aled a shift toward alternative splicing of the pre-mRNA that generate d increased levels of the Delta 1b and Delta 1d mRNA splice variants. The spontaneous c(2j) albino mutation of tyrosinase (in the C57BL/6 st rain) changes the pre-mRNA splicing pattern. In c(2j)/c(2j) melanomas, alternative splicing was again increased. However, while some mRNAs ( notably Delta 1b) present in C/C were obligatorily absent, others (Del ta 3 and Delta 1d) were elevated. In c(2j)/c(2j) melanomas, the percen tage of total tyrosinase transcripts attributable to Delta 3 reached a pproximately 2-fold the incidence in c(2j)/c(2j) or C/C skin melanocyt es. The percentage attributable to Delta 1d rose to approximately 2-fo ld the incidence in c(2j)/c(2j) skin, and to 10-fold that in C/C skin. These differences provide a basis for unique mouse models in which th e melanoma arises in skin grafted from a C/C or c(2j)/c(2j) transgenic donor to a transgenic host of the same or opposite tyrosinase genotyp e. Immunotherapy designs then could be based on augmenting those antig enic peptides that are novel or overrepresented in a tumor relative to the syngeneic host.