No abstract

Prevention of tumors induced by environmental carcinogens has not been achieved. Skin tumors produced by polyaromatic hydrocarbons, such as 7,12-dimethylbenzanthracene (DMBA) often harbor an H-ras point mutation, suggesting that it is a poor target for early immune surveillance. The application of pyrosequencing and allele-specific PCR techniques established that mutations in the genome and expression of the Mut H-ras gene could be detected as early as one day after DMBA application. Further, DMBA sensitization raised Mut H-ras epitope-specific CTLs capable of eliminating Mut H-ras+ pre-neoplastic skin cells, demonstrating that immunosurveillance is normally induced but may be ineffective due to insufficient effector pool size and/or immune suppression. To test whether selective pre-expansion of CD8 T cells with specificity for the single Mut H-ras epitope was sufficient for tumor prevention, MHC class I-epitope-focused lentivector-infected dendritic cell (DC)- and DNA-based vaccines were designed to bias toward CTL rather than Treg induction. Mut H-ras but not wild-type H-ras epitope-focused vaccination generated specific CTL and inhibited DMBA-induced tumor initiation, growth and progression in preventative and therapeutic settings. Transferred Mut H-ras-specific effectors induced rapid tumor regression, overcoming established tumor suppression in tumor bearing mice. These studies support further evaluation of oncogenic mutations for their potential to act as early tumor-specific, immunogenic epitopes to expand relavent immunesurviellance effectors in order to block tumor formation, rather than treating established tumors.