Additionally, attempts to find the transferred cells by specific amplification of mismatched MHC class I alleles of the donor using DNA from the blood at weeks 2, 3 and 4 post-infection, as well as in spleens and tumor samples upon termination of the experiments were limited by the sensitivity of our PCR-based method (1% of CD8+ T cells) and did not detect persistence of the transferred clonal T cell populations (data not shown). This evidence concerns the gene CD8A and infection.