The transgene consists of a lymphotrophic papovavirus (LPV) enhancer/early promoter and a mutant SV40 T antigen sequence truncated after amino acid 121 followed by 11 missense residues. The resulting protein includes the RB1-binding region but lacks the small t antigen and TRP53-binding region. Regulatory sequences direct expression of the transgene in B- and T-lymphocytes and choroid plexus epithelium.