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 and carrying a C4500T point mutation. The resulting protein lacks theSV40 small t antigen and Trp53-binding region and contains a glutamic acid to lysine subsitution at position 107 in the Rb1-binding domain. Regulatory sequences direct expression of the transgene in B- and T-lymphocytes and choroid plexus epithelium. (J:72121)