IMMUNIZATION OF MICE WITH THE N-TERMINAL (1-272) FRAGMENT OF SIMIAN-VIRUS 40 LARGE T-ANTIGEN (WITHOUT ADJUVANTS) SPECIFICALLY PRIMES CYTOTOXIC T-LYMPHOCYTES

Immunization of C57BL/6 (B6) mice (H-2b) with the ''large tumor antige n'' (T-Ag) of simian virus 40 (SV40) in its soluble form without adjuv ants primed CD8+ cytotoxic T lymphocytes (CTL) in vivo. CD8+ CTL prime d in vivo by this non-structural 708-amino acid (aa) viral protein, an d specifically restimulated in vitro, lysed H-2b target cells, either transfected with an SV40 T-Ag-encoding vector, or transformed by SV40 infection. H-2b RMA-S transfectants expressing the complete 708 aa T-A g (which fail to transport peptides through the endoplasmic reticulum membranes) were not lysed. CTL were also efficiently primed in vivo by injection of the N-terminal 272 aa fragment of the T-Ag. Hence, this fragment contains the structure(s) required for a soluble protein to e nter the ''endogenous'' class I-restricted antigen processing and pres entation pathway for CD8+ CTL activation. In soluble form, the complet e T-Ag or the N-terminal T-Ag fragment sensitized in vitro RBL5 cells for lysis by T-Ag-specific CTL lines and clones. This in vitro sensiti zation was blocked by brefeldin A. In contrast, specific recognition o f RBL5 cells pulsed in vitro with synthetic, immunogenic nonapetides ( derived from N-terminal T-Ag epitopes) by CTL lines was insensitive to brefeldin A. Hence, T-Ag and its 272-aa N-terminal fragment can enter the ''endogenous'' processing pathway and prime CD8+ CTL in vivo and in vitro.