In vitro expansion distorts the detectable pattern of specific recognition of in vivo primed cytotoxic T lymphocyte populations.

Injection of the 708-amino-acid (aa) viral protein "large tumor antigen" (T-Ag) of simian virus 40 (SV40) or its N-terminal 272-aa fragment into C57BL/6 (B6) mice (H-2b) primed CD8+ cytotoxic T lymphocytes (CTL) in vivo. Surprisingly, injection of this nonstructural viral protein (or its N-terminal fragment) in soluble form (without adjuvants) was as efficient in priming CD8+ CTL in vivo as the infection of B6 mice with the virus SV40. CTL activated in vivo by immunization with T-Ag proteins or SV40 infection specifically lysed syngeneic RBL5 cells transfected with a T-Ag-encoding vector; these RBL5/M7 transfectants efficiently presented N- and C-terminal T-Ag epitopes in association with H-2 class I restriction elements. N- and C-terminal T-Ag epitopes were recognized by CTL primed in vivo by immunization with the complete T-Ag protein or by infection with SV40, and (as expected) only N-terminal T-Ag epitopes were recognized by CTL primed in vivo by the soluble N-terminal T-Ag fragment. In CD8+ CTL populations primed in vivo by immunization with the complete T-Ag protein or by SV40 infection and restimulated in vitro with RBL5/M7 transfectants in a mixed tumor cell-lymphocyte culture (MTLC), CTL with specificity for C-terminal T-Ag epitopes were selectively expanded in vitro for months. Hence, the in vitro expansion of CTL population with heterogenous recognition specificities can dramatically distort the picture of its specific recognition repertoire primed in vivo.

Immunization with soluble simian virus 40 large T antigen induces a specific response of CD3+ CD4- CD8+ cytotoxic T lymphocytes in mice.

C57BL/6 (B6) mice (H-2b) were immunized with the large tumor antigen (T Ag) of simian virus 40 (SV40). Intraperitoneal or subcutaneous sensitization with soluble T Ag specifically primed cytotoxic lymphocyte precursors (CTLp). T Ag-specific cytotoxic T lymphocytes (CTL) were detected in a cytotoxicity assay after specific in vitro restimulation of effector cell populations from mice immunized with 2-10 micrograms purified, soluble T Ag and boosted with an injection of 2 micrograms T Ag 2-4 weeks after priming. Cells used for in vitro restimulation and as targets in cytotoxicity assays were syngeneic (B6-derived) RBL5 lymphoma cells expressing SV40 T Ag after transfection with a T Ag-encoding expression vector. Effector cells of this response were H-2 class I-restricted CD3+ CD4-CD8+ CTL. The magnitude of the anti-T Ag CTL response of B6 mice stimulated by soluble virus protein was comparable to the anti-T Ag CTL response of SV40-infected B6 mice. Injections of denatured or native T Ag protein primed CTLp equally well, but immunization with an equal dose of antigen emulsified in incomplete Freund's adjuvants inefficiently stimulated CTLp.

Roles of CD4- and CD8-bearing T lymphocytes in the immune response to the erythrocytic stages of Plasmodium chabaudi.

The possible role of CD4- and CD8-bearing T lymphocytes in parasite clearance in vivo was investigated, using Plasmodium chabaudi in C57BL/6 mice as a model. Monoclonal antibodies specific for the CD4 and CD8 molecules were administered in vivo to deplete selectively the appropriate subset of T cells. The efficacy of depletion was ascertained by flow cytometry and functional studies. These mice were then infected with P. chabaudi, and the course of infection was followed. The control groups had maximum parasitemias of approximately 30% 10 days after infection, and the infection was cleared within 27 days. Mice without CD4+ cells had significantly higher parasitemias which they were unable to reduce below 20% for the duration of the experiment. Mice without CD8 cells had slightly higher parasitemias which were cleared after 34 days. Because of the possibility that CD8+ cells alone could not be activated in the absence of growth factors, exogenous interleukin-2 was administered to the mice depleted of CD4 cells. This did not significantly affect parasitemias, and the mice were still unable to clear their infections. The data suggest that CD4+ T cells play a crucial role in the protective immune response to the erythrocytic stages of P. chabaudi.