Efficient direct priming of tumor-specific cytotoxic T lymphocyte in vivo by an engineered APC.
Although numerous studies have documented a role for B7-1 (CD80) in the induction of antitumor CTL immunity, it is presently unclear to what extent expression of this costimulatory molecule truly endows tumors with significant in vivo APC (antigen-presenting cell) capacity. Recent studies have, in fact, demonstrated that cross-priming, rather than direct priming, may constitute the major mechanism of CTL induction by B7-1 expressing tumors. We have, therefore, investigated the requirements for antigen density and costimulatory molecules in direct CTL priming with a prototype cell-based vaccine that uses a signal sequence-containing minigene to direct expression of a tumor-specific CTL epitope to the endoplasmic reticulum. This design limits sources of antigen available to professional APC in the host and, thereby, the contribution of cross-priming. Induction of antitumor CTL immunity by our prototype APC was shown to solely involve direct priming, independent of host APC, NKI.1+ cells, and CD4+ T cell help. CTL induction through this mechanism required the engineered APC to express the B7-1 molecule as well as a sufficiently high density of peptide/MHC complexes at its surface. Our data, in contrast to previous studies using modified tumor cells, clearly define the antigenic and costimulatory requirements for a suitably engineered "artificial" APC to directly prime peptide-specific CTL in vivo, and demonstrate that the signal sequence minigene approach allows the engineering of highly effective and well-defined cellular vaccines for activation of CTL against epitopes of choice.
Department of Immunohematology and Blood Bank, University Hospital Leiden, The Netherlands. sps@liai.org
S P
SP
Schoenberger
L E
LE
Jonges
R J
RJ
Mooijaart
F
F
Hartgers
R E
RE
Toes
W M
WM
Kast
C J
CJ
Melief
R
R
Offringa
D017500:Adenovirus E1A Proteins / Q000276:immunology; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology*; D018122:B7-1 Antigen / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D005260:Female; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D016513:Mice, SCID; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
D017500:Adenovirus E1A Proteins; D018122:B7-1 Antigen