Immunization of C57BL/6 mice with syngeneic cells transformed by simia
n virus 40 large T antigen (SV40 T ag) induces the generation of T ant
igen-specific cytotoxic T lymphocytes (CTL) which are restricted by th
e major histocompatibility class I antigens H-2D(b) and H-2K(b). Previ
ous studies have shown that the H-2D(b)-restricted CTL response is dir
ected to at least three distinct epitopes (I, II/III, and V) in the SV
40 T antigen which have been precisely mapped using deletion mutagenes
is and overlapping synthetic peptides. Although in vivo the CTL respon
se to SV40 T antigen is dominated by the H-2K(b) class I antigen, the
precise location of the H-2K(b)-restricted epitope(s) was not known, a
nd whether there was multiplicity of H-2K(b)-restricted epitopes remai
ned unclear. In this study, we have defined the minimal recognition ep
itope for the SV40-specific H-2K(b)-restricted CTL clone Y-4 as T anti
gen residues 404-411 by using T antigen deletion and point mutants and
synthetic peptides. DNA sequence analysis of the region encoding resi
dues 404-411 from the T antigens expressed in three independently isol
ated CTL clone Y-4 escape variants identified inactivating mutations c
apable of abrogating CTL recognition. Estimation of CTL precursor (CTL
p) frequencies by limiting dilution analysis revealed that CTLp specif
ic for epitope IV represent a large percentage of the total CTL respon
se elicited by the intact T antigen in H-2(b) mice. Immunization of B6
mice with cells expressing a T antigen derivative deleted of residues
404-411 revealed that site IV represents the only immunodominant H-2K
(b)-restricted epitope within T antigen. (C) 1995 Academic Press, Inc.