Evaluation of immunotherapy strategies in mouse models of carcinoma is hamp
ered by the limited number of known murine tumor antigens (Ags). Although t
umor Ags can be identified based on cytotoxic T-cell activation, this appro
ach is not readily accomplished for many tumor types. We applied an alterna
tive strategy based on a humoral immune response, SEREX, to the identificat
ion of tumor Ags in the murine colon adenocarcinoma cell line MC38. Immuniz
ation of syngeneic C57BL/6 mice with MC38 cells by three different methods
induced a protective immune response with concomitant production of anti-MC
38 antibodies. Immunoscreening of an MC38-derived expression library result
ed in the identification of the endogenous ecotropic leukemia virus envelop
e (env) protein and the murine ATRX protein as candidate tumor Ags. Norther
n blot analysis demonstrated high levels of expression of the env transcrip
t in MC38 cells and in several other murine tumor cell lines, whereas expre
ssion in normal colonic epithelium was absent. ATRX was found to be variabl
y expressed in tumor cell lines and in normal tissue. Further analysis of t
he expressed env sequence indicated that it represents a nonmutated tumor A
g. Polynucleotide immunization with DNA encoding the env polypeptide result
ed in strong and specific antibody responses to this self Ag in all immuniz
ed mice. Thus, SEREX offers a rapid means of identifying tumor Ags in murin
e cancer models.