title: Adoptive immunotherapy as an in vivo model to explore antitumor mechanisms induced by a recombinant anticancer vaccine.
abstract: We have described previously the construction, generation, and in vivo biologic consequences of a recombinant vaccinia virus containing the human CEA gene (rV-CEA) in an experimental murine colon carcinoma model. Immunization of C57BL/6 mice with rV-CEA led to antigen-specific inhibition of tumor growth in both prophylactic and therapeutic settings. Although such antitumor effects were correlated with the induction of CEA-specific T-cell responses, their exact contribution in the tumor rejection mechanism remained unclear. In this study, we examined the mechanism of action of rV-CEA, with emphasis on definition of the immune cells important for such antitumor effects. To that end, a cellular adoptive transfer model was established in vivo, which allowed specific functional analysis of donor-derived immune cells in naive, sublethally irradiated, tumor-bearing recipients. Splenocytes from rV-CEA-immunized donors expressed strong antitumor activity in such tumor-bearing recipients, whereas nonimmune donor cells did not. Depletion of immune T cells before cellular transfer abolished the antitumor response. Moreover, depletion of CD8+ T cells before transfer resulted in the loss of antitumor activity, despite the presence of CD4+ T cells. In contrast, antitumor activity was demonstrable with CD8-containing, CD4-depleted effectors, although it was not as effective as with both T-cell subpopulations combined. Finally, in beta 2-microglobulin/CD8+ T-cell-deficient mice, rV-CEA immunization exerted only partial antitumor protection, compared with the immune-competent controls. Overall, we demonstrated that (a) antitumor activity induced by rV-CEA was essentially mediated by CD8+ effectors; and (b) the combination of both CD8+ and CD4+ lymphocytes led to maximal antitumor therapeutic effects, suggesting an important helper or immunoregulatory contribution of the CD4+ subset. Thus, adoptive cellular transfer strategies may have implications for both the study of recombinant anticancer vaccines and the development of potential clinical applications for cancer immunotherapy.
authors.affiliation: Laboratory of Tumor Immunology and Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-1750, USA.
authors.forename: S I
authors.initials: SI
authors.lastname: Abrams
authors.forename: J W
authors.initials: JW
authors.lastname: Hodge
authors.forename: J P
authors.initials: JP
authors.lastname: McLaughlin
authors.forename: S M
authors.initials: SM
authors.lastname: Steinberg
authors.forename: J A
authors.initials: JA
authors.lastname: Kantor
authors.forename: J
authors.initials: J
authors.lastname: Schlom
mesh_terms: D000230:Adenocarcinoma / Q000628:therapy*; D000818:Animals; D000918:Antibody Specificity; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D019496:Cancer Vaccines / Q000627:therapeutic use*; D002272:Carcinoembryonic Antigen / Q000235:genetics*; D002455:Cell Division / Q000276:immunology; D003110:Colonic Neoplasms / Q000628:therapy*; D004195:Disease Models, Animal; D006801:Humans; D016219:Immunotherapy, Adoptive; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D011995:Recombination, Genetic; D013154:Spleen / Q000166:cytology / Q000276:immunology; D014614:Vaccines, Synthetic / Q000627:therapeutic use*
chemical_list: D019496:Cancer Vaccines; D002272:Carcinoembryonic Antigen; D014614:Vaccines, Synthetic