title: Pre-existing tumor-sensitized T cells are essential for eradication of established tumors by IL-12 and cyclophosphamide plus IL-12.
abstract: The antitumor immune response activated by IL-12, especially by a combination of cyclophosphamide and IL-12 (Cy+IL-12), is clinically significant in certain experimental tumor models, in that a number of well-established (10-20 mm in diameter) s.c. tumors are completely eradicated. Furthermore, Cy+IL-12 treatment is also able to eradicate well-established grossly detectable experimental lung metastases and advanced ascites tumors. Despite the dramatic antitumor effects seen in some tumor models, Cy+IL-12 fails to induce regression of other established tumors. Characterization of tumor immunogenicity shows that all tumors responding to IL-12 and Cy+IL-12 treatments are immunogenic tumors, in that an antitumor immune response is detectable in tumor-bearing hosts upon tumor establishment. In contrast, none of the nonimmunogenic tumor responds to IL-12 and Cy+IL-12 treatments. Analysis of cellular requirements for successful tumor rejection through an adoptive cell transfer approach reveals that the presence of tumor-sensitized, but not naive, T cells is essential for tumor rejection by IL-12 and Cy+IL-12. Transfer of these tumor-sensitized T cells must be conducted before, but not after, IL-12 treatment in order for tumor rejection to occur. The requirement of sensitized T cells is also tumor specific. In mice bearing immunogenic tumors, the presence of pre-existing tumor-sensitized T cells is demonstrated by adoptive cell transfer experiments using purified spleen T cells from these mice. Results from our study show that Cy+IL-12-based immunotherapy of cancer may be highly effective and that pre-existing tumor-sensitized T cells are essential for the success of the therapy.
authors.affiliation: Department of Surgery, University of California and San Francisco Veterans Affairs Medical Center, San Francisco, CA 94121, USA.
authors.forename: H N
authors.initials: HN
authors.lastname: Le
authors.forename: N C
authors.initials: NC
authors.lastname: Lee
authors.forename: K
authors.initials: K
authors.lastname: Tsung
authors.forename: J A
authors.initials: JA
authors.lastname: Norton
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D002455:Cell Division; D003520:Cyclophosphamide / Q000494:pharmacology*; D005260:Female; D019672:Genes, T-Cell Receptor; D016219:Immunotherapy, Adoptive; D018664:Interleukin-12 / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000276:immunology* / Q000473:pathology / Q000628:therapy; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology* / Q000637:transplantation
chemical_list: D018664:Interleukin-12; D003520:Cyclophosphamide