Induction of Persistent Tumor-protective Immunity in Mice Cured of Established Colon Carcinoma Metastases¹

The induction of tumor-specific T-cell responses that are effective in eradicating disseminated tumors and in mounting a persistent tumor-protective immunity is one of the major goals of tumor immunotherapy. Here, we demonstrate that we achieved this goal by directing interleukin 2 (IL-2) to the tumor microenvironment of colon carcinoma metastases in syngeneic mice with a recombinant antibody-IL-2 fusion protein (huKS1/4-IL-2). Eradication of established pulmonary metastases is induced by a CD8⁺ T cell-mediated immune response, which can be transmitted to naive syngeneic severe combined immunodeficient mice by adoptive transfer of CD8⁺ T cells from immune animals. This immune response was followed by the induction of a long-lived immunity against challenge up to 5 months later with CT26-KSA or wild-type CT26 murine colon carcinoma cells in BALB/c mice. This memory immune response was confirmed by flow cytometric analyses of CD8⁺ T cells isolated from secondary lymphoid tissue that revealed a phenotypic profile typical of early memory T cells. This long-lived protective tumor immunity was successfully boosted to become optimally effective in all experimental animals by injections of noncurative doses of IL-2 fusion protein 4 days after challenge with tumor cells. Taken together, our results indicate that the huKS1/4-IL-2 fusion protein elicits a long-lived cellular memory immune response that can be amplified by additional applications of IL-2 fusion proteins. This approach could become useful for the treatment of colorectal carcinoma in an adjuvant setting, particularly in patients with minimal residual disease.