Aktiv-spezifische Tumorvakzinierung während Lymphopenie-induzierten Lymphozytenproliferation und Rekonstitution (LRAST) induziert therapeutisch wirksame T-Zellen im murinen Magenkarzinom-Modell

Abstract

Introduction: Lymphopenia induction via chemotherapy and subsequent immune reconstitution followed by active-specific tumor cell vaccination (LRAST) is a promising novel tool to induce tumorspecific T cells with therapeutic efficacy. We have analyzed the relevance of this therapeutic approach for the treatment of gastric cancer in a murine gastric cancer model. Methods: The mGC8 gastric cancer cell line was isolated from a spontaneously growing stomach tumor of a CEA424/SV40 T-antigen transgenic mouse. Lymphopenia was induced by i.p. injection of cyclophosphamide (200 mg/kg). After 24 h, mice were reconstituted with 20 × 10⁶ naive splenocytes followed by s.c. vaccination with irradiated mGC8 cells (10 × 10⁶) with or without mGM-CSF (1 μg) in IFA to induce an activespecific immune response. Naive, non-lymphopenic mice served as control. The therapeutic efficacy of the approach was examined by injection of vital mGC8 tumor cells (3 × 10⁶, s. c.). The mGC8 cells were given either before or after vaccination. S.c. tumor growth was determined twice a week. The induction of tumor-specific T cells in the tumor vaccine-draining lymph nodes (TVDLN) was analyzed by measuring release of IFN-γ and IL-5 in cytokine release assays. Results: Thirty percent of the mice that received vaccination with tumor cells alone displayed protective immunity. In contrast, 80 % of the mice that received LRAST were protected against a subsequent tumor challenge. Moreover, tumor-specific type 1-polarized T cells were detected in the TVDLN of LRAST-treated mice. However, LRAST-treatment could delay, but not prevent, tumor growth in mice with 3-days established s. c. tumors. Increased levels of regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSC) were detected in the spleens of the LRAST-treated mice as compared to mice without tumor cell vaccination and mice treated without cyclophosphamide, respectively. Conclusions: LRAST leads to induction of tumor-specific type 1-polarized T cells in TVDLN and results in a protective immune response. The simultaneous increase in Treg and MDSC, cells that presumably inhibit the antigenspecific immune response, could explain the poor efficacy of the vaccination in mice with established tumors. A specific depletion of Treg or an inhibition of MDSC may improve the efficacy of the LRAST immune therapy.