Early functional activation of natural killer cell and dendritic cell during the antitumor therapeutic response induced by TNFa tumor vessel delivery and melphalan

Introduction: Among the innate cells involved in the rejection and memory process, DCs appear the major APCs able to convey to tumor-specific T cells effective signals for early antigen recognition and T-cell activation. Interestingly, it has also been shown that DCs can interact with NK cells via a cooperative cross-talk that leads to activation of each other and to development of immune TH1 cells and activation of CTL effector response. We previously demonstrated that a single systemic administration of L19mTNFa selectively targets the tumor vasculature, and in combination with melphalan is able to induce a long-lasting therapeutic T cell immune response in two tumor mouse models: WEHI-164 fibrosarcoma, that respond well to the therapy (85%), and C51 colon carcinoma, low cured which showed a poor response to therapy (30%). In the present study we wanted to investigate the role of NK, DC and macrophages during the combined treatment in WEHI-164 and C51 tumors.
Material and method: The induced-immune responses were investigated in spleens, lymph nodes and tumor-infiltrated lymphocytes by flow cytometry, intracellular immunostaining, chromium release cytotoxicity and FACS cell sorting.
Results and discussion: We found that 40h after L19TNFa/melphalan treatment in the WEHI-164, tumor-derived lymph nodes (TDLN) display an increased number of mature CD40+CD86+ DCs, functional NK cells, CD4+ and CD8+ T cells as compared to LN of untreated mice. In the spleens of treated WEHI-164-bearing mice, we also observed TH1 cell polarization, CD8+ T cell activation and an increase in cytotoxic NK cells. With L19TNFa/melphalan treatment, increased mature DC were found among the immune cells infiltrating the tumors in conjunction with NKs, CD4 and CD8 T cells, as compared to control mice early on after the combined treatment. Otherwise, in the TDLN of treated C51 tumor-bearing mice, neither a significant influx of mature DC, nor activation of NK cells was observed. In the spleens there was no activation of NK cells and a high MDSC population. Interestingly in both tumor models, a significant decrease of infiltrating M2-type macrophages was detected after the treatment.
Conclusion: These results strongly suggest that the success of L19TNFa/melphalan is related, in addition to the previous reported T cell responses, to the early activation and polarization of NK cells and DCs.