Tumor immune suppression mechanism of tumor-derived osteopontin and enhanced antitumor immunotherapeutic effect of B cell-based vaccine transduced with modified adenoviral vector

Abstract

Breaking the tumor-derived immunosuppressive environment and initiating strong immune responses against tumor antigens are both necessary for eliminate established tumors. Therefore, we investigated mechanisms of tumor-derived immunosuppression and attempted to develop more effective B cell based vaccine. These two different strategies were described in different sections respectively part I and part II. Tumor cells secrete soluble factors to suppress host immunity against tumor for improvement of their survival. Expansion of myeloid derived suppressor cells (MDSCs) is one of host immune suppression mechanism derived by tumors. Extramedullary myelopoiesis has been known as a common phenomenon in the tumor bearing hosts, which cause abnormal myeloid cell expansion in the peripheral lymphoid organ and tumor site. Although it is assumed that inflammatory mediators contribute to tumor-induced extramedullary myelopoiesis, responsible factor and its contribution remains still elusive. Using cytokine array, we found that osteopontin was increased in both spleen lysates and sera in the tumor bearing mice. Based on this, we investigated whether tumor-derived osteopontin affect extramedullary myelopoiesis and MDSC accumulation in the tumor environment. Knock down and neutralizing of osteopontin in the tumor cells showed reduced tumor growth, splenomegaly and extramedullary myelopoiesis in the tumor bearing mice. In the primary cultured splenocytes, osteopontin increased the proliferation of lineageneg/CD127-/CD117+/Sca1- heterogeneous myeloid progenitor populations (LK cells). Moreover, osteopontin increased migration of bone marrow LK cells. These results suggest that osteopontin induced increased extramedullary myelopoiesis and subsequently accumulated immunosuppressive MDSCs. Taken together, these findings suggested that osteopontin could become therapeutic target to overcome tumor-derived immunosuppressive environment. For successful clinical tumor immunotherapy outcomes, strong immune responses against tumor antigens must be generated. Cell based vaccines compromise one strategy with which to induce appropriate strong immune responses. Previously we established a natural killer T cell (NKT) ligand loaded and Her2/neu introduced modified adenoviral vector (Ad-k35HM) transduced-B cell based anticancer cellular vaccine. An Ad-k35HM transduced B cell vaccine elicited strong antigen specific cellular and humoral immune responses, subsequently showed inhibition of the in vivo growth of established tumors in a mouse model. In this study, we additionally investigated diverse characteristics of Ad-k35HM introduced B cell-based vaccine. Furthermore, the vaccine elicited HLA-A2 epitope specific cytotoxic T cell responses in B6.Cg (CB)-Tg (HLA-A/H2-D) 2Enge/Jat mice (AAD mice). These findings indicated that the Ad-k35 could be appropriate for the preclinical and clinical development of B cell-based anticancer immunotherapies.