Immunotherapeutic Roles Of Agonistic MAb Against 4-IBB Plus Tumor Specific Dendritic Cells And The Associated Mechanisms

Dendritic cells (DCs) constitute a specialized system of antigen presenting cells (APCs) that play a key role in initiation and modulation of T cell responses. Ample evidence exists indicating that dendritic cell based tumor specific vaccines could induce protective/rejection immune responses in animal models and promising preliminary data are reported in human. A variety of pairs of costimulatory receptors on T cells and their ligands on DCs are required for full activation of T cells and DCs. Members of TNFR superfamily such as CD40 and LIGHT can induce DCs maturation and thus improve the ability of the DCs to stimulate a primary CTL response. TNF-related activation-induced cytokine has been shown to both enhance the ability of DCs to prime a T cell response and prolong DCs survival. These observations thus highlight the importance of TNFR superfamily members in the regulation of DCs maturation.4-lBB(CD137) is a member of TNFR superfamily of type I membrane proteins and was originally identified as an inducible gene in activated T cells. A ligand for 4-1 BB(4-1 BBL) was shown to be a type II membrane protein of the TNF superfamily could be detected in DCs, activated macrophages, B cells, and activated T cells. In vitro studies have demonstrated that both agonistic mAb to 4- IBB and its ligand costimulate proliferation and cytokine secretion in both CD4+and CD8+ T cells and interaction between 4-IBB and 4-1 BBL also can prolong T cells survival. In addition, the systemic administration of agonistic mAb against 4-IBB could leads to regression of well-established tumors in various mouse models. Recently, it has been reported that4- IBB and 4-1BBL were coexpressed on DCs and the triggering of this molecule pair increased the secretion of IL-6 and IL-12. Furthermore, infusion of an agonistic 4- IBB mAb into naive mice enhanced the ability of DCs to stimulate T cell proliferation in vitro. It was crucial and useful to discern the biological characteristics of 4- IBB expressions on DCs and its therapeutic role together with DCs vaccines in malignant tumor.In this study, the expression of 4-IBB on DCs was analyzed by FCM and 4-IBB mRNA transcription on DCs were detected by RT-PCR and real-time PCR. Our results indicated that both immature and mature mouse myeloid DCs express 4- IBB molecule which is up-regulated during the process of DCs maturation. Furthermore, DCs stimulated by agonistic mAb against 4- IBB (mAb-2A) induced self-maturation and activation to secrete cytokines such as IL-2 and IL-12 and to mediate T cell proliferation and activation more efficiently. And we also found that TNF-a and 4- IBB played a synergistic role in induction of DCs maturation.Apoptotic A20 tumor cells pulsed DCs were utilized to prepare AP-DC vaccine, which was induced further maturation with 1 Ong/ml TNF-a for 48h. A20 tumor bearing mice were immunized with AP-DC vaccine, mAb-2A, and AP-DC vaccine plus mAb-2A, respectively. It is demonstrated that both administration of agonistic mAb-2A and AP-DC vaccine inhibited tumor growth and prolonged the life-span of tumor bearing mice and induced 12.5% and 25% tumor complete remission respectively. The administration of agonistic mAb-2A plus AP-DC vaccine turned out to be the most effective, and obtained 62.5% tumor complete remission with long-term survival of A20 bearing mice. And tumor growth could not be induced in tumor complete remission mice after the second inoculation of A20. Additionally, spleen T cells from combination therapeutic group mice were more efficient to proliferate and activate in vitro. Furthermore, infiltration proportion of CD4*IFN-y"lT cells increased in combination therapeutic group mice.In conclusion, 4- IBB molecules expressed on mouse myeloid DCs played a key role in the regulation of DCs maturation and activation. And activation of DC-associated 4- IBB played a potent role in anti-tumor immune response.