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Abstract A137: The innate/adaptive immune response triggered in response to local immunotherapy of orthotopically growing bladder cancer tumors

The mouse bladder 49 (MB49) syngeneic tumors respond to various immunotherapies, both stimulatory immunotherapies and check-point blockers; when tumors are cured it is often an antitumor memory response established (previous publications by our group and others). Herein we present data suggesting that bladders of orthotopic MB49 tumor-bearing mice hold a reservoir of lymphocytes surrounding the tumor, wherein they migrate rapidly upon immune adjuvant stimulation. The tumors appear to form an accessible immune microenvironment rich in vessels that mediate the homing of leukocytes to the tumor site. This is in contrast to MB49 tumors that grow subcutaneously and do not appear to provide the same rapid immune cell infiltration capacity. Herein we further examined the immune cell populations of tumors locally treated with CpG ODN 1668, a type B CpG and a strong immunostimulatory agent or dilution buffer, as a control. Interestingly, we identified markers of high-endothelial venules (HEVs) in the vessels present in tumors from both untreated and treated animals. Thus we conclude that HEVs develop naturally in the orthotopic MB49 model and we wished to explore whether manipulation of the tumor microenvironment (TME) can induce HEVs and how this stimuli affect the infiltration of immune cells. Immunohistochemical profiling revealed that CD11c+ dendritic cells, CCL21+ cells along with B and T lymphocytes are present in various ways in different zones of the tumor with HEVs and CD31+ vessels. A correlation with vessel density and the presence of HEVs was identified in untreated animals. In immune-stimulated tumors, this correlation was lost in the early phase post stimuli. We could also identify that CpG treated bladder displayed increased vascularization around the tumor 24 hours post treatment. Interestingly, it appeared as CCL21 expression intratumorally aligned with increased recruitment of CD11c+ DCs in the TME. Intratumorally it was a clear correlation between CCL21 expression with both CD11c+ and CD8+ cell infiltration. As CD11c+ dendritic cells migrate towards gradients of CCL21 via their CCR7 receptor, enabling antigen presentation, it is plausible that antigen-presentation takes place in the TME in relation to this finding. By these preliminary data we conclude that in the orthotopic MB49 tumor model, CCL21 appears to play a role in the induction of adaptive immune responses through the CCL21/CCR7 axis. The role of HEVs, or alternatively lymphatic vessels, for this recruitment is yet to be determined. Currently we are investigating multiplex analyses on bladder tumors, urine and blood from tumor-bearing animals to identify cytokines in the TME or systemically that are correlated the formation of an adaptive immune response. Our future goal is to examine what is the key to raise an effective immune response to the so called immune "hot" orthotopic MB49 tumor. Citation Format: Iliana Kyriaki, Sara M. Mangsbo. The innate/adaptive immune response triggered in response to local immunotherapy of orthotopically growing bladder cancer tumors [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A137.