TNFRSF25, also known as Death Receptor 3 (DR3), is a cell surface receptor of the tumor necrosis factor receptor superfamily (TNFRSF) which is expressed on T cells, innate lymphoid cells, and B cells. Upon binding with TL1A ligand, this co-stimulatory molecule induces T cell activation, leading either to inflammation or cell death. Mouse PTX-35 (mPTX-35) is a TNFRSF25 functional agonist derived from a CDR that was humanized and affinity matured, then fused to a mouse IgG1-Fc backbone. Since costimulatory agonist antibodies have shown limited efficacy in clinical trials, our aims were to (i) determine the anti-tumor efficacy of mPTX-35, (ii) elucidate any mechanisms of resistance, and (iii) identify immune conditions that provide effective anti-tumor immune responses to mPTX-35 treatment. We studied the anti-tumor immune effects of mPTX-35 in both cold and hot tumor models. In a TC-1 cold tumor, we found that treatment with an anti-TNFRSF25 agonist antibody does not affect tumor growth or survival. In contrast, vaccination with an E7 antigen-specific vaccine leads to an environment that reverses primary resistance to the agonist antibody, inhibiting the tumor growth, and enhancing overall survival. Interestingly, we found that similar to other co-stimulatory agonist molecules, the immune effects of the anti-TNFRSF25 agonist are dose-dependent with lower (0.2 mg/kg) and higher (5 mg/kg) doses of mPTX-35 showing a reduced anti-tumor response than a dose of 1 mg/kg, resulting in a bell-shaped response in all tumor models. Similar immune-mediated anti-tumor effects of mPTX-35 were found in a CT26 (hot) tumor model. In conclusion, these results show that anti-TNFRSF25 agonist antibody demonstrates high anti-tumor efficacy in tumors that are infiltrated with T cells while the absence of properly antigen activated CD8 T cells (such as in cold tumors) incurs primary resistance to TNFRSF25 agonist that is reversed by proper priming of CD8 T cells. These results highlight the importance of optimal priming to limit primary resistance mechanisms and drive an efficacious immune response via the TNSFR25 axis. Citation Format: Dareen Sarhan, Lara Rabah, Vikas Tahiliani, Anh M. Trinh, Rahul R. Jasuja, Eric P. Dixon, Matthew Seavey, Vivek Verma, Seema Gupta, Samir N. Khleif. Proper priming of T cells is crucial for the anti-tumor effect of mPTX-35, an anti-TNFRSF25 agonist antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2881.

Introduction: An isolated vaginal metastasis from a primary colorectal adenocarcinoma is extremely rare. Based on meticulous literature review, only seven cases were reported from 1956 – 2013. Case Presentation: We present a case of a 52-year-old female patient diagnosed with rectal adenocarcinoma, underwent low anterior resection of the primary tumor, and then was found to have an asymptomatic isolated vaginal metastasis that was completely excised. Conclusion: Isolated vaginal metastatic disease is one of the rarest entities in surgical oncology with only limited cases being reported in the literature. A diagnosis can be challenging if the metastatic lesion is small and asymptomatic even with the most advanced radiological assessment tools. A meticulous examination should be done pre-operatively in order to rule out such diagnosis.

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