422 A novel multifunctional engineered MSC cell line induces complete tumor regression, and establishes immune memory in an orthotopic GBM model

<h3>Background</h3> Glioblastomas (GBMs) are highly treatment-resistant and aggressive brain tumors. In recent years, immunotherapy strategies have revolutionized the treatment of many cancers, increasing the hope for GBM therapy. However, mostly due to the high, multifactorial immunosuppression occurring in the microenvironment and the presence of the blood-brain barrier, the efficacy of immunotherapy in GBM is still low. Indeed, disappointing initial clinical results have been reported for many mono-immunotherapies for GBM. The lessons learned from clinical trials highlight the importance of targeting different arms of the GBM immunity cycle. In this study, we established mesenchymal stem cell (MSC)-based multipotent novel cells, BM-205, by engineering them to express various therapeutic molecules: (i) tumor-tropic molecules (CXCR2 and CXCR3), (ii) direct tumor cell killing molecules (CD253 and CD::UPRT), (iii) immune-activating cytokines (IL-12 and IL-21), and (iv) tumor microenvironment modulators (TGF-β trap and VEGF trap). In this study, we analyzed the in vitro and in vivo functional characteristics of BM-205. <h3>Methods</h3> In this study, we assessed the in vitro functional characteristics of BM-205 by evaluating tumor tropism, TGF-β/VEGF-trap efficiency, and T-/NK-cell activation potential. Furthermore, we evaluated the in vivo tumor tropism and antitumor efficacy of BM-205, as well as its ability to modulate the tumor microenvironment in an orthotopic GBM model. In addition, tumor-free animals were re-challenged with GBM tumors. <h3>Results</h3> We observed that human PBMCs and NK cells were effectively activated and proliferated in response to BM-205 culture supernatant. Additionally, BM-205 achieved effective TGF-β neutralization. In an orthotopic GBM model, BM-205 exhibited effective migration and infiltration into the tumor from the contralateral brain. Remarkably, a single administration of BM-205 in the orthotopic GBM model resulted in dose-dependent, highly significant antitumor efficacy (40–80% complete regression). Moreover, repeated administration of BM-205 led to complete remission in all animals (100% complete regression). Interestingly, all tumor-free mice re-challenged with tumors maintained antitumor efficacy (100% complete regression), indicating the establishment of tumor-specific immune memory by BM-205. This outcome is attributed to the enhanced activation and infiltration of immune cells induced by BM-205. Indeed, a significant increase in T cells and a substantial decrease in Treg cells were observed within the tumors of BM-205-treated mice. <h3>Conclusions</h3> These results demonstrate that BM-205 not only eliminates GBM but also favorably alters the tumor microenvironment by targeting different arms of the cancer immunity cycle, making it an attractive therapeutic approach for engineered cell-based GBM immunotherapy.