Abstract A105: Induction of an anti-tumor immune response following intratumoral injection of oncolytic virus CF33-hNIS-antiPD-L1 in patients with metastatic triple negative breast cancer (mTNBC)

Abstract Background: CF33-hNIS-anti-PD-L1 is a novel chimeric orthopoxvirus with robust anti-cancer activity in TNBC xenografts. Previously, we showed that CF33-hNIS-anti-PD-L1 increased CD8+ T cell infiltration and favorably altered the tumor microenvironment (TME) in xenograft models. We have observed similar effects in our first-in-human clinical trial of CF33-hNIS-anti-PD-L1 intratumoral (IT) injections in patients with mTNBC. Here we present updated immune analyses of nine patients treated in the phase I, single center, dose escalation trial of CF33-hNIS-anti-PD-L1. Methods: Eligibility criteria included patients with mTNBC that progressed on 2 or more chemotherapy regimens and had at least 1 tumor site amenable to IT injections. Formalin fixed tissue from baseline and on-treatment biopsies were assessed by multiplex immunofluorescence for CD3, CD4, CD8, PD-L1, PD-1 and pan-cytokeratin and digitally quantified for densities of immune phenotypes. Peripheral blood samples were analyzed by 30 marker flow cytometry panels on a Cytek Aurora. The Nanostring GeoMx Immune Profiling Panel of protein markers is being used for ongoing analysis of TME changes over the course of treatment. Results: From October 2021 to August 2023, 9 patients received at least 1 dose of IT CF33-hNIS-antiPDL1 at 1 of 3 dose levels (1x105, 3x105, or 1x106 PFU). The sites injected were axillary lymph node (LN) metastasis in 1 patient, intramuscular mass in 1 patient, matted dermal metastasis in 4 patients, and dermal/subcutaneous nodules in 3 patients. Seven patients had evaluable pre-and post-treatment tumor tissues from intradermal or subcutaneous injections. From baseline to cycle 1 day 2, CD8+ T cells in the TME increased in 5/7 patients, CD4+ T cells increased in 4/7 patients, and PD-L1 expression increased in 5/7 patients. Moreover, 4/7 patients had increased frequencies of PD-1-positive CD8+ T cells in the TME. Two patients had evaluable post-treatment tissues following 2 cycles of treatment (C2D2). These patients had increased PD-L1 expression in the TME, increased tumor-infiltrating T cells, and increased CD8+ T cells within the tumor islands of the TME. Digital spatial profiling of other immune features are ongoing. Additionally, 1 patient had 2 cycles of CF33-hNIS-anti-PD-L1 IT injection into a LN containing mTNBC. This patient had increased PD-L1 expression in the TME, increased PD-1-positive CD4+ and CD8+ T cells within the LN, and increased frequencies of circulating PD-1-positive CD39-positive exhausted CD8+ T cells in the peripheral blood over the course of therapy. Conclusions: CF33-hNIS-anti-PD-L1 induces tumor inflammation and immune activation as marked by increased tumor infiltration of CD4+ and CD8+ T cells, increased PD-L1 expression, and increased PD-1-positive T cells. Combination trials with CF33-hNIS and immune checkpoint inhibitor for the treatment of advanced solid tumors are ongoing. Additionally, more studies are needed to evaluate the use of OV in patients with high-risk stage II-III breast cancers. Citation Format: Colt Egelston, Shyambabu Chaurasiya, Jianying Zhang, Raju Pillai, Leslie Chong, Amanda Seiz, W. Hans Meisen, Yuan Yua, Yuman Fong, Jamie G. Rand. Induction of an anti-tumor immune response following intratumoral injection of oncolytic virus CF33-hNIS-antiPD-L1 in patients with metastatic triple negative breast cancer (mTNBC) [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr A105.