Abstract CT205: A phase I/Ib trial of intratumoral Poly-ICLC in resectable malignant pleural mesothelioma

Abstract Background: Malignant pleural mesothelioma (MPM) is usually fatal, though multimodality therapy— now including immunotherapy— has improved survival. Recurrence after surgery is close to 100%, even with adjuvant chemotherapy and radiation. Our collaborators have performed deep immunophenotyping of treatment-naïve MPM lesions using mass cytometry (CyTOF) and single-cell RNA sequencing (scRNAseq) to define the tumor microenvironment. A population of rare CD141+ dendritic cells (DC1) is disproportionately represented in some MPM lesions analyzed. These DC1 cells— which express high levels of Toll-like receptor 3 (TLR3)— are among the most potent cross-presenters of antigen and are key to priming anti-tumor CD4+ and CD8+ T cell responses. Polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose (poly-ICLC), is a double-stranded RNA host-targeted therapeutic viral-mimic. Poly-ICLC activates multiple innate immune receptors including TLR3 and melanoma differentiation-associated gene 5 (MDA5), leading to cross-presentation of antigen to T cells and induction of strong Th1 response. We hypothesize that injection of poly-ICLC prior to surgical resection may activate intratumoral (IT) DC1s, increase tumor antigen presentation to cytotoxic T cells, and induce tumor-specific immune surveillance. Methods: This is a phase I/Ib study to evaluate the safety of IT poly-ICLC prior to surgical resection for patients with MPM (NCT04525859). The primary endpoint is safety as assessed by frequency and severity of toxicities by CTCAE 5.0. Secondary endpoints are objective response as measured by RECIST 1.1 and recurrence free survival measured from the time of first poly-ICLC injection. Exploratory endpoints include evaluation of circulating immune cells (including regulatory T cells and NK cells), evaluation of immune cell infiltration in pre-injection tumor biopsy and surgically resected tissue, as well as characterization of immune parameters such as local B cell specificity. The protocol features a Simon’s two-stage design, with six patients enrolled in a phase I safety cohort, proceeding to a phase Ib expansion cohort (additional 13 patients) if no more than 1 dose limiting toxicity occurs. Eligible patients must have MPM deemed operable by the treating thoracic surgeon. Eligible subjects may not have uncontrolled immunocompromised states or autoimmune disorders. After enrollment, patients undergo biopsies at which time 2mg poly-ICLC is injected across two sites in the tumor. Patients then undergo resection of the tumor (pleurectomy/decortication or extra pleural pneumonectomy per standard of care) at day 21+/- 7 after poly-ICLC injection. Blood is drawn at three points (prior to poly-ICLC injection, at time of surgery, and at a post-operative visit) for immune profiling. At the time of submission six patients have been treated and phase Ib accrual is continuing as planned. Interim analysis of phase I safety and exploratory endpoints will be reported in late 2022. Citation Format: Bailey G. Fitzgerald, Thomas U. Marron, Robert Sweeney, Jorge Gomez, Nicole Hall, Daniel O'Grady, Christian Rolfo, Raj Veluswamy, Deborah Doroshow, John Mandeli, David Yankelevitz, Nina Bhardwaj, Sacha Gnjatic, Fred R. Hirsch, Miriam Merad, Alexander Tsankov, Raja Flores, Andrea Wolf. A phase I/Ib trial of intratumoral Poly-ICLC in resectable malignant pleural mesothelioma [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 CT205.