Abstract 4603: Single-cell and spatial dissection of the effect of combined PD-L1 and TGFb blockade by bintrafusp alfa from the ICING window-of-opportunity trial in resectable locally advanced HNSCC patients

Abstract Despite high tumor mutational burden, immune checkpoint blockade has shown limited efficacy in head and neck squamous cell carcinoma (HNSCC), highlighting the need for additional therapeutic targets. TGFb signaling has been associated with an immunosuppressive tumor microenvironment as well as a lack of response to anti-PD(L)1 therapy, which led to the development of combined therapeutic approaches. ICING is a prospective (NCT04428047) open label, multicenter, phase II, window-of-opportunity preoperative, single-agent trial. The primary objective was to evaluate the efficacy and biological activity of pre-operative combined PD-L1 and TGFb blockade by bintrafusp alfa in patients with untreated resectable stage III/IV locally advanced HNSCC and its effect on the tumor microenvironment (TME). Tumor samples were harvested at baseline prior to immunotherapy and at surgery after two doses (1200mg; D1 and D15) for pre- and post-treatment comparison. Treatment efficacy was assessed using the pathological response (PathR) with a 10% threshold for response as primary endpoint. Changes in the TME were determined by single-cell RNA sequencing (scRNAseq) and multiplexed imaging. Seven patients were included and six received the full treatment scheme (5 oral cavity and 2 oropharyngeal, all HPV-negative; median age = 61y, range 34y-74y). Four patients had a PathR exceeding 10%, including one with a major PathR above 50%. The TME pre-treatment of this major responder did not differ from the other samples, but this sample was set apart by the presence of proliferative, p16+, HPV-negative tumor cells with mildly higher genomic alterations whilst still classified as low tumor mutational burden. Regardless of treatment response, we report several changes in post-treatment samples: (i) the remodeling of the stromal architecture concomitant with a phenotypic shift in cancer-associated fibroblasts (CAF) with a reduction in activated LRRC15+ CAF and an increase in CD10+IL24+ CAF; (ii) a reduction of TGFb-induced genes in both stromal and cancer cells; (iii) a reduction in both conventional and regulatory CD4+ T cells; (iv) an increase in CD8+ T cell infiltration in previously excluded tumors; (v) an interferon gamma-mediated activation of monocytes, macrophages and dendritic cells expressing CXCL9 and CXCL10. Collectively, our study deciphers the effects of bintrafusp alfa both molecularly and spatially at unprecedented granularity, which is of major importance for the many combined PD(L)1 and TGFb blockade therapeutic approaches currently under clinical development. Citation Format: Caroline Hoffmann, Jan-Timon Werle, Jocelyn Gal, Philemon Sirven, Jerzy Klijanienko, Jeremy Mesple, Benjamin Demaille, Wail Zeitouni, Olivier Choussy, Gregoire Marret, Nathalie Badois, Antoine Dubray-Vautrin, Gilles Dolivet, Lionnel Geoffrois, Maud Kamal, Ivan Bieche, Laure Monard, Clotilde Simon, Christophe Le Tourneau, Helene Salmon. Single-cell and spatial dissection of the effect of combined PD-L1 and TGFb blockade by bintrafusp alfa from the ICING window-of-opportunity trial in resectable locally advanced HNSCC patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4603.