Abstract 6528: Integrin ɑvβ6 upregulation as a mechanism of T-cell evasion in head and neck squamous cell carcinoma

Abstract Head and neck squamous cell carcinoma (HNSCC) encompasses malignancies of the mucosal epithelium in the oral cavity, pharynx, and larynx. The lack of effective screening strategies and the typically late stage of detection are contributors to a considerable annual death toll of HNSCC. Additionally, the anatomical proximity of the malignancy to delicate structures of the head and neck leads to tremendous treatment-related morbidity. Therefore, there is great interest in developing life-saving therapies and strategies for treatment de-escalation. The immune checkpoint inhibitor pembrolizumab (αPD-1) has been approved for recurrent or metastatic HNSCC and as a frontline therapy for unresectable disease. However, only about a quarter of patients respond to αPD-1 therapy. The immunosuppressive effect of TGFβ has been widely described as relevant to the HNSCC tumor microenvironment. However, attempts to blockade TGFβ have failed mainly due to the widespread side effects of disrupting a highly promiscuous cytokine. Integrin αvβ6 is a major activator of the inert latent TGFβ into the active, immunosuppressive form. With its high relative specificity to HNSCC tissue, inhibition of αvβ6 could offer a safer approach for disrupting TGFβ to overcome resistance to immune checkpoint blockade. After screening ɑvβ6 expression levels of HNSCC cell lines via flow cytometry, cell lines FaDu and CAL27 were selected for further investigation due to high endogenous ITGB6 expression (FaDu 35. 57% cells ITGB6+, CAL27 95. 69% cells ITGB6+). The cell lines were transduced with a doxycycline-inducible short hairpin RNA (shRNA) knockdown of αvβ6 using a lentiviral system. Both knockdown and control shRNA cell lines were pretreated with 1 μg/mL of doxycycline for five days to induce the shRNA and subsequently co-cultured with TALL-104 T-cells. Quantitative fluorescence microscopy of the co-culture revealed that the knockdown of αvβ6 substantially increased T-cell killing over 24hrs (FaDu CTRL shRNA 6. 72%±2. 49 dead vs. FaDu ITGB6 shRNA 12. 80%±3. 16 dead, p0. 001). However, treatment of FaDu and CAL27 cell lines with active-TGFβ showed no change in PD-L1 expression via flow cytometric analysis. To determine whether the T cell evasive effect of αvβ6 is driven by other immune checkpoints on the cancer cells or by the direct effect that TGFβ has on immune cells, we show the generation of relevant mouse αvβ6 shRNA knockdown cells. These syngeneic in vivo studies will facilitate cytokine profiling to uncover the dynamics of tumor-immune cell interactions in response to αvβ6 inhibition. Citation Format: William J. MacDonald, Praveen R. Srinivasan, Maximilian Pinho-Schwermann, Shengliang Zhang, Vida Tajiknia, Connor Purcell, Jillian Strandberg, Nolan Stubbs, Wafik S. El-Deiry. Integrin ɑvβ6 upregulation as a mechanism of T-cell evasion in head and neck squamous cell carcinoma 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 (6Suppl): Abstract nr 6528.