Abstract P011: B cell subsets that correlate with anti-PD-1 resistance in a preclinical model of HPV+ oropharyngeal cancer
Authors: Merheb Pamela A. , Castañón Daniel L. , Rivera Michael , Galán Jorge , Dorta-Estremera Stephanie M. 
Published: January 2022

Abstract
A subset of head and neck squamous cell carcinomas (HNSCC) is associated with infection with oncogenic strains of human papillomavirus (HPV) and its prevalence continues to rise in the US. Cancer progression has been associated, in part, with an impaired immunity. Because of this, immunotherapies such as immune checkpoint blockade (ICB) have been FDA approved to treat different types of cancers, including HNSCC. The ICB targeting the molecule programmed death cell-1 (PD-1) is used as treatment for HPV-related HNSCC, however, only around 30% of patients respond. Most studies have focused on characterizing T cell responses, however, B cells, are also present in the tumor microenvironment of HPV-positive HNSCC. Interestingly, different B cell subsets with differential functions that may promote or prevent an effective anti-tumor response are present in tumors and tumor-draining lymph nodes. Therefore, fine regulation of anti-tumor and tumor-promoting B cell subsets may be necessary to promote an effective anti-tumor response and therefore prevent tumor progression. However, the B cells that may be associated with responsiveness to anti-PD-1 in HPV+ oropharyngeal cancer remain undefined. By using the preclinical model for HPV+ oropharyngeal cancer (named mEER) we have determined that tongue-implanted tumors are sensitive to anti-PD-1, where around 50% of the mice clear the tumors, whereas flank-implanted tumors are completely resistant to these treatments. By using this in vivo model, we were able to characterize B cell subsets in anti-PD-1 sensitive and anti-PD-1 resistant tumors. First, we compared B cell subsets in untreated mice between tongue (anti-PD-1 sensitive) and flank-implanted (anti-PD-1 resistant) tumors by flow cytometry. Interestingly, flank-implanted tumors contained more PD-1-expressing B cells, which have been identified as an immunosuppressive population in hepatocellular carcinoma. The presence of immunosuppressive B cells on flank tumors was also supported by our finding that flank implanted tumors grew at a slower rate in B cell-deficient mice compared to wild-type mice. When we compared tongue-bearing tumor mice that responded or not responded to anti-PD-1, we observed that mice that did not respond to anti-PD-1 had a higher frequency of antibody-secreting cells in tumor-draining lymph nodes compared to responders. Lastly, when we cultured naïve B cells with tumor cell supernatant from mEER cells, B cells upregulated PD-1 and were able to produce the immunosuppressive cytokine IL-10. Our data suggest that HPV+ oropharyngeal tumors modulate B cell functions and that a differential infiltration of B cell subsets into tumors and tumor-draining lymph nodes correlates with responsiveness to anti-PD-1 therapy in a preclinical model of HPV+ oropharyngeal cancer. These results will aid in our long-term goal to elucidate novel mechanisms for the modulation of anti-tumor responses by B cells and the development of novel B cell-specific therapies for HPV-related cancers and, therefore, improve clinical outcomes in these patients.
Citation Format: Pamela A. Merheb, Daniel L. Castañón, Michael Rivera, Jorge Galán, Stephanie M. Dorta-Estremera. B cell subsets that correlate with anti-PD-1 resistance in a preclinical model of HPV+ oropharyngeal cancer [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P011.