Abstract P5-04-05: Tumor-infiltrating B lymphocytes produce IL-27 to upregulate PD-L1 expression in the tumor microenvironment and promote breast cancer progression
Authors: Yan Hui , Viswanadhapalli Suryavathi , Chupp Daniel , Fernandez Maria , Wu Shuai , Wang Jingwei , Moroney Justin , Taylor Julia , Im John , Rivera Carlos , Luo Yiliao , Liu Junhao , Sareddy Gangadhara , Curiel Tyler , Casali Paolo , Vadlamudi Ratna , Xu Zhenming 
Published: March 2020

Abstract
The host immune response can be evaded by cancer cells, e.g., through upregulation of the PD-L1/PD-1 immune checkpoint, and even hijacked to promote tumor progression. Here, we show that tumor-infiltrating B lymphocytes play an important role in PD-L1 expression using two different murine models of breast cancer (BCa). Mice deficient in B cells displayed virtually abrogatedtumor growth from transplanted syngeneic BCa cells and expressed less PD-L1 in residual tumors. Mechanistic studies showed that the impact of B cells was through their production of IL-27, a pleotropic cytokine composed of the IL-27p28/EBI3 heterodimer and possessing both pro- and anti-inflammatory functions. Accordingly, mice with B cell-specific deficiency in expressing IL-27p28/EBI3(but not Il12a, which can heterodimerize with EBI3 to form cytokine IL-35) were severely impaired in the BCa tumor growth and tumoral PD-L1 expression. IL-27-producing B cells were generated by priming of B cells with TLR ligands (that are abundant in the tumor microenvironment due to the release by apoptotic cells) followed by stimulation with CD154 and IL-21 (as likely expressed by activated tumor-infiltrating CD4+T cells). Single cell-RNA-sequencing analysis using Il27p28-Gfp reporter mice revealed that IL-27-producing B cells expressed a transcriptome that is distinct than other B cells and IL-27-producing non-B cells. B cell secreted IL-27, induced STAT1 and STAT3 activation, upregulated PD-L1 expression, and enhanced the growth of human and mouse BCa cells in vitro.It also activated STAT1/STAT3 and upregulated PD-L1 in B lymphocytes, which were the immune cell type with the highest PD-L1 expression in murine BCa tumors. In human primaryBCa tumors, stronger IL-27 expression was associatedwith more B cell infiltration and PD-L1 expression, and correlated with a poorer survival in BCa patients. Further, recombinant IL-27 supported human BCa tumor growth in mice with humanized immune system. Collectively, these results demonstrated that B cell production of IL-27 underpins how the host immune system is hijacked to promote BCa tumor progression. Supported by DOD/BCRP grant BC170448 (to R.V. and Z.X.), NIH/NIAID grant AI 135599 and UT Health Mays Cancer Center - Dew Foundation Pilot Grant (to Z.X.).
Citation Format: Hui Yan, Suryavathi Viswanadhapalli, Daniel Chupp, Maria Fernandez, Shuai Wu, Jingwei Wang, Justin Moroney, Julia Taylor, John Im, Carlos Rivera, Yiliao Luo, Junhao Liu, Gangadhara Sareddy, Tyler Curiel, Paolo Casali, Ratna Vadlamudi, Zhenming Xu. Tumor-infiltrating B lymphocytes produce IL-27 to upregulate PD-L1 expression in the tumor microenvironment and promote breast cancer progression [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-04-05.