Plasma cells in human pancreatic ductal adenocarcinoma secrete antibodies to self-antigens

Min Yao, Jonathan Preall, Johannes Yeh, Darryl J. Pappin, Paolo Cifani, Yixin Zhao, Sophia Shen, Philip Moresco, Brian He, Hardik Patel, Amber N. Habowski, Daniel A. King, Kara L. Raphael, Arvind Rishi, Divyesh V. Sejpal, Matthew Weiss, David Tuveson, Douglas T. Fearon

Intratumoral B cell responses are associated with more favorable clinical outcomes in human pancreatic ductal adenocarcinoma (PDAC). However, the antigens driving these B cell responses are largely unknown. We sought to discover these antigens by using single-cell RNA sequencing (scRNA-Seq) and immunoglobulin (Ig) sequencing of tumor-infiltrating immune cells from seven primary PDAC samples. We identified activated T and B cell responses and evidence of germinal center reactions. Ig sequencing identified plasma cell (PC) clones expressing isotype-switched and hyper-mutated Igs, suggesting the occurrence of T cell-dependent B cell responses. We assessed the reactivity of 41 recombinant antibodies that represented the products of 235 PCs and 12 B cells toward multiple cell lines and PDAC tissues, and observed frequent staining of intracellular self-antigens. Three of these antigens were identified: the filamentous actin (F-actin), the nucleic protein, RUVBL2, and the mitochondrial protein, HSPD1. Antibody titers to F-actin and HSPD1 were significantly elevated in the plasma of PDAC patients (n=59) compared to healthy donors (n=61). Thus, PCs in PDAC produce auto-antibodies reacting with intracellular self-antigens, which may result from promotion of pre-existing, autoreactive B cell responses. These observations indicate that the chronic inflammatory microenvironment of PDAC can support the adaptive immune response.