Systematic evaluation of intratumoral and peripheral BCR repertoires in three cancers

Abstract

The current understanding of humoral immune response in cancer patients suggests that tumors may be infiltrated with diffuse B cells of extra-tumoral origin or develop organized lymphoid structures, where somatic hypermutation and antigen-driven selection occur locally. These processes are thought to be significantly influenced by the tumor microenvironment in the form of secretory factors and biased cell-cell interactions. To address the manifestation of this influence, we used deep unbiased immunoglobulin profiling and systematically characterized the relationships between B cells in circulation, draining lymph nodes (DLN), and tumors in 17 patients with three human cancers. We show that DLNs are differentially involved in the interaction with the tumor site and that there is significant heterogeneity even between different parts of a single DLN. Next, we confirmed and elaborated upon previous observations of intratumoral immunoglobulin heterogeneity. We identified BCR clonotypes that were expanded in tumors relative to DLN and blood and observed that these tumor-expanded clonotypes were less hypermutated than non-expanded (ubiquitous) clonotypes. Furthermore, we observed a shift in BCR CDR-H3 properties towards less mature and less specific BCR repertoire in tumor-infiltrating B-cells compared to circulating B-cells, which may indicate less stringent control for antibody-producing B cell development in TME. In addition, we found repertoire-level evidence that B-cells may be selected according to their CDR-H3 physicochemical properties before they activate somatic hypermutation (SHM). Altogether, our work outlines a broad picture of the difference in the tumor BCR repertoire relative to non-tumor tissues and points to the unexpected features of the SHM process.