B cell subset biology in a tumor microenvironment model

Abstract

Abstract The high myeloid to lymphoid ratio of cultured peritoneal cavity (PerC) leukocytes can serve as an in vitro model to study the tumor microenvironment (TME). C57BL/6J PerC T cell responses to TCR ligation (anti-CD3) and mitogen (ConA) are suppressed in these cultures. Likewise, the PerC B cell response to BCR (F[ab’2] anti-IgM) and TLR4 (TLR4L/LPS) ligation are suppressed. T cell suppression can be liberated by neutralizing IFNγ or by blocking iNOS with 1-methyl arginine. The BCR response is recovered by blocking prostaglandin production with indomethacin; the LPS response by neutralizing IL10. To dissect putative receptor-ligand signals in this model, we investigated expression of the inhibitory cell surface marker PDL1/B7H1/CD274 on PerC cells. TCR ligation increased PDL1 expression on macrophages (Mfs), B1, and B2 cells and was reduced by blocking IFNγ. TLR4 ligation increased PDL1 expression on Mfs and both B cell subsets and was reduced by blocking IFNAR1. Interestingly, BCR ligation increased B7H1 and Class II expression on Mfs and B2 cells, but not B-1 cells. Increased B7H1 expression could be reduced by neutralizing IL6, IFNβ, IFNγ, or IFNAR1. TCR ligation led to B1, but not B2, cell division and proliferating B cells increased IL10 production. These findings illustrate that TCR, and surprisingly BCR, ligation can foster immune suppression in macrophage-dense cultures and suggest that regulatory B cells must be considered when designing immunomodulatory cancer therapies.