CD20+ T cells: Phenotype, origin and presence in the tumour microenvironment

Abstract

CD20 is well-known as a lineage marker for B cells in human, although the presence of CD20+ T cells has been reported previously (Schuh et al., 2016). In my experiments we sorted memory CD8+CD20+ and CD20- T cells and subsequently analysed TCRβ CDR3 sequences to determine clonal overlap between populations. I was able to demonstrate TCRβ CDR3 amino acid sequences within the CD20+ T cells that were not found in the CD20- T cells population, suggesting the presence of unique T cell clones. This data suggests possible thymic origin of at least some CD20+ T cells, or an early expression of CD20+ following activation of naïve T cells. This does not however refute the trogocytosis theory where some T cells acquire CD20 from B cell. I analysed a number of published mass cytometry datasets and determined that memory CD20+ T cells express higher levels of CD127, CD27, CD28, PD-1 and CD57 especially by the effector memory (Tem) and effector memory CD45RA revertant (Temra) subsets, suggesting a possible late differentiation state of the CD20+ T cells. Further phenotyping revealed a novel population of CD20+Vα7.2+CD161+ cells in the peripheral blood of healthy donors, which are potentially CD20+ mucosal-invariant T (MAIT) cells. In colon cancer, CD20+ T cells were found within tumour tissue, adjacent normal tissue and showed fewer CD20+ T cells expressing the marker CD39. This may indicate lower numbers of CD20+ T cells within tumour-reactive T cell pool and requires further investigation. Using mass cytometry datasets from colorectal cancer patients, and melanoma patients receiving anti- programmed cells death (PD-1) or anti-cytotoxic T lymphocyte-associated protein-4 (CTLA-4), CD20+ T cells showed similar phenotypes to those found in healthy peripheral blood. Importantly, they produced higher levels of cytokines compared to the CD20- T cells including; TNF-α, IFN-γ, IL-2, IL-17, and MIP-1β. My data, including both primary data and analysis of published datasets, indicates that CD20+ T cells can originate as a separate lineage, in addition to acquiring CD20 by trogocytosis. CD20+ T cells were found to be more highly differentiated, with increased cytokine production and contained a high frequency of CD20+ Vα7.2+CD161+ cells. Although there was no detectable difference in cancer, future work will be required to determine if they play any role within the tumour microenvironment or other pathological scenarios.