Mass Cytometry of Follicular Lymphoma Tumors Reveals Intrinsic Heterogeneity in Proteins Including HLA-DR and a Deficit in Nonmalignant Plasmablast and Germinal Center B-Cell Populations

Abstract

Background: Follicular lymphoma (FL) is an indolent non-Hodgkin lymphoma that has a risk of transformation to more aggressive lymphoma. Relatively little is known about the nonmalignant B-cell and T-cell subset composition within the tumor microenvironment and whether altered phenotypes are associated with patterns of lymphoma B-cell heterogeneity. Methods: Two mass cytometry (CyTOF) panels were designed to immunophenotype B and T cells in FL tumors. Populations of malignant B cells, nonmalignant B cells, and T cells from each FL tumor were identified and their phenotypes compared to B and T cells from healthy human tonsillar tissue. Results: Diversity in cellular phenotype between tumors was greater for the malignant B cells than for nonmalignant B or T cells. The malignant B-cell population bore little phenotypic similarity to any healthy B-cell subset, and unexpectedly clustered closer to naïve B-cell populations than GC B-cell populations. Among the nonmalignant B cells within FL tumors, a significant lack of GC and plasmablast B cells was observed relative to tonsil controls. In contrast, nonmalignant T cells in FL tumors were present at levels similar to their cognate tonsillar T-cell subsets. Conclusion: Mass cytometry revealed that diverse HLA-DR expression on FL cells within individual tumors contributed greatly to tumor heterogeneity. Both malignant and nonmalignant B cells in the tumor bore little phenotypic resemblance to healthy GC B cells despite the presence of T follicular helper cells in the tumor. These findings suggest that ongoing signaling interactions between malignant B cells and intra-tumor T cells shape the tumor microenvironment. © 2016 International Clinical Cytometry Society.