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Front. Immunol. | doi: 10.3389/fimmu.2019.00542

Discrepancies in the tumor microenvironment of spontaneous and orthotopic murine models of pancreatic cancer uncover a new immunostimulatory phenotype for B cells

 Sarah Spear1,  Juliana B. Candido1, Jacqueline R. McDermott1,  Eleni Maniati1,  Stephen A. Beers2, Frances R. Balkwill1,  Hemant M. Kocher1 and  Melania Capasso1, 3*
  • 1Barts Cancer Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, United Kingdom
  • 2Faculty of Medicine, University of Southampton, United Kingdom
  • 3German Center for Neurodegenerative Diseases (DZNE), Germany

B cells are salient features of pancreatic ductal adenocarcinoma (PDAC) tumors, yet their role in this disease remains controversial. Murine studies have indicated a protumoral role for B cells, whereas clinical data show tumor-infiltrating B cells are a positive prognostic factor, both in PDAC and other cancers. This disparity needs to be clarified in order to develop effective immunotherapies. In this study, we provide new evidence that reconcile human and mouse data and highlight the importance of using relevant preclinical tumor models when assessing B cell function. We compared B cell infiltration and activation in both a genetic model of murine PDAC (KPC mouse) and an injectable orthotopic model. A pronounced B cell infiltrate was only observed in KPC tumors and correlated with T cell infiltration, mirroring human disease. In contrast, orthotopic tumors exhibited a relative paucity of B cells. Accordingly, KPC-derived B cells displayed markers of B cell activation (germinal center entry, B cell memory and plasma cell differentiation) accompanied by significant intratumoral immunoglobulin deposition, a feature markedly weaker in orthotopic tumors. Tumor immunoglobulins, however, did not appear to form immune complexes. Furthermore, in contrast to the current paradigm that tumor B cells are immunosuppressive, when assessed as a bulk population, intratumoral B cells upregulated several proinflammatory and immunostimulatory genes, a distinctly different phenotype to that of splenic-derived B cells; further highlighting the importance of studying tumor-infiltrating B cells over B cells from secondary lymphoid organs. In agreement with the current literature, genetic deletion of B cells (µMT mice) resulted in reduced orthotopic tumor growth, however, this was not recapitulated by treatment with B-cell-depleting anti-CD20 antibody and, more importantly, was not observed in anti-CD20-treated KPC mice. This suggests the result from B cell deficient mice might be caused by their altered immune system, rather than lack of B cells. Therefore, our data indicate B cells do not favor tumor progression. In conclusion, our analysis of relevant preclinical models shows B cells to be active members of the tumor microenvironment, producing immunostimulatory factors that might support the adaptive antitumor immune response, as suggested by human PDAC studies.

Keywords: B cells, Immunoglobulins, Tumor microenviroment, Pancreatic Cancer, Murine models

Received: 10 Dec 2018; Accepted: 28 Feb 2019.

Edited by:

Lionel Apetoh, Institut National de la Santé et de la Recherche Médicale (INSERM), France

Reviewed by:

Sophie Siberil, INSERM U1138 Centre de Recherche des Cordeliers, France
Lloyd Bod, Brigham and Women's Hospital, Harvard Medical School, United States  

Copyright: © 2019 Spear, Candido, McDermott, Maniati, Beers, Balkwill, Kocher and Capasso. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Melania Capasso, German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany, melania.capasso@dzne.de