Mammary-tumor-educated B cells acquire LAP/TGF-β and PD-L1 expression and suppress anti-tumor immune responses

Int Immunol. 2016 Sep;28(9):423-33. doi: 10.1093/intimm/dxw007. Epub 2016 Feb 19.


B lymphocytes play a role in inhibiting the immune response against certain tumors, but the underlying mechanisms are poorly understood. EMT-6 mammary tumors grow well in wild-type (WT) mice but show reduced growth in B-cell-deficient μ(-/-) BALB/c mice (BCDM). WT mice demonstrate extensive B-cell infiltration into the tumor bed, reduced CD8(+) T cell and CD49(+) NK cell infiltration, and markedly reduced cytolytic T-cell response relative to BCDM. Expression of LAP/TGF-β1, CD80, CD86 and PD-L1 is significantly increased in tumor-infiltrating B cells (TIL-B) relative to splenic B cells. LAP/TGF-β1 expression on TIL-B progressively increased from 5.4±1.7% on day 8 to 43.1±6.1% by day 21 post tumor implantation. Co-culture of EMT-6 tumor cells with Naive-B cells ex vivo generated B cells (EMT6-B) with a similar immunophenotype to TIL-B. Purified TIL-B, or in-vitro-generated EMT6-B suppressed CD4(+), CD8(+) and CD4(+)CD25(-) T-cell proliferation, and Th1 cytokine secretion, and also suppressed purified NK-cell proliferation in response to IL-15, compared to naive splenic B cells. Acquired B regulatory function required direct tumor cell: B-cell contact, and was partially reversed by antibody to TGF-β or PD-L1, leading to tumor rejection in vivo B-cell acquisition of a suppressive phenotype following tumor infiltration may result in profound inhibition of T-cell anti-tumor responses.

Keywords: B regulatory cells; PD-L1; TGF-β; anti-tumor response.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • B-Lymphocytes, Regulatory / immunology*
  • B-Lymphocytes, Regulatory / pathology
  • B7-1 Antigen / genetics
  • B7-1 Antigen / immunology
  • B7-2 Antigen / genetics
  • B7-2 Antigen / immunology
  • B7-H1 Antigen / genetics
  • B7-H1 Antigen / immunology*
  • CD8-Positive T-Lymphocytes / immunology
  • CD8-Positive T-Lymphocytes / pathology
  • Female
  • Gene Expression Regulation, Neoplastic / immunology*
  • Mammary Neoplasms, Experimental / genetics
  • Mammary Neoplasms, Experimental / immunology*
  • Mammary Neoplasms, Experimental / pathology
  • Mice
  • Mice, Inbred BALB C
  • Mice, Knockout
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / immunology*
  • Th1 Cells / immunology
  • Th1 Cells / pathology
  • Transforming Growth Factor beta / genetics
  • Transforming Growth Factor beta / immunology*


  • B7-1 Antigen
  • B7-2 Antigen
  • B7-H1 Antigen
  • Cd274 protein, mouse
  • Cd86 protein, mouse
  • Neoplasm Proteins
  • Transforming Growth Factor beta