Abstract
BackgroundRegulatory B (Breg) cells represent one of the B cell subsets that infiltrate solid tumors and exhibit distinct phenotypes in different tumor microenvironments. However, the phenotype, function and clinical relevance of Breg cells in human hepatocellular carcinoma (HCC) are presently unknown.MethodsFlow cytometry analyses were performed to determine the levels, phenotypes and functions of TIM-1+Breg cells in samples from 51 patients with HCC. Kaplan-Meier plots for overall survival and disease-free survival were generated using the log-rank test. TIM-1+Breg cells and CD8+ T cells were isolated, stimulated and/or cultured in vitro for functional assays. Exosomes and B cells were isolated and cultured in vitro for TIM-1+Breg cell expansion assays.ResultsPatients with HCC showed a significantly higher TIM-1+Breg cell infiltration in their tumor tissue compared with the paired peritumoral tissue. The infiltrating TIM-1+Breg cells showed a CD5highCD24−CD27−/+CD38+/high phenotype, expressed high levels of the immunosuppressive cytokine IL-10 and exhibited strong suppressive activity against CD8+ T cells. B cells activated by tumor-derived exosomes strongly expressed TIM-1 protein and were equipped with suppressive activity against CD8+ T cells similar to TIM-1+Breg cells isolated from HCC tumor tissue. Moreover, the accumulation of TIM-1+Breg cells in tumors was associated with advanced disease stage, predicted early recurrence in HCC and reduced HCC patient survival. Exosome-derived HMGB1 activated B cells and promoted TIM-1+Breg cell expansion via the Toll like receptor (TLR) 2/4 and mitogen-activated protein kinase (MAPK) signaling pathways.ConclusionsOur results illuminate a novel mechanism of TIM-1+Breg cell-mediated immune escape in HCC and provide functional evidence for the use of these novel exosomal HMGB1-TLR2/4-MAPK pathways to prevent and to treat this immune tolerance feature of HCC.
Highlights
Humoral immunity, in addition to cellular immunity, has recently been reported to play a key role in tumor progression [1, 2]
High infiltration of T cell Ig and mucin domain (TIM)-1+ B cells is correlated with advanced disease stage and poor survival in patients with hepatocellular carcinoma (HCC) We used flow cytometry to analyze the TIM-1 expression of B cells from 30 normal blood samples and 51 HCC specimens (Additional file 1: Table S1) comprising blood samples and paired peritumor liver and tumor tissue samples
Our results showed that the percentage of TIM-1+B cells in lung cancer patients was significantly increased in the tumor compared to the blood and peritumor lung (Additional file 5: Figure S1), which was similar to the HCC results
Summary
In addition to cellular immunity, has recently been reported to play a key role in tumor progression [1, 2]. TIM-1+Breg cells appear to include the highest proportion of IL-10-producing B cells, are 8– 20-fold enriched for IL-10 expression compared with all other B cell subsets, and comprise over 70% of all IL-10 producing-B cells [15]. Their regulatory function and relationship with systemic autoimmune disease or transplantation have been characterized [15,16,17,18]. The biological function of TIM-1+Breg cells in the human tumor microenvironment has not been illustrated. The phenotype, function and clinical relevance of Breg cells in human hepatocellular carcinoma (HCC) are presently unknown
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