Objective  To investigate the role and mechanism of action of colorectal cancer-associated regulatory B cells (Breg) in promoting lymphangiogenesis using a coculture model.

  Methods  The colorectal cancer cells, CT26 and MC38, were cocultured with B cells to induce colorectal cancer-associated Breg cells; the proportion of CD19⁺IL-10⁺Breg cells was determined using flow cytometry; the secretion levels of VEGF-A, VEGF-C, and VEGF-D in conditioned medium of colorectal cancer-associated Breg cells were detected using ELISA; scratch and tube formation assays were used to detect the migration and tube formation abilities of the lymph node endothelial cell line, SVEC4-10, after intervention of Breg-conditioned medium.

  Results  Breg^CT26-induced groups (4.90±0.05) vs. (27.63±1.12) and Breg^MC38-induced groups (5.85±0.86) vs. (24.27±2.27) from the 48h coculture system induced more Breg cells than those from the 24h coculture system; the expression levels of VEGF-A and VEGF-C in colorectal cancer-associated Breg cells were significantly higher than those in cells from the blank group (P<0.05). Moreover, colorectal cancer-associated Breg cells enhanced both the tube formation and migration abilities of SVEC4-10 cells.

  Conclusions  In the tumor microenvironment, colorectal cancer cells induce B cell transformation into Breg cells. This change upregulates the secretion levels of VEGF-A and VEGF-C, enhances the tube formation and migration abilities of SVEC4-10, and promotes tumor lymphangiogenesis.