TGFB1 and neoplasm: TGF‐β is also one of the common molecules secreted by tumor cells, which induces immunosuppressive Bregs, leading to accelerated tumor progression.[46] Thymic stromal lymphopoietin (TSLP) secreted by tumor cells down‐regulates the expression of CXCR4 and VLA4 in B‐cell precursors, which, in turn, promotes premature migration out of the bone marrow and the proliferation and differentiation of B‐cell precursors into Bregs that have tumor‐promoting metastatic effects.[47] In contrast, tumor metastasis is inhibited when B‐cell CXCR4 and VLA4 expression is downregulated.