HDC and colorectal neoplasm: In colorectal tumor microenvironment, histidine decarboxylase (HDC)+ myeloid cells-derived CXCL13/CXCR5 axis that mediated Foxp3 expression and Treg proliferation, which affected CD8+ T cells directly and thus appeared to play key roles in suppressing tumoricidal immunity and facilitated colorectal tumor proliferation36.