High expression of B7-H3 on monocyte/macrophages in tumor microenvironment promotes lung cancer progression by inhibiting apoptosis

•B7-H3 was markedly increased on monocyte/macropages.•The transport of miR-29a-3p by exosomes regulated the expression of B7-H3.•The anti-apoptotic ability of monocyte/macropages was enhanced by B7-H3.•B7-H3 promoted the accumulation of monocyte/macropages in lung cancer.