CD28 and colorectal carcinoma: Two-step MR analysis revealed that two plasma metabolites (Sphingomyelin (d18:1/22:1, d18:2/22:0, d16:1/24:1) and 16α-hydroxy-DHEA-3-sulfate) influence CRC through two immune cell traits (SSC-A on CD14+ monocyte and CD3 on CD28- CD8+ T cell).