SMPD3 and prostate cancer: In the prostate cancer cell line PC3, when the Rab27a gene, which is related to exosome secretion, and the neutral sphingomyelinase 2 (nSMase2) gene, which promotes the budding of intravesicular vesicles, are knocked out, the levels of PD-L1 and the exosomal marker CD63 are significantly decreased.