There were no significant associations between HCC development and the levels of soluble immune checkpoint proteins (sBTLA, sCD27, sCD28, sTIM-3, soluble glucocorticoid-induced TNFR-related [sGITR], soluble lymphocyte-activation gene 3 [sLAG-3], soluble toll-like receptor 2 [sTLR-2], soluble glucocorticoid-induced TNFR-related ligand [sGITRL], sCTLA-4, sCD80, sCD86, and sPD-L1) (Supplementary Fig. 2). Here, SPDL1 is linked to hepatocellular carcinoma.