Purification of human sera and PBMCs

Blood samples were collected in S-Monovette serum-gel vacutainers treated with clotting activator (Sarstedt) for serum preparation and in vacutainer cell preparation tubes (CPT) with sodium-citrate (BD Biosciences) for isolation of PBMCs. Serum was prepared from clotted blood by centrifugation for 10 min at 2500 × g and stored at −80 °C. For PBMC isolation, whole blood was centrifuged for 30 min at 1700 × g, and the PBMC layer was then transferred and washed twice with PBS. The pellet was re-suspended in 0.5 ml freezing medium (either 50% FBS and 50% RPMI 1640 or 12.5% HSA and 87.5% RPMI 1640) and the cell number was determined by trypan blue staining. Following addition of 0.5 ml DMSO medium (either 50% FBS, 30% RPMI 1640, and 20% DMSO or 12.5% HSA, 67.5% RPMI 1640, and 20% DMSO) dropwise, the cells were frozen immediately in a freezing container at −80 °C. After 24 h, PBMCs were transferred into liquid nitrogen.