Immunomodulation due to plasma or plasma-platelet apheresis donation: Events occurring during donation procedures

Background: It has been recently shown that during therapeutic apheresis procedure, a large amount of soluble HLA class I molecules settles onto plastic apheresis circuits, inducing sustained TGFβ₁ pre/post-transcriptional modulation in activated patients' leukocytes. Reportedly, donors' leukocytes may be exposed to similar immunosuppressing activities during donor apheresis procedures. On this basis, it could be hypothesized that such events can cause immune modulation. It is uncertain which blood cell population is most impacted by these events. This study is focused on the effects on the T lymphocytes. Study design and methods: To assess if such events occur, lymphocytes from 20 apheresis donors collected before and after three closely timed plasma and platelet donation procedures were analyzed for sHLA-I mediated immunomodulation. Results: The results confirmed that sHLA-I molecules bind to the apheresis circuit surfaces. Circuits can also transiently activate donors' CD8⁺ T lymphocytes, to which sHLA-I molecules can bind, thus modulating short-lasting immune effects, such as transcriptional and post-transcriptional TGFβ₁ modulation and soluble Fas ligand release. However, no significant change in relative proportions, absolute number and cell viability of lymphocyte subpopulations was found and no ex vivo immune effect was detectable longer than 14 days after procedure in any cell type in all donors. Conclusion: Short-lived sHLA-I mediated immunomodulation was demonstrable in lymphocytes from every donor as a consequence of apheresis procedures, but no enrolled subject experienced any adverse reaction or showed any sign of immunosuppression during 24 months of follow-up after the donations.