Designing a linear accelerator-based "X irradiation system" for platelet products: an efficient, safe, accessible and cost-effective alternative for conventional X- or gamma irradiators.

X-irradiation of blood products is an alternative for gamma-ray to prevent post-transfusion GvHD. However, commercial X-irradiators are not widely available while little is known about their safety and efficacy for platelet products. This study introduces an efficient, accessible and cost-effective "X irradiation system" for platelet concentrates (PCs). By constructing a suitable radiation box (phantom) for a clinically available linear accelerator, an "X irradiation system" was designed specifically for PCs. PCs were divided into three equal bags either exposed to X- and gamma-irradiation or kept unirradiated (control). Irradiation-induced inhibition of T cells proliferation was examined by MTT and cell cycle assays on mononuclear cells (MNCs) obtained from PCs. The inhibitory effect of irradiation on allorecognition ability of MNCs was assessed by mixed lymphocyte reaction where MTT evaluated lymphocyte proliferation responses and flowcytometry examined CD8T lymphocytes activity. Platelet activation was also examined with P-selectin expression and PAC-1 binding by flowcytometry. X- and gamma-irradiation reduced T cell proliferation while disturbing the cell-cycle with reduced entry of T-cells into the S phase and their G2 arrest. Both types of irradiations also effectively reduced "lymphocyte allorecognition responses" while inactivating CD8T lymphocytes in platelet products but with no significant effect on platelet activity. This is the first study that showed "X irradiation system" effectively suppresses T cell proliferation and CD8T lymphocyte activity in platelet products, with no effect to platelet quality and activation markers. This may suggest the LINAC-based "X irradiation system" with a dose of 30Gy as efficient and safe as gamma-irradiation for platelet products.