ABSTRACT
INTRODUCTION: Transfusion-associated graft-versus-host disease (TA-GVHD) is a rare complication after transfusion of components containing viable donor T cells. Gamma irradiation with doses that stop T-cell proliferation is the predominant method to prevent TA-GVHD. Treatment with pathogen inactivation methodologies has been found to also be effective against proliferating white blood cells, including T cells. In this study, T-cell inactivation was compared, between amotosalen/ultraviolet A (UVA) treatment and gamma-irradiation (2500 cGy), using a sensitive limiting dilution assay (LDA) with an enhanced dynamic range. METHODS AND MATERIALS: Matched plasma units (N = 8), contaminated with 1 × 106 peripheral blood mononuclear cells (PBMCs) per mL, were either treated with amotosalen/UVA or gamma irradiation, or retained as untreated control. Posttreatment, cells were cultured under standardized conditions. T-cell proliferation was determined by the incorporation of 3 H-thymidine and correlated with microscopic detection. RESULTS: Range-finding experiments showed that after gamma irradiation (2500 cGy), significant T-cell proliferation could be observed at a 1 × 107 cell culture density, some proliferation at 1 × 106 , and none at 1 × 105 cells/well. Based on these facts, a quantitative comparison was carried out between amotosalen/UVA at the highest challenge of 1 × 107 PBMCs/well, and gamma irradiation at 1 × 106 and 1 × 105 PBMCs/well. Complete inactivation of the T cells after amotosalen/UVA treatment was observed, equivalent to greater than 6.2 log inactivation. Complete inactivation of the T cells was also observed after gamma irradiation when 1 × 105 PBMCs/well were cultured (>4.2 log inactivation). Proliferation was observed when 1 × 106 PBMCs/well were cultured (≤5.2 log inactivation) after gamma irradiation. CONCLUSION: Amotosalen/UVA treatment more effectively inactivates T cells than the current standard of gamma irradiation (2500 cGy) for the prevention of TA-GVHD.