INACTIVATION OF LEUKOCYTES IN PLATELET CONCENTRATES BY PHOTOCHEMICAL TREATMENT WITH PSORALEN PLUS UVA

A photochemical treatment (PCT) process using a novel psoralen and lon g wavelength ultraviolet light (UVA, 320-400 nm) has been developed to inactivate bacteria and viruses in platelet concentrates. This study evaluated the efficacy of PCT for inactivation of leukocytes that cont aminate platelet preparations. Three psoralens, 8-methoxypsoralen (8-M OP), 4'-aminomethyl 4,5',8-trimethylpsoralen (AMT), and the novel psor alen S-59, were compared using the following four independent but comp lementary biological and molecular assays. (1) T-cell viability: Treat ment with 150 mu mol/L S-59 and 1.0 to 3.0 Joules/cm(2) UVA inactivate d >5.4 +/- 0.3 log(10) of T cells in full-sized single-donor plateletp heresis units. Using 1.0 Joule/cm(2) UVA, the lowest dose of S-59, AMT and 8-MOP required to reduce the number of T cells to the limit of de tection was 0.05 mu mol/L, 1.0 mu mol/L, and 10.0 mu mol/L, respective ly. (2) Cytokine synthesis: Treatment with 1.9 Joules/cm(2) UVA and 15 0 mu mol/L S-59 or AMT completely inhibited synthesis of the cytokine IL-8 by contaminating leukocytes during 5 days of platelet storage. Af ter treatment with 75 mu mol/L 8-MOP and 1.9 Joules/cm(2) UVA, only lo w levels of IL-8 were detected. (3) Psoralen-DNA adduct formation: The combination of 1.9 Joules/cm(2) UVA and 150 mu mol/L S-59, AMT, or 8- MOP induced 12.0 +/- 3.0, 6.0 +/- 0.9, and 0.7 psoralen adducts per 1, 000 bp DNA, respectively. (4) Replication competence: Polymerase chain reaction (PCR) amplification of small genomic DNA sequences (242-439 bp) after PCT was inhibited. The degree of PCR amplification inhibitio n correlated with the level of adduct formation (S-59 > AMT > 8-MOP). In contrast, 2,500 cGy gamma radiation, a dose that inactivates >5 log (10) of T cells in blood products, had minimal effect on cytokine synt hesis and did not induce sufficient DNA strand breaks to inhibit PCR a mplification of the same small DNA sequences. These results demonstrat e that leukocytes are sensitive to PCT with psoralens and among the ps oralens tested S-59 is the most effective. Therefore, PCT has the pote ntial to reduce the incidence of leukocyte-mediated adverse immune rea ctions associated with platelet transfusion. (C) 1998 by The American Society of Hematology.