Photochemical decontamination (PCD) of platelet concentrates, with adequate preservation of platelet function, has been shown using 8- methoxypsoralen (8-MOP) and long wavelength UV light (UVA). To further evaluate this technique, models for the inactivation of pathogenic human cell-associated viruses and integrated proviral sequences are required. We have assessed the ability of the PCD technique to inactivate cell-associated human immunodeficiency virus 1 (HIV-1) in platelet concentrates. We correlated PCD inhibition of HIV-1 infectivity with 8-MOP-DNA adduct formation in contaminating nucleated cells, and measured the inhibition of polymerase chain reaction (PCR)- mediated amplification of cellular DNA sequences as a surrogate for inactivation of integrated proviral nucleic acid sequences. After PCD treatment (8-MOP 300 micrograms/mL, UVA 17 mW/cm2) for 60 minutes, 0.5 x 10(6) plaque-forming units (PFU)/mL of cell-associated HIV-1 were inactivated and no virus was detectable by infectivity assay. After 60 minutes of PCD, 15 8-MOP-DNA adducts per 1,000 bp were formed, while in the absence of UVA, no adducts were formed. PCR-mediated amplification of a 242-bp cellular DNA sequence (HLA-DQ-alpha) was inhibited when greater than eight psoralen-DNA adducts per 1,000 bp were present. These studies indicate that high titers of cell-associated HIV-1 in platelet concentrates were inactivated by PCD, and the numbers of 8-MOP- DNA adducts in nucleated cells were sufficient to inhibit amplification of DNA segments that encode for as few as 80 amino acids. Based on the frequency of 8-MOP-DNA adducts, for the 10-kb HIV-1 genome, the probability of an integrated genome without at least one 8-MOP adduct after 60 minutes of PCD was 10(-33).