The use of dimethylmethylene blue for virus photoinactivation of red cell suspensions

Phenothiazine dyes and light have been known to have virucidal properties for over seventy years. This review will describe recent progress in the use of one phenothiazine dye, dimethyl-methylene blue, for photo-inactivation of a number of RNA and DNA viruses in red cell suspensions under conditions that minimally affect red cell in vitro properties during 42-day 1-6 degrees C storage. Dimethylmethylene blue has a higher affinity for nucleic acid than the closely related phenothiazine, methylene blue. Virus photoinactivation appears to be mediated by singlet oxygen. The kinetics of photoinactivation depends on the virus studied, but for a given virus, is similar for both intracellular and extracellular forms. The similarity for inactivation of intracellular and extracellular virus suggests that a common target, such as nucleic acid, is involved. Finally, lymphocytes, which can harbour transfusion-associated viruses and can mediate transfusion-associated-graft-versus host disease, are sensitive to dimethylmethylene blue photoinactivation under virucidal conditions.