Influenza Vaccine Prepared by Photodynamic Inactivation of Virus

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Abstract
Summary and Conclusions: Influenza virus (108 EID50/ml, PR-8 strain of type A) in the presence of 10-5.5 M toluidine blue was photodynamically inactivated by visible light. Although all detectable infectivity was destroyed, the immunizing and hemagglutinating antigens were preserved. The photosensitive influenza-dye complex is readily dissociable, since virus-dye mixtures passed through cation resins yielded dye-free virus that regained its photoresistance. Although the infectivity of virus in infected allantoic fluid could be photodynamically destroyed, the hemagglutinin was not affected. However, upon removal of certain constituents of allantoic fluid by dialysis or by erythrocyte purification of the virus, the viral hemagglutinin became photosensitive in the presence of toluidine blue. The results with the purified hemagglutinin are similar to those found with the mature poliovirus particle, for here also, purification was required for the infective moiety to become photosensitive (9). Influenza virus vaccines inactivated by photodynamic action and by formalin were compared for antigenicity in mice. With the photodynamically inactivated vaccine, the immunologic response in mice was found to be equal to that produced by formalin-inactivated vaccine but somewhat less than that produced by injection of live virus. Such a photodynamically inactivated vaccine might prove advantageous for use with strains that have antigens particularly sensitive to formalin.