Sterilization of HIV with irradiation: Relevance to infected bone allografts

Background: Bone allograft banks commonly sterilize frozen bone by irradiation. The dose-response relationship for HN is calculated and the dose required to inactivate the bioburden of virus that may be present in allograft bone is determined. Methods: A virus titre experiment is performed using irradiated frozen HIV. The virus is maintained on dry ice (approximately -70 degrees C) and is exposed to a cobalt 60 source with 0-40 kGy irradiation at 5 kGy intervals. Lymphocyte cell cultures are exposed to serial dilutions of the irradiated virus. The virus titre is quantified by cytological changes of HIV infection and p24 immunofluorescence. Results: There is a linear relationship between the virus titre and the radiation dose delivered. The inactivation rate of irradiated virus was 0.1134 log(10) tissue culture infective doses (50)/mL per kGy (95% confidence intervals, 0.1248-0.1020). The irradiation dose required to inactivate the HIV bioburden in allograft bone is 35 kGy. The irradiation dose required to achieve a sterility assurance level of 10(-6) is 89 kGy. This dose exceeds current recommendations for sterilizing medical products and the current practice of many bone banks. Conclusions: It is concluded that gamma irradiation should be disregarded as a significant virus inactivation method for bone allografts.