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 HIV 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°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 log₁₀ 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.