Preparation and characterization of human HIV type 1 neutralizing reference sera

Reference neutralizing antibody (NA) reagents are needed for laboratories to be able to compare results of neutralization assays that will be used to monitor HIV-1 vaccine recipients. In an effort to establish such reference reagents two asymptomatic, seropositive patients were identified with medium to high amounts of cross-reactive NA activity against a number of HIV-1 strains. Sera obtained from each individual at three or four sequential phlebotomies were pooled, and the two pools were each distributed in > 3000 aliquots into glass ampoules and lyophilized, and the ampoules were flame sealed. An HIV-1 antibody-negative reference serum was prepared in a similar fashion after pooling serum from four individuals. Ampoules were tested for uniformity of fill, sterility, moisture content, residual oxygen, stability, infectivity, and presence of antibody. An international collaborative study was conducted to determine the potency of the samples in six laboratories, each using their own neutralization assays and reagents. The results indicated reasonable consistency between laboratories and that both sera have sufficient titers against a variety of strains for use as reference reagents. These reference sera have been included in the World Health Organization (WHO) AIDS Reagent Project and are available through the three AIDS reagent repositories.