Abstract
In order to develop an inactivated cell culture vaccine, the RC·HL strain was produced by adapting the RCEH strain to HmLu cell culture after a long term cultivation in Vero cell culture, and by limiting dilution which was performed at passages 21 to 23. The RC·HL strain increased the infectivity and growth capability in CRFK, ESK, Vero and HmLu cell cultures, and also increased the pathogenicity for suckling mice and hamsters; however, the strain was non-pathogenic for adult mice, guinea pigs, rabbits and dogs. The RC·HL strain attained a higher infective titer at 32°C-34°C than at 37°C and at an input multiplicity of infection of 1.0 or 0.1 than at 0.01 or 0.001. The inactivated RC·HL strain reached peak immunogenicity one to two days after the virus attained its maximum infective titer. The virus was purified by two methods, and the virus recovery and protein reduction rate were compared between the two. A method using 10% polyethylene glycol (PEG) was more favorable for the purification of the virus than the ultrafiltration method. The purified virus was inactivated with 0.01 M binary ethylenimine (BEI) or 0.0125%β-propiolactone (BPL) within 30 hours, whereas 0.075% formalin required 7 days for inactivation. The immunogenicity of BPL-inactivated virus was most stably maintained during 8-month storage at 4°C. Based on the data collected, it was considered that the RC·HL strain may be usedas a seed virus for an inactivated cell culture vaccine against rabies.
