Study of a tick-borne encephalitis vaccine

Abstract

Scientific relevance. Tick-borne encephalitis is one of the most significant anthropozoonoses for public health in the Russian Federation. Wide vaccination coverage is required to control this zoonotic infection. However, large-scale immunisation is not feasible without developing novel vaccines with improved safety and efficacy profiles, such as vaccines based on the continuous Vero cell line.Aim. This extended study aimed to investigate the key quality attributes of VeroKSEN, a new tick-borne encephalitis vaccine that was obtained using Vero cells.Materials and methods. The authors implemented current approaches to vaccine development, including propagation of tick-borne encephalitis strain 205 (Far Eastern subtype) in Vero cells, fine purification of the viral antigen by size-exclusion chromatography on polymeric resins, and introduction of additional quality control methods. For VeroKSEN production, the authors used the method protected by utility patent No. 2678431. Quality control of the finished product was performed according to the State Pharmacopoeia of the Russian Federation. The laboratory study of the vaccine and its intermediates in Balb/с mice used novel control methods developed by the authors. Additional methods included polyacrylamide gel electrophoresis, enzyme immunoassay, immunoblotting with total antibodies to tick-borne encephalitis virus and monoclonal antibodies to glycoprotein E, reverse transcription–polymerase chain reaction, and high-performance liquid chromatography. The extended potency study used test strains of different subtypes, including Absettarov (Western), Sofjin (Far Eastern), and Korzukhin (Siberian). The authors studied the infectious activity of tick-borne encephalitis virus in outbred mice using the pharmacopoeial titration method. Statistical analysis of the study results involved calculating the arithmetic mean and the root-mean-square deviation.Results. The authors studied the key quality attributes of VeroKSEN and its intermediates. Selected inactivation conditions reduced the infectious activity of the viral harvest to an undetectable level within 24 h, while its antigenic activity remained approximately 100% of the baseline. The fine purification stages and the methods and techniques developed by the authors provided a whole-virion fraction with a purity of up to 98.2% and removed process-related impurities (residual host-cell DNA, bovine serum albumin, formaldehyde, and bacterial endotoxins) to the levels required by national legislation. The stability study demonstrated that the vaccine met the requirements for up to 36 months.Conclusions. The study showed the high potency of the new vaccine in terms of protection against the Western, Siberian, and Far Eastern subtypes of tick-borne encephalitis, with minimum immunising doses (MID50) of 0.007, 0.00125, and 0.00093 mL, respectively.