Immunogenicity of purified venezuelan equine encephalitis virus inactivated by ionizing radiation

Comparison of the immunological responses and efficacy of gamma-irradiated V3526 vaccine formulations against subcutaneous and aerosol challenge with Venezuelan equine encephalitis virus subtype IAB

We recently developed a gamma-irradiation method to inactivate V3526, a live-attenuated Venezuelan equine encephalitis virus (VEEV) vaccine candidate. Dosage and schedule studies were conducted to evaluate the immunogenicity and efficacy of gamma-irradiated V3526 (gV3526). Subcutaneous (SC) and low dosage intramuscular (IM) administration of gV3526 were highly effective in protecting mice against a SC challenge with VEEV IA/B Trinidad Donkey strain, but not against an equivalent aerosol challenge. More robust immune responses and increased protective efficacy were noted when the IM dosage of gV3526 was increased. IM administration of gV3526 formulated with either CpG or CpG plus Alhydrogel further augmented the immune response in mice and resulted in 100% protection against aerosol challenge.

A multisystem approach for development and evaluation of inactivated vaccines for Venezuelan equine encephalitis virus (VEEV)

A multisystem approach was used to assess the efficiency of several methods for inactivation of Venezuelan equine encephalitis virus (VEEV) vaccine candidates. A combination of diverse assays (plaque, in vitro cytopathology and mouse neurovirulence) was used to verify virus inactivation, along with the use of a specific ELISA to measure retention of VEEV envelope glycoprotein epitopes in the development of several inactivated VEEV candidate vaccines derived from an attenuated strain of VEEV (V3526). Incubation of V3526 aliquots at temperatures in excess of 64 degrees C for periods >30 min inactivated the virus, but substantially reduced VEEV specific monoclonal antibody binding of the inactivated material. In contrast, V3526 treated either with formalin at concentrations of 0.1% or 0.5% (v/v) for 4 or 24 h, or irradiated with 50 kGy gamma radiation rendered the virus non-infectious while retaining significant levels of monoclonal antibody binding. Loss of infectivity of both the formalin inactivated (fV3526) and gamma irradiated (gV3526) preparations was confirmed via five successive blind passages on BHK-21 cells. Similarly, loss of neurovirulence for fV3526 and gV3526 was demonstrated via intracerebral inoculation of suckling BALB/c mice. Excellent protection against subcutaneous challenge with VEEV IA/B Trinidad donkey strain was demonstrated using a two dose immunization regimen with either fV3526 or gV3526. The combination of in vitro and in vivo assays provides a practical approach to optimize manufacturing process parameters for development of other inactivated viral vaccines.

Comparison of gamma and neutron radiation inactivation of influenza A virus

Radiation inactivation of viral pathogens has potential application in sterilization and in the manufacture of biological reagents, including the production of non-infectious viral antigens. Viral inactivation by gamma radiation has been extensively investigated, but few direct comparisons to other qualities of radiation have been explored. Experiments were designed to examine direct radiation damage by both gamma photons (gamma) and neutrons (n) while minimizing methodological differences. Frozen samples of influenza A X31/H3N2 and PR8/H1N1 were exposed to gamma and n at doses between 0 and 15.6 kGy. Other experimental parameters, including dose-rate, were not varied. Virus titers were determined by tissue culture infectious dose (TCID(50)) and plaque forming unit (PFU) assays. D(10) values, kGy per log reduction, were calculated from these assays. PR8 D(10) values based on PFU assays were approximately 2 and 5 kGy for gamma and n exposures, respectively, and those based on TCID(50) were approximately 6 and 14 kGy. Similar results were obtained for the A/X31 strain. The data demonstrate that gamma was 2-3-fold more effective than n, with a relative biological effectiveness (RBE) range of 0.43-0.65. These neutron results are likely the first reported for a medically relevant virus. PAGE analysis of viral proteins and RNAs failed to show macromolecular damage. D(10) values were found to be similar to a broad summary of previously reported gamma inactivation values for other virus types. The dependence of the magnitudes of D(10) on titer assay in this study suggests that more than one titer method should be used to determine if complete inactivation has occurred.

Gamma ray-induced small plaque mutants of western equine encephalitis virus

Small plaque mutants of Western equine encephalitis virus were obtained from the surviving fractions of wild-type virus which was irradiated with gamma rays. The frequency with which small plaque mutants appeared in the surviving fraction increased with the radiation dose. These mutants were not more resistant to radiation than wild-type virus. The growth rate of a mutant, S127, was lower than that of wild-type. Clonally purified mutant virions presented two peaks in a velocity sedimentation profile; peak 1 corresponded to the peak of wild type and peak 2 moved faster than peak 1. Virions of both peaks were infectious and consistently formed small plaques in chicken embryo cells. Virions reisolated from either peak and grown in chicken embryo cells also revealed two peaks in sedimentation analysis. In the electron microscope examination peak 2 proved to consist of giant form particles, each of which contained more than one nucleoid surrounded with a common envelope. Despite this remarkable morphological difference, densities of the wild-type and S127 mutant virions were similar in cesium chloride gradients. The RNAs and proteins of mutant virions could not be distinguished from those of wild type on the basis of size or charge.

Formalin-inactivated Venezuelan equine encephalomyelitis (Trinidad strain) vaccine produced in rolling-bottle cultures of chicken embryo cells

Formalin-inactivated Venezuelan equine encephalomyelitis vaccine was prepared from virus grown in rolling-bottle cultures of chicken embryo cells. Trinidad strain virus was propagated in these cultures with a maintenance medium consisting of serum-free medium 199 containing 0.25% human serum albumin (USP) and antibiotics. Manipulation of multiplicity of inoculum (0.06 to 0.00006) and maintenance medium volume (100 to 300 ml) resulted in high-titered virus yields and only moderate cell destruction when fluids from infected cultures were harvested at 18 to 24 hr. The virus was inactivated at 37 C by 0.05% Formalin within 8 to 10 hr and with 0.1% Formalin within 6 to 8 hr. Single dose, antigen extinction tests in mice performed with 30 small-scale vaccine lots showed excellent potency at either Formalin concentration with inactivation periods ranging from 24 to 96 hr.

Immunogenicity of purified, inactivated chikungunya virus in monkeys

Chikungunya (CHIK) virus, harvested from infected BHK-21 cell cultures and highly purified by a method combining zinc acetate precipitation, Sephadex-Sepharose column chromatography, and sucrose density gradient centrifugation, was subjected to ultraviolet (UV) irradiation and treatment with formalin. Inactivation of the virus by UV light was apparently a first-order reaction. The virus treated with 0.05% formalin at 4 degrees C was inactivated completely after 7 weeks, but when treated with 0.025% formalin retained its plaque infectivity at least 17 weeks. Both UV- and formalin-inactivated viruses induced production of anti-CHIK neutralizing antibodies in Japanese monkeys with no preimmune antibodies. Judging by the titres of antibodies produced, the immunogenic effect of the UV-irradiated virus was superior to that of the formalin-treated virus.

Immunization of mice against encephalomyocarditis virus. II. Intraperitoneal and respiratory immunization with ultraviolet-inactivated vaccine: effect of Bordetella pertussis extract on the immune response

Mice were immunized by intraperitoneal (ip) or respiratory administration of ultraviolet-inactivated virus alone or with Bordetella pertussis extract (BPE) as an adjuvant. The effect of immunization was tested by determination of antibody titers and by survival of a lethal challenge with 200 LD(50) of a virulent (large-plaque variant) strain of EMC virus. For plain vaccine the ip 50% effective dose (ED(50)) was 37 hemagglutination units (HAU; ca. 4 x 10(6) plaque-forming unit equivalents); with adjuvant the ip ED(50) was reduced to 20 HAU. After respiratory immunization by intratracheal injection, an ED(50) value of 100 HAU was found, which was not affected by BPE. After ip vaccination the primary immune response was enhanced by BPE, but the challenge response, measured 3 weeks after challenge, was unaffected. Respiratory immunization induced a primary response which was not influenced by BPE, but here the challenge response was enhanced by the adjuvant. After secondary treatment (challenge or booster vaccination) serum antibodies and protection against challenge persisted for at least 1 year.