Image_1_Experimental Evaluation of the Protective Efficacy of Tick-Borne Encephalitis (TBE) Vaccines Based on European and Far-Eastern TBEV Strains in Mice and in Vitro.PDF

<p>Tick-borne encephalitis (TBE), caused by the TBE virus (TBEV), is a serious public health threat in northern Eurasia. Three subtypes of TBEV are distinguished. Inactivated vaccines are available for TBE prophylaxis, and their efficacy to prevent the disease has been demonstrated by years of implication. Nevertheless, rare TBE cases among the vaccinated have been registered. The present study aimed to evaluate the protective efficacy of 4 TBEV vaccines against naturally circulating TBEV variants. For the first time, the protection was evaluated against an extended number of phylogenetically distinct TBEV strains isolated in different years in different territories. The protective effect did not strongly depend on the infectious dose of the challenge virus or the scheme of vaccination. All vaccines induced neutralizing antibodies in protective titers against the TBEV strains used, although the vaccines varied in the spectra of induced antibodies and protective efficacy. The protective efficacy of the vaccines depended on the individual properties of the vaccine strain and the challenge virus, rather than on the subtypes. The neutralization efficiency appeared to be dependent not only on the presence of antibodies to particular epitopes and the amino acid composition of the virion surface but also on the intrinsic properties of the challenge virus E protein structure.</p

The complete blood count in <i>C. aethiops</i> monkeys before and at the different terms after s/c challenge with 7.3 log₁₀ PFU of OHFV strain Nikitina.

<p>ND – not determined; aspartate aminotransferase (AST); alanine aminotransferase (ALT).</p

Study design.

<p>The flow chart represents the study design and performance. The monkey species used in each experiment is shown in red. Vaccine: the name of the vaccine administered before challenge or “no” vaccine is indicated. ^a - the number of monkeys used in each experiment is shown in parenthesis. ^b - the blue framed box represents the section number, which describes the results of each particular experiment. The challenging virus is shown in blue. “Analysis made”: the types of analysis and parameters used to evaluate the model are listed. “Results0 are presented in”: the results presented in figures or tables in the current study are listed.</p

Viral titers (log₁₀PFU/ml) in CNS and visceral organs of <i>C. aethiops</i> monkeys, immunized twice with TBE inactivated vaccine (FSME-Immun), and in non-immunized monkeys on the 23–26 days after s/c challenge with 6.7 log₁₀ PFU of TBEV, strain Absettarov.

<p>0–<1 PFU in 0.1 ml of 10% suspension.</p

Virus titers (log₁₀ PFU/ml) and the presence or absence of viral RNA (+/−) in CNS and visceral organs of <i>C. aethiops</i> monkeys immunized and non-immunized with inactivated vaccine against TBE (EIPVE) on the 14–16 days after challenge with 7.3 log₁₀ PFU of OHFV, strain Nikitina.

<p>0–<1 PFU in 0.4 ml 10% suspension.</p><p>“−”– RT-PCR is negative for viral RNA.</p><p>“+”– RT-PCR is positive for viral RNA.</p

Virus titers in visceral organs and CNS (log₁₀ PFU/ml) of <i>M. fascicularis</i> monkeys s/c inoculated with TBEV Abs-18 or Sof-16 strains at the early terms after infection (8–10 d.p.i.).

<p>0–<1 PFU in 0.2 ml of 10% suspension; s.c. – spinal cord, l.n. – lymph nodes.</p

Viremia and neutralizing antibody titers in monkeys infected with 7.3 log₁₀ PFU of OHFV.

<p>A. Viremia in two non-vaccinated monkeys (#1 and 3). B. Viremia in two monkeys (# 2 and 4), vaccinated with commercial inactivated vaccine against TBE (EIPVE). Viremia was analyzed in blood clots by plaque assay; the limit of detection of the plaque assay was 0.5 log₁₀ PFU/ml. D.p.i. – days post-infection. C. Average (for two monkeys) reciprocal neutralizing antibody (NA) titers in sera of immunized and non-immunized <i>C. aethiops</i> monkeys before and after challenge. Two different viruses were used for neutralization assay: TBEV or OHFV.</p

Histological lesions in the brain of monkeys infected with 6.0 log₁₀ PFU of Abs-18 at the late terms after infection (27–28 days).

<p>A and B. Brainstem (<i>truncus cerebri</i>) of <i>M. fascicularis</i> monkey #26: multiple small vasculitis (1), perivascular edema (2), degenerative changes in neurons (3). Magnification: (A) ×100, (B) ×200. C and D. Subcortical region of <i>M. fascicularis</i> monkey #26: small vasculitis (1) and nodules of neuronophagia (2). Magnification: (C) ×100, (D) ×400. Cortex of cerebellum: E. Fall out of small groups of Purkinje cells in <i>M. fascicularis</i> monkey #34 (1). Magnification ×100.; F. Non-infected normal control. Magnification ×200. Staining by Nissle method was used.</p

Histological lesions in the liver and spleen of <i>M. fascicularis</i> monkey (#26) at the late terms after infection with 6.0 log₁₀ PFU of Abs-18.

<p>A. Liver: lymphohistiocytic infiltration of portal liver tracts (1). Magnification ×200. B. Spleen: reduction of lymphoid follicles (1); depletion of white pulp along the trabecular arteries (2). Magnification ×400. Staining with hematoxylin and eosin was used.</p

Inhibitors of Tick-Borne Flavivirus Reproduction from Structure-Based Virtual Screening

Flaviviruses form a large family of enveloped viruses affecting millions of people over the world. To date, no specific therapy was suggested for the infected people, making the treatment exclusively symptomatic. Several attempts were performed earlier for the design of fusion inhibitors for mosquito-borne flaviviruses, whereas for the tick-borne flaviviruses such design had not been performed. We have constructed homology models of envelope glycoproteins of tick-transmitted flaviviruses with the detergent binding pocket in the open state. Molecular docking of substituted 1,4-dihydropyridines and pyrido­[2,1-<i>b</i>]­[1,3,5]­thiadiazines was made against these models, and 89 hits were selected for the in vitro experimental evaluation. Seventeen compounds showed significant inhibition against tick-borne encephalitis virus, Powassan virus, or Omsk hemorrhagic fever virus in the 50% plaque reduction test in PEK cells. These compounds identified through rational design are the first ones possessing reproduction inhibition activity against tick-borne flaviviruses