Vaccination with coxsackievirus B3 virus-like particles elicits humoral immune response and protects mice against myocarditis

Coxsackievirus B3 (CVB3), along with other enteroviruses, is involved in about 50% of myocarditis cases and in the pathogenesis of dilated cardiomyopathy. Prevention of CVB3 infection is therefore highly desirable. Virus-like particles (VLPs) are structurally similar to native virus particles and therefore are far better immunogens than any other subunit vaccines. Recombinant baculoviruses carrying either the intact, entire coding region of CVB3 or the four individual coding regions for virus proteins 1-4 (VP1-4) were constructed. Expression of CVB3 capsid proteins in insect cells infected with recombinant baculovirus was detected by immunofluorescence and Western blot analysis. Sucrose gradient ultracentrifugation fractions of the infected cell lysates contained peaks of CVB3 antigen with an approximate density of 1.14 g/ml. Electron microscopy demonstrated the presence of VLP in these sucrose fractions. The CVB3 VLP was non-infectious in tissue culture. SWR (H-2(q)) mice vaccinated with CVB3 VLP developed antibodies to CVB3 capsid proteins after the first boost. Antibody titre was comparable to the level induced by an attenuated CVB3 vaccine. Vaccinated animals were protected from myocarditis when subsequently challenged with cardiovirulent CVB3 (chimera-2). Vaccination with VLP produced from the complete CVB3 coding region gave a greater immune response and afforded better protection than with VLP from the quadruple expression vector. These results demonstrate that CVB3 capsid proteins expressed in insect cells have the intrinsic capacity to assemble into non-infectious VLP, which afforded protection from CVB3 infection to mice when used as a vaccine.