Segments of Puumala Hantavirus Nucleocapsid Protein Inserted into Chimeric Polyomavirus-Derived Virus-Like Particles Induce a Strong Immune Response in Mice

Insertion of a short-sized epitope at four different sites of yeast-expressed hamster polyomavirus major capsid protein VP1 has been found to result in the formation of chimeric virus-like particles. Here, we demonstrate that the insertion of 45 or 120 amino acid–long segments from the N-terminus of Puumala hantavirus nucleocapsid protein into sites 1 (amino acids 80–89) and 4 (amino acids 288–295) of VP1 allowed the highly efficient formation of virus-like particles. In contrast, expression level and assembly capacity of fusions to sites 2 (amino acids 222–225) and 3 (amino acids 243–247) were drastically reduced. Immunization of BALB/c mice with chimeric virus-like particles induced a high-titered antibody response against the hantavirus nucleocapsid protein, even in the absence of any adjuvant. The strongest response was observed in mice immunized with virus-like particles harboring 120 amino acids of hantavirus nucleocapsid protein. According to the immunoglobulin subclass distribution of nucleocapsid protein-specific antibodies a mixed Th1/Th2 response was detected. The VP1 carrier itself also induced a mixed Th1/Th2 response, which was found to be reduced in mice immunized with virus-like particles harboring 120 amino acid–long inserts. In conclusion, hamster polyomavirus VP1 represents a promising carrier moiety for future vaccine development.