Effect of dose and long-term storage on the immunogenicity of murine polyomavirus VP1 virus-like particles

We have analysed the stability and immunogenicity of murine polyomavirus virus-like particles (VLPs) following intranasal administration without adjuvant. No morphological or immunological changes were observed in a preparation of these VLPs stored for 9 weeks at room temperature. Strong humoral and cellular (Th1) responses were obtained after a single 5.55 μg dose immunisation, which are efficiently boosted after a second dose. However, at dose concentrations above 0.22 μg/μl, these VLPs appear to aggregate and, when used for immunisations, they fail to induce a strong cellular response, even though the humoral response is unaffected. These results may reflect the differential processing of VLP aggregates by the immune system or, alternatively, VLP neutralisation by antibodies induced after a primary immunisation.