Polyomavirus-like-particles (PLPs) are empty, non-replicative, non-infectious particles that represent a potent antigen-delivery system against malignant disease. Protective anti-tumour immunity can be induced under therapy conditions by subcutaneous (s.c.) treatment with particulate antigenic structures like chimerical polyomavirus-pentamers (PPs). These PPs displaying an immunodominant H-2Kb-restricted ovalbumin (OVA)257-264 epitope evoked nearly complete tumour remission in MO5 (B16-OVA) melanoma-bearing C57BL/6 mice by two s.c. applications in a weekly interval. The immunotherapeutic intervention started at day 4 after melanoma implant. Furthermore, 40% of melanoma-bearing mice vaccinated with heterologous PPs carrying a H-2Kb-restricted cytotoxic T lymphocyte (CTL) epitope derived from of tyrosinase-related protein 2 (TRP2) survived similar treatment conditions. However, a late immunotherapeutic onset at day 10 post melanoma inoculation revealed no significant differences between the therapeutic values (40-60% survival) of VP1-OVA252-270 and VP1-TRP2180-192 PPs, respectively. These experiments underlined the capacity of PPs to break T cell tolerance against a differentially expressed self-antigen. As a correlate for preventive and therapeutic immunity against MO5 melanoma the number of OVA257-264- or TRP2180-188-specific CD8 T cells were significantly increased within the splenocyte population of treated mice as measured by H-2Kb-OVA257-264-PE tetramer staining or appropriate ELISPOT assays, respectively. These results reveal that heterologous PLPs and even chimerical PPs represent highly efficient antigen carriers for inducing CTL responses underlining their potential as immunotherapeutics against cancer.

Polyomavirus-like-particles (PLPs) are empty, non-replicative, non-infectious particles that represent a potent antigen-delivery system [1]. Due to the high immunogenicity of heterologous PLPs consisting of the major polyomavirus coat protein VP1 and a foreign CD8 T cell epitope at its C-terminus it is possible to protect mice against B16-OVA melanoma [2]. Here we show that in mice protective anti-tumour immunity can be already induced by means of subcutaneous vaccination with particulate antigens, heterologous VP1-pentamers (8-9 nm in size). These VP1-pentamers carrying an immunodominant H-2K b ovalbumin (OVA) 257-264 epitope evoked full protection in C57BL/6 mice against lethal B16-OVA melanoma challenge upon twice subcutaneous immunisations in a weekly interval. Furthermore, 60 % of mice vaccinated with VP1-pentamers carrying an immunodominant H-2K b -restricted self-epitope of tyrosinase-related protein 2 (TRP2) 180-188 survived to lethal B16-OVA challenge. This experiment additionally underlines the capacity of PLPs to break T cell tolerance against a differentially expressed self-antigen. More importantly, heterologous capsoids of VP1-OVA 252-270 (~45 nm in size) cured mice from B16-OVA melanoma cells that had been administered 5 days prior to the first therapeutic treatment. As correlate for protection the number of OVA 257-264 -specific CD8 T cells were significantly increased within the splenocyte population of treated mice even in the absence of an adjuvant (QuilA) as measured by H-2K b -OVA 257-264 -PE tetramers. The weekly treatment intervals appeared to be crucial for vaccine efficacy due to VP1-specific antibody interference. These results reveal that heterologous PLPs and even chimerical polyomavirus-specific pentamers represent highly efficient antigen carriers for inducing cellmediated immunity against malignant diseases underlining their potency in the fight against cancer.