Efficacy of B16OVA Tumour Cell Lysate Conjugated to Rabbit Haemorrhagic Disease Virus Virus-Like Particles as an Anti-Tumour Vaccine

Abstract

By presenting antigen to T cells dendritic cells (DC) carry out a central role in the activation of T cell mediated immunity to cancer. Tumour cell lysate (TL) as a source of tumour antigens offers the advantage over single, defined tumour-associated antigens (TAA) of being able to stimulate polyclonal T cell responses to heterogeneous tumours containing both known and unknown antigens. However TL alone does not generate a robust, long-lasting anti-tumour response. Virus-like particles (VLP) coupled to defined TAA have been shown to stimulate strong anti-tumour responses but the majority of cancer antigens remain undefined. This project aimed to develop VLP-antigen conjugates by coupling unidentified TAAs in TL to Rabbit Haemorrhagic Disease Virus (RHDV) VLP. TL was generated from the melanoma cell line B16OVA that secretes the model antigen, ovalbumin (OVA). Bone-marrow derived DCs (BMDC) were pulsed with VLP-TL and the BMDC maturation response evaluated by assessing upregulation of the key DC surface markers, CD40, CD80, CD86 and MHC-II by flow cytometry. Subsequently antigen-pulsed DC were co-cultured with OVA MHC-I and MHC-II peptide-specific OT-I and OT-II splenocytes and the T cell proliferative and cytotoxic response measured. Carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled OT-I splenocytes proliferated in response to VLP-TL indicating T cell activation; OT-II splenocytes on the other hand showed no such response. IFN-γ was detected in the supernatant of both OT-I and OT-II co-cultures, indicating a cytotoxic response. Inhibition of T cell proliferation and cytotoxicity was seen in the presence of VLP or TL alone and VLP-TL was sometimes able to overcome this inhibition. In vivo CTL-mediated cytotoxicity was also examined with VLP-TL vaccinated mice showing a significant TL-specific cytotoxic response, demonstrating proof of principle for future in vivo assays of VLP-TL. These results indicate that VLP-TL may have a beneficial effect on the ability of DC to stimulate T cell proliferation and anti-tumour cytotoxicity. Further investigations with increased dosages are warranted to ascertain whether or not the effect seen is dose-dependent.