Vaccination against Her2/neu : expressing cancer using chimeric virus-like particles

Abstract: Thanks to the development of vaccines, children are these days protected against infectious diseases like polio, diphtheria and tetanus simply by receiving a few injections. Imagine a scenario where these injections would also result in protection against cancer. Vaccines against virus-induced cancer such as liver and cervical cancer are indeed already in use. Intense research is now focused on the generation of vaccines for protection also against cancer not induced by viruses. The overall aim of this thesis was to develop and determine the pre-clinical efficacy of a vaccine against tumours expressing the antigen Her2/neu. Polyomaviruses are small non-enveloped viruses that are widespread in the population, and probably harmless as long as the immune system is normal. The viral capsid is composed of three structural proteins, the major structural protein VP1, and the two minor proteins VP2 and VP3. The mouse is host to two known polyomaviruses, murine polyomavirus (MPyV) and murine pneumotropic virus (MPtV), respectively. It was known from before that VP1 of MPyV could self-assemble into viral capsids known as virus-like particles (VLPs), named so because of their morphological resemblance to natural viruses. In paper I, we showed that VP1 of MPtV could also self-assemble into VLPs, which were rapidly internalized by all tested cell types, including dendritic cells. However, the VLPs were not very efficient as vectors for gene therapy, possibly due to poor delivery of DNA into the nucleus of target cells. The combination of efficient cellular uptake and poor nuclear delivery indicated that the VLPs could be more efficient as carriers of proteins for presentation to the immune system, since delivery into the cytoplasm would be sufficient in that case. We therefore attached Her2/neu to the inside of VLPs of both MPyV and MPtV and obtained so-called chimeric VLPs (cVLPs). In papers II and III, we showed that Her2/neu-cVLPs could protect against outgrowth of transplantable Her2/neu-expressing tumours in normal mice, as well as against spontaneously arising Her2/neu-positive carcinomas in transgenic mice. Her2/neu-cVLPs from MPtV also induced immunological memory and protected against tumour out-growth in a therapeutic setting. The purpose of paper IV was to determine the immune mechanisms responsible for tumour protection. We could demonstrate that Her2/neu-cVLPs induced Her2/neu-specific CD8+ T cells, but did not induce anti-Her2/neu antibodies. However, we observed that mice were protected against tumour development also after depletion of either CD8+, or CD4+ T cells, but not after combined depletion of CD4+ and CD8+ T cells. This indicated that CD4+ T cells could compensate for the absence of CD8+ T cells and mediate tumour protection by a yet not fully clarified mechanism independent of both antibodies and CD8+ T cells. In conclusion, in this thesis it is shown that Her2/neu-cVLPs based on both MPyV and MPtV are efficient as prophylactic and therapeutic vaccines against Her2/neu-expressing tumours in mice, and that protection involves both CD4+ and CD8+ T cells.