Final Report Summary - LCMVACC (Prophylactic and therapeutic use of recombinant lymphocytic choriomeningitis virus against melanoma)
Cancer is one of the most common reasons for death of people living in the developed countries. There were an estimated 3.2 million new cases of cancer and 1.7 million deaths in the year 2008 in Europe. Among those nearly 70,000 were new cases of melanoma and during that year 14,000 patients succumb to the disease. Melanoma is caused by mutations in melanocytes in the skin, resulting in malignant tumours. The role of the immune system in the fight against cancer is manifold but often not well understood. As cancer cells originate from normal cells of the organisms they are hard to recognise for the immune system, which is usually specialised to detect “foreign” structures (like pathogens) that it encounters within the body. The structures recognised by the immune cells are called antigens. Cancer cells do usually not present altered antigens and therefore behave like stealth infection with malignant eukaryotic cells. To help the immune system recognise cancer cells as foreign, several immunotherapeutic approaches have been tested. Unspecific treatments make use of immune enhancers like IL-12 and IFN-alpha/beta. These cytokines elicit an activation of the immune system that can help to activate present anti-tumour T cells to maturate and attack the malignant cells. Until now, none of these activating cytokines has been licensed for cancer treatment. Efficient treatment has been shown with autologous tumour specific T cells that were expanded ex vivo. Nevertheless, T cells have to be expanded patient by patient, making this treatment very elaborate and therefore expensive. Also, clinical success was modest. Vaccination against cancer could help to treat patients against existing tumours or even prevent their genesis. There have been several attempts to develop cancer vaccines. Some avoid the emergence of cancer by preventing infections with the virus causing the cells to transform. The recently licensed vaccine directed against human papillomavirus causing cervical cancer is a good example. An earlier example for such a vaccine is the hepatitis B vaccine which not only prevents hepatitis B virus infection but, in consequence, also the formation of malignant liver carcinoma. Until now, no vaccine is available that prevents cancer of non-viral origin. One of the biggest problems with the development of anti-cancer vaccines is the identification of an antigen that is either specific for, or at least strongly associated with the respective cancer. For melanoma, several specific altered antigens have been identified. Examples are Melan-A and glycoprotein 100 (gp100, mouse homologue termed pmel 17). Others like Trp2 could also be viable candidate targets.Selection of the vaccine vector is crucial for the delivery of an appropriate antigen. Anti-cancer vaccines have to fulfil certain prerequisites. First, a strong CD8+ T cell response has to be elicited. Second, humoral immunity against the vector has to be minimal. In particular, the target population should have no background immunity against the viral vector. Third, the vaccine vector has to be extremely safe. A recently described vaccine based on a genetically modified recombinant replication-deficient lymphocytic choriomeningitis virus (rLCMV) proved to comply with the mentioned demands. In a mouse melanoma system (with tumour cells expressing a viral antigen), the group of Flatz and colleagues was even able to show increased survival rates in rLCMV vaccinated animals. In the mouse model used, the rLCMV vector had a comparatively better efficacy than poxvirus or adenoviral vaccine vectors. The aim of the proposed project is therefore to further elucidate the usefulness of the rLCMV vector to vaccinate against melanoma, either in a prophylactic or therapeutic approach using original tumour antigens. To do so, different melanoma antigens will be cloned into the rLCMV vector. The vectors expressing different antigens will then be tested in established mouse melanoma models and the resulting immunological reactions will be characterised using mainly FACS-analysis. The results of the proposed experiments will: i) bring the rLCMV vaccine vector closer to a phase I clinical trial, ii) tell us more about the choice of the melanoma antigen, and iii) explore in detail the quality of killer T cell populations important to overcome self-tolerance to tumours and mediate protection from cancer.The focus of the project was put on establishing techniques, preparing animal experiments and training of the fellow. 14 variants of the vaccine vector were produced and characterised and in that way the experimental “tool-box” was filled. The fellow successfully visited a two-week course in Berlin to acquire the FELASA C certificate to enable him to supervise animal experimentation (April 2012). In addition he was trained in the specific Swiss animal law during a one day course organised by the RESAL (Réseau des animaleries lémaniques) (June 2012).The researcher started the work by establishing the necessary virological and molecular biology techniques in the host laboratory. PCR, molecular cloning techniques, virological assays (for quantification) had to be set-up in the new laboratories of the dermatology unit at the CHUV. Following the set-up, vaccine vector production could be started. By end of July 2012, the first animal experiments with characterised and quantified vaccine vector were started. We expect the project to promote the area of cancer vaccination and immunotherapy, respectively. The use of recombinant viral vectors for prophylactic and therapeutic cancer therapy has been investigated in many studies in the past without bringing success in the clinical setting, without helping patients to significantly improve their health. The drawbacks of the vaccine vectors used so far are 1) low stimulation of T cell response against the cancer antigen 2) immunity of the patient population against the vaccine vector 3) questionable biosafety of the vaccine vector.The recombinant lymphocytic choriomeningitis virus (rLCMV) has proven in earlier studies that it is able to strongly stimulate a T cell response. The background immunity in the population which has been investigated so far was extremely low. Furthermore, the vector is safe due to the removal of an essential gene for production of virus progeny and cell entry.Certain parts of the population are at higher risk of developing skin cancer (melanoma). Persons who are exposed to sunlight due to their outdoor-work (gardeners, construction workers) could be vaccinated to reduce their risk to develop melanoma. This, in combination with classical means to reduce the risk (wearing sun protective clothing and using sunscreen) could provide an option so significantly reduce the risk of melanoma development. Also, persons with reduced pigmentation and a therefore natural higher sensitivity to sunlight might be candidates for prophylactic melanoma vaccination. There are also countries and areas in the world with higher melanoma prevalence where it might even be worth to vaccinate wider parts of the population. Among these are Australia and New-Zealand, South-Africa but also Northern-Europe. If the vaccine protects reliably against melanoma would also be safe without side effects, the overall public health benefit could be worth vaccinating whole populations.