Development and Exploration of a Novel Personalized Cancer Vaccine Based on Virus-Like Particles (VLPs) by Incorporating Melanoma Specific T-cell Epitopes
Authors: Mohsen Mona Omar , Bachmann Martin F. 
Published: June 2019

Cancer Immunotherapy has significantly advanced cancer treatment modalities. However, therapeutic cancer vaccine aiming at reactivating anergic or dormant T cells has so far shown modest immune responses. VLPs have made notable strides in the last three decades in vaccine development field, mainly as prophylactic vaccines against VPV and HBV. The current project aims to design and build a multi-step platform for developing personalized therapeutic melanoma VLP-vaccine by integrating immunopeptidomics and exome sequencing approaches using melanoma patient-specific T-cell epitopes. To obtain a proof of concept in murine models, we have performed immunopeptidomics and exome sequencing for B16F10 melanoma cell line. The central goal of this platform (combining immunopeptidomics and exome sequencing) is to integrate the obtained data to develop a pipeline enabling the identification of mutated peptides which would constitute a promising cancer target for vaccine development. Our preliminary data of immunopeptidomics (alone) has shown large number of peptides which we have then prioritize and filter using bio-informatics and via probing with tumorinfiltrating lymphocytes (TILs). Peptides from immunopeptidomics were assessed for number of physical characteristics, such as their length and MHC-class I affinity as well as biological characteristics, such as being melanocyte specific, oncogenic or mutated. One of the key candidate was PMEL (gp100), a 100kDa type I transmembrane protein expressed in pigmented cells of skin and eye (tissue-specificity). A second promising candidate was MTC-1, an anti-oncogene that plays role in cell cycle regulation. If constitutively expressed, MTC-1 increases CDK4/6 kinases in breast cancer and promotes angiogenesis by inhibiting apoptosis. Furthermore, the selected peptides were synthesized and used to stimulate TILs to search for pre-existing immunity. TILs were labelled with CFSE and stimulated with the respective peptides (PMEL, MTC-1, no peptide or a mixture) and proliferation was assessed by determining CFSE dilution of CD8+ T-cells. Both peptides and -in particular the peptide mix- induced proliferation of T-cells, indicating that the transplanted tumor spontaneously induced T-cells against the respective epitopes. In the next step, we have prepared the vaccine using the bio-orthogonal copper-free click chemistry to couple the peptides of interest. Bio-orthogonal copper free click chemistry coupling method has shown efficacy, specificity and safety in our previous experiments. Bacteriophage Qb-VLPs were used and loaded with type-B CpGs which are known to be one of the most potent adjuvants in mice. The prepared vaccine cocktail was tested in C57BL/6 mice bearing B16F10 melanoma tumors with/without checkpoint inhibitors. Our preliminary results have shown significant regression in tumor size as well as significant production of IFN-g. We have also carried out extra analysis to characterize myeloid cells in the tumor microenvironment for each group to assess the effect of vaccination on myeloid cells in the tumor. The results indicated a notable decrease in TAMs characterized by (CD11b+/F4/80+ cells) in the group treated with vaccine+anti-PD1. This multi-step process can later be translated into the clinics and can be applied to other types of solid tumors. We are in the process of integrating exome sequencing data with immunopeptidomics aiming to identify mutated antigens which will increase the efficacy of the developed vaccine.