Characterization of shared neoantigens landscape in Mismatch Repair Deficient Endometrial Cancer

Endometrial cancer (EC) with Mismatch Repair deficiency (MMRd) is characterized by the accumulation of insertions/deletions at microsatellite sites. These mutations lead to the synthesis of frameshift peptides (FSPs) that represent tumor-specific neoantigens (nAg) proved to be shared across patients/tumors with MMRd. In this study, we explored the feasibility of a nAg-based cancer vaccination design in EC with MMRd. We adopted a whole exome sequencing approach and ad hoc bioinformatics pipelines to characterize FSPs in 35 patients with EC. A mean of 146 mutated mononucleotide repeats (MNRs) was identified with enrichment in the patients' group with MLH1 impairment. A high coverage emerged from the comparative analysis of the EC FSPs with the content of the previously validated NOUS-209 vaccine. We obtained pieces of evidence of FSPs translation as expressed proteins from Ribo-seq, supporting the potential as the target of vaccination. The development of a nAgs-based vaccine strategy in MMRd EC may be further explored.