Characterization of the Neoantigen Profile in a Tumor Mutation Burden-high Melanoma Patient With Multiple Metastases.

BACKGROUND/AIM: Recently, neoantigen (NA) profiling has been intensively performed for the development of novel immunotherapy. We previously reported a melanoma case with a high tumor mutation burden that achieved complete remission after anti-programmed death-1 therapy. We herein revisited the same case, characterized the NA profiles of other metastatic lesions using algorithms and CTL assays, and investigated the immunological status, including tumor-infiltrating lymphocytes and the T cell receptor (TCR) repertoire profile, in metastatic sites.

MATERIALS AND METHODS

NA candidates obtained from whole-exome sequencing were applied to the HLA-binding prediction algorithm, NetMHCpan4.1. HLA-A*2402-restricted sequence candidates with a strong binding capacity (<50 nM) and elution affinity (<1%) were selected and evaluated for synthetic peptide candidates. The immunological status in metastatic sites was characterized using gene expression profiling, immunohistochemistry, and a TCR repertoire analysis.

RESULTS

The genomic analysis revealed that all metastatic sites, such as costal, intra-muscular, and brain lesions, had >1,500 SNVs, and 12 driver mutations were common to all sites. New driver mutations were identified in intra-muscular (KMT2C: p.P3292S) and brain (JAK1: p.S404P) metastases and a functional analysis of these mutations revealed that JAK1 mutation exhibited a promoting effect on invasion activity. CTL assays using synthetic NA peptides identified more NA epitopes in brain metastasis.

CONCLUSION

These results might suggest that the heterogeneity of driver gene mutations is unremarkable, while immunological response is variable in metastatic sites. As a result, the genomic and immunological investigation has provided a very valuable and informative suggestion regarding better cancer therapy decisions.