MHC class-I downregulation in PD-1/PD-L1 inhibitor refractory Merkel cell carcinoma and its potential reversal by histone deacetylase inhibition: a case series.

Background: Merkel cell carcinoma (MCC) is an aggressive skin cancer in which PD-1/PD-L1 blockade has shown remarkable response rates. However, a significant proportion of patients shows primary or secondary resistance against PD-1/PD-L1 inhibition, with HLA class-I downregulation and insufficient influx of CD8 T cells into the tumor as possible immune escape mechanisms. Histone deacetylase inhibitors (HDACi) have been demonstrated to reverse low HLA class-I expression caused by epigenetic downregulation of the antigen machinery (APM) in vitro and in pre-clinical models in vivo.

[Merkel cell carcinoma].

Merkel cell carcinoma is a rare, highly aggressive skin tumor with neuroendocrine features found in older people. The pathogenesis is associated with immunosuppression, chronic UV light exposure and the Merkel cell polyomavirus. Clinically, Merkel cell carcinoma presents as a solitary, cutaneous or subcutaneous, red to bluish node.