# The IFNγ‐CIITA‐MHC II axis modulates melanoma cell susceptibility to NK‐cell‐mediated cytotoxicity

## TL;DR

This study explores how melanoma cells resist natural killer (NK) cell attacks and identifies a pathway involving IFNγ, CIITA, and MHC II that could be targeted to improve immunotherapy.

## Contribution

The study identifies the IFNγ-CIITA-MHC II axis as a novel mechanism by which melanoma cells resist NK-cell-mediated cytotoxicity.

## Key findings

- Melanoma cells develop resistance to NK-cell-mediated cytotoxicity through upregulation of CIITA and MHC II.
- Blocking IFNγ signaling or using dimethyl fumarate/simvastatin restores NK-cell cytotoxicity against melanoma cells.
- MHC II surface expression is a critical factor in suppressing NK-cell-mediated killing.

## Abstract

Melanoma, the deadliest form of skin cancer, poses a significant challenge due to its genetic heterogeneity and high metastatic potential. While cytotoxic T cell (CTL)‐based immunotherapies have made remarkable progress in recent years, the therapeutic potential of natural killer‐(NK) cells is increasingly recognized. However, resistance mechanisms to both CTL‐ and NK‐cell‐mediated immunotherapies hinder effective treatment. To evaluate the exclusive role of NK‐cells in anti‐melanoma immunity, we performed 2D and 3D co‐culture‐based cytotoxicity assays under varying conditions. Our findings revealed a protective phenotype in melanoma cells following prolonged exposure to primary NK‐cells. By combining experimental data with bioinformatic analyses, we identified key genes and pathways involved in melanoma cell adaptation to NK‐cell‐mediated killing (NKmK). We found that cytokines such as IFNγ play a major role in suppressing NKmK with MHC II surface expression being a critical factor. Targeting the master regulator CIITA, which governs MHC II expression and is affected by IFNγ, significantly reduced melanoma cell resistance to NKmK. This study provides potential strategies to overcome resistance to NK‐cell‐based immunotherapies and offers novel insights into melanoma immune escape mechanisms.

Natural killer (NK) cells play a central role in anti‐melanoma immunity. However, melanoma cells adapt during co‐culture by upregulating CIITA and MHC II in response to interferon gamma (IFNγ), thereby evading NK‐cell lysis. Blocking IFNγ signaling or treatment with dimethyl fumarate/simvastatin counteracts this immune escape and maintains NK‐cell cytotoxicity.