Pan-cancer evaluation of the association between immune cell infiltration and Necroptosis activity.

Introduction. Necroptosis (NCP) is a form of programmed cell death characterized by the breakdown of the cell membrane followed by the release of cellular elements. Evidence in some tumors showed that high expression of NCP-related genes is associated with high cytotoxic CD8+ T-cell infiltrates, mediated by signaling from Dendritic (DC) and CD4+ T-cells. This study aims at providing a pan-cancer view of the prognostic relevance of NCP and its correlation with a comprehensive set of immune infiltrating cells. Materials and methods. Gene expression RNA-seq data of 5,451 primary solid tumors across 24 different cancer types were downloaded from The Cancer Genome Atlas, excluding cases with treatments before surgery and with residual tumor. B-cells, CD4+ T-cells, CD8+ T-cells, Macrophages and DC infiltration scores were estimated for each sample using the deconvolution algorithm TIMER. The scores were then dichotomized at the 25th and 75h percentiles to create groups of samples at low and high infiltration, respectively. Logistic regression and likelihood ratio test were applied on the gene expression of 163 NCP genes to test their association with each immune cell population, adjusting for tumor purity. Cox regression and log-rank test were applied to evaluate the prognostic relevance of the NCP genes. FDR-adjusted p-values<0.05 were considered for statistical significance. Results and Discussions. A portrait of the interactions between NCP and immune cells across cancer types was provided. DC and CD4+ T-cells infiltration showed significant correlation with more than 50% of NCP genes across the largest number of cancer types: kidney chromophobe, head and neck squamous cell, liver hepatocellular, thyroid carcinoma for both; adrenocortical, kidney renal clear cell, pancreatic, prostate carcinoma for only DC; breast cancer and lung adenocarcinoma for only CD4+ T-cells. In particular, 69 NCP genes were found correlated with DC infiltration, including the main genes defining the necrosome for NCP activation: RIPK1, RIPK3 and MLKL. Of these, 60 and 58 genes showed a prognostic statistical relevance for overall and disease-free survival in at least one cancer type, respectively. Conclusions. This work highlighted the relevant role of NCP in enhancing immune system against tumor, fostering DC-mediated response. Genomic data were shown to be important to characterize the interaction between the tumor and its microenvironment, which is crucial to develop immunotherapy approaches. Validation studies on specific cancer types will be considered.