Tumor immune microenvironment-associated prognostic and mifamurtide-response gene signatures for localized osteosarcoma: a correlative study of the ISG/OS2 trial.

A risk-adapted treatment strategy, the ISG/OS-2 trial, evaluated the use of mifamurtide in P-glycoprotein (Pgp)-positive localized osteosarcoma patients. The primary objective was the identification of prognostic classifiers based on tumor immune microenvironment (TME) gene profiling in all patients and in those undergoing mifamurtide. RNA from pre-treatment FFPE non-decalcified tissues of 62 patients was analyzed with the PanCancer Immune profiling panel (NanoString Technologies, Seattle, WA, US). Thirty three out of sixty-two (53%) Pgp-positive patients underwent chemotherapy (CT)+mifamurtide, 29/62 (47%) Pgp-negative patients received CT alone. Univariate Cox regression, ROC curve and CIBERSORTx algorithm gene deconvolution analyses were performed. A 21-gene signature able to stratify all patients into high-(Hi-R) and low-risk (Lo-R) was identified: 5-year OS for Hi-R 47%; 92% for Lo-R (p = 3e-06). TME of Lo-R vs Hi-R, was significantly enriched in CD8 T-cells, T-regs, and NK activated cells, and diminished in CD4 T- cells. The 21-gene signature was validated in two independent sets: Target-OS TCGA (n=62) and GSE33382 (n=57). For patients treated with CT+mifamurtide 31-mifamurtide related genes able to distinguish Hi-R and Lo-R in terms of OS (p = 1e-09) and EFS (p = 3e-06) were also identified. After multivariate analysis the 21-gene and the 31-gene mifamurtide-related signatures were independently associated with OS (p= 0.00044 and p = 0.000079, respectively). A validated osteosarcoma TME prognostic gene signature has been identified, regardless of mifamurtide treatment. Importantly, a mifamurtide-related signature was also developed. Tumor-immune interactions possibly implicated in disease progression and treatment response were shown.