657 Downregulation of CTLA4 in tumor and blood samples is associated with a worse prognosis in malignant melanoma

CTLA-4 is a negative regulator of T lymphocyte activation, and the inhibition used to treat melanoma but has limited efficacy. We measured CTLA4 mRNA expression in using TCGA tumor data found association decreased with worse patient prognosis. Because constitutively expressed regulatory (Treg) cells upregulated non-Treg cells, we blood samples. Whole samples from an Australian cohort (170 patients 103 healthy controls) were for by qRT-PCR analyzed Kaplan-Meier (K-M), log-rank test, Cox proportional hazards model, multivariate linear regression model. Unlike reported other cancers, was than controls. K-M survival curve demonstrated low survival. While such trend not evident primary patients, analysis metastatic showed association. This confirmed another United States (246 patients). To understand immune cell subsets responsible downregulated melanoma, fractionated blood. Consistent these results, Treg human PBMCs surface protein when cultured condition media lines lines. In summary, demonstrate that lower reduction correlates prognosis especially melanoma. Our unpredicted novel findings call further investigation into role biology, immunity, cancer therapy.