e14534 Background: Nasopharyngeal carcinoma (NPC) is endemic in Southern China and is well-known to be heavily infiltrated by lymphocytes and constitute a unique but poorly defined tumor microenvironment. We aimed at delineating and defining the contribution of idronoxil (IDX), a synthetic flavonoid derivative, in restoring sensitivity to apoptosis and potentially modulating the immune microenvironment of NPC. Methods: Using multiplexed staining, we measured the levels of ENOX2 (IDX’s target), CD8 (cytotoxic T cell) and pan-cytokeratin (tumor marker) in 86 NPC patients’ cancerous specimens in tissue microarray format. NPC tissue bulk RNA-Seq and affymetrix microarray public datasets were gathered to examine ENOX2 significance. Interaction between ENOX2-expressing tumor cell lines (C17 and NPC43) and T cells were also studied. In vivo, antitumor effects of IDX on the growth of NPC43+ve tumors in nude mice and humanized mice were studied. Results: We performed median density as cut-off and tumors can be classified as hot or cold. 68.6% “cold”-phenotype tumors were observed in our cohort and the top 20% patients with highly positive ENOX2-expresing tumor cells showed lower number of CD8 infiltrates. Publicly dataset showed that highly expressed ENOX2 group associated with poorer prognosis (log-rank test p = 0.041). In vitro, we observed increased migration of T cells towards cancer cells when tumor cells were pre-treated with the combination of IDX and cisplatin (IDX+Cis) compared with monotherapy (IDX or cis alone) or untreated. We also observed increased susceptibility of tumor cells to T cell cytotoxicity when both IDX and Cis were added. In nude mice, IDX+Cis significantly decreased the tumor growth compared to saline-treated group. In humanized mice, upon treatment, we found 1.69-fold (p = 0.039) more CD3+ T cells in the tumor than in the blood when compared to control group. In humanized mice, the ratio between human T cell levels in tumor and blood was increased by the IDX+Cis compared to control group (1.67-fold, p = 0.01 by t-test). Conclusions: Distinct immunospatial profiles could be associated with clinicopathologic characteristics. The ability of IDX to modulate T cell populations indicates the potential of IDX to enhance the efficacy of current chemotherapy treatments in NPC by upregulating cellular trafficking toward tumor.[Table: see text]