High transferrin receptor expression marks tumors with increased immune-effector infiltration and expression of targetable checkpoint molecules: Results of a multi-cancer analysis in solid tumors

2613 Background: The cell-surface transferrin receptor, TFR1, encoded by TFRC, imports iron-bound transferrin into cells to drive tumor proliferation. We have found worse prognosis with high TFRC expression across multiple tumor types. The mechanism by which TFRC drives tumor cell- intrinsic oncogenesis is multifactorial, but its interaction with the tumor microenvironment (TME) has not been studied. Here, we assessed TME infiltration by immune effector populations and immune checkpoint expression. Methods: Tissue samples underwent comprehensive molecular profiling at Caris Life Sciences: Next-gen sequencing of DNA (592 Gene Panel, NextSeq, or whole exome sequencing, NovaSeq), RNA- seq (NovaSeq, whole transcriptome sequencing, WTS) and immunohistochemistry. RNA deconvolution analysis by the Microenvironment Cell Populations (MCP)-counter method quantified immune populations to assess T cells, B cells, natural killer cells (NK) and myeloid dendritic cells (MDC). Analyses compared quartiles of TFRC mRNA expression between Q4 ( TFRC-H) high and Q1 ( TFRC-L) low expressors. Results: Among 27,607 patients with non-small cell lung cancer (NSCLC), 5,332 with prostate cancer (PC), and 14,287 with colorectal cancer (CRC), TFRC-H tumors were associated with high tumor mutational burden (TMB-high, ≥10 mutations/MB), and TP53 mutation (q<0.05). Multiple immune checkpoint genes showed significantly higher expression in TFRC-H relative to TFRC-L in all tumor types, including CD274 (PDL1), LAG3, PDCD1LG2 (PDL2), and CTLA4 (Table; All values are statistically significant: q<0.05). Moreover, TME assessment by MCP-counter showed significantly increased infiltration by total T cells, CD8+ cells, B cells, NK cells, and MDCs in TFRC-H (Table). Finally, among patients who received Check-point inhibitors (CPI), TFRC-L had improved survival (HR=0.807 (95% CI 0.76 – 0.85) p<0.00001) in NSCLC but no difference was found in CRC or PC. Conclusions: Our study is the first to reveal the TME characteristics associated with TFRC expression in a variety of solid tumor types. We found TFRC-H tumors have increased infiltration by immune effector populations but also express significantly higher levels of immune checkpoint molecules, highlighting immune exhaustion. Altered iron metabolism has been shown to promote tumorigenesis and here we identify a new role for TFRC in remodeling the TME. TFR1- targeting therapeutic agents are in clinical development and warrant further investigation in combination with CPIs. [Table: see text]