CEACAM1 is an IL-2R-dependent biomarker in patients with multiple autoimmune-diseases undergoing low-dose IL-2 therapy

Abstract

Abstract Low-dose (LD) IL-2 is a promising strategy to boost Tregs in patient with autoimmune diseases. This therapeutic strategy would benefit by identifying biomarkers that are highly and selectively responsive to IL-2R signaling in Treg and Teff cells. To initially address this point, RNA-seq was used to screen for genes that are induced in CD4+ Foxp3+ Treg and CD4+ CD45RO+ T effector/memory (TEM) cells from normal subjects in vitro by IL-2R, but not TCR/CD28, signaling. CEACAM1 was identified as a candidate gene in Tregs 4 and 24 hours post-stimulation. However, CEACAM1 was optimally upregulated in Treg and TEM cells after an extended 5 day culture with anti-CD3/CD28 and IL-2. Notably, anti-IL-2 essentially completely inhibited this upregulation, indicating that CEACAM1 expression was strictly IL-2 dependent. Tregs were shown to express the long isoform of CEACAM1 with inhibitory ITIM domains and the ITIMs may be functionally active as most in vitro activated CEACAM1+ Tregs did not express Ki67. To assess CEACAM1 as an IL-2-dependent biomarker during LD-IL-2 therapy, CD25 and CEACAM1 were evaluated at the protein and RNA levels for patient samples from eight distinct autoimmune diseases. In all samples, CEACAM1 was upregulated after a 5-day induction course of LD-IL-2 in Tregs but not TEM cells. This finding correlated with the effect of LD-IL-2 on CD25. CEACAM1 levels returned to baseline 14 days post-LD-IL-2 treatment. After the induction course of LD-IL-2, most CEACAM1+ Tregs were Ki67−, consisting with an inhibitory role for CEACAM1. Collectively, our findings indicate that CEACAM1 is a biomarker for LD-IL-2 therapy whose expression is highly dependent on IL-2R signaling and suggest that CEACAM1 may function to regulate Treg homeostasis. Supported by R01AI131643