A Crohn's Disease-associated IL2RA Enhancer Variant Determines the Balance of T Cell Immunity by Regulating Responsiveness to IL-2 Signalling

Background and Aims: Differential responsiveness to interleukin [IL]-2 between effector CD4(+) T cells [T-eff] and regulatory T cells [T-reg] is a fundamental mechanism of immunoregulation. The single nucleotide polymorphism [SNP] rs61839660, located within IL2RA [CD25], has been associated with the development of Crohn's disease [CD]. We sought to identify the T cell immune phenotype of IBD patients who carry this SNP. Methods: T-eff and T-reg were isolated from individuals homozygous [TT], heterozygous [CT], or wildtype [CC] for the minor allele at rs61839660, and used for phenotyping [flow cytometry, Cytometry Time Of Flight] functional assays or T cell receptor [TCR] sequencing. Phosphorylation of signal transducer and activator of transcription 5 [STAT5] was assessed in response to IL-2, IL-7, and in the presence of basiliximab, a monoclonal antibody directed against CD25. T-eff pro-inflammatory cytokine expression levels were assessed by reverse transcription quantitative polymerase chain reaction after IL-2 and/or TCR stimulation. Results: Presence of the minor T allele enhances CD25 expression, leading to increased STAT5 phosphorylation and pro-inflammatory cytokine transcript expression by T-eff in response to IL-2 stimulation in vitro. T-eff from TT individuals demonstrate a more activated gut homing phenotype. TCR sequencing analysis suggests that TT patients may have a reduced clonal capacity to mount an optimal regulatory T cell response. Conclusions: rs61839660 regulates the responsiveness of T cells to IL-2 signalling by modulating CD25 expression. As low-dose IL-2 is being trialled as a selective T-reg modulator in CD, these findings highlight the potential for adverse effects in patients with this genotype.

Automated summary

The study reveals that IBD patients carrying the rs61839660 SNP show an enhanced T-eff immune phenotype with increased pro-inflammatory cytokine expression in response to IL-2 stimulation, while individuals with the TT genotype may exhibit a more active gut homing phenotype and reduced T cell clonal capacity.