Low-dose IL-2 administration and amyotrophic lateral sclerosis (ALS): understanding the transcriptional response after treatment

Background: Amyotrophic lateral sclerosis (ALS) is a fatal, neurodegenerative disease whose pathogenesis involves neuroinflammation. Regulatory T cells (Tregs) normally suppress excessive inflammation preventing the onset of autoimmune disorders. However, in ALS, Tregs are dramatically and progressively decreased, with lower levels associated with shorter survival. Low-doses of interleukin-2 (ld-IL-2) promote Treg expansion and restore the physiological immune balance. Additionally, IL-2 has been reported to penetrate the blood-brain barrier and exert protective effects on neurons and glia. Aims: 1) To evaluate ALS peripheral blood transcriptional changes associated with ld-IL-2 in patients participating in the IMODALS trial. 2) To assess effects of IL-2 on patient-derived astrocytes. Methods: 36 patients in the IMODALS trial were randomly assigned to three treatment arms: 1MIU-IL-2, 2MIU-IL-2 or placebo. At four time-points, blood was collected and gene expression profiles were generated. Patient-derived-astrocytes were differentiated from ALS or healthy volunteer fibroblasts, treated in vitro with IL-2 and transcriptionally profiled. IL-2 was also assessed in co-cultures of motor neurons (MN) and patient-derived-astrocytes. Findings: Gene expression analyses revealed longitudinal changes throughout the IMODALS trial. Evidence of a broad immune suppression was provided after the first treatment cycle whilst activation of immune suppressive pathways reached a peak after the third cycle. A time-dependent and dose-dependent activation of Treg markers was identified which suggested a cumulative effect of ld-IL-2. However, inter-individual differences were found amongst patients, who were classified into high, moderate and low-responders. A predictive biomarker analysis identified two genes, whose baseline expression was able to predict patient responsiveness to ld-IL-2. Patient-derived-astrocytes were treated with IL-2 and RNA sequencing revealed evidence of potentially protective changes including activation of axonogenesis and a reduction in oxidative stress. These findings suggest a reduction in the ALS astrocyte-mediated MN toxicity, which is in keeping with preliminary data showing an increase in MN viability when co-cultured with IL-2-treated astrocytes.