Low-dose IL-2 does not preserve β-cells in new-onset type 1 diabetes

Design

Phase 2b, multicentre, double-blind, randomised, placebo-controlled (DIABIL-2)

Population

141 people aged 6–35 with type 1 diabetes of under 3 months

Primary outcome

Change in mixed-meal C-peptide AUC (0–120 min) at 12 months

Effect

Geometric mean ratio 1.06 (95% CI 0.56–2.01), p=0.85 — no difference

DIABIL-2, a phase 2b trial, randomised 141 people aged 6–35 with type 1 diabetes of under three months to one of two low-dose interleukin-2 regimens or placebo, following C-peptide for 12 months. The rationale was that IL-2 expands regulatory T cells, which are deficient in type 1 diabetes.

It missed. C-peptide area under the curve at 12 months did not differ between IL-2 and placebo (geometric mean ratio 1.06, 95% CI 0.56–2.01; p=0.85), even though regulatory T cells expanded clearly, confirming the drug reached its target. It was well tolerated across children and adults.

Target engagement without clinical benefit is a useful negative: it suggests the autoimmune attack at diagnosis is too intense for IL-2 alone and points toward earlier or combination use. Nothing here supports IL-2 monotherapy in clinic.

• Low-dose IL-2 did not preserve C-peptide at 12 months in newly diagnosed type 1 diabetes.
• Regulatory T cells expanded as expected, so the failure is of effect, not of target engagement.
• The drug was well tolerated in both children and adults.
• This closes IL-2 monotherapy at diagnosis; combination or earlier-stage use is the open question.

Why it matters

A clean negative trial redirects type 1 immunotherapy away from IL-2 monotherapy at diagnosis.

Don't overread it

Robust regulatory T-cell expansion is target engagement, not clinical benefit — the two came apart here.

The statistics, in plain English

A ratio of 1.0 means no difference, and the confidence interval (0.56–2.01) spans it widely, so the trial effectively rules in no meaningful benefit rather than leaving it uncertain.

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