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Phase 2Active, not recruitingNCT06111586

FABULINUS: Frexalimab CD40L blockade in recent-onset T1D

Sanofi phase-2b trial of frexalimab, a CD40L antagonist, to preserve the body's own insulin production in children, adolescents and adults with newly diagnosed T1D. Enrolment is now complete at 197 participants and the trial is closed to new joiners; the primary C-peptide readout is expected around the estimated primary completion date of April 2027.

Primary endpoints

  • Part B (ages 12-21) — change from baseline in C-peptide (area under the curve during a 2-hour mixed-meal tolerance test) at week 52
  • Part C (ages 6-11) — change from baseline in C-peptide (area under the curve during a 2-hour mixed-meal tolerance test) at week 26

Results so far

No efficacy results posted or published. Enrolment is complete at 197 participants across 79 sites. Estimated primary completion 28 April 2027; estimated study completion 29 October 2030.

The full picture

What is being tested and why it matters

In type 1 diabetes the immune system destroys the insulin-making beta cells. Frexalimab is an antibody that blocks CD40L, one of the "co-stimulation" signals immune cells use to recruit each other into that attack. FABULINUS is the lead test of this idea in newly diagnosed T1D, and it is worth tracking precisely because it is not another anti-CD3, JAK inhibitor or antigen-specific vaccine — it targets a different point in the immune cascade.12

The question is whether starting frexalimab soon after diagnosis lets people hold on to more of their own insulin production. Even a modest amount of remaining beta-cell function makes glucose steadier and lowers the risk of severe lows.2

Who is in it

The trial enrols people aged 6 to 35 who were recently diagnosed with type 1 diabetes and are on insulin, in three parts: Part A (adults), Part B (ages 12-21) and Part C (ages 6-11).1 Sites span the United States, Canada, the United Kingdom and the EU — 79 in total.1

Note that the published trial-design paper predates the paediatric Part C cohort, so the registry, not the paper, is the current source for who can take part.12

Status: closed to enrolment, waiting for the readout

This is no longer a joinable trial. As of the registry update on 29 June 2026, FABULINUS is active, not recruiting: enrolment is complete at 197 participants.1 If you were looking for a trial to join, this one is full.

What it now offers is a date. The main measure is C-peptide — the body's own insulin output — during a standardised two-hour mixed-meal test: at week 52 in the older cohort (Part B) and at week 26 in the younger Part C cohort.1 Estimated primary completion is 28 April 2027, with estimated study completion in October 2030.1 Both are estimates on the registry, not fixed dates.

What we do and don't know

No efficacy results have been posted to the registry or published.1 Nothing is yet known about whether frexalimab preserves beta-cell function in type 1 diabetes — full enrolment is a milestone in the trial's progress, not evidence that the drug works. The 2027 readout is the first point at which that question gets an answer.

References

  1. ClinicalTrials.gov. FABULINUS: Frexalimab in Preservation of Endogenous Insulin Secretion in Adults, Adolescents and Children With Recently Diagnosed Type 1 Diabetes (NCT06111586). Sanofi. Registry record updated 29 June 2026. https://clinicaltrials.gov/study/NCT06111586 ↩ ↩2 ↩3 ↩4 ↩5 ↩6 ↩7 ↩8

  2. A Phase 2 Trial of Frexalimab, a CD40L Antagonist, in Recent-Onset Type 1 Diabetes. Diabetes, Obesity and Metabolism (2026). https://doi.org/10.1111/dom.70785 ↩ ↩2 ↩3