Teplizumab for new-onset T1D (Tzield)

The approach: protect what's left, after diagnosis

At a stage-3 type 1 diabetes diagnosis, some people still produce measurable insulin. PROTECT studied children and adolescents with a peak stimulated C-peptide of at least 0.2 pmol/mL at entry; C-peptide is used to measure their own insulin secretion. Teplizumab aims to preserve that remaining function. The trial did not demonstrate replacement or regeneration of beta cells.³

A July 2026 observational analysis of the DCCT data repository, as reported in its published abstract, included 1,441 participants followed for a mean 6.5 years. Of 180 diabetic ketoacidosis (DKA) events, 179 followed a stimulated C-peptide measurement of 0.2 nmol/L or below in the prior year. Higher C-peptide was associated with lower DKA risk. This was not a teplizumab trial and does not establish that preserving C-peptide with this drug prevents DKA.¹¹

Teplizumab is an Fc-receptor-nonbinding anti-CD3 monoclonal antibody. It binds CD3 on T cells. The US label says its mechanism may involve deactivation of beta-cell-reactive T cells and reports increases in regulatory T cells and exhausted CD8+ T cells in peripheral blood. The approved stage-3 regimen consists of two infusion courses, with important immune and infection risks described below.³²

This is the same drug already FDA-approved as Tzield to delay the onset of stage 3 disease in stage-2 (presymptomatic) people, which is covered under Preventing. This entry is the distinct new-onset / stage-3 use: giving it after diagnosis to preserve the cells a person still has.⁸

Clinical evidence

A 2002 randomized trial enrolled 24 people within six weeks of diagnosis: one 14-day course maintained or improved insulin production at one year in 9/12 treated participants versus 2/12 untreated controls.⁴ The expanded 42-person trial reported in 2005 found better C-peptide responses through two years after a single 12- or 14-day course, without continuous immunosuppressive medication; controls did not receive placebo.⁵ AbATE subsequently randomized 83 people to a two-course regimen or untreated control. Its reported intention-to-treat analysis included 77 (52 treated, 25 controls): mean two-year C-peptide changes were −0.28 versus −0.46 nmol/L (P=0.002). Its responder subgroup was defined post hoc. The reported 75% advantage referred to the adjusted C-peptide level at two years, not a 75% slower decline.⁷ Protégé randomized 516 people; among 513 who received treatment, the one-year composite of insulin use below 0.5 U/kg/day and HbA1c below 6.5% did not differ significantly between groups.⁶

The phase-3 PROTECT trial (NCT03875729) randomized 328 children and adolescents aged 8–17, diagnosed within six weeks and with peak stimulated C-peptide at least 0.2 pmol/mL, to teplizumab (217) or placebo (111). Two 12-day intravenous courses were planned 26 weeks apart; pandemic restrictions allowed a later second course.³ At 78 weeks, the adjusted between-group difference in C-peptide change was 0.13 pmol/mL (95% CI 0.09–0.17; P<0.001). A prespecified exploratory analysis estimated that 94.9% versus 79.2% retained peak C-peptide ≥0.2 pmol/mL; this exploratory comparison was not adjusted for multiplicity. The four key clinical secondary endpoints — insulin dose, HbA1c, time in range and clinically important hypoglycemia — did not differ significantly in the original intention-to-treat analysis.³

September 2026: a per-protocol analysis

A 10 September 2026 paper analyzes a pre-specified subset of 275 PROTECT participants (180 teplizumab, 95 placebo), selected before unblinding and excluding major protocol deviations or treatment adherence below 80%. At week 78, time in range favored teplizumab by 6.17 percentage points (95% CI 0.13–12.2; nominal P<0.05); insulin dose was lower by 0.17 U/kg/day. HbA1c and the diary-based hypoglycemia endpoint were not significantly different.¹

This is supportive analysis of selected participants from the same trial, not independent replication. Exclusions can change comparability, and nominal P values do not establish confirmatory clinical benefit. The original all-randomized-participant secondary results remain nonsignificant; the scores and confirmatory-trial requirement remain unchanged.

Durability, eligibility and safety

PROTECT measured slower C-peptide decline through 78 weeks after two courses; it did not establish permanent preservation or the benefit of additional courses.³ The US label covers stage 3, ages 8–17, with treatment started within eight weeks of diagnosis, at least one positive islet autoantibody and peak C-peptide of at least 0.2 pmol/mL. The approved regimen is two 12-day courses, normally six months apart.²

The US label carries a boxed warning for potentially life-threatening EBV/CMV reactivation, and contraindicates treatment in immunocompromised patients or those with active viral infection. Infection assessment, blood-count and liver monitoring are required, with viral-reactivation monitoring for at least two months after the last infusion. Other risks include cytokine-release syndrome, serious infection, lymphopenia and hypersensitivity.²

Maturity and availability

In June 2026 the FDA granted accelerated approval for teplizumab to delay the decline in the body's own insulin production in children aged 8–17 recently diagnosed with stage 3 T1D — the first disease-modifying therapy approved for the newly-diagnosed population.⁸⁹ Read the word accelerated carefully: this approval rests on preserved C-peptide, a surrogate endpoint, not on a demonstrated improvement in how people actually live day to day. Sanofi must run a confirmatory trial — BETA-PRESERVE (NCT07088068), now enrolling — to verify clinical benefit, and if it fails, the indication can be withdrawn.⁸¹²⁹ The drug is IV-delivered.⁸

The US stage-3 approval is distinct from the EU authorisation of Teizeild to delay stage 3 in people aged 8 and over who have stage-2 disease. Sanofi said in January 2026 that it would not progress a second EU application for recently diagnosed stage 3 at that time.¹⁴ That dated company statement does not establish current access in every country; the approved indication and local access need to be checked separately.

What's coming

The near-term question is whether the confirmatory BETA-PRESERVE trial verifies clinical benefit. Its registry lists a planned 723 participants aged 1–25 and recruitment in progress, a broader age range than the current US stage-3 label. Enrollment targets and trial eligibility are research plans, not an expansion of the approved indication.¹²²