Can We Predict Who Benefits? Baseline Insulin Secretion as a Gatekeeper for Abatacept Efficacy in Stage 1 T1D

Article Highlights

Biomarker Discovery

Baseline insulin secretion, quantified as phi-total using the Oral Minimal Model (OMM), serves as a critical biomarker for identifying individuals with Stage 1 Type 1 Diabetes (T1D) who are most likely to respond to costimulation inhibition.

Clinical Efficacy

In the high-secretor subgroup, abatacept therapy resulted in a 15.8-month delay in progression to Stage 2 or 3 T1D compared to placebo, with a 54% reduction in the hazard of progression (HR 0.46).

Precision Immunotherapy

This study represents the first evidence that an immune intervention can significantly delay disease progression in Stage 1 T1D, emphasizing the importance of metabolic reserve in treatment response.

Introduction: The Quest for Prevention in Type 1 Diabetes

The management of Type 1 Diabetes (T1D) has historically focused on exogenous insulin replacement and the mitigation of long-term complications. However, the paradigm is shifting toward prevention and disease modification. Type 1 Diabetes is now recognized as a staged disease: Stage 1 is defined by the presence of two or more islet autoantibodies with normoglycemia; Stage 2 involves continued autoimmunity with dysglycemia; and Stage 3 represents clinical diagnosis. Intervening at Stage 1 offers the greatest potential to preserve beta-cell mass before significant metabolic derangement occurs.

Abatacept, a cytotoxic T lymphocyte–associated protein 4 immunoglobulin (CTLA-4 Ig), works by inhibiting T-cell costimulation. While previously evaluated in Stage 1 T1D, initial findings suggested only modest preservation of C-peptide without meeting the primary endpoint. This recent analysis re-examines the data through the lens of baseline metabolic function, suggesting that the initial physiological state of the patient determines the success of the immunotherapy.

Study Design and Methodology: The Oral Minimal Model

The study included 203 participants, with 96 randomized to receive abatacept and 107 to placebo. To move beyond traditional area under the curve (AUC) C-peptide measurements, researchers adopted the Oral Minimal Model (OMM). This sophisticated modeling technique allows for the computation of phi-total (total insulin secretion), a metric that provides a more granular assessment of beta-cell function during oral glucose tolerance tests (OGTTs).

Participants were monitored over 48 months, with OGTTs conducted every 6 months. To test the hypothesis that baseline beta-cell function influences treatment response, the cohort was stratified into high-secretor and low-secretor groups based on whether their baseline phi-total was above or below the 33rd percentile. This stratification allowed researchers to isolate the treatment effect in populations with varying degrees of metabolic reserve.

Key Findings: Stratification Reveals Clinical Benefit

The results of the analysis provide a stark contrast between the two subgroups. Among the 203 participants, 39% of the abatacept group and 47% of the placebo group progressed to Stage 2 or 3 within 96 months. However, the global analysis masked the significant benefits seen in the high-secretor cohort.

High-Secretor Response

Participants in the high-secretor group treated with abatacept gained a remarkable 15.8 progression-free months (95% CI 4.85, 26.68; P = 0.005). The hazard ratio (HR) for progression in this group was 0.46 (95% CI 0.25, 0.84; P = 0.012), representing a 54% reduction in risk compared to placebo. The interaction between treatment effect and secretor status was statistically significant (Interaction HR 2.92; P = 0.015), confirming that baseline insulin secretion is a robust predictor of response.

Metabolic Indices and Risk Scores

Beyond phi-total, other metabolic markers supported the benefit of abatacept in the early stages of treatment. The Index60 and the Diabetes Prevention Trial-Risk Score (DPTRS) showed stable risk profiles for the abatacept group during the first 24 months compared to the placebo group. Specifically, DPTRS remained stable in the abatacept arm while increasing in the placebo group during the first 6 months (P = 0.022), suggesting an immediate stabilizing effect on disease risk that eventually wanes after treatment cessation.

Mechanistic Insights: Why Baseline Secretion Matters

The differential response based on baseline insulin secretion suggests a “window of opportunity” for T-cell costimulation inhibition. In high secretors, the immune system may still be in a state where blocking the CD28-CD80/86 pathway can effectively dampen the autoimmune assault on a relatively robust beta-cell population. Conversely, in low secretors, the autoimmune process may have already progressed to a point where T-cell inhibition alone is insufficient to halt the decline, or the remaining beta-cell mass is too small to demonstrate clinical preservation.

This finding aligns with the broader concept of metabolic reserve. In the early stages of T1D, the pancreas can compensate for immune-mediated loss. Abatacept appears to protect this compensatory capacity, but only if the intervention occurs before the beta-cell function drops below a critical threshold.

Expert Commentary: Shifting the Paradigm toward Precision Immunotherapy

For clinicians and researchers, these findings are transformative. They suggest that future clinical trials for T1D preventatives should not treat Stage 1 patients as a monolithic group. Instead, metabolic staging via the OMM or similar metrics should be used to enrich trials for potential responders.

While the trial showed that the benefits of a 12-month course of abatacept eventually diminish after treatment stops, the 16-month delay in progression is clinically significant. It suggests that extended or maintenance dosing of abatacept might lead to even more durable protection. Furthermore, combining abatacept with other therapies—such as B-cell depleting agents or IL-2 therapies—might be necessary for those identified as low secretors at baseline.

One limitation noted is the post-hoc nature of the secretor-status analysis. While the sensitivity analysis validated the 33rd percentile threshold, prospective validation in a new cohort will be essential to solidify phi-total as a standard-of-care biomarker.

Conclusion: A Milestone for Stage 1 Intervention

This study provides the first clear evidence that an immune intervention can delay the progression of Stage 1 Type 1 Diabetes. By identifying baseline insulin secretion as a predictor of success, the research paves the way for a precision medicine approach to T1D prevention. For the first time, we have a metric to identify which at-risk individuals are most likely to benefit from T-cell costimulation blockade, moving us one step closer to a future where T1D can be managed or delayed before it ever reaches the stage of clinical symptoms.

References

Galderisi A, Carr ALJ, Taylor P, et al. Baseline Insulin Secretion Determines Response to Abatacept in Stage 1 Type 1 Diabetes. Diabetes. 2026;75(2):229-240. doi:10.2337/db25-0801.