Interaction Between Post-Transplant Diabetes Mellitus and Regulatory T Cell Phenotype

Post-transplant diabetes mellitus (PTDM) is a common complication that is associated with numerous medical conditions affecting the long-term survival of patients undergoing allogeneic hematopoietic cell transplantation (HCT). Immune dysregulation manifested by chronic low-grade inflammation and decreased frequencies of regulatory T cells (Tregs) in visceral adipose tissue are key determinants in the transition from insulin resistance to overt diabetes mellitus. We tested the hypothesis that new-onset PTDM is associated with measurable changes in cellular immunity and Treg subsets during HCT.

Patients aged ≥ 18 years undergoing HCT who were simultaneously enrolled in two independent clinical trials examining either PTDM or tissue-specific Tregs were included in this analysis (N= 36). Fasting glucose levels were assessed weekly until day +100. New-onset PTDM was defined as a fasting glucose ≥ 126 mg/dL or random glucose ≥ 200 mg/dL after HCT in an individual without history of diabetes mellitus. Tregs were identified using polychromatic flow cytometry by the following phenotype: CD45RO⁺CD25⁺Foxp3⁺CD127^lo. The frequency of circulating Tregs was quantified within the CD4⁺ T-lymphocyte population at the time of neutrophil engraftment. CLA⁺ Tregs (considered skin-homing) and α₄ β₇⁺ Tregs (considered gut-homing) were enumerated as their respective subpopulations within the total Treg population.

New-onset PTDM occurred in 24 (66.7%) patients at a median of 24.5 days post-HCT (range, 7–100 days). PTDM was diagnosed prior to grade II-IV acute graft-versus-host disease (GVHD) (N= 28) or the start of systemic corticosteroids (N= 28) in 12 (50%) and 14 (58%) patients, respectively. Clinical characteristics, including acute GVHD or treatment with corticosteroids, were not associated with the development of PTDM. Median follow-up was 2.9 years (range, 0.5–4.0 years) for surviving patients (N= 22). Overall survival and non-relapse mortality at 2 years was 45.8% and 29.2% among patients with PTDM and 100% and 0% for those without diabetes (P= 0.052, P= 0.017). PTDM was not associated with relapse. Treg analysis was performed at a median of 19 days (range, 12–27 days) post-HCT and prior to the diagnosis of PTDM in 9 (37.5%) patients. The percentage of circulating CLA⁺ Tregs at engraftment was significantly lower in patients with PTDM (median, 1.53% vs. 3.99%; P= 0.002). Conversely, PTDM was associated with increased frequencies of α₄ β₇⁺ Tregs [median, 17.9% vs. 10.7%; P= 0.048 (PTDM vs. no PTDM)]. The skewing of the Treg phenotype was demonstrated further by the ratio of α₄ β₇⁺ Tregs to CLA⁺ Tregs, which was significantly higher in patients with PTDM (median, 8.93% vs. 1.85%; P= 0.004). The cumulative incidence of day+100 PTDM was 75.0% in individuals with ratios of α₄ β₇⁺ Tregs to CLA⁺ Tregs greater than or equal to the cohort median of 6.32, compared with 44.4% in those with a ratio less than the median (P= 0.005). The analyses were repeated using only patients who had grade II-IV acute GVHD treated with systemic corticosteroids (N= 26). Similar results were found, with decreased CLA⁺ Tregs (P= 0.013) and increased α₄ β₇⁺ Tregs (P= 0.048) among HCT recipients with PTDM. There was no significant association between PTDM and the percentage of CD4⁺ memory T cells, CD4⁺CLA⁺ T cells, CD4⁺ α₄ β₇⁺ T cells, or total Tregs (not accounting for homing properties). Using logistic regression (adjusted for conditioning, donor type, and corticosteroids), patients with PTDM continued to demonstrate an elevated ratio of α₄ β₇⁺ Tregs to CLA⁺ Tregs (odds ratio, 10.6; 95%CI, 1.55–71.9; P= 0.016).

The distribution of Tregs with specific tissue-homing properties was markedly altered in patients who developed PTDM. These data suggest that PTDM and insulin resistance are associated with cellular immune responses post-HCT including Treg subset frequencies and immune regulation. PTDM and the related metabolic syndrome could represent an important new therapeutic target to modulate alloreactivity and clinical outcomes following HCT.

No relevant conflicts of interest to declare.