Interaction Between Post-Transplant Diabetes Mellitus and Regulatory T Cell Phenotype
Authors: Engelhardt Brian G , Griffith Michelle L , Crowe James E , Savani Bipin N. , Kassim Adetola A. , Yoder Sandra M , Rock Michael T , Jagasia Shubhada M , Jagasia Madan H. 
Published: October 2019

Abstract
Abstract 3039

Background:
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.

Methods:
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+CD127lo. 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.

Results:
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).

Conclusion:
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.

Disclosures:
No relevant conflicts of interest to declare.