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In View: Research Highlights

Research Highlights

Luo, Xunrong PhD, MD1

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doi: 10.1097/TP.0000000000003655
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Dipeptidyl Peptidase 4 Inhibition for Prophylaxis of Acute Graft-versus-host Disease

Farag SS, Zaid MA, Schwartz JE, et al. N Engl J Med. 2021;384(1):11–19.

Dipeptidyl peptidase-4 (DPP4), also known as CD26, is a costimulatory molecule expressed on T cells. In addition to its signal transduction and costimulation function, CD26 also possesses enzymatic activity and cleaves a broad range of substrates. Its best-known substrate is the incretin GLP-1. Consequently, chemical inhibition of DPP4 results in a prolongation of the half-life of incretin and is used as an effective treatment for diabetes. However, much less is known about the relationship between its enzymatic and costimulatory activity, namely, and the potential to interfere with costimulation. It has been previously shown that treatment with a humanized monoclonal anti-CD26 results in prevention of acute graft-versus-host disease (GVHD).1 However, whether inhibition of its enzymatic activity may also prevent GVHD has been unclear.

Farag et al2 conducted a 2-stage, phase 2 clinical trial to determine whether sitagliptin, a DPP4-specific enzymatic inhibitor, in addition to conventional tacrolimus and sirolimus, will reduce the incidence of GVHD after allogeneic stem cell transplantation.

A total of 36 patients were enrolled for matched-related or -unrelated stem cell transplants, treating hematological malignancies. The study evaluated the efficacy of adding sitagliptin (600 mg orally every 12 h) from day −1 to day +14 in mitigating grade II to IV acute GVHD during the first 100 days following stem cell transplants. A “2-stage” design was chosen to ensure that the stopping rule was not met after stage 1 during which 23 patients have been enrolled and evaluated. Following completion of stage 1, an additional 13 patients were enrolled for a total of 36 patients in this single-arm study. The authors found that the addition of sitagliptin did not affect stem cell engraftment but significantly reduced the incidence of grade II to IV acute GVHD. In detail, only 2 of 36 patients experienced acute GVHD by day 100. Encouragingly, the reduction of GVHD did not lead to a reduction of graft-versus-leukemia effects, as disease relapse rates were comparable to those reported in studies of established GVHD prophylaxis regimens. Although grade III to IV adverse events were observed within 30 days after transplantation, none were attributed to sitagliptin. Of additional relevance, no episodes of hypoglycemia were noted.

Mechanistically, the authors demonstrated that sitagliptin treatment indeed led to a systemic inhibition of DPP-4 activity. In addition, low plasma levels of cytokines and acute GVHD biomarkers, including TNF-α, Mig, IL-1β, IL-2, IL-6, IL-8, IL-10, IFN-γ, ST2, Reg3α, IL-2Rα, and TNFR-1, were detected.

This study reveals an intriguing potential of the oral hypoglycemic agent sitagliptin to be repurposed for T-cell inhibition with relevance for organ transplantation. As a next step, it will be interesting to see if this agent is also efficacious in allogeneic organ and/or cell transplantation, preventing rejection or GVHD. Such studies may also help to identify treatment dose and duration in different transplant scenarios. Whether or not the addition of sitagliptin would allow minimization of other immunosuppression such as calcineurin inhibitors should also been examined. Furthermore, the potential added benefit of sitagliptin to other costimulation blockade regimens either currently in clinical use, such as CTLA4-Ig, or in development, such as anti-CD40, should be determined. On the mechanistic side, whether the enzymatic activity and the costimulatory activity have redundant, additive or synergistic effects on T-cell activation appears of interest. With the availability of the necessary tools, namely DPP4 inhibitors, anti-CD26, and CD26−/− mice, these question can be readily modeled in vitro and/or in animal models. Answers would provide us with the necessary information to best target CD26 for inhibiting alloimmunity in transplantation.

In summary, the study by Farag et al provides clinical evidence of the utility of sitagliptin in suppressing alloimmunity in stem cell transplantation. A better understanding of the many facets of CD26 in T-cell activation may provide new opportunities for targeting this pathway to broadly benefit transplant graft survival.

A Sequential Two-step Cell-based Assay Predicts Immunosuppression-related Adverse Events

Bouchard-Boivin F, Desy O, Beland S, et al. J Immunol. 2020;205(12):3291–3299.

It is generally accepted that life-long immunosuppression is needed for organ transplant recipients. However, the minimal degree of immunosuppression will prevent rejection while permitting immune competency, thus avoiding opportunistic and/or recurrent infections and malignancies has been extremely difficult to define. This judgment is therefore often left to empiricism by transplant physicians, which frequently leads to overimmunosuppression and underimmunosuppression. Establishing a reliable and practical biomarker has thus long been a quest in the field of transplantation.

Bouchard-Boivin et al1 validated such a biomarker for measuring the immune reserve. They took a sequential 2-step approach using a cell-based assay to identify overimmunosuppression (OIS), with the first step ensuring sensitivity and the second step enhancing specificity. OIS was defined as the occurrence of at least 1 of the following: an opportunistic infection, recurring infection (≥3 episodes) in the absence of a predisposing factor, or de novo cancer. Specifically, in the first step, the authors quantified TNF-α+ cells among CD14+16+ intermediate monocytes following incubation of patients’ peripheral blood mononuclear cells (PBMCs) with Epstein-Barr virus (EBV) peptides. This step identified OIS by a cutoff of %TNF-α+ monocytes (set at <73%) with a sensitivity of 83%–90%.

In a second step, a subset of early mature B cells (abbreviated as “eBm5,” identified as CD38+IgD B cells) among PBMCs has been identified following their incubation with the same EBV peptides. This step enhances the specificity of identifying OIS to 88% by a cutoff of eBm5 set at <6000 cells/ml. In the adjusted model, when patients were classified as positive by this 2-step cell-based assay, the hazard ratio of OIS was 12.2 in comparison to those classified as negative. Although validation of the first step was previously published,2 the current study sought to validate the second step. To do so, the authors took PBMCs of a cohort of 87 kidney transplant recipients, of which 40 met the cutoff of step 1 and entered them into a step 2 analysis. Twenty of 40 patients were randomly assigned to the training set to construct ROC curves that identified potential thresholds with their respective sensitivity and specificity. These thresholds were then validated in 12 patients with OIS and 8 control patients to determine the optimized threshold (<6000 cells/ml eBm5) with the best specificity of 88%. Last, the eBm5 cell counts showed a good diagnostic accuracy across tertiles of age and time posttransplant.

This study demonstrates that the 2-step cell-based assay using PBMCs in response to EBV peptide stimulation provides good sensitivity and specificity in predicting OIS in a cohort of kidney transplant recipients. The authors demonstrated a tight interassay coefficient of variability. The assay itself can be relatively easily standardized. An interesting confounder in this study was a statistically significantly higher dose of prednisone and higher level of tacrolimus in patients with OIS. Thus, whether this 2-step cell-based assay contributes independent value in predicting OIS needs to be determined. Moreover, the utility of this assay in predicting OIS and therefore altering the course of immunosuppression should be further examined in prospective large cohort studies.


1. Hatano R, Ohnuma K, Yamamoto J, et al. Prevention of acute graft-versus-host disease by humanized anti-CD26 monoclonal antibody. Br J Haematol. 2013; 162:263–277.
2. Farag SS, Abu Zaid M, Schwartz JE, et al. Dipeptidyl peptidase 4 inhibition for prophylaxis of acute graft-versus-host disease. N Engl J Med. 2021; 384:11–19.


1. Bouchard-Boivin F, Désy O, Béland S, et al. A sequential two-step cell-based assay predicts immunosuppression-related adverse events. J Immunol. 2020; 205:3291–3299.
2. Vallin P, Désy O, Béland S, et al. Impaired secretion of TNF-α by monocytes stimulated with EBV peptides associates with infectious complications after kidney transplantation. Transplantation. 2018; 102:1005–1013.
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