Relapse after allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains one of the central challenges in the treatment of acute leukemia. Minimal residual disease (MRD) positivity serves as an important early warning signal for relapse, and identifying effective interventions during this critical window has become a major focus of clinical research. In recent years, PD-1 inhibitors have shown potential in eliminating residual leukemic cells. However, their efficacy and safety in the post-transplant setting—particularly their impact on graft-versus-host disease (GVHD)—remain unclear.
At the 52nd EBMT Annual Meeting held in Madrid, Spain, from March 22 to 25, 2026, a study conducted by the team of Prof. Xingyu Cao from Lu Daopei Hospital was presented, systematically evaluating the role of PD-1 inhibitors in patients with MRD-positive acute leukemia after transplantation. This article features a detailed overview of the study by first author Dr. Bixin Li.
Study Background
Allogeneic HSCT is a potentially curative treatment for acute leukemia, yet relapse occurs in approximately 20%–40% of patients and remains the leading cause of transplant failure.
MRD is a key early biomarker of hematologic relapse. Preemptive intervention based on MRD status may reduce relapse risk and improve survival outcomes. Although PD-1 inhibitors have the potential to eradicate residual disease, they may also trigger or exacerbate GVHD, making their use in the post-transplant setting controversial. Factors influencing their efficacy remain unclear.
Methods
This retrospective study included patients with MRD-positive acute leukemia after allo-HSCT who received PD-1 monoclonal antibody therapy between January 17, 2020, and December 1, 2025, at Beijing Lu Daopei Hospital and Hebei Yanda Lu Daopei Hospital.
Patients with morphological relapse or extramedullary relapse were excluded. MRD status was assessed using polymerase chain reaction (PCR) and multiparameter flow cytometry.
All patients had previously received MRD-directed interventions without success, including tapering of immunosuppressive agents and/or donor lymphocyte infusion (DLI).
Among the cohort:
- 7 patients received camrelizumab (5 at 200 mg, 1 at 93 mg, 1 at 35 mg; 1 patient completed 2 cycles)
- 13 patients received tislelizumab (12 at 100 mg, 1 at 200 mg; 2 patients completed 1 and 3 cycles, respectively)
- 1 patient received a combination of both antibodies (each at 100 mg)
Follow-up was conducted until December 1, 2025.
Results
The median age was 13 years (range, 6–41), including 12 males and 9 females. Diagnoses included AML (n = 16), ALL (n = 4), and mixed phenotype acute leukemia (n = 1).
Conditioning regimens included busulfan-based (n = 10), total body irradiation–based (n = 9), and melphalan-based (n = 2). Five patients had undergone a second transplant, and three had undergone a third transplant.
Before PD-1 inhibitor therapy, 28.5% of patients had a history of GVHD, and 33.3% were receiving immunosuppressive therapy. Baseline peripheral blood T-cell PD-1 expression was assessed in 9 patients, with a median expression level of 48.2% (range, 14.15%–89.64%).
After PD-1 inhibitor treatment, one patient died of viral infection and was excluded from efficacy analysis. Among the remaining 20 patients, response was evaluated at a median of 20.5 days (range, 11–42 days).
The overall response rate (ORR) was 70% (14/20), including:
- MRD negativity in 50% (10/20)
- MRD reduction in 20% (4/20)
The median time to MRD negativity was 31 days (range, 11–68 days), and the median duration of sustained MRD negativity was 140 days (range, 22–248 days). Six patients (30%) showed no response.
In subgroup analysis:
- The tislelizumab group (n = 13) achieved an ORR of 76.9%, MRD negativity rate of 61.5%, and a median duration of sustained MRD negativity of 140 days (range, 73–248 days)
- The camrelizumab group (n = 6) had an ORR of 50%, MRD negativity rate of 16.7%, and a duration of MRD negativity of 22 days
- The single patient receiving combination therapy achieved MRD negativity with a duration of 215 days
Seventeen patients experienced treatment-related adverse events, most commonly acute GVHD (76.4%) and viral infections (19%). One patient developed veno-occlusive disease (VOD).
Univariate analysis showed that the use of tislelizumab was associated with improved MRD negativity (P = 0.092). In contrast, pre-existing GVHD (P = 0.016) and ongoing immunosuppressive therapy (P = 0.035) were independent adverse factors affecting MRD clearance.
Conclusion
In patients with MRD-positive acute leukemia after allo-HSCT, preemptive treatment with PD-1 inhibitors can achieve a relatively high response rate.
However, patients with pre-existing GVHD or those receiving immunosuppressive therapy before PD-1 inhibitor initiation have significantly lower rates of MRD clearance.
Expert Profiles
Xingyu Cao, MD, PhD Lu Daopei Hospital
Prof. Cao is a chief physician and transplant specialist, serving as Director (vice president level) of the Bone Marrow Transplantation Department at Beijing Lu Daopei Hospital and Hebei Yanda Lu Daopei Hospital. She holds multiple academic positions in hematology and transplantation societies in China and has extensive experience in allogeneic stem cell transplantation.
Bixin Li, MD Lu Daopei Hospital
Dr. Li is a physician in the Department of Hematopoietic Stem Cell Transplantation at Hebei Yanda Lu Daopei Hospital. She graduated from China Medical University and specializes in the clinical management of hematologic diseases.
