A groundbreaking study titled “MRD and NK-Cell Chimerism Predict Transplant Outcomes in Allogeneic Hematopoietic Stem Cell Transplantation Recipients” has been recently published online in the American Journal of Hematology. This work was co-authored by Professors Xiaoxia Hu and Xiangqin Weng from Ruijin Hospital, Shanghai Jiao Tong University School of Medicine; Professor Yang Cao from Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology; and Professor Yanmin Zhao from the Bone Marrow Transplantation Center of the First Affiliated Hospital, Zhejiang University School of Medicine. The study is the first to reveal that NK-cell chimerism has significant prognostic value in patients who maintain minimal residual disease (MRD)-negative status following allogeneic hematopoietic stem cell transplantation (allo-HSCT). The findings suggest that combined monitoring of lineage-specific chimerism and MRD levels may offer a novel and effective strategy for assessing relapse risk after transplantation.Background
Allogeneic hematopoietic stem cell transplantation (allo-HSCT) represents a potentially curative option for various hematologic malignancies. However, disease relapse remains the primary cause of treatment failure. Donor-derived immune cells play a crucial role in eradicating residual malignant cells through the graft-versus-leukemia (GvL) effect. Although mixed chimerism (MC) may indicate reduced GvL efficacy and heightened relapse risk, prior studies have yielded inconsistent results, implying the limited predictive power of single-lineage chimerism assessment. MRD monitoring has become a vital tool for evaluating relapse risk, yet approximately half of patients lack disease-specific MRD markers, underscoring the need for complementary predictive approaches. Integrating MRD surveillance with lineage-specific donor chimerism assessment may improve relapse prediction accuracy and warrants further investigation.
Methods and Results
This retrospective study reviewed data from patients with acute leukemia or myelodysplastic syndromes (MDS) who underwent allo-HSCT at three transplant centers between June 2017 and August 2022. A total of 359 patients who achieved MRD-negative (nMRD) status one month after transplant were included. MRD was assessed using multiparameter flow cytometry (MFC) at months 1, 2, 3, 6, 9, 12, and every three months thereafter, with a positivity threshold set at 0.01% (pMRD). Donor chimerism was analyzed using multiplex PCR, with mixed chimerism (MC) defined as <95% and complete chimerism (CC) as ≥95%.
01. MRD Positivity and Transplant Outcomes
During the 24 months following transplantation, 64 patients (17.8%) exhibited at least one instance of MRD positivity, with a median time to event of six months (range: 1–21 months). Occurrence of pMRD was positively correlated with non-remission status at transplant (NR) and pre-transplant MRD positivity (P=0.004, P<0.001, respectively), and negatively correlated with chronic graft-versus-host disease (cGvHD) (P=0.035). Additionally, pMRD was significantly associated with poor-risk classification per 2022 ELN criteria (P=0.004) and high-risk cytogenetic abnormalities in patients with acute myeloid leukemia (AML) (P=0.011).
The study found that patients with positive MRD (pMRD) after transplant had significantly poorer outcomes compared to those who remained MRD-negative (nMRD). Specifically, the 2-year overall survival (OS) was 46.88% in the pMRD group versus 90.77% in the nMRD group (P<0.001), and the relapse-free survival (RFS) was 15.56% versus 95.11% (P<0.001), respectively. The 2-year cumulative relapse rate was also markedly higher in pMRD patients (84.44% vs. 4.71%; P<0.001). Multivariate Cox regression confirmed that pMRD significantly increased the risk of death (HR=8.76; 95% CI: 5.48–13.99; P<0.001).
Chimerism and Outcomes
Out of 356 patients, bone marrow mononuclear cells (BMNCs), NK cells, T cells, and B cells were collected at planned timepoints. Forty-five patients (12.64%) experienced at least one episode of BMNC mixed chimerism (MC), with a median first occurrence at 6 months post-transplant. Both NR status before transplantation and pMRD were associated with BMNC-MC. Compared with complete chimerism (BMNC-CC), patients with BMNC-MC had significantly worse 2-year OS (46.47% vs. 88.34%; P<0.001), lower RFS (75.86% vs. 90.81%; P<0.001), and higher relapse rates (86.21% vs. 8.96%; P<0.001).
Lineage-specific analysis revealed that NK-MC was a particularly strong negative prognostic marker. Patients with NK-MC had significantly lower 2-year OS (53.33% vs. 89.51%) and RFS (27.27% vs. 91.26%) compared to NK-CC, both P<0.001. Relapse incidence was also markedly higher (72.73% vs. 8.58%; P<0.001). Similar trends were observed in patients with T-MC and B-MC. Multivariate analysis indicated that multi-lineage MC was an independent adverse prognostic factor.
Predictive Value of Lineage-Specific Chimerism
Cox regression showed that NK-MC (HR=3.20; 95% CI: 1.02–10.07; P=0.046), T-MC (HR=2.35; 95% CI: 1.22–4.52; P=0.01), and BMNC-MC (HR=2.32; 95% CI: 1.14–4.72; P=0.020) were significantly associated with reduced RFS. Importantly, even among patients who remained MRD-negative, both BMNC-MC (HR=10.42; 95% CI: 2.97–37.00; P=0.001) and NK-MC (HR=15.54; 95% CI: 2.58–93.50; P=0.003) continued to carry significant prognostic weight.
For event-free survival (EFS), lineage-specific MC also had negative implications. In the pMRD group, NK-MC (HR=3.74; 95% CI: 1.45–9.66; P=0.006), T-MC (HR=2.54; 95% CI: 1.45–4.45; P=0.001), and B-MC (HR=3.02; 95% CI: 1.18–7.74; P=0.021) were all associated with worse EFS. Among nMRD patients, only NK-MC retained significant prognostic relevance for EFS (HR=4.98; 95% CI: 1.10–22.51; P=0.037).
Landmark analysis showed that the predictive value of BMNC-MC and lineage-specific MC increased over time post-transplant, with NK-MC and BMNC-MC emerging as the most powerful indicators. Harrell’s C-index analysis confirmed that their predictive ability significantly improved from month 1 to month 15 after transplant. At month 15, the combined C-index for NK-MC and BMNC-MC reached 0.8177, suggesting a synergistic effect in relapse prediction.
Ruijin Hospital, Shanghai Jiao Tong University School of Medicine
- Chief Physician, PhD, Doctoral Supervisor, Translational Medicine Center, Ruijin Hospital
- Specializes in basic and clinical research on hematopoietic stem cell transplantation
- Member, 6th Hematologic Oncology Committee, Chinese Anti-Cancer Association
- Member, Hematological Physiology Committee, Chinese Society for Physiology
- Recognized as Outstanding Young Medical Talent of Shanghai
- Named Excellent Academic Leader in the Shanghai Health System
- Honored as Outstanding Young Talent in the Shanghai Health System
- First or corresponding author of over 40 publications in journals such as Blood, JCI, Leukemia, BCJ, JCI Insight, and AJH
- Second contributor to a project awarded the First Prize of Shanghai Science and Technology Progress Award
Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology
- Associate Professor and Chief Physician, Department of Hematology, Tongji Hospital
- Member, Leukemia and Lymphoma Group, Hematology Branch, Chinese Medical Association
- Secretary, T-cell Transplantation and Cellular Immunotherapy Group, Hematology Committee, Chinese Anti-Cancer Association
- Deputy Chair, Youth Committee of Hematologic Oncology, Hubei Anti-Cancer Association
- Secretary, T-cell Transplantation and Cellular Immunotherapy Group, Hubei Anti-Cancer Association
- Specializes in basic and clinical research on hematopoietic stem cell transplantation and cellular immunotherapy
- Principal investigator of projects funded by the National Natural Science Foundation of China (NSFC), including general and youth programs, as well as the Ministry of Education’s fund for new faculty in key disciplines
- Participant in multiple national research programs, including the 973 Program, 863 Program, and key NSFC projects
- Published over 20 research articles in the field, including numerous first-author and corresponding-author papers in international SCI journals such as The Journal of Experimental Medicine (JEM)
The First Affiliated Hospital, Zhejiang University School of Medicine
- MD, Chief Physician, Doctoral Supervisor, and Distinguished Research Fellow
- Deputy Director, Hematology and Bone Marrow Transplantation Center
- Youth Member, Hematologic Oncology Committee, Chinese Anti-Cancer Association
- Member, Hematopoietic Stem Cell Transplantation and Cellular Therapy Committee, Chinese Association of Medical Education
- Deputy Chair, Youth Committee of the Hematology Branch, Zhejiang Medical Association
- Outstanding Young Scholar, Zhejiang Immunological Society
- Secretary, Clinical Trial Hematology Group, The First Affiliated Hospital of Zhejiang University
- Recognized Talent under Zhejiang Province’s “551 Talent Program” for high-level healthcare professionals
- Principal investigator of one Youth Project and three General Projects funded by the National Natural Science Foundation of China (NSFC); key contributor to China’s National Key R&D Program
- Editorial board member of Cell Transplantation
- Published over 40 SCI papers as first or corresponding author in Journal of Hematology & Oncology, JAMA Network Open, and American Journal of Hematology
- Frequent invited speaker at international conferences such as ASH, EHA, EBMT, and APBMT
- Recipient of Zhejiang Provincial Science and Technology Progress First Prize (1st Class) and National Science and Technology Progress Award (2nd Class) as a core contributor
