Pilot Study of Donor-Engrafted Clonal Hematopoiesis Evolution and Clinical Outcomes in Allogeneic Hematopoietic Cell Transplantation Recipients Using a National Registry

Abstract

Improved treatment options, such as reduced-intensity conditioning (RIC), enable older patients to receive potentially curative allogeneic hematopoietic cell transplantation (HCT). This progress has led to increased use of older HLA-matched sibling donors. An unintended potential risk associated with older donors is transplantation of donor cells with clonal hematopoiesis (CH) into patients. We aimed to determine the prevalence of CH in older HLA-matched sibling donors pretransplantation and to assess the clinical impact of donor-engrafted CH on HCT outcomes. This was an observational study using donor peripheral blood samples from the Center for International Blood and Marrow Transplant Research repository, linked with corresponding recipient outcomes. To explore engraftment efficiency and evolution of CH mutations following HCT, recipient follow-up samples available through the Bone Marrow Transplant Clinical Trials Network (Protocol 1202) were included. Older donors and patients (both ≥55 years) receiving first RIC HCT for myeloid malignancies were eligible. DNA from archived donor blood samples was used for targeted deep sequencing to identify CH. The associations between donor CH status and recipient outcomes, including acute graft-versus-host disease (aGVHD), chronic GVHD (cGVHD), overall survival, relapse, nonrelapse mortality, disease-free survival, composite GVHD-free and relapse-free survival, and cGVHD-free and relapse-free survival, were analyzed. A total of 299 donors were successfully sequenced to detect CH. At a variant allele frequency (VAF) ≥2%, there were 44 CH mutations in 13.7% (41 of 299) of HLA-matched sibling donors. CH mostly involved DNMT3A (n = 27; 61.4%) and TET2 (n= 9; 20.5%). Post-HCT samples from 13 recipients were also sequenced, of whom 7 had CH⁺ donors. All of the donor CH mutations (n = 7/7; 100%) were detected in recipients at day 56 or day 90 post-HCT. Overall, mutation VAFs remained relatively constant up to day 90 post-HCT (median change, .005; range, -.008 to .024). Doubling time analysis of recipient day 56 and day 90 data showed that donor-engrafted CH mutations initially expand then decrease to a stable VAF; germline mutations had longer doubling times than CH mutations. The cumulative incidence of grade II-IV aGVHD at day 100 was higher in HCT recipients with CH⁺ donors (37.5% versus 25.1%); however, the risk for aGVHD by donor CH status did not reach statistical significance (hazard ratio, 1.35; 95% confidence interval, .61 to 3.01; P = .47). There were no statistically significant differences in the cumulative incidence of cGVHD or any secondary outcomes by donor CH status. In subset analysis, the incidence of cGVHD was lower in recipients of grafts from DNMT3A CH⁺ donors versus donors without DNMT3A CH (34.4% versus 57%; P = .035). Donor cell leukemia was not reported in any donor-recipient pairs. CH in older HLA-matched sibling donors is relatively common and successfully engrafts and persists in recipients. In a homogenous population (myeloid malignancies, older donors and recipients, RICr, non-cyclophosphamide-containing GVHD prophylaxis), we did not detect a difference in cGVHD risk or other secondary outcomes by donor CH status. Subgroup analyses suggest potential differential effects by clinical characteristics and CH mutations. Larger prospective studies are needed to robustly determine which subsets of patients and CH mutations elicit meaningful impacts on clinical outcomes.

Keywords: Allogeneic transplantation; CIBMTR; Clonal evolution; Clonal hematopoiesis; Outcomes.

Figure 1.. Clonal hematopoiesis (CH) mutations in donors and recipient engraftment.

(A) CH mutations detected in matched sibling donors. Each column represents a donor and each row represents a CH mutation. Colors indicate different functional types of mutations. (B) Change in variant allele frequency (VAF) of CH mutations from donor to recipient over time. Data shown for pre-HCT donor samples and post-HCT recipient peripheral blood samples at day 56 (D56) and day 90 (D90). Colors indicate whether the mutation was in DNMT3A (blue), TET2 (red), or KDM6A (green); gray line is the median change in VAF of the mutations. (C) Doubling time of CH-like mutations in recipients. De novo mutations are CH-like mutations that were not observed in donor samples, but appeared in a single recipient post-HCT; the remaining bars are donor-engrafted CH mutations. Bars show medians and interquartile range; values are the medians.

Figure 2.. Multivariate analysis of recipient clinical outcomes by clonal hematopoiesis (CH) status of donors.

Referent group is recipients with CH− donors; therefore, hazard ratios (HR) less than one represent decreased risk with CH+ donors. The primary outcome of interest was chronic graft-versus-host disease (cGVHD). Each outcome was tested independently. Variables entered into the models included: recipient age, recipient gender, Karnofsky performance score, disease, disease status at transplant, donor age, donor-recipient gender match, donor-recipient CMV serostatus, GVHD prophylaxis, and year of transplant. CI: confidence interval; OS: overall survival; DFS: disease-free survival; NRM: non-relapse mortality; GRFS: graft-versus-host disease-free relapse-free survival; CRFS: cGVHD-free relapse-free survival.