Role of Donor Clonal Hematopoiesis in Allogeneic Hematopoietic Stem-Cell Transplantation

Purpose

Clonal hematopoiesis of indeterminate potential (CHIP) occurs in the blood of approximately 20% of older persons. CHIP is linked to an increased risk of hematologic malignancies and of all-cause mortality; thus, the eligibility of stem-cell donors with CHIP is questionable. We comprehensively investigated how donor CHIP affects outcome of allogeneic hematopoietic stem-cell transplantation (HSCT).

Methods

We collected blood samples from 500 healthy, related HSCT donors (age ≥ 55 years) at the time of stem-cell donation for targeted sequencing with a 66-gene panel. The effect of donor CHIP was assessed on recipient outcomes, including graft-versus-host disease (GVHD), cumulative incidence of relapse/progression (CIR/P), and overall survival (OS).

Results

A total of 92 clonal mutations with a median variant allele frequency of 5.9% were identified in 80 (16.0%) of 500 donors. CHIP prevalence was higher in donors related to patients with myeloid compared with lymphoid malignancies (19.2% v 6.3%; P ≤ .001). In recipients allografted with donor CHIP, we found a high cumulative incidence of chronic GVHD (cGVHD; hazard ratio [HR], 1.73; 95% CI, 1.21 to 2.49; P = .003) and lower CIR/P (univariate: HR, 0.62; 95% CI, 0.40 to 0.97; P = .027; multivariate: HR, 0.63; 95% CI, 0.41 to 0.98; P = .042) but no effect on nonrelapse mortality. Serial quantification of 25 mutations showed engraftment of 24 of 25 clones and disproportionate expansion in half of them. Donor-cell leukemia was observed in two recipients. OS was not affected by donor CHIP status (HR, 0.88; 95% CI, 0.65 to 1.321; P = .434).

Conclusion

Allogeneic HSCT from donors with CHIP seems safe and results in similar survival in the setting of older, related donors. Future studies in younger and unrelated donors are warranted to extend these results. Confirmatory studies and mechanistic experiments are warranted to challenge the hypothesis that donor CHIP might foster cGVHD development and reduce relapse/progression risk.

EGR2 mutations define a new clinically aggressive subgroup of chronic lymphocytic leukemia

Recurrent mutations within EGR2 were recently reported in advanced-stage chronic lymphocytic leukemia (CLL) patients and associated with a worse outcome. To study their prognostic impact, 2403 CLL patients were examined for mutations in the EGR2 hotspot region including a screening (n=1283) and two validation cohorts (UK CLL4 trial patients, n=366; CLL Research Consortium (CRC) patients, n=490). Targeted deep-sequencing of 27 known/postulated CLL driver genes was also performed in 38 EGR2-mutated patients to assess concurrent mutations. EGR2 mutations were detected in 91/2403 (3.8%) investigated cases, and associated with younger age at diagnosis, advanced clinical stage, high CD38 expression and unmutated IGHV genes. EGR2-mutated patients frequently carried ATM lesions (42%), TP53 aberrations (18%) and NOTCH1/FBXW7 mutations (16%). EGR2 mutations independently predicted shorter time-to-first-treatment (TTFT) and overall survival (OS) in the screening cohort; they were confirmed associated with reduced TTFT and OS in the CRC cohort and independently predicted short OS from randomization in the UK CLL4 cohort. A particularly dismal outcome was observed among EGR2-mutated patients who also carried TP53 aberrations. In summary, EGR2 mutations were independently associated with an unfavorable prognosis, comparable to CLL patients carrying TP53 aberrations, suggesting that EGR2-mutated patients represent a new patient subgroup with very poor outcome.