DNMT3A clonal Hematopoiesis in Older Donors Is Associated with Improved Survival in Recipients after Allogeneic Hematopoietic Cell Transplant

Background: Clonal hematopoiesis (CH) is an age-related condition in which somatic mutations can be detected in the blood of healthy individuals. In the non-transplant setting, CH is associated with an elevated risk of developing hematologic malignancy and an increased risk of non-hematologic outcomes due to altered inflammatory signaling. During hematopoietic cell transplantation (HCT), CH in older donors can engraft in recipients and could therefore influence outcomes through effects on graft immunologic function or by causing donor cell leukemia. A definitive link between donor CH and recipient outcomes has not been established. We therefore evaluated the impact of CH in donors aged 40 years or older on recipient clinical outcomes in 1727 donor-recipient pairs. Methods: We performed targeted, error-suppressed sequencing of 46 genes on 1727 samples from donors age 40 and older. We defined CH as pathogenic mutations at variant allele fraction (VAF) 0.005 or greater. Median donor age was 51 (range 40-80) and median recipient age was 55 (range 1-78). There were 889 matched related donors (51.5%), 454 haploidentical donors (26.3%), 273 matched unrelated donors (15.8%), 71 mismatched unrelated donors (4.1%), and 38 mismatched related donors (2.2%). 929 recipients (53.8%) had myeloid malignancies, 718 (41.6%) had lymphoid malignancies, and 80 (4.6%) had non-malignant diseases. 1022 (59.2%) recipients received peripheral blood stem cell products and 703 (40.7%) received bone marrow. 672 recipients (38.9%) received post-transplant cyclophosphamide (PTCy) for graft versus host disease (GVHD) prophylaxis. Median follow-up for survivors was 6.0 years. Results: We identified CH in 388 of 1727 (22.5%) donor samples. Mutations in DNMT3A were most common (302 mutations in 253 donors), followed by TET2 (96 mutations in 89 donors), ASXL1 (n=22) and PPM1D (n=14). No other genes were mutated in more than 10 donors (0.5%). The presence of donor CH was independently associated with older donor age, but not with donor sex, donor-recipient relatedness, graft source, or recipient disease. The presence of donor CH at VAF 0.01 or greater was associated with improved progression-free survival (PFS) in a multivariable model that included donor and recipient age, HCT-CI, disease category, Disease Risk Index score, conditioning intensity, and donor type (HR for death or relapse 0.81, 95% CI 0.68-0.97, P=0.019). This effect was driven by DNMT3A mutations, which were independently associated with improved overall survival (HR for death 0.75; 0.59-0.95, P=0.016) and reduced risk of relapse (sHR 0.76; 0.59-0.97, P=0.029) in the same model. CH involving other gene mutations, including TET2 and genes other than DNMT3A/TET2, was not significantly associated with any recipient outcome. Smaller clones (VAF 0.005-0.01) had no effect on any outcome. The association between donor DNMT3A-CH and recipient outcomes was limited to those who did not receive PTCy for GVHD prophylaxis (Figure 1A-C). In the model described above, donor DNMT3A-CH in the absence of PTCy was independently associated with improved PFS (HR 0.61; 0.45-0.84, P=0.002), reduced risk of relapse (sHR 0.59; 0.39-0.9, P=0.014) and an elevated risk of chronic GVHD (sHR 1.36; 1.01-1.83, P=0.042) compared to those without DNMT3A-CH. In recipients who received PTCy, there was no significant effect of donor DNMT3A-CH on PFS, relapse, or cGVHD (1D). Eight recipients developed donor cell leukemia (DCL), for a cumulative incidence of 0.7% at 10 years. In seven of these cases, we identified gene mutations in the corresponding donor products that matched the mutations found in the subsequent DCL, including 2 with TP53 mutations, 3 with splicing factor mutations, and 2 with germline DDX41 mutations that were present in both donor and recipient. No recipients who received products with sole DNMT3A-CH developed DCL. Conclusions: In HCT donors age 40 or older, the presence of DNMT3A clonal hematopoiesis at VAF >/= 0.01 is independently associated with prolonged overall and progression-free survival in transplant recipients. This effect is driven by reduced risk of disease relapse and confined to recipients who do not receive PTCy, suggesting that it is mediated at least in part by effects on donor T cells. The risk of direct evolution of DNMT3A-CH to donor cell leukemia is low, and most DCLs were traced to atypical donor CH involving MDS-associated genes or germline risk alleles. Disclosures Nikiforow: Novartis: Honoraria; Nkarta Therapeutics: Honoraria; Kite/Gilead: Honoraria. DeZern:MEI: Consultancy; Abbvie: Consultancy; Astex: Research Funding; Celgene: Consultancy, Honoraria. Ritz:Rheos Medicines: Consultancy; Infinity Pharmaceuticals: Consultancy; Amgen: Research Funding; Equillium: Research Funding; Kite Pharma: Research Funding; Avrobio: Consultancy; Falcon Therapeutics: Consultancy; TScan Therapeutics: Consultancy; Talaris Therapeutics: Consultancy; LifeVault Bio: Consultancy. Soiffer:VOR Biopharma: Consultancy; Kiadis: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy; Juno: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; alexion: Consultancy; Be the Match/ National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy; Mana Therapeutics: Consultancy; Precision Bioscience: Consultancy; Cugene: Consultancy; Rheos Therapeutics: Consultancy. Lindsley:Jazz Pharmaceuticals: Consultancy, Research Funding; Takeda Pharmaceuticals: Consultancy; MedImmune: Research Funding; Bluebird Bio: Consultancy.

Donor Cell Acute Myeloid Leukemia after Transplant for Follicular Lymphoma

Donor cell leukemia is postulated to account for up to 5% of all leukemia "relapses" after hematopoietic stem cell transplant (SCT), though in many cases this is the first leukemia diagnosis for the patient if their transplant was for non-leukemia primary diseases. The rarity of the condition and heterogeneity of disease create challenges in diagnosis and management. In the present case, donor cell leukemia (DCL) developed in a 68-year-old female after allogeneic SCT 18 years earlier for follicular lymphoma. Only one other case of DCL after transplantation for follicular lymphoma has been reported (Boulton-Jones et al., Bone Marrow Transplantation, 2005). Furthermore, this case is atypical in that the presentation occurred many years after transplantation, since very few cases of DCL occur more than 15 years after original transplant. Case In 1993, the patient was diagnosed with stage IIIA follicular lymphoma at age 50. She achieved a complete remission with CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) for 4 years. She relapsed in 1998 and received treatment with fludarabine and mitoxantrone. In 1999, she enrolled in a toxitumomab clinical trial (NCT00268203) but discontinued therapy secondary to side effects. Due to persistent disease, she proceeded with SCT and received EPOCH-F (etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin, and fludarabine) prior to allogeneic SCT from her brother in 2000 (6/6 HLA match), augmented with TH2 cells. She received graft versus host disease (GVHD) prophylaxis with cyclosporine, however her post transplant course was complicated by engraftment syndrome and gastrointestinal and skin GVHD. In 2019, she presented to hematology for evaluation of worsening chronic neutropenia and thrombocytopenia persistent for three years, noted during work-up for symptomatic cholelithiasis. Bone marrow biopsy revealed acute myeloid leukemia (AML) with a hypocellular marrow with 30% blasts and myelodysplasia related changes. Her cytogenetics showed 46XY, +1, der(1;7)(q10;p10)/47,sl,+8/46,XY. FISH analyses demonstrated deletion 7q31 D7S486 locus in 156/200 cells (78%). NGS panel showed IDH1 (VAF16%) and U2AF1 (VAF 26%) mutations. Based on cytogenetics and chimerism studies showing 100% donor, the patient was diagnosed with donor-derived AML secondary to allogeneic SCT from her brother. The brother currently has no known hematologic problems. The patient was treated with CPX-351 (liposomal cytarabine and daunorubicin) and achieved a complete remission, followed by consolidation with CPX-351. Given her complex cytogenetics and poor prognosis, the patient proceeded to non-myeloablative haploidentical peripheral blood SCT from her son, with post-transplant cyclophosphamide. She subsequently had complications of neutropenic fever and C. dificile colitis, with progressive colitis leading to her death on day 22 after SCT. Discussion Though cytogenetic and molecular studies along with functional status assist clinicians in treatment decisions for DCL patients, the benefits and risks of treatment remain difficult to balance for this unique subset of leukemia. Of patients that achieve remission for greater than 18 months, many undergo second allogeneic SCT, however a similar number of patients have remissions of at least 18 months treated with chemotherapy alone (Wiseman, Biology of Blood and Bone Marrow Transplantation, 2011). In 15 reported cases that went to SCT, approximately 50% lived longer than 12 months after their DCL diagnosis. Second allogeneic SCT is often favored after initial remission in patients with good performance status due to high risk for relapse. This case illustrates the challenge in management of donor cell leukemia, a rather rare entity with very few cases in the literature developing greater than 15 years after transplant. Limited robust evidence favoring a particular treatment supports the need for further prospective studies. Disclosures Lai: Agios: Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Speakers Bureau; Astellas: Speakers Bureau.

Donor Cell Leukemia: The Role of Recipient Microenvironment

Acute myeloid leukemia (AML) is one of the extreme outcomes of age-related clonal hematopoiesis (ARCH). In recent years, data on differences between pre-AML and ARCH have emerged. However, it is still enigmatic why ARCH is prevalent in the general aging population, whereas only very few individuals eventually develop AML. Whether ARCH is solely related to abnormal hematopoiesis or originates from impaired microenvironment (ME) needs to be elucidated. The current study aimed to explore dynamics of molecular changes occurring in rare patients developing late post-transplant donor cell leukemia (DCL) and the relation of these aberrations to ARCH and/or ME. We herein present two DCL cases, where the molecular profile was evaluated using deep error corrected sequencing (coverage ~4000X). In the first case, a female patient (26 y.o.) was diagnosed with AML secondary to myelodysplastic syndrome (MDS) and transplanted from her haplo-matched father (73 y.o.). Mutations at primary AML diagnosis were U2AF1 and TP53. Seventeen years later she devolved high-risk MDS, carrying PPM1D and EZH2 mutations. At the time of the DCL-MDS the patient had full donor chimerism and 100% XY donor cells by cytogenetics; however, both mutations could not be detected in the donor peripheral blood (PB). In the second case: a male patient (58 y.o.) with AML was transplanted in complete remission from his matched sister (52 y.o.). Primary AML mutations at diagnosis were U2AF1 S34F and RUNX1. Nine years later a second AML evolved, carrying new mutations, including U2AF1 (S34Y instead of original S34F), DNMT3a and IDH1. At the time of DCL-AML the patient had full chimerism and 100% XX donor cells by cytogenetics. Remarkably, none of these mutations could be detected in the donor PB or germ line either at the time of presentation or years later. The chances of the same patient to develop AML twice in the same position (U2AF1 S34) or in the same pathway (TP53 and PPM1D) are less than 1:500,0002. While inherited predisposition to AML can explain such cluster of AMLs in the same patient, it is less likely to occur in the current cases, as no other leukemia has been reported among other family members. To further investigate the contribution of ME to leukemogenesis, longitudinal complete blood counts (CBC) were analyzed. While most of the CBC normalized in the years after the allogeneic bone marrow transplantation (allo-BMT), in both cases red blood cell distribution width (RDW) remained elevated, which could suggest underlying MDS. To explore this RDW pattern, we have followed various CBC indexes in a cohort of 71 allo-BMT survivors, from the dataset of the Clalit Healthcare Provider. Four years after allo-BMT, RDW was found to be significantly elevated, while red blood cell counts were significantly lower compared to those of age-matched controls. Other CBC parameters normalized 2-3 years post-transplant (Figure 1). Overall, these results suggest that at least in some AML cases even after allo-BMT, hematopoiesis cannot be fully normalized and the main manifestations are in the red cell lineage. Our unique DCL cases imply that the patient ME is involved in the abnormal hematopoiesis (increased RDW) and in the tendency of evolving a second AML, which has not developed in the donors. Disclosures Zuckerman: Cellect Biotherapeutics Ltd: Consultancy.