High Incidences of Acute and Chronic Graft-Versus-Host Disease after Hematopoietic Cell Transplants for Acute Myeloid Leukemia Using Thiotepa, Busulfan, and Fludarabine Pretransplant Conditioning

Dear Editor,

Allogeneic hematopoietic cell transplants are widely used to treat acute myeloid leukemia (AML) [1]. Busulfan with cyclophosphamide (BuCy) or fludarabine with Busulfan is common pretransplant conditioning [2]. Thiotepa, busulfan, and fludarabine (TBF) is a new pretransplant conditioning regimen for AML with promising outcomes but concern over high incidences of acute and chronic graft-versus-host disease (GvHD) [3‒5]. We studied 52 subjects, 35 of whom developed acute and 26, chronic GvHD. Our data suggest increased risks of acute and chronic GvHD. With few subjects and no parallel controls validation of our observation is needed.

We used the Bone Marrow Transplantation Program-Cancer Registry of King Hussein Cancer Center (KHCC) to identify 52 consecutive subjects >18 years with AML receiving an allotransplant with TBF pretransplant conditioning from January 2017 to September 2020. Thirty-seven subjects received myeloablative and 15 received reduced-intensity conditioning. Conventional calcineurin inhibitors combined with methotrexate or mycophenolate in RIC-transplants were used for GvHD prophylaxis, 4 subjects received post-transplant cyclophosphamide and one received one dose of ATG of 2.5 mg/kg. Donors were completely or partially HLA-matched relatives. We scored donors age as 0–2 with a cutoff at 30 and 40 years, and we scored recipients age as 0–2 with a cutoff at 40 and 60 years. When added together, patients could be scored 0–4. Score 0–1 represents young patients and young donors, and score 4 represents older patients (>60 years) grafted from older donors (>40 years); score 2–3 represent donor and recipients of intermediate age [6]. Acute and chronic GvHD were diagnosed using published criteria [7, 8].

Recipient and donor co-variates analyzed included sex, sex- and ABO-matching, diagnosis, disease state, cytomegalovirus serology, degree of HLA disparity, numbers of CD34- and CD3-positive cells in the graft, and donor-recipient combined age score. Statistical analyses were done using SAS version 9.4 (SAS Institute Inc, Cary, NC, USA). p values are 2-sided and considered significant when <0.05.

Subject-, disease-, and transplant-related co-variates are displayed in Table 1. 37 subjects were male. Median recipient and donor ages were 41 years (range, 19–66 years) and 37 years (range, 11–63 years). Thirty-one had a combined age score of ≥2. Thirty-seven subjects received a high-dose regimen. Twenty-six were in 1st complete remission and the others in ≥2nd complete remission.

Complete donor chimerism was achieved in 34 by day 100 post-transplant [9]. Two subjects received post-transplant azacitidine, and 2 pre-emptive donor lymphocytes infusions (DLI). Fifteen of 29 subjects were measurable residual disease (MRD)-positive by multiparameter flow cytometry or next-generation sequencing pretransplant became MRD-test-negative post-transplant [9, 10].

Thirty-five subjects develop acute GvHD which was ≥ grade 2 in 22 and ≥ grade 3 in 11. Twenty-six subjects developed chronic GvHD, moderate to severe in 20 (as shown in Fig. 1). 7 subjects had corticosteroid-resistant acute GvHD, and 8 corticosteroid-resistant chronic GvHD. There was no difference in incidences of acute or chronic GvHD based on donor type, remission state or timing of tapering immune suppression, conditioning intensity (all p values >0.20), but there was a trend toward increased risk of acute GvHD for patients with combined D-R age score of ≥2 (p values 0.08) and grafted from donor, age ≥2, (p values 0.09).

In conclusion, data whether risks of acute and/or chronic GvHD are increased in persons with AML receiving TBF compared with FluBu or BuCy are contradictory. We found high rates of both aGvHD and cGvHD compared with historical controls in recipients of FluBu or BuCy pretransplant conditioning. Young patients grafted from young donors had less GvHD, whereas old patients (>60) grafted from old donors (>40) had higher risk of developing acute and chronic GvHD. Bacigalupo et al. [3] reported on 425 patients with myeloid malignancies, who received haploidentical allotransplants but with unmanipulated marrow grafts with a modified post-transplant cyclophosphamide regimen [7]. There is a lower incidence of aGvHD grade 2–4 (28% vs. 67%); grade 3–4 (3% vs. 31%); higher aGvHD grade 2–4 in patients with D-R combined age score ≥2 (62% vs. 44%), in patients receiving grafts from donors under median age of 34 years; higher cGvHD (61% vs. 50%), and lower moderate to severe cGvHD (18% vs. 77%) compared with our results. In his report, D-R combined age score was the only predictive of aGvHD and cGvHD, which is comparable with our results.

One-year transplant-related mortality was 11% +/− 4% (7–15%) in our series with increased risk of relapse (27.5%). We could not draw any conclusions in regard to the association of cGvHD and the risk of relapse and non-relapse mortality due to small number of patients. However, we found high risk of acute and chronic GvHD, but this does not translate into higher non-relapse mortality. GvHD attributed to death of only 4 cases.

Our study has important limitations including few heterogeneous subjects and disease- and transplant-related co-variates different TBF intensities and no parallel comparator cohort. As such our conclusion needs validation in a randomized controlled trial.