Conditioning Hematopoietic Stem Cell Transplantation Research Articles

The impact of age and renal function on the pharmacokinetics and protein binding characteristics of fludarabine in paediatric and adult patients undergoing allogeneic haematopoietic stem cell transplantation conditioning.

To evaluate the population pharmacokinetics of unbound F-Ara-A (the circulating metabolite of fludarabine) in 211 patients (age range, 0.1-63.4years) undergoing allogeneic haematopoietic stem cell transplantation conditioning. Total (n = 2480) and unbound (n = 1403) F-Ara-A concentrations were measured in blood samples collected at timed intervals after fludarabine doses ranging from 10 to 50mg/m2 and infused over 0.42-1.5h. A three-compartment population pharmacokinetic model was developed based on unbound plasma concentrations and used to estimate F-Ara-A unbound pharmacokinetic parameters and fraction unbound (fu). A number of covariates, including glomerular filtration rate (GFR) and post-menstrual age (PMA), were evaluated for inclusion in the model. The base population mean estimates ± relative standard error (%RSE) for unbound clearance from the central compartment (CLu) and inter-compartmental clearances (Q2u, Q3u) were 3.42 ± 3%, 6.54 ± 24% and 1.47 ± 16% L/h/70kg, respectively. The population mean estimates (%RSE) for the unbound volume of distribution into the central (V1u) and peripheral compartments (V2u, V3u) were 9.65 ± 8%, 8.17 ± 9% and 16.4 ± 10% L/70kg, respectively, and that for fu was 0.877 ± 1%. Covariate model development involved differentiating F-Ara-A CLu into non-renal (1.81 ± 9% L/h/70kg) and renal components (1.02 ± 9%*GFR L/h/70kg). A sigmoidal maturation factor was applied to renal CLu, with population mean estimates for the Hill exponent and PMA at 50% mature of 2.97 ± 4% and 69.1 ± 8%weeks, respectively. Patient age and GFR are predictors of unbound F-Ara-A CLu. This has the potential to impact dose requirements. Dose individualisation by target concentration intervention will be facilitated by this model once it is externally validated.

Emapalumab therapy for hemophagocytic lymphohistiocytosis before reduced-intensity transplantation improves chimerism

AbstractHemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory disorder driven by interferon gamma (IFN-γ). Emapalumab, an anti–IFN-γ antibody, is approved for the treatment of patients with primary HLH. Hematopoietic stem cell transplantation (HSCT) is required for curing HLH. Reduced-intensity conditioning (RIC) HSCT is associated with improved survival but higher incidences of mixed chimerism and secondary graft failure. To understand the potential impact of emapalumab on post-HSCT outcomes, we conducted a retrospective study of pediatric patients with HLH receiving a first RIC-HSCT at our institution between 2014 and 2022 after treatment for HLH, with or without this agent. Mixed chimerism was defined as <95% donor chimerism and severe mixed chimerism as <25% donor chimerism. Intervention-free survival (IFS) included donor lymphocyte infusion, infusion of donor CD34-selected cells, second HSCT, or death within 5 years after HSCT. Fifty patients met the inclusion criteria; 22 received emapalumab within 21 days before the conditioning regimen, and 28 did not. The use of emapalumab was associated with a markedly lower incidence of mixed chimerism (48% vs 77%; P = .03) and severe mixed chimerism (5% vs 38%; P < .01). IFS was significantly higher in patients receiving emapalumab (73% vs 43%; P = .03). Improved IFS was even more striking in infants aged <12 months, a group at the highest risk for mixed chimerism (75% vs 20%; P < .01). Although overall survival was higher with emapalumab, this difference was not significant (82% vs 71%; P = .39). We show that the use of emapalumab for HLH before HSCT mitigates the risk of mixed chimerism and graft failure after RIC-HSCT.

Antiemetic prophylaxis regimens in haematologic malignancies patients undergoing a hematopoietic stem cell transplantation. Which is the best standard of care? A systematic review.

This systematic review, adhering to PRISMA guidelines, aimed to evaluate the efficacy and safety of antiemetic prophylaxis in haematological patients undergoing high-dose chemotherapy as part of their hematopoietic stem cell transplantation (HSCT) conditioning regimens. We performed a comprehensive search in PubMed, EMBASE, ClinicalTrials.gov and the Cochrane database to identify randomised controlled trials (RCTs) and systematic reviews of antiemetic prophylaxis. Studies in English, French, Italian or Spanish were included. This review is registered with PROSPERO, ID CRD42023406380. Eight RCTs were analysed. The antiemetic regimens evaluated ranged from monotherapy with 5-Hydroxytryptamine Receptor 3 antagonists (5-HT3RAs) to complex combinations including olanzapine, neurokinin-1 receptor antagonists, 5-HT3RAs and corticosteroids. Complete response rates for triplet or quadruple regimens varied between 23.5% and 81.9%. Although no significant adverse effects were observed, minor symptoms such as diarrhoea, constipation, sedation and headaches were reported. Existing evidence on HSCT antiemetic therapy highlights its benefits but fails to provide clear clinical directions. The choice between triplet and quadruplet therapies for different patient scenarios is still uncertain. Until more detailed research is available, healthcare providers must rely on the latest guidelines and their judgement to customise antiemetic care for each patient's specific needs and risks.

Haematopoietic stem cell transplantation after reduced intensity conditioning in children and adolescents with chronic myeloid leukaemia: A prospective multicentre trial of the I-BFM Study Group.

This prospective multicentre trial evaluated the safety and the efficacy of a thiotepa/melphalan-based reduced intensity conditioning (RIC) haematopoietic stem cell transplantation (HSCT) in children and adolescents with chronic myeloid leukaemia (CML) in chronic phase (CP). Thirty-two patients were transplanted from matched siblings or matched unrelated donors. In 22 patients, HSCT was performed due to insufficient molecular response or loss of response to first- or second-generation tyrosine kinase inhibitor (TKI), with pretransplant BCR::ABL1 transcripts ranging between 0.001% and 33%. The protocol included a BCR::ABL1-guided intervention with TKI retreatment in the first year and donor lymphocyte infusions (DLI) in the second-year post-transplant. All patients engrafted. The 1-year transplant-related mortality was 3% (confidence interval [CI]: 0%-6%). After a median follow-up of 6.3 years, 5-year overall survival and event-free survival are 97% (CI: 93%-100%) and 91% (CI: 79%-100%) respectively. The current 5-year leukaemia-free survival with BCR::ABL1 <0.01% is 97% (CI: 88%-100%) and the current TKI- and DLI-free survival is 95% (CI: 85%-100%). The incidence of chronic graft-versus-host disease (GvHD) was 32%, being severe in four patients (13%). At last follow-up, 31 patients are GvHD-free and have stopped immunosuppression. RIC HSCT following pretreatment with TKI is feasible and effective in children and adolescents with CP-CML with an excellent disease-free and TKI-free survival.

Autologous hematopoietic stem cell transplantation conditioning regimens and chimeric antigen receptor T cell therapy in various diseases.

Conditioning regimens employed in autologous stem cell transplantation have been proven useful in various hematological disorders and underlying malig nancies; however, despite being efficacious in various instances, negative consequences have also been recorded. Multiple conditioning regimens were extracted from various literature searches from databases like PubMed, Google scholar, EMBASE, and Cochrane. Conditioning regimens for each disease were compared by using various end points such as overall survival (OS), progression free survival (PFS), and leukemia free survival (LFS). Variables were presented on graphs and analyzed to conclude a more efficacious conditioning regimen. In multiple myeloma, the most effective regimen was high dose melphalan (MEL) given at a dose of 200/mg/m2. The comparative results of acute myeloid leukemia were presented and the regimens that proved to be at an admirable position were busulfan (BU) + MEL regarding OS and BU + VP16 regarding LFS. In case of acute lymphoblastic leukemia (ALL), BU, fludarabine, and etoposide (BuFluVP) conferred good disease control not only with a paramount improvement in survival rate but also low risk of recurrence. However, for ALL, chimeric antigen receptor (CAR) T cell therapy was preferred in the context of better OS and LFS. With respect to Hodgkin's lymphoma, mitoxantrone (MITO)/MEL overtook carmustine, VP16, cytarabine, and MEL in view of PFS and vice versa regarding OS. Non-Hodgkin's lymphoma patients were administered MITO (60 mg/m2) and MEL (180 mg/m2) which showed promising results. Lastly, amyloidosis was considered, and the regimen that proved to be competent was MEL 200 (200 mg/m2). This review article demonstrates a comparison between various conditioning regimens employed in different diseases.

Phase 1 Study of Bortezomib, Fludarabine, and Melphalan, With or Without Total Marrow Irradiation, as Allogeneic Hematopoietic Stem Cell Transplant Conditioning for High-risk or Relapsed/Refractory Multiple Myeloma.

We conducted a phase 1 study of a conditioning regimen with or without total marrow irradiation (TMI) before allogeneic hematopoietic stem cell transplantation for patients with high-risk or refractory multiple myeloma. Eighteen patients were enrolled on one of 2 strata. Patients with no prior radiation received TMI (900 cGy), fludarabine (FLU), and melphalan (MEL) conditioning, with bortezomib added in the second cohort (stratum I). Patients with prior radiation received FLU, MEL, and bortezomib, without TMI (stratum II). Eight patients were enrolled in the TMI arm (stratum I). One of 3 patients in cohort 1 experienced dose-limiting toxicity (DLT), which led to the expansion to 3 more patients with no DLT. Cohort 2 enrolled only 2 patients due to low accrual, with bortezomib, added at 0.5 mg/m 2 ; neither experienced DLT. Nine patients were enrolled in the non-TMI arm (stratum II). Three patients were enrolled in cohort 1 (bortezomib 0.5 mg/m 2 ) and none experienced DLT. Three were enrolled in cohort 2 (bortezomib 0.7 mg/m 2 ), and 1 experienced DLT; therefore, the cohort expanded to 3 more patients. One more patient experienced DLT. Median overall survival on strata I and II was 44.5 months (95% CI: 1.73-not reached) and 21.6 months (95% CI: 4.1-72.7), respectively. Median progression-free survival on strata I and II was 18.1 months (95% CI: 1.73-not reached) and 8.9 months (95% CI: 2.7-24.4), respectively. TMI 900 cGy, FLU, and MEL are considered feasible as conditioning for allogeneic stem cell transplantation and may warrant further investigation due to favorable response rates and survival.

Post-transplant cyclophosphamide versus anti-thymocyte globulin after reduced intensity peripheral blood allogeneic cell transplantation in recipients of matched sibling or 10/10 HLA matched unrelated donors: final analysis of a randomized, open-label, multicenter, phase 2 trial

The use of post-transplantation cyclophosphamide (PTCy) for graft-versus-host disease (GVHD) prophylaxis is not established after reduced intensity conditioning (RIC) hematopoietic stem cell transplantation (HSCT) from fully matched donors. This was a randomized, open-label, multicenter, phase 2 trial. All patients received a RIC regimen with fludarabine, intravenous busulfan for 2 days (Flu-Bu2), and a peripheral blood stem cell (PBSC) graft from a matched related or 10/10 HLA-matched unrelated donor. Patients were randomly assigned to receive anti-thymocyte globulin (ATG) 5 mg/kg plus standard GVHD prophylaxis or PTCy 50 mg/kg/d at days +3 and +4 plus standard GVHD prophylaxis. The primary endpoint was the composite endpoint of GVHD- and relapse-free survival (GRFS) at 12 months after HSCT. Eighty-nine patients were randomly assigned to receive either PTCy or control prophylaxis with ATG. At 12 months, disease-free survival was 65.9% in the PTCy group and 67.6% in the ATG group (P = 0.99). Cumulative incidence of relapse, non-relapse mortality, and overall survival were also comparable in the two groups. GRFS at 12 months was 54.5% in the PTCy group versus 43.2% in the ATG group (P = 0.27). The median time to neutrophil and platelet count recovery was significantly longer in the PTCy group compared to the ATG group. Except for day +30, where EORTC QLQ-C30 scores were significantly lower in the PTCy compared to the ATG group, the evolution with time was not different between the two groups. Although the primary objective was not met, PTCy is effective for GVHD prophylaxis in patients receiving Flu-Bu2 conditioning with a PBSC graft from a fully matched donor and was well tolerated in term of adverse events and quality of life. This trial was registered at clinicaltrials.gov: NCT02876679.

Determination of Busulfan and Melphalan in Plasma by Turbulent Flow Chromatography-Tandem Mass Spectrometry.

Melphalan and busulfan are DNA-alkylating agents that are often used concurrently in hematopoietic stem cell transplant (HCT) conditioning regimens. Studies have demonstrated that this combination of alkylating agents is very effective and well-tolerated prior to HCT. This combination is widely used for acute leukemia, advanced lymphoid malignancies, and multiple myeloma. Our goal was to develop an assay for the rapid measurement of both compounds simultaneously in the hopes that rapidly measuring their concentrations could possibly shorten the length of hospital stay. It would also simplify specimen handling in the clinic and the laboratory, reduce the amount of blood drawn, and allow for rapid reporting of the drug levels, thereby facilitating rapid dose adjustments.This chapter describes a validated method that measures both compounds simultaneously. Melphalan and busulfan were extracted from plasma with methanol containing deuterated internal standards. Turbulent flow chromatography coupled with reversed-phase HPLC was used for separation, while the mass spectrometer was set in the positive ion mode. This method has proven accurate and rapid and allowed for timely dose adjustments. The assay was linear over the clinically relevant ranges; the analytical measurement range for busulfan and melphalan was 10-5000ng/mLand 10-15,000 ng/mL, respectively. Specimens containing elevated drug levels were diluted yielding a final clinically reportable range of 10-25,000ng/mL for busulfan and 10-75,0000ng/mL for melphalan. This method is very suitable for simultaneous measurements of these drugs and is currently being used to support pharmacokineticstudies.

Hematopoietic Stem Cell Transplantation (HCT) Conditioning Leads to NK Cell Cytotoxicity Limiting Endogenous Thymus Regeneration

The thymus is highly sensitive to acute injury such as the cytoreductive conditioning given pre-hematopoietic stem cell transplant (HCT). The thymus is capable of regeneration, however its reparative capacity and T cell productivity decline with age. This leaves HCT recipients vulnerable to relapse of malignancy and opportunistic infection - the leading causes of post-HCT mortality - during a prolonged period of lymphopenia. Better understanding the endogenous mechanisms by which thymus regeneration is regulated may inform therapeutic interventions to improve T cell reconstitution in these patients. Here, we report that HCT conditioning leads to rises in stimulatory cytokine IL-18, subsequent activation of NK cells and increased cytotoxicity, which aberrantly suppresses organ recovery. Our group has reported that HCT-conditioning by ionizing radiation leads to increased Caspase-1 mediated immunogenic cell death within the thymus (Kinsella 2023 BioRxiv). Consistent with the cleavage of Caspase-1, we found an increase in release of the inflammatory cytokines IL-1b and IL-18. Although mice deficient for IL-1b signaling receptor ( Il1r -/-) did not show any modulation in their ability to regenerate after TBI, we found that mice deficient for IL-18 signaling (Il18 -/-) exhibited increased thymic cellularity one week following acute damage by sublethal irradiation (SL-TBI) (Fig. 1A left). This led us to conclude that post-damage activation and release of IL-18 suppresses thymus regeneration. We found that IL-18R was not expressed on most developing thymocytes and although a minority of thymic epithelial cells expressed the receptor, mice with a deficiency in IL-18R restricted to TECs ( Il18r1fl/fl:Foxn1-Cre +) showed no difference in regenerative capacity following conditioning. To rule out an effect on hematopoietic progenitors, for which IL-18R expression has been reported ( Silberstein 2016 Cell Stem Cell 6;19), we performed a competitive transplantation of Il18r1 -/- and WT bone marrow and measured T cell production, which showed no competitive advantage of Il18r1 -/- donor cells; this demonstrated that IL-18 does not directly regulate progenitor cells themselves, but rather, more likely acts via a bystander thymus-resident population. Within the thymus, IL-18R was expressed by highly radioresistant NK1.1 + NKT and NK cells. Depletion of both populations with anti-NK1.1 monoclonal antibody improved thymus cellularity in WT mice (Fig. 1A middle). Notably, NKT deficient CD1d -/- mice showed no defective repair which suggested that the depletion upon NK1.1 + cell depletion is largely mediated by NK cells. Depletion of NK1.1 + cells in Il18 -/- mice did not improve regeneration further, suggesting that NK-mediated suppression is IL-18 dependent. Given the known role of IL-18 in NK cell activation, we hypothesized that the HCT-conditioning resultant rise in IL-18 stimulates NK cells leading to “accidental” targeting of regeneration promoting cells. NK cell production of cytotoxic factors including IFNg, GzmB and Perforin increases following radiation conditioning, although only mice deficient for Perforin and not IFNg -exhibited improved thymus cellularity 7 days post HCT-conditioning (Fig 1A right). Further supporting this hypothesis, IL-18R +CD49b + NK cells isolated from the thymus 2-days post-irradiation induced more target cell death in head-to-head cytotoxicity assays compared to NK cells isolated pre-radiation (Fig 1B). Finally, we observe TEC downregulation of NK cytotoxicity inhibitory ligand MHC-I following radiation conditioning, suggesting that critical regeneration promoting stroma may be the targets of these activated NK cells. These findings suggest that, while necessary for successful transplantation, conditioning regimens may induce cytotoxicity of bystander NK cells which suppresses thymus recovery. Furthermore, we implicate conditioning induced immunogenic cell death and increased IL-18 in the stimulation of these suppressive cytotoxic cells and suggest that therapeutically targeting IL-18 and NK cell cytotoxicity may improve T cell reconstitution post-HCT.

Feasibility of Utilizing a Virtual Health Assistant during Inpatient Reduced-Intensity Allogeneic Transplantation

Background:Artificial intelligence (AI) promises to revolutionize hematology care.Patients undergoing inpatient allogeneic hematopoietic stem cell transplantation (HCT) often experience psychological consequences, some of which may be attributed to anxiety about how to optimally care for themselves when returning home.Care.coach Avatar TM is a tablet-based ‘human-in-the-loop’ virtual health assistant (VHA) that utilizes generative AI and deterministic software to provide psychosocial support and health coaching to inpatients. It has been shown to improve loneliness, depression, anxiety, hospital delirium, and falls in older adults in the hospital (Chi, Geriatr Nurs 2017; Bott, J Med Internet Res 2019). Methods: We adapted the care.coach Avatar TM VHA for inpatient HCT, designing an education program to prepare patients for safe return to the home setting. The VHA engages patients with reminders for hydration, medications, food, or activity; education modules adapted for HCT; playing games such as jeopardy, chess, blackjack, trivia, or bingo; playing the news or music; having free-form conversations; going through therapeutic activities and exercises; and practicing mindfulness and guided meditation. Avatar protocols were updated based on feedback from a structured focus group (n=10) of nurse navigators, inpatient HCT nurses, and HCT physicians at the Dana-Farber/Harvard Cancer Center that was convened to discuss perspectives on implementation of care.coach Avatar TM VHA for HCT. Seven HCT-specific educational modules were created. A feasibility pilot was then performed in 3 sequential cohorts of 6 patients receiving reduced intensity conditioning (RIC) HCT. In the first cohort, patients were given the VHAs without any recommendations for how long to use them. The second cohort was given a recommendation for 30 minutes per day, and the third cohort was offered a $20 gift card for completion of at least 4 modules. Responses were measured through patient surveys and engagement data analysis. The predefined retention rate for feasibility was 67%, a standard for introduction of a novel AI technology (Teresi, Med Care 2022). Dissatisfaction rate for the overall VHA experience was defined as responding “disagree” or “strongly disagree” with recommending the VHA to others. Results: The study included 18 patients, with a majority female (61%) and white (72%; Table). The median age of the patients was 63 (interquartile range [IQR] 56-66). The retention rate from enrollment to discharge or three weeks (whichever came first) was 78% (95% exact confidence interval: 52-94%). The median length of use was 9 days (IQR 6-11). A post-pilot survey was completed by 16 patients (90%), revealing a dissatisfaction rate of 28%. The dissatisfaction rates decreased from 50% to 20% to 0% across the 3 cohorts. Frequency of completion of the post-pilot survey for the full study was 72% within 1 week of disenrollment, and 90% overall. Average completion rate was 52% for all seven HCT modules in the whole study population. Across cohorts, module completion rates changed from 5% to 88% to 62%, reflecting evolving guidance to patients at study initiation. The median average daily interaction time with the avatar for all 18 patients was 28 minutes with an interquartile range from 20 to 38 minutes. The most frequently used VHA functions by time of usage were music (35%), exercise (20%), and education (15%; Figure). The least frequently used VHA functions were the rounds optimizer (a tool to remind patients of their questions during rounds; 1%) and humor (1%). Overall, 52% of time using the VHA was spent on social engagement activities. Conclusions: The pilot study demonstrated the feasibility of implementing the care.coach Avatar TM VHA for inpatient HCT patients. Despite modest dissatisfaction and variability in completion rates, the VHA showed promise in providing HCT education, social, and emotional support for inpatient RIC HCT. Further research is needed to assess the impact of this novel technologic intervention on HCT outcomes and quality of life, as well as application to the outpatient HCT setting.

Radiation and Busulfan-Free Hematopoietic Stem Cell Transplantation Using Briquilimab (JSP191) Anti-CD117 Antibody-Conditioning, Transient Immunosuppression and TCRαβ + T-Cell/CD19 + B-Cell Depleted Haploidentical Grafts in Patients with Fanconi Anemia

Introduction: Fanconi anemia (FA) is a rare, genetic disorder clinically characterized by congenital abnormalities, progressive bone marrow failure (BMF), and a predisposition to malignancies. Allogeneic hematopoietic stem cell transplantation (HSCT) is currently the only curative treatment for BMF. In patients with FA who do not have a matched sibling donor, HSCT conditioning regimens typically use reduced doses of cyclophosphamide, fludarabine and anti-thymocyte globulin (ATG) with total body irradiation (TBI) or busulfan. However, treatment is complicated by conditioning related toxicities, graft vs host disease (GvHD) and increased predisposition to malignancies later in life. Prior attempts to remove TBI from FA conditioning regimens have been unsuccessful due to increased risk of graft rejection - and alternative approaches have replaced TBI with busulfan which is still genotoxic. Objective: To reduce acute and long-term treatment-related toxicities, we have developed a first of its kind treatment intended to improve the safety of allo-HSCT through: 1) a TBI- and busulfan-free conditioning regimen consisting of briquilimab, rabbit ATG (rATG - Thymoglobulin), fludarabine, cyclophosphamide and rituximab - briquilimab (formerly called JSP191) is a monoclonal antibody (mAb) that targets human CD117 to deplete host HSCs enabling blood and immune reconstitution with minimal toxicity with the other agents being used for transient immune suppression to prevent immunologic rejection; 2) transplantation of TCRαβ + T-cell/CD19 + B-cell hematopoietic grafts - a stem cell therapy that enhances donor hematopoietic and immune reconstitution while decreasing GvHD; and 3) a pre- and post-transplant monitoring protocol to maximize engraftment. This is the first HSCT regimen to use anti-CD117 mAb-based conditioning in immunocompetent patients without concurrent use of irradiation. Methods: Patients with FA in BMF were eligible to be enrolled in this Phase 1b/2a trial to receive allo-HSCT with TCRαβ + T-cell/CD19 + B-cell depleted hematopoietic grafts from 10/10 unrelated, 9/10 unrelated or haploidentical family donors. Per the treatment schema, in this regimen a fixed dose of briquilimab was administered at 0.6 mg/kg in combination with standard FA dosing of rATG, fludarabine, cyclophosphamide and rituximab as lymphodepletion (Figure 1). Prospective pharmacokinetic measurements of briquilimab, rATG and fludarabine are included in the protocol. Results: Treatment of all of the patients on the Phase 1b portion of the study has been completed with each of the three patients showing promising safety and efficacy results (Table 1). Importantly, briquilimab treatment was well tolerated without any complications with appropriate antibody clearance of &amp;lt; 500 ng/ml prior to HSCT in all three patients. Each of the patients achieved full blood count recovery by Day +14 post HSCT with haploidentical grafts that were within specifications of the protocol. Total, CD34 +, and CD15 + donor chimerism of &amp;gt; 98% in the bone marrow has been observed in all patients with &amp;gt; 91% chimerism in all immune subsets (CD3, CD19 and CD56) at the last follow-up with 1 year of follow-up post HSCT in the first patient. None of the patients have developed acute or chronic GvHD at the time of reporting. Conclusions: All three patients in the Phase 1b portion of the study show early safety and efficacy of this approach. Briquilimab was well tolerated and all patients have shown prompt and durable donor engraftment. This data indicates that it might be possible to remove irradiation or alkylator chemotherapy from the conditioning regimen in patients with FA without matched sibling donors thus decreasing the chances for cancer predisposition in these patients that have inherited DNA repair defects.

Emapalumab, a Fully Human Anti-Interferon Gamma Monoclonal Antibody, in Pediatric Patients with Primary Hemophagocytic Lymphohistiocytosis: Long-Term Follow-up of a Phase 2/3 Study

Background: Primary hemophagocytic lymphohistiocytosis (pHLH) is a rare, life-threatening genetically heterogeneous, autosomal recessive disorder, characterized by immune dysregulation and hyperinflammation. Acute treatment of pHLH has traditionally involved immunochemotherapy with glucocorticoids and etoposide to suppress hyperinflammation and facilitate the patient undergoing allogeneic hematopoietic stem cell transplantation (HSCT), the only potentially curative therapy. Emapalumab, a fully human immunoglobulin G1 anti-interferon-γ (IFNγ) monoclonal antibody, binds free and receptor-bound IFNγ, neutralizing its biologic activity. Emapalumab has demonstrated efficacy in patients with pHLH and has a favorable safety profile with no increase in the risk of adverse events (AEs), including infections, with increasing drug exposure prior to patients undergoing HSCT. Objective: To monitor the long-term safety and efficacy of emapalumab in patients with pHLH, including the period after undergoing HSCT. Methods: Long-term follow-up study (NCT02069899) of patients with pHLH who had received ≥1 dose of emapalumab in a multicenter, single-arm, open-label phase 2/3 clinical trial who were followed for 1 year after HSCT or last administration of emapalumab in the parent study (NCT01818492). Patients received emapalumab for 4 to 8 weeks in the parent study, which included a 4-week short-term follow-up period, during which patients could have undergone HSCT. Treatment with emapalumab could continue according to the parent study protocol during follow-up, if a favorable benefit/risk assessment was established. Any concomitant treatment ongoing at the time of study entry was continued as considered necessary by the investigators. Endpoints included safety, 1-year survival, and HSCT outcomes. Results: Overall, 37/45 patients who participated in the phase 2/3 study entered long-term follow-up, with 24 patients (64.9%) completing the study; 13 patients (35.1%) withdrew from the study, most commonly because of AEs (6 patients [46.2%]) and withdrawal of informed consent (2 patients [15.4%]). All patients had ≥1 concomitant medications including systemic corticosteroids and ≥1 systemic antimicrobial. Emapalumab treatment continued during long-term follow-up for 22 patients (59.5%). All patients experienced at least one AE during follow-up ( Table), most commonly infections or infestations (27 patients [73.0%] reported an infection AE). Most AEs were mild or moderate in intensity. Four patients (10.8%) had study drug-related AEs. Overall, 56.8% of patients experienced at least one severe AE. 28 patients (75.7%) experienced at least 1 serious AE (SAE), but only 1 patient (2.7%) had a treatment-related SAE (Coombs positive hemolytic anemia). Infusion-related reactions of rash were observed in 2 patients (5.4%), but these reactions were temporary and resolved without treatment. No patients experienced AEs leading to study drug discontinuation. Nine patients died during the study (4 prior to HSCT conditioning and 5 during the post-conditioning period). No study drug-related deaths were reported. 28 (75.7%) patients were alive at last observation or 1 year after last emapalumab dose and 33 (89.2%) survived to undergo HSCT or until 1 year after last emapalumab dose (whichever came first). 29 patients (78.4%) underwent HSCT, including 18 during long-term follow-up. 24 of the 29 (82.8%) patients who underwent HSCT were alive at last observation or 1 year after last emapalumab dose. Sustained engraftment was achieved in 23 patients (79.3%; 95% confidence interval, 61.6-90.2%). During the follow-up period, 6 patients (20.7%; 95% confidence interval [CI], 9.8-38.4%) experienced primary or secondary graft failure after undergoing HSCT and 7 patients (24.1%; 95% CI, 1.2-42.1%) had acute or chronic graft-versus-host disease. At the 12-months post-transplant visit, 25/26 (96.2%) patients maintained a complete response, while 1 (3.8%) patient was reported to have maintained a partial response. No pHLH reactivation was reported during the study. Conclusions: The long-term outcomes for patients with pHLH treated with emapalumab are consistent with observations made during a phase 2/3 study. A favorable safety profile was maintained, and a high proportion of patients received HSCT and achieved long-term survival.

Revumenib Maintenance Therapy Following Revumenib-Induced Remission and Transplant

Background: The potent and selective oral menin-histone-lysine N-methyltransferase 2A (KMT2A) inhibitor revumenib (SNDX-5613) induced complete remissions with clearance of residual disease in acute leukemias refractory to multiple previous lines of therapy ( Nature. 2023;615:920-924). Here we report outcomes following the resumption of revumenib after hematopoietic stem cell transplant (HSCT). Methods: Patients aged ≥30 days with relapsed or refractory (R/R) acute leukemias with genetic alterations associated with HOXA overexpression, including KMT2A-rearranged ( KMT2Ar) or nucleophosmin 1 ( NPM1)-mutated leukemias, were enrolled in the AUGMENT-101 phase 1/2, multicenter, open-label, dose-escalation study (NCT04065399). Patients received revumenib every 12 hours (q12h) in 28-day continuous cycles. Patients who achieved a complete response (composite definition [CRc]), morphological leukemia-free state, or partial response could undergo HSCT without leaving the study. Revumenib was stopped before the HSCT conditioning regimen but, per a protocol amendment, could be resumed after HSCT if the patient was in CRc. Measurable residual disease (MRD) was assessed using multiparameter flow cytometry and/or polymerase chain reaction. Results: Between November 5, 2019, and June 28, 2023, a total of 131 phase 1 patients were enrolled and treated in the AUGMENT-101 study. Nine patients with acute myeloid leukemia (AML) from the AUGMENT-101 study resumed revumenib (8 after transplant and 1 after a stem cell boost [Table 1]). Seven patients had KMT2Ar and 1 patient each had nucleoporin 98 rearranged (NUP98r) and mutated NPM1. Revumenib was resumed 59 to 180 days after HSCT (Table 2). Dose was reduced for 4 of 9 patients to mitigate adverse events of thrombocytopenia (n=3) and leg pain (n=1), and revumenib was discontinued in 4 of 9 patients because of progressive disease (n=2), cytopenias (n=1), and not reported (n=1). Revumenib duration of treatment (DOT) in the maintenance setting at the time of this analysis ranged from 23 to 588 days, with treatment ongoing for 5 of the 9 patients. CRc was maintained in 6 of 9 patients after HSCT and maintenance revumenib. One patient with reported MRD after HSCT converted to MRD-negative status following initiation of revumenib maintenance therapy. Overall, MRD-negative remissions were maintained in 5 patients as of the data cut off. Conclusions: With 3 patients on revumenib maintenance therapy for more than a year, long-term responses, including conversion to MRD-negative status, were seen in these heavily pretreated patients with AML. Resuming revumenib post HSCT had a tolerable safety profile consistent with that previously reported for the AUGMENT-101 study.

Outcomes for Children with High Risk Acute Myeloid Leukemia on the Myechild 01 International Phase III Clinical Trial

Background: Outcomes for pediatric acute myeloid leukemia (AML) remain disappointing, particularly for patients with poor risk cytogenetic/molecular genetic abnormalities and those who fail to achieve complete remission following course 1 of induction chemotherapy. Despite upfront allogeneic hematopoietic stem cell transplantation (HSCT) for these patients, high rates of relapse persist. The optimal approach to chemotherapy intensification and timing of HSCT for high risk (HR) patients remains unknown, with variable approaches employed by cooperative trial groups. Methods: The MyeChild 01 international phase III trial (NCT02724163) in children with de novo AML allocated patients up to 3 doses of gemtuzumab ozogamicin (GO 3mg/m 2/dose) during the first course of induction chemotherapy (mitoxantrone 12 mg/m2/dose x4; cytarabine 100 mg/m2/dose x20). Patients classified as HR after course 1 received FLA-Ida for course 2 followed by allogeneic HSCT. If required, a third course of bridging therapy (FLA) was given prior to HSCT. HR patients in MyeChild 01 included those with NUP98 fusions, selected KMT2A fusions ( KMT2A::MLLT10, KMT2A::MLLT4, KMT2A::AFF1, KMT2A::ABI1), CBFA2T3::GLIS2, DEK::NUP214, MECOM ( EVI1) rearrangements and all 12p abnormalities including MNX1::ETV6, in addition to the traditional HR abnormalities -7, -5/del(5q) and FLT3-ITD (without concurrent good risk abnormalities, including NPM1 mutations). Patients with induction failure after course 1 (≥ 5% blasts confirmed by flow) and those with non-HR cytogenetics/molecular genetics who remained MRD positive after course 2 (intermediate risk cytogenetics) or 3 (good risk cytogenetics) were also classified as HR. Here, we report the estimated 2-year outcomes for patients assigned HR post course 1 who received mitoxantrone and cytarabine and at least 1 dose of GO during course 1 (MA-GO). Outcomes of trial randomisations (1 vs 2 or 3 GO doses; consolidation for standard risk patients; HSCT conditioning) will be reported separately. Results: Of 749 patients enrolled at initial diagnosis, 183 received MA-GO during course 1 and were assigned HR post course 1. Of these, 172 (94%) patients had poor risk cytogenetic/molecular genetics, of which 32 also failed to achieve CR. Additionally, 11 (6%) patients did not have poor risk cytogenetic/molecular genetics but failed to achieve CR with MA-GO and thus were assigned to the HR group. Post course 1, 140 (77%) of these HR patients achieved CR/CRi, with 102/155 (66%) patients with evaluable samples achieving MRD negativity post course 1. Following course 1, 174 (95%) remained on trial and received FLA-Ida as course 2 and 163 patients (89%) proceeded to HSCT, 55 on trial and 108 following discontinuation from the trial. Estimated event-free survival (EFS) and overall survival (OS) at 2 years was 62% (95% CI: 56-70%) and 71% (64-78%) respectively (Figure 1 &amp; 2). Estimated cumulative incidence of relapse (CIR) and death in remission at 2 years was 26% (19-33%) and 7% (3-11%) respectively. For HR patients who received MA-GO in course 1, on trial FLA-Ida as course 2 and on or off trial HSCT (n = 156), 2 year estimated outcomes were EFS 69% (62-77%), OS 77% (70-85%) and CIR 24% (17-32%). The most common cytogenetic/molecular genetic abnormalities were rearrangements of KMT2A (50/183, 27%), with KMT2A::MLLT10 predominating (70%). FLT3-ITD (19%), NUP98 fusions (14%), -7 (13%), abn(12p) (11%), del(5q) (8%) and CBFA2T3::GLIS2 (6%) accounted for the majority of other abnormalities with outcomes varying by subtype. Collectively, KMT2A-rearranged patients had EFS and OS of 68% (55-83%) and 71% (59-86%) respectively and CIR of 26% (12-40%). For FLT3-ITD, the EFS and OS was 75% (62-92%) and 83% (69-99%) respectively with a CIR of 14% (1-26%). Of the 25 patients with a NUP98 fusion, 17 (68%) were NUP98::NSD1. The EFS and OS for patients with NUP98 fusions was 71% (55-92%) and 96% (88-100%) respectively with CIR 25% (1-48%). Conclusions: Two intensive courses of induction chemotherapy, including GO and mitoxantrone in course 1 and FLA-Ida in course 2, consolidated with allogeneic HSCT, appears to be an effective approach for most HR patients. 2 year estimated outcomes for HR patients compare favourably to recent trials of GO in pediatric AML, with particularly encouraging data for patients with KMT2A-r and FLT3-ITD.

Addition of Myeloablative Doses of Total Marrow Irradiation (TMI) to Myeloablative Fludarabine/Busulfan Conditioning for Allogeneic HSCT in Patients with High-Risk AML, CML, or Myelodysplastic Syndrome: A Phase II Clinical Trial

In allogeneic hematopoietic stem cell transplantation (HSCT) for high-risk myeloid disorders, the intensity of the conditioning regimen correlates with the risk of relapse, but its benefit may be offset by its risk of toxicity. The addition of increasing doses of TMI to myeloablative conditioning was previously shown to have acceptable toxicity in a phase I trial by our group (PMID 25234438), but the efficacy of this strategy remains uncertain. From 2017 to 2023, 31 patients with high-risk acute myeloid leukemia (AML, n=20) or myelodysplastic syndrome (MDS, n=5), or chronic myeloid leukemia (CML, n=3) in accelerated phase or blast crisis, were enrolled into a prospective phase II clinical trial of allogeneic HSCT using myeloablative TMI at 9Gy in combination with standard myeloablative fludarabine (160 mg/m2) and targeted IV busulfan (daily exposure of AUC 4800 μM*min over 3 hours) (FluBu4) chemotherapy. TMI was delivered by using volumetric modulated arc therapy (VMAT) at 1.5Gy twice per day for 3 days for a total of 9Gy. The primary objective of the trial was to achieve &amp;gt;50% Disease-Free Survival (DFS) at 1 year. Here, we report the results on 28 patients who received the TMI-based transplant, whereas among the remaining 3, 1 had not started the conditioning yet and 2 became ineligible due to progression of disease and deterioration of performance status, respectively. The study included patients with matched related donors (MRD, n=9) receiving TMI/FluBu4 as a preparative regimen and patients with matched unrelated (MUD, n=13) or 1-antigen mismatched unrelated (MMUD, n=6) donors receiving conditioning with TMI/FluBu4 + rabbit anti-thymocyte globulin (rATG). Graft-versus-host disease (GVHD) prophylaxis was with methotrexate and tacrolimus, and palifermin was used to prevent severe mucositis. Patients' gender ratio was 16 female/12 male; race was Caucasian in 17 patients, African American in 4, Latino in 7; and median age was 53 years (range: 20-68). The median HCT-Comorbidity Index (HCT-CI) was 3 (range: 0-7). All 20 AML patients were at high risk of relapse because of adverse cytogenetic or molecular profile at diagnosis (n=13), or in second complete remission (CR2) (n=2), or with active disease at the time of transplant (n=5). All patients received peripheral blood stem cells (PBSC) (median CD34+ cell dose: 8.5 x 10 6/kg, range: 2.4-19.9) and fully engrafted. The median time to absolute neutrophil count (ANC) and platelet engraftment was 14 (range: day 9-22) and 15 (range: day 9-43) days, respectively. Grade 3-4 extramedullary toxicities were: mucositis in 57% (n=16), nausea/vomiting in 11% (n=3) and diarrhea in 7% (n=2) of the patients. Acute GVHD grade III-IV was seen in 3 patients (10%). Moderate/severe chronic GVHD was observed in 10 patients (36%). With a median follow-up of 1315 days (range: 158-1925 days) for patients alive, the overall 1 year and current overall survival were 73% and 64%, respectively. GVHD-Free Relapse-Free Survival (GRFS) at 1-year was 54%. Of 5 AML patients transplanted with active disease, 3 were alive and in remission at 1 year and at current date, while 2 died of relapsed disease. Of 28 patients in the study, 6 relapsed/progressed (21%) and 5 of them died of the disease (18%); whereas 5 patients (18%) died of transplant-related mortality (TRM) (2 deaths from septic shock, 1 from disseminated toxoplasmosis, 1 from idiopathic pneumonia and 1 from unknown causes). Kaplan Meyer curves for Overall Survival (OS) and DFS are shown in Figure 1 and 2, respectively. Addition of myeloablative TMI at 9Gy to standard myeloablative targeted FluBu4 was well tolerated and achieved very encouraging results in a group of patients with myeloid malignancies at high risk of relapse (clinicaltrials.gov Identifier: NCT03121014).

Efficacy of the Allosteric MEK Inhibitor Trametinib in Relapsed and Refractory Juvenile Myelomonocytic Leukemia: A Report from the Children's Oncology Group

Background: Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative neoplasm of infants and toddlers. Upfront therapies typically include high-dose cytarabine or azacitidine, but the only definitive treatment is hematopoietic stem cell transplantation (HSCT). While HSCT cures ~50% of patients, the prognosis is dismal for those who relapse. In the absence of a second HSCT, patients who relapse have a 2-year overall survival of ~10%. JMML is initiated by germline and somatic driver mutations in NF1, KRAS, NRAS, PTPN11, and CBL. These mutations converge on Ras signaling, leading to elevated levels of active Ras-GTP in specific cell lineages. Genetically engineered mouse (GEM) models accurately model key molecular, biologic, and biochemical features of JMML. Preclinical trials of the allosteric MEK inhibitors in Kras and Nf1 mutant mice demonstrated dramatic phenotypic responses with reduction in white blood cell counts, resolution of splenomegaly, and reversion to normal erythropoiesis. Based on the promising efficacy signal in GEM models, we evaluated trametinib, an orally bioavailable allosteric inhibitor of MEK1/2, in a prospective clinical trial in children with relapsed or refractory JMML to determine the overall response rate to trametinib. Results: Ten infants and children with JMML (median age 23.6 months) were enrolled and all were evaluable for safety and efficacy. Patients received age-adjusted dosing of trametinib for 28-day cycles and could remain on study for up to 12 cycles in the absence of disease progression or toxicity. A clonal Ras pathway mutation was confirmed in the blood and/or bone marrow of all patients. The objective response rate was 50% (two complete and three partial clinical responses). Four patients proceeded to HSCT after receiving protocol therapy and remain alive in complete remission with undetectable levels of the Ras pathway mutation identified at enrollment. Three additional patients completed 12 cycles of trametinib and continue to receive off-protocol therapy 6-24 months later with no change in the variant allele frequency of the underlying Ras pathway mutation. The remaining three patients had progressive disease with two demonstrating molecular evolution by the end of cycle 2. Paired pre- and post-trametinib RNASeq and proteomic analyses confirmed on-target biochemical effects of trametinib with down-regulation of both Ras/MAPK pathway related gene expression and MEK1/2 kinase activity, respectively. To gain deeper insight into how trametinib might affect distinct populations of hematopoietic cells, we generated single cell RNASeq data before and after treatment. The most prominent finding was a reduction in the proportions of classical and non-classical monocytes and broad downregulation of immune-related pathways in all cell populations. However, the downregulation of MAPK signaling genes was confined to specific cell types including, macrophages, classical monocytes, and granulocyte-monocyte progenitors, which uniquely displayed downregulated KRAS-related signatures following treatment. High DNA methylation and the presence of &amp;gt;1 mutation at enrollment correlated with lack of response to trametinib. Conclusions: We conducted an open label, phase 2 trial of trametinib in children with relapsed or refractory JMML. This is the first completed study of a MEK inhibitor in any hematologic malignancy in children. The trial met its primary objective and demonstrated a 50% objective response rate with 70% of patients bridging to a successful HSCT or completing the maximum 12 cycles permitted on study. The three patients who completed 12 cycles continue to receive trametinib off study for as long as 2 years. Although limited by a small number of patients, the long-term survival, and correlative molecular analyses from this trial raise provocative questions about whether certain patients with JMML might be spared the long-term adverse health risks of genotoxic HSCT conditioning regimens based on favorable molecular characteristics at diagnosis. This hypothesis will now be tested in a national, risk-stratified therapeutic trial (NCT05849662) of trametinib in combination with azacitidine in newly diagnosed patients. The authors would like to acknowledge funding and support from: NCTN Operations Center Grant (U10CA180886), NCTN Statistics &amp; Data Center Grant (U10CA180899), and the St. Baldrick's Foundation.

Safety and survival analysis of haplo-identical hematopoietic stem cell transplantation in patients with severe aplastic anemia who had previous failure to antithymoglobulin treatment

Objective: To investigate the safety and efficacy of haplo-identical hematopoietic stem cell transplantation (haplo-HSCT) conditioning with the same dosage form of antithymoglobulin (ATG) in patients with severe aplastic anemia (SAA) failure to ATG. Methods: This was a retrospective cohort study. A total of 65 patients with SAA who failed ATG treatment and received haplo-HSCT conditioning with the same dosage of ATG at the Institute of Hematology, Peking University People's Hospital between July 2008 and October 2020 were included as the ATG treatment failure group. An additional 65 SAA patients who applied ATG for the first time during haplo-HSCT were randomly selected by stratified sampling as the first-line haplo-HSCT group. Baseline clinical data and follow-up data of the two groups were collected. Conditioning-related toxicity within 10 days after ATG application and long-term prognosis were analyzed. The Kaplan-Meier was used to calculate the overall survival rate, and the Log-rank test was applied to compare the rates of the two groups. Results: In the ATG treatment failure group, there were 36 males and 29 females, and the age at the time of transplantation [M (Q1, Q3)] was 16 (8, 25) years. In the first-line haplo-HSCT group, there were 35 males and 30 females, with a median age of 17 (7, 26) years. Within 10 days of ATG application, the incidence of noninfectious fever, noninfectious diarrhea, and liver injury in the ATG treatment failure group was 78% (51 cases), 45% (29 cases), and 28% (18 cases), respectively, and in the first-line haplo-HSCT group was 74% (48 cases), 54% (35 cases), and 25% (16 cases), respectively; the difference between the two groups was not statistically significant for any of these three parameters (all P>0.05). For graft-versus-host disease (GVHD), there was no significant difference between the ATG treatment failure group and the first-line haplo-HSCT group in the development of 100 day Ⅱ to Ⅳ acute GVHD (29.51%±0.35% vs. 25.42%±0.33%), Ⅲ to Ⅳ acute GVHD (6.56%±0.10% vs. 6.78%±0.11%), and 3-year chronic GVHD (26.73%±0.36% vs. 21.15%±0.30%) (all P>0.05). Three-year overall survival (79.6%±5.1% vs. 84.6%±4.5%) and 3-year failure-free survival (79.6%±5.1% vs. 81.5%±4.8%) were also comparable between these two groups (both P>0.05). Conclusions: Compared with no exposure to ATG before HSCT, similar early adverse effects and comparable survival outcomes were achieved in patients with SAA who failed previous ATG treatment and received haplo-HSCT conditioning with the same dosage form of ATG. This might indicate that previous failure of ATG treatment does not significantly impact the efficacy and safety of salvaging haplo-HSCT in patients with SAA.

Low rate of nonrelapse mortality in under-4-year-olds with ALL given chemotherapeutic conditioning for HSCT: a phase 3 FORUM study

AbstractAllogeneic hematopoietic stem cell transplantation (HSCT) is highly effective for treating pediatric high-risk or relapsed acute lymphoblastic leukemia (ALL). For young children, total body irradiation (TBI) is associated with severe late sequelae. In the FORUM study (NCT01949129), we assessed safety, event-free survival (EFS), and overall survival (OS) of 2 TBI-free conditioning regimens in children aged <4 years with ALL. Patients received fludarabine (Flu), thiotepa (Thio), and either busulfan (Bu) or treosulfan (Treo) before HSCT. From 2013 to 2021, 191 children received transplantation and were observed for ≥6 months (median follow-up: 3 years). The 3-year OS was 0.63 (95% confidence interval [95% CI], 0.52-0.72) and 0.76 (95% CI, 0.64-0.84) for Flu/Thio/Bu and Flu/Thio/Treo (P = .075), respectively. Three-year EFS was 0.52 (95% CI, 0.41-0.61) and 0.51 (95% CI, 0.39-0.62), respectively (P = .794). Cumulative incidence of nonrelapse mortality (NRM) and relapse at 3 years were 0.06 (95% CI, 0.02-0.12) vs 0.03 (95% CI: <0.01-0.09) (P = .406) and 0.42 (95% CI, 0.31-0.52) vs 0.45 (95% CI, 0.34-0.56) (P = .920), respectively. Grade >1 acute graft-versus-host disease (GVHD) occurred in 29% of patients receiving Flu/Thio/Bu and 17% of those receiving Flu/Thio/Treo (P = .049), whereas grade 3/4 occurred in 10% and 9%, respectively (P = .813). The 3-year incidence of chronic GVHD was 0.07 (95% CI, 0.03-0.13) vs 0.05 (95% CI, 0.02-0.11), respectively (P = .518). In conclusion, both chemotherapeutic conditioning regimens were well tolerated and NRM was low. However, relapse was the major cause of treatment failure. This trial was registered at www.clinicaltrials.gov as #NCT01949129.

Treosulfan-Based Conditioning Regimen In Pediatric Hematopoietic Stem Cell Transplantation: A Retrospective Analysis on Behalf of the Spanish Group for Hematopoietic Transplantation and Cellular Therapy (GETH-TC)

Data on treosulfan-based conditioning regimens are little by little increasing, and the benefits of this approach are consistent, particularly regarding acute toxicity. This study aims to describe the results of treosulfan-based conditioning regimens in children, focusing on toxicity and outcomes when used to treat both malignant and non-malignant diseases. Retrospective observational study on pediatric patients treated in Spain with treosulfan-based conditioning regimens before hematopoietic stem cell transplantation (HSCT), based on data collection from electronic clinical records. One hundred and sixty treosulfan-based conditioning HSCTs to treat non-malignant diseases (n=117) or malignant diseases (n=43) in 158 children and adolescents are reported. Median age at HSCT was 5.1 years (IQR: 2-10). The most frequent diagnoses were primary immunodeficiency (n=42; 36%) and sickle cell disease (n=42; 36%) in the non-malignant cohort and acute lymphoblastic leukemia (n=15; 35%) in the malignant cohort. Engraftment occurred in 97% of the patients. There was a longer median time to neutrophil engraftment (17 vs. 14 days; p=0.008) and platelet engraftment (20 vs. 15 days; p=0.002) in the non-malignant cohort. The 1-year cumulative incidence of VOD was 7.98 (95%CI [4.6-13.6]), with no significant differences between cohorts. The 1-year cumulative incidence of grade III-IV aGvHD was higher in the malignant cohort (18% vs. 3.2%; p=0.011). Overall, cGvHD was more frequently observed in the malignant cohort for both total incidence (9 vs. 3%; p<0.001) and 2-year cumulative incidence of total cGvHD (16 vs. 1.9%; p<0.001). The 2-year cumulative TRM was 15%, with no differences between cohorts. 5-year Overall Survival was 80% (95%CI [72-86]) and was higher in the non-malignant cohort (87 vs. 61%; p=0.01). The 2-year cumulative incidence of relapse in the malignant cohort was 25%. 5-year cumulative GRFS rate was 60% (95%CI [51-70]) and was higher in the non-malignant cohort (72 vs. 22%; p<0.001). The treosulfan-based radiation-free conditioning regimen is feasible, achieving a high engraftment rate and 5-year overall survival. A treosulfan-based conditioning regimen is an emerging option for the first HSCT in non-malignant diseases.

Treosulfan Versus Busulfan-based Conditioning in Pediatric Patients Undergoing Hematopoietic Stem Cell Transplantation: A Systematic Review and Meta-analysis.

It is unclear whether there is a difference in outcomes with treosulfan or busulfan-based conditioning in pediatric patients undergoing hematopoietic stem cell transplantation (HSCT). We reviewed the evidence on this topic through a systematic review and meta-analysis, the comparison between treosulfan and busulfan-based conditioning in pediatric patients undergoing HSCT for instance. Six studies were included. Meta-analysis showed that there was no difference in the incidence of acute graft versus host disease (odds ratio [OR]: 0.96; 95% CI: 0.57, 1.61), grade II to IV acute graft versus host disease (OR: 1.19; 95% CI: 0.83, 1.72), chronic GVHD (OR: 1.18; 95% CI: 0.70, 2.00), and veno-occlusive disease (OR: 0.92; 95% CI: 0.22, 3.85) between treosulfan and busulfan groups. Pooled analysis indicated marginally better survival with treosulfan-based conditioning (OR: 1.57; 95% CI: 1.00, 2.44), however, these results were unstable on sensitivity analysis. A meta-analysis found no difference in transplant-related mortality (OR: 0.70; 95% CI: 0.34, 1.42) between the two groups. Retrospective data from a heterogenous population indicates that there is no difference in the rate of GVHD after treosulfan versus busulfan-based conditioning for pediatric HSCT. A marginal improvement in survival was noted with treosulfan but the results remained unstable. Future randomized controlled trials are needed to provide better evidence.