Blinatumomab Therapy Is Associated with Favorable Outcomes after Allogeneic Hematopoietic Cell Transplantation in Pediatric Patients with B Cell Acute Lymphoblastic Leukemia.

Blinatumomab, a bispecific T cell engager that binds CD19 in leukemic cells and CD3 in cytotoxic T cells and leads to leukemic blast lysis, is often used in pediatric patients with relapsed/refractory (R/R) B cell acute lymphoblastic leukemia (B-ALL) prior to allogeneic hematopoietic cell transplantation (allo-HCT). Concerns about the potential risk of blinatumomab-related immune-mediated toxicities after allo-HCT have not been adequately addressed. These include graft-versus-host disease (GVHD), delayed engraftment, and graft failure or rejection. Pediatric-specific data reporting post-HCT outcomes of patients treated with blinatumomab are scarce and limited to small cohorts. We sought to investigate the clinical outcomes of pediatric patients with R/R B-ALL who received blinatumomab therapy pre-HCT, focusing on overall survival (OS), leukemia-free survival (LFS), cumulative incidence of relapse (CIR), and nonrelapse mortality (NRM), as well as the incidence of immune-mediated post-HCT complications including GVHD, delayed neutrophil or platelet engraftment, graft failure, and graft rejection. We also investigated blinatumomab's effects on B cell reconstitution based on achievement of i.v. immunoglobulin (IVIG) independence post-HCT. This single-center, retrospective study included patients with B-ALL receiving blinatumomab therapy before undergoing allo-HCT, with transplantation performed between 2016 and 2021 at our institution. Patients receiving blinatumomab for relapse after allo-HCT were excluded. Patients receiving chemotherapy alone before allo-HCT during the same period composed the control group. Seventy-two patients were included, 31 of whom received blinatumomab before allo-HCT. Survival estimates were obtained using the Kaplan-Meier method, and the log-rank test was used to analyze differences between groups. Categorical variables were compared between groups using the chi-square test or Fisher exact test, and continuous variables were compared using the Wilcoxon rank-sum test. Cumulative incidences were estimated using the competing risks method, and Gray's test was used to analyze differences between groups. A Cox proportional hazards regression model was used for univariate and multivariable analyses for OS. Landmark analysis was performed at the set time points of 30 days and 100 days post-allo-HCT. Most patients in the study cohort had high-risk relapsed B-ALL. Blinatumomab therapy induced minimal residual disease (MRD)-negative remissions in all patients, whereas 5 patients (12.2%) receiving chemotherapy alone had persistent MRD pre-allo-HCT. Time from the start of therapy to the date of allo-HCT was shorter for patients who received blinatumomab compared with those who received chemotherapy (P < .0001). Blinatumomab therapy was associated with greater LFS compared to chemotherapy alone (P = .049), but when limited to 1 year, LFS was not significantly different from control (P = .066). There appeared to be higher OS, lower CIR, and lower NRM in patients receiving blinatumomab compared to the control group; however, the differences were not significant. None of the variables assessed in multivariable analysis was associated with differences in OS. When compared to the controls, blinatumomab therapy did not result in a higher incidence of acute or chronic GVHD, delayed neutrophil or platelet engraftment, or graft failure or rejection. The time to IVIG infusion independence post-allo-HCT was similar in the 2 groups. This study supports the use of blinatumomab salvage therapy for R/R B-ALL before allo-HCT given its efficacy in inducing MRD-negative remissions and optimizing LFS, as well as its lack of association with an increased incidence of post-allo-HCT adverse immune-mediated toxicities. Larger, prospective studies are needed to confirm these findings and to investigate blinatumomab's effects in long-term post-allo-HCT events.

Hematopoietic stem cell transplantation for B-thalassemia major with alemtuzumab.

While matched related donor (MRD) allogeneic hematopoietic stem cell transplantation (HSCT) is a curative option for transfusion-dependent beta-thalassemia (TDT), the use of alternative sources has increased, resulting in the exploration of novel transplant-conditioning regimens to reduce the contribution of graft-versus-host disease (GVHD) and graft failure (GF) to transplant-related morbidity and mortality. Alemtuzumab is a CD52 monoclonal antibody that has been successfully incorporated into myeloablative conditioning regimens for other hematologic conditions, yet there have been limited studies regarding the use of alemtuzumab in HSCT for TDT. The purpose of this study was to evaluate engraftment, incidence of GVHD, and transplant related morbidity and mortality in patients with TDT who received alemtuzumab in addition to standard busulfan-based conditioning. The primary endpoint was severe GVHD-free, event-free survival (GEFS). Our cohort included 24 patients with a median age of 6.8 years (range 1.5-14.9). Eleven patients received a 10/10 MRD HSCT, eleven 10/10 unrelated donor (UD), and two mismatched UD. All patients achieved primary engraftment. For all patients, 5-year GEFS was 77.4% and 5-year overall survival (OS) was 91%. The 5-year cumulative incidence of GF (attributed to poor graft function) without loss of donor chimerism was 13.8% (95% CI: 4.5, 35.3). We report low rates of significant acute GVHD grade II-IV (12.5%) and chronic GVHD (4.4%). Younger age and MRD were associated with significantly improved GEFS, OS and EFS. Our results show that the use of alemtuzumab promotes stable engraftment, may reduce rates of severe GVHD, and results in acceptable GEFS, OS, and EFS.

Cord blood transplantation for nonmalignant disorders: early functional immunity and high survival.

There is no consensus on the best donor for children with nonmalignant disorders and immune deficiencies in the absence of a matched related donor (MRD). We evaluated the 2-year overall survival (OS) after umbilical cord blood transplantation (UCBT) in patients with nonmalignant disorders from 2009 to 2020 enrolled in a prospective clinical trial using either 5/6 or 6/6 UCB as the cell source. Patients receive a fully ablative busulfan, cyclophosphamide, and fludarabine without serotherapy. Fifty-five children were enrolled, median age 5 months (range, 1-111 months); primary immune deficiency (45), metabolic (5), hemophagocytic lymphohistiocytosis (1), and hematologic disorders (4). Twenty-six patients had persistent infections before transplant. Nineteen of them (34%) were 6/6 matched, and 36 (66%) were 5/6 human leukocyte antigen-matched. The OS at 2 years was 91% (95% cumulative incidence, 79-96), with a median follow-up of 4.3 years. The median time to neutrophil and platelet recovery were 17 days (range, 5-39 days) and 37 days (range, 20-92 days), respectively. All but one evaluable patient achieved full donor chimerism. The cumulative incidence of acute GVHD grades 2-4 on day 100 was 16% (n = 9). All patients with viral infections at the time of transplant cleared the infection at a median time of 54 days (range, 44-91 days). All evaluable patients underwent correction of their immune or metabolic defects. We conclude that in the absence of MRD, UCBT following myeloablative conditioning without serotherapy is an excellent curative option in young children with nonmalignant disorders. This trial has been registered at www.clinicaltrials.gov as NCT00950846.

Rituximab as adjunctive therapy to BEAM conditioning for autologous stem cell transplantation in Hodgkin lymphoma.

While high-dose chemotherapy followed by autologous stem cell transplantation (ASCT) leads to improved disease-free survival (DFS) for children and adults with relapsed/refractory Hodgkin lymphoma (HL), relapse remains the most frequent cause of mortality post-transplant. Rituximab has been successfully incorporated into regimens for other B-cell lymphomas, yet there have been limited studies of rituximab in HL patients. We hypothesized that adding rituximab to BEAM (carmustine, etoposide, cytarabine, melphalan) conditioning would reduce relapse risk in HL patients post-transplant. Here, we retrospectively review the outcomes of patients with relapsed/refractory HL who received rituximab in addition to BEAM. The primary outcome was DFS. Our cohort included 96 patients with a median age of 28 years (range, 6-76). Majority of patients (57%) were diagnosed with advanced (Stage III-IV) disease, and 62% were PET negative pre-transplant. DFS was 91.5% at 1 year [95% CI 86-98%], and 78% at 3 years [95% CI 68-88%]. NRM was 0% and 3.5% at 1-year [95% CI 0-3%] and 3-years [95% CI 0-8.5%], respectively. 25% of patients developed delayed neutropenia, with 7% requiring infection-related hospitalizations, and one death. We have demonstrated excellent outcomes for patients receiving rituximab with BEAM conditioning for relapsed/refractory HL. Future comparative studies are needed to better determine whether rituximab augments outcomes post-transplant.

Matched related hematopoietic cell transplant for sickle cell disease with alemtuzumab: the Texas Children's Hospital experience.

Serotherapeutic agents facilitate engraftment and prevent graft-versus-host disease (GVHD) following hematopoietic stem cell transplant. Anti-thymocyte globulin is generally added to conditioning chemotherapy for matched related donor transplant (MRD-HCT) for sickle cell disease (SCD). Alemtuzumab, however, is appealing due to its broad lymphocyte killing that may achieve very low rejection and GVHD rates. To assess the impact of alemtuzumab in MRD-HCT for SCD, we retrospectively reviewed transplant-related outcomes and markers of immunity in 38 consecutive patients at Texas Children's Hospital having received myeloablative conditioning with alemtuzumab. Median follow-up was 4.8 years (range: 0.2-17). All patients engrafted. Donor chimerism was mixed in 47.1% of patients at ≥2-years. Donor chimerism <50% was uncommon (n = 2). One patient with low myeloid chimerism (19%) had sickle-related hemolysis at 10-years. Incidence of acute GVHD grade II-IV (5.3%) and extensive chronic GVHD (2.8%) was very low. Five-year event-free survival (EFS) and composite chronic GVHD-EFS were excellent at 94.7% (95% CI: 80.3, 98.6) and 89.2% (95% CI: 73.7, 95.8), respectively. Infections did not contribute to mortality although cytomegalovirus reactivation occurred commonly in the first 3 months after transplant. Our data suggest potential for alemtuzumab in myeloablative transplant for children with SCD although further evaluation in older patients and with unrelated donors is warranted.

Safety and feasibility of virus-specific T cells derived from umbilical cord blood in cord blood transplant recipients.

Adoptive transfer of virus-specific T cells (VSTs) has been shown to be safe and effective in stem cell transplant recipients. However, the lack of virus-experienced T cells in donor cord blood (CB) has prevented the development of ex vivo expanded donor-derived VSTs for recipients of this stem cell source. Here we evaluated the feasibility and safety of ex vivo expansion of CB T cells from the 20% fraction of the CB unit in pediatric patients receiving a single CB transplant (CBT). In 2 clinical trials conducted at 2 separate sites, we manufactured CB-derived multivirus-specific T cells (CB-VSTs) targeting Epstein-Barr virus (EBV), adenovirus, and cytomegalovirus (CMV) for 18 (86%) of 21 patients demonstrating feasibility. Manufacturing for 2 CB-VSTs failed to meet lot release because of insufficient cell recovery, and there was 1 sterility breach during separation of the frozen 20% fraction. Delayed engraftment was not observed in patients who received the remaining 80% fraction for the primary CBT. There was no grade 3 to 4 acute graft-versus-host disease (GVHD) associated with the infusion of CB-VSTs. None of the 7 patients who received CB-VSTs as prophylaxis developed end-organ disease from CMV, EBV, or adenovirus. In 7 patients receiving CB-VSTs for viral reactivation or infection, only 1 patient developed end-organ viral disease, which was in an immune privileged site (CMV retinitis) and occurred after steroid therapy for GVHD. Finally, we demonstrated the long-term persistence of adoptively transferred CB-VSTs using T-cell receptor-Vß clonotype tracking, suggesting that CB-VSTs are a feasible addition to antiviral pharmacotherapy.

Childhood Rhabdomyosarcoma in Association With a RASopathy Clinical Phenotype and Mosaic Germline SOS1 Duplication.

Childhood rhabdomyosarcoma (RMS) accounts for approximately 3.5% of cancer cases among children 0 to 14 years of age. Genetic conditions associated with high risk of childhood RMS include Li-Fraumeni syndrome, pleuropulmonary blastoma, Beckwith-Wiedemann syndrome, and some RASopathies, such as neurofibromatosis type 1, Costello syndrome (CS), and Noonan syndrome (NS). Here, we report the rare case of a 4-year-old girl with clinical features of NS who developed an embryonal RMS of the chest and needed emergent treatment. Molecular genetic testing identified a de novo, large, mosaic duplication of chromosome 2 encompassing the SOS1 gene, presumably caused by a mosaic, unbalanced translocation between chromosomes 2 and 17 found on routine cytogenetic analysis. Sequence analysis of all known genes causing Noonan spectrum disorders was negative. RMS has been reported in a few patients with NS, associated in very few with germline SOS1 mutations, but none with copy number abnormalities. This is the first report to our knowledge of early-onset RMS developing in a child with features of NS and a mosaic RAS pathway gene aberration, a large SOS1 duplication. We hypothesize that the inciting event for tumor development in this case is due to the germline mosaic duplication of SOS1, which was duplicated in all cells of the tumor, and the ultimate development of the tumor was further driven by multiple chromosomal aberrations in the tumor itself, all described as somatic events in isolated RMS tumors.