Exagamglogene Autotemcel for Severe Sickle Cell Disease

BACKGROUND

Exagamglogene autotemcel (exa-cel) is a nonviral cell therapy designed to reactivate fetal hemoglobin synthesis by means of ex vivo clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 gene editing of autologous CD34+ hematopoietic stem and progenitor cells (HSPCs) at the erythroid-specific enhancer region of BCL11A.

METHODS

We conducted a phase 3, single-group, open-label study of exa-cel in patients 12 to 35 years of age with sickle cell disease who had had at least two severe vaso-occlusive crises in each of the 2 years before screening. CD34+ HSPCs were edited with the use of CRISPR-Cas9. Before the exa-cel infusion, patients underwent myeloablative conditioning with pharmacokinetically dose-adjusted busulfan. The primary end point was freedom from severe vaso-occlusive crises for at least 12 consecutive months. A key secondary end point was freedom from inpatient hospitalization for severe vaso-occlusive crises for at least 12 consecutive months. The safety of exa-cel was also assessed.

RESULTS

A total of 44 patients received exa-cel, and the median follow-up was 19.3 months (range, 0.8 to 48.1). Neutrophils and platelets engrafted in each patient. Of the 30 patients who had sufficient follow-up to be evaluated, 29 (97%; 95% confidence interval [CI], 83 to 100) were free from vaso-occlusive crises for at least 12 consecutive months, and all 30 (100%; 95% CI, 88 to 100) were free from hospitalizations for vaso-occlusive crises for at least 12 consecutive months (P<0.001 for both comparisons against the null hypothesis of a 50% response). The safety profile of exa-cel was generally consistent with that of myeloablative busulfan conditioning and autologous HSPC transplantation. No cancers occurred.

CONCLUSIONS

Treatment with exa-cel eliminated vaso-occlusive crises in 97% of patients with sickle cell disease for a period of 12 months or more. (CLIMB SCD-121; ClinicalTrials.gov number, NCT03745287.).

Antiviral cellular therapy for enhancing T-cell reconstitution before or after hematopoietic stem cell transplantation (ACES): a two-arm, open label phase II interventional trial of pediatric patients with risk factor assessment

Viral infections remain a major risk in immunocompromised pediatric patients, and virus-specific T cell (VST) therapy has been successful for treatment of refractory viral infections in prior studies. We performed a phase II multicenter study (NCT03475212) for the treatment of pediatric patients with inborn errors of immunity and/or post allogeneic hematopoietic stem cell transplant with refractory viral infections using partially-HLA matched VSTs targeting cytomegalovirus, Epstein-Barr virus, or adenovirus. Primary endpoints were feasibility, safety, and clinical responses (>1 log reduction in viremia at 28 days). Secondary endpoints were reconstitution of antiviral immunity and persistence of the infused VSTs. Suitable VST products were identified for 75 of 77 clinical queries. Clinical responses were achieved in 29 of 47 (62%) of patients post-HSCT including 73% of patients evaluable at 1-month post-infusion, meeting the primary efficacy endpoint (>52%). Secondary graft rejection occurred in one child following VST infusion as described in a companion article. Corticosteroids, graft-versus-host disease, transplant-associated thrombotic microangiopathy, and eculizumab treatment correlated with poor response, while uptrending absolute lymphocyte and CD8 T cell counts correlated with good response. This study highlights key clinical factors that impact response to VSTs and demonstrates the feasibility and efficacy of this therapy in pediatric HSCT.

An International Learning Collaborative Phase 2 Trial for Haploidentical Bone Marrow Transplant in Sickle Cell Disease

In the setting of a learning collaborative, we conducted an international multicenter phase 2 clinical trial testing the hypothesis that non-myeloablative related haploidentical BMT with thiotepa and post-transplant cyclophosphamide (PTCy) will result in 2-year event-free survival (no graft failure or death) of at least 80%. A total of 70 participants (median age 19.1 (IQR 14.1 - 25.0) were evaluable based on the conditioning protocol. Graft failure occurred in 11.4% (8/70) and only in participants <18 years (p=0.001); all had autologous reconstitution. After a median follow-up of 2.4 years (IQR 1.5-3.9), the 2-year Kaplan-Meier-based probability of event-free survival was 82.6% (95% CI 71.4%-89.7%). The 2-year overall survival was 94.1% (95% CI 84.9%-97.7%) with no difference between the child and adult participants (p=0.889). After excluding participants with graft failure (n=8), participants with engraftment had median whole blood donor chimerism values at D+180 and D+365 post-transplant of 100.0% (IQR 99.8 - 100.0%; n=59) and 100.0% (IQR 100.0 - 100.0%; n=58), respectively, and 96.6% (57/59) were off immunosuppression at 1-year post-transplant. The 1-year grades III-IV acute graft versus host disease (GvHD) rate was 10.0% (95% CI 4.6 - 18.6%), and the 2-year moderate-severe chronic GvHD rate was 10.0% (95% CI 4.6 - 18.6%). Five participants (7.1%) died from infectious complications. We demonstrate that non-myeloablative haploidentical BMT with thiotepa and PTCy is a readily available curative therapy for most adults, even those with organ damage, instead of the more expensive myeloablative gene therapy and gene editing. Additional strategies are required for children to decrease graft failure rates (ClinicalTrials.gov identifier NCT01850108).

Long-Term Organ Function After HCT for SCD: A Report From the Sickle Cell Transplant Advocacy and Research Alliance

Hematopoietic cell transplantation (HCT) is an established cure for sickle cell disease (SCD) supported by long-term survival, but long-term organ function data are lacking. We sought to describe organ function and assess predictors for dysfunction in a retrospective cohort (n = 247) through the Sickle cell Transplant Advocacy and Research alliance. Patients with <1-year follow-up or graft rejection/second HCT were excluded. Organ function data were collected from last follow-up. Primary measures were organ function, comparing pre- and post-HCT. Bivariable and multivariable analyses were performed for predictors of dysfunction. Median age at HCT was 9.4 years; the majority had HbSS (88.2%) and severe clinical phenotype (65.4%). Most received matched related (76.9%) bone marrow (83.3%) with myeloablative conditioning (MAC; 57.1%). Acute and chronic graft-versus-host disease (GVHD) developed in 24.0% and 24.8%. Thirteen patients (5.3%) died ≥1 year after HCT, primarily from GVHD or infection. More post-HCT patients had low ejection or shortening fractions than pre-HCT (0.6% → 6.0%, P = .007 and 0% → 4.6%, P = .003). The proportion with lung disease remained stable. Eight patients (3.2%) had overt stroke; most had normal (28.3%) or stable (50.3%) brain magnetic resonance imaging. On multivariable analysis, cardiac dysfunction was associated with MAC (odds ratio [OR] = 2.71; 95% confidence interval [CI], 1.09-6.77; P = .033) and severe acute GVHD (OR = 2.41; 95% CI, 1.04-5.62; P = .041). Neurologic events were associated with central nervous system indication (OR = 2.88; 95% CI, 2.00-4.12; P < .001). Overall organ dysfunction was associated with age ≥16 years (OR = 2.26; 95% CI, 1.35-3.78; P = .002) and clinically severe disease (OR = 1.64; 95% CI, 1.02-2.63; P = .043). In conclusion, our results support consideration of HCT at younger age and use of less intense conditioning.

Gene Editing for Sickle Cell Disease and Transfusion Dependent Thalassemias- A cure within reach

Sickle cell disease (SCD) is associated with significant morbidity and shortened life expectancy. Similarly, patients with transfusion dependent beta thalassemia (TdT) require life-long transfusion therapy, chelation therapy and significant organ dysfunction. Allogeneic transplantation from a matched family donor provided the only curative option for patients with SCD and TdT. Unfortunately, less than 20% of patients have a fully matched related donor and results using unrelated donor transplant were associated with high rate of complications. Ex vivo gene therapy through globin gene addition has been investigated extensively and recent encouraging preliminary data resulted in regulatory approval in patients with TdT. Recent improvements in our understanding of the molecular pathways controlling erythropoiesis and globin switching from fetal hemoglobin to adult hemoglobin offer a new and exciting therapeutic options. Rapid and substantial advances in genome editing tools using CRISPR/Cas9, have raised the possibility of genetic editing and correction in patient derived hematopoietic stem and progenitor cells. We will review results of gene editing approach that can induce fetal hemoglobin production in patients with SCD and TdT.

Comparison of hematopoietic cell transplant conditioning regimens for hemophagocytic lymphohistiocytosis disorders

BACKGROUND

Allogeneic hematopoietic cell transplantation for hemophagocytic lymphohistiocytosis (HLH) disorders is associated with substantial morbidity and mortality.

OBJECTIVE

The effect of conditioning regimen groups of varying intensity on outcomes after transplantation was examined to identify an optimal regimen or regimens for HLH disorders.

METHODS

We studied 261 patients with HLH disorders transplanted between 2005 and 2018. Risk factors for transplantation outcomes by conditioning regimen groups were studied by Cox regression models.

RESULTS

Four regimen groups were studied: (1) fludarabine (Flu) and melphalan (Mel) in 123 subjects; (2) Flu, Mel, and thiotepa (TT) in 28 subjects; (3) Flu and busulfan (Bu) in 14 subjects; and (4) Bu and cyclophosphamide (Cy) in 96 subjects. The day 100 incidence of veno-occlusive disease was lower with Flu/Mel (4%) and Flu/Mel/TT (0%) compared to Flu/Bu (14%) and Bu/Cy (22%) (P < .001). The 6-month incidence of viral infections was highest after Flu/Mel (72%) and Flu/Mel/TT (64%) compared to Flu/Bu (39%) and Bu/Cy (38%) (P < .001). Five-year event-free survival (alive and engrafted without additional cell product administration) was lower with Flu/Mel (44%) compared to Flu/Mel/TT (70%), Flu/Bu (79%), and Bu/Cy (61%) (P = .002). The corresponding 5-year overall survival values were 68%, 75%, 86%, and 64%, and did not differ by conditioning regimen (P = .19). Low event-free survival with Flu/Mel is attributed to high graft failure (42%) compared to Flu/Mel/TT (15%), Flu/Bu (7%), and Bu/Cy (18%) (P < .001).

CONCLUSIONS

Given the high rate of graft failure with Flu/Mel and the high rate of veno-occlusive disease with Bu/Cy and Flu/Bu, Flu/Mel/TT may be preferred for HLH disorders. Prospective studies are warranted.

Parvovirus B19-associated graft failure after allogeneic hematopoietic stem cell transplantation

Background

Parvovirus B19 (PVB19) infection has been implicated in allograft failure or dysfunction in solid organ transplantation (SOT) and allogeneic hematopoietic stem cell transplantation (allo‐HSCT), but the literature is limited.

Case

Two pediatric patients were diagnosed with PVB19 infection around the time of allo‐HSCT graft failure. Both cases were secondary graft failure and required second allo‐HSCT.

Conclusion

There are many risk factors and potential confounders in determining the exact etiology of graft failure after allo‐HSCT. These two cases highlight the importance of including PVB19 in the diagnostic evaluation for graft failure. PVB19 infection may be an important risk factor for allo‐HSCT graft failure.

Clinical risks and healthcare utilization of hematopoietic cell transplantation for sickle cell disease in the USA using merged databases

Advances in allogeneic hematopoietic cell transplantation for sickle cell disease have improved outcomes, but there is limited analysis of healthcare utilization in this setting. We hypothesized that, compared to late transplantation, early transplantation (at age <10 years) improves outcomes and decreases healthcare utilization. We performed a retrospective study of children transplanted for sickle cell disease in the USA during 2000-2013 using two large databases. Univariate and Cox models were used to estimate associations of demographics, sickle cell disease severity, and transplant-related variables with mortality and chronic graft-versus-host disease, while Wilcoxon, Kruskal-Wallis, or linear trend tests were applied for the estimates of healthcare utilization. Among 161 patients with a 2-year overall survival rate of 90% (95% confidence interval [CI] 85-95%) mortality was significantly higher in those who underwent late transplantation versus early (hazard ratio (HR) 21, 95% CI 2.8-160.8, P=0.003) and unrelated compared to matched sibling donor transplantation (HR 5.9, 95% CI 1.7-20.2, P=0.005). Chronic graftversus host disease was significantly more frequent among those translanted late (HR 1.9, 95% CI 1.0-3.5, P=0.034) and those who received an unrelated graft (HR 2.5, 95% CI 1.2-5.4; P=0.017). Merged data for 176 patients showed that the median total adjusted transplant cost per patient was $467,747 (range: $344,029-$799,219). Healthcare utilization was lower among recipients of matched sibling donor grafts and those with low severity disease compared to those with other types of donor and disease severity types (P<0.001 and P=0.022, respectively); no association was demonstrated with late transplantation (P=0.775). Among patients with 2-year pre- and post-transplant data (n=41), early transplantation was associated with significant reductions in admissions (P<0.001), length of stay (P<0.001), and cost (P=0.008). Early transplant outcomes need to be studied prospectively in young children without severe disease and an available matched sibling to provide conclusive evidence for the superiority of this approach. Reduced post-transplant healthcare utilization inpatient care indicates that transplantation may provide a sustained decrease in healthcare costs over time.

Effect of race on outcomes after allogeneic hematopoietic cell transplantation for severe aplastic anemia

We compared outcomes after hematopoietic cell transplantation in patients of African American (n = 84) and Caucasian (n = 215) descent with severe aplastic anemia. African Americans and Caucasians were matched for age, donor-recipient human leukocyte antigen match, graft type, and transplantation year. The median follow-up of surviving patients was 5 years. In multivariate analysis, overall mortality risks were higher for African Americans compared to Caucasians (relative risk 1.73, P = 0.01). The 5-year probabilities of overall survival adjusted for interval from diagnosis to transplantation, and performance score was 58% for African Americans and 73% for Caucasians. The day-100 cumulative incidence of grade III-IV, but not grade II-IV acute graft-versus-host disease (GVHD), was higher in African Americans compared to Caucasians (29% vs. 13%, P = 0.006). Although the 5-year cumulative incidence of chronic GVHD was not significantly different between the racial groups, African Americans were more likely to have extensive chronic GVHD compared to Caucasians (72% vs. 49%, P = 0.06). Survival differences between Caucasians and African Americans can be attributed to multiple factors. Our data suggest that some of the observed survival differences between Caucasians and African Americans may be explained by higher rates of acute GVHD and severity of chronic GVHD.

Adherence to transcranial Doppler screening guidelines among children with sickle cell disease

BACKGROUND

Little is known about adherence to guidelines recommending yearly screening with transcranial Doppler (TCD) ultrasonography to detect stroke risk for children with severe sickle cell disease. The objective was to determine the proportion of children with hemoglobin SS (HbSS) or sickle-β(0) -thalassemia (HbSβ(0) ) aged 2-16 years who received recommended TCD screening from 1997 to 2008, and to identify factors associated with adherence.

PROCEDURE

A retrospective cohort study included patients enrolled in Tennessee Medicaid with HbSS or HbSβ(0) who received care at the two largest sickle cell centers in Tennessee. The outcome of interest was adherence with guidelines for annual screening TCD's, identified from computer claims and validated through medical record review. The cumulative rate of children who received a TCD per year was calculated using the Kaplan-Meier method. Cox proportional hazards regression was used to examine the association of child, family, and health care use characteristics with receiving a TCD.

RESULTS

Among 338 TCD eligible at-risk children, 232 (68.6%) had at least one TCD during the study period. The yearly cumulative incidence of annual TCD's increased from 2.5% in 1997 to 68.3% in 2008. In multivariate models, calendar year, maternal education, and increased number of sickle cell related outpatient visits were associated with an increased rate of receiving a TCD.

CONCLUSIONS

Publicly insured children with HbSS or HbSβ(0) had increasing adherence with TCD screening guidelines between 1997 and 2008, though 31% had no TCD at all during follow-up. Increasing number of sickle cell related outpatient visits was associated with increasing adherence to screening guidelines.

Chronically transfused pediatric sickle cell patients are protected from cardiac iron overload

Iron overload is a major toxicity of chronic transfusions. Myocardial iron overload is associated with cardiac dysfunction. Cardiac and liver magnetic resonance imaging (MRI) was performed on 14 chronically transfused sickle cell disease (SCD) and non-sickle cell disease (non-SCD) patients seen at Vanderbilt Children's Hospital from 1 January 2000 to 10 March 2010. Retrospective review was conducted to assess cardiac T2*, liver T2*, ventricular dimensions and function, echocardiogram, length of transfusion, hemoglobin, and ferritin measurements. Ten patients had SCD and 4 had non-SCD, including α-thalassemia, β-thalassemia, and Diamond-Blackfan anemia. Cardiac T2* was normal in all SCD patients (mean 39 ± 12 ms), but abnormal in 3 of 4 non-SCD patients (mean 11.8 ± 2.4 ms). Liver T2* was similar between SCD (mean 6.2 ± 1.6 ms) and non-SCD patients (mean 5.9 ± 1.9 ms), and did not correlate with serum ferritin. Comparing SCD and non-SCD patients with similar transfusion duration, SCD patients had normal cardiac T2* and non-SCD patients had abnormal cardiac T2*. No patients had cardiomyopathy, but ventricular dilatation was common among SCD patients. Chronically transfused pediatric SCD patients are relatively spared of myocardial iron overload, which is unlikely to be due to lower total body iron burden in SCD patients than non-SCD patients.

A case of pediatric PTLD following autologous stem cell transplantation and review of the literature

The development of PTLD is a rare severe adverse event following ASCT. We report on a child with DS who developed PTLD following autologous transplant for relapsed Hodgkin's disease. He was successfully treated with cyclophosphamide, prednisone and rituximab. We also present a comprehensive review of the literature of PTLD in pediatric patients following ASCT.

Autologous stem cell transplant in a patient with Down syndrome and relapsed Hodgkin lymphoma

Children with Down syndrome (DS) are at increased risk for the development of acute leukemia but they rarely develop other hematologic malignancies or solid tumors. Despite aggressive supportive care, DS patients have increased risk of treatment related morbidity and mortality compared to other children. There are few reported cases of Hodgkin disease in children with DS, and no reported cases of successful therapy for patients with relapsed disease. We report on a child with DS and relapsed Hodgkin disease who was successfully treated with high-dose chemotherapy and autologous stem cell transplant.