Abatacept for acute graft-versus-host disease prophylaxis after unrelated donor hematopoietic cell transplantation.

Abatacept plus calcineurin inhibitors/methotrexate (CNI/MTX) is the first FDA-approved regimen for acute graft-versus-host disease (aGVHD) prophylaxis during unrelated-donor hematopoietic cell transplantation (URD-HCT). We investigated its impact in URD-HCT patients using Center for International Blood and Marrow Transplant Research data for 7/8-human leukocyte antigen (HLA)-mismatched (MMUD) or 8/8-HLA-matched (MUD) URD-HCT recipients between 2011-2018. Primary outcomes included day-180, 1-year, and 2-year overall survival (OS) and relapse-free survival (RFS) for abatacept+CNI/MTX vs CNI/MTX, CNI/MTX+antithymocyte globulin (ATG), and post-transplant cyclophosphamide-based prophylaxis (PT-Cy); other outcomes included aGVHD, chronic GVHD, non-relapse mortality, and relapse. For 7/8-MMUDs, day-180 OS (primary endpoint supporting FDA approval) was significantly higher for abatacept+CNI/MTX vs CNI/MTX (98%vs75%; p=0.0028). Two-year OS was significantly higher for abatacept+CNI/MTX vs CNI/MTX (83%vs55%; p=0.0036), CNI/MTX+ATG (83%vs46%; p=0.0005) and similar to PT-Cy (80%vs68%; p=0.2325). Two-year RFS was significantly higher for abatacept+CNI/MTX vs CNI/MTX (74%vs49%; p=0.0098) and CNI/MTX+ATG (77%vs35%; p=0.0002), and similar vs PT-Cy (72%vs56%; p=0.1058). For 8/8-MUDs, 2-year OS was similar with abatacept+CNI/MTX vs CNI/MTX (70%vs62%; p=0.2569), CNI/MTX+ATG (75%vs64%; p=0.1048), and PT-Cy (74%vs69%; p=0.5543). Two-year RFS for abatacept+CNI/MTX was numerically higher vs CNI/MTX (63%vs52%; p=0.1497) with an improved hazard ratio (HR: 0.46 [0.25-0.86]), and vs CNI/MTX+ATG (66%vs55%; p=0.1193; HR: 0.39 [0.21-0.73]). Two-year RFS was similar vs PT-Cy (68%vs57%; p=0.2356; HR: 0.54 [0.26-1.11]). For both 7/8-MMUD and 8/8-MUD recipients, abatacept+CNI/MTX prophylaxis improved survival outcomes vs CNI/MTX and CNI/MTX+ATG; outcomes were similar to PT-Cy-based regimens. Abatacept+CNI/MTX has potential to facilitate unrelated donor pool expansion for HCT.

Higher abatacept exposure after transplant decreases acute GVHD risk without increasing adverse events.

In the ABA2 study, the T-cell costimulation blockade agent, abatacept, was safe and effective in preventing acute graft-versus-host disease (aGVHD) after unrelated-donor hematopoietic cell transplant (HCT), leading to US Food and Drug Administration approval. Here, we performed a determination of abatacept pharmacokinetics (PK), which enabled an examination of how abatacept exposure-response relationships affected clinical outcomes. We performed a population PK analysis of IV abatacept using nonlinear mixed-effect modeling and assessed the association between abatacept exposure and key transplant outcomes. We tested the association between the trough after dose 1 (Ctrough_1) and grade (GR) 2 or 4 aGVHD (GR2-4 aGVHD) through day +100. An optimal Ctrough_1 threshold was identified via recursive partitioning and classification tree analysis. This demonstrated that abatacept PK was characterized by a 2-compartment model with first-order elimination. The ABA2 dosing regimen was based on previous work targeting a steady-state abatacept trough of 10 µg/mL. However, a higher Ctrough_1 (≥39 µg/mL, attained in ∼60% of patients on ABA2) was associated with a favorable GR2-4 aGVHD risk (hazard ratio, 0.35; 95% confidence interval, 0.19-0.65; P < .001), with a Ctrough_1 <39 µg/mL associated with GR2-4 aGVHD risk indistinguishable from placebo (P = .37). Importantly, no significant association was found between Ctrough_1 and key safety indicators, including relapse, and cytomegalovirus or Epstein-Barr virus viremia. These data demonstrate that a higher abatacept Ctrough_1 (≥39 µg/mL) was associated with a favorable GR2-4 aGVHD risk, without any observed exposure-toxicity relationships. This trial was registered at www.clinicaltrials.gov as #NCT01743131.

The genetic basis and cell of origin of mixed phenotype acute leukaemia.

Mixed phenotype acute leukaemia (MPAL) is a high-risk subtype of leukaemia with myeloid and lymphoid features, limited genetic characterization, and a lack of consensus regarding appropriate therapy. Here we show that the two principal subtypes of MPAL, T/myeloid (T/M) and B/myeloid (B/M), are genetically distinct. Rearrangement of ZNF384 is common in B/M MPAL, and biallelic WT1 alterations are common in T/M MPAL, which shares genomic features with early T-cell precursor acute lymphoblastic leukaemia. We show that the intratumoral immunophenotypic heterogeneity characteristic of MPAL is independent of somatic genetic variation, that founding lesions arise in primitive haematopoietic progenitors, and that individual phenotypic subpopulations can reconstitute the immunophenotypic diversity in vivo. These findings indicate that the cell of origin and founding lesions, rather than an accumulation of distinct genomic alterations, prime tumour cells for lineage promiscuity. Moreover, these findings position MPAL in the spectrum of immature leukaemias and provide a genetically informed framework for future clinical trials of potential treatments for MPAL.

Hematopoietic stem cell transplant referral patterns for children with sickle cell disease vary among pediatric hematologist/oncologists' practice focus: A Sickle Cell Transplant Advocacy and Research Alliance (STAR) study.

BACKGROUND: Hematopoietic stem cell transplantation (HSCT) provides a curative therapy for children severely affected by sickle cell disease (SCD). Rejection-free survival after matched sibling donor (MSD) HSCT is very high, but adoption of HSCT as a curative SCD therapy has been slow. In this study, we assess providers' perceptions about MSD HSCT for children with variable SCD severity, and determine the influence of provider characteristics on HSCT referrals. PROCEDURE: After our Institutional Review Board deemed the study exempt, American Society of Pediatric Hematology/Oncology Clinical Forum listserv subscribers and American Society of Hematology members who self-identified as pediatric hematologists/oncologists (PHO) were emailed a survey. Analysis was performed to describe and evaluate correlations between participant demographics (including practice focus within PHO) and likelihood of HSCT referral for each scenario. RESULTS: Spearman's rank correlation analysis did not reveal any significant relationship between demographic characteristics except practice focus and likelihood to refer to HSCT for any scenarios. Providers focused on SCD and HSCT were more likely to refer a child who had never been admitted to the hospital or had suboptimal adherence to hydroxyurea than general PHOs. A significantly higher proportion of all respondents would refer a child with ß-thalassemia major (87%) than an asymptomatic child with HbSS (47%, P < .00001) or non-HbSS variant (23%, P < .00001). CONCLUSION: PSCD and HSCT physicians are more likely to refer for MSD HSCT in almost every condition than general PHO practitioners, likely because of increased awareness of long-term effects of SCD and safety of MSD HSCT for children with SCD.

Mixed-phenotype acute leukemia: A cohort and consensus research strategy from the Children's Oncology Group Acute Leukemia of Ambiguous Lineage Task Force.

BACKGROUND: Optimal chemotherapy for treating mixed-phenotype acute leukemia (MPAL) and the role of hematopoietic stem cell transplantation (HSCT) remain uncertain. Major limitations in interpreting available data are MPAL's rarity and the use of definitions other than the currently widely accepted criteria: the World Health Organization 2016 (WHO2016) classification. METHODS: To assess the relative efficacy of chemotherapy types for treating pediatric MPAL, the Children's Oncology Group (COG) Acute Leukemia of Ambiguous Lineage Task Force assembled a retrospective cohort of centrally reviewed WHO2016 MPAL cases selected from banking studies for acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). Patients were not treated in COG trials; treatment and outcome data were captured separately. The findings were then integrated with the available, mixed literature to develop a prospective trial in pediatric MPAL. RESULTS: The central review confirmed that 54 of 70 cases fulfilled WHO2016 criteria for MPAL. ALL induction regimens achieved remission in 72% of the cases (28 of 39), whereas AML regimens achieved remission in 69% (9 of 13). The 5-year event-free survival (EFS) and overall survival (OS) rates for the entire cohort were 72% ± 8% and 77% ± 7%, respectively. EFS and OS were 75% ± 13% and 84% ± 11%, respectively, for those receiving ALL chemotherapy alone without HSCT (n = 21). CONCLUSIONS: The results of the COG MPAL cohort and a literature review suggest that ALL chemotherapy without HSCT may be the preferred initial therapy. A prospective trial within the COG is proposed to investigate this approach; AML chemotherapy and/or HSCT will be reserved for those with treatment failure as assessed by minimal residual disease. Embedded biology studies will provide further insight into MPAL genomics.

Human leukocyte antigen (HLA) class I antibodies and transfusion support in paediatric HLA-matched haematopoietic cell transplant for sickle cell disease.

The relevance of donor-specific human leukocyte antigen (HLA) antibodies in HLA-mismatched haematopoietic cell transplant (HCT) is known, but the importance of HLA antibodies in HLA-matched HCT is unclear. We hypothesized that HLA antibodies detected before HCT would cause platelet transfusion refractoriness during HCT and investigated this in a multi-centre study. Pre-HCT samples from 45 paediatric patients with sickle cell disease (SCD) undergoing HLA-matched HCT were tested for HLA class I antibodies. The number of platelet transfusions received before day +45 was compared between those with and without antibodies. Thirteen of 45 (29%) patients had a positive HLA class I antibody screen, and these patients received significantly more platelet transfusions than patients without antibodies (median 19 vs. 7·5, P = 0·028). This platelet transfusion association remained significant when controlling for conditioning regimen. Among alloimmunized patients, there was no association between the panel-reactive antibody and the number of platelet transfusions. Patients with HLA class I antibodies also had a higher incidence of acute graft-versus-host disease (GVHD): 6/13 (46%) vs. 3/32 (9%), P = 0·011. Pre-HCT HLA class I alloimmunization is associated with increased platelet transfusion support and acute GVHD in paediatric HLA-matched HCT for SCD. Further studies are needed to investigate the pathobiology of this association.

Treatment strategies for adolescent and young adult patients with acute myeloid leukemia.

Adolescents and young adults (AYAs) form a unique group of patients with newly diagnosed acute myeloid leukemia (AML). They differ in terms of disease biology, psychosocial challenges, survival, and in other important respects from children as well as from middle-aged and older adults. AYAs may be treated using pediatric protocols developed in trials composed primarily of younger patients, or using adult protocols developed in trials composed primarily of older patients. After reviewing the distinguishing characteristics of AYAs with AML, we compare and contrast the chemotherapy approaches and argue that neither the pediatric nor adult approaches may be ideally suited for AYAs and the development of AYA-specific approaches merits further consideration. We finish by putting forth ideas for future research to optimize chemotherapy treatment of AYAs with AML.

Influence of Age on Acute and Chronic GVHD in Children Undergoing HLA-Identical Sibling Bone Marrow Transplantation for Acute Leukemia: Implications for Prophylaxis.

Relapse remains the major cause of mortality after hematopoietic cell transplantation (HCT) for pediatric acute leukemia. Previous research has suggested that reducing the intensity of calcineurin inhibitor-based graft-versus-host disease (GVHD) prophylaxis may be an effective strategy for abrogating the risk of relapse in pediatric patients undergoing matched sibling donor (MSD) HCT. We reasoned that the benefits of this strategy could be maximized by selectively applying it to those patients least likely to develop GVHD. We conducted a study of risk factors for GVHD, to risk-stratify patients based on age. Patients age <18 years with leukemia who received myeloablative, T cell-replete MSD bone marrow transplantation and calcineurin inhibitor-based GVHD prophylaxis between 2000 and 2013 and were entered into the Center for International Blood and Marrow Transplant Research registry were included. The cumulative incidence of grade II-IV acute GVHD (aGVHD) was 19%, that of grade II-IV aGVHD 7%, and that of chronic GVHD (cGVHD) was 16%. Compared with age 13 to 18 years, age 2 to 12 years was associated with a lower risk of grade II-IV aGVHD (hazard ratio [HR], .42; 95% confidence interval [CI], .26 to .70; P = .0008), grade II-IV aGVHD (HR, .24; 95% CI, .10 to .56; P = .001), and cGVHD (HR, .32; 95% CI, .19 to .54; P < .001). Compared with 2000-2004, the risk of grade II-IV aGVHD was lower in children undergoing transplantation in 2005-2008 (HR, .36; 95% CI, .20 to .65; P = .0007) and in 2009-2013 (HR, .24; 95% CI. .11 to .53; P = .0004). Similarly, the risk of grade III-IV aGVHD was lower in children undergoing transplantation in 2005-2008 (HR, .23; 95% CI, .08 to .65; P = .0056) and 2009-2013 (HR, .16; 95% CI, .04 to .67; P = .0126) compared with those doing so in 2000-2004. We conclude that aGVHD rates have decreased significantly over time, and that children age 2 to 12 years are at very low risk for aGVHD and cGVHD. These results should be validated in an independent analysis, because these patients with high-risk malignancies may be good candidates for trials of reduced GVHD prophylaxis.

Early blood stream infection following allogeneic hematopoietic stem cell transplantation is a risk factor for acute grade III-IV GVHD in children and adolescents.

BACKGROUND: Graft-versus-host disease (GVHD) remains a major cause of mortality and morbidity in allogeneic hematopoietic stem cell transplantation (HSCT). In adults, early blood stream infection (BSI) and acute GVHD (AGVHD) have been reported to be related. The impact of BSI on risk for AGVHD, however, has not been assessed in pediatric patients. PROCEDURE: We conducted a retrospective analysis to test the hypothesis that early BSI (before day +30) predisposes allogeneic pediatric transplant patients to severe AGVHD. We analyzed 293 allogeneic HSCT performed at Children's Healthcare of Atlanta between 2005 and 2014 that met eligibility criteria. RESULTS: The cumulative incidence of acute grade III-IV GVHD at 100 days after HSCT was 17.1%. In multivariate analysis, risk for acute grade III-IV GVHD was associated with HLA-mismatched donor (hazard ratio [HR] = 4.870, P < 0.001), and BSI between day 0 and +30 prior to AGVHD (HR = 3.010, P = 0.001). CONCLUSIONS: These results indicate that early BSI appears to be a risk factor for acute grade III-IV GVHD. Further research is needed to determine if the link is causal.

African American Race Is a Newly Identified Risk Factor for Postengraftment Blood Stream Infections in Pediatric Allogeneic Blood and Marrow Transplantation.

Blood stream infections (BSI) are a major source of morbidity and mortality both in allogeneic blood and marrow transplant (BMT) recipients. Various risk factors for BSI in BMT have been identified. The impact of race and cytomegalovirus (CMV) viremia, a common complication after engraftment, however, has not been rigorously assessed. This is important because both CMV infection and ganciclovir, the mainstay of pre-emptive therapy, have myelosuppressive and immunosuppressive effects. We conducted a retrospective analysis to test the hypothesis that race and CMV viremia predispose allogeneic BMT patients to postengraftment BSI. We analyzed 278 allogeneic BMT performed at Children's Healthcare of Atlanta between January 1, 2005 and December 31, 2014 that met eligibility criteria. We performed a multivariate analysis to estimate the effect of CMV viremia on risk for BSI in the postengraftment period (days +30 to 100). Risk for BSI was associated with CMV viremia (hazard ratio [HR], 3.34; 95% confidence interval [CI], 1.51 to 7.36; P = .003); grade III and IV acute graft-versus-host disease (HR, 3.28; 95% CI, 1.55 to 6.92; P = .002), and African American race (HR, 2.22; 95% CI, 1.09 to 4.51; P = .027). The results of our study highlight the importance of a novel risk factor for postengraftment BSI, not previously considered-African American race.

CMV reactivation drives posttransplant T-cell reconstitution and results in defects in the underlying TCRß repertoire.

Although cytomegalovirus (CMV) reactivation has long been implicated in posttransplant immune dysfunction, the molecular mechanisms that drive this phenomenon remain undetermined. To address this, we combined multiparameter flow cytometric analysis and T-cell subpopulation sorting with high-throughput sequencing of the T-cell repertoire, to produce a thorough evaluation of the impact of CMV reactivation on T-cell reconstitution after unrelated-donor hematopoietic stem cell transplant. We observed that CMV reactivation drove a >50-fold specific expansion of Granzyme B(high)/CD28(low)/CD57(high)/CD8(+) effector memory T cells (Tem) and resulted in a linked contraction of all naive T cells, including CD31(+)/CD4(+) putative thymic emigrants. T-cell receptor ß (TCRß) deep sequencing revealed a striking contraction of CD8(+) Tem diversity due to CMV-specific clonal expansions in reactivating patients. In addition to querying the topography of the expanding CMV-specific T-cell clones, deep sequencing allowed us, for the first time, to exhaustively evaluate the underlying TCR repertoire. Our results reveal new evidence for significant defects in the underlying CD8 Tem TCR repertoire in patients who reactivate CMV, providing the first molecular evidence that, in addition to driving expansion of virus-specific cells, CMV reactivation has a detrimental impact on the integrity and heterogeneity of the rest of the T-cell repertoire. This trial was registered at www.clinicaltrials.gov as #NCT01012492.

Haematopoietic stem cell transplantation for sickle cell disease - current practice and new approaches.

Sickle cell disease is an inherited disorder that affects over 5 million people worldwide. Current maintenance therapy has been successful in reducing complications and enhancing life expectancy; yet subclinical complications persist. To date, allogeneic haematopoietic stem cell transplant (HSCT) remains the only available curative therapy for sickle cell disease. With declining incidences of rejection and transplant- related mortality, disease-free survival after human leucocyte antigen-identical sibling transplant exceeds 90%. However, the majority of individuals with sickle cell disease do not have an human leucocyte antigen (HLA)-identical sibling; therefore, research is expanding to focus on new approaches to alternative donor transplant. Advances in supportive care and conditioning regimens have led to expansion of the pool of donors to unrelated donors and haploidentical donors. Challenges remain in improving the safety and efficacy of HSCT from alternate donors. Early results from gene therapy may provide another curative option in patients with sickle cell disease. These approaches show early promise, but larger, longitudinal studies are needed to better determine the optimal clinical circumstances for transplant in sickle cell disease.

Transplantation for children with acute myeloid leukemia: a comparison of outcomes with reduced intensity and myeloablative regimens.

The safety and efficacy of reduced-intensity conditioning (RIC) regimens for the treatment of pediatric acute myeloid leukemia is unknown. We compared the outcome of allogeneic hematopoietic cell transplantation in children with acute myeloid leukemia using RIC regimens with those receiving myeloablative-conditioning (MAC) regimens. A total of 180 patients were evaluated (39 with RIC and 141 with MAC regimens). Results of univariate and multivariate analysis showed no significant differences in the rates of acute and chronic graft-versus-host disease, leukemia-free, and overall survival between treatment groups. The 5-year probabilities of overall survival with RIC and MAC regimens were 45% and 48%, respectively (P = .99). Moreover, relapse rates were not higher with RIC compared with MAC regimens (39% vs 39%; P = .95), and recipients of MAC regimens were not at higher risk for transplant-related mortality compared with recipients of RIC regimens (16% vs 16%; P = .73). After carefully controlled analyses, we found that in this relatively modest study population, the data supported a role for RIC regimens for acute myeloid leukemia in children undergoing allogeneic hematopoietic cell transplantation. The data also provided justification for designing a carefully controlled randomized clinical trial that examines the efficacy of regimen intensity in this population.

Leukoreduced red blood cell transfusions do not induce platelet glycoprotein antibodies in patients with sickle cell disease.

BACKGROUND: Alloimmunization to red blood cell (RBC) antigens after transfusion is well described in patients with sickle cell disease (SCD). We recently demonstrated that leukocyte-reduced RBC transfusions appeared to induce human leukocyte antigen (HLA) antibodies in some children with SCD; now, we hypothesize that residual platelets contained in transfused RBC products may lead to platelet glycoprotein antibody formation. STUDY DESIGN AND METHODS: A cross-sectional study was conducted among never pregnant pediatric patients with SCD who either had received many RBC transfusions or had never received any transfusions. Serum was tested for antibodies to platelet-specific glycoproteins using a commercial enzyme immunoassay. RESULTS: Platelet-specific glycoprotein antibodies were found in 12 of 90 patients (13%) in the transfused group versus 5 of 24 patients (21%) in the never transfused group (p = 0.35). The prevalence of antibodies as well as the median standardized optical density for these two groups was not significantly different for any of the studied platelet glycoprotein antigens. There was no association with the presence of platelet-specific glycoprotein antibodies with either RBC or HLA antibodies. CONCLUSIONS: Leukocyte-reduced RBC transfusions do not appear to induce platelet-specific glycoprotein antibodies. The positive platelet-specific glycoprotein antibody results from this study may represent platelet autoantibodies, platelet alloantibodies, or false-positive reactions. A better understanding of the immunobiology of patients with SCD at baseline and after blood product exposure may help improve future transfusion and transplantation.

Improved Splenic Function After Hematopoietic Stem Cell Transplant for Sickle Cell Disease.

BACKGROUND: Splenic dysfunction is a significant complication of sickle cell disease (SCD). Hematopoietic stem cell transplant (HSCT) is a proven cure for SCD; however, its long-term effect on splenic function is not well characterized. PROCEDURE: We conducted a retrospective cohort study of pediatric patients who had HSCT for SCD at two transplant centers. (99m) Tc liver-spleen (LS) scans were blindly reviewed and classified as demonstrating absent, decreased, or normal splenic uptake. RESULTS: Considering all engrafted nonsplenectomized Hb SS and Sß(0) -thalassemia patients with LS scans available, at a median of 2.0 years post-HSCT (range 1.0-9.3 years) eight of 53 (15%) had normal, 40 of 53 (75%) decreased, and five of 53 (9%) absent splenic uptake. More patients had splenic uptake after HSCT: pre-HSCT 14/38 (37%) versus post-HSCT 34/38 (89%), P < 0.0001. Older age at HSCT was associated with worse splenic function post-HSCT (median age at HSCT for absent uptake 16.6 years vs. present uptake 8.0 years, P = 0.030). Extensive chronic GVHD was also more common in patients with absent splenic uptake compared to patients with present uptake (absent 40% vs. present 6%, P = 0.064). CONCLUSIONS: HSCT significantly improves splenic function for most pediatric patients with SCD, but older patient age at time of HSCT and extensive chronic GVHD appear to be risk factors for poor post-HSCT splenic function.

Use of Alefacept for Preconditioning in Multiply Transfused Pediatric Patients with Nonmalignant Diseases.

Transfusion-related alloimmunization is a potent barrier to the engraftment of allogeneic hematopoietic stem cells in patients with nonmalignant diseases (NMDs). Memory T cells, which drive alloimmunization, are relatively resistant to commonly used conditioning agents. Alefacept, a recombinant leukocyte function antigen-3/IgG1 fusion protein, targets CD2 and selectively depletes memory versus naive T cells. Three multiply transfused pediatric patients with NMD received a short course of high-dose i.v. alefacept (.25 mg/kg/dose on days -40 and -9 and .5 mg/kg/dose on days -33, -26, -19, and -12) before undergoing unrelated allogeneic transplant in the setting of reduced-intensity pretransplant conditioning and calcineurin inhibitor-based post-transplant graft-versus-host disease (GVHD) prophylaxis. Alefacept infusions were well tolerated in all patients. Peripheral blood flow cytometry was performed at baseline and during and after alefacept treatment. As expected, after the 5 weekly alefacept doses, each patient demonstrated selective loss of CD2(hi)/CCR7(-)/CD45RA(-) effector memory (Tem) and CD2(hi)/CCR7(+)/CD45RA(-) central memory (Tcm) CD4(+) and CD8(+) T cells with relative preservation of the CD2(lo) Tem and Tcm subpopulations. In addition, depletion of CD2(+) natural killer (NK) cells also occurred. Neutrophil recovery was rapid, and all 3 patients had 100% sorted (CD3/CD33) peripheral blood donor chimerism by day +100. Immune reconstitution (by absolute neutrophil, monocyte, and lymphocyte counts) was comparable with a cohort of historical control patients. All 3 patients developed GVHD but are all now off immune suppression and >2 years post-transplant with stable full-donor engraftment. These results suggest that alefacept at higher dosing can deplete both memory T cells and NK cells and that incorporating CD2-targeted depletion into a reduced-intensity transplant regimen is feasible and safe in heavily transfused patients.

Using fludarabine to reduce exposure to alkylating agents in children with sickle cell disease receiving busulfan, cyclophosphamide, and antithymocyte globulin transplant conditioning: results of a dose de-escalation trial.

High-dose busulfan, cyclophosphamide, and antithymocyte globulin (BU-CY-ATG) is the most commonly used conditioning regimen in HLA-matched related hematopoietic cell transplantation for children with sickle cell disease. Disease-free survival with this regimen is now approximately 95%; however, it produces significant morbidity. We hypothesized we could create a less toxic regimen by adding fludarabine (FLU) to BU-CY-ATG and reduce the dosages of busulfan and cyclophosphamide. We conducted a multicenter dose de-escalation trial with the objective of decreasing the doses of busulfan and cyclophosphamide by 50% and 55%, respectively. Using day +28 donor-predominant chimerism as a surrogate endpoint for sustained engraftment, we completed the first 2 of 4 planned levels, enrolling 6 patients at each and reducing the total dose of cyclophosphamide from 200 mg/kg to 90 mg/kg. On the third level, which involved a reduction of i.v. busulfan from 12.8 mg/kg to 9.6 mg/kg, the first 2 patients had host-predominant T cell chimerism, which triggered trial-stopping rules. All 14 patients survive disease-free. No patients suffered severe regimen-related toxicity. Our results suggest BU-FLU-CY-ATG using lower dose CY could be a less toxic yet effective regimen. Further evaluation of this regimen in a full-scale clinical trial is warranted.

Red blood cell transfusions are associated with HLA class I but not H-Y alloantibodies in children with sickle cell disease.

Blood transfusions can induce alloantibodies to antigens on red blood cells (RBCs), white blood cells and platelets, with these alloantibodies affecting transfusion and transplantation. While transfusion-related alloimmunization against RBC antigens and human leucocyte antigens (HLA) have been studied, transfusion-related alloimmunization to minor histocompatibility antigens (mHA), such as H-Y antigens, has not been clinically characterized. We conducted a cross-sectional study of 114 children with sickle cell disease (SCD) and tested for antibodies to 5 H-Y antigens and to HLA class I and class II. Few patients had H-Y antibodies, with no significant differences in the prevalence of any H-Y antibody observed among transfused females (7%), transfused males (6%) and never transfused females (4%). In contrast, HLA class I, but not HLA class II, antibodies were more prevalent among transfused than never transfused patients (class I: 33% vs. 13%, P = 0·046; class II: 7% vs. 8%, P = 0·67). Among transfused patients, RBC alloantibody history but not amount of transfusion exposure was associated with a high (>25%) HLA class I panel reactive antibody (Odds ratio 6·8, 95% confidence interval 2·1-22·3). These results are consistent with immunological responder and non-responder phenotypes, wherein a subset of patients with SCD may be at higher risk for transfusion-related alloimmunization.

Immune parameter analysis of children with sickle cell disease on hydroxycarbamide or chronic transfusion therapy.

Sickle cell disease (SCD) is increasingly appreciated as an inflammatory condition associated with alterations in immune phenotype and function. In this cross-sectional study we performed a multiparameter analysis of 18 immune markers in 114 paediatric SCD patients divided by treatment group [those receiving hydroxycrabamide (HC, previously termed hydroxyurea), chronic transfusion (CT), or no disease-modifying therapy] and 29 age-matched African American healthy controls. We found global elevation of most immune cell counts in SCD patients receiving no disease-modifying therapy at steady state. Despite the decrease in percentage of haemoglobin S associated with CT therapy, the abnormal cellular immune phenotype persisted in patients on CT. In contrast, in both univariate and multivariate analysis, treatment with HC was associated with normalization of the vast majority of leucocyte populations. This study provides additional support for HC treatment in SCD, as it appears that HC decreases the abnormally elevated immune cell counts in patients with SCD.