Comparison of Two Doses of Antithymocyte Globulin in Reduced-Intensity Conditioning Allogeneic Hematopoietic Stem Cell Transplantation

The appropriate dose of antithymocyte globulin (ATG) to be used in reduced-intensity conditioning (RIC) allogeneic hematopoietic stem cell transplantation (allo-HSCT) is yet to be determined. We retrospectively analyzed the outcomes of patients who underwent unrelated or mismatch related RIC allo-HSCT for hematologic malignancies and received r-ATG (4.5 mg/kg, 141 patients) versus R-ATG (6 mg/kg, 216 patients). There was a higher incidence of cytomegalovirus (P < .001) and Epstein-Barr virus viremia (P =.03) in the R-ATG group than in the r-ATG group. The cumulative incidences of acute graft-versus-host disease (aGVHD) grades II to IV at day 180 in the r-ATG and R-ATG groups were 59% and 44% (P = .006) and grades III to IV 20% and 12% (P = .029), respectively. In multivariable models adjusting for disease diagnosis, the risk of aGVHD grades III to IV did not reach statistical significance (P = .087). The respective cumulative incidences of chronic GVHD in the r-ATG and R-ATG groups were 26% and 15% (P = .10), respectively. There were no significant differences in relapse rate (P = .24), nonrelapse mortality (P = .96), progression-free survival (P = .24), overall survival (P = .70), and GVHD-free relapse-free survival (P = .24). In this retrospective analysis, aGVHD incidence was higher in those treated with r-ATG compared with R-ATG, but this did not translate into significant differences of clinical outcome. Given the increasing use of RIC allo-HSCT for treating malignant hematologic conditions, the correct dose and schedule of ATG administration should be defined by prospective randomized controlled trials.     

Preconditioning Absolute Lymphocyte Count and Transplantation Outcomes in Matched Related Donor Allogeneic Hematopoietic Stem Cell Transplantation Recipients with Reduced-Intensity Conditioning and Antithymocyte Globulin Treatment

The integration of antithymocyte globulin (ATG) into therapy has significantly reduced the incidence of graft-versus-host disease (GVHD) and is being actively used in allogeneic hematopoietic stem cell transplantation (allo-HSCT). The ATG dosage is determined by the recipient's body weight, but some insist that this approach does not reflect the actual target of ATG. In this respect, weight-based dosing may lead to ATG overdose, particularly in recipients with a relatively low absolute lymphocyte count (ALC). We retrospectively analyzed 84 patients with acute leukemia or myelodysplastic syndrome who underwent matched related donor (MRD) allo-HSCT with reduced-intensity conditioning (RIC) at a single institution. Patients were dichotomized according to the ALC measured on the first day of conditioning (day -7) to investigate the associations of the ALC with GVHD and survival outcomes. The median duration of follow-up was 29 months. The preconditioning ALC was closely correlated with the ALC at the first ATG administration (day -3). The cumulative incidences of both acute GVHD and chronic GVHD were significantly lower in the preconditioning ALC <500/μL group compared with the ALC ≥500/μL group. There was no significant difference in disease relapse incidence between the 2 groups; however, mortality was significantly higher in the ALC <500/μL group. Multivariate analysis including disease status, modified European Blood and Marrow Transplantation score, and preconditioning ALC (≥500/μL versus <500/μL) identified disease status and ALC as being independently associated with overall survival (OS). In particular, infection was the most common cause of death in the ALC <500/μL group. Our data suggest that uniform weight-based ATG dosing in MRD allo-HSCT with RIC is associated with an increase in nonrelapse mortality and a relatively inferior OS in patients with a significantly low preconditioning ALC. Therefore, alternative strategies for the integration of ATG should be considered in allo-HSCT, at least for patients with a substantially low preconditioning ALC.     

Donor Chimerism Early after Reduced-Intensity Conditioning Hematopoietic Stem Cell Transplantation Predicts Relapse and Survival

The impact of early donor cell chimerism on outcomes of T cell–replete reduced-intensity conditioning (RIC) hematopoietic stem cell transplantation (HSCT) is ill defined. We evaluated day 30 (D30) and 100 (D100) total donor cell chimerism after RIC HSCT undertaken between 2002 and 2010 at our institution, excluding patients who died or relapsed before D30. When available, donor T cell chimerism was also assessed. The primary outcome was overall survival (OS). Secondary outcomes included progression-free survival (PFS), relapse, and nonrelapse mortality (NRM). We evaluated 688 patients with hematologic malignancies (48% myeloid and 52% lymphoid) and a median age of 57 years (range, 18 to 74) undergoing RIC HSCT with T cell–replete donor grafts (97% peripheral blood; 92% HLA-matched), with a median follow-up of 58.2 months (range, 12.6 to 120.7). In multivariable analysis, total donor cell and T cell chimerism at D30 and D100 each predicted RIC HSCT outcomes, with D100 total donor cell chimerism most predictive. D100 total donor cell chimerism <90% was associated with increased relapse (hazard ratio [HR], 2.54; 95% confidence interval [CI], 1.83 to 3.51; P < .0001), impaired PFS (HR, 2.01; 95% CI, 1.53 to 2.65; P < .0001), and worse OS (HR, 1.50; 95% CI, 1.11 to 2.04, P = .009), but not with NRM (HR, .76; 95% CI, .44 to 2.27; P = .33). There was no additional utility of incorporating sustained D30 to D100 total donor cell chimerism or T cell chimerism. Low donor chimerism early after RIC HSCT is an independent risk factor for relapse and impaired survival. Donor chimerism assessment early after RIC HSCT can prognosticate for long-term outcomes and help identify high-risk patient cohorts who may benefit from additional therapeutic interventions.     

Thiotepa,Busulfan, and Fludarabine Conditioning Regimen in T Cell-Replete HLA-Haploidentical Hematopoietic Stem Cell Transplantation

We report the outcomes of 51 patients who underwent unmanipulated haploidentical hematopoietic stem cell transplantation (haplo-HSCT) with post-transplantation cyclophosphamide (PT-Cy) and antithymocyte globulin (ATG), from peripheral blood stem cells (PBSCs) or bone marrow, after receipt of a TBF (thiotepa, busulfan, and fludarabine) conditioning regimen. Their median age was 55 years (range, 16 to 72 years). Hematologic diagnoses included acute leukemias (n = 31), lymphoid neoplasm (n = 12), myeloproliferative neoplasm (n = 5), and myelodysplastic syndromes (n = 3). Thirty-seven patients (73%) were in complete remission. Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine and mycophenolate for all patients, associated with ATG in 39 patients (76.5%). The median time to neutrophil engraftment was 17 days (range, 12 to 34 days). The cumulative incidences of grade II-IV and grade III-IV acute GVHD were 27.5% and 14%, respectively. In patients receiving a PBSC graft and ATG prophylaxis, grade II-IV aGVHD occurred in 16% of patients. The use of ATG and a lower thiotepa dose (5 mg/kg versus 10 mg/kg) were associated with a reduced cumulative incidence of grade II-IV acute GVHD (P = .03 and .005, respectively). The 2-year cumulative incidence of chronic GVHD was 29% and was significantly reduced to 13% with the lower thiotepa dose (P = .002). After a median follow-up of 25 months (range, 12 to 62 months), the cumulative incidences of nonrelapse mortality, relapse, overall survival (OS), disease-free survival (DFS), and GVHD-free, relapse-free survival (GFRFS) were 20%, 22.5%, 67%, 58%, and 51%, respectively. Pretransplantation disease status (complete remission versus others) was the main factor associated with OS, DFS, and GFRFS. In conclusion, the TBF conditioning regimen is an appealing platform in the haplo-HSCT setting with PT-Cy in terms of engraftment rate, toxicity, and disease control. We found no benefit of a thiotepa dose of 10 mg/kg compared with a dose of 5 mg/kg. ATG reduced the risk of acute GVHD without comprising outcomes.     

Allogeneic Hematopoietic Stem Cell Transplantation Using Reduced-Intensity Conditioning for Adult T Cell Leukemia/Lymphoma: Impact of Antithymocyte Globulin on Clinical Outcome

Allogeneic hematopoietic stem cell transplantation (HSCT) is an effective treatment for adult T cell leukemia/lymphoma (ATLL), but shows high mortality. We evaluated the feasibility of reduced-intensity transplantation using fludarabine and busulfan, with particular focus on the clinical impact of antithymocyte globulin (ATG) in the conditioning regimen. Fourteen elderly patients with aggressive ATLL were enrolled in the current study without ATG, and were compared to those in 15 patients who were treated similarly, but with ATG, in our previous study. Engraftment was prompt, and treatment was tolerable. Overall (OS) and progression-free survival (PFS) at 3 years were 36% and 31%, respectively. HTVL-1 proviral load became undetectable by the polymerase chain reaction in 62% of patients. Compared to the previous study with ATG, complete donor chimera was significantly delayed. Although early relapse tended to be decreased, OS or PFS was not improved significantly. Analysis of combined data from both our current and previous studies disclosed that grade I-II acute GVHD was the only factor that favorably affected OS and PFS. These data suggested the presence of a graft-versus-ATLL effect and the feasibility of a transplant procedure without ATG in elderly ATLL patients, but could not demonstrate the clinical benefit of incorporating ATG.     

Prospective Study of Allogeneic Hematopoietic Stem Cell Transplantation with Post-Transplantation Cyclophosphamide and Antithymocyte Globulin from HLA-Mismatched Related Donors for Nonmalignant Diseases

Allogeneic hematopoietic stem cell transplantation (HSCT) is performed as a curative treatment for children with nonmalignant diseases, such as bone marrow failure syndromes and primary immunodeficiencies. Because graft-versus-host-disease (GVHD) is a major factor affecting survival probability and quality of life after HSCT, the availability of HLA-matched donors restricts the application of HSCT. Recently, HSCT with post-transplantation cyclophosphamide (PTCy) has emerged as a potent method to prevent GVHD after HSCT from HLA-haploidentical donors, and some studies have suggested the safety of PTCy-HSCT for nonmalignant diseases. We conducted a prospective clinical trial aiming to help confirm the safety of HSCT and further reduction of GVHD using a combination of PTCy and low-dose antithymocyte globulin (ATG) from HLA-mismatched related donors for children with nonmalignant diseases. Six patients underwent HSCT and achieved engraftment at a median of 14.5 days, and no patient developed severe acute GVHD. All patients had sustained donor chimerism without developing chronic GVHD at the last follow-up. In conclusion, HSCT with PTCy and low-dose ATG from an HLA-mismatched related donor were feasible to control GVHD for nonmalignant diseases in the children involved in our study.© 2020 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.     

Hematopoietic Cell Transplantation with Reduced Intensity Conditioning Using Fludarabine/Busulfan or Fludarabine/Melphalan for Primary Immunodeficiency Diseases

Purpose

The purpose of our study was to compare the safety and efficacy of hematopoietic cell transplantation (HCT) using fludarabine (Flu)-based reduced intensity conditioning (RIC) with busulfan (BU) or melphalan (Mel) for primary immunodeficiency diseases (PID).

Methods

We retrospectively analyzed transplant outcome, including engraftment, chimerism, immune reconstitution, and complications in 15 patients with severe combined immunodeficiency (SCID) and 27 patients with non-SCID PID. The patients underwent Flu-based RIC-HCT with BU (FluBU: 7 SCID, 16 non-SCID) or Mel (FluMel: 8 SCID, 11 non-SCID). The targeted low-dose BU with therapeutic drug monitoring was set to 30 mg hour/L for SCID.

Results

The 2-year overall survival of all patients was 79.6% and that of patients with SCID in the FluBU and FluMel groups was 100% and 62.5%, respectively. In the FluBU group, all seven patients achieved engraftment, good immune reconstitution, and long-term survival. All five patients receiving umbilical cord blood transplantation achieved complete or high-level mixed chimerism and sufficient specific IgG production. In the FluMel group, six of eight patients achieved complete or high-level mixed chimerism. Viral reactivation or new viral infection occurred in one FluBU group patient and four FluMel group patients. In the non-SCID group, 10 of 11 patients (91%) who received FluMel achieved complete or high-level mixed chimerism but had variable outcomes. Patients with WAS (2/2 patients), NEMO deficiency (2/2 patients), and X-linked hyper IgM syndrome (2/3 patients) who received FluBU achieved complete or high-level mixed chimerism and long-term survival.

Conclusions

RIC-HCT with FluBU is a safe and effective strategy for obtaining high-level donor chimerism, immune reconstitution including B cell function, and long-term survival in patients with SCID. In patients with non-SCID PID, the results varied according to the subtype of the disease. Further prospective studies are required to optimize the conditioning regimen for non-SCID PID.

     

Fludarabine and Busulfan versus Fludarabine,Cyclophosphamide, and Rituximab as Reduced-Intensity Conditioning for Allogeneic Transplantation in Follicular Lymphoma

Large, multicenter studies comparing commonly used reduced-intensity conditioning (RIC) approaches in follicular lymphoma (FL) have not been performed. Using the Center for International Blood and Marrow Transplant Research database, we report the outcomes of the 2 most commonly used RIC approaches, fludarabine and busulfan (Flu/Bu) versus fludarabine, cyclophosphamide, and rituximab (FCR) in FL patients. We evaluated 200 FL patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT) who received RIC with either Flu/Bu (n?=?98) or FCR (n?=?102) during 2008 to 2014. All patients received peripheral blood grafts, and graft-versus-host disease (GVHD) prophylaxis was limited to calcineurin inhibitor–based approaches. Median follow-up of survivors in the Flu/Bu and FCR groups was 48 months and 46 months, respectively. On univariate analysis in the Flu/Bu and FCR groups, the 3-year rates of nonrelapse mortality (11% versus 11%, P?=?.94), relapse/progression (18% versus 15%, P?=?.54), progression-free survival (PFS) (71% versus 74%, P?=?.65), and overall survival (OS) (73% versus 81%, P?=?.18) were not significantly different. On multivariate analysis no difference was seen between the FCR and Flu/Bu cohorts in terms of grades II to IV (relative risk [RR],?1.06; 95% confidence interval [CI],?.59 to 1.93; P?=?.84) or grades III to IV (RR,?1.18; 95% CI, .47 to 2.99; P?=?.72) acute GVHD, nonrelapse mortality (RR,?.83; 95% CI, .38 to 1.82; P?=?.64), relapse/progression (RR,?.99; 95% CI, .49 to 1.98; P?=?.97), PFS (RR,?.92; 95% CI, .55 to 1.54; P?=?.76), or OS (RR,?.70; 95% CI, .40 to 1.23; P?=?.21) risk. However, RIC with FCR was associated with a significantly reduced chronic GVHD risk (RR,?.52; 95% CI, .36 to .77; P?=?.001). RIC with either Flu/Bu or FCR in patients with FL undergoing allo-HCT provides excellent 3-year OS, with acceptable rates of nonrelapse mortality. FCR-based conditioning was associated with a lower risk of chronic GVHD.     

Second Solid Cancers after Allogeneic Hematopoietic Cell Transplantation Using Reduced-Intensity Conditioning

We examined risk of second solid cancers after allogeneic hematopoietic cell transplantation (AHCT) using reduced-intensity/nonmyeloablative conditioning (RIC/NMC). RIC/NMC recipients with leukemia/myelodysplastic syndrome (MDS) (n = 2833) and lymphoma (n = 1436) between 1995 and 2006 were included. In addition, RIC/NMC recipients 40 to 60 years of age (n = 2138) were compared with patients of the same age receiving myeloablative conditioning (MAC, n = 6428). The cumulative incidence of solid cancers was 3.35% at 10 years. There was no increase in overall cancer risk compared with the general population (leukemia/MDS: standardized incidence ratio [SIR] .99, P = 1.00; lymphoma: SIR .92, P = .75). However, risks were significantly increased in leukemia/MDS patients for cancers of lip (SIR 14.28), tonsil (SIR 8.66), oropharynx (SIR 46.70), bone (SIR 23.53), soft tissue (SIR 12.92), and vulva (SIR 18.55) and skin melanoma (SIR 3.04). Lymphoma patients had significantly higher risks of oropharyngeal cancer (SIR 67.35) and skin melanoma (SIR 3.52). Among RIC/NMC recipients, age >50 years was the only independent risk factor for solid cancers (hazard ratio [HR] 3.02, P < .001). Among patients ages 40 to 60 years, when adjusted for other factors, there was no difference in cancer risks between RIC/NMC and MAC in leukemia/MDS patients (HR .98, P = .905). In lymphoma patients, risks were lower after RIC/NMC (HR .51, P = .047). In conclusion, the overall risks of second solid cancers in RIC/NMC recipients are similar to the general population, although there is an increased risk of cancer at some sites. Studies with longer follow-up are needed to realize the complete risks of solid cancers after RIC/NMC AHCT.     

Choosing a Reduced-Intensity Conditioning Regimen for Allogeneic Stem Cell Transplantation,Fludarabine/Busulfan versus Fludarabine Melphalan: A Systematic Review and Meta-Analysis

Fludarabine with busulfan (FB) or melphalan (FM) are 2 more commonly used reduced-intensity conditioning (RIC) regimens for allogeneic stem cell transplantation (HCT).We present a systematic review and meta-analysis of studies comparing these 2 RIC regimens. We searched electronic databases from inception through November 1, 2017 for literature searches to identify relevant studies. A DerSimonian random effects model was used to measure efficacy outcomes; hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) are reported. Seven studies, including a total of 1955 patients, met criteria for inclusion, of which 6 were included in the overall pooled analysis because of repetition of some patients in 2 studies. Three studies were included in the subgroup analysis of acute myelogenous leukemia (AML)/myelodysplastic syndrome (MDS) and 2 in the subgroup analysis of lymphoid malignancies. Overall survival (OS) and progression-free survival were not statistically significantly different between the 2 RIC regimens in analysis of all studies. However, OS was better with FM in subgroup analysis of AML/MDS studies (HR, .83; 95% CI, .73 to .95). Nonrelapse mortality was lower with FB (HR, .64; 95% CI, .46 to .89), whereas relapse was lower with FM (HR, 1.52; 95% CI, 1.13 to 2.06) in the analysis of all studies. This meta-analysis shows that FB and FM are associated with a similar OS in patients undergoing HCT. Relapse rates are lower with FM but at the cost of higher nonrelapse mortality.     

HLA-Mismatched Unrelated Donors as an Alternative Graft Source for Allogeneic Stem Cell Transplantation after Antithymocyte Globulin-Containing Conditioning Regimen

Between August 1996 and December 2004, 369 patients with a median age of 41 years (range: 1-68 years) received stem cell transplantation (SCT) from unrelated donors after an antithymocyte-globulin (ATG)-containing conditioning regimen. In 268 patients, complete molecular typing (4-digit) of HLA-A, -B, -C, -DRB1, and -DQB1 was available: 110 patients were completely matched for 10 alleles, 91 patients had 1 allele-mismatch (9/10), and 67 patients were mismatched for 2-4 alleles (6-8/10). The incidence of grade II-IV acute graft-versus-host disease (aGVHD) was 33% in the 10/10, 41% in the 9/10, and 40% in the 6-8/10 group, respectively (P = .1). The cumulative incidence of treatment-related mortality (TRM) and relapse among the groups were similar (27%, 31%, and 32%, P = .2; and 28%, 27%, and 26%, P = .9. After a median follow-up of 35 months (range: 3-120 months), the estimated 5-year disease-free survival (DFS) was 42% and did not differ among the 10/10, the 9/10, and the 6-8/10-mismatched groups (45% versus 42% versus 39%) (P = .5). In multivariate analysis, only age (hazard ratio [HR] 1.013) (P = .004) and bad-risk disease (HR 1.975) (P < .001) were independent risk factors for DFS. In conclusion, pretransplant ATG allows allogeneic SCT from unrelated donors with HLA disparities.     

Optimizing Antithymocyte Globulin Dosing for Unrelated Donor Allogeneic Hematopoietic Cell Transplantation Based on Recipient Absolute Lymphocyte Count

Antithymocyte globulin (ATG) is used as prophylaxis against graft-versus-host disease (GVHD). Current dosing regimens for ATG are empiric and weight-based, and do not account for patient-specific factors. Furthermore, the target of ATG, recipient T cells post-cytotoxic chemotherapy, is not a function of recipient weight. We hypothesized the recipient peripheral blood absolute lymphocyte count (ALC) on the day of ATG administration would interact with the dose of ATG administered to predict transplantation outcomes. We retrospectively analyzed 135 patients who received ATG for GVHD prophylaxis for unrelated allogeneic hematopoietic cell transplantation at 3 different doses: 10?mg/kg, 7.5?mg/kg, and 5?mg/kg. There was no difference in 2-year overall survival (OS) among ATG dosing groups; however, deaths from infectious complications were significantly higher with higher doses of ATG (3.7% versus 19% versus 26.7%; P?=?.02). Severity of chronic GVHD was lower with higher doses of ATG (28% versus 24% versus 4%; P?=?.03). In multivariate analysis, the median peripheral blood ALC on day of ATG administration and the total amount of ATG interacted to predict OS (hazard ratio, .09; P?=?.03). For low recipient ALC (10th percentile, or .56 × 10²/µL), a higher total ATG dose was associated with a greater risk of death, whereas for high recipient ALC (90th percentile, or 24.96 × 10²/µL), a higher ATG dose was associated with a lower risk of death. Our findings suggest that the interaction between ATG and its target, the recipient lymphocyte, could represent a new paradigm for ATG dosing.     

Early Donor Chimerism Levels Predict Relapse and Survival after Allogeneic Stem Cell Transplantation with Reduced-Intensity Conditioning

The success of hematopoietic stem cell transplantation (HSCT) with reduced-intensity conditioning (RIC) is limited by a high rate of disease relapse. Early risk assessment could potentially improve outcomes by identifying appropriate patients for preemptive strategies that may ameliorate this high risk. Using a series of landmark analyses, we investigated the predictive value of early (day-30) donor chimerism measurements on disease relapse, graft-versus-host disease, and survival in a cohort of 121 patients allografted with a uniform RIC regimen. Chimerism levels were analyzed as continuous variables. In multivariate analysis, day-30 whole blood chimerism levels were significantly associated with relapse (hazard ratio [HR] = .90, P < .001), relapse-free survival (HR = .89, P < .001), and overall survival (HR = .94, P = .01). Day-30 T cell chimerism levels were also significantly associated with relapse (HR = .97, P = .002), relapse-free survival (HR = .97, P < .001), and overall survival (HR = .99, P = .05). Multivariate models that included T cell chimerism provided a better prediction for these outcomes compared with whole blood chimerism. Day-30 chimerism levels were not associated with acute or chronic graft-versus-host disease. We found that high donor chimerism levels were significantly associated with a low lymphocyte count in the recipient before transplant, highlighting the impact of pretransplant lymphopenia on the kinetics of engraftment after RIC HSCT. In summary, low donor chimerism levels are associated with relapse and mortality and can potentially be used as an early predictive and prognostic marker. These findings can be used to design novel approaches to prevent relapse and to improve survival after RIC HSCT.     

Association of Antiepileptic Medications with Outcomes after Allogeneic Hematopoietic Cell Transplantation with Busulfan/Cyclophosphamide Conditioning

High-dose busulfan (BU) followed by high-dose cyclophosphamide (CY) before allogeneic hematopoietic cell transplantation (HCT) has long been used as treatment for hematologic malignancies. Administration of phenytoin or newer alternative antiepileptic medications (AEMs) prevents seizures caused by BU. Phenytoin induces enzymes that increase exposure to active CY metabolites in vivo, whereas alternative AEMs do not have this effect. Lower exposure to active CY metabolites with the use of alternative AEMs could decrease the risk of toxicity but might increase the risk of recurrent malignancy after HCT. Previous studies have not determined whether outcomes with alternative AEMs differ from those with phenytoin in patients treated with BU/CY before allogeneic HCT. We studied a cohort of 2155 patients, including 1460 treated with phenytoin and 695 treated with alternative AEMs, who received BU/CY before allogeneic HCT between 2004 and 2014. We found no differences suggesting decreased overall survival or relapse-free survival or increased risks of relapse, nonrelapse mortality, acute or chronic graft-versus-host disease, or regimen-related toxicity associated with the use of alternative AEMs compared with phenytoin. The risk of dialysis was lower in the alternative AEM group than in the phenytoin group. Alternative AEMs are safe for prevention of seizures after BU administration and can avoid the undesirable toxicities and drug interactions caused by phenytoin.     

Standard Antithymocyte Globulin Dosing Results in Poorer Outcomes in Overexposed Patients after Ex Vivo CD34+ Selected Allogeneic Hematopoietic Cell Transplantation

Antithymocyte globulin (ATG) use mitigates the risk of graft rejection and graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (allo-HCT), but ATG overexposure in the setting of lymphopenia negatively affects immune recovery. We hypothesized that standard empiric weight-based dosing of ATG, used to prevent graft rejection in ex vivo CD34-selected allo-HCT, may lead to serious adverse consequences on outcomes in certain patients. We evaluated 304 patients undergoing myeloablative-conditioned ex vivo CD34-selected allo-HCT with HLA-matched donors for the treatment of hematologic malignancies. Patients received rabbit ATG at a dose of 2.5 mg/kg/day i.v. on days -3 and/or -2. An ATG dosing cutoff of 450 mg was used for statistical analyses to assess the relationship between ATG and overall survival (OS). Among all patients, median total ATG dose was 360 mg (range, 130 to 510 mg); 279 (92%) received a total dose of ATG ≤450 mg, and 25 (8%) received a total dose >450 mg. On the first day of ATG administration (day -3), the median absolute lymphocyte count was .0 K/µL. For patients who received a total dose of ATG >450 mg or ≤450 mg, the incidences of acute and late-acute GVHD grade II-IV were statistically similar. At 3 years post-HCT, for patients who received a total dose of ATG >450 mg or ≤450 mg, nonrelapse mortality (NRM) rates were 35% and 18%, respectively (P = .029), disease-free survival (DFS) rates were 37% and 61%, respectively (P = .003), and OS rates were 40% and 67%, respectively (P = .001). Among all patient and HCT characteristics in multivariable analyses, receipt of a total dose of ATG >450 mg was associated with an increased risk of NRM (hazard ratio [HR], 2.9; P = .01), shorter DFS (HR, 2.0; P = .03), and inferior OS (HR, 2.1; P = .01). In summary, the use of weight-based ATG at a time of relative lymphopenia before ex vivo CD34-selected allo-HCT results in overdosing in heavier patients, leading to higher NRM and lower DFS and OS. Further pharmacokinetic investigation in this setting is critical to determining the optimal dosing strategy for ATG.     

Unrelated Donor Allogeneic Hematopoietic Stem Cell Transplantation for Patients with Hemoglobinopathies Using a Reduced-Intensity Conditioning Regimen and Third-Party Mesenchymal Stromal Cells

Allogeneic hematopoietic stem cell transplantation for patients with a hemoglobinopathy can be curative but is limited by donor availability. Although positive results are frequently observed in those with an HLA-matched sibling donor, use of unrelated donors has been complicated by poor engraftment, excessive regimen-related toxicity, and graft-versus-host disease (GVHD). As a potential strategy to address these obstacles, a pilot study was designed that incorporated both a reduced-intensity conditioning and mesenchymal stromal cells (MSCs). Six patients were enrolled, including 4 with high-risk sickle cell disease (SCD) and 2 with transfusion-dependent thalassemia major. Conditioning consisted of fludarabine (150 mg/m²), melphalan (140 mg/m²), and alemtuzumab (60 mg for patients weighing > 30 kg and .9 mg/kg for patients weighing <30 kg). Two patients received HLA 7/8 allele matched bone marrow and 4 received 4-5/6 HLA matched umbilical cord blood as the source of HSCs. MSCs were of bone marrow origin and derived from a parent in 1 patient and from an unrelated third-party donor in the remaining 5 patients. GVHD prophylaxis consisted of cyclosporine A and mycophenolate mofetil. One patient had neutropenic graft failure, 2 had autologous hematopoietic recovery, and 3 had hematopoietic recovery with complete chimerism. The 2 SCD patients with autologous hematopoietic recovery are alive. The remaining 4 died either from opportunistic infection, GVHD, or intracranial hemorrhage. Although no infusion-related toxicity was seen, the cotransplantation of MSCs was not sufficient for reliable engraftment in patients with advanced hemoglobinopathy. Although poor engraftment has been observed in nearly all such trials to date in this patient population, there was no evidence to suggest that MSCs had any positive impact on engraftment. Because of the lack of improved engraftment and unacceptably high transplant-related mortality, the study was prematurely terminated. Further investigations into understanding the mechanisms of graft resistance and development of strategies to overcome this barrier are needed to move this field forward.