Effects of different serum-levels of ATG after unrelated donor umbilical cord blood transplantation

Optimal Active Anti-Thymocyte Globulin Exposure Associated with Minimum Risk of Virus Reactivation and Comparable Acute Graft-Versus-Host Disease Under Adult Myeloablative Haploidentical Peripheral Blood Stem Cell Transplantation

Anti-thymocyte globulin (ATG) is often included in the conditioning regimen to prevent graft-versus-host disease (GVHD) in allogeneic hematopoietic cell transplantation (allo-HCT). However, the risk of virus reactivation increases significantly. We conducted a single-center prospective study to identify the optimal ATG exposure that ensures engraftment, effectively prevents acute GVHD, and reduces the risk of virus reactivation without increasing relapse of malignant diseases in haploidentical peripheral blood stem cell transplantation (haplo-PBSCT). From September 2018 to June 2020, 106 patients (median age, 32 years) with malignant hematological diseases who received haplo-PBSCT for the first time were enrolled. All patients received 10 mg/kg rabbit ATG (thymoglobulin) divided for 4 days (days -5 to -2). Pre-transplant, post-transplant, and total areas under the concentration-time curve (AUCs) of active ATG were calculated. Total AUC of active ATG was shown to be the best predictor for virus reactivation and acute GVHD of grades II to IV or grades III and IV. The optimal total AUC range of active ATG was 100 to 148.5 UE/mL/day. The median time was 14 versus 13 days (P = .184) for myeloid engraftment and 13 versus 13 days (P = .263) for platelet engraftment in the optimal and non-optimal AUC groups, respectively. The optimal AUC group showed a lower cumulative incidence of cytomegalovirus (CMV) reactivation and persistent CMV viremia than the non-optimal AUC group: 60.6% (95% confidence interval [CI], 48.3%-73.1%) versus 77.1% (95% CI, 64.5%-87.7%; P = .016) and 31.5% (95% CI, 21.2%-45.3%) versus 56.3% (95% CI, 42.9%-70.4%; P = .007), respectively. The cumulative incidence of persistent Epstein-Barr virus (EBV) viremia in the optimal AUC group was significantly lower than the non-optimal total AUC group: 33.1% (95% CI, 22.5%-46.8%) versus 52.6% (95% CI, 39.3%-67.2%; P = .048). However, there was no difference in EBV reactivation (P = .752). Similar outcomes were observed for grade II to IV and grade III and IV acute GVHD between the two groups: 48.6% (95% CI, 36.8%-62.0%) versus 37.0% (95% CI, 24.8%-52.5%; P = .113) and 10.4% (95% CI, 4.8%-21.7%) versus 4.2% (95% CI, 1.0%-15.6%; P = .234, respectively. Relapse, non-relapse mortality, and disease-free survival demonstrated no significant differences between the two groups. But, overall survival at 2 years tended to increase in the optimal AUC group: 75.7% (95% CI, 62.4%-84.8%) versus 57.8% (95% CI, 42.4%-70.4%; P = .061). These data support an optimal active ATG exposure of 110 to 148.5 UE/mL/day in haplo-PBSCT. Individualized dosing of ATG in allo-HCT might reduce the risk of virus reactivation and effectively prevent acute GVHD simultaneously.

Lower Absolute Lymphocyte Count Before Conditioning Predicts High Relapse Risk in Patients After Haploidentical Peripheral Blood Stem Cell Transplantation With Low Dose Anti-Thymocyte Globulin/Post-Transplant Cyclophosphamide for GvHD Prophylaxis

Standard anti-thymocyte globulin (ATG) weight-based dosing often resulted in highly variable ATG exposure, which had profound effects on relapse and survival, especially in recipients with relatively low absolute lymphocyte count (ALC) before conditioning. Data regarding rabbit ATG pharmacokinetics and pharmacodynamics in the setting of HLA-haploidentical peripheral blood stem cell transplantation (haplo-PBSCT) is lacking. We conducted a retrospective study on 90 consecutive patients who underwent haplo-PBSCT with low dose rabbit ATG (5 mg/kg) plus low dose post-transplant cyclophosphamide (50 mg/kg) based regimen for graft-versus-host disease (GvHD) prophylaxis. We compared serum concentration of ATG and post-transplant results between patients with ALC<500/μl and ALC≥500/μl before conditioning. Patients with ALC<500/μl had higher ATG concentrations, delayed immune reconstitution, lower incidence of grade II-IV acute GvHD (0 vs. 19.42%, P = 0.043), higher risk of Epstein-Barr virus infection within 100 days post-transplant (47.78% vs. 22.22%, P = 0.020) and 1-year relapse rate (33.33% vs.11.59%, P = 0.041), and lower 1-year overall survival (OS) (52.38% vs.79.71%, P = 0.004), 1-year relapse free survival (RFS) (47.62% vs. 75.36% for RFS, P = 0.014), and 1-year GvHD free relapse-free survival (GRFS) (42.89% vs. 65.22%, P = 0.043). ALC<500/μl before conditioning was a significant poor risk factor for relapse, OS, RFS, and GRFS.

Influence of anti-thymocyte globulin plasma levels on outcome parameters in stem cell transplanted children

INTRODUCTION

Allogenic hematopoietic stem cell transplantation is a curative option for malignant and non-malignant pediatric diseases. Serotherapy is often employed to avoid graft-versus-host disease (GvHD) on one hand and graft rejection on the other hand. Therapeutic drug monitoring is increasingly used to allow for more precise dosing especially in pediatric patients due to their specific pharmacological characteristics. Application of T-cell directed antibodies is not routinely monitored, but may benefit from more precise dosing regimens.

METHODS

Two different preparations of rabbit anti-thymocyte globulin (rATG), Thymoglobuline® and ATG-F (Grafalon®), are frequently used to prevent GvHD in pediatric patients by in vivo T-cell depletion. Total rATG levels and active rATG levels were analyzed prospectively in pediatric patients undergoing HSCT. Clinical and laboratory outcome parameters were recorded.

RESULTS

rATG levels were measured in 32 patients, 22 received thymoglobuline and 10 received ATG-F. The median total peak plasma level was 419.0 µg/ml for ATG-F and 60.4 µg/ml for thymoglobuline. For ATG-F, exposure could be predicted from the calculated dose more precisely than for thymoglobuline. Active peak plasma levels neither of ATG-F, nor of thymoglobuline correlated significantly with the number of lymphocytes prior to serotherapy. There was no significant difference in incidence of aGvHD, cGvHD, rejection, mixed chimerism or viral infections in the two cohorts. However, in our cohort, patients with high thymoglobuline exposure showed a compromised reconstitution of T cells.

CONCLUSIONS

ATG-F and thymoglobuline show different pharmacological and immunological impact in children, whose clinical significance needs to be investigated in larger cohorts.

Host and Graft Factors Impacting Infection Risk in Hematopoietic Cell Transplantation

Infection contributes significantly to morbidity and mortality in hematopoietic cell transplantation. A complex interplay of host, graft, and technical factors contributes to infectious risk in the recipient. Host factors such as age, underlying disease, and comorbidities; central venous access; and the preparative regimen contribute to mucosal disruption, organ dysfunction, and immunodeficiency before hematopoietic cell transplantation. Graft factors, including donor histocompatibility, cell source, and graft components, along with immunosuppression and graft-versus-host disease, contribute to the speed of immune reconstitution. Evaluation of these factors, plus previous and posttransplant exposure to pathogens, is necessary to best assess an individual recipient's infection risk.

Prospective, Randomized, Double-Blind, Phase III Clinical Trial of Anti-T-Lymphocyte Globulin to Assess Impact on Chronic Graft-Versus-Host Disease-Free Survival in Patients Undergoing HLA-Matched Unrelated Myeloablative Hematopoietic Cell Transplantation

Purpose Several open-label randomized studies have suggested that in vivo T-cell depletion with anti-T-lymphocyte globulin (ATLG; formerly antithymocyte globulin-Fresenius) reduces chronic graft-versus-host disease (cGVHD) without compromising survival. We report a prospective, double-blind phase III trial to investigate the effect of ATLG (Neovii Biotech, Lexington, MA) on cGVHD-free survival. Patients and Methods Two hundred fifty-four patients 18 to 65 years of age with acute leukemia or myelodysplastic syndrome who underwent myeloablative HLA-matched unrelated hematopoietic cell transplantation (HCT) were randomly assigned one to one to placebo (n =128 placebo) or ATLG (n = 126) treatment at 27 sites. Patients received either ATLG or placebo 20 mg/kg per day on days -3, -2, -1 in addition to tacrolimus and methotrexate as GVHD prophylaxis. The primary study end point was moderate-severe cGVHD-free survival. Results Despite a reduction in grade 2 to 4 acute GVHD (23% v 40%; P = .004) and moderate-severe cGVHD (12% v 33%; P < .001) in ATLG recipients, no difference in moderate-severe cGVHD-free survival between ATLG and placebo was found (2-year estimate: 48% v 44%, respectively; P = .47). Both progression-free survival (PFS) and overall survival (OS) were lower with ATLG (2-year estimate: 47% v 65% [ P = .04] and 59% v 74% [ P = .034], respectively). Multivariable analysis confirmed that ATLG was associated with inferior PFS (hazard ratio, 1.55; 95% CI, 1.05 to 2.28; P = .026) and OS (hazard ratio, 1.74; 95% CI, 1.12 to 2.71; P = .01). Conclusion In this prospective, randomized, double-blind trial of ATLG in unrelated myeloablative HCT, the incorporation of ATLG did not improve moderate-severe cGVHD-free survival. Moderate-severe cGVHD was significantly lower with ATLG, but PFS and OS also were lower. Additional analyses are needed to understand the appropriate role for ATLG in HCT.

Association between anti-thymocyte globulin exposure and survival outcomes in adult unrelated haemopoietic cell transplantation: a multicentre, retrospective, pharmacodynamic cohort analysis

BACKGROUND

Anti-thymocyte globulin (ATG) is used to prevent graft-versus-host disease (GvHD) after allogeneic haemopoietic cell transplantation (HCT). However, ATG can also cause delayed immune reconstitution of T cells, negatively affecting survival. We studied the relation between exposure to ATG and clinical outcomes in adult patients with acute leukaemia and myelodysplastic syndrome.

METHODS

We did a retrospective, pharmacokinetic-pharmacodynamic analysis of data from patients with acute lymphoid leukaemia, acute myeloid leukaemia, or myelodysplastic syndrome receiving their first T-cell repleted allogeneic peripheral blood stem cell HCT with ATG (thymoglobulin) as part of non-myeloablative conditioning from March 1, 2004, to June 1, 2015. Patients received a cumulative intravenous dose of 8 mg/kg divided over 4 days, starting on day -8 before HCT. Active ATG concentrations were measured using a validated bioassay and pharmacokinetic exposure measures (maximum concentration, concentration at time of infusion of the graft, time to reach a concentration of 1 arbitary unit [AU] per day/mL, area under the curve [AUC], and the AUC before and after HCT) were calculated with a validated population pharmacokinetic model. The main outcome of interest was 5-year overall survival, defined as days to death from any cause or last follow-up. Other outcomes were relapse-related mortality, non-relapse mortality, event-free survival, acute and chronic GvHD, and assessment of current and optimum dosing. We used Cox proportional hazard models and Fine-Gray competing risk models for the analyses.

FINDINGS

146 patients were included. ATG exposure after HCT was shown to be the best predictor for 5-year overall survival. Optimum exposure after transplantation was determined to be 60-95 AU per day/mL. Estimated 5-year overall survival in the group who had optimum exposure (69%, 95% CI 55-86) was significantly higher than in the group who had below optimum exposure (32%, 20-51, p=0·00037; hazard ratio [HR] 2·41, 95% CI 1·15-5·06, p=0·020) and above optimum exposure (48%, 37-62, p=0·030; HR 2·11, 95% CI 1·04-4·27, p=0·038). Patients in the optimum exposure group had a greater chance of event-free survival than those in the below optimum exposure group (HR 2·54, 95% CI 1·29-5·00, p=0·007; HR for the above optimum group: 1·83, 0·97-3·47, p=0·063). Above-optimum exposure led to higher relapse-related mortality compared with optimum exposure (HR 2·66, 95% CI 1·12-6·31; p=0·027). Below optimum exposure increased non-relapse mortality compared with optimum exposure (HR 4·36, 95% CI 1·60-11·88; p=0·0040), grade 3-4 acute GvHD (3·09, 1·12-8·53; p=0·029), but not chronic GvHD (2·38, 0·93-6·08; p=0·070). Modelled dosing based on absolute lymphocyte counts led to higher optimum target attainment than did weight-based dosing.

INTERPRETATION

Exposure to ATG affects survival after HCT in adults, stressing the importance of optimum ATG dosing. Individualised dosing of ATG, based on lymphocyte counts rather than bodyweight, might improve survival chances after HCT.

FUNDING

Netherlands Organization for Health Research and Development and Queen Wilhelma Fund for Cancer Research.

Pharmacokinetics, Pharmacodynamics, and Pharmacogenomics of Immunosuppressants in Allogeneic Hematopoietic Cell Transplantation: Part II

Part I of this article included a pertinent review of allogeneic hematopoietic cell transplantation (alloHCT), the role of postgraft immunosuppression in alloHCT, and the pharmacokinetics, pharmacodynamics, and pharmacogenomics of the calcineurin inhibitors and methotrexate. In this article (Part II), we review the pharmacokinetics, pharmacodynamics, and pharmacogenomics of mycophenolic acid (MPA), sirolimus, and the antithymocyte globulins (ATG). We then discuss target concentration intervention (TCI) of these postgraft immunosuppressants in alloHCT patients, with a focus on current evidence for TCI and on how TCI may improve clinical management in these patients. Currently, TCI using trough concentrations is conducted for sirolimus in alloHCT patients. Several studies demonstrate that MPA plasma exposure is associated with clinical outcomes, with an increasing number of alloHCT patients needing TCI of MPA. Compared with MPA, there are fewer pharmacokinetic/dynamic studies of rabbit ATG and horse ATG in alloHCT patients. Future pharmacokinetic/dynamic research of postgraft immunosuppressants should include '-omics'-based tools: pharmacogenomics may be used to gain an improved understanding of the covariates influencing pharmacokinetics as well as proteomics and metabolomics as novel methods to elucidate pharmacodynamic responses.

Excellent T-cell reconstitution and survival depend on low ATG exposure after pediatric cord blood transplantation

Successful immune reconstitution (IR) is associated with improved outcomes following pediatric cord blood transplantation (CBT). Usage and timing of anti-thymocyte globulin (ATG), introduced to the conditioning to prevent graft-versus-host disease and graft failure, negatively influences T-cell IR. We studied the relationships among ATG exposure, IR, and clinical outcomes. All pediatric patients receiving a first CBT between 2004 and 2015 at the University Medical Center Utrecht were included. ATG-exposure measures were determined with a validated pharmacokinetics model. Main outcome of interest was early CD4⁺ IR, defined as CD4⁺ T-cell counts >50 × 10⁶/L twice within 100 days after CBT. Other outcomes of interest included event-free survival (EFS). Cox proportional-hazard and Fine-Gray competing-risk models were used. A total of 137 patients, with a median age of 7.4 years (range, 0.2-22.7), were included, of whom 82% received ATG. Area under the curve (AUC) of ATG after infusion of the cord blood transplant predicted successful CD4⁺ IR. Adjusted probability on CD4⁺ IR was reduced by 26% for every 10-point increase in AUC after CBT (hazard ratio [HR], 0.974; P < .0001). The chance of EFS was higher in patients with successful CD4⁺ IR (HR, 0.26; P < .0001) and lower ATG exposure after CBT (HR, 1.005; P = .0071). This study stresses the importance of early CD4⁺ IR after CBT, which can be achieved by reducing the exposure to ATG after CBT. Individualized dosing of ATG to reach optimal exposure or, in selected patients, omission of ATG may contribute to improved outcomes in pediatric CBT.

Correlation of rabbit antithymocyte globulin serum levels and clinical outcomes in children who received hematopoietic stem cell transplantation from an alternative donor

We analyzed the correlation between rabbit ATG (rATG) serum levels and clinical outcomes in 37 children who received rATG at a total dose of 10 or 15 mg/kg during HSCT conditioning from an alternative donor. Fourteen patients had advanced malignant diseases, 13 had severe AA, and 10 had inherited disorders. Complete engraftment was achieved in all patients, and no rejection occurred. The cumulative incidence of grades II-IV acute GVHD and extensive chronic GVHD was 27% (95% CI, 12.5-39.6%) and 8.1% (95% CI, 0-23.1%), respectively. Multivariate analysis identified lower rATG levels at week 4 as an independent risk factor in the development of grades II-IV acute GVHD (p = 0.037). Serious infections were not observed in any patient following HSCT. No correlation was found between EBV reactivation and rATG levels at week 2 and week 4 after HSCT. Furthermore, no correlation was found between relapse and rATG levels two and four wk post-transplantation. The probability of five-yr OS among patients was 70.3% (95% CI, 59.8-79.2%). Our results suggest that targeted rATG administration may protect patients from severe acute GVHD without increasing the risk of EBV reactivation or relapse.

Population pharmacokinetic modeling of Thymoglobulin(®) in children receiving allogeneic-hematopoietic cell transplantation: towards improved survival through individualized dosing

BACKGROUND AND OBJECTIVES

To prevent graft-versus-host disease and rejection in hematopoietic cell transplantation (HCT), children receive Thymoglobulin(®), a polyclonal antibody acting mainly by depleting T cells. The therapeutic window is critical as over-exposure may result in delayed immune reconstitution of donor T cells. In this study, we describe the population pharmacokinetics of Thymoglobulin(®) as a first step towards an evidence-based dosing regimen of Thymoglobulin(®) in pediatric HCT.

METHODS

Serum active Thymoglobulin(®) concentrations were measured in all pediatric HCTs performed between 2004 and 2012 in two pediatric HCT centers in The Netherlands. Population pharmacokinetic analysis was performed using NONMEM(®) version 7.2.

RESULTS

A total of 3,113 concentration samples from 280 pediatric HCTs were analyzed, with age ranging from 3 months to 23 years old. The cumulative Thymoglobulin(®) dose was 10 mg/kg in 94 % of the patients given in 4 consecutive days. A model incorporating parallel linear and concentration-dependent clearance of Thymoglobulin(®) was identified. Body weight [for linear clearance (CL) and central volume of distribution] as well as lymphocyte count pre-Thymoglobulin(®) infusion (for CL) were important covariates. As such, the current dosing regimen results in higher exposure in children with a higher bodyweight and/or a lower lymphocyte count pre-Thymoglobulin(®) infusion.

CONCLUSION

This model can be used to develop an individual dosing regimen for Thymoglobulin(®), based on both body weight and lymphocyte counts, once the therapeutic window has been determined. This individualized regimen may contribute to a better immune reconstitution and thus outcome of allogeneic HCT.

Association between anti-thymocyte globulin exposure and CD4+ immune reconstitution in paediatric haemopoietic cell transplantation: a multicentre, retrospective pharmacodynamic cohort analysis

BACKGROUND

Anti-thymocyte globulin (ATG) was introduced into the conditioning regimen in haemopoietic cell transplantation (HCT) to prevent graft-versus-host-disease (GvHD) and graft failure. However, ATG can also cause delayed immune reconstitution of donor T cells. We studied the relation between exposure to active ATG and clinical outcomes in children.

METHODS

In this retrospective analysis, all patients (age 0·2-23 years) receiving their first HCT between April 1, 2004, and April 1, 2012, who received ATG (thymoglobulin) in two Dutch paediatric HCT programmes were included. The cumulative dose of ATG was chosen according to local protocols and was given intravenously over 4 days consecutively. ATG exposure measures (maximum concentration, concentration at time of HCT, clearance, days to reach a concentration below the lympholytic concentration of one arbitrary unit [AU] per mL, total area under the curve [AUC], AUC before HCT, and AUC after HCT) were calculated using a validated population pharmacokinetic model. The main outcome of interest was immune reconstitution (defined as CD4+ T cells >0·05 × 10(9) cells per L in two consecutive measurements within 100 days). Other outcomes of interest were survival, acute and chronic GvHD, and graft failure. We used Cox proportional hazard models, logistic regression models, and Fine-Gray competing risk regressions for analyses.

FINDINGS

251 patients were included. The chance of successful immune reconstitution decreased as the ATG AUC after HCT increased (odds ratio 0·991, 95% CI 0·987-0·996; p<0·0001). Within the cord blood group, we noted decreased immune reconstitution above the lowest AUC quartile (≥ 20 AU × day/mL; p=0·0024), whereas in the bone marrow or peripheral blood stem cell group, decreased immune reconstitution was noted only in the highest quartile (≥ 100 AU × day/mL; p=0·0024). Successful immune reconstitution by day 100 was associated with increased overall survival (hazard ratio [HR] 0·49, 95% CI 0·29-0·81; p=0·0047) caused by reduced non-relapse mortality (0·40, 0·21-0·77; p=0·0062), and relapse-related mortality in myeloid leukaemia (0·25, 0·08-0·76; p=0·015). An AUC before transplantation of at least 40 AU × day/mL resulted in a lower incidence of acute GvHD (grade 2-4 HR 0·979, 95% CI 0·963-0·994; p=0·0081; and grade 3-4 0·975, 0·952-0·998; p=0·033), chronic GvHD (0·983, 0·968-0·998; p=0·029), and graft failure (0·981, 0·965-0·997; p=0·020) compared with an AUC of less than 40 AU × day/mL.

INTERPRETATION

These results stress the importance of improving the efficacy and safety of ATG in HCT by amending dosage and timing. Individualised dosing and timing of ATG to aim for optimum exposure before and after HCT could result in improved outcomes after paediatric HCT.

FUNDING

Dutch Organization for Scientific Research.

Impact of thymoglobulin prior to pediatric unrelated umbilical cord blood transplantation on immune reconstitution and clinical outcome

In vivo T-cell depletion might contribute to the delayed immune reconstitution observed after unrelated umbilical cord blood transplantation (UCBT). We studied the impact of early, late, and no antithymocyte globulin (ATG) on immune reconstitution and outcome. One hundred twenty seven children receiving UCBT in London or Utrecht were divided into 3 groups: early ATG (days -9 to -5; n = 33), late ATG (days -5 to 0; n = 48), and no ATG (n = 46). The no-ATG group received mycophenolate mofetile + cyclosporin A as graft-versus-host disease (GVHD) prophylaxis, while the ATG groups received cyclosporin A + prednisone. End points studied were survival, immune recovery, infections, and GVHD. The probability of survival was similar in all groups: no ATG, 71% ± 8%; early ATG, 68% ± 9%; and late ATG, 61% ± 7%. CD3(+), CD4(+), and CD4(+)-naive T-cell counts were significantly higher (P < .001) in the no-ATG group at 1, 2, 3, 6, and 12 months post-UCBT. In the no-ATG group, significantly fewer viral reactivations (P = .021) were noted. A higher probability of severe acute GVHD (aGVHD; 31%) was found in the no-ATG group compared with 18% (P = .018) for early-ATG and 5% (P < .001) for late-ATG groups. This was not associated with more chronic GVHD (cGVHD).