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

Dual T-cell depletion with individually tailored anti-thymocyte globulin and attenuated dose of post-transplant cyclophosphamide in haploidentical peripheral stem cell transplantation

This study aimed to assess the efficacy of dual T-cell suppression using individually tailored doses of antithymocyte globulin (ATG) and attenuated dose of post-transplant cyclophosphamide (PTCy) in haploidentical hematopoietic stem cell transplantation (haplo-HSCT). We conducted a retrospective analysis of 78 adults with acute leukemia or myelodysplastic syndrome who underwent haplo-HSCT using intravenous busulfan and fludarabine conditioning. Thirty-two patients received attenuated ATG/PTCy, while 46 patients received ATG (7.5 mg/kg) as GVHD prophylaxis. The 100-day cumulative incidence of grade III-IV (9.7% vs. 32.4%, P = 0.018) acute GVHD, as well as 2-year moderate-severe chronic GVHD (13.9% vs. 43.9%, P = 0.018) in the ATG/PTCy group were significantly lower than those in the ATG group. The 2-year overall survival was comparable between the two groups. However, 2-year GVHD-free, relapse-free survival in the ATG/PTCy group was significantly higher compared to that in the ATG group (38.9% vs. 21.7%, P = 0.021). Moreover, during post-engraftment period, the ATG/PTCy group exhibited lower incidences of life-threatening bacterial (12.5% vs. 37%, P = 0.033) and viral infection (0% vs. 17.4%, P = 0.035) than the ATG group. In conclusion, the combination of individually tailored ATG and low-dose PTCy appears to be a promising strategy in haplo-HSCT.

Anti-T-lymphocyte globulin improves GvHD-free and relapse-free survival in myelofibrosis after matched related or unrelated donor transplantation

Acute and chronic graft-versus-host disease (GvHD) are major complications of allogeneic hematopoietic cell transplantation (alloHCT). In vivo T-cell depletion with anti-T-lymphocyte globulin (ATLG) as part of the conditioning regimen prior to alloHCT is frequently used as GvHD prophylaxis, but data on its role in myelofibrosis is scarce. We took advantage of an international collaborative network to investigate the impact of ATLG in myelofibrosis undergoing first alloHCT. We included 707 patients (n = 469 ATLG and n = 238 non-ATLG prophylaxis). The cumulative incidence of acute GvHD grade II-IV was 30% for the ATLG group vs. 56% for the non-ATLG group (P < 0.001). Acute GvHD grade III-IV occurred in 20% vs. 25%, respectively (P = 0.01). Incidence of mild-to-severe chronic GvHD was 49% vs. 50% (P = 0.52), while ATLG showed significantly lower rates of severe chronic GvHD (7% vs. 18%; P = 0.04). GvHD-free and relapse-free survival (GRFS) at 6 years was 45% for the ATLG group vs. 37% for the non-ATLG group (P = 0.02), driven by significantly improved GRFS of ATLG in matched related and matched unrelated donors. No significant differences in risk for relapse, non-relapse mortality, and overall survival were observed. Multivariable modeling for GRFS showed a 48% reduced risk of GvHD, relapse, or death when using ATLG.

Post-transplant сyclophosphamide after matched donor hematopoietic stem cell transplantation in children with acute leukemia

INTRODUCTION

The data on post-transplant cyclophosphamide (PTCy) in pediatric acute leukemia after matched allo-HSCT are limited to case series. The present study aimed to assess the results of PTCy-based GVHD prophylaxis in a large cohort of children with acute leukemia after matched allo-HSCT.

METHODS

A retrospective analysis of 190 pediatric patients with acute leukemia who had a first allograft between 2008 and 2020 from a matched sibling donor (MSD) or matched unrelated donor (MUD) was carried out. In the MSD setting, GVHD prophylaxis consisted of PTCy alone (n = 28) for the study group, and calcineurin inhibitor (CNI) ± antimetabolite (n = 30) for the control group. In MUD setting, most patients in the study group received GVHD prophylaxis with PTCy+CNI+mycophenolate mofetil (n = 42, 66.7%) or PTCy+CNI+sirolimus (n = 12, 19%). All patients (n = 69) in the control group received ATG+CNI+antimetabolite.

RESULTS

After MUD allo-HSCT, the incidences of acute GVHD grade III-IV and moderate/severe chronic GVHD were significantly lower in the PTCy group compared to control (6.6% vs. 35.0% and 12.7% vs. 47.1%, respectively, p < .0001). Five-year GVHD-free, relapse-free survival (GRFS) after MUD allo-HSCT was higher in the PTCy group compared to control (35.1% vs. 7.3%, p < .0001). At the same time, there was no significant difference between both groups after MSD allo-HSCT.

CONCLUSIONS

In pediatric acute leukemia, PTCy-based GVHD prophylaxis for MUD allo-HSCT is a feasible and effective option that results in a low incidence of GVHD. Compared to the ATG-based approach, PTCy provides better control of GVHD in children. In pediatric allo-HSCT from MSD, PTCy demonstrates comparable effectiveness to conventional GVHD prophylaxis.

Combining post-transplant cyclophosphamide with antithymocyte globulin for graft-versus-host disease prophylaxis in hematological malignancies

In search of an ideal partner or alternative to conventional immunosuppressive agents, rabbit anti-thymocyte globulin (ATG) and, more recently, post-transplant cyclophosphamide (PT-Cy) have both emerged as valid and efficient options for preventing graft-versus-host disease (GvHD). To further reduce the risk of GvHD, strategies combining ATG and PT-Cy have recently been investigated. In a haploidentical setting, retrospective studies suggest that combining PT-Cy and ATG may result in a lower incidence of chronic GvHD without increasing the risks of infection or relapse, when compared to PT-Cy without ATG. In haploidentical or unrelated donor settings, adding reduced doses of PT-Cy to ATG may reduce the risk of acute and chronic GvHD and improve survival, particularly GvHD-free, relapse-free survival (GRFS), when compared to ATG without PT-Cy. Overall, the combination of PT-Cy and ATG is a safe and promising approach for patients with hematological malignancies undergoing allogeneic hematopoietic stem cell transplantation (HSCT).

Impact of the Recipient's Pre-Treatment Blood Lymphocyte Count on Intended and Unintended Effects of Anti-T-Lymphocyte Globulin in Allogeneic Hematopoietic Stem Cell Transplantation

Background: In allogeneic hematopoietic stem cell transplantation (HSCT), Anti-T-Lymphocyte Globulin (ATLG) may be used for the prevention of severe graft-versus-host disease (GVHD). ATLG targets both the recipient's lymphocytes and those transferred with the graft. Assuming an inverse relation between the recipient's absolute lymphocyte count (ALC) and exposure of remaining ATLG to the graft, we aim to evaluate the impact of the recipient's ALC before the first ATLG administration on the benefits (prevention of GVHD and GVHD-associated mortality) and potential risks (increased relapse incidence) associated with ATLG. Methods: In recipients of HLA-matched, ATLG-based HSCT (n = 311), we assessed the incidence of acute GVHD, GVHD-related mortality and relapse, as well as other transplant-related outcomes, in relation to the respective ALC (divided into tertiles) before ATLG. Results: The top-tertile ALC group had a significantly increased risk of aGVHD (subhazard ratio (sHR) 1.81; [CI 95%; 1.14-2.88]; p = 0.01) and aGVHD-associated mortality (sHR 1.81; [CI 95%; 1.03-3.19]; p = 0.04). At the highest ATLG dose level (≥45 mg/kg), recipients with lowest-tertile ALC had a trend towards increased relapse incidence (sHR 4.19; [CI 95%; 0.99-17.7]; p = 0.05, n = 32). Conclusions: ATLG dosing based on the recipient's ALC may be required for an optimal balance between GVHD suppression and relapse prevention.

Time series clustering of T cell subsets dissects heterogeneity in immune reconstitution and clinical outcomes among MUD-HCT patients receiving ATG or PTCy

Introduction

Anti-T-lymphocyte globulin (ATG) or post-transplant cyclophosphamide (PTCy) prevent graft-versus-host disease (GVHD) after hematopoietic cell transplantation (HCT), yet individual patients benefit differentially.

Methods

Given the sparse comparative data on the impact of cellular immune reconstitution in this setting, we studied flow cytometry and clinical outcomes in 339 recipients of 10/10 matched-unrelated donor (MUD) HCT using either ATG (n=304) or PTCy (n=35) for in vivo T cell manipulation along with a haploidentical PTCy control cohort (n=45). Longitudinal cellular immune reconstitution data were analyzed conventionally and with a data science approach using clustering with dynamic time warping to determine the similarity between time-series of T cell subsets.

Results

Consistent with published studies, no significant differences in clinical outcomes were observed at the cohort level between MUD-ATG and MUD-PTCy. However, cellular reconstitution revealed preferences for distinct T cell subpopulations associating with GVHD protection in each setting. Starting early after HCT, MUD-PTCy patients had higher regulatory T cell levels after HCT (p &lt;0.0001), while MUD-ATG patients presented with higher levels of γδ T- or NKT cells (both p &lt;0.0001). Time-series clustering further dissected the patient population’s heterogeneity revealing distinct immune reconstitution clusters. Importantly, it identified phenotypes that reproducibly associated with impaired clinical outcomes within the same in vivo T cell manipulation platform. Exemplarily, patients with lower activated- and αβ T cell counts had significantly higher NRM (p=0.032) and relapse rates (p =0.01).

Discussion

The improved understanding of the heterogeneity of cellular reconstitution in MUD patients with T cell manipulation both at the cohort and individual level may support clinicians in managing HCT complications.

Different effects of thymoglobulin on acute leukemia with pre-transplant residual blasts in HLA mismatch transplantation

Anti-thymocyte globulin (ATG) is widely used to reduce acute and chronic graft-versus-host disease (a/cGVHD), one of the leading causes of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). As the removal of alloreactive T cells by ATG may also reduce the graft-versus-leukemia effect, the question of whether ATG use affects relapse incidence and survival outcomes in acute leukemia patients with pre-transplant bone marrow residual blasts (PRB) remains controversial. Here, we evaluated the impact of ATG on transplant outcomes in acute leukemia patients with PRB (n = 994) who underwent HSCT from HLA 1-allele mismatched unrelated donors (MMUD) or HLA 1-antigen mismatched related donors (MMRD). In MMUD with PRB (n = 560), multivariate analysis demonstrated that ATG use significantly decreased grade II-IV aGVHD (hazard ratio [HR], 0.474; P = 0.007) and non-relapse mortality (HR, 0.414; P = 0.029) and marginally improved extensive cGVHD (HR, 0.321; P = 0.054) and GVHD-free/relapse-free survival (HR, 0.750; P = 0.069). We concluded that ATG had different effects on transplant outcomes using MMRD and MMUD, and its use would be beneficial to decrease a/cGVHD without increasing non-relapse mortality and relapse incidence in acute leukemia patients with PRB following HSCT from MMUD.

Comparison of Benefits and Risks Associated with Anti-T-Lymphocyte Globulin (ATLG) Serotherapy in Methotrexate (MTX)- versus Mycophenolate Mofetil (MMF)-Based Hematopoietic Stem Cell Transplantation

Background: Serotherapy with anti-T lymphocyte globulin (ATLG, Grafalon, formerly ATG-Fresenius) is established for the prevention of severe graft-versus-host disease (GVHD) after hematopoietic stem cell transplantation (HSCT). The evidence from prospective studies is predominantly derived from a setting where methotrexate (MTX) and a calcineurin inhibitor (CNI) are used as the backbone of GVHD prophylaxis. The efficacy of ATLG in combination with CNI and mycophenolate mofetil (MMF) has not been investigated as much, particularly in terms of a direct comparison with its effects when combined with CNI/MTX. A total of 401 HSCTs from two Austrian transplant centers were retrospectively evaluated. We included peripheral blood transplants from early- or intermediate-stage (excluding advanced/refractory) hematological diseases from matched siblings or 10/10 or 9/10 matched unrelated donors with CNI/MTX or CNI/MMF prophylaxis, either without (n = 219) or with ATLG (n = 182). Overall, ATLG significantly reduced the risk for all-cause mortality by multivariate Cox analysis (HR 0.53; p = 0.002). Stratification by postgrafting prophylaxis type revealed a significant survival advantage for ATLG in the CNI/MMF cohort (HR 0.49; p = 0.001; n = 193), while its effect on survival in the CNI/MTX cohort was not significant (HR 0.87; p = 0.56; n = 208). In unrelated HSCT with CNI/MMF prophylaxis, ATLG exhibited its greatest survival benefit (HR 0.34; p = 0.001; n = 104). In the context of CNI/MMF, ATLG may provide even greater benefits than in the setting of CNI/MTX for post-grafting immunosuppression. Future prospective studies on ATLG should therefore focus on CNI/MMF-based transplants, which are widely performed in elderly or comorbid patients not expected to tolerate a standard course of MTX.

Pre-Transplant Total Lymphocyte Count Determines Anti-Thymocyte Globulin Exposure, Modifying Graft-versus-Host Disease Incidence and Post-Transplant Thymic Restoration: A Single-Center Retrospective Study

The use of anti-thymocyte globulin (ATG) as part of conditioning to prevent graft-versus-host disease (GVHD) may severely impair immune reconstitution (IR). We analyzed relationships between ATG exposure, the recipient lymphocyte count, IR, and transplant outcome. We retrospectively reviewed patients aged ≤ 18 years who underwent allogeneic HSCT between April 2005 and April 2020. The outcomes of interest included the incidence of GVHD, overall survival (OS), and IR. IR was analyzed through thymic magnetic resonance imaging (MRI) and by quantifying T CD4+ and recent thymic emigrants (RTEs). The ATG-exposed group was split into a low ATG/lymphocyte ratio subgroup (ratio < 0.01) and a high ATG/lymphocyte ratio subgroup (ratio > 0.01). The low ratio subgroup had a higher incidence of GVHD (29 [59%] vs. 7 [16.6%]) but a better IR in both laboratory and MRI imaging assessments (p < 0.0001). The median thymic volume in the low ratio subgroup was significantly higher (14.7 cm3 vs. 4.5 cm3, p < 0.001). This was associated with a better OS and lower transplant-related mortality (TRM) (80.4% vs. 58.0%, p = 0.031) and (13.1% vs. 33.0%, p = 0.035). An individualized approach to ATG dosing allows for the obtainment of rapid thymic reconstitution and the best transplant-related outcomes.

Prognostic Role of Cell Blood Count in Chronic Myeloid Neoplasm and Acute Myeloid Leukemia and Its Possible Implications in Hematopoietic Stem Cell Transplantation

Numerous prognostic indexes have been developed in hematological diseases based on patient characteristics and genetic or molecular assessment. However, less attention was paid to more accessible parameters, such as neutrophils, lymphocytes, monocytes, and platelet counts. Although many studies have defined the role of neutrophil-to-lymphocyte or platelet-to-lymphocyte in lymphoid malignancies, few applications exist for myeloid neoplasm or hematopoietic stem cell transplantation procedures. In this review, we synthesized literature data on the prognostic value of count blood cells in myeloid malignancies and hematopoietic stem cell transplantation in the context of classical prognostic factors and clinical outcomes.

Association between the pharmacokinetics of rabbit anti-thymocyte globulin and acute graft-versus-host disease in patients who received haploidentical hematopoietic stem cell transplantation

Anti-thymocyte globulin (ATG) is an important prophylactic drug against acute graft-versus-host disease (aGVHD) after haploidentical hematopoietic stem cell transplantation (haplo-HSCT). This study analyzed the pharmacokinetics of rabbit ATG 2.5 mg/kg and its effect against aGVHD in 24 patients undergoing unmanipulated haplo-HSCT. All patients had hematological malignancies not in remission. The median absolute lymphocyte count (ALC) before rabbit ATG administration was 9.5/µL (range 0-41/µL). The grade ≥ II aGVHD group had a significantly lower median rabbit ATG concentration on days 0 (C₀) and 7 (C₇) and areas under the curve on days 0-7 (AUC_0-7) and 0-32 (AUC_0-32) than the grade 0-I aGVHD group. Among the four parameters, C₀ was the most optimal for predicting aGVHD according to the receiver-operating characteristic (ROC) analysis (area under the ROC curve 0.893; 95% confidence interval 0.738-1.000). The high C₀ (≥ 27.8 µg/mL) group had significantly lower cumulative incidence of grade ≥ II aGVHD on day 100 than the low C₀ (< 27.8 µg/mL) group (13.8% vs. 88.9%, p < 0.001). In haplo-HSCT, the C₀ of rabbit ATG is a good predictor of grade ≥ II aGVHD, even though ALC before rabbit ATG administration is not a predictor of aGVHD.

Association between preconditioning absolute lymphocyte count and transplant outcomes in patients undergoing matched unrelated donor allogeneic hematopoietic stem cell transplantation with reduced-intensity conditioning and anti-thymocyte globulin

Background:

Allogeneic stem cell transplantation (alloSCT) offers cure chance for various hematologic malignancies, but graft-versus-host disease (GVHD) remains a major impediment. Anti-thymocyte globulin (ATG) is used for prophylactic T-cell depletion and GVHD prevention, but there are no clear guidelines for the optimal dosing of ATG. It is suspected that for patients with low absolute lymphocyte counts (ALCs), current weight-based dosing of ATG can be excessive, which can result in profound T-cell depletion and poor transplant outcome.

Methods:

The objective of the study is to evaluate the association of low preconditioning ALC with outcomes in patients undergoing matched unrelated donor (MUD) alloSCT with reduced-intensity conditioning (RIC) and ATG. We conducted a single-center retrospective longitudinal cohort study of acute leukemia and myelodysplastic syndrome patients over 18 years old undergoing alloSCT. In total, 64 patients were included and dichotomized into lower ALC and higher ALC groups with the cutoff of 500/μl on D-7.

Results:

Patients with preconditioning ALC <500/μl were associated with shorter overall survival (OS) and higher infectious mortality. The incidence of acute GVHD and moderate-severe chronic GVHD as well as relapse rates did not differ according to preconditioning ALC. In multivariate analyses, low preconditioning ALC was recognized as an independent adverse prognostic factor for OS.

Conclusion:

Patients with lower ALC are exposed to excessive dose of ATG, leading to profound T-cell depletion that results in higher infectious mortality and shorter OS. Our results call for the implementation of more creative dosing regimens for patients with low preconditioning ALC.

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.

Antithymocyte globulin exposure in CD34+ T-cell depleted allogeneic hematopoietic cell transplantation

In CD34⁺ TCD allogeneic-HCT, optimum post-HCT rATG exposure decreases NRM driven by faster CD4⁺ IR and improves survival.

Personalized rATG exposure using a PK-directed strategy may improve survival after allogeneic CD34⁺ TCD HCT.

Traditional weight-based dosing results in variable rabbit antithymocyte globulin (rATG) clearance that can delay CD4⁺ T-cell immune reconstitution (CD4⁺ IR) leading to higher mortality. In a retrospective pharmacokinetic/pharmacodynamic (PK/PD) analysis of patients undergoing their first CD34⁺ T-cell–depleted (TCD) allogeneic hematopoietic cell transplantation (HCT) after myeloablative conditioning with rATG, we estimated post-HCT rATG exposure as area under the curve (arbitrary unit per day/milliliter [AU × day/mL]) using a validated population PK model. We related rATG exposure to nonrelapse mortality (NRM), CD4⁺ IR (CD4⁺ ≥50 cells per µL at 2 consecutive measures within 100 days after HCT), overall survival, relapse, and acute graft-versus-host disease (aGVHD) to define an optimal rATG exposure. We used Cox proportional hazard models and multistate competing risk models for analysis. In all, 554 patients were included (age range, 0.1-73 years). Median post-HCT rATG exposure was 47 AU × day/mL (range, 0-101 AU × day/mL). Low post-HCT area under the curve (<30 AU × day/mL) was associated with lower risk of NRM (P < .01) and higher probability of achieving CD4⁺ IR (P < .001). Patients who attained CD4⁺ IR had a sevenfold lower 5-year NRM (P < .0001). The probability of achieving CD4⁺ IR was 2.5-fold higher in the <30 AU × day/mL group compared with 30-55 AU × day/mL and threefold higher in the <30 AU × day/mL group compared with the ≥55 AU × day/mL group. In multivariable analyses, post-HCT rATG exposure ≥55 AU × day/mL was associated with an increased risk of NRM (hazard ratio, 3.42; 95% confidence interval, 1.26-9.30). In the malignancy subgroup (n = 515), a tenfold increased NRM was observed in the ≥55 AU × day/mL group, and a sevenfold increased NRM was observed in the 30-55 AU × day/mL group compared with the <30 AU × day/mL group. Post-HCT rATG exposure ≥55 AU × day/mL was associated with higher risk of a GVHD (hazard ratio, 2.28; 95% confidence interval, 1.01-5.16). High post-HCT rATG exposure is associated with higher NRM secondary to poor CD4⁺ IR after TCD HCT. Using personalized PK-directed rATG dosing to achieve optimal exposure may improve survival after HCT.

Low-dose thymoglobulin for prevention of chronic graft-versus-host disease in transplantation from an HLA-matched sibling donor

Despite the proven efficacy of anti-T-cell or antithymocyte globulin (ATG) for chronic graft-versus-host disease (GVHD) prevention in transplantation from an unrelated donor, dosing protocols and the effects of ATG on relapse and infection remain controversial. In the setting of transplantation from an HLA-matched sibling (MSD-T), few randomized studies have been conducted. We conducted a prospective, single-center, open-label, randomized study of low-dose thymoglobulin (2.5 mg/kg) for chronic GVHD prevention. A total of 120 patients with acute leukemia were randomly assigned in a 1:1 ratio. After a median follow-up of 27 months, the cumulative incidence of chronic GVHD in the ATG and non-ATG groups was 25.0% and 65.4% (p < 0.001), respectively. The ATG group had an increased relapse rate compared with the non-ATG-group (20.0% vs. 9.3%; p = 0.055), with risks that differed according to cytogenetic subgroup (high-risk, 29.6% vs. 9.3%, p = 0.042; non-high-risk, 12.2% vs. 9.2%, p = 0.596). Chronic GVHD-free and relapse-free survival (cGRFS) was higher in the ATG group (46.7% vs. 19.4%; p = 0.070), and the difference was significant in a cytogenetic non-high-risk subgroup (45.5% vs. 0%; p = 0.038). No differences were observed in other survival outcomes. Improved physical components in quality-of-life scores were observed in the ATG group at 12 months after transplantation. A higher rate of Epstein-Barr virus reactivation was observed in the ATG group (21.8% vs. 5.1%; p = 0.013), whereas no between-group differences for other complications. In conclusion, the low-dose thymoglobulin effectively prevented chronic GVHD in MSD-T, resulting in improvement in quality-of-life and cGRFS, whereas the necessity of caution for high-risk acute leukemia.

The impact of different doses of antithymocyte globulin conditioning on immune reconstitution upon hematopoietic stem cell transplantation

INTRODUCTION

Anti-thymocyte globulin (ATG) is used prior to allogeneic hematopoietic stem cell transplantation (allo-HSCT) for graft-versus-host disease (GVHD) prophylaxis. Two different ATG doses (7.5 or 10 mg/kg) were evaluated in comparison with a group without ATG therapy.

METHODS

We retrospectively analyzed 132 patients who were transplanted with HSCT without ATG (non-ATG), or who received 7.5 mg/kg ATG (ATG-7.5) or 10 mg/kg ATG (ATG-10) prior to transplantation. The immune cells (CD3⁺CD4⁺ T cells, CD3⁺CD8⁺ T cells, CD19⁺ B cells and CD16⁺CD56⁺ NK cells) were examined in peripheral blood every three months post-HSCT for 12 months.

RESULTS

Compared with non-ATG group, combined ATG-7.5/ATG-10 groups had significantly lower CD3⁺CD4⁺ T cells and higher CD3⁺CD8⁺ T cells at 3, 6, 9, 12 months post-HSCT; thus, displaying a lower CD4/CD8 ratio in the ATG groups compared to non-ATG group. The ratio of CD19⁺ B cells was statistically lower (at 3rd month, p = .014; at 6th month, p = .025) in combined ATG-7.5/ATG-10 groups at 3 and 6 months post-HSCT, but not at 9 and 12 months after HSCT. The ratios of CD3⁺CD4⁺ T cells, CD3⁺CD8⁺ T cells, CD19⁺ B cells and CD16⁺CD56⁺ NK cells were similar between the ATG-7.5 and ATG-10 groups at all examined time points. The overall survival (OS), progression-free survival (PFS), relapse and acute GVHD (aGVHD) were comparable among recipients without ATG therapy and with ATG-7.5 or/and ATG-10 therapies. Multivariate analysis revealed that immune cells ratios were not independent factors affecting prognosis.

CONCLUSION

The ATG therapy at higher and lower doses led to a delayed reconstitution of T cells and the inversion of CD4/CD8 ratio for at least one year after HSCT.

Impact of CMV reactivation on relapse of acute myeloid leukemia after HCT is dependent on disease stage and ATG

The impact of CMV reactivation on hematologic relapse after HCT is modulated by AML stage (CR1 or advanced) and in vivo T cell depletion.

Following CMV reactivation, NRM was increased in CR1 patients without ATG, but not in patients with ATG or advanced disease stages.

Cytomegalovirus (CMV) reactivation is a frequent complication after allogeneic hematopoietic cell transplantation (HCT), whose impact on clinical outcome, in particular on leukemic relapse, is controversial. We retrospectively analyzed 687 HCT recipients with acute myeloid leukemia (AML) and ciclosporin-based immunosuppression to better understand the differential impact of CMV on transplant outcomes depending on AML disease stage and in vivo T cell depletion with antithymocyte globulin (ATG). Without ATG, CMV reactivation associated with significantly reduced relapse, yet its effect was more pronounced for advanced disease AML (P = .0002) than for patients in first complete remission (CR1, P = .0169). Depending on the disease stage, ATG exposure abrogated relapse protection following CMV reactivation in advanced stages (P = .796), while it inverted its effect into increased relapse for CR1 patients (P = .0428). CMV reactivation was associated with significantly increased nonrelapse mortality in CR1 patients without ATG (P = .0187) but not in those with advanced disease and ATG. Following CMV reactivation, only patients with advanced disease had significantly higher event-free survival rates as compared with patients without CMV. Overall, our data suggest that both ATG and disease stage modulate the impact of post-HCT CMV reactivation in opposite directions, revealing a level of complexity that warrants future studies regarding the interplay between antivirus and antitumor immunity.

Graft-Versus-Host Disease Prophylaxis Using Low-Dose Antithymocyte Globulin in Peripheral Blood Stem Cell Transplantation-A Matched-Pair Analysis

Antithymocyte globulin (ATG) decreases chronic graft-versus-host disease (cGVHD) in peripheral blood stem cell transplantation (PBSCT); however, the optimal ATG dose has not been elucidated. We conducted a matched-pair analysis to evaluate whether low-dose ATG could inhibit cGVHD in HLA-matched PBSCT after myeloablative conditioning. A total of 70 patients who were enrolled in the JSCT-ATG15 study, a multicenter phase II clinical trial of 2 mg/kg of ATG (thymoglobulin) given on days -2 and -1, were compared with 210 patients not receiving ATG, who were matched for age, sex, disease, and calcineurin inhibitor selected from the database in Japan. The primary endpoint, cumulative incidence of extensive cGVHD at 2 years was significantly less in the ATG group than that in the non-ATG group (8.7% [95% CI, 3.5%-16.8%] versus 26.2% [95% CI, 20.3%-32.5%], P = .002). ATG significantly reduced the incidence of overall cGVHD and inhibited multiple organ involvement. The ATG group had favorable outcome compared to the non-ATG group in GVHD-free, and relapse-free survival at 2 years. In conclusion, low-dose ATG effectively inhibits chronic GVHD in PBSCT.

Low-dose antithymocyte globulin inhibits chronic graft-versus-host disease in peripheral blood stem cell transplantation from unrelated donors

Antithymocyte globulin (ATG) has been shown to reduce chronic graft-versus-host disease (GVHD) particularly in allogeneic peripheral blood stem cell transplantation (PBSCT) from unrelated donors; however, anti-GVHD effects of lower doses of ATG remains to be elucidated. We conducted a nationwide retrospective study to compare the outcomes of unrelated PBSCT with or without rabbit ATG (thymoglobulin) in 287 patients. A median ATG dose was 2.0 mg/kg. The primary endpoint, the cumulative incidence of moderate-severe chronic GVHD at 2 years was 22.1% in the ATG group, which was significantly less than that in the non-ATG group (36.3%, P = 0.025). The ATG group had a higher incidence of immunosuppressant discontinuation, GVHD-free, relapse-free survival, and moderate-severe chronic GVHD-free, relapse-free survival at 2 years compared to the non-ATG group. The incidences of grade III-IV aGVHD and moderate-severe chronic GVHD were significantly higher in patients with high absolute lymphocyte count (ALC) before the administration of ATG, whereas relapse rate was significantly higher in patients with low ALC before ATG. In conclusion, low-dose ATG effectively suppresses chronic GVHD in unrelated PBSCT, and ALC before ATG may be a potential predictor for GVHD and relapse.

Lower dose of ATG combined with post-transplant cyclophosphamide for HLA matched RIC alloHCT is associated with effective control of GVHD and less viral infections

This study compares the outcomes before and after reducing the ATG dose from 4.5 to 2 mg/kg, in a combination of PTCy and CsA for GVHD prevention, in 250 patients treated with HLA matched RIC PB-alloHCT (70% received 4.5 mg/kg and 30% received 2 mg/kg). The incidences of grade II-IV and III-IV aGVHD at day +100, and moderate/severe cGVHD at 1-year were 12.6% vs. 20% (p = 0.431), 3.6% vs. 4.5% (p = 0.935), and 10.9% vs. 26.1% (p = 0.480), respectively. PTLD (9.1% vs. 1.3%, p = 0.026) and viral infections (30.3% vs. 12%; p = 0.001) were lower for those treated with 2 mg/kg of ATG. The reduction of the ATG dose resulted in a comparable OS (2-year: 64.7% vs. 64.7%), GRFS (2-year: 48.0% vs. 44.5%), RFS (2-year: 57.0% vs. 62.0%), and NRM (2-year: 17.8 vs. 14.9). The use of (2 mg/kg) ATG-PTCy-CsA for HLA matched RIC alloHCT results in lower viral infections, and incomparable GVHD preventive effect and survival rates.

Comparison of 2 Different Doses of Antithymocyte Globulin in Conditioning Regimens for Haploidentical Hematopoietic Stem Cell Transplantation

OBJECTIVES

Antithymocyte globulin is extensively used for prophylaxis of graft-versus-host disease in patients undergoing haploidentical hematopoietic stem cell transplantation. However, different doses of antithymocyte globulin are administered in clinical practice. This study aimed to identify the optimal dose of antithymocyte globulin (thymoglobulin) in haploidentical hematopoietic stem cell transplantation.

MATERIALS AND METHODS

We retrospectively analyzed the effects of 10 mg/kg (2.5 mg/kg on days -5 to -2) versus 7.5 mg/kg thymoglobulin (2.5 mg/kg on days -4 to -2) on patients receiving haploidentical hematopoietic stem cell transplantation with myeloablative conditioning.

RESULTS

We observed significant differences between the 2 treatment groups with regard to cumulative incidence of grade II to IV acute graft-versus-host disease (15.3% vs 14.6%; P = .93) and 3-year chronic graft-versus-host disease (12.1% vs 14.3%; P = .77). The probabilities of 3-year overall survival (68.9% vs 73.5%; P = .98) and graft-versus-host disease-free/relapse-free survival (66.7% vs 53.1%; P = .14) were comparable between the 2 groups. However, there was a trend for lower cumulative incidence of hemorrhagic cystitis in the 7.5 mg/kg treatment group compared with the 10 mg/kg treatment group (40.7% vs 24.4%; P = .07).

CONCLUSIONS

For patients who received a reduced dose of antithymocyte globulin (7.5 vs 10 mg/kg), there was no impaired effect on prophylaxis of graft-versus-host disease, with a trend of reduced incidence of hemorrhagic cystitis. Further studies of the 7.5 mg/kg dose of antithymocyte globulin are warranted for patients receiving haploidentical hematopoietic stem cell transplantation.

Predicting response of severe aplastic anemia to immunosuppression combined with eltrombopag

Pretreatment blood counts, particularly an absolute reticulocyte count ≥25×10⁹/L, correlate with response to immunosuppressive therapy in severe aplastic anemia. In recent trials, eltrombopag combined with standard immunosuppressive therapy yielded superior responses than those to immunosuppressive therapy alone. Our single institution retrospective study aimed to elucidate whether historical predictors of response to immunosuppressive therapy alone were also associated with response to immunosuppressive therapy plus eltrombopag. We sought correlations of blood counts, thrombopoietin levels and the presence of paroxysmal nocturnal hemoglobinuria clones with both overall and complete responses in 416 patients with severe aplastic anemia, aged 2-82 years (median, 30 years), initially treated with immunosuppressive therapy plus eltrombopag between 2012 and 2019 (n=176) or with immunosuppressive therapy alone between 1999 and 2010 (n=240). Compared to non-responders, patients in the group of overall responders to immunosuppressive therapy plus eltrombopag had significantly higher pretreatment absolute reticulocyte counts, higher neutrophil counts and reduced thrombopoietin levels, as also observed for the group treated with immunosuppressive therapy alone. Addition of eltrombopag markedly improved the overall response in subjects with an absolute reticulocyte count between 10-30×10⁹/L from 60% (54 of 90) to 91% (62 of 68). Absolute lymphocyte count correlated with complete response in the groups treated with immunosuppressive therapy with or without eltrombopag, especially in adolescents aged ≥10 years and adults, but the correlation was reversed in younger children. Platelet count and the presence of a paroxysmal nocturnal hemoglobinuria clone did not correlate with responses to immunosuppressive therapy. Blood counts remain the best predictors of response to nontransplant therapies in severe aplastic anemia. Addition of eltrombopag to immunosuppressive therapy shifted patients with a lower absolute reticulocyte count into a better prognostic category.

High lymphocyte counts before antithymocyte globulin administration predict acute graft-versus-host disease

Antithymocyte globulin (ATG) reduces severe acute and chronic graft-versus-host disease (GVHD) in allogeneic peripheral blood stem cell transplantation (PBSCT). However, risk factors for severe acute GVHD in PBSCT using ATG remain to be determined. We conducted a single-center, retrospective study to analyze the association of acute GVHD requiring systemic corticosteroid (SC-aGVHD) with absolute lymphocyte counts (ALC) before the administration of ATG or conditioning in 53 patients with HLA-matched PBSCT using low-dose thymoglobulin (2 mg/kg) after myeloablative conditioning. The cumulative incidence of SC-aGVHD was 17.0% and ALC before ATG were significantly higher in patients with SC-aGVHD compared to that in patients without it (median, 0.15 × 10⁹/L vs 0.06 × 10⁹/L, P = 0.047). The cumulative incidence of SC-aGVHD was significantly higher in patients with high ALC before ATG (≥ 0.15 × 10⁹/L) than in those with low ALC (38.5% vs 10.0%, P = 0.016). Non-relapse mortality (NRM) was also significantly higher in the high ALC before ATG group than the low ALC before ATG group (2-year NRM: 23.9% vs 6.0%, P = 0.048), leading to worse survival (2-year overall survival: 69.2% vs 83.5%, P = 0.039). Our study suggested that high ALC before ATG is a risk factor for SC-aGVHD.

Antithymocyte globulin administration in patients with profound lymphopenia receiving a PBSC purine analog/busulfan-based conditioning regimen allograft

Graft-versus host disease (GVHD) remains one of the main causes of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (ASCT). Prophylactic T cell depletion via antithymocyte globulin (ATG) during ASCT conditioning is one of the standards of care for GVHD prophylaxis, although the optimal dosing strategy is still unclear. Recent studies have reported that absolute lymphocyte count at the time of ATG administration could predict survivals in ASCT from unrelated donors. Here this issue was examined in 116 patients receiving peripheral blood stem cells (PBSC) ASCT with purine analog/busulfan-based conditioning regimens between 2009 and 2019 in our department. The impact of lymphopenia at the time of ATG administration was evaluated in terms of overall survival, disease-free survival and GVHD-free/relapse-free survival. After a median follow-up of 4 years, no adverse effect of a profound lymphopenia was observed on patients' outcome. Notably, a reduced dose of ATG in patients with profound lymphopenia did not translate into better survivals. This study indicates that ATG can be administered whatever the recipient's lymphocyte counts in patients receiving a PBSC purine analog/busulfan-based conditioning regimen ASCT.

Impact of antithymocyte globulin on outcomes of allogeneic hematopoietic cell transplantation with TBI

The impact of the use of antithymocyte globulin (ATG) following a total body irradiation (TBI)-based myeloablative conditioning regimen has been poorly explored. We retrospectively analyzed 724 patients who underwent a first allogeneic hematopoietic cell transplantation (allo-HCT) following a TBI-based conditioning regimen for acute myeloid leukemia (AML) and compared the outcomes of 251 (35%) patients who received ATG (ATG group) with 473 (65%) patients who did not (non-ATG group). Median follow-up of surviving patients was 59 months (interquartile range, 28-83). The cumulative incidence of grade II-IV acute graft-versus-host disease (aGVHD) for non-ATG and ATG groups in the first 100 days was 33% vs 24%, respectively (P = .0098). The 2-year cumulative incidence of chronic graft-versus-host disease (cGVHD) was reduced significantly in the ATG group in comparison with the non-ATG group (46% vs 34%, P = .003). Using multivariate analysis, in vivo T-cell depletion (ATG group) was independently associated with a decreased incidence of grade II-IV aGVHD (hazard ratio [HR], 0.28; P < .001), grade III-IV aGVHD (HR, 0.21; P < .001), cGVHD (HR, 0.63; P = .02), and nonrelapse mortality (NRM) (HR, 0.54; P = .02). Relapse risk, overall survival, and leukemia-free survival were similar between the 2 groups. Our results suggest that the addition of ATG to TBI-based myeloablative conditioning for allo-HCT in AML patients results in a significant reduction in aGVHD and cGVHD, translating into a significant reduction in NRM without increasing the relapse rate.

Low-dose anti-thymocyte globulin for GVHD prophylaxis in HLA-matched allogeneic peripheral blood stem cell transplantation

Allogeneic peripheral blood stem cell transplantation (PBSCT) is associated with an increased risk of severe acute and chronic graft-versus-host disease (GVHD) compared to bone marrow transplantation. Anti-thymocyte globulin (ATG) can reduce severe acute and chronic GVHD in PBSCT; however, an optimal dose of ATG remains undefined. We conducted a multicenter phase II study to investigate safety and efficacy of low-dose ATG (a total of 2 mg/kg Thymoglobulin) in patients undergoing HLA-matched PBSCT after myeloablative conditioning. The primary endpoint was grades III-IV GVHD at 100 days. Seventy-seven patients were enrolled and 72 patients with a median age of 46.5 years were eligible for analysis. The primary endpoint, cumulative incidence of grades III-IV acute GVHD at 100 days was 1.4% (95% CI, 0.1-6.7%), which was greatly less than our pre-defined statistical threshold value (18.0%). The incidence of chronic GVHD at 1 year was also low (all-grade; 15.3%, moderate to severe; 5.6%). Non-relapse mortality, relapse, overall survival, disease-free survival, and GVHD-free, relapse-free survival at 1 year were 4.2%, 20.8%, 84.7%, 75.0%, and 69.4%, respectively. Low dose thymoglobulin is promising to reduce severe acute and chronic GVHD in HLA-matched PBSCT following myeloablative conditioning.

Anti-thymocyte globulin in haematology: Recent developments

Anti-thymocyte globulin (ATG) is a polyclonal antiserum introduced into clinical medicine more than 30 years ago. It induces a broad non-specific immunosuppression. In haematology, standard indications are severe aplastic anaemia and prophylaxis and treatment of graft-versus-host disease (GVHD) (after allogeneic transplantation). For aplastic anaemia, ATG from horses has been found to be superior to ATG from rabbits. In the situation of allogeneic transplantation, ATG lessens the risk of chronic GVHD but may not improve survival. There is current controversy regarding which patients benefit most from ATG and what the ideal dosage is. It is likely that in the coming years a more specific immunosuppressive will be developed that will minimize GVHD while maintaining the graft-versus-malignancy effect.

Clinical outcomes with low dose anti-thymocyte globulin in patients undergoing matched unrelated donor allogeneic hematopoietic cell transplantation

Anti-thymocyte globulin (ATG) has been associated with decreased rates graft versus host disease (GVHD) but with a potential risk of increasing risk of infection and relapse. We retrospectively studied the impact of single dose low dose (2.5 mg/kg) ATG in patients undergoing allogenic hematopoietic cell transplantation (HCT) from 8/8 matched unrelated donors (MUD). Of the total 209 patients identified, 129 received ATG. At baseline, the ATG group had more intermediate and high disease risk index (DRI) (64.6% vs. 54.3%) (28.3% vs. 23.7%) p < .001, respectively, and who received reduced intensity or non-myeloablative conditioning (RIC) (69.0% vs. 47.5%, p .003). There was no significant difference in the overall survival (OS) HR = 1.3, 95% CI [0.99, 1.0], p = .350 or relapse-free survival (RFS) HR = 1.2, 95% CI [0.74, 1.8], p = .526 between the two groups. Patients receiving ATG had a lower incidence of chronic GVHD (cGVHD) (10.1% vs. 25%, p = .007) and less moderate to severe cGVHD (8.5% vs. 25%, p = .002). ATG was associated with a reduced incidence of moderate to severe cGVHD OR = 0.28, 95% CI [0.12, 0.61], p < .01. There was no difference in the incidence of Epstein-Barr Virus (EBV) or cytomegalovirus (CMV) reactivation, CMV disease, invasive fungal infection, or grade III-IV acute GVHD (aGVHD). Our study shows that low dose ATG results in similar OS and RFS with lower rates of cGVHD. Additional prospective studies are needed to confirm these findings.

Proceeding of the European Group for Blood and Marrow Transplantation (EBMT) congress on sickle cell disease, 16-17 may 2019, Regensburg, Germany: What is the impact of antithymocyte globulin pharmacokinetics on haploidentical hematopoietic stem cell transplantation?

Antithymocyte globulin (ATG) is a widely accepted part of the conditioning regimen applied in the setting of hematopoietic stem cell transplantation (HSCT) to prevent graft rejection and graft-versus-host disease. Although weight-based dosing of ATG has been introduced to optimize ATG dosing, substantial variance in clearance of active ATG, the actual lymphocyte binding component, remains a challenge. Therefore, further research regarding ATG pharmacokinetics and pharmacodynamics in different HSCT settings and in patients with different types of underlying diseases is required.

Immune cytopenia post-cord transplant in Hurler syndrome is a forme fruste of graft rejection

Umbilical cord blood (UCB) is the preferred donor cell source for children with Hurler syndrome undergoing transplant, and its use has been associated with improved "engrafted survival" rates. However, as in other pediatric recipients of UCB transplants for nonmalignant disease, immune-mediated cytopenia (IMC) is a significant complication. This article describes 8 episodes of IMC in 36 patients with Hurler syndrome undergoing UCB transplant. The incidence of IMC was increased in those with a higher preconditioning absolute lymphocyte count and in those conditioned with fludarabine-containing regimens rather than cyclophosphamide, and it included red cell alloantibodies directed at cord blood group antigens that are novel to the recipient. In several cases, IMC was a precursor to immune-mediated complete graft rejection. We describe IMC as part of a spectrum of graft rejection by a residual competent host immune system and a forme fruste of complete graft rejection.

Optimizing anti-T-lymphocyte globulin dosing to improve long-term outcome after unrelated hematopoietic cell transplantation for hematologic malignancies

Prophylaxis of graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (HCT) remains challenging. Because prospective randomized trials of in-vivo T cell depletion using anti-T-lymphocyte globulin (ATLG) in addition to a calcineurin inhibitor and methotrexate (MTX) led to conflicting outcome results, we evaluated the impact of ATLG on clinical outcome, lymphocyte- and immune reconstitution survival models. In total, 1500 consecutive patients with hematologic malignancies received matched unrelated donor (MUD) HCT with cyclosporin and MTX (N = 723, 48%) or with additional ATLG (N = 777, 52%). In the ATLG cohort, grades III-IV acute (12% vs 23%) and extensive chronic GVHD (18% vs 34%) incidences were significantly reduced (P < .0001). Nonrelapse mortality (27% vs 45%) and relapse (30% vs 22%) differed also significantly. Event-free and overall survival estimates at 10 years were 44% and 51% with ATLG and 33% and 35% without ATLG (P < .002 and <.0001). A dose-dependent ATLG effect on lymphocyte- and neutrophil reconstitution was observed. At ATLG exposure, lymphocyte counts and survival associated through a logarithmically increasing function. In this survival model, the lymphocyte count optimum range at exposure was between 0.4 and 1.45/nL (P = .001). This study supports additional ATLG immune prophylaxis and is the first study to associate optimal lymphocyte counts with survival after MUD-HCT.

The impact of anti-thymocyte globulin on the outcomes of Patients with AML with or without measurable residual disease at the time of allogeneic hematopoietic cell transplantation

Measurable residual disease (MRD) status pre-allogeneic hematopoietic cell transplantation (allo-HCT) has been shown to predict transplant outcomes. We investigated the effect of Anti-Thymocyte Globulin (ATG) on acute myelogenous leukemia (AML) relapse by pretransplant MRD status. AML patients undergoing allo-HCT in first complete remission from either a matched sibling or unrelated donor during the 2006-2017 period were selected. Outcomes of 1509 patients (MRD⁺, n = 426) were studied. ATG was used in 561 (52%) and 239 (58%) patients within the MRD^- and MRD⁺ cohorts, respectively. In MRD^- patients, ATG did not affect relapse incidence (RI) (HR = 0.80, p = 0.17), but was associated with reduced incidence of grade II-IV acute GVHD, grade II-IV and chronic GVHD, reduced nonrelapse mortality (HR = 0.66, p = 0.05), improved leukemia-free survival (HR = 0.74, p = 0.02), overall survival (HR = 0.69, p = 0.01), and GVHD-relapse free survival (HR = 0.62, p < 0.01). In MRD⁺ patients, ATG was associated with a lower incidence of chronic GVHD (total, HR 0.56 p = 0.03; extensive, HR 0.40 P = 0.01), without an impact on other allo-HCT outcome parameters, including RI(HR = 1.02, p = 0.92). The use of ATG was associated with reduced risk for GVHD. ATG did not increase RI, even in high-risk AML patients who were MRD⁺ before allo-HCT.

Personalizing rabbit anti-thymocyte globulin therapy for prevention of graft-versus-host disease after allogeneic hematopoietic cell transplantation: is there an optimal dose?

The efficacy of anti-thymocyte globulin (ATG) as prophylaxis for graft-versus-host disease (GVHD) has been investigated by many clinical studies over the past decade, including some randomized controlled trials. Intriguingly, although ATG is commonly used as prophylaxis for GVHD, there is still controversy about the optimal dose of ATG for prophylaxis of GVHD after allogeneic hematopoietic cell transplantation (allo-HCT). Indeed, the dose and formulation of ATG, as well as the degree of clinical benefit, has varied among studies, which makes it difficult to fully determine the clinical benefit of ATG. The aim of this review is to summarize the information regarding the optimal ATG dose of each formulation according to stem cell source, and to discuss how best to determine the personalized optimal dose of ATG in each allo-HCT recipient.

Differential Interaction of Peripheral Blood Lymphocyte Counts (ALC) With Different in vivo Depletion Strategies in Predicting Outcomes of Allogeneic Transplant: An International 2 Center Experience

Dosing regimens for antithymocyte globulin (ATG) and anti-CD52 antibody (alemtuzumab) for graft vs. host disease prophylaxis (GVHD) are empiric or weight-based, and do not account for individual patient factors. Recently, it has been shown that recipient peripheral blood absolute lymphocyte count (ALC) on the day of ATG administration interacts with the dose of ATG administered to predict transplantation outcome. Similarly, we wanted to analyze if the recipient ALC interacts with alemtuzumab dosing to predict outcomes. We retrospectively compared 364 patients, 124 patients receiving ATG (anti-thymocyte globulin) for GVHD prophylaxis, and undergoing unrelated first allogeneic transplant for myeloid and lymphoid malignancies (group 1) to 240 patients receiving alemtuzumab (group 2), in similar time period. There was no difference in survival or acute and chronic GVHD between 60 and 100 mg of alemtuzumab dosing. Unlike ATG (where the pre-transplant recipient ALC interacted with ATG dose on day of its administration (day 1) to predict OS and DFS (p = 0.05), within alemtuzumab group, the recipient ALC on second day of alemtuzumab administration (day 2) and its interaction with alemtuzumab dose strongly predicted OS, DFS and relapse (p = 0.05, HR-1.81, 1.1–3.3; p = 0.002, HR-2.41, CI, 1.3–4.2; and p = 0.003, HR-2.78, CI, 1.4–5.2), respectively. ALC (day 2) of 0.08 × 10⁹/lit or higher, had a specificity of 96% in predicting inferior DFS. Like ATG, there is definite but differential interaction between the recipient peripheral blood ALC and alemtuzumab dose to predict OS, DFS, and relapses.

Characterization of Viral Infections after Antithymocyte Globulin-Based Conditioning in Adults Undergoing Allogeneic Hematopoietic Stem Cell Transplantation

Antithymocyte globulin (ATG) has been shown to reduce the incidence of graft-versus-host-disease (GVHD) after matched related donor (MRD) and matched unrelated donor (MUD) hematopoietic stem cell transplantation (HCT); however, because of increased risks of infection and relapse, this use has not translated into a significant improvement in post-transplant survival. The goal of this single-center, retrospective cohort analysis was to quantify the incidence of viral reactivation and viral end-organ disease (EOD) within the first 100 days after MUD HCT with ATG-based conditioning compared with MRD HCT without ATG. Fifty-nine adult patients underwent ATG-based MUD HCT compared with 64 patients receiving MRD HCT without ATG. Cytomegalovirus reactivation was the most frequent event in both groups (65% MUD versus 61% MRD), followed by BK virus reactivation (26% versus 24%) and Epstein-Barr virus reactivation (20% versus 9%). A higher percentage of MUD patients experienced viral EOD by day +100 when compared with MRD patients (34% versus 16%, P = .022). This was most notable for EOD involving BK virus (15% versus 6%, P = .14) and Epstein-Barr virus (7% versus 0%, P = .050). Correspondingly, more patients in the MUD group experienced virus-related complications, including hospitalization (24% versus 3%, P < .001), intensive care unit admission (10% versus 6%, P = .19), and mortality (8% versus 4%, P = .44). There were no significant differences in either relapse-free survival (RFS; 62% versus 78%, P = .07) or overall survival (OS; 72% versus 86%, P = .07) at 6 months post-HCT. However, when using the final time point of 21 months in the MUD/ATG group and 23 months in the MRD/no ATG group, MUD patients who received ATG had inferior survival (OS: 27% versus 77%, P = .009; RFS: 40% versus 59%, P = .042). Our results add to and further quantify the infectious risks associated with the use of ATG in MUD transplants and promote the implementation of more intensive preemptive viral monitoring practices in patients receiving ATG-based MUD transplants.

Comparable Outcomes of First-Line Hematopoietic Stem Cell Transplantation from Unrelated and Matched Sibling Donors in Adult Patients with Aplastic Anemia: A Retrospective Single-Center Study

To explore the feasibility of upfront unrelated donor (URD) hematopoietic stem cell transplantation (HSCT) in the treatment of adult aplastic anemia (AA), we conducted a retrospective, single-center study and compared the outcomes of adult patients who underwent first-line URD HSCT or matched sibling donor (MSD) HSCT between August 2012 and June 2018. In all, 23 URD HSCT recipients had an increased cumulative incidence of grade II acute graft-versus-host disease (aGVHD) (21.7% versus 3.4%; P =.007), but similar rates of secondary graft failure (8.7 ± 6.0% versus 6.9 ± 3.4%; P = .764), chronic GVHD (cGVHD) (18.2% versus 8.8%; P = .285), extensive cGVHD (9.1% versus 3.5%; P = .328), 5-year estimated overall survival (87.0% versus 94.2%; P = .501), and 5-year estimated failure-free survival (82.0% versus 89.3%; P = .404) compared with 58 MSD HSCT recipients treated during the same period. After using propensity score matching to reduce the influence of potential confounders, the 2 groups were well balanced in terms of pretransplantation clinical factors. The median survival time was similar, and no significant differences in the aforementioned outcomes were observed between the 2 groups. Our results suggest that URD HSCT may be an effective and feasible option for first-line therapy in adult AA patients who lack an MSD.

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.

Rabbit Antithymocyte Globulin Serum Levels: Factors Impacting the Levels and Clinical Outcomes Impacted by the Levels

Antithymocyte globulin (ATG) levels and clearance vary significantly among patients receiving the same weight-based dose of ATG. To date, ATG area under the curve (AUC), its determinants, and its impact on clinical outcomes have been examined in pediatric hematopoietic cell transplant (HCT) and adult nonmyeloablative HCT. Here we set out to examine ATG AUC in 219 uniformly treated adults undergoing myeloablative allogeneic HCT at our institution. Sera were collected for the determination of pre- or post-HCT ATG AUC. The lowest quintiles of pre- and post-HCT AUC were associated with inferior chronic graft-versus-host disease (GVHD) and relapse-free survival (cGRFS) and a higher risk of acute GVHD, respectively. The highest pre- or post-HCT ATG AUC quintiles were not associated with risk of death, nonrelapse mortality, or relapse. Factors most strongly associated with AUC were day -2 recipient absolute lymphocyte count, body mass index (BMI), and graft lymphocyte content. To achieve ideal pre-HCT AUC (avoiding low AUC to maximize cGRFS) in this HCT setting, ATG dosing will need to take into consideration recipient weight, BMI, and blood and graft lymphocyte counts. Further studies are required to develop a modern ATG dosing schema and to demonstrate that adjusting ATG dose to target a particular AUC is feasible and leads to improved outcomes.

Low-Dose Anti-T Lymphoglobulin as Prophylaxis for Graft-versus-Host Disease in Unrelated Donor Transplantations for Acute Leukemias and Myelodysplastic Syndromes

Chronic graft-versus-host disease (cGVHD) is a major complication after stem cell transplantation (HSCT). Several randomized studies already demonstrated that anti-T lymphoglobulin (ATLG) is effective in preventing GVHD after myeloablative unrelated and HLA-identical sibling transplants. However, the issue of doses and the potential increase of relapses still remain unsolved. Here we report data on 190 patients with acute leukemia and myelodysplastic syndrome who underwent an unrelated HSCT with low-dose ATLG (15 to 30 mg/kg) given at an earlier timing (days -6 to -2). HSCT was performed from HLA 10/10 (n = 62, 33%), 9/10 (n = 91, 48%), 8/10 (n = 30, 16%), and <8/10 (n = 7, 4%) identical unrelated donor. Peripheral blood was the stem cell source in 42% (n = 80). Median follow-up was 51 months. Grades II to IV and III to IV acute GVHD were 26% and 9%, respectively, and 2-year overall and moderate to severe cGVHD were 23% and 14%, respectively. The 3-year incidences of relapse and nonrelapse mortality were 26% and 18%, respectively. The rates of 3-year overall survival (OS), disease-free survival (DFS), and GVHD-free and relapse-free survival (GRFS) were 60%, 56% and 44%, respectively. Factors such as younger donor, good performance status, and early disease were associated with better outcome in terms of OS, DFS, and GRFS. Our data indicate that doses of ATLG lower that those used in randomized clinical trials can be used for GVHD prevention, even in the adult setting, without clear increases in relapse and infections; these findings need to be further validated by a prospective randomized study.