A comprehensive and quantitative analysis of the major specificities in rabbit antithymocyte globulin preparations

Comparison of ATG-thymoglobulin with atg-fresenius in patients with hematological malignancies who undergo allogeneic hematopoietic stem cell transplantation: a propensity score-matched analysis

We retrospectively compared the outcomes of 166 patients with hematological malignancies who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT) using ATG-Thymoglobulin (ATG-T) at 10 mg/kg or ATG-Fresenius (ATG-F) at 20 mg/kg. Propensity score matching (PSM) analysis was applied, with 44 patients assigned to each group. The ATG-T group showed a trend toward a higher incidence of bacterial infections (72.7% vs. 65.9%, P = 0.064). Additionally, the ATG-T group had a significantly higher incidence of other viral infections, including BK virus and herpes zoster virus (40.9% vs. 15.9%, P = 0.003), compared to the ATG-F group. Furthermore, the ATG-F group experienced a lower incidence of high fever (4.5% vs. 50.0%, P < 0.001) and reduced ATG treatment costs [¥ 45100 (28700-82000) vs. ¥ 56250 (38000-85000), P < 0.001] compared to ATG-T. The incidences of acute GVHD, grade III-IV aGVHD, grades of aGVHD, chronic GVHD, 3-year overall survival (OS), transplantation-related mortality (TRM), non-relapse mortality (NRM), disease-free survival (DFS), and GVHD-free and relapse-free survival (GRFS) were similar between the ATG-T and ATG-F groups. In conclusion, our study suggests that ATG-F is superior to ATG-T in terms of viral infections, fever rate, and treatment cost.

Differential Clinical and Immunological Impacts of Anti-T-Lymphocyte Globulin (ATLG) vs. Anti-Thymocyte Globulin (ATG) in Preventing Graft-Versus-Host Disease Post-Allogeneic Hematopoietic Stem Cell Transplantation: A Comparative Study

Both anti-T-lymphocyte globulin (ATLG-Grafalon) and anti-thymocyte globulin (ATG-Thymoglobulin) prevent acute and chronic graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Despite distinct manufacturing and biological characteristics, the two brands of rabbit anti-lymphocyte globulins have never been compared in a prospective way. In this monocentric study, 114 adult patients transplanted with a matched related or unrelated donor after receiving either ATG (n = 50) or ATLG (n = 64) were included to compare their clinical outcomes and broad immune reconstitution parameters. The use of ATLG, compared with ATG, was associated with a 2-fold reduction in Grade II-IV acute GvHD incidence (Cox HR = 0.29; 95% CI 0.14-0.62, p = 0.006), similar relapse incidence, and improved severe GvHD and relapse-free survival (GRFS) (Cox HR = 0.51; 95% CI 0.29-0.91, p = 0.027). Biologically, reduced IL-15 but increased IL-21 serum concentrations and a significant reduction of PD1+ T cells, mainly across all differentiated stages of CD8+ T cells, were observed in the ATLG group. Immunosequencing of vβ T cell receptor (TCR) repertoires showed similar quantitative characteristics in terms of clonality and diversity across the two groups but different qualitative features, with reduced hyper-expanded T cell clones and higher variability in the distribution of complementarity-determining region 3 (CDR3) lengths in the ATLG group. Altogether, these results suggest that ATLG more effectively regulates alloreactive T cell activation, leading to better prevention of acute GvHD while preserving the graft-versus-leukemia response. These findings led us to initiate a multicentric Phase III randomized trial comparing the two anti-lymphocyte globulins. Trial Registration: The biological REAL GREFFE study was registered in clinicaltrial.gov under the number: NCT03357172.

Low dose ATG-Fresenius for GVHD prophylaxis: a comparative study with ATG-Thymoglobulin

Background

Anti-Thymocyte Globulin (ATG) is commonly used to prevent graft-versus-host disease (GVHD), but the optimal dosage and type of ATG remains to be determined.

Objective

We compared retrospectively the safety and efficacy outcomes of allogeneic transplantation using low-dose ATG-Fresenius (15mg/kg) and ATG-Thymoglobulin (10mg/kg) for GVHD prevention.

Study design

Ninety-eight patients were included, with 46 in the ATG-T group and 52 in the ATG-F group. The median age was 48 years in the ATG-T group (range 20-71) and 50 years in the ATG-F group (range 18-73). Baseline characteristics were similar, with slightly more HLA mismatched donors and single-agent cyclosporine GVHD prophylaxis use in the ATG-T group. Additionally, the ATG-F group had more myeloid leukemia and myelodysplastic syndrome patients, while the ATG-T group had more lymphoma patients.

Results

The cumulative incidence of acute GVHD (aGVHD) grade II-IV and chronic GVHD (cGVHD) showed no significant differences. Multivariate analysis indicated that donor HLA mismatch influenced aGVHD risk significantly (p=0.005), and myeloablative conditioning increased cGVHD risk. Bacteremia and CMV reactivation rates were similar, but EBV DNA viremia was higher in the ATG-T group (22% vs. 8%, p=0.047), with one case of Post-Transplant Lymphoproliferative Disorder (PTLD) in the ATG-T group. Cumulative incidence of overall survival (OS), relapse incidence, non-relapse mortality (NRM) and GVHD free, Relapse free Survival (GRFS) did not significantly differ.

Conclusions

This study highlights the safety and efficacy of low-dose ATG-F compared to a relatively high dose ATG-T. Prospective studies are necessary to validate the safety and efficacy of low dose ATG-F for GVHD prevention.

Higher risk of GVHD but better long-term survival: impact of p-ALG versus r-ATG in high-risk hematological malignancy patients following MSDT

PURPOSE

Disease relapse and graft-versus-host disease (GVHD) represent significant clinical challenges for high-risk hematological malignancies (HM) patients undergoing HLA-matched sibling donor transplantation (MSDT). How to balance the effect of GVHD and Graft versus leukemia (GVL) remains unclear for high-risk HM patients receiving MSDT. Here, we conducted a retrospective study to compare the efficacy in preventing disease relapse of 2 lymphocyte-depleting antibodies (r-ATG vs p-ALG) as the GVHD prevention strategy.

METHOD

A retrospective analysis was conducted on 48 patients with high-risk HM patients who underwent MSDT at our center from January 2019 to January 2024. Among them, 22 patients were in the p-ALG group (45mg/kg), and 26 patients were in the r-ATG group (3.5-4.5mg/kg). The primary end point of this study was disease relapse.

RESULTS

We found that the p-ALG group had a higher 3-year cumulative incidence of chronic GVHD than the r-ATG group (64.4% ± 13.6% vs. 28.8% ± 9.7%, P = 0.016). There was no significant difference in total acute GVHD (aGVHD) (54.5% ± 11% vs.26.9% ± 8.9%, P = 0.81) and 3-year extensive cGVHD (20.3% ± 11.3% vs. 7.9% ± 5.5%, P = 0.27) between the 2 groups. In terms of patient prognosis, the p-ALG group showed a higher 3-year overall survival rate compared to the r-ATG group (100% vs. 75.5% ± 8.8%, P = 0.039). The 3-year disease-free survival (DFS) rate was significantly higher in the p-ALG group compared to the r-ATG group (95.5% ± 4.4% versus 61% ± 10.6%, P = 0.046). Furthermore, the p-ALG group exhibited a longer duration of disease remission after transplantation, as evidenced by a lower 3-year cumulative incidence of post-transplantation Minimal Residual Disease positivity (post-MRD+) compared to the r-ATG group (4.5% ± 4.4% versus 40.5% ± 11%, P = 0.022).

CONCLUSION

In comparison to r-ATG, the administration of low-dose p-ALG (45mg/kg) in high-risk HM patients receiving MSDT is associated with an increased incidence of GVHD but results in a more favorable survival prognosis.

A comprehensive analysis of the major specificities of anti-human T lymphocyte porcine immunoglobulin (p-ATG)

BACKGROUND

Anti-human T lymphocyte porcine immunoglobulin (p-ATG) is a potent immunosuppressive agent derived from porcine sources used in various immunotherapy applications. It is compared with similar products derived from other species, such as rabbit anti-thymocyte globulin (r-ATG) and ATG-Fresenius (ATG-F), which have distinct biological and therapeutic properties. This study aims to elucidate the mechanisms of action and comparative efficacy of p-ATG in relation to r-ATG and ATG-F through a comprehensive in vitro analysis.

METHODS

A comparative analysis of p-ATG, r-ATG and ATG-F was performed, focusing on E rosette inhibitory potency, lymphocyte toxic potency, blocking activities of 24 CD molecules, and flow quantitative potency. Flow cytometric analysis was used to quantify these characteristics and assess the potency of the immunoglobulins.

RESULTS

p-ATG exhibited lower E rosette inhibitory and lymphocyte toxic potencies compared to r-ATG but was significantly more potent than ATG-F at equivalent concentrations. At protein concentrations above 12.5 µg/mL, p-ATG showed slightly lower potency than r-ATG and much higher potency than ATG-F in flow cytometry assays. Both p-ATG and r-ATG exhibited similar killing effects on lymphocytes within the peripheral blood mononuclear cells (PBMCs), including CD3 + T cells, with a dose-dependent response. Notably, p-ATG displayed more pronounced blocking activities against CD8, CD99, and TCR α/β compared to r-ATG.

CONCLUSION

p-ATG offers certain advantages over r-ATG and ATG-F, particularly in its ability to inhibit specific CD molecules and its overall potency in immunosuppressive assays, providing valuable insights for assisting clinical decision-making regarding the selection of ATG types based on patient-specific needs and treatment objectives.

Haploidentical hematopoietic stem cell transplantation for hematologic malignancies: a novel conditioning regimen with anti-T lymphocyte immunoglobulin instead of anti-thymocyte globulin for in vivo T cell depletion

We evaluated the safety and efficacy of a novel protocol for haploidentical stem cell transplantation (haplo-SCT) in 312 patients with hematologic malignancies. The protocol evolved from the Beijing platform replacing ATG with ATLG; adding Fludarabine and removing cytarabine and Simustine. GVHD prophylaxis combined Basiliximab and low-dose cyclophosphamide post-transplant; overall, the conditioning duration was shortened. Median times to neutrophil and platelet recovery were both 11 days. Graft rejection occurred in 0.96% of patients. Cumulative incidences of grades II-IV and III-IV acute GVHD by day 200 were 35.3% and 8.9%, respectively. Probabilities of total and extensive chronic GVHD at 2 years were 40.7% and 14.7%. CMV viremia was observed in 35.6% of patients, with a 1.9% 100-day CMV pneumonia incidence and no CMV-related mortality. Cumulative incidences of non-relapse mortality at 100 days, 1 year, and 2 years were 2.9, 4.4, and 6.6%. The 4-year OS, RFS, and GRFS rates were 78.9, 70.7, and 47.3%. Older recipient age was associated with higher NRM, while positive pre-transplant MRD predicted worse OS, RFS, and higher relapse incidence. Our novel protocol for haplo-SCT is associated with low infection rates and acceptable risks of graft failure, severe GVHD, and mortality, representing a safe and effective haploidentical transplantation strategy.

Outcomes with low dose anti-thymocyte globulin based graft versus host disease prophylaxis after mismatched unrelated donor allogeneic hematopoietic cell transplantation

BACKGROUND

Anti-thymocyte globulin (ATG) based graft versus host disease (GVHD) prophylaxis is widely used for mismatched unrelated donor allogeneic hematopoietic cell transplantation (HCT) although optimal dose remains unclear. Although recent literature suggested improved outcomes with PTCy-based regimens when compared to ATG-based regimens these studies used doses of ATG ≥5 mg/kg. Thus, we analyzed outcomes of HLA 9/10 MMUD allogeneic HCTs using lower-dose ATG-based regimens at our center.

METHODS

We retrospectively analyzed outcomes of HLA 9/10 MMUD allogeneic HCTs using lower dose ATG-based regimens for all adults undergoing allogeneic HCT at The Ottawa Hospital from 2015 to 2022. Data regarding demographics, conditioning regimen, dose of ATG, rates of GVHD, duration of remission, and survival, were collected and analyzed.

RESULTS

Seventy-seven (n = 77) patients (males 62.3%; median age 50 years) underwent allogeneic HCT from MMUD. Majority(81%; n = 63) received 2.5 mg/kg of rabbit ATG and remaining 18.2% (n = 14) received 4.5 mg/kg. Grade II-IV acute GVHD occurred in 24.7% (n = 19) while any chronic GVHD occurred in 32.5% (n = 25) patients. After a median follow-up of 21 months, relapse occurred in 28.6% of patients. Two-year OS, GRFS, CIR, and NRM were 60.6%, 45.3%, 16.9%, and 18.2% respectively. Dose of ATG (2.5 mg/kg vs. 4.5 mg/kg) was not associated with outcomes in either univariate or multivariate analyses.

CONCLUSIONS

When compared to published studies using ATG doses ≥5 mg/kg, GVHD prophylaxis using lower dose ATG may potentially lead to improved outcomes in patients undergoing MMUD allogeneic HCT. Further studies are needed to directly compare lower dose ATG to PTCy-based regimens to determine ideal GVHD prophylaxis for these patients.

Effects of two immunosuppression regimens on T-lymphocyte subsets in elderly kidney transplant recipients

Background

Despite the growing number of elderly kidney transplant (Ktx) recipients, few studies have examined the effects of immunosuppression on their lymphocyte profiles.

Methods

We evaluated the early conversion from mycophenolate sodium (MPS) to everolimus (EVL) after rabbit antithymocyte globulin (rATG) 2 mg/kg induction in elderly kidney recipients. Three groups of KTx patients were compared: (a) Young (n=20, 36 ± 7 y) receiving standard immunosuppression (Group A1) (prednisone, tacrolimus, and MPS), (b) Elderly (n=35, 65 ± 3 y) receiving standard immunosuppression (Group B1), and (c) Elderly (n=16, 65 ± 3 y) with early (mean 30 d) conversion from MPS to EVL (Group B2). Naive, memory, and regulatory peripheral blood TCD4+ lymphocytes were quantified at 0, 30, and 365 d.

Results

Results are reported as [mean(p25-p75)]. Young recipients had higher lymphocyte counts at baseline [2,100(1,630-2,400) vs. 1,310 (1,000-1,600)/mm3, p<0.0001] maintained higher counts within 365 d [1,850(1,590-2,120) vs. 1,130(460-1,325)/mm3, p=0.018 and vs. 1,410(805-1,895)/mm3, p=0.268]. Elderly recipients showed a decrease in lymphocytes within 30 d [1,310(1,000-1,600) vs. 910(700-1,198)/mm3, p=0.0012] with recovery within 365 d. The same pattern was observed in total lymphocytes and TCD4+ counts. Rabbit antithymocyte globulin induced a reduction in central memory T-cell percentages at 30 d in both young recipients [6.2(3.77-10.8) vs. 5.32(2.49-7.28)% of CD4+, p=0.036] and in elderly recipients [8.17(5.28-12.88) vs. 6.74(4.36-11)% of CD4+, p=0.05] on standard immunosuppression, returning to baseline at 365 d in elderly recipients but not in young recipients. Regulatory T CD39+ cells (Treg) percentages decreased at 30 d in elderly recipients [2.1(1.23-3.51) vs. 1.69(0.8-2.66)% of CD4+, p=0.0028] and in young recipients [1.29(0.45-1.85) vs. 0.84(0.18-1.82)% of CD4+, p=0.0038], returning to baseline at 365 d in elderly recipients [2.1(1.23-3.51) vs. 2.042(0.88-2.42)% of CD4+], but not in young recipients [1.29(0.45-1.85) vs. 0.86(0.7-1.34) % of CD4+]. The elderly everolimus conversion group did not show significant changes in cell profile over time or compared to elderly recipients with standard immunosuppression.

Conclusion

Aging favored the maintenance of Treg during the late transplantation period despite ongoing immunosuppression. Lymphocyte depletion due to rATG was more prominent in elderly recipients and affected memory subsets with a temporary reduction in central memory T cells. However, conversion to everolimus did not impact Treg profile. Reducing the dose of rATG in elderly recipients seems necessary for the expected lymphocyte changes with EVL to occur.

Clinical trial registration

nEverOld Trial, identifier NTC01631058.

Peripheral nervous system immune-related adverse events due to checkpoint inhibition

Immune checkpoint inhibitors have revolutionized cancer therapy and are increasingly used to treat a wide range of oncological conditions, with dramatic benefits for many patients. Unfortunately, the resulting increase in T cell effector function often results in immune-related adverse events (irAEs), which can involve any organ system, including the central nervous system (CNS) and peripheral nervous system (PNS). Neurological irAEs involve the PNS in two-thirds of affected patients. Muscle involvement (immune-related myopathy) is the most common PNS irAE and can be associated with neuromuscular junction involvement. Immune-related peripheral neuropathy most commonly takes the form of polyradiculoneuropathy or cranial neuropathies. Immune-related myopathy (with or without neuromuscular junction involvement) often occurs along with immune-related myocarditis, and this overlap syndrome is associated with substantially increased mortality. This Review focuses on PNS adverse events associated with immune checkpoint inhibition. Underlying pathophysiological mechanisms are discussed, including antigen homology between self and tumour, epitope spreading and activation of pre-existing autoreactive T cells. An overview of current approaches to clinical management is provided, including cytokine-directed therapies that aim to decouple anticancer immunity from autoimmunity and emerging treatments for patients with severe (life-threatening) presentations.

Real-World Impact of Routine Addition of Antithymocyte Globulin to Standard GVHD Prophylaxis in Myeloablative Unrelated Donor Transplants: Important Gains in Graft-versus-Host Disease Prevention though No Difference in Overall Survival

INTRODUCTION

Antithymocyte globulin (ATG) has been demonstrated to reduce the incidence of graft-versus-host disease (GVHD); however, it remains controversial whether these gains are offset by an increase in relapse.

METHODS

We conducted a retrospective historical control study consisting of patients (n = 210) who underwent myeloablative allogeneic hematopoietic stem-cell transplantation (HSCT) from 2014 to 2020.

RESULTS

The incidence of acute GVHD was lower in the ATG group (51.4%) than the non-ATG group (control) (70.0%, p = 0.010). The incidence of chronic GVHD was also lower in the ATG group at 1-year (36.4% vs. 62.9%, p < 0.001) and 2-year (40.0% vs. 65.7%, p < 0.001) post-HSCT. The mortality due to GVHD was higher in the control (18.5%) than the ATG group (4.3%; p = 0.024). The severe GVHD-relapse-free survival was higher in the ATG group (36.4%) than the control (12.9%; p < 0.001). Nevertheless, the 2-year overall survival was similar.

CONCLUSION

Our results confirm the effectiveness of ATG in prevention of GVHD in the real-world setting and enhanced GVHD-free survival. An important result is the equalization of overall survival between the ATG and control groups at 1- and 2-year post-HSCT and implies that earlier GVHD-associated mortality may be offset by later relapse mortality producing similar overall survival over time.

Model-Based Antithymocyte Globulin in αβhaplo-Hematopoietic Stem Cell Transplantation Facilitates Engraftment, Expedites T Cell Recovery, and Mitigates the Risk of Acute Graft-versus-Host Disease

In αβ T-cell/CD19 B-cell depleted hematopoietic stem cell transplantation (αβhaplo-HSCT) recipients, antithymocyte globulin (ATG; Thymoglobulin) is used for preventing graft rejection and graft-versus-host disease (GVHD). The optimal dosing remains to be established, however. Here we present the first comparative analysis of 3 different ATG dosing strategies and their impact on immune reconstitution and GVHD. Our study aimed to evaluate the effects of 3 distinct dosing strategies of ATG on engraftment success, αβ+ and γδ+ T cell immune reconstitution, and the incidence and severity of acute GVHD in recipients of αβhaplo-HSCT. This comparative analysis included 3 cohorts of pediatric patients with malignant (n = 36) or nonmalignant (n = 8) disease. Cohorts 1 and 2 were given fixed ATG doses, whereas cohort 3 received doses via a new nomogram, based on absolute lymphocyte count (ALC) and body weight (BW). Cohort 3 showed a 0% incidence of day 100 grade II-IV acute GVHD, compared to 48% in cohort 1 and 27% in cohort 2. Furthermore, cohort 3 (the ALC/BW-based cohort) had a significant increase in CD4+ and CD8+ naïve T cells by day 90 (P = .04 and .03, respectively). Additionally, we found that the reconstitution and maturation of γδ+ T cells post-HSCT was not impacted across all 3 cohorts. Cumulative ATG exposure in all cohorts was lower than previously reported in T cell-replete settings, with a lower pre-HSCT exposure (<40 AU*day/mL) correlating with engraftment failure (P = .007). Conversely, a post-HSCT ATG exposure of 10 to 15 AU*day/mL was optimal for improving day 100 CD4+ (P = .058) and CD8+ (P = .03) immune reconstitution without increasing the risk of relapse or nonrelapse mortality. This study represents the first comparative analysis of ATG exposure in αβhaplo-HSCT recipients. Our findings indicate that (1) a 1- to 2-fold ATG to ATLG bioequivalence is more effective than previously established standards, and (2) ATG exposure post-HSCT does not adversely affect γδ+ T cell immune reconstitution. Furthermore, a model-based ATG dosing strategy effectively reduces graft rejection and day 100 acute GVHD while also promoting early CD4+/CD8+ immune reconstitution. These insights suggest that further optimization, including more distal administration of higher ATG doses within an ALC/BW-based strategy, will yield even greater improvements in outcomes.

Graft-Specific Regulatory T Cells for Long-Lasting, Local Tolerance Induction

BACKGROUND

Solid organ transplantation is hindered by immune-mediated chronic graft dysfunction and the side effects of immunosuppressive therapy. Regulatory T cells (Tregs) are crucial for modulating immune responses post-transplantation; however, the transfer of polyspecific Tregs alone is insufficient to induce allotolerance in rodent models.

METHODS

To enhance the efficacy of adoptive Treg therapy, we investigated different immune interventions in the recipients. By utilizing an immunogenic skin transplant model and existing transplantation medicine reagents, we facilitated the clinical translation of our findings. Specifically, antigen-specific Tregs were used.

RESULTS

Our study demonstrated that combining the available induction therapies with drug-induced T-cell proliferation due to lymphopenia effectively increased the Treg/T effector ratios. This results in significant Treg accumulation within the graft, leading to long-term tolerance after the transfer of antigen-specific Tregs. Importantly, all the animals achieved operational tolerance, which boosted the presence of adoptively transferred Tregs within the graft.

CONCLUSIONS

This protocol offers a means to establish tolerance by utilizing antigen-specific Tregs. These results have promising implications for future trials involving adoptive Treg therapy in organ transplantation.

Immunosuppressive Induction Therapy Using the Antithymocyteglobulin Grafalon: A Single-Center Non-Interventional Study

Background: Induction therapy with depleting antibodies in the setting of liver transplantation (LT) is discussed controversially to this day. The rabbit antithymocyteglobulin (ATG) Thymoglobulin (rATG) was introduced as early as 1984 and was frequently used as a standard regime for induction therapy after LT. There are no public reports characterizing Grafalon (ATG-F), a novel ATG, as an induction agent after LT. Objectives: The aim of this observational non-interventional study was to investigate the safety and efficacy of Grafalon induction therapy and characterize its clinical effects in the setting of LT. Methods: A cohort of 80 patients undergoing deceased donor LT at the Medical University of Vienna and receiving Grafalon as part of the clinical standard immunosuppressive regimen was prospectively included between March 2021 and November 2022. Patients were monitored closely for leukocytopenia and thrombocytopenia during the first postoperative week and followed up for incidence and severity of biopsy-proven acute rejection (BPAR), overall survival, and bacterial infections in the first year after LT. Results: The incidences of thrombocytopenia and leukocytopenia following Grafalon treatment peaked on postoperative day four, with 64% and 31%, respectively. However, there were no cases of severe leukocytopenia after the first postoperative week. Induction therapy with Grafalon resulted in a rate of localized bacterial infections and bacteremia of 28% and 21%, respectively. The rate of BPAR was 12.5% in the first year after LT; the one-year survival rate in this cohort was 90%. Conclusions: Overall, this study provides evidence of the safety and efficacy of Grafalon as an induction agent. Further studies investigating the potential long-term effects of Grafalon, as well as comparison studies with different immunosuppressive regimens, are needed in order to draw further conclusions.

Comparing the Outcomes of Matched and Mismatched Unrelated Allogeneic Hematopoietic Stem Cell Transplantation with Different Anti-Thymocyte Globulin Formulations: A Retrospective, Double-Centre Experience on Behalf of the Polish Adult Leukemia Group

Despite notable advancements in immunotherapy in the past decades, allogeneic hematopoietic stem cell transplantation (allo-HCT) remains a promising, potentially curative treatment modality. Only a limited number of studies have performed a direct comparison of two prevalent rabbit anti-thymocyte globulin (r-ATG) formulations-specifically, Thymoglobuline (ATG-T, formerly Genzyme) and Grafalon (ATG-G, formerly Fresenius). The primary objective of our retrospective analysis was to compare the outcomes of adult patients undergoing matched or mismatched unrelated donor (MUD/MMUD) allo-HCT, with a graft-versus-host disease (GvHD) prophylaxis based on either ATG-T or ATG-G. A total of 87 patients who had undergone allo-HCT between 2012 and 2022 were included. We observed no significant differences between ATG-T and ATG-G concerning the occurrence of acute graft-versus-host disease (aGvHD), regardless of its severity. Conversely, chronic graft-versus-host disease (cGvHD) occurred less frequently in the ATG-T group compared to the ATG-G group (7.5% vs. 38.3%, p = 0.001). The negative impact of ATG-G on cGvHD was confirmed by multivariate analysis (HR 8.12, 95% CI 2.06-32.0, p = 0.003). Patients treated with ATG-T manifested a higher incidence of cytomegalovirus (CMV) reactivations (70% vs. 31.9%, p < 0.001), with a shorter time between transplant and CMV (<61 days, 77.8% vs. 33.3%, p = 0.008) and a higher median CMV copy number (1000 vs. 0, p = 0.004). Notably, despite a higher occurrence of CMV reactivations in the ATG-T cohort, most patients were asymptomatic compared to ATG-G (85.7% vs. 43.8%, p = 0.005). By multivariate analysis, only aGvHD had an influence on CMV reactivations (HR 0.18, 95% CI 0.04-0.75, p = 0.019). Finally, we observed no significant differences in terms of 5-year overall survival (OS) and 3-year relapse-free survival (RFS) while comparing ATG-T and ATG-G (32.0% vs. 40.3%, p = 0.423; 66.7% vs. 60.4%, p = 0.544, respectively).

Comparison of rabbit ATLG and ATG for GVHD prophylaxis in hematological malignancies with haploidentical hematopoietic stem cell transplantation

Rabbit anti-human T lymphocyte globulin (ATLG) and anti-thymocyte globulin (ATG) are commonly used for graft-versus-host disease (GVHD) prophylaxis in allogeneic hematopoietic stem cell transplantation (HSCT). Yet, their efficacy and safety have seldom been compared in hematological malignancies with haploidentical HSCT. A retrospective analysis with 28 ATLG (total dosage, 20-30 mg/kg) and 18 ATG (total dosage, 8-10 mg/kg) patients were performed. The cumulative incidences of chronic GVHD and relapse were comparable between both groups. ATLG showed a trend towards a lower acute GVHD incidence (28.6% vs. 44.4%, P = 0.242) and 3-year non-relapse mortality (10.7% vs. 27.8%, P = 0.160), and had a significantly higher 3-year overall survival (OS, 64.3% vs. 33.3%, P = 0.033) and GVHD-free and relapse-free survival (GRFS, 32.1% vs. 11.1%, P = 0.045) compared with ATG. Multivariate Cox regression analysis demonstrated ATLG was independently associated with a favorable OS (hazard ratio [HR] = 0.37, 95% confidence interval [CI]: 0.16-0.86, P = 0.020) and GRFS (HR = 0.51, 95%CI: 0.26-1.00, P = 0.051). Furthermore, ATLG had a lower risk of fever (25.0% vs. 61.1%, P = 0.014) and hemorrhage cystitis (7.1% vs. 38.9%, P = 0.008) than ATG-T. In conclusion, ATLG confers more survival benefit and a better safety profile than ATG and can be used in hematological malignancies with haploidentical HSCT. Prospective designed trials with a larger sample size are warranted to confirm the results in the future.

Outcomes of haploidentical peripheral blood stem cell transplantation following myeloablative conditioning using two types of rabbit ATG: a propensity score-matched analysis

During hematopoietic stem cell transplantation (HSCT), ATG depletes T cells in-vivo to improve engraftment and prevent graft-versus-host disease (GVHD). Here, we compared the clinical efficacy of two different types of ATGs: thymoglobulin and anti-human T-lymphocyte immunoglobulin (Grafalon). A total of 469 patients who received haploidentical transplantation were enrolled in this retrospective study. We applied a propensity score (PS)-matched analysis and 209 patients were assigned to each group. Clinical outcomes were compared between two groups and primary outcome was overall survival (OS). There was no significant difference in OS between two groups. Within the first 180 days after HSCT, Grafalon was associated with lower incidences of Epstein-Barr virus (EBV) viremia (31.6 vs. 54.5%, P < 0.0001) and cytomegalovirus viremia (CMV) viremia (54.5 vs. 67.9%, P = 0.005) compared to thymoglobulin. Patients receiving Grafalon had a higher rate of moderate/severe chronic GVHD (26.3 vs. 18.2%, P = 0.046). However, the incidences of engraftment failure, grade II-IV acute GVHD, relapse, non-relapse mortality (NRM), and GVHD-free relapse-free survival (GRFS) did not differ greatly between groups. In the subgroup analysis, Grafalon improved the OS of lymphoid malignancies with young ages (< 40 years old) (HR, 0.55; P = 0.04) or with a high/very high disease risk index (HR, 0.36; P = 0.04). In the myeloid cohort, Grafalon reduced NRM in the patients who received non-female for male transplantation grafts (HR, 0.17; P = 0.02). Our results suggest the two types of ATG may differentially influence transplant outcomes and it may optimize ATG selection according to the condition of patients.

Interrogating ligand-receptor interactions using highly sensitive cellular biosensors

Interactions of membrane-resident proteins are important targets for therapeutic interventions but most methods to study them are either costly, laborious or fail to reflect the physiologic interaction of membrane resident proteins in trans. Here we describe highly sensitive cellular biosensors as a tool to study receptor-ligand pairs. They consist of fluorescent reporter cells that express chimeric receptors harboring ectodomains of cell surface molecules and intracellular signaling domains. We show that a broad range of molecules can be integrated into this platform and we demonstrate its applicability to highly relevant research areas, including the characterization of immune checkpoints and the probing of cells for the presence of receptors or ligands. The platform is suitable to evaluate the interactions of viral proteins with host receptors and to test for neutralization capability of drugs or biological samples. Our results indicate that cellular biosensors have broad utility as a tool to study protein-interactions.

Comparison of Different Rabbit Anti-Thymocyte Globulin Formulations in the Prophylaxis of Graft-Versus-Host Disease: A Systematic Review

Allogeneic hematopoietic stem cell transplantation (allo-HCT) is a potentially curative treatment modality, frequently used for patients suffering from haematological malignancies. In the last two decades, there have been multiple randomised controlled trials (RCTs), review articles, and meta-analyses addressing the efficacy of rabbit anti-thymocyte globulin (r-ATG) as a graft-versus-host disease (GvHD) prophylaxis. Nevertheless, only a few aimed to compare the effectiveness of different r-ATG formulations. Since the last article we retrieved comparing different r-ATGs in GvHD prophylaxis dates back to 2017, we performed a systematic literature review of articles published since 2017 to this day, utilising PubMed, Scopus, Cochrane, and MEDLINE, with the main endpoints being prophylaxis of acute GvHD (aGvHD) and chronic GvHD (cGvHD). We subjected to scrutiny a total of five studies, of which four compared the differences between Thymoglobulin (ATG-T) and Grafalon (ATG-G), and one discussed the impact of ATG-T dose. Overall, cGvHD, aGvHD grades II-IV, TRM, OS, NRM, LFS, relapse, overall infections, and EBV reactivation do not seem to be affected by the type of utilised rATG. However, data on aGvHD grades III-IV, GRFS, moderate-severe cGvHD, and CMV reactivation is conflicting. Through our research, we sought to summarise the most recent findings concerning r-ATGs in allo-HCT, and provide insight into the differences between the targets and origin of various ATG formulations.

LIS1, a glyco-humanized swine polyclonal anti-lymphocyte globulin, as a novel induction treatment in solid organ transplantation

Anti-thymocyte or anti-lymphocyte globulins (ATGs/ALGs) are immunosuppressive drugs used in induction therapies to prevent acute rejection in solid organ transplantation. Because animal-derived, ATGs/ALGs contain highly immunogenic carbohydrate xenoantigens eliciting antibodies that are associated with subclinical inflammatory events, possibly impacting long-term graft survival. Their strong and long-lasting lymphodepleting activity also increases the risk for infections. We investigated here the in vitro and in vivo activity of LIS1, a glyco-humanized ALG (GH-ALG) produced in pigs knocked out for the two major xeno-antigens αGal and Neu5Gc. It differs from other ATGs/ALGs by its mechanism of action excluding antibody-dependent cell-mediated cytotoxicity and being restricted to complement-mediated cytotoxicity, phagocyte-mediated cytotoxicity, apoptosis and antigen masking, resulting in profound inhibition of T-cell alloreactivity in mixed leucocyte reactions. Preclinical evaluation in non-human primates showed that GH-ALG dramatically reduced CD4+ (p=0.0005,***), CD8+ effector T cells (p=0.0002,***) or myeloid cells (p=0.0007,***) but not T-reg (p=0.65, ns) or B cells (p=0.65, ns). Compared with rabbit ATG, GH-ALG induced transient depletion (less than one week) of target T cells in the peripheral blood (<100 lymphocytes/L) but was equivalent in preventing allograft rejection in a skin allograft model. The novel therapeutic modality of GH-ALG might present advantages in induction treatment during organ transplantation by shortening the T-cell depletion period while maintaining adequate immunosuppression and reducing immunogenicity.

Antithymocyte Globulin Inhibits CD8+ T Cell Effector Functions via the Paracrine Induction of PDL-1 on Monocytes

BACKGROUND

Antithymocyte globulins (ATG) are T cell-depleting antibodies used in solid organ transplantation for induction therapy in sensitized patients with a high risk of graft rejection. Previously described effects besides the depletion of T cells have suggested additional modes of action and identified further cellular targets.

METHODS

We examined the transcriptional changes arising in immune cells from human blood after ex vivo stimulation with ATG at the single-cell level to uncover additional mechanisms by which ATG regulates T cell activity and effector functions.

FINDINGS

Analysis of the paracrine factors present in the plasma of ATG-treated whole blood revealed high levels of chemokines and cytokines, including interferon-γ (IFN-γ). Furthermore, we identified an increase in the surface expression of the programmed death ligand 1 (PDL-1) on monocytes mediated by the released paracrine factors. In addition, we showed that this induction is dependent on the activation of JAK/STAT signaling via the binding of IFN-γ to interferon-γ receptor 1 (IFN-γR1). Lastly, we demonstrated that the modulation of the immune regulatory axis of programmed cell death protein 1 (PD1) on activated CD8⁺ T cells with PDL-1 found on monocytes mediated by ATG potently inhibits effector functions including the proliferation and granzyme B release of activated T cells.

INTERPRETATION

Together, our findings represent a novel mode of action by which ATG exerts its immunosuppressive effects.

Pre-transplant CD69+ extracellular vesicles are negatively correlated with active ATLG serum levels and associate with the onset of GVHD in allogeneic HSCT patients

Graft versus host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (HSCT). Rabbit anti-T lymphocyte globulin (ATLG) in addition to calcineurin inhibitors and antimetabolites is a suitable strategy to prevent GVHD in several transplant settings. Randomized studies already demonstrated its efficacy in terms of GVHD prevention, although the effect on relapse remains the major concern for a wider use. Tailoring of ATLG dose on host characteristics is expected to minimize its side effects (immunological reconstitution, relapse, and infections). Here, day -6 to day +15 pharmacokinetics of active ATLG serum level was first assayed in an explorative cohort of 23 patients by testing the ability of the polyclonal serum to bind antigens on human leukocytes. Significantly lower levels of serum active ATLG were found in the patients who developed GVHD (ATLG_AUC_CD45: 241.52 ± 152.16 vs. 766.63 +/- 283.52 (μg*day)/ml, p = 1.46e^-5). Consistent results were obtained when the ATLG binding capacity was assessed on CD3+ and CD3+/CD4+ T lymphocytes (ATLG_AUC_CD3: 335.83 ± 208.15 vs. 903.54 ± 378.78 (μg*day)/ml, p = 1.92e^-4; ATLG_AUC_CD4: 317.75 ± 170.70 vs. 910.54 ± 353.35 (μg*day)/ml, p = 3.78e^-5. Concomitantly, at pre-infusion time points, increased concentrations of CD69+ extracellular vesicles (EVs) were found in patients who developed GVHD (mean fold 9.01 ± 1.33; p = 2.12e^-5). Consistent results were obtained in a validation cohort of 12 additional ATLG-treated HSCT patients. Serum CD69+ EVs were mainly represented in the nano (i.e. 100 nm in diameter) EV compartment and expressed the leukocyte marker CD45, the EV markers CD9 and CD63, and CD103, a marker of tissue-resident memory T cells. The latter are expected to set up a host pro-inflammatory cell compartment that can survive in the recipient for years after conditioning regimen and contribute to GVHD pathogenesis. In summary, high levels of CD69+ EVs are significantly correlated with an increased risk of GVHD, and they may be proposed as a tool to tailor ATLG dose for personalized GVHD prevention.

Comparison of Thymoglobulin and Grafalon as Induction Agents in Renal Transplantation: A Prospective Study

BACKGROUND

Induction immunosuppression is used to reduce the incidence of acute rejection and prevent delayed graft function. The 2 rabbit anti-thymocyte globulins- thymoglobulin and Grafalon (ATG Fresenius) have been commonly used for induction immunosuppression and treatment of acute rejection in solid organ transplantation. There are very few studies comparing the efficacy and side effects of both the anti-thymocyte globulins therefore this prospective study comparing the 2 types of anti-thymocyte globulins would be of clinical interest.

PATIENTS AND METHODS

This prospective single center study was conducted at Rabindranath Tagore International Institute of Cardiac Sciences, Kolkata, India from April 2019 to June 2020. Sixty-two ABO-compatible renal transplant recipients were included in the study. They were divided in 2 groups of 31 patients each. One group received thymoglobulin (3 mg/kg) and the second group received Grafalon (6 mg/kg). All patients were followed up for 12 months and the 2 groups were compared for incidence of rejections, infections, graft function, patient survival, and graft survival.

RESULTS

There was no significant difference in the incidence of rejections, infective episodes, graft function, posttransplant diabetes mellitus, graft survival and patient survival in thymoglobulin or Grafalon groups. The hematological parameters were similar in both groups at 7 days, 1 month, and 6 months of follow-up. The absolute lymphocyte count was significantly lower in the thymoglobulin group at 12 months posttransplant.

CONCLUSIONS

Thymoglobulin and Grafalon were found to be equivalent in terms of safety and efficacy in short term, with no difference in rejections, infections, graft survival, or patient survival.

Anti-T-Lymphocyte Immunoglobulin (Grafalon) as an Induction Agent for Renal Transplantation: A Real-World, Retrospective, Single-Center Experience

OBJECTIVES

Polyclonal antithymocyte globulins are widely used in the induction regimens of solid-organ transplant recipients; however, their doses and outcomes remain to be standardized in Indian patients. We report our clinical experience from the real-world use of Grafalon (an anti-T-lymphocyte globulin; ATG-Fresenius) as an induction agentin renal transplant recipients from India.

MATERIALS AND METHODS

In this retrospective, single- center, observational study, we analyzed the medical records of 177 consecutive, kidney-only transplant recipients who received induction therapy with Grafalon from September 2016 to March 2018 at our center. Incidences of biopsy-proven acute rejection and graft dysfunction, immunosuppression protocol, Grafalon dosage, 18-month post-transplant graft and patient survival, treatment-related adverse events, and infective complications were reported.

RESULTS

Mean age of patients was 41.46 years (range, 14-68 years), (85% were males). The average dose of Grafalon was 5.81 ± 1.95 mg/kg (range, 2.41 to 10.07 mg/kg). Graft dysfunction (ie, at least 20% increase in serum creatinine from baseline) was observed in 26 patients (14%): 11 patients (6.2%) had biopsy-proven acute rejections, 11 patients (6.2%) had acute tubular necrosis, and 4 patients (2.2%) had calcineurin inhibitor toxicity. Seven deaths were recorded: 2 each from fungal pneumonia, bacterial pneumonia, and acute coronary syndrome and 1 with urinary tract infection with septicemia. Death-censored graft survival was 100% at 12 months and 98% at 18-month follow-up; overall patient survival was 96%. Infective complications occurred in 40 patients (22.5%), with the most common being urinary tract infection in 32 patients (18%). No malignancies were reported.

CONCLUSIONS

Use of a potent induction therapy like anti-T-lymphocyte globulin (Grafalon) is often restricted by the risk of side effects and lack of local clinical evidence supporting its role in long-term graft survival. Real-world evidence support the safe and effective use of anti-T-lymphocyte globulin as an induction agent in renal transplant recipients with an individualized dosing approach.

One-Year Outcomes with Use of Anti-T-Lymphocyte Globulin in Patients Undergoing Kidney Transplantation: Results from a Prospective, Multicentric, Observational Study from India

INTRODUCTION

Large-scale Indian data on the use of anti-T-lymphocyte globulin (ATLG) (Grafalon^®) as induction therapy in kidney transplantation (KT) patients is lacking. The aim of this study was to determine the 1-year patient and graft survival outcomes with the use of ATLG as induction regimen in KT.

METHODS

In a prospective, multicentric, observational study, adult patients who underwent ABO-compatible KT and had received ATLG as a part of induction were included in the study. The primary outcome measure was overall survival and death-censored graft survival at 12 months. The primary safety outcome was assessed by development of infectious complications and graft rejection.

RESULTS

In total, 359 patients were included in this study. The mean age was 42.77 ± 12.30 years and 83% were male. The average ATLG dose per patient was 6.2 ± 2.2 mg/kg whereas average cumulative dose per patient was 389.6 ± 149.8 mg. The rate of graft dysfunction was 13.4% of patients and 6.7% had biopsy-proven acute rejection (BPAR). There were a total of 12 (3.3%) deaths and one graft loss. Overall survival and death-censored graft survival at 12 months were 96.65% and 99.44%, respectively. The rate of infections was 13.6% with urinary tract infections being most common.

CONCLUSION

ATLG at an average dose of 6 mg/kg is an effective and safe induction regimen immunosuppressant for ABO-compatible KT with favourable impact on survival and graft function in Indian patients.

Study protocol: Minimum effective low dose: anti-human thymocyte globulin (MELD-ATG): phase II, dose ranging, efficacy study of antithymocyte globulin (ATG) within 6 weeks of diagnosis of type 1 diabetes

INTRODUCTION

Type 1 diabetes (T1D) is a chronic autoimmune disease, characterised by progressive destruction of the insulin-producing β cells of the pancreas. One immunosuppressive agent that has recently shown promise in the treatment of new-onset T1D subjects aged 12-45 years is antithymocyte globulin (ATG), Thymoglobuline, encouraging further exploration in lower age groups.

METHODS AND ANALYSIS

Minimal effective low dose (MELD)-ATG is a phase 2, multicentre, randomised, double-blind, placebo-controlled, multiarm parallel-group trial in participants 5-25 years diagnosed with T1D within 3-9 weeks of planned treatment day 1. A total of 114 participants will be recruited sequentially into seven different cohorts with the first cohort of 30 participants being randomised to placebo, 2.5 mg/kg, 1.5 mg/kg, 0.5 mg/kg and 0.1 mg/kg ATG total dose in a 1:1:1:1:1 allocation ratio. The next six cohorts of 12-15 participants will be randomised to placebo, 2.5 mg/kg, and one or two selected middle ATG total doses in a 1:1:1:1 or 1:1:1 allocation ratio, as dependent on the number of middle doses, given intravenously over two consecutive days. The primary objective will be to determine the changes in stimulated C-peptide response over the first 2 hours of a mixed meal tolerance test at 12 months for 2.5 mg/kg ATG arm vs the placebo. Conditional on finding a significant difference at 2.5 mg/kg, a minimally effective dose will be sought. Secondary objectives include the determination of the effects of a particular ATG treatment dose on (1) stimulated C-peptide, (2) glycated haemoglobin, (3) daily insulin dose, (4) time in range by intermittent continuous glucose monitoring measures, (5) fasting and stimulated dry blood spot (DBS) C-peptide measurements.

ETHICS AND DISSEMINATION

MELD-ATG received first regulatory and ethical approvals in Belgium in September 2020 and from the German and UK regulators as of February 2021. The publication policy is set in the INNODIA (An innovative approach towards understanding and arresting Type 1 diabetes consortium) grant agreement (www.innodia.eu).

TRIAL REGISTRATION NUMBER

NCT03936634; Pre-results.

Grafalon® vs. Thymoglobulin® as an Induction Agent in Renal Transplantation - A Retrospective Study

Introduction

Antihuman thymocyte immunoglobulin, used as an induction agent in renal transplantation, is of two types - thymoglobulin and grafalon (formerly ATG-Fresenius). In this study, we compared outcomes with these two agents.

Methods

This was a single-center retrospective study of patients transplanted from January 2017 to October 2019, who received either grafalon or thymoglobulin induction. Grafalon or thymoglobulin was given at 6 and 3 mg/kg, respectively, followed by standard triple immunosuppression of tacrolimus, MMF, and prednisolone.

Results

Median follow up was 22 (3-36) months. Thymoglobulin was given to 255 patients, whereas 78 patients received grafalon. Baseline demographics were similar between the two groups although significantly more patients in the grafalon group received ABO incompatible transplant (15% vs. 4.3%; P = 0.002). Patient survival was similar between the two groups (99% in grafalon vs. 98.8% in thymoglobulin; P = 1.0). Death censored graft survival was also similar (99% in grafalon vs. 100% in thymoglobulin; P = 0.23). Biopsy proven acute rejection (BPAR) was significantly higher in the grafalon group (12.8% vs. 5.1%, P = 0.04). The significance persisted after multivariable regression analysis (P = 0.02). Other outcomes such as infection rate and estimated glomerular filtration rate on last follow up were comparable between the two groups.

Conclusions

Grafalon (6 mg/kg dose) when used as an induction agent was associated with significantly higher rate of BPARs as compared to thymoglobulin (3 mg/kg dose) although with comparable short-term patient and death censored graft survival, graft function, and infection rates.

Changes in hemostatic factors after kidney transplantation: A retrospective cohort study

Chronic kidney disease affects hemostasis in complex ways, producing both thrombotic and hemorrhagic diatheses. These changes may impact patient morbidity and mortality pre-transplantation, as well as allograft survival after kidney transplantation (KT). This study was conducted to analyze changes in hemostatic factors in the early post-KT period.We retrospectively analyzed 676 recipients of kidney allografts from December 2009 to December 2014. Patients receiving plasmapheresis pre- or post-KT, experiencing early allograft failure, or receiving anticoagulants or antiplatelet agents pre- or post-KT were excluded.Of the 367 included patients, acute (≤1 month) rejection occurred in 4.1% and delayed graft function occurred in 3.3%. Postoperative bleeding complications occurred in 7.9% of patients and thrombotic complications in 3.3%. Pre-transplantation, recipients had below normal hemoglobin, above normal d-dimer and homocysteine levels, and elevated rates of antiphospholipid antibodies. Hemoglobin increased to almost normal by postoperative day (POD) 28 (P  < .001). d-dimer increased on POD7, 14, and 28, although the values were not significantly different from pre-KT. The pattern of d-dimer changes suggested that they were a nonspecific consequence of major surgery. Homocysteine decreased to normal by POD7 (P  < .001). The percentage of patients with ≥1 prothrombotic factor was 82.0% pre-KT and only 14.2% on POD28 (P  < .001).The most of patients exhibited prothrombotic tendencies, including increased d-dimer and homocysteine, and increased prevalence of antiphospholipid antibodies before transplantation. They also had pre-transplantation anemia, suggesting a concomitant bleeding diathesis. However, most of these abnormal hemostatic factors improved or resolved after KT.

Generation of recombinant hyperimmune globulins from diverse B-cell repertoires

Plasma-derived polyclonal antibody therapeutics, such as intravenous immunoglobulin, have multiple drawbacks, including low potency, impurities, insufficient supply and batch-to-batch variation. Here we describe a microfluidics and molecular genomics strategy for capturing diverse mammalian antibody repertoires to create recombinant multivalent hyperimmune globulins. Our method generates of diverse mixtures of thousands of recombinant antibodies, enriched for specificity and activity against therapeutic targets. Each hyperimmune globulin product comprised thousands to tens of thousands of antibodies derived from convalescent or vaccinated human donors or from immunized mice. Using this approach, we generated hyperimmune globulins with potent neutralizing activity against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in under 3 months, Fc-engineered hyperimmune globulins specific for Zika virus that lacked antibody-dependent enhancement of disease, and hyperimmune globulins specific for lung pathogens present in patients with primary immune deficiency. To address the limitations of rabbit-derived anti-thymocyte globulin, we generated a recombinant human version and demonstrated its efficacy in mice against graft-versus-host disease.

A comparative study of human-and rhesus-specific antithymocyte globulins in Rhesus macaques

Rabbit antithymocyte globulin (RATG) preparations are widely used in transplantation. They are developed in vivo against thymocytes and contain polyclonal antibodies specific for myriad cellular targets. The rhesus monkey is commonly used as a preclinical transplant model, but the fidelity of commercially available human-specific RATGs to anticipate the effects of RATGs in rhesus has not been established. We therefore developed two rhesus-specific ATGs (rhATG) and compared them to human-specific RATG (huATG, Thymoglobulin^® ) in rhesus monkeys, assessing the magnitude and phenotype of depletion peripherally and in lymph nodes. Four primates were assigned to each group and received 20 mg/kg of drug. Depletion, repopulation, and changes in lymphocyte subsets were evaluated in peripheral blood and lymph nodes by flow cytometry over four months. We observed similar qualitative changes in lymphocyte subsets, but a generally more profound depletion with huATG compared to either rhATG. Peripheral homeostatic proliferation rather than thymic output was the major mechanism for repopulation with all RATGs. Repopulation was slower but qualitatively similar when examining RATGs in additional animals receiving concomitant chronic immunosuppression. Depletional induction is similar to human- and rhesus-specific RATGs in rhesus macaques. Both rhesus- and human-specific agents appear appropriate for preclinical modeling of clinical RATG use.

Impact of anti-thymocyte globulin dose for graft-versus-host disease prophylaxis in allogeneic hematopoietic cell transplantation from matched unrelated donors: a multicenter experience

Despite the widespread use of rabbit anti-thymocyte globulin (ATG) to prevent acute and chronic graft-versus-host disease (aGVHD, cGVHD) after allogeneic hematopoietic cell transplantation (allo-HCT), convincing evidence about an optimal dose is lacking. We retrospectively evaluated the clinical impact of two different ATG doses (5 vs 6-7.5 mg/kg) in 395 adult patients undergoing HSCT from matched unrelated donors (MUD) at 3 Italian centers. Cumulative incidence of aGVHD and moderate-severe cGVHD did not differ in the 2 groups. We observed a trend toward prolonged overall survival (OS) and disease-free survival (DFS) with lower ATG dose (5-year OS and DFS 56.6% vs. 46.3%, p=0.052, and 46.8% vs. 38.6%, p=0.051, respectively) and no differences in relapse incidence and non-relapse mortality. However, a significantly increased infection-related mortality (IRM) was observed in patients who received a higher ATG dose (16.7% vs. 8.8% in the lower ATG group, p=0.019). Besides, graft and relapse-free survival (GRFS) was superior in the lower ATG group (5-year GRFS 43.1% vs. 32.4%, p=0.014). The negative impact of higher ATG dose on IRM and GRFS was confirmed by multivariate analysis. Our results suggest that ATG doses higher than 5 mg/kg are not required for MUD allo-HCT and seem associated with worse outcomes.

Rabbit antithymocyte globulin induces human lymphocyte activation, proliferation, and apoptosis in the absence of complement: an experimental study

Rabbit antithymocyte globulin (rATG) has become the first choice for induction therapy in HLA-presensitized patients undergoing organ transplantation. Meanwhile, complement inhibitors have been approved for preventing or treating antibody-mediated rejection in these patients. The biological effects of rATG on lymphocytes in cases of complement deficiency or significant inhibition are not yet clear. We measured lymphocyte activation, proliferation, and apoptosis in response to rATG treatment in the absence of complement. T-cell subsets were analyzed transcriptomically features to rATG stimulation. Activation-related phenotypes on T cells were determined in patients after rATG administration. We found that rATG treatment led to lymphocyte activation and proliferation in vitro without the addition of complement. A dose-dependent apoptosis in rATG-treated lymphocytes was detected, which was partially caspase-3-dependent but Fas/FasL-independent. T cells were more sensitive to rATG stimulation than were non-T cells. Both CD4⁺ T cells and CD8⁺ T cells upregulated a series of genes related to cell activation, cytokine production and apoptosis to rATG stimulation. CD69 and CD25 levels in surviving T cells were increased in patients after rATG administration. These findings indicate that rATG can stimulate lymphocyte activation, proliferation, and apoptosis in the absence of complement. Biologic effects of rATG other than complement-dependent cytotoxicity need to be concerned.

Strategies for Liver Transplantation Tolerance

Liver transplant (LT) recipients require life-long immunosuppression (IS) therapy to preserve allograft function. The risks of chronic IS include an increased frequency of malignancy, infection, renal impairment, and other systemic toxicities. Despite advances in IS, long-term LT outcomes have not been improved over the past three decades. Standard-of-care (SoC) therapy can, in rare cases, lead to development of operational tolerance that permits safe withdrawal of maintenance IS. However, successful IS withdrawal cannot be reliably predicted and, in current prospective studies, is attempted several years after the transplant procedure, after considerable exposure to the cumulative burden of maintenance therapy. A recent pilot clinical trial in liver tolerance induction demonstrated that peri-transplant immunomodulation, using a regulatory T-cell (Treg) approach, can reduce donor-specific alloreactivity and allow early IS withdrawal. Herein we review protocols for active tolerance induction in liver transplantation, with a focus on identifying tolerogenic cell populations, as well as barriers to tolerance. In addition, we propose the use of novel IS agents to promote immunomodulatory mechanisms favoring tolerance. With numerous IS withdrawal trials underway, improved monitoring and use of novel immunomodulatory strategies will help provide the necessary knowledge to establish an active liver tolerance induction protocol for widespread use.

A Prospective Controlled Trial to Evaluate Safety and Efficacy of in vitro Expanded Recipient Regulatory T Cell Therapy and Tocilizumab Together With Donor Bone Marrow Infusion in HLA-Mismatched Living Donor Kidney Transplant Recipients (Trex001)

Background: The induction of donor-specific immunological tolerance could improve outcome after kidney transplantation. However, no tolerance protocol is available for routine clinical use. Chimerism-based regimens hold promise, but their widespread application is impeded in part by unresolved safety issues. This study tests the hypothesis that therapy with polyclonal recipient regulatory T cells (Tregs) and anti-IL6R (tocilizumab) leads to transient chimerism and achieves pro-tolerogenic immunomodulation in kidney transplant recipients also receiving donor bone marrow (BM) without myelosuppressive conditioning of the recipient.

Methods/design: A prospective, open-label, controlled, single-center, phase I/IIa academic study is performed in HLA-mismatched living donor kidney transplant recipients.

Study group: Recipients of the study group receive in vitro expanded recipient Tregs and a donor bone marrow cell infusion within 3 days after transplantation and tocilizumab for the first 3 weeks post-transplant. In addition they are treated with thymoglobulin, belatacept, sirolimus, and steroids as immunosuppression. Starting 6 months post-transplant, sirolimus and steroids are withdrawn in a step-wise manner in stable patients.

Control group: Recipients of the control group are treated with thymoglobulin, belatacept, sirolimus, and steroids as immunosuppression. Co-primary endpoints of safety (impaired graft function [eGFR <35 mL/min/1.73 m²], graft-vs.-host disease or patient death by 12 months) and efficacy (total leukocyte donor chimerism within 28 days post-transplant) are assessed. Secondary endpoints include frequency of biopsy-proven acute rejection episodes and subclinical rejection episodes on surveillance biopsies, assessment of kidney graft function, and the evaluation whether the study protocol leads to detectable changes in the immune system indicative of pro-tolerogenic immune modulation.

Discussion: The results of this trial will provide evidence whether treatment with recipient Tregs and donor BM is feasible, safe and efficacious in leading to transient chimerism. If successful, this combination cell therapy has the potential to become a novel treatment option for immunomodulation in organ transplantation without the toxicities associated with myelosuppressive recipient conditioning.

Trial registration: European Clinical Trials Database EudraCT Nr 2018-003142-16 and clinicaltrials.gov NCT03867617.

Differentiation and activation of human CD4 T cells is associated with a gradual loss of myelin and lymphocyte protein

Upon generation of monoclonal antibodies to the T cell antigen receptor/CD3 (TCR/CD3) complex, we isolated mAb MT3, whose reactivity correlates inversely with the production of IFN‐γ by human peripheral blood T lymphocytes. Using eukaryotic expression cloning, we identified the MT3 antigen as myelin‐and‐lymphocyte (MAL) protein. Flow cytometry analysis demonstrates high surface expression of MAL on all naïve CD4⁺ T cells whereas MAL expression is diminished on central memory‐ and almost lost on effector memory T cells. MAL^– T cells proliferate strongly in response to stimulation with CD3/CD28 antibodies, corroborating that MAL⁺ T cells are naïve and MAL^– T cells memory subtypes. Further, resting MAL^– T cells harbor a larger pool of Ser59‐ and Tyr394‐ double phosphorylated lymphocyte‐specific kinase (Lck), which is rapidly increased upon in vitro restimulation. Previously, lack of MAL was reported to prevent transport of Lck, the key protein tyrosine kinase of TCR/CD3 signaling to the cell membrane, and to result in strongly impaired human T cell activation. Here, we show that knocking out MAL did not significantly affect Lck membrane localization and immune synapse recruitment, or transcriptional T cell activation. Collectively, our results indicate that loss of MAL is associated with activation‐induced differentiation of human T cells but not with impaired membrane localization of Lck or TCR signaling capacity.

Serotherapy as Graft-Versus-Host Disease Prophylaxis in Haematopoietic Stem Cell Transplantation for Acute Lymphoblastic Leukaemia

Serotherapy comprising agents such as anti-thymocyte globulin, anti-T-lymphocyte globulin, and the anti-CD52 monoclonal antibody alemtuzumab is used widely to reduce the incidence of graft-versus-host disease (GvHD) after paediatric haematopoietic stem cell transplantation (HSCT). The outcome of transplants using matched unrelated donors now approaches that of matched sibling donors. This is likely due to better disease control in recipients, the use of donors more closely human-leukocyte antigen (HLA)-matched to recipients, and more effective graft-versus-host disease (GvHD) prophylaxis. The price paid for reduced GvHD is slower immune reconstitution of T cells and thus more infections. This has led to studies looking to optimise the amount of serotherapy used. The balance between prevention of GvHD on one side and prevention of infections and relapse on the other side is quite delicate. Serotherapy is given with chemotherapy-/radiotherapy-based conditioning prior to HSCT. Due to their long half-lives, agents used for serotherapy may be detectable in patients well after graft infusion. This exposes the graft-infused T cells to a lympholytic effect, impacting T-cell recovery. As such, excessive serotherapy dosing may lead to no GvHD but a higher incidence of infections and relapse of leukaemia, while under-dosing may result in a higher chance of serious GvHD as immunity recovers more quickly. Individualised dosing is being developed through studies including retrospective analyses of serotherapy exposure, population pharmacokinetic modelling, therapeutic drug monitoring in certain centres, and the development of dosing models reliant on factors including the patient's peripheral blood lymphocyte count. Early results of "optimal" dosing strategies for serotherapy and conditioning chemotherapy show promise of improved overall survival.

Siplizumab, an Anti-CD2 Monoclonal Antibody, Induces a Unique Set of Immune Modulatory Effects Compared to Alemtuzumab and Rabbit Anti-Thymocyte Globulin In Vitro

Antibodies are commonly used in organ transplant induction therapy and to treat autoimmune disorders. The effects of some biologics on the human immune system remain incompletely characterized and a deeper understanding of their mechanisms of action may provide useful insights for their clinical application. The goal of this study was to contrast the mechanistic properties of siplizumab with Alemtuzumab and rabbit Anti-Thymocyte Globulin (rATG). Mechanistic assay systems investigating antibody-dependent cell-mediated cytotoxicity, antibody-dependent cell phagocytosis and complement-dependent cytotoxicity were used to characterize siplizumab. Further, functional effects of siplizumab, Alemtuzumab, and rATG were investigated in allogeneic mixed lymphocyte reaction. Changes in T cell activation, T cell proliferation and frequency of naïve T cells, memory T cells and regulatory T cells induced by siplizumab, Alemtuzumab and rATG in allogeneic mixed lymphocyte reaction were assessed via flow cytometry. Siplizumab depleted T cells, decreased T cell activation, inhibited T cell proliferation and enriched naïve and bona fide regulatory T cells. Neither Alemtuzumab nor rATG induced the same combination of functional effects. The results presented in this study should be used for further in vitro and in vivo investigations that guide the clinical use of immune modulatory biologics.

Impact of Immunosuppressive Strategies on Post-Kidney Transplantation Thrombocytopenia

BACKGROUND

Thrombocytopenia after kidney transplantation is a common complication, partly induced by immunosuppressive therapies. Peritransplant thrombocytopenia may cause serious hemorrhages. We assessed the incidence of early posttransplantation thrombocytopenia (defined as a platelet count of <150,000 mm³ or <150 G/L) in de novo kidney transplant recipients (KTRs) across 4 immunosuppressive regimens.

METHODS

This was a single-center observational study that included all consecutive KTRs who received either Thymoglobulin (THY) or Grafalon (GRA) and maintenance therapy of either mycophenolate-mofetil (MMF) or everolimus (EVR), associated with tacrolimus/corticosteroids.

RESULTS

Between July 27, 2016, and September 7, 2018, 237 KTRs were included; 64.6% experienced thrombocytopenia within the first week. Thrombocytopenia was significantly more frequent (P = .004) among GRA-treated patients (73.4%) compared to THY-treated patients (61.3%). These patients also had lower nadir platelet count (120 ± 52 vs 142 ± 48 G/L; P = .002) and lower platelet count at discharge (227 ± 94 vs 243 ± 92 G/L; P = .25). More of the GRA-EVR group had thrombocytopenia (81.0% vs 61.4% in THY-MMF, 60.9% in THY-EVR, and 69.8% in GRA-MMF; P = .081) and a worse nadir platelet count (109 ± 41 in GRA-EVR vs 141 ± 47G/L in THY-MMF, 145 ± 52 G/L in THY-EVR, and 125 ± 56 G/L in GRA-MMF; P = .011) but GRA was the only risk factor for thrombocytopenia in multivariate analyses (P = .002). Rates of hemorrhage, red blood cell transfusions, reoperations needed within the first week, delayed graft function, acute rejection, graft loss, and death did not differ between the groups after a mean follow-up of 25 ± 8 months.

CONCLUSIONS

GRA associated with EVR led to more frequent and severe thrombocytopenia, although we found no significant clinical consequences.

Monitoring of CMV-specific cell-mediated immunity with a commercial ELISA-based interferon-γ release assay in kidney transplant recipients treated with antithymocyte globulin

Monitoring for cytomegalovirus (CMV)-specific cell-mediated immunity (CMV-CMI) may be useful for individualizing valganciclovir (VGCV) prophylaxis after kidney transplantation (KT). We performed a commercial ELISA-based interferon (IFN)-γ release assay (QTF-CMV) from posttransplant months 2-5 (362 points) in 120 CMV-seropositive KT recipients that received antithymocyte globulin as induction therapy and VGCV prophylaxis (median of 92 days). Forty-seven patients (39.3%) had CMV infection after discontinuation of prophylaxis. The QTF-CMV assay was reactive, nonreactive, and indeterminate in 264 (72.9%), 90 (24.9%), and 8 points (2.2%). The QTF-CMV assay at prophylaxis discontinuation exhibited suboptimal accuracy for predicting protective CMV-CMI (sensitivity: 77.4%; specificity: 34.3%; positive predictive value [PPV]: 64.1%; negative predictive value [NPV]: 50.0%), with no differences in 1-year CMV infection rates between patients with negative (nonreactive or indeterminate) or reactive results (45.8% vs 36.1%; P = .244). Specificity and PPV to predict protective CMV-CMI improved by elevating the IFN-γ cutoff value to 1.13 IU/mL (65.7% and 71.4%) and 7.0 IU/mL (85.7% and 76.2%), although NPVs decreased. The QTF-CMV assay as per manufacturer's interpretative criteria performed poorly to predict protection from CMV infection following discontinuation of VGCV prophylaxis among ATG-treated CMV-seropositive KT recipients. This performance is slightly improved by modifying the IFN-γ positivity threshold.

Lower Platelet Count Following Rabbit Antithymocyte Globulin Induction Is Associated With Less Acute Cellular Rejection in Heart Transplant Recipients

BACKGROUND

Unlike lymphodepletion, a decrease in platelet count following induction immunosuppressive therapy with polyclonal rabbit antithymocyte globulin (rATG) is deemed as an adverse event. However, this phenomenon may represent a particular rATG antirejection mechanism.

METHODS

This retrospective single-center study included 156 patients who received a heart transplant (HTx) between 2010 and 2018. All patients received rATG induction therapy for 5 days. Absolute lymphocyte count (ALC) and platelet counts were assessed on days 0, 7, and 14 following HTx. The primary outcome of the study was the first occurrence of acute cellular rejection (ACR) defined as grade ≥ 1B within 24 months after HTx.

RESULTS

Both ALC and platelet counts decreased rapidly after induction. During the 24-month follow-up period, 17% of patients had ACR. Patients with ACR had significantly higher platelet count on day 7 (145 vs 104, P < .001) and higher ALC on day 14 (162 vs 130, P = .035) than those without rejection. Patients in the highest platelet count quartile showed more ACR (50% in quartile 4 vs 0% in quartile 1, P = .006) as well as a higher cumulative total rejection score. Univariate analysis showed that ACR was associated with platelet count on day 7, recipient age, and pretransplant cytomegalovirus IgG serology. In multivariable regression analysis, platelet count on day 7 was the most accurate predictor of ACR.

CONCLUSIONS

Lower platelet count after induction with rATG is associated with less ACR. This suggests platelet involvement in antirejection mechanisms of rATG and a possible rationale for targeting platelets in future immunosuppressive strategies.

Attenuation of canonical NF-κB signaling maintains function and stability of human Treg

Nuclear factor ‘κ‐light‐chain‐enhancer’ of activated B cells (NF‐κB) signaling is a signaling pathway used by most immune cells to promote immunostimulatory functions. Recent studies have indicated that regulatory T cells (Treg) differentially integrate TCR‐derived signals, thereby maintaining their suppressive features. However, the role of NF‐κB signaling in the activation of human peripheral blood (PB) Treg has not been fully elucidated so far. We show that the activity of the master transcription factor forkhead box protein 3 (FOXP3) attenuates p65 phosphorylation and nuclear translocation of the NF‐κB proteins p50, p65, and c‐Rel following activation in human Treg. Using pharmacological and genetic inhibition of canonical NF‐κB signaling in FOXP3‐transgenic T cells and PB Treg from healthy donors as well as Treg from a patient with a primary NFKB1 haploinsufficiency, we validate that Treg activation and suppressive capacity is independent of NF‐κB signaling. Additionally, repression of residual NF‐κB signaling in Treg further enhances interleukin‐10 (IL‐10) production. Blockade of NF‐κB signaling can be exploited for the generation of in vitro induced Treg (iTreg) with enhanced suppressive capacity and functional stability. In this respect, dual blockade of mammalian target of rapamycin (mTOR) and NF‐κB signaling was accompanied by enhanced expression of the transcription factors FOXP1 and FOXP3 and demethylation of the Treg‐specific demethylated region compared to iTreg generated under mTOR blockade alone. Thus, we provide first insights into the role of NF‐κB signaling in human Treg. These findings could lead to strategies for the selective manipulation of Treg and the generation of improved iTreg for cellular therapy.

Cell Versus Cytokine - Directed Therapies for Hemophagocytic Lymphohistiocytosis (HLH) in Inborn Errors of Immunity

Hemophagocytic lymphohistiocytosis (HLH) is a heterogeneous hyperinflammatory syndrome with different pathways of pathogenesis resulting in similar clinical presentations. It is best defined and understood if presenting in the context of genetic immunodeficiencies associated with defects of lymphocyte cytotoxicity. In these "primary" forms of HLH, cellular and soluble immune effectors are relatively well characterized. While etoposide-based broad cell-directed therapies remain standard of care, more specific therapies targeting these effectors individually are increasingly available. Anti-CD52 as a cell-directed therapy and anti-IFN-gamma, IL-18BP, and JAK-inhibition as cytokine-directed therapies are expected to broaden the therapeutic options, but the precise role of these drugs in first-line and rescue treatment indications remains to be defined. A number of additional inborn errors of immunity are associated with episodes of immune activation fulfilling the clinical criteria of HLH. Impaired pathogen control is a key driver of hyperinflammation in some conditions, while others are characterized by a strong autoinflammatory component. This heterogeneity of disease-driving factors and the variable severity in disease progression in these conditions do not allow a simple adaptation of protocols established for "primary" HLH to HLH in the context of other inborn errors of immunity. Cytokine-directed therapies hold significant promise in these increasingly recognized disorders.

Comparison of ATG-thymoglobulin with ATG-Fresenius for Epstein-Barr virus infections and graft-versus-host-disease in patients with hematological malignances after haploidentical hematopoietic stem cell transplantation: a single-center experience

Two anti-thymocyte globulin (ATG) forms are used in graft-versus-host disease (GVHD) prophylaxis during haploidentical hematopoietic stem cell transplantations (haplo-HSCTs): ATG-thymoglobulin (ATG-T) and ATG-fresenious (ATG-F). However, comparable dosages for haplo-HSCT remain unclear. We compared and evaluated the effects of ATG-T (7.5 mg/kg) or ATG-F (20 mg/kg) dosages in a relatively homogenous population in haplotype HSCT settings. Patients administered ATG-T 7.5 mg/kg (n = 81) or ATG-F 20 mg/kg (n = 35) as part of GVHD prophylaxis during haplo-HSCT were enrolled. Incidence and severity of GVHD, Epstein–Barr virus (EBV) infection, and immune cell recovery were compared using the Mann-Whitney U rank test and chi-square test. Cumulative incidences of GVHD, EBV infection and its subgroups, and relapse mortality were computed; overall survival (OS) was analyzed using the Kaplan-Meier method, with the log-rank test used for univariate comparison. Risk factors for OS were analyzed by the Cox proportional hazards model. Incidence and cumulative incidence of all grades of acute GVHD and subgroups were comparable in both groups (all p > 0.05); however, cumulative incidence of any grade and limited chronic GVHD was significantly higher in the ATG-T group (p = 0.002, p = 0.007, respectively). Cumulative incidences of EBV infections, EBV-DNAemia, and EBV-related diseases were similar; relapse mortality and OS rates were comparable between both groups (all p > 0.05). ATG-T dosage (7.5 mg/kg) appeared comparable to ATG-F dosage (20 mg/kg) for haplo-HSCT. Currently approved ATG-T and ATG-F doses appear efficient to balance the risk–benefit ratio of GVHD, OS, relapse mortality, and EBV infection in haplo-HSCT.

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.

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.

New Strategy of Acute Graft-vs-Host Disease: Investigation of a Reduced Dose of Antithymocyte Globulin in Haploidentical Hematopoietic Stem Cell Transplantation

Graft-vs-host disease (GVHD) is one of the biggest challenges in haploidentical hematopoietic stem cell transplantation. Antithymocyte globulins (ATGs) are widely used to overcome GVHD, but excessive immunosuppression increases the chances of relapse and infection following transplantation. No defined standard of the appropriate dose of ATG usage is recognized. The study included 11 patients who were treated with a reduced dose of ATG to prevent GVHD in haploidentical hematopoietic stem cell transplantation. A reduced dose of ATG-Thymoglobulin (total dose of 5 mg/kg) was used in the pretreatment protocol for 2 consecutive days. All patients had successful transplantation. The median time of neutrophil engraftment was 12 days. All chimerism tests passed on day 30, 60, and 90 post transplantation. None of the patients had acute GVHD, while only 2 patients had I to II degree chronic GVHD (18.2%). No transplantation-related deaths were observed. The current findings suggest that the reduced dose of ATG can effectively prevent the incidence of acute GVHD in haploidentical hematopoietic stem cell transplantation.

Differential Elimination of Anti-Thymocyte Globulin of Fresenius and Genzyme Impacts T-Cell Reconstitution After Hematopoietic Stem Cell Transplantation

Anti-thymocyte globulin (ATG) is a lymphocyte depleting agent applied in hematopoietic stem cell transplantation (HSCT) to prevent rejection and Graft-vs.-Host Disease (GvHD). In this study, we compared two rabbit ATG products, ATG-Genzyme (ATG-GENZ), and ATG-Fresenius (ATG-FRES), with respect to dosing, clearance of the active lymphocyte binding component, post-HSCT immune reconstitution and clinical outcome. Fifty-eigth pediatric acute leukemia patients (n = 42 ATG-GENZ, n = 16 ATG-FRES), who received a non-depleted bone marrow or peripheral blood stem cell graft from an unrelated donor were included. ATG-GENZ was given at a dosage of 6-10 mg/kg; ATG-FRES at 45-60 mg/kg. The active component of ATG from both products was cleared at different rates. Within the ATG-FRES dose range no differences were found in clearance of active ATG or T-cell re-appearance. However, the high dosage of ATG-GENZ (10 mg/kg), in contrast to the low dosage (6-8 mg/kg), correlated with prolonged persistence of active ATG and delayed T-cell reconstitution. Occurrence of serious acute GvHD (grade III-IV) was highest in the ATG-GENZ-low dosage group. These results imply that dosing of ATG-GENZ is more critical than dosing of ATG-FRES due to the difference in clearance of active ATG. This should be taken into account when designing clinical protocols.

Filgrastim enhances T-cell clearance by antithymocyte globulin exposure after unrelated cord blood transplantation

Residual antithymocyte globulin (ATG; Thymoglobulin) exposure after allogeneic hematopoietic (stem) cell transplantation (HCT) delays CD4⁺ T-cell immune reconstitution (CD4⁺ IR), subsequently increasing morbidity and mortality. This effect seems particularly present after cord blood transplantation (CBT) compared to bone marrow transplantation (BMT). The reason for this is currently unknown. We investigated the effect of active-ATG exposure on CD4⁺ IR after BMT and CBT in 275 patients (CBT n = 155, BMT n = 120; median age, 7.8 years; range, 0.16-19.2 years) receiving their first allogeneic HCT between January 2008 and September 2016. Multivariate log-rank tests (with correction for covariates) revealed that CD4⁺ IR was faster after CBT than after BMT with <10 active-ATG × day/mL (P = .018) residual exposure. In contrast, >10 active-ATG × day/mL exposure severely impaired CD4⁺ IR after CBT (P < .001), but not after BMT (P = .74). To decipher these differences, we performed ATG-binding and ATG-cytotoxicity experiments using cord blood- and bone marrow graft-derived T-cell subsets, B cells, natural killer cells, and monocytes. No differences were observed. Nevertheless, a major covariate in our cohort was Filgrastim treatment (only given after CBT). We found that Filgrastim (granulocyte colony-stimulating factor [G-CSF]) exposure highly increased neutrophil-mediated ATG cytotoxicity (by 40-fold [0.5 vs 20%; P = .002]), which explained the enhanced T-cell clearance after CBT. These findings imply revision of the use (and/or timing) of G-CSF in patients with residual ATG exposure.