2025 EBMT最佳实践建议：兔抗胸腺细胞／抗T淋巴细胞球蛋白（ATG／ATLG）在恶性血液病异基因造血细胞移植中的应用

Usage of rabbit anti-thymocyte / anti-T-lymphocyte globulins (ATG / ATLG) for hematological malignancies in allogeneic hematopoietic cell transplantation: Best practice recommendations from the EBMT Practice Harmonisation and Guidelines Committee

Giorgia Battipaglia $^{1}$,$^{1}$,$^{15}$, Claudia Wehr $^{2}$,$^{1}$,$^{2}$,$^{15}$, Rick Admiraal $^{3}$,$^{1}$,$^{3}$,$^{15}$, Stefan Nierkens $^{1}$,$^{3}$,$^{4}$, Florent Malard $^{1}$,$^{5}$,$^{4}$, Robert Zeiser $^{2}$,$^{2}$,$^{3}$,$^{4}$,$^{6}$,$^{7}$,$^{8}$,$^{9}$,$^{10}$,$^{11}$,$^{12}$,$^{13}$,$^{14}$,$^{15}$,$^{16}$,$^{17}$,$^{18}$,$^{19}$,$^{11}$,$^{12}$,$^{13}$,$^{14}$,$^{16}$,$^{17}$,$^{18}$,$^{19}$,$^{11}$,$^{12}$,$^{13}$,$^{14}$,$^{16}$,$^{17}$,$^{18}$,$^{19}$,$^{11}$,$^{12}$,$^{13}$,$^{14}$,$^{16}$,$^{17}$,$^{18}$,$^{19}$,$^{11}$,$^{12}$,$^{13}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14}$,$^{14

© The Author(s), under exclusive licence to Springer Nature Limited 2025

Rabbit anti-thymocyte globulin (ATG) and anti-T-lymphocyte globulin (ATLG) are widely used in allogeneic hematopoietic cell transplantation (allo-HCT) to prevent graft rejection and reduce the risk of graft-versus-host disease. Despite their broad application, clinical practice varies substantially in terms of product selection, dosing, and timing. Distinct differences in manufacturing, pharmacokinetics, and immunological effects between ATG and ATLG complicate efforts to standardize their use across transplant platforms. This review presents the most recent insights into the pharmacology, mechanisms of action, clinical efficacy, and toxicity profiles of both agents. It highlights their differential impact across various allo-HCT settings. Key topics such as re-exposure, immune reconstitution, adverse events, and individualized dosing strategies guided by pharmacokinetic modeling are discussed. These analyses informed consensus recommendations developed through a dedicated expert workshop within the EBMT to support optimized, context-specific use of rabbit ATG and ATLG in allo-HCT for hematologic malignancies.

Bone Marrow Transplantation; https://doi.org/10.1038/s41409-025-02742-8

# INTRODUCTION - CURRENT STATE OF THE ART

AT(L)G refers to a heterogeneous group of polyclonal antibodies derived from the serum of animals immunized with either human thymocytes or the Jurkat T-cell leukemia line (Fig. 1). Various animal species have been explored for optimal efficacy in humans, but currently, rabbit and horse preparations are in use. The two rabbit-derived formulations available are anti-thymocyte globulin (Thymoglobulin®, referred to as ATG throughout this manuscript) and anti-T-lymphocyte globulin (ATG-Grafalon®, formerly ATG-Fresenius®, referred to as ATLG throughout this manuscript). Alemtuzumab, a monoclonal anti-CD52 antibody, is used for similar indications, while horse ATG is typically reserved for treating severe aplastic anemia. Both agents are outside the scope of this review. Use of AT(LG) in the setting of allogeneic

hematopoietic cell transplantation (allo-HCT) for non-malignant hematological disease is also out of the scope of this manuscript.

The pharmacological effects of AT(L)G include in vivo depletion of recipient T-cells and antigen-presenting cells, and, depending on the timing of administration relative to graft infusion, donor-derived T-cells. The incorporation of AT(L)G into allo-HCT protocols has been shown to reduce the incidence of graft-versus-host disease (GvHD) and graft failure. However, no consistent survival benefit has been demonstrated in most landmark trials [1–7]. This may reflect a trade-off between beneficial immunosuppression and the detrimental consequences of overexposure, including increased infection risk and attenuation of the GVHD due to delayed immune reconstitution, ultimately compromising survival. Individualization of dosing, and timing of AT(L)G may help guide

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 the clinician's final decision-making process. This manuscript reviews the current best practices for the use of rabbit AT(L)G in the setting of allo-HCT for hematologic malignancies.

# Pharmacology of AT(L)G

From a pharmacological perspective, AT(L)G is a rather unique drug. Most clinically available antibodies are designed to bind to one, or at most two, specific targets. These monoclonal antibodies are typically produced using engineered myeloma and B-cell cultures (hybridomas) that generate the desired protein [8]. In contrast, AT(L)G is produced by inoculating rabbits with thymic tissue or human lymphocyte cell lines, which induces rabbits to generate antibodies against a wide array of epitopes present in the inoculum [9] (Figs. 1 and 2). Consequently, AT(L)G contains a diverse mix of antibodies targeting not only lymphocyte antigens but also antigens found on other leukocytes, including natural killer cells, as well as non-hematopoietic tissues such as stromal cells [10] (Fig. 2). Furthermore, because AT(L)G consists of non-selected rabbit immunoglobulin G (lgG), only a fraction of the product is directed against human targets as found in peripheral blood mononuclear cells (referred to as active AT(L)G), while the entire infused preparation is referred to as total AT(L)G, the sum of active and non-active antibody fractions [11]. The available preparations of rabbit-derived AT(L)G include Thymoglobulin® (Sanofi, France, referred to as ATG), in which rabbits are immunized with a suspension of human thymocytes [9]. This thymic tissue is typically harvested during pediatric cardiac surgery, as the thymus often needs to be partially removed to access the heart. The other rabbit-derived AT(L)G preparation is Grafalon® (Neovii, Switzerland, referred to as ATLG), produced by immunizing rabbits with the Jurkat T-cell line (Grafalon SPC). The latter are immortalized human T lymphocytes originally derived from a patient with acute T-cell leukemia, thus providing a broad array of human T-cell antigens to elicit polyclonal antibody production in rabbits. These two AT(L)G products differ not only in

their manufacturing processes but also in the quantity and specificity of active AT(L)G components. Despite these differences, both preparations are associated with potent T-cell depletion and broad immunosuppressive activity.

# Production and quality control

Importantly, there is no published information on how batch-to-batch variability is controlled, either in terms of the proportion of active AT(L)G or the percentage of active AT(L)G targeting specific antigens (e.g., anti-CD3AT(L)G). While changes to manufacturing processes or methods are submitted to and reviewed by national regulatory authorities, the timing and nature of these adjustments are not publicly disclosed.

For ATG [12], one human thymus is used to immunize ten rabbits. These thymic tissues are sourced from donors of various ethnic backgrounds, provided the donor country complies with the manufacturer's organ trafficking policies. Each batch is tested for product activity and specifications are in place to ensure batch-to-batch comparability.

For ATLG, Jurkat T-cells are cultured, processed, and prepared for immunization within the manufacturer's cell culture facility [13]. According to the manufacturer, a cell bank system is in place to provide a consistent supply of immunogen with reproducible properties. A standardized immunization protocol is employed, and several hundred individual sera are pooled to generate a consistent starting material, helping to reduce variability. Final product testing is conducted using validated methods to confirm identity, purity, and potency; however, information on the reference materials used in these assays is not publicly available.

# Basic biology of AT(L)G

Both ATG and ATLG are polyclonal rabbit antibody preparations that bind a broad spectrum of antigens. The active fraction of antibodies, i.e., those that react with human immune antigens, can be quantified using various methods. The active fraction of ATG

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 targeting lymphocytes has been reported to be approximately 7% [14], while it was found to be 26% in ATLG and 68% in ATG when assessed against peripheral blood stem cells (PBSC) [15]. The clinical efficacy of AT(L)G depends not only on the antibody formulation itself but also on host- and graft-related factors, such as the lymphocyte content of the graft (e.g., PBSC vs. BM vs. manipulated grafts vs. cord blood) and the extent of depletion in recipient lymphoid tissues (see Pharmacokinetics). In vitro, AT(L)G binds to a wide array of antigens (Fig. 2), including T-cell specific markers, leukocyte adhesion molecules, and MHC molecules. The antigen binding profile differs markedly between ATG and ATLG. However, the downstream effects of antigen binding and the specific impact on different cell types remain only partially understood.

A key effect of AT(L)G is T-lymphocyte depletion, which modulates immune responses and reduces the risk of graft rejection. The main mechanisms of cell death include antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, and activation-induced cell death. Treatment results in profound peripheral lymphopenia. In non-human primate models, treatment with ATG led to depletion of T, B, and NK cells in spleen and lymph nodes, while sparing CD4*CD8+ thymocytes [16]. In vitro studies have shown that ATG can expand regulatory T-cells, suggesting immunomodulatory effects beyond depletion [17]. However, other reports have described for ATG the upregulation of FOXP3 without induction of a regulatory phenotype [15]. ATG has also been shown to induce apoptosis of alloreactive T-cells via caspase-3-dependent pathways [18] and to cause complement-independent apoptosis in B-cells [19]. More recent in vitro data suggest that myeloid cells are also targets of ATLG. Treatment induced PD-L1 expression on monocytes through an IFN-γ-dependent, JAK/STAT-mediated pathway, results in reduced T-cell proliferation [20]. In summary, AT/LG exerts its immunosuppressive and immunomodulatory effects through multiple mechanisms, many of which are still not fully understood. Notably, these mechanisms differ across AT/LG formulations, but the specific immunologic distinctions and their impact on post-

transplant immune reconstitution and clinical outcomes remain undefined.

# Pharmacokinetics of AT(L)G

Early descriptive studies reported that total ATG has a long half-life, ranging from 30 days to 6 weeks [21–23]. Additionally, the presence of pre-existing or de novo anti-rabbit antibodies can significantly accelerate ATG clearance, particularly in patients previously exposed to rabbit proteins, e.g. prior AT(L)G use, animal exposure or occupational contact, potentially compromising its efficacy in preventing GvHD [11]. Non-compartmental studies suggest that pharmacokinetics (PK) differ between ATG and ATLG [24]. Across all descriptive studies, active ATG shows high interpatient variability in PK, likely due to differences in distribution and elimination, resulting in unpredictable drug exposures and clinical outcomes.

More recently, population PK models have been developed for AT(L)G, offering quantitative insights into PK variability and enabling model-based dosing. These models outperform earlier descriptive PK studies [1–4] by identifying clinically relevant predictors. For active ATG, PK models in both pediatric and adult populations have identified body weight and absolute lymphocyte count (ALC) on the day of first dose ATG administration as key predictors of clearance [25, 26]. In adult patients, total ATG clearance has also been associated with albumin, IgG levels, and T-cell dose [27]. For ATLG, a pediatric model in acute lymphoblastic leukemia patients identified body weight as a predictor, although ALC was not found to be significant, likely due to limited variability in ALC within that cohort [28].

ALC appears to be critical determinant of AT(L)G exposure and clinical outcomes, although it is influenced by several factors, including prior treatments and the type of conditioning regimen. Antibody clearance is generally governed by specific (via target binding and subsequent degradation) and nonspecific clearance (via intracellular protein catabolism) [29]. As a major target of AT(L) G, ALC likely drives specific clearance, thereby influencing drug exposure and therapeutic effect [25]. In an adult randomized

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Fixed mg/kg dosing

 clinical trial comparing ATLG to placebo, no difference in moderate-to-severe chronic GvHD-free survival was observed overall [3]. However, a post hoc analysis revealed that poor outcomes were limited to patients receiving ATLG with low ALC prior to ATG administration; patients with high ALC had outcomes like those in the placebo group. Similarly, patients with higher ALC exhibited higher rates of acute and chronic GvHD than those with low ALC when comparing ATG and ATLG, regardless formulation type. Smaller case series support these findings [30, 31]. However, heterogeneous modalities of incorporation of the ALC variable are reported across studies (either considered as a continuous variable or on arbitrarily defined thresholds), making comparisons and standardization difficult. As a result, despite ALC being a promising key parameter in the dosing and personalization of AT(L)L, ALC-guided dosing is not yet uniformly implemented in clinical practice. Future efforts should aim to harmonise the timing of ALC assessment and its integration into validated dosing models, potentially enabling a more precise, exposure-targeted use of ATG in both pediatric and adult transplant settings.

Therapeutic window of AT(L)G and model-based dosing

Given the inter-individual variability in AT(L)G PK, investigators hypothesized that these differing levels might also affect immune reconstitution and, consequently, clinical outcomes. Indeed, a pivotal study demonstrated that overexposure of the graft to ATG (post-HCT exposure to ATG) is detrimental to early T-cell recovery [32]. Achieving early T-cell recovery, defined as >50 CD4* T-cells/μL at two consecutive time points within the first 100 days-transplant, was associated with improved overall survival (OS), lower non-relapse mortality (NRM), and fewer viral reactivations. The adverse impact of post allo-HCT ATG overexposure on early CD4* T-cell recovery, and the resulting worse clinical outcomes, have been confirmed in multiple independent studies [32–38], although performed by only very selected centers. Despite this low number of centers, the beneficial effects of successful early

CD4+ T-cell reconstitution have been validated in diverse transplant settings, including T-cell-replete, cord blood, and CD34+-selected grafts, in both adults and children [35, 36, 38, 39]. The proposed mechanism is that excessive in vivo exposure to ATG depletes donor-derived T-cells infused with the graft, cells essential for early immune reconstitution within the first 1–2 years post allo-HCT. Based on this, model-based dosing using population PK can be considered to optimize pre-allo-HCT exposure while minimizing post-allo-HCT exposure, thereby promoting T-cell recovery without increasing the risks of GvHD or graft rejection. In pediatric patients undergoing CD34-selected haploidentical allo-HCT, higher post allo-HCT exposure to ATG was also associated with inferior disease-free survival, suggesting that model-based dosing could improve outcomes in this setting as well [39].

Although fewer data are available, one recent study indicated that prolonged ATLG exposure may affect both GvHD and immune reconstitution [28]. Unlike ATG however, no validated personalized dosing strategies currently exist for ATLG. Although a PK model has been developed, its applicability remains limited, particularly across the broader pediatric population, with even fewer data available for adults [28]. Given this, and the likely narrow therapeutic window of ATLG, the currently used fixed mg/kg dosing may yield suboptimal outcomes compared to what could be achieved with individualized model-based approaches.

Model-based dosing (Fig. 3), based on population PK models, is a tool to further individualize dosing to achieve optimal drug exposure. Successful model-based dosing requires large, representative PK studies to generate reliable predictions. For ATG, model-based dosing strategies have been developed for both pediatric and adult populations, incorporating simplified dosing tables that do not require therapeutic drug monitoring. The prospective single-arm PARACHUTE trial validated this approach in pediatric patients, demonstrating a 20% improvement in early CD4+ immune reconstitution compared to well-characterized historical controls, along with significantly reduced viral reactivations (Epstein-Barr virus and adenovirus) [40]. Long-term follow-up confirmed improved OS in patients who received model-based dosing of ATG [41]. These results have been replicated in three independent cohorts: two in pediatric αβ T-cell-depleted haploidentical allo-HCT [42, 43], and one in a general pediatric population [44]. However, additional evidence is needed to substantiate this approach and support broader implementation. On one hand, further validation of the clinical outcomes using the established model-based dosing tables should be performed in new cohorts. On the other hand, the dosing tables themselves may be further validated by repeating the underlying pharmacokinetic and pharmacodynamic analyses. For the latter strategy, standardization of the assays used for drug measurement is pivotal. The costs associated with measuring ATG and re-performing the pharmacokinetic and pharmacodynamic analyses must be considered, although potential long-term benefits, such as reduced incidence of chronic GvHD, lower infection-related morbidity, shorter duration of immunosuppression, and decreased hospital readmissions, may counterbalance the initial resource burden.

Guiding selection of either ATG or ATLG for allo-HCT

Few direct comparisons of ATG and ATLG exist. In one cohort study evaluating other endpoints, adult patients who received ATG (5 mg/kg) had a higher hand, the dosing tables themselves those who received ATLG (15 mg/kg for matched related donors and 30 mg/kg for matched unrelated donors), though survival and relapse rates did not differ [45]. Other retrospective studies have reported inconsistent results, complicated by varying doses both within and between studies. Some found superior outcomes with ATG [46], others with ATLG [47], and some found no difference [48]. A network meta-analysis of published randomized clinical

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trials found that ATLG was associated with a lower incidence of GvHD, while ATG use trended toward better OS [49]. However, no prospective head-to-head randomized trial has been conducted to definitively compare the two products preventing any firm conclusions regarding the preferential use of one over the other.

Clinical evidence for ATLG usage for matched related and unrelated donors

Several prospective randomized trials have investigated the impact of adding ATG or ATLG to standard GvHD prophylaxis with a calcineurin inhibitor and methotrexate in the setting of human leukocyte antigen-matched related and unrelated allo-HCT (Table 1) [1–3, 7, 50]. Although comparisons across trials are limited by differences in inclusion criteria, conditioning regimen, stem cell source, underlying hematologic disease, and variation in AT(L)G type and dosing, results overall support the addition of AT(L)G for GvHD prevention.

In unrelated donor allo-HCT, early randomized trials evaluated ATG at doses of 7.5 mg/kg and 15 mg/kg using bone marrow (BM) as the stem cell source, prior to the introduction of high-resolution human leukocyte antigen typing. Both doses significantly reduced acute and chronic GvHD compared to controls, though the 15 mg/kg dose was associated with a higher infection-related mortality (30 vs. 8% [50]. Long-term follow-up showed lower rates of chronic lung dysfunction (19% vs. 51%) and better performance status in the ATG group [5]. In a more recent randomized trial of unrelated donor allo-HCT with predominantly matched donors (81–84%), ATG was administered at a total dose of 4.5 mg/kg. The study included both myeloablative and non-myeloablative conditioning regimens (33%) and used BM (12%) and PBSC (88%) as stem cell sources. ATG significantly reduced both acute and chronic GvHD and enabled more patients to discontinue immunosuppressants at one year (37% vs. 16%). Patients receiving ATG reported fewer chronic GvHD-related symptoms and improved quality of life [51]. Two other retrospective studies, support the use of ATG at 5 mg/kg in unrelated donor allo-HCT, demonstrating a balance between GvHD prevention and acceptable toxicity [52, 53].

In matched related donor allo-HCT, ATLG has been studied in a phase III trial at a total dose of 30 mg/kg following myeloablative conditioning with PBSC as the stem cell source. ATLG significantly reduced chronic GvHD and improved chronic GvHD/relapse-free survival (36.6% vs. 16.8%), while fewer patients remained on immunosuppression at long-term follow-up (9.6% vs. 28.3%) [7]. Quality of life was also improved in the ATLG group [54]. In unrelated donor allo-HCT, a randomized trial evaluated ATLG at a total dose of 60 mg/kg in patients undergoing mostly matched but also some mismatched transplants (~40%). Both BM and PBSC were used, with the latter being more common. ATLG significantly reduced grade II–IV acute GvHD, chronic GvHD of all grades, and extensive chronic GvHD (12% vs. 45%). A higher proportion of patients were off immunosuppressive therapy at 3 years (52.9% vs. 16.9%) [1, 55]. However, another trial using the same ATLG dose (60 mg/kg) also in unrelated donor allo-HCT found lower OS and progression-free survival in the ATLG group. The primary endpoint—moderate-to-severe chronic GvHD-free survival—was not significantly different (48% vs. 44%) [3]. These findings have contributed to a shift in clinical practice favoring a reduced ATLG dose of 30 mg/kg.

Together, these prospective trials support the use of ATG and ATLG for GvHD prophylaxis in myeloablative allo-HCT from related or unrelated donors. ATG is effective at lower doses such as 2.5–5 mg/kg, while evidence suggests that ATLG may be optimally used at 30 mg/kg rather than higher doses. No randomized clinical trials have specifically evaluated ATG or ATLG in reduced-intensity conditioning allo-HCT. However, retrospective studies have supported the feasibility and potential benefit of ATL(G) in this setting. Although limited by their design, these studies provide

important real-world data to inform clinical practice. The largest available retrospective analyses are derived from national and international registries, as summarized in Table 2 [56–62]. While these studies confirm the benefit of adding ATG to GvHD prophylaxis, the lack of detailed information on AT(L)G brand, dose, and timing represents a significant limitation.

In pediatric populations, few randomized studies have evaluated ATG or ATLG, primarily in unrelated donor allo-HCT. One randomized trial reported better survival with 15 mg/kg of ATLG compared to 30 mg/kg, with no difference in GvHD incidence [4]. Most non-randomized studies comparing two ATLG doses or ATLG vs. no ATLG did not demonstrate significant survival differences [21, 63]. In contrast, a study on model-based dosing of ATG demonstrated significantly improved early T-cell recovery, lower therapy-related mortality, and OS compared to a well-matched historical control [40].

Studies assessing ATG concentration or exposure generally found that higher exposure was associated with reduced GvHD, but with impaired immune recovery. Lower doses of ATG were associated with improved T-cell reconstitution. Several studies suggested that excessive exposure of the graft to ATG could negatively impact survival, although not all results were consistent. The only study evaluating ATLG exposure did not find a relationship between drug exposure and survival [28].

Use of AT(L)G in cord blood transplantation

The use of standard dos of AT(L)G in cord blood transplantation may have compromised the success of this stem cell source. One key limitation of cord blood transplants is delayed T-cell recovery, attributed to the low number of infused cells compared to other graft sources [64]. This impaired immune reconstitution may be exacerbated by overexposure to AT(L)G, leading to depletion of graft-derived T-cells. Data from large registry analyses, have suggested that AT(L)G may, as in other settings, reduce both acute and chronic GvHD rates but at the cost of increased NRM (mainly attributable to infections) translating to lower OS [65–67]. On the other hand, evidence from model-based dosing of AT(L)G shows that when appropriately tailored, T-cell recovery in cord blood recipients can match the kinetics observed with other stem cell sources [40], and is comparable to patients receiving a cord blood transplant without ATG in the conditioning regimen [33]. No studies to date have evaluated the optimal dose or exposure of ATLG specifically in the cord blood setting. In conclusion, the use of AT(L)G in cord blood allo-HCT remains highly controversial and is often omitted. However, using an individualized approach, considering disease status, infection history, and PK modeling to determine the optimal dose, could be considered.

Use of AT(L)G in haploidical allo-HCT without post-transplant cyclophosphamide

While post-transplant cyclophosphamide (PTCy) has become the dominant conditioning regimen in most patients receiving haploidentical allo-HCT, alternative approaches have incorporated the use of ATG or ATLG. One such strategy is the T-cell-replete protocol developed in Beijing, known as the GIAC protocol. GIAC stands for G-CSF stimulation of the donor; Intensified immunosuppression through post-transplantation cyclosporine, mycophenolate mofetil, and short-course methotrexate; ATG added to conditioning to help prevent GvHD and aid engraftment; and Combination of PBSC and BM allografts [68]. In this protocol, ATG is administered at a total dose of 20 mg/kg from day -4 to day -1. Despite this intensified regimen, high rates of severe acute and chronic GvHD have been reported. Another approach involved the use of megadose ex vivo T-cell-depleted allografts with ATLG given at 20 mg/kg from day -4 to day -1 as part of the conditioning [69]. However, this strategy was associated with high NRM. Although refined over time through selective T-cell depletion, this approach has largely been abandoned due to unfavorable outcomes.

SPRINGER NATURE

|Brand|Total dose, mg/kg|Timing|N|Donor type, %|PBSC/ BM, %|MAC/ RIC, %|Gr. II-IV aGvHD|Gr. III-IV aGvHD|All grades cGvHD|RI|NRM|OS|Reference| |---|---|---|---|---|---|---|---|---|---|---|---|---|---| |ATLG|30|10 mg/kg from d-3 to d-1|ATLG, 83 No ATLG, 72|MRD, 100|100/-100/-|100/-18.1%|10.8% vs. 18.1%|2.4% vs. 8.3%|2 y: 32.2% vs. 68.7%|2 y: 32.2% vs. 25.5%|2 y: 14% vs. 12%|2 y: 74.1% vs. 77.9%|[7]| |ATG|7.5|3.75 mg/kg on d-4 and d-3|ATG, 28 No ATG, 25|MUD, 100|-/100/-100/-|69% vs. 72%|41% vs. 36%|38% vs. 65%|3 y: 0% vs. 12%|3 y: 43% vs. 39%|3 y: 56% vs. 55%|[50]|[50]| |ATG|15|3.75 mg/kg from d-5 to d-2|ATG, 27 No ATG, 29|MUD, 100|-/100/-100/-|100/-|37% vs. 79%|11% vs. 50%|59% vs. 41%|1 y: 36% vs. 18%|1 y: 47% vs. 49%|1 y: 43% for both|[50]| |ATLG|60|20 mg/kg from d-3 to d-1|ATLG, 126 No ATLG, 128|MUD, 100|75.4/ 17.5 78.9/ 21.1|100/-|23% vs. 40%|4.3 vs. 11%|16% vs. 38%|2 y: 32% vs. 21%|2 y: 21% vs. 13.5%|59% vs. 74%|[3]| |ATLG|60|20 mg/kg from d-3 to d-1|ATLG, 103 No ATLG, 98|MUD/ MMUD,61/39 MUD/ MMUD, 58/ 42|21/82 16/82|100/-|11.7% vs. 24.5%|33% vs. 51%|3 y: 12.2% vs. 45%|3 y: 32.6% vs. 28.2%|3 y: 19.4% vs. 33.5%|3 y: 55.2% vs. 43.3%|[1]| |ATG|4.5|0.5 mg/kg on d-2; 2 mg/kg on d-2, d-1 and d+1|ATG, 97 No ATG, 99|MUD/ MMUD 81/19 MUD/ MMUD/ 84/16|88/12 89/11|68/32 67/33|50% vs. 65%|28% for both|1 y: 22% vs. 33%|1 y: 11% vs. 16%|1 y: 23% vs. 24%|1 y: 75% vs. 65%|[2]|

Values in bold are those found as being statistically significant (p < 0.05). ATLG anti T-lymphocyte globulin, d day, ATG antithymocyte globulin, N number, MRD matched-related donor, MUD matched unrelated donor, MMUD mismatched unrelated donor, PBSC peripheral blood stem cells, BM bone marrow, MAC myeloablative conditioning, RIC reduced intensity conditioning, Gr. grade, aGvHD acute graft-versus-host disease, cGVHD chronic graft-versus-host disease, y year, RI relapse incidence, NRM non-relapse mortality, OS overall survival.

Bone Marrow Transplantation

|Disease|N|Donor type, %|PBSC/BM, %|MAC/RIC, %|Gr. II-IV aGvHD|Gr. III-IV aGvHD|All grades cGvHD|Ext cGvHD|RI|NRM|OS|Reference| |---|---|---|---|---|---|---|---|---|---|---|---|---| |Various|ATG, 584 No ATG, 879 Alemtuzumab, 213|MRD 39/ MUD 61 MRD 59/ MUD 32 MRD 22/ MUD 78|14/86 9/91 17/83|-/100|38% vs. 40% vs. 19%|22% vs. 52% vs. 11%|3 y: 40% vs. 52% vs. 24%|-|3 y: 49% vs. 38% vs. 51%|3 y: 26% vs. 23% vs. 21%|3 y: 38% vs. 46% vs. 50%|[56]| |AML|ATG < 6 mg/kg, 195 ATG ≥ 6 mg/kg, 39|Only MRD|100/-|-/100|13% vs. 21% vs. 10%|7% vs. 10%|2 y: 40% vs. 40%|2 y: 18% vs. 19%|26% vs. 52%|14% vs. 15%|64% vs. 49%|[57]| |AML|ATG, 444 No ATG, 554 Alemtuzumab, 252|Only MRD|100/-|-/100|18% vs. 21% vs. 10%|9% vs. 10% vs. 2%|3 y: 39% vs. 57% vs. 37%|3 y: 19% vs. 38% vs. 10%|3 y: 35% vs. 31% vs. 33%|3 y: 13% vs. 17% vs. 15%|3 y: 59% vs. 55% vs. 58%|[58]| |Ph- ALL|ATG, 404 No ATG, 520|MRD, 24/ MUD 76 MRD, 76/ MUD 24|100/-|78/22 87/13|33% vs. 33%|10% vs. 12%|33% vs. 55%|13% vs. 30%|29% vs. 25%|14% vs. 17%|64% vs. 67%|[59]| |Ph+ ALL|ATG, 550 No ATG, 620|MRD, 22/ MUD 78 MRD, 76/ MUD 24|100/-|69/31 80/20|36% vs. 34%|12% vs. 15%|2 y: 35% vs. 52%|2 y: 16% vs. 26%|26% vs. 27%|21% vs. 20%|67% vs. 67%|[60]| |AML|ATG, 145 No ATG, 421|Only MRD|93/7 80/20|100/-|15% vs. 22%|4% vs. 8%|2 y: 31% vs. 52%|2 y: 8% vs. 26%|2 y: 23% vs. 27%|2 y: 11% vs. 17%|72% vs. 59%|[61]| |AML, ALL, MDS|ATG, 51 No ATG, 120|Only MUD|31/67 26/74|100/-|57% vs. 53%|20% vs. 36%|2 y: 32% vs. 44%|2 y: 4% vs. 32%|2 y: 29% vs. 22%|2 y: 29% vs. 31%|2 y: 54% vs. 54%|[62]|

Values are reported as percentages unless otherwise indicated. Where multiple treatment arms are shown (e.g., ATG vs. no ATG vs. alemtuzumab), outcomes are presented in the same order. Values in bold indicate statistically significant difference (p < 0.05). References correspond to numbered citations in the bibliography. AML acute myeloid leukemia, ALL acute lymphoblastic leukemia, Ph+ Philadelphia chromosome-positive, MDS myelodysplastic syndrome, ATG anti-thymocyte globulin, N number, MRD matched related donor, MUD matched unrelated donor, PB peripheral blood, BM bone marrow, MAC myelablative conditioning, RIC reduced-intensity conditioning, Gr. Grade, aGvHD acute graft-versus-host disease, cGVHD chronic graft-versus-host disease, cGVHD chronic graft-versus-host disease, ext cGVHD extensive chronic GVHD, RI relapse incidence, NRM non-relapse mortality, OS overall survival, y year.

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Use of AT(L)G in allo-HCT with post-transplant cyclophosphamide

With the increasing use of PBSC, ATG has also been evaluated alone or in combination with PTCy in MUD, MRD, or haploidentical transplantation. While some studies reported advantages in reducing the risk of acute or chronic GvHD when ATG was combined with PTCy compared with PTCy alone in adult [70–74] and pediatric patients [75, 76], the most recent and to date largest study in haploidentical donors suggested that, despite potential benefits in lowering GvHD, ATG may have a deleterious effect on OS and disease-free survival [74] (Table 3). The association of the two drugs has also the potential to reduce the overall transplant toxicity by using lower doses of both agents, with early results suggesting that this combined approach does not increase the risk of infections or relapse, while reducing both acute and chronic GvHD, thus warranting further validation in prospective studies [77]. More recent multicenter analyses across different donor types and patient populations have further explored the combination of AT(L)G with PTCy. This includes the role of female donors [78, 79], immunological analyses [80] and impact on secondary malignancies [81].

In children, only limited data are available regarding the optimal use and dosing of ATG or ATLG in haploidentical allo-HCT [75, 76, 82]. One of the earliest protocols using ATG in unmanipulated haploidentical transplantation without PTCy was developed in Beijing [82]. Evidence suggests that lower cumulative doses of ATG (e.g., 5 mg/kg) may be associated with better outcomes, both in the presence [83] and absence [84] of PTCy. A large registry study by the EBMT in pediatric patients with BM failure receiving haploidentical transplants found that serotherapy with ATLG was associated with inferior outcomes compared to other platforms such as αβ T-cell depletion [85]. To date, however, there are no published studies providing specific dose recommendations for AT(L)G in the haploidentical transplant setting and PTCy remains the most frequently used platform in both Europe and the United States.

Use AT(L)G in αβT/CD19-depleted grafts

αβT/CD19-depleted grafts are increasingly used in Europe for both children and adults [86] and have been reported in one retrospective study to provide superior outcomes in terms of GvHD-free/relapse-free survival compared to T-cell replete transplantations with or without ATG [87]. ATL (G87). ATL (G9) is part of the conditioning regimen when using TCR-αβ/CD19-depleted grafts, and engraftment critically depends on the timing of AT(L)G. In pediatric patients the most common reported dose is AT(L)G at 12 mg/kg administered from day -3 to -3 [88]. Indeed, high post-transplant exposure to ATG was associated with inferior disease-free survival in children and young adolescents with hematologic malignancies receiving haploidentical TCR-αβ/CD19-depleted grafts [43]. In a recent study comparing three ATG dosing strategies, dosing based on ALC and body weight was found to be superior to a fixed ATG dose, significantly enhancing CD4" and CD8" naïve T-cell reconstitution, though it had surprisingly limited impact on numbers in γδT-cells [42]. However, it has not been investigated whether the transcriptomic quality of yδT-cells (key effectors of the graft-versus-leukemia response) may be altered [89]. These findings suggest that ATG dosing, when close to transplantation, will benefit from a lymphocyte count-based strategy in terms of transplant outcomes. Alternatively, a very early administration of ATG such as (e.g. from day -12) may lead to the same effect. This is important when using ATG [90, 91], and ATLG [92], to ensure sufficient clearance of ATLG before donor T-cell infusion and to support immune reconstitution.

METHODOLOGY, SEARCH STRATEGY, AND SELECTION CRITERIA

An international panel of experts convened in Lille, France, in September 2024 for a two-day EBMT-endorsed workshop to

develop consensus recommendations on the use of ATG and ATLG in allogeneic hematopoietic cell transplantation (allo-HCT). The process followed the methodology established by the EBMT Practice Harmonisation and Guidelines Committee [93]. Participants included invited representatives from the Cellular Therapy and Immunobiology and Acute Leukemia Working Parties, selected for their clinical and research expertise, along with external key opinion leaders to ensure broad multidisciplinary input in transplant immunology and cellular therapy. Ahead of the meeting, each expert conducted an independent literature review focused on their area of expertise to generate key questions for group discussion. A comprehensive search of PubMed/MEDLINE and EMBASE was performed using predefined terms (e.g., "anti-thymocyte globulin", "ATLG", "allo-HCT", "GvHD prophylaxis", "immune reconstitution", "pharmacokinetics"). Peer-reviewed English-language publications, including original research, systematic reviews, meta-analyses, clinical trials, cohort studies, and expert opinions, were considered without date restriction. Selection criteria emphasized scientific rigor, clinical relevance, and alignment with the scope of the review. During the in-person workshop, key questions and evidence summaries were discussed in depth to reach consensus on each section. Post-meeting, subgroups refined assigned topics through iterative drafting. The resulting guidance reflects current data, expert clinical judgment, and consensus among the panel (see also Supplementary Material: AGREE Reporting Checklist and an implementation algorithm). To ensure ongoing relevance, the panel recommends that these guidelines be re-evaluated and updated at regular intervals, or sooner if significant new evidence emerges that could alter clinical practice.

PANEL RECOMMENDATIONS ON THE USE OF AT(L)G IN ALLO-HCT

Indication of AT(L)G

The use of AT(L)G in allo-HCT remains a cornerstone of immunosuppressive therapy. Based on evidence from prospective studies, AT(L)G should be incorporated as part of GvHD prophylaxis in both matched related and unrelated donor allo-HCT, particularly when peripheral blood is used as the stem cell source.

- Matched Related and Unrelated Donors: AT(L)G is effective in reducing GvHD in matched donor allo-HCT, with optimal dosing being critical.

- Cord Blood Transplantation: AT(L)G use in cord blood transplantation is controversial. Tailored dosing may mitigate risks, but omission or extreme caution is often preferred.

- Haploidentical Allo-HCT with PT-Cy: The role of AT(L)G in haploidentical HCT remains under investigation. While some approaches show promise, data support cautious use, particularly regarding dose and timing.

- aβT/CD19-Depleted Grafts: Precise timing and individualized dosing of AT(L)G are vital in αβT/CD19-depleted transplants to support immune recovery and improve survival outcomes.

Optimal selection of the agent

Due to insufficient comparative data, the panel cannot recommend one formulation over the other.

In the absence of conclusive comparative data, the choice between ATG and ATLG in allo-HCT is often guided by institutional protocols, product availability, and clinician preference. While both are used for the same indications, they differ substantially in manufacturing, immunologic targets, and dosing, ATLG generally requiring higher mg/kg doses than ATG. These decisions are often influenced more by local experience than by high-level evidence, as confirmed by a recent EBMT survey showing that brand

Bone Marrow Transplantation

|Disease|N|Donor type, %|PBSC/ BM, %|MAC/ RIC, %|Gr. II-IV aGvHD|Gr. III-IV aGvHD|All grades cGvHD|Ext cGvHD|RI|NRM|OS|Reference| |---|---|---|---|---|---|---|---|---|---|---|---|---| |Adults patients|Adults patients|Adults patients|Adults patients|Adults patients|Adults patients|Adults patients|Adults patients|Adults patients|Adults patients|Adults patients|Adults patients|Adults patients| |Various|ATG, 22 ATG+PTCy, 44|Haplo|100/-|100/-|18.2% vs. 18.2%|0% vs. 2.3%|1 y: 44.8% vs. 45.5%|1 y: 15.6% vs. 23.2%-|1 y: 4.8% vs. 2.3%|1 y: 0% vs. 2.3%|1 y: 83.3% vs. 97.7%|[70]| |Various|ATG+PTCy, 55|Haplo|100/-|-/100|25%|9.1%|NA|1 y: 3.6%|1 y: 9%|19%|1 y: 71.6%|[71]| |Various|ATG, 84 ATG(4.5)+PTCy, 127 ATG(2)+PTCy, 233|MUD|100/-|46/54 10/90 27/73|35.7% vs. 23.3% vs. 16.5%|21.6% vs. 8.0% vs. 4.9%|NA|2 y: 19.7% vs. 19.4% vs. 5.4%|2 y: 14.1% vs. 31% vs. 33%|2 y: 28.1% vs. 22.0% vs. 23.4%|2 y: 62.9% vs. 63.0% vs. 68.6%|[72]| |AML, ALL|ATG+PTCy, 29 PTCy, 41|MRD, 72/ MUD 14/ Haplo, 14 MRD, 71/ MUD 10/ Haplo, 20|100/-|90/10 68/32|31.8% vs. 30.2%|31.8% vs. 13.2%|NA|23.5% vs. 12.3%|1 y: 37.2% vs. 24.6%|1 y: 37.2% vs. 24.6%|1 y: 58.7% vs. 70.1%|[73]| |Various|PTCy, 4519 ATG+PTCy, 675|Haplo|100/-|44/56 40/60|32.2% vs. 34%|11.1% vs. 15%|2 y: 28.4% vs. 18.5%|2 y: 12.2% vs. 7.8%|2 y: 24.2% vs. 28.1%|2 y: 25.5% vs. 26.1%|2 y: 56.9% vs. 52.5%|[74]| |Pediatric patients|Pediatric patients|Pediatric patients|Pediatric patients|Pediatric patients|Pediatric patients|Pediatric patients|Pediatric patients|Pediatric patients|Pediatric patients|Pediatric patients|Pediatric patients|Pediatric patients| |AML, ALL|ATG, 22 ATG+PTCy, 35|MRD, 27/ MUD 14/ Haplo, 59 MRD, 29/ MUD 0/ Haplo, 71|9/91* 14/86*|100/-|45.5% vs. 14.3%|22.7% vs. 5.7%|-|1 y: 40% vs. 3.1%|2 y: 13.6% vs. 17.1%|2 y: 4.8% vs. 11.5%|2 y: 4.8% vs. 74.2%|[75]| |Various|ATG+PTCy, 35|Haplo|100/-|NA|34%|11%|2 y: 26%|2 y: 12%|2 y: 29% vs. 22%|2 y: 29% vs. 31%|2 y: 89%|[76]|

Values are reported as percentages unless otherwise indicated. Where multiple treatment arms are shown (e.g., ATG vs. ATG+PTCy), outcomes are presented in the same order. Values in bold indicate statistically significant difference (ρ < 0.05). References correspond to numbered cut it in the bibliography. AMI acute myeloid leukemia, ALL acute lymphoblastic leukemia, ATG anti-thymocyte globulin, PTCy post-transplant cyclophosphamide, N number, MRD matched related donor, MUD matched unrelated donor, RSC peripheral blood stem cell, BM bone marrow, MAC myelablative conditioning, RIC reduced-intensity conditioning, Gr. Grade, aGvHD acute graft-versus-host disease, cGVHD chronic graft-versus-host disease, Ext cGVHD extensive chronic GVHD, RI relapse incidence, NRM non-relapse mortality, OS overall survival, y year.* BM + PBSC.

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|Setting|ATG (Dose / Timing)|ATLG (Dose / Timing)| |---|---|---| |Adults||| |MRD (PBSC)|2.5-5 mg/kg, day -3 to -1; lower doses when closer to graft infusion|30 mg/kg, day -3 to -1; consider dose reduction if not in CR| |MUD (PBSC)|2.5-5 mg/kg, day -3 to -1; consider pharmacokinetic-guided adjustment|30 mg/kg, day -3 to -1; lower dose preferred over 60 mg/kg| |αβT/CD19-depleted grafts (MRD, MUD, Haplo)|1.5 mg/kg, day -12 to -9|30 mg/kg, day -12 to -9| |Haplo|No standard recommendation; if used in combination with PTCy, consider ≤5 mg/kg|No standard recommendation| |Cord Blood|In principle not recommended. If used, prefer model-based or reduced dosing to avoid overexposure|No recommendation; lacks data| |Pediatric||| |MRD (PBSC/BM)|Model-based dosing (weight + ALC), starting day -9 r 10 mg/kg on day -9 or -5 (less preferred)|15 mg/kg, day -3 to -1| |MUD (PBSC/BM)|Model-based dosing (weight + ALC), starting day -9 r 10 mg/kg on day -9 or -5 (less preferred)|15-30 mg/kg, day -3 to -1; consider 30 mg/kg for PBSC graft| |αβT/CD19-depleted grafts (MRD, MUD, Haplo)|1.5 mg/kg, day -12 to -9|12 mg/kg administered from day -5 to -3| |Haplo|No formal recommendation; ATG 5-10 mg/kg used in some protocols|No formal recommendation| |Cord Blood|In principle not recommended. If used consider model-based dosing (weight + ALC), start day -9|No recommendation; limited data|

Recommended dosing and timing of rabbit anti-thymocyte globulin (ATG) and anti-T lymphocyte globulin (ATLG) across different allogeneic hematopoietic cell transplantation settings in adults and children. Doses are expressed as total mg/kg body weight, with timing relative to the day of graft infusion (day 0). Recommendations are stratified by donor type and graft manipulation. The strength of evidence is based on prospective and retrospective studies, pharmacokinetic and pharmacodynamic data, and expert consensus. MRD matched-related donor, PBSC peripheral blood stem cells, CR complete remission, MUD matched unrelated donor, Haplo haploidentical, PTCy post-transplant cyclophosphamide.

selection, timing, and dosing practices are primarily center-driven [94]. National regulatory differences and product availability, such as the preferential use or exclusive availability of ATG over ATLG in some countries (e.g., France), further shape clinical practice. Finally, the availability of model-based dosing as described earlier may also impact the choice of AT(L)G.

Dosing and timing of AT(L)G

Dosing and timing is essential to balance the risks of graft rejection, GvHD, and infectious complications. Based on current evidence and expert consensus, panel recommendations are provided in Table 4. Personalization of AT(L)G use, based on transplant platform, donor type, stem cell source, patient-specific risk factors, and institutional protocols, is expected to become increasingly important for optimizing outcomes. The panel emphasizes that individualized strategies, particularly those guided by PK and pharmacodynamic modeling, having the potential to improve the safety and efficacy of AT(L)G in both adult and pediatric populations.

Side effects and management of AT(L)G infusion

Common side effects of AT(L)G include cytokine release syndrome, infusion reactions, serum sickness, and increased risk of infections [95]. Pre-medications such as corticosteroids, acetaminophen, and antihamines are commonly used to prevent or mitigate infusion-related reactions. Long-term complications, including post-transplant lymphoproliferative disorder, also require monitoring, particularly in patients receiving high doses or prolonged ATG therapy. However, based on current evidence, rituximab cannot be recommended as prophylaxis for post-transplant lymphoproliferative disorder [96], but is rather used as pre-emptive treatment in patients with Epstein-Barr virus viremia [97]. Practical recommendations

for the management for AT(L)G toxicities and complications are summarized in Table 5.

Re-exposition to AT(L)G

Re-exposure to AT(L)G may be required in the setting of second allo-HCT. Due to the biological and non-human origin of AT(L)G, patients can develop anti-drug antibodies that may neutralize circulating AT(L)G. These antibodies can be of the IgG, IgM, or IgA isotype, with IgG considered the most clinically relevant [11]. The incidence of IgG anti-drug antibodies has been reported as 12%, and 14% in two studies [11, 28]. However, clinical relevance appears limited to patients who develop these antibodies very early after administration, a phenomenon observed in only 4 of 72, and 0 of 121 patients, respectively. When anti-drug antibodies develop at low AT(L)G concentrations, typically after most of the drug has been cleared, they are unlikely to influence the efficacy of the current course but may have implications for future AT(L)G use in subsequent transplants. Due to the lower frequency of second transplants, data on the clinical impact of anti-drug antibodies in this setting are lacking. Switching between ATG and ATLG is therefore unlikely to circumvent this issue, as both products are derived from rabbits and share constant immunogenic regions targeted by these antibodies. In the absence of reported clinical intolerance or antibody-mediated failure in second transplant settings, anti-drug antibodies are unlikely to pose a significant clinical issue, and switching between types of AT(L)G is not recommended if a second allo-HCT is needed.

RESIDUAL QUESTIONS

$\bullet$ Additional real-world data are needed to validate current approaches. Standardization across centers is essential for

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|Aim|Recommended Measures| |---|---| |Prevent serum sickness and allergic reactions|Premedicate with H1 blocker 30-60 min before infusion. Premedicate with steroids (adults: 100 mg prednisolone or 1 mg/kg methylprednisolone; children: 2 mg/kg prednisolone) and paracetamol (1000 mg) 30-60 min before infusion. Repeat medication daily during treatment. ATLG: Administer a test dose one day prior (e.g., 1 mg/kg ATLG over 4 h) to identify severe allergic responses.| |Improve tolerability and reduce infusion-related reactions|Slowly increase the infusion rate (i.e. 10-20 ml/hour every 30 min if well tolerated) Deliver the total daily dose over a minimum of 6-8 h. Administer post-infusion steroids (e.g., 100 mg prednisolone) two hours after completion in case of allergic reaction.| |Early recognition and management of acute side effects|Monitor vital signs (heart rate, BP, SpO₂) during and for at least 3-4 h after infusion. Check platelet counts pre-infusion and 2 h post-infusion. Perform daily labs (creatinine, sodium, potassium, bilirubin, CBC) during AT(L)G therapy.| |Manage allergic or inflammatory reactions|For suspected allergic reaction: stop infusion, administer rescue medication (H1 blocker, steroids, adrenaline), monitor vitals, restart infusion at reduced rate ≥30 min after symptom resolution. For inflammatory reactions (e.g., cytokine release): provide supportive care; repeat H1 blocker and administer corticosteroids (e.g., hydrocortisone 4 mg/kg if post-initial infusion).| |Differentiate inflammatory toxicity from sepsis|Monitor for systemic inflammatory response (elevated CRP, IL-6, PCT). Always rule out sepsis: obtain blood/urine cultures; manage per institutional protocols. Elevated PCT is common post-AT(L)G and should be interpreted according to clinical context. Consider stopping antibiotics after 48-72 h if cultures remain negative and patient is afebrile.| |Prevent bleeding due to thrombocytopenia|Monitor platelet counts closely; consider transfusion prior to AT(L)G if below institutional thresholds. Anticipate increased platelet consumption and adjust monitoring frequency accordingly.| |Optimize timing and co-administration|Administer AT(L)G early in the day (should be started ideally between 09:00-10:30). On chemotherapy days, administer chemotherapy first, then H1 blocker, steroid, paracetamol, and finally AT(L)G.| |Address missed or incomplete doses|If infusion is interrupted, calculate the residual dose and discuss with the treating physician. For 4-day regimens: if ≥50% of dose missed, administer on day 5; if <50%, add to day 4 dose. Ensure appropriate pre-/post-medication and adjust infusion time if administering an extra dose.|

The table summarizes consensus-based strategies aimed at minimizing adverse events, improving drug tolerability, ensuring early recognition and management of side effects, and optimizing timing and supportive measures. Recommendations are based on institutional protocols and expert experience across both adult and pediatric populations. Clinical judgment and local guidelines should be applied when implementing these measures.

implementing individualized dosing. Cost and feasibility must be considered when validating model-based dosing tables.

$\bullet$ Further research into individualized and biomarker-guided dosing is encouraged to improve precision and minimize toxicity.

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AUTHOR CONTRIBUTIONS

MM and JK: leaders of the current workshop, MM, ISO, FO, ALR, IYA and JK: conceived and designed the manuscript topics to be covered. MM, GB, CW, RA, SN, FM, RZ, ALR and JK: literature research, interpretation of data, as well as the recommendations to be made, and preparation of figures. FO, ISO, ALR and IYA: formatting the manuscript to be aligned with the EMBT PH & G committee and writing of the unanswered questions section. All co-authors: played an important role in interpreting results, revised the manuscript, approved the final version, and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. MM, ALR, IYA and JK: accept final responsibility for the decision to submit for publication.

FUNDING

The European Group for Blood and Bone Marrow transplantation (EBMT) is a non-for-profit medical and scientific organisation. The EBMT performed administrative and legal management, as well as funding acquisition. No pharmaceutical company and no other funding source were involved in any way or had a role in the study design, data collection, data analysis, data interpretation, or writing of the report. No medical writer or editor was involved.

COMPETING INTERESTS

ALR: reports honoraria from Gilead. CW: reports honoraria or travel support from Jazz Pharmaceuticals and Mundipharma, and is receiving a research grant from Takeda. FM: reports honoraria from BMS, Therakos, AstraZeneca, MSD, Sanofi, Priothera, and Novartis. FO: reports honoraria from Takeda, Kyowa Kirin, and Medac Pharma; and support for attending meetings from Jazz Pharmaceuticals and Kyowa Kirin. GB: reports honoraria from Sanofi. ISO: Not reported. IYA: received honoraria from Novartis, Gilead/Kite, BMS, and Pfizer. He declares no conflict of interest related to this work. JK: is cofounder and shareholder of gadeta Founders B.V., inventor on patents related to ySVR±T&RLig and genetic engineering, and has received research funding from Novartis. Miltenyi Biotech, and Gadeta. For full disclosure, see: https://researchinformation.umcutrecht.nl/en/persons/jurgen-kuball. MM reports honoraria and/or serving on advisory boards for Adaptive Biotechnologies, Amgen, Astellas Pharma, Bristol-Myers Squibb, GlaxoSmithKline, Janssen Cilag EMEA, Jazz Pharmaceuticals, MedAC PHARMA, INC., Novartis, OncoPep, Inc., Pfizer, Sanofi, Stemline Therapeutics Inc., Takeda Oncology, and Therakos. He has also received research grants from Janssen Clag EMEA, Jazz Pharmaceuticals, and Sanofi. Dr. Mohty serves as a board member (volunteer, no compensation) for the EBMT, Intergroupe Francophone du Myelome, International Academy for Clinical Hematology, and the International Myeloma Society. He is a journal editor for Springer (receives honoraria) and holds academic positions at Assistance Publique - Hôpitaux de Paris and Université Sorbonne Paris Cité. RA: reports an unrestricted research grant from Sanofi. RZ: reports honoraria from Novartis, Incyde, Medac, Sanofi, and Neovii. SN: Not reported.

ADDITIONAL INFORMATION

Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s41409-025-02742-8.

Correspondence and requests for materials should be addressed to Jürgen Kuball.

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