Anti-thymocyte globulins capable of binding to T and B cells reduce graft-vs-host disease without increasing relapse

A fully validated flow cytometry method to quantitatively analyze active rATG in human serum and its application in pharmacokinetic study for therapeutic drug monitoring

Rabbit anti-thymocyte globulin (rATG) has been widely used to prevent graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). The therapeutic window of rATG is narrow, and it may increase the risk of relapse, viral reactivation, delayed immune reconstitution and GvHD when overexposed or underexposed. Therefore, a reliable method for detecting the rATG concentration in human serum by flow cytometry was established and fully validated for therapeutic drug monitoring. In this method, Jurkat T cells were used to capture active rATG in human serum, and PE-labeled donkey anti-rabbit IgG was used as a secondary antibody. The method showed good specificity, selectivity and excellent linearity at concentration of 0.00300-20.0 AU/mL. The intra- and interday precision values were all within 20% at four concentration levels for the analyte. The stock solutions of rATG showed no significant degradation after storage at ambient temperature for 8 h and at - 80 °C for 481 days. No significant degradation of rATG in serum was observed at ambient temperature for 6 h, during six freezethaw cycles and at - 80 °C for at least 373 days. This method was fully validated and successfully applied to monitor active rATG concentration in serum of patients with haploid-identical hematopoietic stem cell transplantation.

Haploidentical donor stem cell transplantation had a lower incidence of bronchiolitis obliterans syndrome compared with HLA-matched sibling donor transplantation in patients with hematologic malignancies: Benefit from ATG?

Background

Haploidentical donor stem cell transplantation (HID-SCT) based on antithymocyte globulin (ATG) for graft-versus-host disease (GVHD) prophylaxis had achieved a similar incidence of chronic graft-versus-host disease (cGVHD) with human leukocyte antigen (HLA)-matched sibling donor stem cell transplantation (MSD-SCT). However, bronchiolitis obliterans syndrome (BOS), which serves as pulmonary cGVHD, was rarely compared between HID and MSD transplantation.

Methods

One thousand four hundred five patients with hematologic malignancies who underwent allogeneic SCT were enrolled in this retrospective study. Based on donor type, we divided the patients into three groups: HID, MSD, and match unrelated donor (MUD) groups. The cumulative incidences and risk factors of BOS were analyzed.

Results

The 5-year cumulative incidence of BOS was 7.2% in the whole population. HID transplantation had a lower 5-year cumulative incidence of BOS than MSD transplantation (4.1% vs. 10.0%, p < 0.001) and a similar incidence with MUD transplantation (4.1% vs. 6.2%, p = 0.224). The 5-year cumulative incidence of BOS was lower in the ATG group than that in the non-ATG group in both the whole and MSD populations (4.6% vs. 11.2%, p < 0.001, and 4.1% vs. 11.2%, p = 0.042, respectively). The 5-year incidence of BOS in mixed grafts [peripheral blood stem cell (PBSC) plus bone marrow] group was also lower than that in the PBSC group (4.2% vs. 9.1, p = 0.001). Multivariate analysis showed that HID, ATG, and mixed grafts were protective factors for BOS [odds ratio (OR) 0.3, 95% CI 0.2-0.6, p < 0.001; OR 0.3, 95% CI 0.2-0.7, p = 0.001; OR 0.3, 95% CI 0.1-0.8, p = 0.013], and acute graft-versus-host disease (aGVHD) and cGVHD were independent risk factors for BOS (OR 2.1, 95% 1.1-4.3, p = 0.035; OR 10.1, 95% CI 4.0-25.0, p < 0.001).

Conclusions

HID transplantation had a lower incidence of BOS than MSD transplantation, which might be associated with ATG and mixed grafts.

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

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

Optimizing antithymocyte globulin dosing in haploidentical hematopoietic cell transplantation: long-term follow-up of a multicenter, randomized controlled trial

Given that randomized studies testing the long-term impact of antithymocyte globulin (ATG) dosing are scarce, we report the results of an extended follow-up from the original trial. In our prospective, multicenter, randomized trial, 408 leukemia patients 14-65 years of age who underwent haploidentical hematopoietic cell transplantation (haplo-HCT) under our original "Beijing Protocol" were randomly assigned one-to-one to ATG doses of 7.5 mg/kg (n = 203, ATG-7.5) or 10 mg/kg (n = 205, ATG-10.0) at four sites. Extended follow-up (median 1968 d (range: 1300-2710 d) indicated comparable 5-year probabilities of moderate-to-severe chronic graft-versus-host disease (GVHD) (hazard ratio (HR): 1.384, 95% confidence interval (CI): 0.876-2.189, P = 0.164), nonrelapse mortality (HR: 0.814, 95% CI: 0.526-1.261, P = 0.357), relapse (HR: 1.521, 95% CI: 0.919-2.518, P = 0.103), disease-free survival (HR: 1.074, 95% CI: 0.783-1.473, P = 0.658), and GVHD-free/relapse-free survival (HR: 1.186, 95% CI: 0.904-1.555, P = 0.219) between groups (ATG-7.5 vs. ATG-10.0). The 5-year rate of late effects did not differ significantly. However, the cytomegalovirus/Epstein-Barr virus-related death rate was much higher in the ATG-10.0 cohort than in the ATG-7.5 cohort (9.8% vs. 1.5%; P = 0.003). In summary, patients undergoing haplo-HCT benefit from 7.5 mg/kg ATG compared to 10.0 mg/kg ATG based on a balance between GVHD and infection control. ATG (7.5 mg/kg) is potentially regarded as the standard regimen in the platform. These results support the optimization of ATG use in the "Beijing Protocol", especially considering the potential economic advantage in developing countries.

Risk factors for post-transplant Epstein-Barr virus events in pediatric recipients of hematopoietic stem cell transplants

BACKGROUND

Epstein-Barr virus (EBV) can cause severe disease following hematopoietic stem cell transplant (HSCT), including post-transplant lymphoproliferative disorder (PTLD). The objective was to analyze risk factors associated with post-transplant EBV outcomes among pediatric allogeneic HSCT recipients.

METHODS

We used data from 156 pediatric allogeneic HSCT recipients enrolled in the Canadian multicenter TREASuRE study. Cox and Prentice-Williams-Petersen models were used to analyze risk factors for post-transplant EBV events including occurrence and recurrence of EBV DNAemia, increase in EBV viral load (EBV-VL), and preemptive use of rituximab, an effective therapy against PTLD.

RESULTS

Females were at higher risk for increasing EBV-VL (adjusted hazard ratio (HR) = 2.83 [95% confidence intervals (CI): 1.33-6.03]) and rituximab use (HR = 3.08 [1.14-8.30]), but had the same EBV DNAemia occurrence (HR = 1.21 [0.74-1.99]) and recurrence risks (HR=1.05 [0.70-1.58]) compared to males. EBV DNAemia was associated with recipient pre-transplant EBV seropositivity (HR = 2.47 [1.17-5.21]) and with graft from an EBV-positive donor (HR = 3.53 [1.95-6.38]). Anti-thymocyte globulin (ATG) was strongly associated with all EBV outcomes, including the use of rituximab (HR = 5.33 [1.47-19.40]). Mycophenolate mofetil (MMF) significantly decreased the risk of all EBV events including the rituximab use (HR = 0.13 [0.03-0.63]).

CONCLUSION

This study in pediatric allogeneic HSCT patients reveals a reduced risk of all EBV outcomes with the use of MMF. Risk factors for EBV events such as EBV-VL occurrence and recurrence include EBV positivity in the donor and recipient, and use of ATG, whereas risk factors for the most severe forms of EBV outcome (EBV-VL and the use of rituximab) include female sex and ATG use.

Factors Associated with Post-Transplant Active Epstein-Barr Virus Infection and Lymphoproliferative Disease in Hematopoietic Stem Cell Transplant Recipients: A Systematic Review and Meta-Analysis

This systematic review was undertaken to identify risk factors associated with post-transplant Epstein-Barr virus (EBV) active infection and post-transplant lymphoproliferative disease (PTLD) in pediatric and adult recipients of hematopoietic stem cell transplants (HSCT). A literature search was conducted in PubMed and EMBASE to identify studies published until 30 June 2020. Descriptive information was extracted for each individual study, and data were compiled for individual risk factors, including, when possible, relative risks with 95% confidence intervals and/or p-values. Meta-analyses were planned when possible. The methodological quality and potential for bias of included studies were also evaluated. Of the 3362 titles retrieved, 77 were included (62 for EBV infection and 22 for PTLD). The overall quality of the studies was strong. Several risk factors were explored in these studies, but few statistically significant associations were identified. The use of anti-thymocyte globulin (ATG) was identified as the most important risk factor positively associated with post-transplant active EBV infection and with PTLD. The pooled relative risks obtained using the random-effect model were 5.26 (95% CI: 2.92-9.45) and 4.17 (95% CI: 2.61-6.68) for the association between ATG and post-transplant EBV infection and PTLD, respectively. Other risk factors for EBV and PTLD were found in the included studies, such as graft-versus-host disease, type of conditioning regimen or type of donor, but results are conflicting. In conclusion, the results of this systematic review indicate that ATG increases the risk of EBV infection and PTLD, but the link with all other factors is either nonexistent or much less convincing.

Long-term outcomes and risk factor analysis of steroid-refractory graft versus host disease after hematopoietic stem cell transplantation

Steroid-refractory graft versus host disease (GVHD) represents a fearsome complication after allogeneic hematopoietic stem cell transplantation (HSCT). We conducted a retrospective study on outcomes and risk factors associated with acute and chronic steroid-refractory GVHD in a large cohort of 1207 patients receiving HSCT in Saint Louis Hospital between 2007 and 2017. Among patients who developed an acute and/or a chronic GVHD, the cumulative incidences of acute and chronic steroid-refractory disease were 31% and 48%, respectively, at day +100 and 1-year post-HSCT. Through a multivariable analysis we selected several risk factors associated with the development of a steroid-refractory disease. For acute GVHD steroid refractoriness, we identified (1) a very high disease risk index, (2) an unrelated donor, (3) the absence of in vivo T-depletion as GVHD prophylaxis, and (4) a reduced intensity conditioning regimen. For chronic GVHD, (1) the use of peripheral blood stem cells, (2) unrelated donors, and (3) absence of in vivo T-depletion were more likely associated with a steroid-refractory disease. After the construction of a multistate dynamic model, we found that the probability of being alive without relapse after the resolution of all GVHD episodes was about 36% in the long term.

Antirelapse effect of pretransplant exposure to rabbit antithymocyte globulin

It remains unknown why rabbit antithymocyte globulin (ATG; Thymoglobulin) has not affected relapse after hematopoietic cell transplantation (HCT) in randomized studies. We hypothesized that high pre-HCT ATG area under the curve (AUC) would be associated with a low incidence of relapse, whereas high post-HCT AUC would be associated with a high incidence of relapse. We measured serum levels of ATG capable of binding to mononuclear cells (MNCs), lymphocytes, T cells, CD4 T cells, or CD33 cells. We estimated pre- and post-HCT AUCs in 152 adult recipients of myeloablative conditioning and blood stem cells. High pre-HCT AUCs of MNC- and CD33 cell-binding ATG were associated with a low incidence of relapse and high relapse-free survival (RFS). There was a trend toward an association of high post-HCT AUC of lymphocyte-binding ATG with a high incidence of relapse and low RFS. High pre-HCT AUCs were also associated with faster engraftment and had no impact on graft-versus-host disease (GVHD) or fatal infections. High post-HCT AUCs were associated with a low risk of GVHD, seemed associated with an increased risk of fatal infections, and had no impact on engraftment. In conclusion, pre-HCT AUC seems to have a positive, whereas post-HCT AUC seems to have a negative, impact on relapse.

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

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

[Application of low-dose ATG for GVHD prophylaxis in patients undergoing PBSCT aged over forty years old]

目的

探讨在供、受者年龄均≥40岁同胞相合外周血干细胞移植（MSD-PBSCT）移植物抗宿主病（GVHD）预防方案中增加低剂量抗胸腺细胞球蛋白（ATG）的效果。

方法

回顾性分析2013年3月至2017年4月行MSD-PBSCT且供、受者年龄均≥40岁恶性血液病患者的临床资料。43例患者在常规急性GVHD预防方案（环孢素A或他克莫司联合短疗程甲氨蝶呤）中加入ATG 1.5 mg·kg⁻¹·d⁻¹×3 d（ATG组），55例患者应用常规GVHD预防方案（对照组）。

结果

①ATG组中性粒细胞植入中位时间短于对照组[13（11~17）d对14（12~24）d，P=0.001]，血小板植入中位时间差异无统计学意义[14（11~43）d对15（11~42）d，P=0.071）]。②ATG组+100 d内急性GVHD累积发生率低于对照组[25.6%（95%CI 13.7%~39.3%）对49.1%（95%CI 35.2%~61.6%），P=0.018]，Ⅱ~Ⅳ度急性GVHD、慢性GVHD发生率差异无统计学意义[18.6%（95%CI 8.6%~31.5%）对23.6%（95%CI 13.4%~35.6%），P=0.509；49.6%（95%CI 31.6%~65.3%）对56.4%（95%CI 41.4%~69.0%），P=0.221]。③ATG组与对照组移植后1年巨细胞病毒血症累积发生率差异无统计学意义[21.1%（95%CI 10.3%~34.5%）对31.1%（95%CI 18.8%~44.2%），P=0.429]。④ATG组及对照组移植后2年累积复发率[24.0%（95%CI 11.5%~38.9%）对24.0%（95%CI 12.1%~38.2%），P=0.608]、非复发死亡率[10.2%（95%CI 3.1%~22.1%）对21.6%（95%CI 9.4%~37.0%），P=0.411]及无病生存率[65.8%（95%CI 50.3%~81.3%）对54.4%（95%CI 37.7%~71.1%），P=0.955]差异均无统计学意义，但ATG组移植后2年总生存率优于对照组[83.8%（95%CI 71.8%~90.0%）对58.0%（95%CI 42.2%~73.9%），P=0.019]。

结论

对于年龄较大的MSD-PBSCT患者，在常规GVHD预防方案基础上加入低剂量ATG可以显著降低移植后急性GVHD发生率、改善OS率，病毒感染发生率和复发率无明显增加。

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

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

The Role of Anti-Thymocyte Globulin or Alemtuzumab-Based Serotherapy in the Prophylaxis and Management of Graft-Versus-Host Disease

Allogeneic hematopoietic stem cell transplant is an established treatment modality for hematologic and non-hematologic diseases. However, it is associated with acute and long-term sequelae which can translate into mortality. Graft-versus-host disease (GVHD) remains a glaring obstacle, especially with the advent of reduced-intensity conditioning. Serotherapy capitalizes on antibodies which target T cells and other immune cells to mitigate this effect. This article focuses on the utility of two such agents: anti-thymocyte globulin (ATG) and alemtuzumab. ATG has demonstrated benefit in prophylaxis against GVHD, especially in the chronic presentation. However, there is limited impact of ATG on overall survival and it has little utility in the treatment context. There may be an initial improvement, particularly in skin manifestations, but no substantial benefit has been elicited. Alemtuzumab has shown benefit in both prophylaxis and treatment of GVHD, but at the consequence of a more profound immunosuppressive phase, mandating aggressive viral prophylaxis. There remains heterogeneity in the doses and regimens of the agents, with no standardized protocol in place. Furthermore, it seems that once steroid-refractory GVHD has been established, there is little that can be offered to offset the ultimately dismal outcome. Here we present a systematic overview of ATG- or alemtuzumab-based serotherapy in the prophylaxis and management of GVHD.

Dissecting the mechanisms involved in anti-human T-lymphocyte immunoglobulin (ATG)-induced tolerance in the setting of allogeneic stem cell transplantation - potential implications for graft versus host disease

Polyclonal anti-human thymocyte globulins (ATG) have been recently shown to significantly reduce the incidence of graft versus host disease (GVHD) post allogeneic stem cell transplantation (HSCT) from both sibling and unrelated donors. Induction of regulatory T cells has been suggested as one of the possible mechanisms. The aim of current study was to further characterize the T cell populations induced by ATG treatment and to delineate the mechanisms involved in ATG-induced tolerance. Phenotypic characterization revealed a significant increase in the expression of FoxP3, GITR, CD95, PD-1 and ICOS as well as the complement inhibitory molecules CD55, CD58 and CD59 on CD4+CD25+ T cells upon ATG treatment. Addition of ATG-treated cells to autologous and allogeneic peripheral blood mononuclear cells (PBMCs) stimulated with anti-CD3/anti-CD28 antibodies resulted in significant inhibition of proliferation. Moreover, T-cell activation and IFNγ secretion were reduced in the presence of ATG-induced Treg cells. The CD4+CD25+CD127-low Treg fraction sorted from ATG-treated culture demonstrated greater suppressive potency than negative fraction. Conditioned medium produced by ATG-treated but not IgG-treated cells contained TGFβ and suppressed T cell proliferation and activation in a TGFβ receptor-dependent manner. TGFβ receptor kinase inhibitor SB431542 interfered with the suppressive activity of ATG-primed cells, enabling partial rescue of proliferation and IFNγ secretion. Moreover, SB431542 prevented Treg phenotype induction upon ATG treatment. Altogether, our data reveal the role of TGFβ signaling in ATG-mediated immunosuppression and further support the use of ATG, a potent inducer of regulatory T cells, for prevention of GVHD post HSCT and potentially other therapeutic applications.

Anti-thymocyte globulin as graft-versus-host disease prevention in the setting of allogeneic peripheral blood stem cell transplantation: a review from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation

Allogeneic hematopoietic stem cell transplantation is increasingly used as treatment for patients with life-threatening blood diseases. Its curative potential is largely based on immune-mediated graft-versus-leukemia effects caused by donor T cells contained in the graft. Unfortunately, donor T cells are also the cause of graft-versus-host disease. The vast majority of human leukocyte antigen-matched allogeneic hematopoietic stem cell transplants are nowadays carried out with peripheral blood stem cells as the stem cell source. In comparison with bone marrows, peripheral blood stem cells contain more hematopoietic stem/progenitor cells but also one log more T cells. Consequently, the use of peripheral blood stem cells instead of bone marrow has been associated with faster hematologic recovery and a lower risk of relapse in patients with advanced disease, but also with a higher incidence of chronic graft-versus-host disease. These observations have been the basis for several studies aimed at assessing the impact of immunoregulation with anti-thymocyte globulin on transplantation outcomes in patients given human leukocyte antigen-matched peripheral blood stem cells from related or unrelated donors. After a brief introduction on anti-thymocyte globulin, this article reviews recent studies assessing the impact of anti-thymocyte globulin on transplantation outcomes in patients given peripheral blood stem cells from human leukocyte antigen-matched related or unrelated donors as well as in recipients of grafts from human leukocyte antigen haploidentical donors.

The MICA-129 dimorphism affects NKG2D signaling and outcome of hematopoietic stem cell transplantation

The MHC class I chain-related molecule A (MICA) is a highly polymorphic ligand for the activating natural killer (NK)-cell receptor NKG2D. A single nucleotide polymorphism causes a valine to methionine exchange at position 129. Presence of a MICA-129Met allele in patients (n = 452) undergoing hematopoietic stem cell transplantation (HSCT) increased the chance of overall survival (hazard ratio [HR] = 0.77, P = 0.0445) and reduced the risk to die due to acute graft-versus-host disease (aGVHD) (odds ratio [OR] = 0.57, P = 0.0400) although homozygous carriers had an increased risk to experience this complication (OR = 1.92, P = 0.0371). Overall survival of MICA-129Val/Val genotype carriers was improved when treated with anti-thymocyte globulin (HR = 0.54, P = 0.0166). Functionally, the MICA-129Met isoform was characterized by stronger NKG2D signaling, triggering more NK-cell cytotoxicity and interferon-γ release, and faster co-stimulation of CD8⁺ T cells. The MICA-129Met variant also induced a faster and stronger down-regulation of NKG2D on NK and CD8⁺ T cells than the MICA-129Val isoform. The reduced cell surface expression of NKG2D in response to engagement by MICA-129Met variants appeared to reduce the severity of aGVHD.

Myeloablative, but not Reduced-Intensity, Conditioning Overcomes the Negative Effect of Flow-Cytometric Evidence of Leukemia in Acute Myeloid Leukemia

Stringent complete remission (CR) in acute myeloid leukemia (AML) requires the absence of both morphologic and flow cytometric evidence of disease. We have previously shown that persistent AML detected by flow cytometry (FC+) before reduced-intensity conditioning (RIC) allogeneic hematopoietic cell transplantation (alloHCT) was associated with significantly increased relapse, shorter disease-free survival (DFS), and poorer overall survival (OS), independent of morphologic blast count. We evaluated the effect of FC status on outcomes of alloHCT for AML after either myeloablative conditioning (MAC) or RIC regimens in 203 patients (MAC, n = 80, and RIC, n = 123) with no morphologic evidence of persistent AML pretransplant on marrow biopsy. The allografts included 130 umbilical cord blood (UCB) and 73 sibling donors. We performed central review of pretransplant standard sensitivity FC to identify detectable FC+. Twenty-five patients were FC+, including 15 (18.7%) receiving MAC and 10 (8.1%) RIC alloHCT. Among RIC patients FC+ was associated with significantly inferior relapse, DFS, and OS (multiple regression HR, 3.8; 95% CI, 1.7 to 8.7; P < .01 for relapse; HR, 2.9; 95% CI, 1.4 to 5.9; P < .01 for DFS; and HR, 3.4; 95% CI, 1.7 to 7; P < .01 for OS). In contrast, FC+ status was not associated with relapse or decreased OS after MAC. These data suggest that MAC, but not RIC, overcomes the negative effect of pretransplant FC+ after sibling or UCB alloHCT. Therefore, a deeper pretransplant leukemia-free state is preferred for those treated with RIC.

Anti-thymocyte globulin could improve the outcome of allogeneic hematopoietic stem cell transplantation in patients with highly aggressive T-cell tumors

The early experiment result in our hospital showed that anti-thymocyte globulin (ATG) inhibited the proliferation of lymphoid tumor cells in the T-cell tumors. We used the ATG as the part of the conditioning regimen and to evaluate the long-term anti-leukemia effect, the safety and complication in the patients with highly aggressive T-cell lymphomas. Twenty-three patients were enrolled into this study. At the time of transplant, six patients reached first or subsequent complete response, three patients had a partial remission and 14 patients had relapsed or primary refractory disease. The conditioning regimen consisted of ATG, total body irradiation, toposide and cyclophosphamide. The complete remission rate after transplant was 95.7%. At a median follow-up time of 25 months, 16 (69.6%) patients are alive and free from diseases, including nine patients in refractory and progressive disease. Seven patients died after transplant, five from relapse and two from treatment-related complications. The incidence of grades II–IV acute graft-vs-host disease (GvHD) was 39.1%. The maximum cumulative incidence of chronic GvHD was 30%. The most frequent and severe conditioning-related toxicities observed in 8 out of 23 patients were grades III/IV infections during cytopenia. Thus, ATG-based conditioning is a feasible and effective alternative for patients with highly aggressive T-cell tumors.

Sufficient Immunosuppression with Thymoglobulin Is Essential for a Successful Haplo-Myeloid Bridge in Haploidentical-Cord Blood Transplantation

In haploidentical (haplo)-cord blood (CB) transplantations, early haplo donor engraftment serves as a myeloid bridge to sustainable CB engraftment and is associated with early neutrophil recovery. The conditioning regimens as published for haplo-cord protocols usually contain serotherapy, such as rabbit antithymocyte globulin (ATG) (Thymoglobulin, Genzyme, Cambridge, MA). However, reducing or omitting serotherapy is an important strategy to improve early immune reconstitution after transplantation. The need for serotherapy in successful haplo-cord transplantation, defined as having a haplo-derived myeloid bridge to CB engraftment, has not been investigated before. Two consecutive cohorts of patients underwent transplantation with haplo-CB. The first group underwent transplantation with haplo-CB for active infection and/or an underlying condition with expected difficult engraftment without a conventional donor available. They received a single unit (s) CB and haplo donor cells (CD34(+) selected, 5 × 10(6) CD34(+)/kg). The second cohort included patients with poor-risk malignancies, not eligible for other treatment protocols. They received a sCB and haplo donor cells (CD19/αβTCR-depleted; 5 × 10(6) CD34(+)/kg). Retrospectively in both cohorts, active ATG (Thymoglobulin) levels were measured and post-hematopoietic cell transplantation area under the curve (AUC) was calculated. The influence of ATG exposure for having a successful haplo-myeloid bridge (early haplo donor engraftment before CB engraftment and no secondary neutropenia) and transplantation-related mortality (TRM) were analyzed as primary endpoints. Twenty patients were included (16 in the first cohort and 4 in the second cohort). In 58% of evaluable patients, there was no successful haplo-derived myeloid bridge to CB engraftment, for which a low post-transplantation ATG exposure appeared to be a predictor (P <.001). TRM in the unsuccessful haplo-bridge group was 70% ± 16% versus 12% ± 12% in the successful haplo-bridge group (P = .012). In conclusion, sufficient in vivo T depletion with ATG is required for a successful haplo-myeloid bridge to CB engraftment.

Impact of serotherapy on immune reconstitution and survival outcomes after stem cell transplantations in children: thymoglobulin versus alemtuzumab

The outcome of allogeneic hematopoietic stem cell transplantation (HSCT) is strongly affected by the kinetics of reconstitution of the immune system. This study compared the effects of antithymocyte globulin (ATG) and alemtuzumab on various outcome parameters after HSCT. The study cohort consisted of 148 children, with a median age of 9.6 years (range, .4 to 19.0), who underwent HSCT for malignant and benign hematological disorders in a single HSCT unit. Conditioning included ATG (n = 110) or alemtuzumab (n = 38). Cox proportional hazard regression analysis showed that alemtuzumab significantly delayed the recovery of CD3(+) T cells and CD4(+)as well as CD8(+) T cell subsets (P ≤ .001) and natural killer (NK) cells (P = .008) compared with ATG. In both ATG- and alemtuzumab-treated patients, shorter drug exposure lead to significantly faster recovery of T cells. Alemtuzumab was associated with lower donor chimerism 3 and 6 months after transplantation and a higher risk of disease relapse (P = .001). The overall survival and event-free survival risks were significantly lower for alemtuzumab-treated patients (P = .020 and P < .001, respectively). Patients who received alemtuzumab showed a trend to lower risk of acute graft-versus-host disease, more human adenovirus, and less Epstein-Barr virus reactivations compared with patients who received ATG. These data indicate that children treated with alemtuzumab as part of the conditioning regimen have a slower T cell and NK cell reconstitution compared with those treated with ATG, which compromises the overall and event-free survival. Prolonged length of lympholytic drug exposure delayed the T cell recovery in both ATG- and alemtuzumab-treated patients. Therefore, we recommend detailed pharmacokinetic/pharmacodynamic (PK/PD) analyses in a larger cohort of patients to develop an algorithm aiming at optimization of the serotherapy containing conditioning regimen.

Less graft-versus-host disease after rabbit antithymocyte globulin conditioning in unrelated bone marrow transplantation for leukemia and myelodysplasia: comparison with matched related bone marrow transplantation

One of the major drawbacks for unrelated donor (UD) bone marrow transplantation (BMT) is graft-versus-host disease (GVHD). Despite results from randomized trials, antithymocyte globulin (ATG) is not routinely included for GVHD prophylaxis in UD BMT by many centers. One of ways to demonstrate the usefulness of rabbit ATG in UD BMT is to evaluate how its results approximate to those observed in matched related (MRD) BMT. Therefore, we compared the outcomes between UD BMT with rabbit ATG (Thymoglobulin) for GVHD prophylaxis (n = 25) and MRD BMT (n = 91) for leukemia and myelodysplasia. All but one patient received a myeloablative conditioning regimen. Grades II–IV acute GVHD were similar (39.5% vs. 36%, p = 0.83); however, MRD BMT recipients developed more moderate-severe chronic GVHD (36.5% vs. 8.6%, p = 0.01) and GVHD-related deaths (32.5% vs. 5.6%, p = 0.04). UD BMT independently protected against chronic GVHD (hazard ratio 0.23, p = 0.04). The 6-month transplant-related mortality, 1-year relapse incidence, and 5-year survival rates were similar between patients with non-advanced disease in the MRD and UD BMT groups, 13.8% vs. 16.6% (p = 0.50), 20.8% vs. 16.6% (p = 0.37), and 57% vs. 50% (p = 0.67), respectively. Stable full donor chimerism was equally achieved (71.3% vs. 71.4%, p = 1). Incorporation of rabbit ATG in UD BMT promotes less GVHD, without jeopardizing chimerism evolution, and may attain similar survival outcomes as MRD BMT for leukemia and myelodysplasia especially in patients without advanced disease.

Rabbit anti-T-lymphocyte globulin (ATG) persists with differential reactivity in patients' sera after full hematopoetic regeneration from allogeneic stem cell transplantation

BACKGROUND

Rabbit polyclonal anti-T-lymphocyte Globulin (ATG-F®, Fresenius) is widely used for GvHD prophylaxis in allogeneic stem cell transplantation (SCT). ATG has a wide epitope spectrum and has been shown to react with all compartments of peripheral blood mononuclear cells (PBMNCs). ATG induces apoptosis in all cellular compartments. In this study we investigated the binding of ATG in sera from ten patients treated with rabbit ATG to PBMNCs and subcellular compartments after full hematopoetic regeneration on day 21 post SCT.

METHODS

Sera from ten patients treated with unrelated donor allogeneic SCT for hematologic malignancy were collected after full hematopoetic regeneration on day 21 post SCT and incubated with healthy donor PBMNCs. Rabbit ATG on PBMNCs was detected by staining with fluorochrome labeled anti-rabbit IgG antibody. PBMNC compartments were investigated by counterstaining with lineage markers CD4, CD8, CD14 CD20 and CD56. Positive control was the fresh ATG preparation.

RESULTS

We found that patient's' sera retained activity towards PBMNCs in all patients, yet at reduced intensity. When cell compartments were analyzed we found a differential pattern of ATG reactivity within sera. The mean percentage of total cells reacting with serum ATG from ten patients compared to fresh ATG (100%) was 44% of CD4 positive and 58% of CD8 positive T-lymphocytes, 41% of CD56 positive NK-cells, 83% of CD20 positive B-lymphocytes and 98% of CD14 positive monocytes. However, inter-individual variations were high with a wide spread around the mean especially for T-lymphocytes.

CONCLUSION

We conclude that upon PBMNC regeneration following SCT and immunosuppressive treatment with ATG subpopulations of T-lymphocytes (CD4, CD8) and NK cells (CD56) are selected that lose epitopes recognized by ATG while B-lymphocytes (CD20) and monocytes (CD14) maintain a homogeneity with respect to epitopes recognized by ATG. This may be due to loss of idiotypes reacting with subpopulations of high frequency and turnover. Further studies should investigate the subphenotype of these populations and functional effects of extremely high or low reactivity with one or more compartments in some patients on GvHD and disease outcome.

Immune cell subset counts associated with graft-versus-host disease

Graft-versus-host disease (GVHD) is a major transplantation complication. The purpose of this study was to measure immune cell subsets by flow cytometry early after transplantation (before median day of GVHD onset) to identify subsets that may play a role in GVHD pathogenesis. We also measured the subsets later after transplantation to determine which subsets may be influenced by GVHD or its treatment. We studied 219 patients. We found that acute GVHD (aGVHD) was preceded by high counts of CD4 T cells and CD8 T cells. It was followed by low counts of total and naive B cells, total and cytolytic NK cells, and myeloid and plasmacytoid dendritic cells. Chronic GVHD (cGVHD) was preceded by low counts of memory B cells. In conclusion, both CD4 and CD8 T cells appear to play a role in the pathogenesis of aGVHD. Generation of B cells, NK cells, and dendritic cells may be hampered by aGVHD and/or its treatment. Memory B cells may inhibit the development of cGVHD.

IL15 levels on day 7 after hematopoietic cell transplantation predict chronic GVHD

Chronic GVHD (cGVHD) is an important complication of allogeneic hematopoietic cell transplantation (HCT). As preemptive therapy might be efficacious if administered early post transplant, we set out to determine whether cGVHD can be predicted from the serum level of a biomarker on day 7 or 28. In a discovery cohort of 153 HCT recipients conditioned with BU, fludarabine and rabbit antithymocyte globulin (ATG), we determined serum levels of B-cell-activating factor, vascular endothelial growth factor, soluble TNF-α receptor 1, soluble IL2 receptor α, IL5, IL6, IL7, IL15, γ-glutamyl transpeptidase, cholinesterase, total protein, urea and ATG. Patients with low levels of IL15 (<30.6 ng/L) on day 7 had 2.7-fold higher likelihood of developing significant cGVHD (needing systemic immunosuppressive therapy) than patients with higher IL15 levels (P<0.001). This was validated in a validation cohort of 105 similarly-treated patients; those with low IL15 levels had 3.7-fold higher likelihood of developing significant cGVHD (P=0.001). Low IL15 was not associated with relapse; it trended to be associated with acute GVHD and was associated with low infection rates. In conclusion, low IL15 levels on day 7 are predictive of cGVHD, and thus could be useful in guiding preemptive therapy.