Polyclonal Rabbit Antithymocyte Globulin Research Articles

Treatment of early borderline lesions in low immunological risk kidney transplant patients: a Spanish multicenter, randomized, controlled parallel-group study protocol: the TRAINING study

BackgroundSubclinical inflammation, including borderline lesions (BL), is very common (30–40%) after kidney transplantation (KT), even in low immunological risk patients, and can lead to interstitial fibrosis/tubular atrophy (IFTA) and worsening of renal function with graft loss. Few controlled studies have analyzed the therapeutic benefit of treating these BL on renal function and graft histology. Furthermore, these studies have only used bolus steroids, which may be insufficient to slow the progression of these lesions. Klotho, a transmembrane protein produced mainly in the kidney with antifibrotic properties, plays a crucial role in the senescence-inflammation binomial of kidney tissue. Systemic and local inflammation decrease renal tissue expression and soluble levels of α-klotho. It is therefore important to determine whether treatment of BL prevents a decrease in α-klotho levels, progression of IFTA, and loss of kidney function.MethodsThe TRAINING study will randomize 80 patients with low immunological risk who will receive their first KT. The aim of the study is to determine whether the treatment of early BL (3rd month post-KT) with polyclonal rabbit antithymocyte globulin (Grafalon®) (6 mg/kg/day) prevents or decreases the progression of IFTA and the worsening of graft function compared to conventional therapy after two years post-KT, as well as to analyze whether treatment of BL with Grafalon® can modify the expression and levels of klotho, as well as the pro-inflammatory cytokines that regulate its expression.DiscussionThis phase IV investigator-driven, randomized, placebo-controlled clinical trial will examine the efficacy and safety of Grafalon® treatment in low-immunological-risk KT patients with early BL.Trial registrationclinicaltrials.gov: NCT04936282. Registered June 23, 2021, https://clinicaltrials.gov/ct2/show/NCT04936282?term=NCT04936282&draw=2&rank=1. Protocol Version 2 of 21 January 2022. Sponsor: Canary Isles Institute for Health Research Foundation, Canary Isles (FIISC). mgomez@fciisc.org.

Impact of Two Different Types of Rabbit ATG on Immune Reconstitution and Overall Results after Allogeneic Hematopoetic Stem Cell Transplantation for Acute Lymphoblastic Leukemia in Children

Introduction Thymoglobulin® and Grafalon® are 2 polyclonal rabbit anti-thymocyte globulin (ATG) used in allogeneic hematopoietic stem cell transplantation (allo-HSCT) to prevent graft rejection and graft-versus-host disease (GvHD). Differences in manufacturing lead to different types and concentrations of antibodies in each product. Few studies compare their effects on post-transplant immune reconstitution: indeed, the latter is essential to prevent post-transplant infections as well as relapse (in case of hematological malignancies). Methods We conducted a retrospective study on children or adolescents who received a first unrelated allo-HSCT for an Acute Lymphoblastic Leukemia (ALL) between 2007 and 2018, in the department of pediatric hematology of the Robert Debré Hospital in Paris, France. During this time period, 2 types of ATG were used: Thymoglobulin® at 7.5mg/kg or Grafalon® at 60mg/kg. We included patients with a B or T phenotype ALL aged 2 to 18 years at the time of HSCT indication. Stem cell source could be from unrelated matched or mismatched bone marrow, peripheral blood or cord blood. All patients received a myeloablative conditioning regimen consisting of 12 grays total body irradiation and etoposide (60mg/kg). We compared patients for engraftment, counts of total lymphocytes, B and T lymphocytes, T CD4+ and CD8+ lymphocytes and their sub-types (naïve, effector memory, central memory and effector memory RA+), regulatory T cells, NK cells, and compared lymphocyte proliferation assays at 1, 3, 6 and 12 months after transplant. We used joint models of longitudinal and survival data to further analyze evolution of total lymphocytes, B and T cells, T CD4+ and T CD8+ cells, and NK cells. Finally, we compared clinical outcomes between the 2 groups. Statistical analyses were performed according to EBMT guidelines (Iacobelli, 2013). Results 76 children were included: 23 received Thymoglobulin® and 53 received Grafalon®. Stem cell source was peripheral blood or bone marrow for 61 patients and cord blood for 15 patients. Initial characteristics of patients, disease status and HSCT were similar between the two groups except for the median total nucleated cells and CD34+ progenitor cells of the graft, that were significantly higher in the Grafalon® group. We found a delayed cumulative incidence of engraftment in patients who received Grafalon® compared to those who received Thymoglobulin®: 29 days [interquartile range 22-36] versus 22 days [19.5-29.5], p=0.004. We observed significantly higher counts of total and T CD4+ lymphocytes 1 month after transplant in patients who received Thymoglobulin® as compared to those who received Grafalon®: 238/mm3 [172-466] versus 137/mm3 [51-306] respectively (p=0.005), and 40/mm3 [31.5-70.5] versus 16/mm3 [2.5-41.5], respectively (p=0.011). No differences in immune cell population counts were found 3, 6 and 12 months after transplant (figure 1). However, joint models found no difference in the evolution of lymphocyte subsets analyzed depending on the ATG used, except a non-significant difference in slopes over time for CD8+ cells (p=0.13). In patients given Thymoglobulin® compared to those given Grafalon®, we found a higher proliferation in response to stimulation by CD3 3 month after HSCT (CD3 index 20.4 [12.4;41] versus 5.9 [3.3;6.4] respectively, p=0.0039), and a higher proliferation in response to stimulation by adenovirus (ADV) antigen 1 year after HSCT (ADV index 78.6 [58.8;163.1] versus 15.7 [2.8;59.3] respectively, p=0.027). We found no effect of ATG type on overall survival (OS), disease-free survival (DFS), treatment-related mortality and chronic GvHD. In a multivariate analysis, we observed no effect of the type of ATG on OS and DFS. Conclusions We found a higher count of total and T CD4+ lymphocytes 1 month after unrelated allo-HSCT for ALL in children who received Thymoglobulin® at 7.5mg/kg compared to those who received Grafalon® at 60mg/kg. From 3 months after HSCT, we found no difference in immune reconstitution. Joint models for longitudinal data and survival found no significant difference in evolution of the lymphocyte subsets analyzed. Clinical outcomes were similar between the two groups. However, we compared an intermediate dose of Thymoglobulin® to a high dose of Grafalon® that is not still the standard in clinical practice. A prospective study comparing Thymoglobulin® to a lower dose of Grafalon® would be needed. Disclosures Baruchel: Novartis: Consultancy, Honoraria; Servier: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; Bellicum: Consultancy. Dalle:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi-Genzyme: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bellicum: Consultancy, Honoraria; Medac: Consultancy, Honoraria; Orchard: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; bluebird bio: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria; AbbVie Pharmacyclics: Membership on an entity's Board of Directors or advisory committees.

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

BackgroundUnlike lymphodepletion, a decrease in platelet count following induction immunosuppressive therapy with polyclonal rabbit antithymocyte globulin (rATG) is deemed as an adverse event. However, this phenomenon may represent a particular rATG antirejection mechanism. MethodsThis retrospective single-center study included 156 patients who received a heart transplant (HTx) between 2010 and 2018. All patients received rATG induction therapy for 5 days. Absolute lymphocyte count (ALC) and platelet counts were assessed on days 0, 7, and 14 following HTx. The primary outcome of the study was the first occurrence of acute cellular rejection (ACR) defined as grade ≥ 1B within 24 months after HTx. ResultsBoth ALC and platelet counts decreased rapidly after induction. During the 24-month follow-up period, 17% of patients had ACR. Patients with ACR had significantly higher platelet count on day 7 (145 vs 104, P < .001) and higher ALC on day 14 (162 vs 130, P = .035) than those without rejection. Patients in the highest platelet count quartile showed more ACR (50% in quartile 4 vs 0% in quartile 1, P = .006) as well as a higher cumulative total rejection score. Univariate analysis showed that ACR was associated with platelet count on day 7, recipient age, and pretransplant cytomegalovirus IgG serology. In multivariable regression analysis, platelet count on day 7 was the most accurate predictor of ACR. ConclusionsLower platelet count after induction with rATG is associated with less ACR. This suggests platelet involvement in antirejection mechanisms of rATG and a possible rationale for targeting platelets in future immunosuppressive strategies.

Low Immunologic Risk Living Related Renal Transplant Using Very Low-Dose Antithymocyte Globulin as Induction Therapy: A Single Tertiary Hospital Experience

The aim of induction therapy in the management of kidney transplant is to reduce the incidence of acute rejection and delayed graft function after kidney transplant. The agent for induction therapy differs depending on the recipient risks. The regimen can be either polyclonal (rabbit antithymocyte globulin [rATG]) or monoclonal antibody (basiliximab). Basiliximab is commonly used in patients with low immunologic risk. However, to date we know that the use of rATG on T cell depletion is dose dependent and more potent antirejection therapy. Therefore, we would like to look at 1-year graft function of very low-dose rATG in low immunologic risk recipients.All low immunologic risk patients who received low-dose rATG (0.5 mg/kg of body weight daily) during transplant (day 0) and on days 1 and 2 were recruited. Their renal function, HLA donor-specific antibodies, lymphocyte counts, protocol biopsy results, and cytomegalovirus (CMV) polymerase chain reaction were monitored as per clinical practice.All 10 patients had immediate graft function. Low-dose rATG caused lymphocyte counts to deplete immediately on day 0, and the effect lasted about 1 month post-transplant. All the patients had stable graft function without any significance episode of rejection. Only one patient had de novo HLA-DQ antibody. It is good to know that without prophylaxis antiviral in CMV+ donor to CMV+ recipient, the incidence of CMV viremia is considerably low in our cohort.Very low-dose rATG is an effective induction immunosuppression in low immunologic risk patients with acceptable infection risk.

Quantification of T Cell Binding Polyclonal Rabbit Anti-thymocyte Globulin in Human Plasma with Liquid Chromatography Tandem-Mass Spectrometry

The addition of rabbit anti-human thymocyte globulin (ATG) to the conditioning regimen prior to allogeneic hematopoietic cell transplantation has significantly reduced the risk of graft-versus-host disease (GvHD) and graft failure. However, ATG has a small therapeutic window. Overexposure of ATG post-HCT hampers T cell immune reconstitution and has been associated with increased relapse rates and viral reactivations, whereas underexposure has been associated with an increased incidence of GvHD, both of which lead to increased mortality. Therapeutic drug monitoring of T cell binding ATG plasma levels provides a means to optimize dosing for patients at high risk for graft failure to ensure timely T cell immune reconstitution and subsequently increase survival chances. This manuscript describes the first liquid chromatography tandem-mass spectrometry (LC-MS/MS) method to quantify the pharmacologically active fraction of polyclonal ATG in plasma. This was achieved through immunoaffinity purification of active ATG from plasma with Jurkat T cells. After the binding and washing, samples were eluted, denatured, and trypsin-digested. Signature peptides originating from the IgG constant chain were measured with LC-MS/MS. Critical method parameters were optimized, and the method was successfully validated following European Medicines Agency (EMA) guidelines. The method covered the therapeutic range of ATG and was validated at a lower limit of quantification (LLOQ) of 1 AU/mL with an overall CV and bias of 11.8% and − 2.5%, respectively. In conclusion, we developed a LC-MS/MS-based method to quantify active polyclonal rabbit ATG in human plasma. We suggest that this novel assay can be used to monitor and optimize dosing of ATG in clinical practice.

Efficacy and safety of antibody induction therapy in the current era of kidney transplantation.

Antibody induction with polyclonal rabbit-antithymocyte globulin (rATG) or an interleukin-2 receptor antagonist (IL-2RA) is widely used in kidney transplantation. Collaborative Transplant Study data from 38 311 first deceased-donor kidney transplants (2004-13) were analysed. Transplants were classified as 'normal risk' or 'increased risk' according to current guidelines. Cox regression analysis was applied to subpopulations of propensity score-matched recipients. rATG or IL-2RA induction was given to 64% of increased-risk and 53% of normal-risk patients, respectively. rATG and IL-2RA induction were each associated with reduced risk for graft loss versus no induction in increased-risk patients [hazard ratio (HR) 0.85, P = 0.046 and HR 0.89, P = 0.011, respectively]. The HR values for incidence of treated rejection in increased-risk patients for rATG and IL-2RA versus no induction were 0.75 (P = 0.037) and 0.77 (P < 0.001), respectively. In the normal risk subpopulation, neither induction therapy significantly affected the risk of graft loss or treated rejection. Hospitalization for infection was increased by rATG (P < 0.001) and IL-2RA (P < 0.001) induction. In contrast to patients transplanted during 1994-2003, among patients transplanted during 2004-13, rATG did not significantly affect the risk of non-Hodgkin's lymphoma versus no induction (P = 0.68). Induction therapy following kidney transplantation should be targeted to increased-risk transplants. In this analysis, a beneficial effect of antibody induction in normal-risk transplants could not be demonstrated.

The impact of terminal complement blockade on the efficacy of induction with polyclonal rabbit antithymocyte globulin in living donor renal allografts

BackgroundEculizumab, a potent inhibitor of terminal complement activation, appears promising in reducing early antibody-mediated rejection in positive crossmatch kidney transplantation. However, its concomitant use with polyclonal rabbit antithymocyte globulin (rATG) might reduce the efficacy of rATG. This study aimed to evaluate the effect of eculizumab on the efficacy of rATG in vivo and determine the role of complement in rATG-induced lymphocyte cell depletion. Patients and methodsThirty-six kidney transplant recipients were classified into 3 groups according to induction regime: anti-IL-2 receptor antibody alone induction group (basiliximab, n=8); rATG induction (n=20), and rATG+eculizumab induction group (n=8). Peripheral blood T-cell subsets and NK cells were measured 3–4days after transplant (after 3 doses of rATG). ResultsCompared to anti-IL-2 receptor antibody induction group, both groups treated with rATG demonstrated significant depletion of all T-cell subsets (CD3-positive cells) (P<0.0001 for rATG vs. anti-IL-2 receptor antibody induction group; P<0.001 for rATG+eculizumab vs. anti-IL-2 receptor antibody group). However, while T-cell counts were low in all rATG-treated patients, eculizumab treatment resulted in higher peripheral blood T-cell counts in rATG treated patients (P=0.005). Before induction, median total lymphocyte counts were normal for the three study groups. By 1, 4months and 1year, median the total lymphocyte count was normal for the anti-IL-2 receptor antibody group but was below normal range or at the lower edge of normality for rATG and rATG+eculizumab groups. ConclusionsThis small-sample size study suggests that peripheral T cells are depleted by rATG in the presence of terminal complement inhibition. However, eculizumab appears to have a mild inhibitory effect on peripheral blood T-cell depletion by rATG in kidney transplant recipients.

Polyclonal Rabbit Antithymocyte Globulin Induces Apoptosis and Has Cytotoxic Effects on Human Leukemic Cells

The possibility of antileukemic activity of antithymocyte globulin (ATG) was investigated in 8 human leukemic cell lines and primary leukemic cells from 15 leukemia patients. The study demonstrated that ATG induced apoptosis and reduced proliferation in both cell lines and primary leukemic cells, particularly in lymphatic origin cells, indicating that ATG has broad-spectrum antileukemic activity, especially for cells of lymphatic origin. Polyclonal ATGs are currently used to prevent graft-versus-host disease in allogeneic stem cell transplantation patients and to treat patients with severe aplastic anemia. It contains antibodies against antigens expressed on various hematopoietic cells, we hypothesized that it induces cell death not only in healthy cells but also in malignant hematopoietic cells. In this study, several human leukemic cell lines and primary leukemic cells from 15 patients with leukemia were used to investigate the ability of polyclonal ATGs to induce apoptosis and proliferation. Polyclonal ATGs induced cell apoptosis in primary leukemic cells and in cell lines in a dose-dependent manner, and induced apoptosis in different populations through a variety of targets. Cell proliferation was significantly reduced in the presence of polyclonal ATGs; it arrested cells in the G0-G1 phase by cell cycle analysis. Treatment with polyclonal ATGs plus complement increased cytolysis of the leukemic cells; complement augments polyclonal ATG-induced leukemic cell death. These data show that polyclonal ATG has broad-spectrum antileukemic activity, especially for cells of lymphatic origin, as it induced cell death through a variety of targets. This study provides an experimental basis for the application of polyclonal ATGs in allogeneic hematopoietic stem cell transplantation and in patients with lymphatic leukemia.

Regulatory T cells in kidney transplant recipients: the effect of induction immunosuppression therapy

Regulatory T cells have been suggested to down-regulate the alloimmune response. The aim of this prospective open study was to evaluate the effects of different inductive agents on peripheral blood regulatory T cells in kidney transplant patients and to analyse their association with short-term graft outcome. Regulatory and effector T cell numbers in peripheral blood were determined by flow cytometry in 71 prospectively followed kidney transplant recipients at postoperative day 0, 7, 14, 21, 28, 60 and 90. Patients were treated with a calcineurin inhibitor-based triple immunosuppression with polyclonal rabbit anti-thymocyte globulin (rATG, n = 28), basiliximab, the anti-CD25 monoclonal antibody (n = 18) or without induction (controls, n = 25). Flow cytometry data were correlated to rejection incidence. Compared to controls, CD4(+)CD25(+)FoxP3(+) regulatory T-cell expansion among CD4(+) T cells was noticed in the rATG group at all post-transplant time-points by Day 14 (P < 0.001). A significant decrease in Treg frequency (P < 0.001) and concurrently a transient increase of CD4(+)CD25(low/-)FoxP3(+) population were observed in basiliximab-treated patients 7-60 days post-transplantation. Biopsy-proven acute rejection occurred in 16.7% of controls, 10.7% of the rATG group and in 11.1% of the basiliximab group. Higher CD4(+)FoxP3(+)/CD8(+)CD45RA(+)CD62L(-) ratios were observed repeatedly in those patients after basiliximab induction who were rejection free (P < 0.01). In this study, the rATG induction therapy was associated with an expansion of regulatory cells. Sustained high CD4(+)FoxP3(+)/Teff ratios were associated with the absence of rejection after basiliximab induction.

Natural killer cell receptor—Repertoire and functions after induction therapy by polyclonal rabbit anti-thymocyte globulin in unsensitized kidney transplant recipients

Polyclonal rabbit anti-thymocyte globulin (rATG) is widely used in solid organ transplantation (SOT) as induction therapy or to treat corticosteroid-resistant rejection. In vivo, the effect of rATG on natural killer (NK) cells has not been studied. These cells are of particular relevance after SOT because classical immunosuppressive drugs do not inhibit or even can activate NK cells. A cohort of 20 recipients at low immunological risk, that had been receiving rATG as induction therapy, was analyzed for receptor repertoire, cytotoxicity and capacity of NK cells to secrete IFN-γ before kidney transplantation and at different time points thereafter. NK cells expressed fewer killer-cell immunoglobulin-like receptors (KIR), fewer activating receptors NKG2D, but more inhibitory receptor NKG2A compatible with an immature phenotype in the first 6 months post transplantation. Both cytotoxicity of NK cells and the secretion of IFN-γ were preserved over time after transplantation.

Targeting of Natural Killer Cells by Rabbit Antithymocyte Globulin and Campath-1H: Similar Effects Independent of Specificity

T cell depleting strategies are an integral part of immunosuppressive regimens widely used in the hematological and solid organ transplant setting. Although it is known to induce lymphocytopenia, little is known about the effects of the polyclonal rabbit antithymocyte globulin (rATG) or the monoclonal anti-CD52 antibody alemtuzumab on Natural Killer (NK) cells in detail. Here, we demonstrate that induction therapy with rATG following kidney/pancreas transplantation results in a rapid depletion of NK cells. Treatment of NK cells with rATG and alemtuzumab in vitro leads to impairment of cytotoxicity and induction of apoptosis even at a 10-fold lower concentration (0.1 µg/ml) compared with T and B cells. By generating Fc-parts of rATG and alemtuzumab we illustrate that their ligation to FcγRIII (CD16) is sufficient for the significant induction of degranulation, apoptosis and inflammatory cytokine release (FasL, TNFα and IFNγ) exclusively in CD3−CD56dim NK cells whereas application of rATG and alemtuzumab F(ab) fragments abolishes these effects. These findings are of general importance as our data suggest that NK cells are also mediators of the clinically relevant cytokine release syndrome and that their targeting by therapeutic antibodies should be considered as they are functionally relevant for the effective clearance of opportunistic viral infections and anti-tumor activity posttransplantation.

Proteasome Inhibition Causes Apoptosis of Normal Human Plasma Cells Preventing Alloantibody Production

Antibody production by normal plasma cells (PCs) against human leukocyte antigens (HLA) can be a major barrier to successful transplantation. We tested four reagents with possible activity against PCs (rituximab, polyclonal rabbit antithymocyte globulin (rATG), intravenous immunoglobulin (IVIG) and the proteasome inhibitor, bortezomib) to determine their ability to cause apoptosis of human bone marrow-derived PCs and subsequently block IgG secretion in vitro. IVIG, rituximab and rATG all failed to cause apoptosis of PCs and neither rituximab nor rATG blocked antibody production. In contrast, bortezomib treatment led to PC apoptosis and thereby blocked anti-HLA and antitetanus IgG secretion in vitro. Two patients treated with bortezomib for humoral rejection after allogeneic kidney transplantation demonstrated a transient decrease in bone marrow PCs in vivo and persistent alterations in alloantibody specificities. Total IgG levels were unchanged. We conclude that proteasome activity is important for PC longevity and its inhibition may lead to new techniques of controlling antibody production in vivo.

Mechanisms of Action of Thymoglobulin

Thymoglobulin (Genzyme Transplant, Cambridge, MA) is a polyclonal rabbit anti-thymocyte globulin that consists of a mixture of different antibody specificities that interact with immune response antigens, adhesion molecules, cell-trafficking molecules, and a variety of other antigens involved in heterogeneous pathways. Thymoglobulin acts as a rapid T-cell depleting agent, primarily through complement-dependent cell lysis in the blood compartment and apoptotic cell death in lymphoid tissues. Although the primary immunosuppressive effect is T-cell depletion, Thymoglobulin has also been shown to modulate cell surface markers, including a number of integrins and intercellular adhesion molecules that facilitate leukocyte adhesion to the endothelium. Treatment with Thymoglobulin has been shown to be associated with both short- and long-term changes in T-cell populations, generating altered homeostasis characterized by expansion of specific T-cell subsets that have been shown to exhibit regulatory suppressor functions. Further exploration of the mechanisms of action of Thymoglobulin will be important to guiding therapy with this widely used agent in the transplant setting, as well as in emerging therapeutic areas.

Therapeutic Antibody Agents for B-Cell Immunomodulation in Renal Transplantation

B cells are increasingly being recognized as a major contributor to both T- and B-cell mediated allograft rejection, and as a barrier to transplantation in allosensitized and autoimmune patients. B-cell functions of interest to solid organ and bone marrow transplantation include antibody production, antigen presentation, and provision of costimulatory signals for T-cell activation. Several therapeutic antibody preparations induce apoptosis or complement-mediated B-cell death, and hold promise for use as immunomodulating agents in solid organ transplantation. In this review, we discuss the anti-B-cell activity of polyclonal rabbit antithymocyte globulin (Thymoglobulin), the monoclonal antibodies, rituximab and alemtuzumab, and pooled intravenous human immunoglobulin.

Rescue cardiac transplantation for failing staged palliation in patients with hypoplastic left heart syndrome

Orthotopic heart transplantation is considered a rescue option for children with failing staged palliation or repair of hypoplastic left heart syndrome. We present our strategy for management, and outcomes, for these complex patients. We transplanted 68 consecutive children, with diagnoses of hypoplastic left heart syndrome in 31, cardiomyopathy in 20, and post-operative complex congenital heart disease in 17. Of these patients, 9 (13.2%) were neonates, and 46 (67.6%) were infants. Median age was 118.5 days. Operative technique involves bicaval cannulation and anastamoses with continuous low flow bypass, and either short periods of circulatory arrest or continuous low flow antegrade cerebral perfusion for reconstruction of the aortic arch. Initial reperfusion of the donor heart utilizes glutamate and aspartate substrate enriched white blood cell filtered cardioplegia. Immunosuppressive therapy includes induction (pulse steroids, gamma globulin, and polyclonal rabbit antithymocyte globulin) and initial maintenance (calcineurin inhibitor, an anti-proliferative agent, and a weaning steroid protocol). Of the 31 patients with hypoplastic left heart syndrome, 23 underwent primary transplantation, and 8 underwent rescue transplantation from failing staged palliation in seven, or attempted biventricular repair in one. Of the seven patients who had failing staged palliation, three had undergone only the Norwood Stage 1 operation, 2 had undergone a Norwood Stage 1 operation and a Glenn superior cavopulmonary anastomosis and two had undergone a Norwood Stage 1 operation, a Glenn superior cavopulmonary anastomosis, and a completion Fontan operation. The group undergoing primary transplantation was younger (p equals 0.007), weighed less (p equals 0.003), and waited longer for an appropriate donor heart (p equals 0.021) compared to those requiring rescue transplantation. No significant difference exists between the groups with regards to donor heart ischaemic time or post-transplant length of hospital stay. Thirty day survival (p equals 0.156) and overall survival (p equals 0.053) was better in those having primary transplantation, although these differences were not statistically significant when a p value of less than 0.05 is considered to be significant. In those having primary transplantation, no patients had elevated panel reactive antibody greater than 10%. Half of the 8 requiring rescue transplantation had panel reactive antibody greater than 10%, and this subgroup did especially poorly. Cardiac transplantation can offer children with failing staged palliation their only chance of survival. Transplantation, however, carries a high risk in this subgroup, especially in the setting of elevated panel reactive antibody.

Thymoglobulin (Polyclonal Rabbit Anti Thymocyte Globulin) Has In Vivo Activity in a Mouse Model of Myeloma.

Background: Multiple myeloma remains incurable with current approaches and newer therapies are needed to improve the outcome of these patients. While monoclonal antibody based therapies have been successful in some of the hematological malignancies, such approaches have had limited efficacy in the setting of myeloma. Thymoglobulin (polyclonal rabbit antithymocyte globulin, Genzyme) (Thymo) has been extensively evaluated in the setting of allogeneic blood and marrow transplantation and solid organ transplants. Given the polyclonal nature of this product, with antibodies against different B cell antigens, we evaluated the in vitro and in vivo activity of Thymo in myeloma.Methods: MM cell lines were cultured in RPMI 1640 containing 10% fetal bovine serum supplemented with L-Glutamine, penicillin, and streptomycin. The KAS-6/1 cell line was also supplemented with 1 ng/ml IL-6. Cytotoxicity following drug treatment was measured using the MTT viability assay. Apoptosis was measured by flow cytometry using Annexin V/PI in cell lines and Apo 2.7 in primary patient plasma cells. Shifts in expression of a variety of different B cell and plasma cell antigens were examined on several different myeloma cell lines following Thymo treatment in order to identify the potential antigenic targets. In vivo activity of thymo was evaluated in a SCID plasmacytoma model injected with RPMI myeloma cell lines.Results: rATG was cytotoxic in vitro to several MM cell lines (RPMI 8226, U266, OPM1, OPM2) including the IL-6 dependent cell line Kas6/1 with LC50 of around 1 mg/mL. Additionally, thymo was cytotoxic MM cell lines resistant to conventional agents such as doxorubicin (Dox40), melphalan (LR5) and dexamethasone (MM1R). Thymo induced apoptosis in MM cell lines and in patient derived primary myeloma cells. When tested in combination with other anti-myeloma agents an additive effect was seen with doxorubicin, PS341 and melphalan. Using competitive flow cytometry, we identified CD138, CD38, Cd45, CD126, CD49d (VLA4), as well as CD20 as antigens likely to be targeted by Thymo. Tumor bearing mice injected with Thymo at two different doses (5 mg/kg and 10 mg/kg for five days) had significantly delayed tumor growth compared to non-injected mice, and this translated into a better survival for these mice. Mice receiving 10 mg/kg dose had a slower tumor growth compared to 5 mg/kg dose (Figure).Conclusions: Thymoglobulin has promising in vitro and in vivo activity in the setting of myeloma. These studies will provide the rational for future clinical development of this agent in myeloma alone or in combination with other agents. Based on these results, we are in the process of initiating a clinical trial combining Thymo with Melphalan. [Display omitted]

Mechanisms of Platelet Activation by Antithymocyte Globulin (ATG).

We have previously shown that polyclonal rabbit ATG from Fresenius (ATG-F) can induce non-overt DIC in patients undergoing hematopoietic stem cell transplantation (HSCT) [Weber et al. 2003]. The compensated state of the coagulopathy suggested that the severe drop in platelet counts (>60%) observed in patients with normal pretreatment levels was not solely due to thrombin generation and platelet consumption. We thus further investigated the mechanisms of ATG-F-induced thrombocytopenia, hypothesizing that ATG-F had direct platelet-stimulating activity. Using an indirect flow cytometric binding assay we found that, compared to control IgG, ATG-F dose-dependently (1–100 μg/ml) bound to the surface of resting and TRAP-activated platelets, showing an up to 50fold increase in MFI at 50–100 μg/ml. In a washed platelet system, in which baseline positivity for CD62P was generally <15%, ATG-F alone had no effect on platelet aggregation. However, when platelets were primed with low concentrations of ADP (1–2 μM) or epinephrine (0.5 μM), ATG-F induced strong and stable aggregation of up to 80–100% in a dose-dependent manner (25–100 μg/ml), whereas control IgG did not. The priming effect of ADP was dependent on both P2Y1 and P2Y12 as evidenced by respective ADP receptor antagonists. Preincubation of platelets with inhibitory CD32 mAb completely abolished ATG-F-induced platelet aggregation, suggesting that clustering of, and signalling through, FcγRIIA was crucial for this platelet response. Similarly, ATG-F-derived F(ab′)2 had no effect on ADP-triggered platelet aggregation. Furthermore, preliminary studies indicated that responsiveness of platelet donors to ATG-F was associated with the FcγRIIA-R/R131 polymorphism, which has previously been shown to confer increased in vitro platelet responsiveness to heparin/PF4 antibodies from patients with HIT. In a 14C-serotonin release assay, in which prolonged incubation at 370C under shaking conditions increases baseline platelet activation and ensures constant platelet-platelet contacts, ATG-F (100 μg/ml), but not control IgG, induced strong FcγRIIA-dependent dense-granule release of up to 80%. In contrast, using diluted platelet-rich plasma under static conditions, ATG-F had only minor effects on platelet activation, increasing CD62P+ platelets from 2±1 to 15±5% (n=5). In a cohort of 16 consecutive HSCT patients receiving ATG-F, two patients were identified with normal pretreatment platelet counts and soluble CD62P (sCD62P) plasma levels of >51 ng/ml (mean+2SD of 23 controls). In these patients, an ATG-F-induced drop in platelet count to 38 and 19% of baseline was associated with a 1.7 and 2.2fold increase in sCD62P, respectively, indicating further platelet activation. In summary, strong binding of ATG-F to resting platelets may accelerate their clearance by the reticulo-endothelial system, thus contributing to the pathophysiology of thrombocytopenia. While ATG-F alone had negligible effects on resting platelets, it significantly enhanced activation of prestimulated platelets. Patients with normal-to-high platelet counts and evidence of in vivo platelet activation may especially be prone to this potentially hazardous side effect.

Ten-year Follow-up of a Prospective, Randomized Trial of BT563/BB10 Versus Anti-thymocyte Globulin as Induction Therapy After Heart Transplantation

Alloantigen-activated T cells express high-affinity interleukin-2 receptor (IL-2R). Specific blockade of this receptor has been associated with lower rejection episodes in clinical transplantation when compared with placebo. The first short-term results of the newer IL-2R antagonists are becoming available but little is known about the long-term effects of these drugs. The aim of the study was to compare the clinical efficacy of the IL-2R antagonist BT563 with polyclonal rabbit anti-thymocyte globulin (ATG) in heart transplant recipients. Forty patients undergoing cardiac transplantation were randomly assigned to receive either BT563 or rabbit ATG as induction therapy, combined with triple immunosuppression thereafter. Ten-year surveillance for rejection, infection, allograft vasculopathy and tumorgenicity was performed. Allograft rejection and vasculopathy were assessed by endomyocardial biopsy and coronary angiography, respectively. Screening for infection included blood, urine or tracheobronchial cultures and serology. No difference was detected in terms of 10-year survival between the two groups (50% for the IL-2R group and 70% for the ATG group, p = 0.16). Actuarial incidence of severe rejection was significantly higher in the IL-2R group (55% vs 10% at 10 years post-operatively, p = 0.028; 55% vs 5% during the first month post-operatively, p = 0.0005). Patients receiving ATG had a higher incidence of viral infection. Freedom from allograft vasculopathy was significantly higher in the ATG group (80% vs 60%, p = 0.031). BT563/BB10 is less effective than ATG for prevention of both acute allograft rejection and allograft vasculopathy after cardiac transplantation. Clinically relevant infections or tumorgenicity were not increased with the use of ATG.

Apoptosis and complement-mediated lysis of myeloma cells by polyclonal rabbit antithymocyte globulin

AbstractCurrent monoclonal antibody therapies for multiple myeloma have had limited success, perhaps due to narrow target specificity. We have previously described the ability of polyclonal rabbit antithymocyte globulin (rATG) to induce caspase- and cathepsin-mediated apoptosis in human B and plasma cells. We now extend this observation to myeloma cells. Complement independent cell death was measured after addition of rATG (1-1000 μg/mL) to cultures of myeloma cell lines or primary CD138+ isolates from patient bone marrow aspirates. rATG induced significant levels of apoptosis in myeloma cells as assayed by caspase induction, annexin V binding, subdiploid DNA fragmentation, plasma-membrane permeability, and loss of mitochondrial-membrane potential. Addition of complement greatly augmented myeloma-cell death. Binding of rATG to individual myeloma cell-surface proteins, primarily CD38, CD52, CD126, and CD138, was demonstrated by competitive inhibition experiments with targeted monoclonal antibodies. Three pathways of cell death were identified involving caspase activation, cathepsin D, and the genistein sensitive tyrosine kinase pathway. F(ab′)2 fragments of rATG had reduced proapoptotic activity, which was restored by coincubation with Fc fragments, and anti-CD32 or anti-CD64 antibodies. We conclude that rATG is an effective agent for in vitro induction of apoptosis in multiple myeloma, and that exploratory clinical trials may be warranted.

Thymoglobulin (Polyclonal Rabbit Anti Thymocyte Globulin) Has In Vitro Activity in Multiple Myeloma.

Background: Multiple myeloma is a plasma cell malignancy that remains incurable with current approaches and newer therapies are needed to improve the outcome of patients with MM. While monoclonal antibody base therapies have been successful in some of the hematological malignancies, especially lymphoma, such approaches have not been very useful in the setting of myeloma. Targeting of antigens like CD138 on the myeloma cell surface has been hampered by the ubiquitous nature of this protein in the body. Thymoglobulin (polyclonal rabbit antithymocyte globulin, Genzyme) has been extensively evaluated in the setting of allogeneic blood and marrow transplantation and is currently in clinical use. Given the polyclonal nature of this product, it has antibodies against several B cell antigens and forms the rationale for its evaluation in B cell malignancies like myeloma.Methods: MM cell lines were cultured in RPMI 1640 containing 10% fetal bovine serum supplemented with L-Glutamine, penicillin, and streptomycin. The KAS-6/1 cell line was also supplemented with 1 ng/ml IL-6. Cytotoxicity following drug treatment was measured using the MTT viability assay. Drug induced apoptosis in the cell lines was measured by flow cytometry after staining with Annexin V-FITC and propidium iodide (PI). Apoptosis in primary patient derived plasma cells following treatment was measured after staining for Apo 2.7.Results: rATG was cytotoxic in vitro to several MM cell lines (RPMI 8226, U266, OPM1, OPM2) including the IL-6 dependent cell line Kas6/1. The LC50 in most of the cytotoxicity assays was around 1 mg/mL. Additionally, rATG was cytotoxic MM cell lines resistant to conventional agents such as doxorubicin (Dox40), melphalan (LR5) and dexamethasone (MM1R). The drug retained its cytotoxicity when myeloma cells were grown in the presence of various cytokines like IL-6, IGF-1 and VEGF. rATG treatment resulted in a time and dose dependent induction of apoptosis in MM cell lines. rATG was also able to induce apoptosis of freshly isolated myeloma cells from patient marrows. When tested in combination with other anti-myeloma agents an additive effect was seen with doxorubicin, PS341 and melphalan.Conclusions: Thymoglobulin appear to have in vitro activity against various myeloma cell lines as well as patient derived primary myeloma cells. Ability of the drug to overcome resistance to conventional drugs as well as the effect of combining rATG with these agents points towards non-overlapping mechanisms of action. Ongoing studies are trying to identify the particular B-cell antigens that are targeted by correlating response to expression of various B cell antigens expressed by these cell lines. These studies will provide the rational for future clinical development of this agent in myeloma alone or in combination with other agents.