Jurkat cell-reactive anti-thymocyte globulin assessed ex vivo by flow cytometry persists three weeks in circulation

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.

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

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

A comparison of Jurkat cell-reactive anti-T lymphocyte globulin and fetal anti-thymocyte globulin preparations in the treatment of aplastic anemia

OBJECTIVE

The aim of this study was to investigate the success rate and effects on survival of different anti-thymocyte globulin (ATG) preparations in patients diagnosed with aplastic anemia.

SUBJECTS AND METHODS

Of the total 24 patients included in the study, 12 were male and 12 female with a median age of 44 years (range 16-72). Nine patients received Lymphoglobulin®, 7 Thymoglobulin® and ATG-Fresenius® (ATG-F). There was no significant difference between the three treatment groups in terms of severity of aplastic anemia.

RESULTS

The estimated 6-month survival rates for ATG-F, Lymphoglobulin and Thymoglobulin groups were 42.9, 77.8 and 71.4%, respectively. The difference in overall survival rates between groups was not significant, most likely due to the low number of patients. The most striking result was that none of the patients in the ATG-F preparation group showed any response to treatment. The ATG-F group was found to have a significantly inferior response rate (p = 0.07).

CONCLUSION

Our data showed that none of the patients responded to ATG-F treatment. Hence, despite the small number of the patients, we recommend that ATG-F should not be used for treatment of severe aplastic anemia.

Antithymocyte globulin impairs T-cell/antigen-presenting cell interaction: disruption of immunological synapse and conjugate formation

Antithymocyte globulin (ATG) is employed for the treatment and prevention of acute organ rejection after transplantation. However, the mechanisms underlying its immunomodulatory capacities beyond cellular depletion remains ill defined. A stable interaction between T-cells and professional antigen-presenting cells (APC) and full T-cell stimulation requires a complex molecular rearrangement at the T-cell/APC interface, the so called immunological synapse. Here we investigated, whether ATG affects T-cell/APC interactions. ATG concentration and time-dependently inhibited relocalization of the T-cell receptor/CD3 complex as well as adhesion molecules and cytoskeletal proteins of human peripheral blood T-cells and a human T-cell line towards the APC contact site. Moreover, ATG-treated peripheral blood T-cells were incapable to form conjugates with APCs. In conclusion, ATG impairs T-cell/APC conjugate formation, a mechanism that may help to understand the functional inactivation of peripheral blood T-cells that have escaped cellular depletion after ATG treatment.

Immunosuppressive therapy for acquired severe aplastic anemia (SAA): a prospective comparison of four different regimens

OBJECTIVE

This study was designed to investigate four different immunosuppressive therapy (IST) regimens as treatment of acquired severe aplastic anemia (SAA).

PATIENTS AND METHODS

142 consecutive SAA patients were randomized to receive one of the following IST regimens: equine anti-human thymocyte immunoglobulin (E-ATG) alone (IST regimen I); E-ATG and cyclosporine A (CSA) (IST regimen II); E-ATG, CSA plus recombinant human granulocyte-macrophage colony-stimulating factor (rhuGM-CSF) and rhu erythropoietin (rhuEPO) (IST regimen III); or rabbit ATG (ATG-F), CSA, rhuGM-CSF, and rhuEPO (IST regimen IV). No repeated courses of E-ATG or ATG-F were given for nonresponders. All patients also received stanozolol or testosteron propionate.

RESULTS

The overall response rate to IST regimen I was 58%. The response to IST regimen II (79%) was significantly higher (p = 0.04), more rapid and complete than after IST regimen I. The response rate to IST regimen IV (53%) was significantly lower than that of IST regimen III (73%, p = 0.039). The additional use of growth factors did not reduce early deaths and did not accelerate hematopoietic recovery after IST. Of the 142 patients enrolled in this trial, 92 (65%) are alive at a median follow-up time of 102 months (range, 54-166 months). The 5-year actuarial survival for IST regimens I, II, III, and IV was 58%, 81%, 80%, and 66%, respectively.

CONCLUSION

The combination of E-ATG and CSA remains the best combination for the treatment of SAA patients, producing a survival advantage at 5 years. The addition of growth factors did not improve these results. Rabbit ATG-F appeared less effective than E-ATG.

Comparison between antithymocyte globulin and alemtuzumab and the possible impact of KIR-ligand mismatch after dose-reduced conditioning and unrelated stem cell transplantation in patients with multiple myeloma

We compared antithymocyte globulin (ATG) with alemtuzumab in 73 patients with multiple myeloma, who underwent reduced conditioning with melphalan/fludarabine, followed by allogeneic stem cell transplantation from human leucocyte antigen-matched or -mismatched unrelated donors. The ATG group had more prior high-dose chemotherapies (P < 0.001), while bone marrow was used more as the stem cell source in the alemtuzumab group (P < 0.001). Alemtuzumab resulted in faster engraftment of leucocytes (P = 0.03) and platelets (P = 0.02) and in a lower incidence of acute graft versus host disease (GvHD) grades II-IV (24% vs. 47%, P = 0.06). More cytomegalovirus (CMV) seropositive patients in the alemtuzumab group experienced CMV reactivation (100% vs. 47%, P = 0.001). The cumulative incidence of treatment-related mortality at 2 years was 26% [95% confidence interval (CI) = 12-37%] for ATG vs. 28% (95% CI = 15-55%) for alemtuzumab, P = 0.7. There was no significant difference in the estimated 2-year overall and progression-free survival between ATG and alemtuzumab: 54% (95% CI: 39-75%) vs. 45% (95% CI: 28-73%) and 30% (95% CI: 16-55%) vs. 36% (95% CI: 20-62%) respectively. In multivariate analysis, treatment with alemtuzumab had a higher risk for relapse (hazard ratio: 2.37; P = 0.05) while killer immunoglobulin-like receptor (KIR)-ligand mismatch was protective for relapse (P < 0.0001). We conclude that alemtuzumab produced less acute GvHD, but higher probability of relapse. The data implicated a major role of KIR-ligand mismatched transplantation in multiple myeloma.

Antithymocyte Globulin Induces Ex Vivo and In Vivo Depletion of Myeloid and Plasmacytoid Dendritic Cells

We investigate the in vivo and ex vivo effect of rabbit antithymocyte globulin (ATG) on myeloid dendritic cells (MDCs) and plasmacytoid dendritic cells (PDCs). After incubation with ATG and complement, the mean number of MDCs and PDCs decreases from 3,168 to 739 x 10/mL (P=0.004) and from 5,314 to 790 x 10/mL (P=0.01), respectively. In vivo ATG given as part of the conditioning regimen before allogeneic stem-cell transplantation induces a stronger reduction of circulating MDCs and PDCs than chemotherapy alone (reduction: 100% vs. 78%-98%). These data show that ATG induces depletion of circulating MDCs and PDCs, which might be in addition to the T-cell depletion a further mechanism to reduce graft-versus-host disease after allogeneic stem-cell transplantation.

Reduced-intensity conditioning with busulfan and fludarabine with or without antithymocyte globulin in HLA-identical sibling transplantation – a retrospective analysis

It is unknown whether the addition of antithymocyte globulin (ATG) to reduced-intensity conditioning with busulfan (BU) and fludarabine (FLU) is beneficial in HLA-identical sibling transplantation. Therefore, we analyzed retrospectively data on 83 patients, who received peripheral blood stem cells from HLA-identical siblings after conditioning with either 8 mg/kg BU and 150 mg/m2 FLU (n=45) or 8 mg/kg BU, 180 mg/m2 FLU and 40 mg/kg ATG (n=38). Graft-versus-host disease (GVHD) prophylaxis consisted of CSA alone (n=32) or a combination with either MTX or MMF (n=51). The median age was 52 years. Graft failure occurred in two patients after BU/FLU and in three after BU/FLU/ATG (P=0.66). After conditioning with BU/FLU, platelet recovery was significantly faster (P=0.017), and less platelet (P<0.001) and red blood cell (P=0.002) support was needed. Incidences of acute GVHD grades II and IV were 46 and 49%, respectively. Limited chronic GVHD occurred more often after BU/FLU compared to BU/FLU/ATG (54 vs 23%, P=0.02). The overall survival, non-relapse and relapse mortality did not differ significantly. We conclude that in peripheral blood stem cell transplantation from HLA-identical siblings after reduced-intensity conditioning with BU and FLU, ATG has no major impact on the rate of graft rejection and acute GVHD, but it reduces the incidence of limited chronic GVHD.

ATG as part of the conditioning regimen reduces transplant-related mortality (TRM) and improves overall survival after unrelated stem cell transplantation in patients with chronic myelogenous leukemia (CML)

Matched unrelated donor transplants have an increased risk of severe graft-versus-host disease and transplant-related mortality (TRM). ATG has been introduced to decrease GvHD and to facilitate engraftment. We conducted a retrospective analysis of 333 patients with chronic myelogenous leukemia, who were treated with Fresenius ATG (n=145, average=90 mg/kg bw, range 40-90 mg/kg bw) or standard immunosuppression without ATG (n=188). Both groups were comparable regarding distribution of age, sex, HLA-matched vs mismatched donors. ATG Fresenius led to a faster leukocyte engraftment, decreased the incidence of acute GvHD and TRM (P=0.01 and P=0.03) and led to a significant better overall survival (70 vs 57%, P=0.03). We concluded that a prospective randomized study is needed to evaluate the definite role of ATG in hemopoietic stem cell transplantation.