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

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

Outcomes of patients with hematological malignancies who undergo unrelated donor hematopoietic stem cell transplantation with ATG-Fresenius versus ATG-Genzyme

To compare the outcomes of patients with hematological malignancies who received ATG-Fresenius (ATG-F) 20 mg/kg versus those who received ATG-Genzyme (ATG-G) 10 mg/kg in an unrelated donor hematopoietic stem cell transplantation (HSCT) procedure, a total of 186 patients who underwent their first allogeneic HSCT with an unrelated donor were retrospectively analyzed. One hundred and seven patients received ATG-F, and seventy-nine patients received ATG-G. Multivariate analysis showed that the type of ATG preparation had no effect on neutrophil engraftment (P = 0.61), cumulative incidence of relapse (P = 0.092), nonrelapse mortality (P = 0.44), grade II-IV acute graft-versus-host disease (GVHD) (P = 0.47), chronic GVHD (P = 0.29), overall survival (P = 0.795), recurrence-free survival (P = 0.945) or GVHD-free relapse-free survival (P = 0.082). ATG-G was associated with a lower risk of extensive chronic GVHD and a higher risk of cytomegaloviremia (P = 0.01 and HR = 0.41, P < 0.001 and HR = 4.244, respectively). The results of this study suggest that the preparation of rabbit ATG used for unrelated HSCT should be selected based on the incidence of extensive chronic GVHD of each center, and the posttransplant management strategy should be adjusted according to the ATG preparation.

Comparison of 2 Different Rabbit Anti-Thymocyte Globulin (r-ATG) Preparations: Thymocyte r-ATG versus T Lymphoblast Cell Line r-ATG in Allogeneic Hematopoietic Stem Cell Transplantation for Acquired Severe Aplastic Anemia: Propensity Score-Matched Analysis

We retrospectively analyzed the outcomes of 214 patients with severe aplastic anemia (SAA) who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT) with rabbit anti-thymocyte globulin (r-ATG) or ATG-Fresenius (ATG-F). Using propensity score matching, we performed a case-control study comparing 44 and 23 patients in the r-ATG and ATG-F groups, respectively. The median time was 11 versus 11 days (P = .368) for myeloid engraftment and 11 versus 13 days (P = .030) for platelet engraftment in the r-ATG and ATG-F groups, respectively. The r-ATG group showed a lower incidence of grade III to IV acute graft-versus-host disease (GVHD) than the ATG-F group (2.27% versus 17.39%, P = .026). Similar outcomes were observed between the r-ATG and ATG-F groups for infection rate (59.09% versus 56.52%, P = .840), grade II to IV acute GVHD (20.45% versus 21.74%, P = .948), overall incidence of chronic GVHD (26.83% versus 22.73%, P = .704), moderate to severe chronic GVHD (9.76% versus 13.64%, P = .648), and transplantation-related mortality (11.36% versus 4.35%, P = .614). There was no statistical difference in 5-year overall survival (86.40% versus 95.7%, P = .245); GVHD-free, failure-free survival (77.30% versus 78.30%, P = .986); or health-related quality of life (P > .05) between r-ATG and ATG-F.

Allogeneic hematopoietic stem cell transplantation for aplastic anemia with pre-transplant conditioning using fludarabine, reduced-dose cyclophosphamide, and low-dose thymoglobulin: A KSGCT prospective study

The optimal pre-transplant conditioning for aplastic anemia (AA) remains unclear. We performed a prospective study on allogeneic transplantation from a related or unrelated donor for adult patients with AA. We assessed whether reduced-dose cyclophosphamide (CY) could decrease toxicity while maintaining engraftment, and low-dose thymoglobulin could safely prevent graft-vs-host disease (GVHD). The pre-transplant conditioning regimen consisted of fludarabine 120 mg/m² , CY 100 mg/kg, and thymoglobulin 2.5 mg/kg with or without 2 Gy of total body irradiation. Twenty-seven patients with a median age of 36 years were analyzed. Sixteen patients received graft from related donors. The stem cell source was bone marrow in 26 patients. All of the patients but one, who died early, achieved neutrophil engraftment at a median of 19 days. Mixed chimerism was observed in six and five patients at days 30 and 90, respectively. Only one patient experienced secondary engraftment failure with complete donor-type chimerism. None of the patients developed severe acute GVHD. The cumulative incidence of chronic GVHD was 37.7% at 1 year. The overall survival rate was 96.3% at 1 year and 3 years. A high EB virus-DNA load was detected in one patient at days 60. No one developed EBV-lymphoproliferative disorder within a year. The results suggest that the conditioning regimen in this study was safe and effective. However, relatively high incidence of chronic GVHD needs further improvement.

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.

Early and Long-Term Impaired T Lymphocyte Immune Reconstitution after Cord Blood Transplantation with Antithymocyte Globulin

Immune reconstitution is crucial to the success of allogeneic hematopoietic stem cell transplantation. Umbilical cord blood transplantation (UCBT) has been associated with delayed immune reconstitution. We characterized the kinetics and investigated the risk variables affecting recovery of the main lymphocyte subsets in 225 consecutive pediatric and adult patients (males, n = 126; median age, 15; range, .3 to 60; interquartile range, 4 to 35) who underwent myeloablative single UCBT between 2005 and 2015 for malignant and nonmalignant disorders. Low CD4⁺ and CD8⁺ T cell counts were observed up to 12 months after UCBT. In contrast, B and natural killer cells recovered rapidly early after transplantation. In a multivariate regression model, factors favoring CD4⁺ T cell recovery ≥ 200 cells/µL were lower dose antithymocyte globulin (ATG) (hazard ratio [HR], 3.93; 95% confidence interval [CI], 2.3 to 5.83; P = .001), negative recipient cytomegalovirus (CMV) serostatus (HR, 3.76; 95% CI, 1.9 to 5.74; P = .001), and younger age (HR, 2.61; 95% CI, 1.01 to 3.47; P = .03). Factors favoring CD8⁺ T cell recovery ≥ 200 cells/µL were lower dose ATG (HR, 3.03; 95% CI, 1.4 to 5.1; P = .03) and negative recipient CMV serostatus (HR, 1.9; 95% CI, 1.63 to 2.15; P = .01). Our results demonstrate the significant negative impact of ATG on lymphocyte recovery. A reduction of the dose or omission of ATG could improve immune reconstitution and perhaps reduce opportunistic infections after UCBT.

Immune reconstitution after cord blood transplantation: peculiarities, clinical implications and management strategies

Umbilical cord blood (UCB) is now widely used as an alternative hematopoietic stem cell source for patients lacking closely matched related or unrelated adult donors. UCB transplantation has traditionally been associated with delayed engraftment, poor immune reconstitution and consequent increased risk of infection. More recent clinical studies, however, suggest that conditioning regimens and in particular the omission of in vivo T-cell depletion may play a crucial role in post-transplant T-cell expansion, facilitating a uniquely rapid immune recovery after UCB transplantation. The peculiar characteristics of UCB cells, the importance of thymic function and the role of conditioning regimens and graft-versus-host disease influencing immune reconstitution are described. The last part of the review reports available data on UCB, as well as third-party peripheral blood derived anti-viral cell therapy, which provides a novel approach to rescue UCB recipients with viral complications in the post-transplant period.

Comparing Two Types of Rabbit ATG prior to Reduced Intensity Conditioning Allogeneic Hematopoietic SCT for Hematologic Malignancies

Different rabbit polyclonal antilymphocyte globulins (ATGs) are used in allogeneic hematopoietic stem cell transplantation (alloHSCT) to prevent graft-versus-host disease (GvHD). We compared 2 different ATGs in alloHSCT after reduced intensity conditioning (RIC) for hematological malignancies. We reviewed 30 alloHSCT for hematologic malignancies performed between 2007 and 2010 with fludarabine and i.v. busulfan as conditioning regimen. Patients alternatingly received Thymoglobulin or ATG-F. Median followup was 3.3 (2.5-4.5) years. Adverse events appeared to occur more frequently during Thymoglobulin infusion than during ATG-F infusion but without statistical significance (P = 0.14). There were also no differences in 3-year overall survival (OS), disease-free survival (DFS), relapse incidence, and transplant related mortality (TRM) in the Thymoglobulin versus ATG-F group: 45.7% versus 46.7%, 40% versus 33.7%, 40% versus 33.3%, and 20% versus 33.3%. The same held for graft failure, rejection, infectious complications, immune reconstitution, and acute or chronic GvHD. In patients transplanted for hematologic malignancies after RIC, the use of Thymoglobulin is comparable to that of ATG-F in all the aspects evaluated in the study. However due to the small number of patients in each group we cannot exclude a possible difference that may exist.

Rabbit antithymocyte globulin as first-line therapy for severe aplastic anemia

Rabbit antithymocyte globulin (rATG) was proven effective as salvage therapy for refractory aplastic anemia (AA), or for relapse after initial therapy with horse ATG (hATG). Several clinical trials were performed to assess the efficiency of rATG as a first-line therapy for AA patients; however, their results were variable. The aim of the present study was to assess hematologic response and survival in severe AA (SAA) and very severe AA (VSAA) patients treated with rATG and cyclosporin A (CsA) in our center. The factors involved in these outcomes were also explored. A total of 292 patients with newly diagnosed, acquired SAA or VSAA received a combination of rATG and CsA as first-line therapy, and the results were retrospectively assessed. The median age was 18 years (range = 2-73 years). The early death rate was 5.5%, and the total response rates were 49.0% (143 responders), 60.3% (176 responders), 65.8% (192 responders), and 68.5% (200 responders) at 3, 6, 9, and 12 months, respectively, after immunosuppressive therapy. In multivariate analysis, initial response to granulocyte colony-stimulating factor (G-CSF) was the predictive factor for response to therapy at 12 months. Median follow-up of surviving patients was 34 months (range = 0-117 months). Five-year overall survival was 83.2%, and the 5-year, event-free survival was 67.2%. Independent prognostic factors for overall survival were neutrophil count and achievement of any response following rATG therapy. Our results indicate that rATG/CsA is a safe and effective first-line treatment for SAA/VSAA.

Induction of suppressive allogeneic regulatory T cells via rabbit antithymocyte polyclonal globulin during homeostatic proliferation in rat kidney transplantation

Experimental studies have shown that rabbit antithymocyte polyclonal globulin (ATG) can expand human CD4+CD25++Foxp3+ cells (Tregs). We investigated the major biological effects of a self-manufactured rabbit polyclonal anti-rat thymoglobulin (rATG) in vitro, as well as its effects on different peripheral T-cell subsets. Moreover, we evaluated the allogeneic suppressive capacity of rATG-induced Tregs in an experimental rat renal transplant model. Our results show that rATG has the capacity to induce apoptosis in T lymphocyte lymphocytes as a primary mechanism of T-cell depletion. Our in vivo studies demonstrated a rapid but transient cellular depletion of the main T cell subsets, directly proportional to the rATG dose used, but not of the effector memory T cells, which required significantly higher rATG doses. After rATG administration, we observed a significant proliferation of Tregs in the peripheral blood of transplanted rats, leading to an increase in the Treg/T effector ratio. Importantly, rATG-induced Tregs displayed a strong donor-specific suppressive capacity when assessed in an antigen-specific allogeneic co-culture. All of these results were associated with better renal graft function in rats that received rATG. Our study shows that rATG has the biological capacity immunomodulatory to promote a regulatory alloimmune milieu during post-transplant homeostatic proliferation.

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.

Comparison of different rabbit ATG preparation effects on early lymphocyte subset recovery after allogeneic HSCT and its association with EBV-mediated PTLD

PURPOSE

Rabbit antithymocyte globulin (ATG) is commonly used before allogeneic hematopoietic stem cell transplantation (allo-HSCT) to prevent graft-versus-host disease. Studies comparing the effect of different ATG preparations and dosages on immune reconstitution and risk for Epstein-Barr virus (EBV)-mediated post-transplant lymphoproliferative disorder (PTLD) are rare.

METHODS

In this retrospective study, we determined T and B cell subsets by flow cytometry after allo-HSCT in children, who received ATG-Genzyme (ATG-G, n = 15), ATG-Fresenius (ATG-F, n = 25) or no-ATG treatment (n = 19). Additionally, PCR-quantified EBV-genome copy counts were correlated with incidence of PTLD.

RESULTS

We could confirm a dose-dependent impairment of CD8(+) and CD4(+) T cell regeneration by ATG-G, including naïve and memory CD4(+) T cells. No differences were seen between the currently applied dosages of 5-10 mg/kg ATG-G and 20-60 mg/kg ATG-F. Significantly delayed T cell subset reconstitution was determined only at high dosages of 20-60 mg/kg ATG-G compared to ATG-F. B cell reconstitution was comparably impaired in ATG-G- and ATG-F-treated patients. Although the incidence of EBV reactivation was similar in both ATG groups, EBV copy counts of >10(4) copies/10(5) peripheral blood mononuclear cells and the occurrence of PTLD were only found in ATG-G-treated patients.

CONCLUSIONS

We conclude that high, but importantly not currently applied low dosages of ATG-G, impair thymic T cell regeneration and memory T cell immunity to a greater extent than ATG-F in pediatric patients. In addition, our results suggest an increased risk for EBV-PTLD when treated with ATG-G. Prospective studies are warranted to compare different ATG preparations with regard to the immune reconstitution and EBV-PTLD.

A combination of fludarabine, half-dose cyclophosphamide, and anti-thymocyte globulin is an effective conditioning regimen before allogeneic stem cell transplantation for aplastic anemia

Conditioning regimens consisting of reduced-dose cyclophosphamide (CY) and fludarabine (FDR) have been investigated for use in allogeneic hematopoietic stem cell transplantation (allo-HSCT) in patients with aplastic anemia to reduce the toxicities associated with CY. However, the ideal dose of CY has not been identified. In addition, little information is available regarding donor cell chimerism after allo-HSCT with these regimens. Therefore, we retrospectively analyzed 13 patients who underwent allo-HSCT with half-dose CY (100 mg/kg in total), FDR, and anti-thymocyte globulin at total doses of 2.5-10 mg/kg at our center. All the patients except one, who died due to encephalopathy on day 20, achieved neutrophil engraftment a median of 18.5 days after HSCT with complete donor-type chimerism. Two patients who received a graft from an HLA-matched donor subsequently developed mixed chimerism (MC) associated with transfusion-dependent cytopenia. One became transfusion-independent after donor lymphocyte infusion, but continues to exhibit MC. The other regained complete donor-type chimerism after the cessation of cyclosporine, but remains transfusion-dependent. These findings suggest that a conditioning regimen with half-dose CY and FDR is effective for achieving neutrophil engraftment and complete donor-type chimerism. However, subsequent MC may be observed, especially after HLA-matched HSCT.

Double umbilical cord blood transplantation in patients with hematologic malignancies using a reduced-intensity preparative regimen without antithymocyte globulin

Reduced-intensity conditioning (RIC) regimens in cord blood transplant (CBT) are increasingly utilized for older patients and those with comorbidities. However, the optimal conditioning regimen has not yet been established and remains a significant challenge of this therapeutic approach. Antithymocyte globulin (ATG) has been incorporated into conditioning regimens in order to decrease the risk of graft failure; however, use of ATG is often associated with infusion reactions and risk of post-transplant complications. We report the results of a non-ATG-containing RIC regimen, where patients received 2 Gy TBI unless they were considered to be at higher risk of graft failure, in which case they received 3 Gy of TBI. Thirty patients underwent CBT using this protocol for high-risk hematological malignancies. There was only one case of secondary and no cases of primary graft failure. At 1 year, estimates of non-relapse mortality, OS and PFS were 29%, 53% and 45%, respectively. The cumulative incidences of grade III-IV acute and chronic GVHD were 14% and 18%, respectively. In summary, the results of this study demonstrate that this non-ATG-containing conditioning regimen provides a low incidence of graft failure without increasing regimen-related toxicity.

Immune reconstitution after anti-thymocyte globulin-conditioned hematopoietic cell transplantation

BACKGROUND AIMS

Anti-thymocyte globulin (ATG) is being used increasingly to prevent graft-versus-host disease (GvHD); however, its impact on immune reconstitution is relatively unknown. We (i) studied immune reconstitution after ATG-conditioned hematopoietic cell transplantation (HCT), (ii) determined the factors influencing the reconstitution, and (iii) compared it with non-ATG-conditioned HCT.

METHODS

Immune cell subset counts were determined at 1-24 months post-transplant in 125 HCT recipients who received ATG during conditioning. Subset counts were also determined in 46 non-ATG-conditioned patients (similarly treated).

RESULTS

(i) Reconstitution after ATG-conditioned HCT was fast for innate immune cells, intermediate for B cells and CD8 T cells, and very slow for CD4 T cells and invariant natural killer T (iNKT) (iNKT) cells. (ii) Faster reconstitution after ATG-conditioned HCT was associated with a higher number of cells of the same subset transferred with the graft in the case of memory B cells, naive CD4 T cells, naive CD8 T cells, iNKT cells and myeloid dendritic cells; lower recipient age in the case of naive CD4 T cells and naive CD8 T cells; cytomegalovirus recipient seropositivity in the case of memory/effector T cells; an absence of GvHD in the case of naive B cells; lower ATG serum levels in the case of most T-cell subsets, including iNKT cells; and higher ATG levels in the case of NK cells and B cells. (iii) Compared with non-ATG-conditioned HCT, reconstitution after ATG-conditioned HCT was slower for CD4 T cells, and faster for NK cells and B cells.

CONCLUSIONS

ATG worsens the reconstitution of CD4 T cells but improves the reconstitution of NK and B cells.

Different outcomes between cyclophosphamide plus horse or rabbit antithymocyte globulin for HLA-identical sibling bone marrow transplant in severe aplastic anemia

The standard regimen for HLA-identical sibling bone marrow transplant (BMT) in severe aplastic anemia (SAA) is cyclophosphamide (Cy) and horse antithymocyte globulin (ATG). Horse ATG has been replaced by rabbit ATG in many countries due to the unavailability of the former product. This study was designed to assess if these ATG preparations are interchangeable in the preparative regimen for matched related BMT in SAA. Forty consecutive BMTs were retrospectively analyzed: 20 received Cy plus horse ATG and 20 received Cy plus rabbit ATG as the preparative regimen. Conditioning with rabbit ATG was protective against acute graft-versus-host disease (aGVHD) grades II-IV and moderate-severe chronic GVHD (cGVHD), with incidence rates of 0% versus 35.2% (P = .009) and 0% versus 34.0% (P = .04), respectively. On day +100, the probability of proven/probable invasive fungal disease (IFD) was higher in patients conditioned with rabbit ATG, 31.2% versus 5.5%, respectively (P = .04). Earlier cytomegalovirus (CMV) reactivation (40 versus 50 days; P = .02) was observed with rabbit ATG. An inferior lymphocyte count on days +30 (0.360 versus 0.814 × 10(9)/L; P = .01) and +90 (0.744 versus 1.330 × 10(9)/L; P = .006) was noticed in recipients of rabbit ATG. The incidence of stable mixed chimerism was higher in recipients of rabbit ATG (18.2% versus 80%, respectively; P = .004). These results suggest that horse and rabbit ATG preparations have different biological and clinical properties and should not be used interchangeably in the preparative regimen for related BMT in SAA.

Apoptotic effects of antilymphocyte globulins on human pro-inflammatory CD4+CD28- T-cells

Background

Pro-inflammatory, cytotoxic CD4⁺CD28⁻ T-cells with known defects in apoptosis have been investigated as markers of premature immuno-senescence in various immune-mediated diseases. In this study we evaluated the influence of polyclonal antilymphocyte globulins (ATG-Fresenius, ATG-F) on CD4⁺CD28⁻ T-cells in vivo and in vitro.

Principal Findings

Surface and intracellular three colour fluorescence activated cell sorting analyses of peripheral blood mononuclear cells from 16 consecutive transplant recipients and short-term cell lines were performed. In vivo, peripheral levels of CD3⁺CD4⁺CD28⁻ T-cells decreased from 3.7±7.1% before to 0±0% six hours after ATG-F application (P = 0.043) in 5 ATG-F treated but not in 11 control patients (2.9±2.9% vs. 3.9±3.0%). In vitro, ATG-F induced apoptosis even in CD4⁺CD28⁻ T-cells, which was 4.3-times higher than in CD4⁺CD28⁺ T-cells. ATG-F evoked apoptosis was partially reversed by the broad-spectrum caspase inhibitor benzyloxycarbonyl (Cbz)-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD-fmk) and prednisolon-21-hydrogensuccinate. ATG-F triggered CD25 expression and production of pro-inflammatory cytokines, and induced down-regulation of the type 1 chemokine receptors CXCR-3, CCR-5, CX3CR-1 and the central memory adhesion molecule CD62L predominately in CD4⁺CD28⁻ T-cells.

Conclusion

In summary, in vivo depletion of peripheral CD3⁺CD4⁺CD28⁻ T-cells by ATG-F in transplant recipients was paralleled in vitro by ATG-F induced apoptosis. CD25 expression and chemokine receptor down-regulation in CD4⁺CD28⁻ T-cells only partly explain the underlying mechanism.