Polyclonal Antithymocyte Globulin Research Articles

Induction of bona fide regulatory T cells after liver transplantation - the potential influence of polyclonal antithymocyte globulin

T-cell-depleting strategies are an integral part of immunosuppressive regimens used in the hematological and solid organ transplant setting. Besides prevention of alloreactivity, treatment with rabbit antithymocyte globulin (rATG) has been related to the induction of immunoregulatory T cells (Treg) in vitro and in vivo. To investigate Treg induced by rATG, we prospectively studied the effect of rATG induction therapy in liver-transplanted recipients in vivo (n = 28). Treg induction was further evaluated by means of Treg-specific demethylation region (TSDR) analysis within the FOXP3 locus. Whereas no induction of CD4(+) CD25(high) CD127(-) Treg could be observed by phenotypic analysis, we could demonstrate an induction of TSDR(+) T cells within CD4(+) T cells exclusively for rATG-treated patients in the long-term (day 540) compared with controls (P = NS). Moreover, although in vitro experiments confirm that rATG primarily led to a conversion of CD4(+) CD25(-) into CD4(+) CD25(+) T cells displaying immunosuppressive capacities, these cells cannot be classified as bona fide Treg based on their FOXP3 demethylation pattern. Consequently, the generation of Treg after rATG co-incubation in vitro does not reflect the mechanisms of Treg induction in vivo and therefore the potential clinical relevance of these cells for transplant outcome remains to be determined.

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.

Induction immunosuppressive therapies in renal transplantation

Induction immunosuppressive therapies for patients undergoing renal transplantation are reviewed. The goal of induction therapy is to prevent acute rejection during the early posttransplantation period by providing a high degree of immunosuppression at the time of transplantation. Induction therapy is often considered essential to optimize outcomes, particularly in patients at high risk for poor short-term outcomes. All of the induction immunosuppressive agents currently used are biological agents and are either monoclonal (muromonab-CD3, daclizumab, basiliximab, alemtuzumab) or polyclonal (antithymocyte globulin [equine] or antithymocyte globulin [rabbit]) antibodies. Although antithymocyte globulin (rabbit) is not labeled for induction therapy, it is used for this purpose more than any other agent. Basiliximab is not considered as potent an immunosuppressive agent but has a much more favorable adverse-effect profile compared with antithymocyte globulin (rabbit) and is most commonly used in patients at low risk for acute rejection. Rituximab is being studied for use as induction therapy but to date has not demonstrated any significant benefits over placebo. While head-to-head data are available comparing most induction agents, the final decision on the most appropriate induction therapy for a transplant recipient is highly dependent on preexisting medical conditions, donor characteristics, and the maintenance immunosuppressive regimen to be used. No standard induction immunosuppressive regimen exists for patients undergoing renal transplantation. Antithymocyte globulin (rabbit) is the most commonly used agent, whereas basiliximab appears safer. The choice of regimen depends on the preferences of clinicians and institutions.

Can We Eliminate Both Calcineurin Inhibitors and Steroids?

Calcineurin inhibitors (CNIs) and steroids, the cornerstone of most immunosuppressive regimens in the past 20 years, have undesirable chronic effects. This has led to the use of new strategies with sirolimus (SRL) and mycophenolate mofetil (MMF). In the SPIESSER study, de novo CNI avoidance and early steroid withdrawal were evaluated in 145 renal recipients randomized to receive either SRL ( n = 71) or cyclosporine (CsA; n = 74). All patients received polyclonal antithymocyte globulin for 5 days, MMF, and steroids withdrawn at 6 months. At 12 months, the incidence of biopsy-proven acute rejection was low (14.3% for SRL vs 8.6% for CsA). At 3 years, renal function (Nankivell) was better in the SRL group, particularly in patients who remained on treatment according to the protocol (71 ± 22 vs 60 ± 17 mL/min; P < .01). Steroids were withdrawn in 70.5% of SRL-treated patients and in 66.7% of CsA-treated patients. In the CONCEPT study, early conversion from CsA to SRL was evaluated in 192 renal recipients prospectively randomized at week 12 to switch from CsA to SRL ( n = 95) or to continue CsA ( n = 97). At 12 months, estimated glomerular filtration rate (Modification of Diet in Renal Disease) was significantly higher with SRL (61 ± 16 vs 54 ± 15 mL/min; P = .002, intent-to-treat analysis). The significant improvement in renal function was maintained at 30 months. In both studies graft and patient survival were similar, with better renal function and a tendency for fewer cancers observed at follow-up in patients receiving a maintenance regimen with SRL and MMF. At 30 months, steroids had been withdrawn in 72% of SRL-treated patients and in 70% of CsA-treated patients.

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.

A Novel Clinically Relevant Approach to Tip the Balance Toward Regulation in Stringent Transplant Model

Regulatory T cells (Tregs) actively regulate alloimmune responses and promote transplantation tolerance. Thymoglobulin, a rabbit polyclonal antithymocyte globulin (ATG), is a widely used induction therapy in clinical organ transplantation that depletes peripheral T cells. However, resistance to tolerance induction is seen with certain T-cell depleting strategies and is attributed to alterations in the balance of naive, memory and Tregs. The exact mechanism of action of ATG and its effects on the homeostasis and balance between Tregs and T-effector-memory cells (Tem) are unknown. A novel antibody reagent, rabbit polyclonal anti-murine thymocyte globulin (mATG), generated by the same process used to manufacture thymoglobulin, was used alone or in combination with CTLA4Ig or sirolimus (SRL) in a stringent fully major histocompatibility complex-mismatched murine skin allograft model to study graft survival and mechanisms involved. mATG depletes T cells but preferentially spares CD25+ natural Tregs which limit skewing of T-cell repertoire toward Tem phenotype among the recovering T cells. T-cell depletion with mATG combined with CTLA4Ig and SRL synergize to prolong graft survival by tipping the Treg/Tem balance further in favor of Tregs by preserving Tregs, facilitating generation of new Tregs by a conversion mechanism and limiting Tem expansion in response to alloantigen and homeostatic proliferation. Simultaneous T-cell depletion with ATG and costimulatory blockade, combined with SRL, synergizes to promote regulation and prolong allograft survival in a stringent transplant model. These results provide the rationale for translating such novel combination therapy to promote regulation in primate and human organ transplantation.

Sequential treatment of cytomegalovirus infection or disease with a short course of intravenous ganciclovir followed by oral valganciclovir: efficacy, safety, and pharmacokinetics

Oral (p.o.) or intravenous (IV) ganciclovir (GCV) has been the first-line agent for prevention and treatment of cytomegalovirus (CMV) infection and disease in solid organ transplantation (SOT). The introduction of p.o. valganciclovir, with higher bioavailability than p.o. GCV, has proven to be a suitable approach toward outpatient p.o. therapy for CMV infection/disease. The present single-arm, exploratory pilot trial performed with 21 patients investigates the efficacy and safety of a short therapeutic course (21 days) based on an initial IV treatment with GCV (5 mg/kg twice daily, for 5 days) followed by p.o. valganciclovir (900 mg twice daily, for 16 days) for CMV infection/disease in SOT patients. In all cases, doses were adjusted for renal function. Moreover, the study allowed comparison of exposure to GCV after p.o. valganciclovir with respect to IV GCV in the same patients. Response to treatment was monitored until day 180. Viral load eradication was achieved in 66.7% of patients, on day 21. Although not statistically significant, a trend was seen toward increased persistence of viral load on day 21 for patients with donor positive/recipient negative CMV serostatus or receiving either anti-rejection therapy or polyclonal anti-thymocyte globulin. CMV clinical infection recurred in 14.3% of patients, with higher recurrence rates in patients with risk factors for persistence of viremia. Exposures to GCV after using IV GCV or p.o. valganciclovir showed comparable values (P=0.054). This short course, combining initial IV GCV and subsequent p.o. valganciclovir, may provide effective exposure and therapeutic response in the treatment of CMV infection in SOT patients with adequate drug exposure and with the additional potential benefit of shortening the length of hospital stay, which may result in cost reduction and improved patient comfort.

New Approaches to De Novo Immunosuppression and Steroid Elimination

Calcineurin inhibitors (CNIs) and steroids, the cornerstone of most immunosuppressive regimens in the past 20 years, have undesirable long-term side effects. This has led to the investigation of potential new strategies with sirolimus (SRL) and mycophenolate mofetil (MMF). In the SPIESSER study, de novo CNI avoidance and early steroid withdrawal were evaluated in 145 renal recipients randomized to receive either SRL (n = 71) or cyclosporine (CsA; n = 74). All patients received polyclonal anti-thymocyte globulin (ATG) for 5 days, MMF, and steroids withdrawn at 6 months. At 12 months, patient and graft survival, incidence of biopsy-proven acute rejection (BPAR), and rates of steroid withdrawal were not statistically different (97% vs 97%, 90% vs 93%, 14.3% vs 8.6%, and 82.8% vs 84.1%, respectively). In patients who remained on treatment according to the protocol, estimated glomerular filtration rate (eGFR) was significantly higher with SRL (69 ± 19 vs 60 ± 14 mL/min; P < .01). In the CONCEPT study, early conversion from CsA to SRL was evaluated. One hundred ninety-two renal recipients were prospectively randomized at week 12 to switch from CsA to SRL (n = 95) or to continue CsA (n = 97). At 12 months, patient survival rates (100% vs 100%) and graft survival rates (100% vs 98%), incidence of acute rejection (17% vs 8%), and rates of steroid withdrawal (72% vs 78%) were not significantly different between the SRL and the CsA groups. eGFR was significantly higher with SRL (68.9 vs 64.4 mL/min; P = .017; intent-to-treat analysis). In both studies, a significant improvement in renal function was observed at 12 months in patients receiving a maintenance regimen with SRL and MMF. In addition, steroids could be withdrawn in 70% of these patients.

Anti–IL-2 Receptor Antibodies versus Anti-Thymocyte Globulin for Induction Therapy in Kidney Transplantation

The latest annual report from the Scientific Registry of Transplant Recipients showed that in 2006 21% of kidney recipients in the United States received no induction therapy at the time of transplantation, whereas 42% received anti-thymocyte globulin (ATG) and 29% received anti–IL-2 receptor antibodies.1 A number of different induction agents deplete T lymphocytes, including monoclonal OKT3 and polyclonal ATG, ATGAM, and ALG. Of these four, ATG (Thymoglobulin), made from rabbits immunized with thymocytes, has been used more frequently every year since its introduction in 1998, whereas use of the others has been negligible in the past 5 yr. MAbs to the IL-2 receptor (IL-2R Abs) block T cell activation and proliferation. The two Food and Drug Administration–approved IL-2R Abs, daclizumab (Zenapax) and basiliximab (Simulect), have similar efficacy and adverse effects, but basiliximab is administered as two doses within 4 d of transplantation, whereas daclizumab is administered as five infusions over 8 wk. This difference in convenience of administration likely explains the more frequent use of basiliximab.1 The IL-2R Abs were introduced in 1997, and their use increased until approximately 2001 but has declined somewhat since then with the rising popularity of ATG.1 Interestingly, no randomized, controlled trials of ATG versus placebo have been performed. In contrast, IL-2R Abs have been the subject of numerous placebo-controlled, randomized trials, …

Daclizumab versus Antithymocyte Globulin in High-Immunological-Risk Renal Transplant Recipients

Nondepleting anti-CD25 monoclonal antibodies (daclizumab) and depleting polyclonal antithymocyte globulin (Thymoglobulin) both prevent acute rejection, but these therapies have not been directly compared in a high-risk, HLA-sensitized renal transplant population. We randomly assigned 227 patients, who were about to receive a kidney graft from a deceased donor, to either Thymoglobulin or daclizumab if they met one of the following risk factors: current panel reactive antibodies (PRA) >30%; peak PRA >50%; loss of a first kidney graft from rejection within 2 yr of transplantation; or two or three previous grafts. Maintenance immunosuppression comprised tacrolimus, mycophenolate mofetil, and steroids. Compared with the daclizumab group, patients treated with Thymoglobulin had a lower incidence of both biopsy-proven acute rejection (15.0% versus 27.2%; P = 0.016) and steroid-resistant rejection (2.7% versus 14.9%; P = 0.002) at one year. One-year graft and patient survival rates were similar between the two groups. In a comparison of rejectors and nonrejectors, overall graft survival was significantly higher in the rejection-free group (87.2% versus 75.0%; P = 0.037). In conclusion, among high-immunological-risk renal transplant recipients, Thymoglobulin is superior to daclizumab for the prevention of biopsy-proven acute rejection, but there is no significant benefit to one-year graft or patient survival.

Rabbit Polyclonal Mouse Antithymocyte Globulin Administration Alters Dendritic Cell Profile and Function in NOD Mice to Suppress Diabetogenic Responses

Mouse antithymocyte globulin (mATG) prevents, as well as reverses, type 1 diabetes in NOD mice, through mechanisms involving modulation of the immunoregulatory activities of T lymphocytes. Dendritic cells (DC) play a pivotal role in the generation of T cell responses, including those relevant to the autoreactive T cells enabling type 1 diabetes. As Abs against DC are likely generated during production of mATG, we examined the impact of this preparation on the phenotype and function of DC to elucidate novel mechanisms underlying its beneficial activities. In vivo, mATG treatment transiently induced the trafficking of mature CD8(-) predominant DC into the pancreatic lymph node of NOD mice. Splenic DC from mATG-treated mice also exhibited a more mature phenotype characterized by reduced CD8 expression and increased IL-10 production. The resultant DC possessed a potent capacity to induce Th2 responses when cultured ex vivo with diabetogenic CD4(+) T cells obtained from BDC2.5 TCR transgenic mice. Cotransfer of these Th2-deviated CD4(+) T cells with splenic cells from newly diabetic NOD mice into NOD.RAG(-/-) mice significantly delayed the onset of diabetes. These studies suggest the alteration of DC profile and function by mATG may skew the Th1/Th2 balance in vivo and through such actions, represent an additional novel mechanism by which this agent provides its beneficial activities.

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.

New Approaches to De Novo Immunosuppression and Steroid Elimination

Calcineurin inhibitors (CNIs) and steroids, the cornerstones of most immunosuppressive regimens over the past 20 years, have undesirable chronic side effects, leading to the application of new strategies with sirolimus (SRL) and mycophenolate mofetil (MMF). We evaluated de novo CNI avoidance and early steroid withdrawal among 145 renal recipients randomized to receive either SRL ( n = 71) or cyclosporine (CsA; n = 74). All patients received polyclonal antithymocyte globulin (ATG) for 5 days, MMF, and steroid withdrawal at 6 months (SPIESSER study). At 12 months, patient and graft survivals, incidence of biopsy-proven acute rejection (BPAR), and rates of steroid withdrawal were not statistically different namely, 97% versus 97%; 90% versus 93%, 14.3% versus 8.6%, and 82.8% versus 84.1%, respectively. Among patients who remained on treatment according to the protocol, the estimated glomerular filtration rate (eGFR) was significantly higher with SRL (69 ± 19 versus 60 ± 14 mL/min; P < .01). In another study of delayed introduction of SRL, 192 renal recipients were prospectively randomized at week 12 to switch from CsA to SRL ( n = 95) or to continue CsA ( n = 97; CONCEPT study). At 12 months, patient and graft survivals of the randomized patients, incidence of BPAR, and rates of steroid withdrawal were not significantly different: 100% versus 100%, 100% versus 98%, 17% versus 8%, and 72% versus 78%, respectively. Upon ITT eGFR was significantly higher with SRL (68.9 vs 64.4 mL/min; P = .017). In both studies, a significant improvement in renal function was observed at 12 months among patients receiving a maintenance regimen with SRL plus MMF. Furthermore, steroids could be withdrawn in three quarters of the patients.

Immunopathology of ATG Prior to Bone Marrow Transplantation in Mouse Model

Introduction: Polyclonal anti-thymocyte globulin (ATG) is mainly used in hematopoietic stem cell transplantation, as a prevention for graft rejection as well as for GVHD. Immunosuppressive properties of ATG have been considered primarily from the depletion of peripheral lymphocytes. However direct or indirect effects of ATG on other immune components still is controversial. In the present study we evaluated the immunopathologic effects of ATG on immune system in a mouse model.Methods Ten to fourteen weeks old BALB/c and C57BL/6 mice, were injected intra- peritoneally or intravenously with different doses of ATG (0.2mg/kg -25mg/kg) at three dosage schedules. Considering bone marrow transplantation as day 0, ATG were given at days -10, -7 and -5 or -7, -5 and -1 or -5, -3 and -1. At day 0, mice were killed; spleen (SP), bone marrow (BM), lymph nodes (LN) and thymus were removed and analyzed for T-, B-, DC, NK-, T-reg and myeloid cells.To evaluate the efficacy of immunosuppressive effect of ATG, a group of BALB/c mice were conditioned using busulfan (Bu) and ATG and compared to a control group of BALB/c conditioned with Bu (80mg/kg) followed by cyclophosphamide (200mg/kg). Both groups transplanted with BM and spleen cells from C57BL/6 and followed for engraftment and/or GVHD.Results The administration of ATG (0.2- 4.5mg/kg) has resulted in an increase in spleen cellularity while in lymph node and thymus a decreased cellularity was observed. We have found that injecting 4.5mg/kg of ATG at day -7, -5 and -3 significantly decreased T-cell population in spleen and LN compare to Bu-Cy conditioning. The ratio CD4/CD8 increased after ATG treatment showing that CD8 cells are six-fold more sensitive to ATG treatment compared to CD4 lymphocyte. Interestingly T-reg cell population increase after ATG at day 0, however, the increment was negatively correlated with the administration time and positively correlated with the dose.ATG treatment has resulted in an increase in B-cell population by two- and three- fold in spleen and lymph nodes, respectively. Moreover, 1.2- to 3.5-fold increase in DCs, NK and myeloid cells was observed in SP and LN. Thymus cellularity and cell phenotype was less affected while BM cellularity was not affected by ATG treatment. No differences in the ATG effect on cellularity or cell phenotype between IP and IV route was observed.Despite the high immunosuppressive effect observed in T-cell population compared to that seen in Bu-Cy conditioning, no chimerism was observed when Cy was substituted with ATG (4.5 – 10 mg/kg).Conclusion No donor chimerism could be obtained using ATG as a single agent up to 25mg/kg. ATG dose and the administration time are important factors affecting the repopulation of residual T-cells in spleen and lymph node that have to be considered in bone marrow transplantation setting.

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.

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.

A Late-Onset Epstein-Barr Virus–Related Lymphoma Completely Remitted in a Child With Renal Allograft

Lymphomas are frequently encountered malignancies following renal transplantations. A 17-year-old boy was found to have lymphoma 1.5 years after a the first cadaveric transplantation performed due to reflux nephropathy. Polyclonal anti-thymocyte globulin (induction) with prednisolone (PRD), azathioprine (AZT), and tacrolimus (Tac) regimen had been given after the transplantation. A hypoechoic mass (25 mm) was detected in the upper pole of the allograft by renal Doppler ultrasound performed due to graft dysfunction with a high basal serum creatinine (Cr) (2.2 mg/dL). The renal biopsy revealed a large B-cell lymphoma with CD20 staining in the medulla. The serum displayed a positive Epstein-Barr virus (EBV), immunoglobulin (Ig)G, negative IgM with negative DNA-polymerase chain reaction. However, the biopsy was positive for EBV-LMA. The viral status at the time of transplant was unknown. After withdrawing AZT and Tac therapies, a chemoimmunotherapeutic regimen consisting of PRD, cyclophosphamide, and anti-CD20 monoclonal antibody was administered twice. The patient excreted the necrosed tumor particles over a 2-month interval with hydronephrotic colic attacks. The basal Cr improved at 6 months (to 1.4 mg/dL). A low dose of Tac (0.5 mg/d) was added to PRD. The patient has remained in complete remission for 2.5 years with a well-functioning renal allograft. Although this case was a late-onset lymphoma, the patient displayed a picture like excreting stones from the allograft and remitted completely. This case illustrates that localization of a tumor may play a more important role than the elapsed time from transplant in the diagnosis in EBV-related posttransplant lymphoproliferative disease.

CD154 Blockade, Sirolimus, and Donor-Specific Transfusion Prevents Renal Allograft Rejection in Cynomolgus Monkeys Despite Homeostatic T-Cell Activation

CD154-specific antibodies have been shown to prevent acute rejection in many preclinical models including nonhuman primates (NHPs). However, they have been ineffective in pilot clinical trials, suggesting a need for more robust preclinical analysis. One factor affecting the disparate results may be related to the recipient's immune activation state. Specifically, adult humans have a high percentage of memory-phenotype T cells compared to young animals. Postdepletional homeostatic repopulation has been shown to enrich for memory-phenotype T cells and interfere with CD154-based therapies in rodents. We developed a NHP model nonspecifically enriched for peripheral memory-phenotype T cells. Thymectomized cynomolgus macaques underwent depletion with polyclonal anti-thymocyte globulin followed by repopulation. Peripheral phenotype was serially determined using polychromatic flow cytometry. In vitro response to donor and environmental antigens was also confirmed before and after manipulation. We then tested a regimen previously successful in rhesus monkeys combining anti-CD154, sirolimus, and donor-specific blood transfusion (DST), in a second primate species with and without the provocation of increased peripheral homeostatic T-cell activation. Monkeys that were thymectomized (n=3) and depleted recovered via homeostatic repopulation with a repertoire enriched for cells with a memory surface phenotype compared to unmanipulated controls (n=3). Despite a repertoire markedly enriched for memory-phenotype cells, the regimen effectively prevented acute rejection for the duration of therapy. Cynomolgus monkeys can be rendered memory phenotype enriched using homeostatic repopulation. Despite a generally activated T-cell repertoire, anti-CD154, sirolimus, and DST effectively prevents rejection in cynomolgus monkeys.

Polyclonal Anti-Thymocyte Globulin Exhibits Consistent Immunosuppressive Capabilities Beyond Cell Depletion

Polyclonal Anti-Thymocyte Globulin Exhibits Consistent Immunosuppressive Capabilities Beyond Cell Depletion