ATG Based Conditioning Regimen in HLA Related HSCT for Aggressive T-cell Tumors

Aggressive T-cell lymphomas (ATCLs), including peripheral T-cell lymphoma and T lymphoblastoid cell lymphoma/leukemia, represent 10% to 15% of non-Hodgkin's lymphomas (NHLs) in adults(1). ATCLs show a worse prognosis than that of B-cell lymphomas. Myeloablative allogeneic stem cell transplantation (allo-SCT) may be the only way to cure these patients, but the recurrence of the primary disease after transplantation is still an important prognostic factor (2). Optimizing the conditioning regimen is always the research hot topics in hematology fields. Polyclonal antithymocyte globulin (rabbit anti-thymocyte globulin, r-ATG) are currently used to prevent graft-versus -host(GVHD) disease in allogeneic stem cell transplantation, and also widely used for the prevention and treatment of acute rejection after solid organ transplant because of its strong immunomodulatory effects. ATG is used in allogeneic SCT for the prophylaxis of graft versus host disease by in vivo T cell depletion, including the complement-dependent cytotoxic response, antibody-dependent cell-mediated cytotoxicity, the opsonophagocytic role of phagocytic cells and induced apoptosis(3). But some scholars reported the ATG delayed immune reconstitution and hematologic reconstitution and leaded to the increase of the incidence of virus and fungal infections after transplantation. But it is often curable and does not affect the overall survival and quality of life of the patients (4). Because of its strong immune suppression and regulation, also on the basis of the above facts, ATG as GVHD prophylaxis is generally limited to the unrelated donor, or human leukocyte antigen（HLA）-mismatched related donor transplantation. But There are many issues still need to be studied. ATG has shown efficacy in preventing acute GVHD（aGVHD) in allo-SCT, but its efficacy in chronic GVHD (cGVHD) and long-term outcomes remains controversial. A systematic review and meta-analysis from Du k et al（5） reported that prophylactic use of ATG exerted a favorable effect in reducing cGVHD without survival impairment in a long term, although a higher relapse rate is a major threat. Does the ATG also have the killing effect on the tumor cells of the lymphatic system? The vitro studies have confirmed this point recently. Grüllich(6) et al and the investigators study(7) both found that ATG can inhibit the proliferation and induce high level of apoptosis in the human lymphoblastic cell lines, such as Jurkat, Daudi, DG-75 , and myeloblastic cell lines K562, HL-60, KG1, and U937. ATG also has pro-apoptotic activity against the majority of primary leukemia cells, particularly those cells from lymphatic origin. In addition, ATG will not result in apoptosis of normal hematopoietic cells. Low-dose ATG can also stimulate normal hematopoietic colony growth. Therefore, ATG may be used as anti-lymphocyte tumor bio-therapeutics (such as rituximab) to increase the role of chemo-radiotherapy in the conditioning regimen. And ATG can remove the residual tumor lesions, which reduced the rate of tumor recurrence after transplantation. The result of our retrospective study in our hospital had already be published in blood cancer journal. We used the ATG as the part of the conditioning regimen and to evaluate the long-term antileukemia effect, the safety and complication in the patients with highly aggressive T-cell lymphomas. Twenty-three patients were enrolled into this study. At the time of transplant, six patients reached first or subsequent complete response, three patients had a partial remission and 14 patients had relapsed or primary refractory disease. The conditioning regimen consisted of ATG, total body irradiation, toposide and cyclophosphamide. The complete remission rate after transplant was 95.7%. At a median follow-up time of 25 months, 16 (69.6%) patients are alive and free from diseases, including nine patients in refractory and progressive disease. Seven patients died after transplant, five from relapse and two from treatment-related complications. The incidence of grades II-IV acute graft-vs-host disease (GvHD) was 39.1%. The maximum cumulative incidence of chronic GvHD was 30%. The most frequent and severe conditioning-related toxicities observed in 8 out of 23 patients were grades III/IV infections during cytopenia. Thus, ATG based conditioning is a feasible and effective alternative for patients with highly aggressive T-cell tumors（8）. In view of this convincing result, we designed a multi-center, open, randomized controlled clinical study.

As noted earlier, a higher relapse rate may be a major threat after ATG use（5）.In China, the conventional dose of 2.5mg/kg/day, 2-3 days of Thymoglobulin is commonly used as GVHD prophylaxis in the unrelated donor, or HLA-mismatched related donor transplantation but not in the HLA matched related donor transplantation (9). In order to observe the anti-tumor effect of this conditioning regimen in the aggressive T-cell lymphomas patients(complete remission, partial remission), we designed a multi-center, open, randomized controlled clinical study. The donors are all HLA matched related donors. In the therapy group, we added in the Thymoglobulin dose in the conditioning regimen for four days 10mg/kg. We expect that this ATG based conditioning regimen does play anti-tumor effect, reduce primary disease recurrence after transplantation, improve disease-free survival (DFS) and overall survival rate (OS) , as well as reduce the incidence and severity of GVHD, but the incidence of infection need to be observed.

Reference:1. Rudiger T, Weisenburger DD, Anderson JR et al. Peripheral T-cell lymphoma (excluding anaplastic large-cell lymphoma): results from the Non-Hodgkin's Lymphoma Classification Project. Ann Oncol 2002; 13:140-149.

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2. Du K, Hu Y, Wu K, Huang H et al. Long-term outcomes of antithymocyte globulin in patients with hematological malignancies undergoing myeloablative allogeneic hematopoietic cell transplantation: a systematic review and meta-analysis.Clin Transplant. 2013 Mar;27(2):E91-E100.
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