Involvement of Fas and TNF pathways in the induction of apoptosis of T cells by antithymocyte globulin

Abstract

Antithymocyte globulin (ATG) is the treatment of choice for those aplastic anemia patients who are not suitable for bone marrow transplantation (BMT). ATG is also used for the treatment of rejections in organ transplantation and as a conditioning regimen in BMT. Despite the proven efficacy of ATG in these areas, its mechanism of action is not known. Profound T-cell lymphopenia observed in vivo with ATG treatment is supposed to contribute to its therapeutic effect. We have previously shown that apoptosis is one of the mechanisms responsible for ATG-induced lymphopenia. Our next objective was to investigate the effect of ATG on modulation of Fas and TNF pathways, the two main pathways of T-cell apoptosis. Maximum surface expression of Fas on T cells was observed after 24 h at an ATG dose of 100 microg/ml; at this dose 88% of cells expressed Fas as compared to 26% of untreated cells. Surface expression of FasL was found to peak after 24 h at an ATG dose of 1000 microg/ml when 34% of cells were positive for FasL as compared to 1.5% of untreated T cells. Tumor necrosis factor (TNF)-alpha production was found to be maximum after 6 h at 1000 microg/ml dose (20%) as measured by intracellular cytokine staining of T cells. TNF-alpha production was also measured by enzyme-linked immunosorbent assay (ELISA) in the supernatant of lymphocytes treated with ATG for 6 h. A dose-dependent increase in TNF-alpha production was found in these supernatants with a plateau being achieved at an ATG dose of 1000 micro g/ml. We conclude that ATG-induced apoptosis in T cells involves both Fas and TNF pathways and TNF-alpha is produced much earlier than Fas and FasL expression.

Up-regulation of fas and fasL pro-apoptotic genes expression in type 1 diabetes patients after autologous haematopoietic stem cell transplantation

“…The increase in expression of the proapoptotic genes fas and fasL in PBMCs isolated from T1D patients after HDI-AHSCT suggest a re-establishment of tolerance mechanisms mediated by AICD and an increase in the apoptosis susceptibility of residual autoreactive lymphocytes. These results are in agreement with previous observations in the literature that showed up-regulation of the Fas molecule on immune cells after immunosuppression with anti-thymocyte globulin (ATG) treatment [57][58][59] and an increased frequency of CD4 + Fas + and CD8 + Fas + cells in multiple sclerosis patients during the first months of immune reconstitution after AHSCT [60].…”

Alemtuzumab markedly reduces chronic GVHD without affecting overall survival in reduced-intensity conditioning sibling allo-SCT for adults with AML

“…15,16 Alemtuzumab is a monoclonal humanized antibody that binds specifically to the pan-lymphocyte marker CD52. 15,17,18 The in vivo administration of alemtuzumab results in profound immunosuppression, significantly reducing GVHD when compared with T-cell replete transplants for a variety of haematological malignancies. 12,13,[18][19][20][21][22][23][24][25] Conversely, as a result of the depletion of the lymphocytes and APCs involved in GVL as well as GVHD, alemtuzumab has been associated with increased risk of relapse 26 In addition, alemtuzumab is associated with poor immune recovery post transplant, 26 and it is now apparent that an increased risk of infections after transplant with alemtuzumab is a significant cause of morbidity and mortality.…”

Apoptotic Effects of Antilymphocyte Globulins on Human Pro-inflammatory CD4+CD28− T-cells

“…The supramitogenic dosages of ATG-F with 300 µg/ml and 1000 µg/ml were chosen, because induction of cytokine production are dose-dependent and doses as high as 1000 µg/ml stimulated TNF-α production in a previous study using horse ATG [49]. After cell surface staining for CD28 and CD4 with subsequent fixation and permeabilisation, cells were stained with FITC-conjugated anti-IFN-γ, TNF-α and IL-4 mAb or control Ig (R&D Systems, Inc., MN, USA).…”