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Summary:Older age has been linked to increased transplant-related mortality from graft-versus-host disease (GvHD). Depletion of T cells from stem cell grafts seems to protect from complications of GvHD particularly in older patients. After myeloablative conditioning, patients with haematological malignancies received allogeneic grafts from HLA identical siblings. For GvHD prophylaxis, PBPC grafts were treated ex vivo with anti-CD52, and therapeutic doses of cyclosporin until day +90. Survival of patients younger or older than the population age median was analysed. In all, 62 consecutive patients with a median age of 42.5 years were studied. Death was procedure related in 17% and from relapse of malignancy in five. At a median, follow-up is 662 (7–2316) days, 74% survive disease free. The rate of haematopoietic recovery and treatment-related mortality was similar in both groups. A total of 73% of 30 individuals in the younger group and 75% (P=0.8) in the older cohort survive at a median follow-up of 444 and 806 days (P=0.4). GvHD occurred in 13% and was the only adverse factor for survival (P<0.04). Myeloablative conditioning is well tolerated up to the age of 59 in patients receiving T-cell-depleted grafts. This information is useful to more precisely select patients who would benefit most from reduced intensity conditioning schedules.Bone Marrow Transplantation (2005) 36, 675–682. doi:10.1038/sj.bmt.1705119; published online 22 August 2005 [ABSTRACT FROM AUTHOR]

Background We examined the strategy of T-cell depletion of HLA-identical sibling grafts for the prevention of GvHD, as well as disease control and overall survival. Patients and methods The myeloablative conditioning was radiation based. The source of stem cells was BM in 62, and cytokine-mobilized PBPC in 68 patients. GvHD prophylaxis was by ex vivo incubation of the stem-cell concentrates with Campath-1G (anti-CD52; n=76) or Campath-1H (n=/54). Results Patients receiving PBPC grafts were older (median 38.5) than those undergoing BMT (median 31; P=/0.002). More patients in the PBPC group developed chronic GvHD (pB/0.01). While no post-transplant GvHD prophylaxis was given to BMT recipients, prednisone 30 mg daily was prescribed to 12 and CYA for 90 days to a further 32 patients who had received PBPC grafts. Median follow-up was 1055 (range 28=4867) days. Although there was no difference in the survival between patients who received BMT or PBPC, death was from disease recurrence in 16 and nine (p=/0.03; χ ² test) subjects, respectively. Multivariate analysis showed that outcome was particularly favorable in those who were given

We evaluated the outcome of two modes of T cell depletion for HLA-identical sibling stem cell transplants in 34 consecutive adult patients: group A (n = 11) received PBSC post CliniMACs immuno-magnetic enrichment of CD34+ cells and group B (n = 23) received bone marrow following in vitro incubation with CAMPATH-1M and complement. All patients received an identical conditioning regimen which consisted of in vivoCAMPATH-1H 20 mg over 5 days, thiotepa 10 mg/kg, cyclophosphamide 120 mg/kg and 14.4 Gy TBI. No additional graft-versus-host disease prophylaxis was given. The mean T cell dose administered was 0.02 ± 0.05 × 106/kg for group A and 2.8 ± 2.8 106/kg for group B (P < 0.001). With a median follow-up of 28 months overall survival was 36.4% for group A at 12 months compared to 78.3% for group B (P = 0.001). Transplant-related mortality in group A at 12 months was 63.6% as compared to 18.0% in group B (P = 0.003). Most of the procedure-related deaths in group A occurred secondary to infection. These results suggest that extensive in vitro T cell depletion of peripheral blood stem cells in combination with in vivo T cell depletion may have profound effects upon the incidence of infections following allogeneic stem cell transplantation and this may adversely effect transplant-related mortality. Bone Marrow Transplantation (2001) 28, 827–834. [ABSTRACT FROM AUTHOR]

We report the results of a retrospective single-center study comparing engraftment, acute and chronic GVHD, relapse and survival in patients with malignant hematological disorders transplanted with allogeneic peripheral blood stem cells (alloPBSCT, n = 40) or bone marrow cells (alloBMT, n = 42). All transplants were T cell depleted by in vitro incubation with the Campath-1 monoclonal antibody. Primary graft failure occurred in none of the patients receiving an alloPBSCT compared with 3/42 of the recipients of an alloBMT. In addition, two patients in the alloBMT group showed no platelet engraftment. Recipients of PBSC had a more rapid recovery of neutrophils (median 14 days) compared to BM transplant recipients (median 32 days). Platelet recovery was also accelerated in PBSC recipients compared to BM recipients (11 vs 38 days). There was an increase in the incidence of grade II acute GVHD and chronic GVHD in patients after alloPBSCT (18% and 23%, respectively) compared to patients receiving alloBMT (5% and 8%, respectively). The 2-year cumulative incidence of relapse was similar in both groups (47%). At 6 months after transplantation, transplant-related mortality (TRM) was lower in PBSCT recipients than in BMT recipients. However, at a follow-up of 3 years TRM was similar in both groups. The disease-free survival rate at 3 years after transplantation did not differ between the groups (42% for PBSCT and 41% for BMT recipients). Our results indicate that T cell-depleted alloPBSCT compared to alloBMT is associated with a more rapid hematopoietic reconstitution and a decreased TRM at 6 months follow-up after transplantation. However, at a follow-up of 3 years, no sustained survival benefits were observed. Bone Marrow Transplantation (2001) 27, 1053–1058. [ABSTRACT FROM AUTHOR]

Background: CAMPATH-1 (CD52) Abs have been used in stem-cell transplants for the prevention of GvHD and graft rejection. These complications can effectively be prevented by depletion of T lymphocytes from both donor and recipient. However, donor lymphocytes might contribute an anti-leukemia effect and lymphocyte depletion may exacerbate problems with immune reconstitution. There is a fine balance between the risks of GvHD and host-versus-graft reactions, relapse and infection. Methods: Clinical outcomes for 4264 patients were reported to a central registry and analyzed by univariate and multivariate methods to determine the superior protocols. Various protocols of lymphocyte depletion were tested, using either CAMPATH-1M (IgM) plus complement or CAMPATH-1G (IgG2b) to treat the donor BM ex vivo and CAMPATH-1G in vivo to treat the recipient. The humanized antibody CAMPATH-1H has recently replaced CAMPATH-1G. A meeting of the clinical collaborators was convened to discuss the results and to review the experiences of individual centers. Results: Interest focused on the use of mobilized PBSC for transplantation and on the use of reduced-intensity conditioning regimens ('mini' or 'non-Correspondence myeloablative' transplants). These approaches are likely to become increasingly important in the future and will allow transplant procedures to be used for relatively older patients. The use of CAMPATH-1G or CAMPATH-1H was associated with a low incidence of GvHD or rejection, though there were some differences that might be related to the longer half-life of the humanized antibody. An unexpected and apparently paradoxical effect of post-transplant CYA was observed — it appeared to reduce the risk of dying from infection after 6 months. Although part of the benefit could be explained by a reduction in GvHD, the effect was still evident when patients with GvHD or graft rejection were excluded from analysis. Discussion: CAMPATH-1H appears to have a useful role in the prevention of graft rejection and GvHD, particularly in patients who are at high risk of these complications. It can equally well be used by admixture with the infused stem cells, or by administration to the patient prior to the transplant. Future studies will seek to understand the mechanism of the CYA effect and to improve the quality of immune reconstitution. [ABSTRACT FROM AUTHOR]

Background : Ex vivo T-cell depletion of allogeneic BM (BM) grafts can effectively reduce graft versus host disease (GvHD) and may also apply to transplantation of allogeneic peripheral blood stem cell (PBSC) transplants. Methods : Here we have evaluated T-cell depletion and progenitor cell recovery by antibody-mediated cells lysis using three CD52 monoclonal antibodies (MAbs) at different concentrations and cell densities. Results : CAMPATH-1M was superior to CAMPATH-1H for T-cell depletion of BM samples. Treatment with CAMPATH-1M resulted in up to 2.55 log depletion of CD3 + cells, with recoveries of ≥45% CD34 + cells, ≥67% CFU-GM and ≥65% BFU-E. CAMPATH-1H treatment resulted in up to 1.64 log depletion of CD3 + cells and similar recoveries of CD34 + cells, CFU-GM and BFU-E as seen with CAMPATH-1M. Depletion of CD19 + cells was similar to that observed for CD3 + cells while natural killer (NK) cells were relatively spared compared with the T and B cell populations. Log depletions of T cells from PBSC, as determined by immunofluorescence studies and limiting dilution analyses, were similar using CAMPATH-1M, -1H, and -1G. There were also no differences in the depletion of CD19 + cells or NK cells using the three MAbs. Similar results were obtained for recoveries of CD34 + cells, CFU-GM and BFU-E using all three MAbs, although the recovery of CD34 + cells using the highest concentration of MAbs was significantly greater in CAMPATH-1H treated samples. Increasing the number of PBSC treated with CAMPATH-1H and -1M had no effect on the log depletion of T, B or NK cells and there were no major differences in the log depletions achieved with CAMPATH-1H or -1M. Likewise, the higher PBSC density had no effect on the recoveries of CD34 + cells or committed progenitors and once again CAMPATH-1H gave similar recoveries to those obtained using CAMPATH-1M. Discussion : Although CAMPATH-1M resulted in greater ex vivo T-cell depletion of BM than CAMPATH-1H, in all other respects, the humanised CAMPATH-1H was just as effective as CAMPATH-1M and -1G. [ABSTRACT FROM AUTHOR]

Mechanisms by which T and B lymphocytes co-operate in the in vitro secondary antibody response to trinitrophenyl-conjugated soluble protein antigens were investigated. The generation of antibody responses was analyzed when haptenic and carrier determinants were either linked or non-linked. Ability to co-operate through each of these mechanisms was influenced by the experimental conditions employed, particularly the mode of preparation of the T cells and the antigen concentration used. Nylon wool filtration of T cells may deplete a T helper population involved in non-linked recognition interactions.

Reports on thymocytes adoptively transferred into syngeneic irradiated recipients which can be primed with antigen (KLH) to generate two types of helper function termed 'specific' and 'non-specific.' Finding that large doses of KLH given in adjuvant generate high levels of both types of helper T cell.

Examines the heterogeneity of spleen B cells reacting with T-cell factors in BALC/c mice. Stimulation of spleen C cells with Concanavalin A; Existence of T cell subsets; Cooperation between helper T cells for activation of B cells.

T cells involved in specific and nonspecific co-operation belong to a long-lived population. However, under conditions of limiting dilution of T cells it is not a common event to detect both types of co-operative event in a single microculture well. Likewise, as far as specific co-operation is concerned, the simultaneous expression of both direct and indirect PFC responses in a single microculture well is also unusual. Estimates obtained of the number of PFC generated by one T cell in specific co-operation correspond well to those generated by a single B cell; and it would seem that under conditions of the microculture system there is a marked restriction in the number of B cells that a single T cell may interact with in the short term. This restriction seems to be of a one T-cell to one B-cell relationship. [ABSTRACT FROM AUTHOR]

Procedures have been described which are suitable for experiments utilizing a microculture system whereby one can easily study the function of single helper T cells. These are: (a) the elimination of the background anti-hapten response by preliminary anti-θ+guinea-pig complement treatment of the 'hapten-primed' population; (b) the removal of any contaminating hapten-specific B cells from the carrier-primed population by passage through nylon wool; (c) irradiation of long-term primed 'nylon wool' enriched helper cells to prevent cell division; (d) the partition of individual helper cells by limiting dilution. [ABSTRACT FROM AUTHOR]

A population of T cells sensitive to ALS treatment release a non-specific factor (NSF) capable of replacing T cells in the response of nude spleen cells to erythrocyte antigens. This factor cannot be removed by immunoadsorbents with specificities directed towards products of the H2 complex, nor by lentil lectin, unlike certain specific T-cell factors. Furthermore, it functions across histocompatibility differences between mouse strains. It has been directly demonstrated that this factor can influence both proliferation and differentiation of B cells in response to a restricted group of T-dependent antigens, of which donkey and sheep erythrocytes are such special cases. [ABSTRACT FROM AUTHOR]

One thymus-independent immunogen, trinitrophenylated lipopolysaccharide (TNP-LPS) has been studied in vivo and in vitro in C3H/He and C3H/ HeJ strains of mice. C3H/HeJ mice have been shown to be low responders, and C3H/He mice high responders to this immunogen. This ‘low responder’ status of C3H/HeJ mice has been demonstrated to be consequent to an intrinsic defect present at least at the level of B cells. It was demonstrated that high responder cells or ‘in vivo milieu’ could not restore this deficit to C3H/HeJ cells. It is proposed that the adjuvanticity, mitogenicity and polyclonal activating capacity of LPS are all fundamental to its property of acting as a thymus-independent carrier for the TNP determinant. This observation is discussed from the point of view that the T-cell independence for an antigen cannot derive solely from its multivalency but must depend upon the intrinsic adjuvanticity of that molecule. [ABSTRACT FROM AUTHOR]

Limiting dilution analysis has been applied to the study of T-cell 'helper' function in vitro. Using the microculture system one can estimate the numbers of (a) 'helper' T cells involved in specific collaboration with B cells and (b) those T cells which are able, on being activated by their specific antigen, to facilitate the response of B cells to another antigen. Such studies have enabled us to demonstrate that: (1) a single helper' T cell was able to activate a single B-cell precursor to detectable antibody production; (2) the `helper' function of primed T cells was radio-resistant; (3) a minimal estimate of `helper' frequencies could be obtained in defined cell populations; (4) non- specific facilitation was directed towards virtually all available B cells of a given specificity if these were challenged with their appropriate particulate antigen; (5) the microculture system offers the opportunity to determine whether specific and non-specific T-cell helper' effects are a consequence of the activity of one T-cell type or of different subpopulations of T cells. [ABSTRACT FROM AUTHOR]

Polymerized flagellin and E. coli lipopolysaccharide both express adjuvanticity in vivo and in vitro for responses to hapten conjugated to sheep crythrocytes, and hapten conjugated to soluble thymus-dependent antigens. In the case of erythrocyte-bound hapten, adjuvanticity is expressed in the absence of thymus-derived cells (T-cells). However, in the case of responses to soluble thymus-dependent conjugate, carrier-specific T cells would appear to be necessary for adjuvanticity to be expressed. On the basis of these observations on hypothesis for the mechanism of B-cell induction and tolerance is proposed. [ABSTRACT FROM AUTHOR]

Evidence is presented which suggests that T cell-dependent non-specific factor (NSF) cannot be the sole mediator of 'co-operation' for all types of thymus-dependent antibody response. NSF can replace the requirement for T cells in responses to hapten conjugated to particulate carriers, but cannot do so in responses to hapten conjugates of soluble thymus-dependent carriers. [ABSTRACT FROM AUTHOR]

Supernatants were obtained from cultures of keyhole limpet haemocyanin (KLH) primed mouse spleen cells, and also from cultures of KLH-educated, thymus-derived lymphocytes (T cells) after re-exposure of cells to the original priming antigen, KLH. These supernatants were able to facilitate the immune response of bone marrow-derived lymphocytes (B cells) to sheep erythrocytes (SRBC). Certain physical and biological properties of such supernatant activities are described. [ABSTRACT FROM AUTHOR]

Both murine CD4+ and CD8+ cells are found in the thyroid infiltrate in experimental autoimmune thyroiditis (EAT) induced with mouse thyroglobulin (MTg). MTg activation of immune cells in vitro enables CD4+ cells to transfer thyroiditis adoptively and to aid the cytotoxic capacity of CD8+ cells for thyroid monolayers. To dissect their relative contribution to pathogenesis in vivo, depleting doses of paired rat monoclonal antibodies (MoAb) recognizing two distinct CD4 or CD8 epitopes were injected alone or in combination. Early treatment with CD4 MoAb interfered with the induction and development of EAT, whereas similar treatment with CD8 MoAb reduced infiltration moderately and did not enhance antibody response. To examine the long-term effect of therapy on advancing EAT, administration of MoAb was delayed to days 21 and 25, and thyroids were analysed immunohistochemically on days 28 and 70. Whereas control mice showed about 30% CD4+ and CD8+ cells at a 2:1 ratio (the remainder being mostly macrophages) on both days 28 and 70, the CD4 therapy regime led to reduced severity and the lesions on day 70 contained very low percentage of CD4+ cells, but elevated percentage of CD8+ cells (ratio 1:3-5). The CD8 therapy regime led to reduced CD8+ cells without changing the range of CD4+ cells (ratio 4:1). Thus, subset involvement may be influenced by the MoAb used. When CD4 and CD8 MoAb were combined, > 50% of the thyroids were cleared of all inflammatory cells; lesions when found were very small and contained < 10% T cells (ratio 1:1). Since emerging T cells were not retained in the thyroid despite ongoing antigenic stimulus leading to increased antibody titres, the therapeutic effect of MoAb, even at an advanced stage of disease, was long lasting. [ABSTRACT FROM AUTHOR]

An advantage of CD34+ cell selection over antibody purging is that a component allograft is produced comprising a stem cell enriched and an unadsorbed fraction, the latter containing T cells which may be used for post-transplant immunotherapy. Initial reports with PBSC allografts suggested that T cell depletion (TCD) by CD34+ cell selection and post-graft cyclosporin A ± methotrexate was insufficient prophylaxis against acute GVHD. We compared sequential TCD (of a CD34+ cell-selected fraction) using a second (CD2) immunoaffinity step or Campath-1M monoclonal antibody and complement. Since a high stem cell ‘dose’ enhances engraftment across HLA barriers and improves overall post-transplant outcome, the recovery of CD34+ cells and progenitors were assessed. Sequential positive (CD34+) and negative (CD2+) immunoaffinity selection resulted in a 3.4 log depletion of T cells as compared to a 4.05 log depletion when CD34+ cell selection was followed by Campath-1M treatment. Recoveries of CD34+ cells, CFU-GM and BFU-E following double depletion using CD34+ cell selection plus CD2+ cell depletion were 28, 25 and 17% as compared to 20, 18 and 16% when CD34+ cells were treated with Campath-1M. The unadsorbed fraction contained 85% of the original T cells, from which donor leukocyte infusions in the range of 105 to 107 CD3+ cells per kg body weight of the recipient were harvested. Despite the advantages of component allografts, the loss of stem/progenitor cells may restrict sequential TCD steps unless single BM harvests are supplemented and/or replaced with mobilised PBSCs. [ABSTRACT FROM AUTHOR]

In order to determine the role of different T lymphocyte subsets in the pathogenesis of low-dose streptozotocin (LD-Sz) induced diabetes, we treated mice with Sz together with repeated injections of rat monoclonal antibodies (MoAb) with specificity towards the mouse T cell differentiation markers L3T4 ('helper/inducer' T cells and some macrophages). Lyt-2 ('cytotoxic/suppressor' T cells and NK cells) and Thy-I (pan T lymphocytes). Treatment depleted target cells in peripheral blood and spleen: decreased the ability of spleen cells to respond to mitogens; and, in the case of depletion of the L3T4 T cell subset, prevented a humoral immune response to SRBC. Treatment with MoAb against either of the two T cell subtypes could protect from hyperglycaemia and loss of body weight, suggesting that both T cell subsets were implicated in the development of LD-Sz induced diabetes. Immunocytochemical analysis of pancreatic sections showed that both L3T4' and Lyt-2+ cells participated in islet infiltration together with macrophages. Treatment with MoAb markedly reduced islet infiltration by both L3T4+ and Lyt-2+ cells but not by macrophages. The suppressive effect of MoAb against either L3T4 or Lyt-2 on diabetes development suggests that the pathomechanism involved is different from that in experimental autoimmune neuritis and adjuvant arthritis where Lyt-2 cells are not involved. [ABSTRACT FROM AUTHOR]

This study aimed to analyse the roles of Lyt 2+ and L3T4+ memory T-cell subpopulations in murine influenza infection. Previous work has shown that Lyt 2+ cytotoxic T-cell (Tc) clones can adoptively transfer protection. We therefore wished to see whether L3T4+ (Th) cells could also act as protective effector cells. Donors for adoptive cell transfer were thymectomized mice, depleted in vivo of either Lyt 2+ or L3T4+ T cells with monoclonal antibodies (MAb) and then infected with influenza virus (A/X31). Primed spleen cells, after removal of the B cells, were transferred into irradiated hosts infected simultaneously or persistently with a heterologous influenza virus and the effect on lung virus replication determined. Depletion of L3T4+ T cells suppressed the formation of IgG antibodies after influenza virus infection, indicating significant depletion of T-helper function. Yet Lyt 2+ class I MHC-restricted TL cells were effectively primed in these mice, albeit to half the normal level. Adoptive transfer of the Lyt 2+ memory T cells cleared virus in a persistent infection within 6 days. Spleen cells selected fur L3T4+ T cells cleared virus within 21 days of transfer in a simultaneous infection and reduced viral titres in a persistent infection, but not as effectively as L3T4+-depleted spleen cells. Although no Lyt 2+ cells were detected by fluorescence staining in Lyt 2+-depleted spleens, we could detect low levels of class I MHC-restricted influenza-specific Tc memory cells in host spleens following influenza infection. Therefore, whether the early viral clearance is solely due to L3T4+ T cells is not clear. Lyt 2+ memory T cells appear more efficient in this respect than L3T4+ memory T cells. [ABSTRACT FROM AUTHOR]

Major histocompatibility complex (MHC) restrictions in the secondary antibody response in vitro to the soluble protein antigen trinitrophenyl keyhole limpet haemocyanin (TNP-KLH) were investigated in this study. Experimental conditions were employed which ensured that co-operation between KLH-primed T cells and TNP-primed B cells was possible only through linked recognition of carrier and haptenic determinants. Under such conditions co-operation between T and B cells appears to be MHC-restricted.

Supernatants were collected from keyhole limpet haemocyanin (KLH) primed spleen cells which had been incubated in tissue culture medium with their priming antigen KLH. These non-specific factor (NSF) containing supernatants were then tested in a microculture system for their ability to facilitate an anti-SRBC response of nu/nu or AT x BM spleen cells. It was concluded that: (a) NSF was able to engage a large number of the available pool of sheep erythrocyte (SRBC) specific B cells into an antibody response; (b) this response was characterized by the development of clones expressing plaque-forming cells (PFC), the number of PFC produced within a clone being dependent upon the amount of NSF available in that culture; (c) NSF probably acted directly on B cells, and not via other accessory cell types. [ABSTRACT FROM AUTHOR]

The article offers a discussion on the interaction process between the T and B lymphocytes with antibody formation as a vital part of gaining a full understanding of immune deficiency diseases in Great Britain. In the views of the author, T-B immunology served as a bridge towards the humans system as cellular basis of interaction, a helper and suppressor in cell interaction, and a requirement of understanding genetic identity.

The demonstration in the 1960s that T cells collaborated with B cells in enabling antibody responses to simple protein antigens opened up the challenge of how to investigate the interactions of two rare antigen-specific lymphocytes within a vast population. One idea was that T cells made soluble factors that could activate B cells at a distance; the other was that rare T cells and B cells came into contact. Using limiting dilution analysis, we asked the question‘How many B cells could a single T cell collaborate with in the short term?’ Unequivocally, the answer was just one. This implied a need for cell contact, and coupled with the observation for genetic restriction in T-cell/B-cell co-operation, seemed to make a watertight case for direct coupling. Claims of diffusible antigen-specific factors undermined the importance of our findings at that time. Remarkably, those claims have not yet been retracted and our original findings that collaborating T cells and B cells must come into contact have never achieved the recognition that they deserved. [ABSTRACT FROM AUTHOR]

Focuses on studies on microbiology. Information on false-positive pregnancy tests pretransplant; Use of ceprate CD34-positive selection system for depletion of t cells;

Campath 6, a rat IgG2b monoclonal antibody to the interleukin 2 receptor on activated T cells, was used to treat three patients with active rheumatoid arthritis unresponsive to conventional treatment. Two patients had an excellent response for about three months. There were no significant side effects. The results suggest that activated T cells are of importance in the pathogenesis of rheumatoid arthritis. Although infusions of rat monoclonal antibodies could not be repeated because of the risk of sensitisation, the development of humanised monoclonal antibodies targeted against specific T cell sets would allow repeated courses of treatment to be given. [ABSTRACT FROM PUBLISHER]

Abstract: Clinical intervention trials evaluating the efficacy of antibody immunotherapy in type 1 diabetes are in progress. We tested effects on prediabetic islet antigen-specific autoreactive T cells of antithymocyte globulin (ATG) and humanized monoclonal antibodies against CD3 (ChAglyCD3) or CD25 (daclizumab) with regard to downmodulation of the target protein, proliferation, cytokine production, complement-dependent cytotoxicity (CDC), antibody-dependent cell cytotoxicity (ADCC), and survival. ATG leads to depletion of autoreactive CD4+ T cells by ADCC, CDC, and apoptosis, whereas anti-CD3 and anti-CD25 inhibited T-cell autoreactivity in a nondepleting fashion. ATG treatment led to a cytokine burst of Th1- and Th2-associated cytokines. Modulation of cytokine release through humanized monoclonal antibodies was moderate and selective: anti-CD25 led to increased release of IL-2 and reduced production of TNFα, whereas anti-CD3 decreased release of interferon-y and IL-5 and increased secretion of IL-10. ATG and the humanized monoclonal antibodies displayed contrasting mechanisms of action. [Copyright &y& Elsevier]