Immunosuppressive treatment of acquired aplastic anemia and immune-mediated bone marrow failure syndromes

Novel Small Molecule, UTS-1401, as a Radioprotector for Total-Body Irradiation

We report on a new radioprotector, UTS-1401, a small molecule that was synthesized (by one of us, JS) and evaluated here for its radioprotective effect against total-body irradiation (TBI). Female and male NIH Swiss mice were subjected to TBI at doses of 6.5, 7.5 and 8.5 Gy either with or without a 24 h pretreatment of UTS-1401 given ip and observed for 30 days. Survival rates were significantly increased when mice were treated with UTS-1401 compared to those not treated. The radioprotective effect of UTS-1401 was drug-dose dependent for male mice exposed to 8.5 Gy TBI with 150 mg/kg of UTS-1401 as the optimal dose. The radioprotective effect of UTS-1401 on female mice exposed to 8.5 Gy TBI was observed at 50, 100, and 150 mg/kg, with no dose response relationship noted. Female mice were more radioresistant than male mice with LD50/30 values of 7.8 Gy vs. 6.8 Gy, respectively. Weight changes after UTS-1401 alone showed a significant body weight increase at 150 mg/kg. Both the ip and iv route for UTS-1401 were similarly effective for male mice exposed to 8 Gy TBI. Further analysis using an endogenous spleen colony assay demonstrated that pretreatment of UTS-1401 for up to 72h prior to TBI protected both spleen weight and hematopoietic stem cells with a treated/untreated ratio between 2.0 and 3.2 for the latter for times between 0.5 h and 72 h. A separate in vivo study showed that pretreatment of UTS-1401 protected bone marrow CFU-GM for mice exposed to TBI. In summary, UTS-1401 is a promising small-molecule radioprotective agent as demonstrated by whole animal, hematopoietic stem cell and bone marrow myeloid progenitor cell survival.

Altered naive and memory CD4+ T-cell homeostasis and immunosenescence characterize younger patients with myelodysplastic syndrome

Response to immunosuppressive therapy (IST) in younger patients with myelodysplastic syndrome (MDS) has been linked to a T-cell-dominant autoimmune process that impairs hematopoiesis. Analysis of the age-adjusted CD4:CD8 ratio in 76 MDS patients compared with 54 healthy controls showed that inadequate CD4+, rather than expansion of CD8+ T cells, was associated with a lower ratio in a group that included both lower and higher risk MDS patients defined by the International Prognostic Scoring System. In younger MDS patients, naive and memory phenotypes defined by CD45RA and CD62L display showed depletion of naive CD4+ and CD8+ T cells, suggesting a possible relationship to IST responsiveness. To determine the correlation between T-cell subset distribution, T-cell turnover and autoimmunity, a cohort of 20 patients were studied before and after IST. The CD4:CD8 ratio correlated inversely with the proliferative T-cell index before treatment in IST-responsive patients, suggesting that proliferation may be linked to accelerated CD4+ T-cell turnover and hematopoietic failure. Our data show seminal findings that both CD4+ and CD8+ T-cell subsets are dysregulated in MDS. Association between these T-cell defects and response to IST suggests that aberrant T-cell homeostasis and chronic activation are critical determinants influencing autoimmune hematopoietic suppression in younger patients.

Umbilical cord-blood transplantations from unrelated donors in patients with inherited metabolic diseases: Single-institute experience

We evaluated the feasibility of UCBT from unrelated donors and a myeloablative preparative regimen that did not involve anti-thymocyte globulin in five children with lysosomal and peroxisomal diseases. Patients with MPS II (n = 1), adrenoleukodystrophy (n = 1), metachromatic leukodystrophy (n = 2), and Krabbe disease (n = 1) received UCBT between December 2001 and September 2005. All patients received oral Bu (600 mg/m2), CY (200 mg/kg IV), and fludarabine (180 mg/m2 IV). Prophylaxis for GVHD consisted of a combination of tacrolimus and a short methotrexate course. Neutrophil engraftment occurred a median of 24 days (range, 21-25) after transplantation. None had graft rejection. One patient developed grade III acute GVHD and the other four patients had grade I acute GVHD; none had extensive chronic GVHD. One patient developed hemorrhagic cystitis. There were no treatment-related deaths. Although one child with MPS II died of PTLD 10 months after the UCBT, four of the five children are alive 14, 20, 31, and 55 months after transplantation with complete donor chimerism. These results suggest the feasibility of the UCBT with Bu, fludarabine, and CY-preparative regimen for patients with inherited metabolic diseases.

Clinical impact of HLA-DR15, a minor population of paroxysmal nocturnal haemoglobinuria-type cells, and an aplastic anaemia-associated autoantibody in children with acquired aplastic anaemia

Aplastic anaemia (AA) is defined as a pancytopenia caused by bone marrow failure, and its pathogenesis is thought to involve autoimmune processes. Several predictive markers of the response to immunosuppressive therapy (IST) have been proposed, which appear to reflect the immune pathophysiology. We prospectively investigated the presence of human leucocyte antigen (HLA)-DR15, a minor population of paroxysmal nocturnal haemoglobinuria (PNH)-type cells, and antibodies to the recently identified autoantigen postmeiotic segregation increased 1 (PMS1) in 103 children with AA enrolled in a multicentre study. In contrast to adults, children with AA did not show an increased frequency of HLA-DR15. In addition, a sensitive flow cytometric assay revealed that children with AA have a much lower prevalence of PNH-type cells (21.4%) than reported for adults with this disease. An immunoblotting assay detected anti-PMS1 antibody in 15 of 103 (14.6%) of the children. Finally, the response rate to IST was not significantly different between patients with and without DR15 (45.5% vs. 54.0%), PNH-type cells (68.2% vs. 53.1%) or anti-PMS1 antibody (40.0% vs. 59.1%). The current study did not confirm a correlation between these markers and the response to IST, suggesting that there is a difference in the pathophysiologies of adult and paediatric AA.

Immature and mature monocyte-derived dendritic cells in myelodysplastic syndromes of subtypes refractory anemia or refractory anemia with ringed sideroblasts display an altered cytokine profile

Dendritic cells (DC) are pivotal for T cell-mediated immunity. We investigated the early and terminal maturation of monocyte-derived DC (MoDC) in myelodysplastic syndromes (FAB subtypes refractory anemia (MDS-RA) or refractory anemia with ringed sideroblasts (MDS-RARS)). Immature MoDC were obtained by culture of monocytes with GM-CSF and IL-4 for 8 days. To obtain mature MoDC, TNF-alpha was added during the final three culture days. T cell proliferation and T cell cytokine secretion in mixed lymphocyte reactions (MLR) unveiled a strong reduction of allostimulatory capacity of mature but also of immature MoDC from MDS patients. Immature MoDC from MDS patients exhibited an almost normal immunophenotype, but secreted substantially less IL-12 and more IL-10 in response to LPS/IFN-gamma than normal controls. Terminal addition of TNF-alpha to GM-CSF/IL-4 treated monocytes failed to extinguish cytokine production by MDS MoDC and failed to induce the expected membrane upregulation of costimulatory and other ligands as in normal controls. While our data provide further support for previous studies that have indicated an impaired differentiation of immature towards mature MoDC, they also clearly demonstrate a qualitatively and quantitatively altered cytokine secretion at the level of immature MoDC, which may in part explain the reduced allostimulatory capacity of these cells. These alterations may contribute to immune modulation of the clinical phenotype of marrow failure in MDS, and may have to be considered when designing DC-based immunotherapeutic strategies for MDS.

T-bet, a Th1 transcription factor, is up-regulated in T cells from patients with aplastic anemia

In aplastic anemia, immune destruction of hematopoietic cells results in bone marrow failure. Type 1 cytokines, especially IFN-gamma, have been implicated in the pathophysiology of T-cell-mediated, Fas-mediated stem cell apoptosis of hematopoietic cells. Here, we show that the transcription factor T-bet (T-box expressed in T cells) is increased in T cells from patients with aplastic anemia. Patients' T-bet bound directly to the proximal site of the IFN-gamma promoter without any prior stimulation, in contrast to healthy controls. Increased levels of Itk kinase participated in T-bet up-regulation and active transcription of the IFN-gamma gene observed in these patients. Blocking PKC-, a kinase that lies downstream of Itk kinase, decreased T-bet protein and IFN-gamma intracellular levels. These data suggest that the increased IFN-gamma levels observed in aplastic anemia patients are the result of active transcription of the IFN-gamma gene by T-bet. Blocking the transcription of the IFN-gamma gene with kinase inhibitors might lead to the development of novel therapeutic agents for patients with aplastic anemia and other autoimmune diseases.

Autoantibodies frequently detected in patients with aplastic anemia

Although accumulating evidence strongly suggests that aplastic anemia (AA) is a T cell-mediated autoimmune disease, no target antigens have yet been described for AA. In autoimmune diseases, target autoantigens frequently induce not only cellular T-cell responses but also humoral B-cell responses. We hypothesized that the presence of antigen-specific autoantibodies could be used as a "surrogate marker" for the identification of target T-cell autoantigens in AA patients. We screened a human fetal liver library for serologic reactivity against hematopoietic stem/progenitor cell antigens and isolated 32 genes. In 7 of 18 AA patients, an immunoglobulin G (IgG) antibody response was detected to one of the genes, kinectin, which is expressed in all hematopoietic cell lineages tested including CD34+ cells. No response to kinectin was detected in healthy volunteers, multiply transfused non-AA patients, or patients with other autoimmune diseases. Epitope mapping of IgG autoantibodies against kinectin revealed that the responses to several of the epitopes were shared by different AA patients. Moreover, CD8+ cytotoxic T cells raised against kinectin-derived peptides suppressed the colony formation of granulocyte macrophage colony-forming units (CFU-GMs) in an HLA class I-restricted fashion. These results suggest that kinectin may be a candidate autoantigen that is involved in the pathophysiology of AA.

Direct binding of antithymoctye globulin to haemopoietic progenitor cells in aplastic anaemia

Antithymocyte globulin (ATG) is widely used in the treatment of aplastic anaemia (AA) and a response occurs in 60-80% of patients. However, its exact mechanism of action in the treatment of AA has yet to be determined. Previously, we have shown that ATG increases colony growth from purified bone marrow CD34+ cells of AA patients in vitro, and decreases stem cell apoptosis and the expression of soluble Fas receptor after ATG therapy in vivo. The aim of this study was to further examine the association of ATG with AA haemopoietic progenitor cells. We describe here that ATG bound directly to CD34+ cells. Forty-six patients and 20 normal control subjects were studied. ATG bound to CD34+ cells in normal control subjects (mean 90.38%) as determined by flow cytometry. The mean percentage of CD34+ cells binding to ATG was 59.90% in untreated aplastic patients, 83.24% in partial responders, 58.3% in non-responders and 62.73% in relapsed patients. In completely recovered patients, ATG binding was indistinguishable from control subjects. The functionality of AA patients' haemopoietic progenitor cells was assessed using colony assays. These results demonstrate the direct binding of ATG to CD34+ cells and suggest that differences in its binding to AA CD34+ cells could reflect functional differences in the haemopoietic stem cell compartment throughout the disease process.

Antithymocyte globulin and cyclosporine for severe aplastic anemia: association between hematologic response and long-term outcome

CONTEXT

In most patients, aplastic anemia results from T-cell-mediated immune destruction of bone marrow. Aplastic anemia can be effectively treated by stem cell transplantation or immunosuppression.

OBJECTIVE

To assess long-term outcomes after immunosuppressive therapy.

DESIGN, SETTING, AND PATIENTS

Cohort of 122 patients (31 were < or =18 years and 91 were >18 years) with severe aplastic anemia, as determined by bone marrow cellularity and blood cell count criteria, were enrolled in a single-arm interventional research protocol from 1991 to 1998 at a federal government research hospital.

INTERVENTIONS

A dose of 40 mg/kg per day of antithymocyte globulin administered for 4 days, 10 to 12 mg/kg per day of cyclosporine for 6 months (adjusted for blood levels), and a short course of corticosteroids (1 mg/d of methylprednisolone for about 2 weeks).

MAIN OUTCOME MEASURES

Survival, improvement of pancytopenia and transfusion-independence, relapse, and evolution to other hematologic diseases.

RESULTS

Response rates were 60% at 3 months after initiation of treatment, 61% at 6 months, and 58% at 1 year. The blood cell counts of patients who responded no longer satisfied severity criteria and they were transfusion-independent. Overall actuarial survival at 7 years was 55%. Survival was associated with early satisfaction of response criteria (86% vs 40% at 5 years; P<.001) and by blood counts at 3 months (reticulocyte count or platelet count of >50 x 10(3)/ microL predicted survival at 5 years of 90% [64/71] vs 42% [12/34] for patients with less robust recovery [P<.001 by log-rank test]). There were no deaths among responders more than 3 years after treatment. Relapse was common, but severe pancytopenia usually did not recur. Relapse did not influence survival. Thirteen patients showed evolution to other hematologic diseases, including monosomy 7.

CONCLUSIONS

Approximately half of patients with severe aplastic anemia treated with antithymocyte globulin and cyclosporine have durable recovery and excellent long-term survival. These outcomes were related to the quality of hematologic recovery.