Late transplant-associated thrombotic microangiopathy verified in bone marrow biopsy specimens is associated with chronic GVHD and viral infections.

OBJECTIVES: To describe late transplant-associated thrombotic microangiopathy (TA-TMA) as chronic endothelial complication in bone marrow (BM) after allogeneic hematopoietic stem cell transplantation (HSCT). METHODS: BM specimens along with conventional diagnostic parameters were assessed in 14 single-institutional patients with late TA-TMA (more than 100 days after HCST), including 11 late with history of early TA-TMA, 10 with early TA-TMA (within 100 days), and 12 non TA-TMA patients. Three non-HSCT patients served as control. The time points of BM biopsy were +1086, +798, +396, and +363 days after HSCT, respectively. RESULTS: Late TA-TMA patients showed an increase of CD34+ and von Willebrand Factor (VWF)+ microvascular endothelial cells with atypical VWF+ conglomerates forming thickened VWF+ plaque sinus in the BM compared to patients without late TA-TMA and non-HSCT. Severe chronic (p = .002), steroid-refractory GVHD (p = .007) and reactivation of HHV6 (p = .002), EBV (p = .003), and adenovirus (p = .005) were pronounced in late TA-TMA. Overall and relapse-free survival were shorter in late TA-TMA than in patients without late TA-TMA (5-year OS and RFS: 78.6% vs. 90.2%, 71.4% vs. 86.4%, respectively). CONCLUSION: Chronic allo-immune microangiopathy in BM associated with chronic, steroid-refractory GVHD and/or viral infections are key findings of late, high-risk TA-TMA, which deserves clinical attention.

The FLAMSA concept-past and future.

The FLAMSA reduced intensity (RIC) concept, also known as "sequential therapy", is a conceptual platform for the treatment of leukemia separated in several parts: induction therapy, a sequence of antileukemic and immunosuppressive conditioning for allogeneic stem cell transplantation, and immune restitution supported by donor lymphocyte transfusions. The antileukemic part consists of fludarabine, cytosine arabinoside, and amsacrine (FLAMSA); non-cross reactive agents like fludarabine and amsacrine have been successfully used in cases of refractoriness and relapse. Immunosuppressive conditioning and transplantation follow after only 3 days of rest. This way, the toxicity of allogeneic transplantation could be reduced and the anti-leukemia effects by using allogeneic immune cells could be optimized. This review summarizes available data on efficacy and toxicity of this approach. Further, possible strategies for improvements are discussed in order to provide better chances for elderly and frail patients and patients with advanced and high-risk disease. Among others, several new agents are available that target molecular changes of leukemia for induction of remission and allow for bridging the time after transplantation until adoptive immunotherapy becomes safe and effective.

Imatinib dose reduction in major molecular response of chronic myeloid leukemia: results from the German Chronic Myeloid Leukemia-Study IV.

Standard first-line therapy of chronic myeloid leukemia is treatment with imatinib. In the randomized German Chronic Myeloid Leukemia-Study IV, more potent BCR-ABL inhibition with 800 mg ('high-dose') imatinib accelerated achievement of a deep molecular remission. However, whether and when a de-escalation of the dose intensity under high-dose imatinib can be safely performed without increasing the risk of losing deep molecular response is unknown. To gain insights into this clinically relevant question, we analyzed the outcome of imatinib dose reductions from 800 mg to 400 mg daily in the Chronic Myeloid Leukemia-Study IV. Of the 422 patients that were randomized to the 800 mg arm, 68 reduced imatinib to 400 mg after they had achieved at least a stable major molecular response. Of these 68 patients, 61 (90%) maintained major molecular remission on imatinib at 400 mg. Five of the seven patients who lost major molecular remission on the imatinib standard dose regained major molecular remission while still on 400 mg imatinib. Only two of 68 patients had to switch to more potent kinase inhibition to regain major molecular remission. Importantly, the lengths of the intervals between imatinib high-dose treatment before and after achieving major molecular remission were associated with the probabilities of maintaining major molecular remission with the standard dose of imatinib. Taken together, the data support the view that a deep molecular remission achieved with high-dose imatinib can be safely maintained with standard dose in most patients. Study protocol registered at clinicaltrials.gov 00055874.

Paramunity-inducing Factors (PINDs) in dendritic cell (DC) cultures lead to impaired antileukemic functionality of DC-stimulated T-cells.

INTRODUCTION: Paramunity-inducing-Factors (PINDs) consist of attenuated/inactivated viruses of various poxvirus-genera, used in veterinary medicine as non-antigen-specific, non-immunising stimulators of the innate immune system against infectious and malignant diseases. Their danger-signaling-interactions were tested for their capacity to improve leukemic antigen-presentation on DC generated from AML-patients' blasts ('DCleu') and DC-stimulation/activation of antileukemic T-cells. METHODS: We analyzed, whether the addition of PINDs during DC cultures (15 healthy, 22 leukemic donors) and mixed lymphocyte culture (MLC, n = 15) with autologous (n = 6), allogeneic (n = 2) or T-cells after stem cell transplantation (SCT; n = 7) would alter the quality and quantity of DC, the composition of T-cell-subsets, and/or their antileukemic functionality (AF) as studied by FACS and functional Fluorolysis-cytotoxicity-assays. RESULTS: Effects on 1. DC-cultures: PINDs in DC-cultures lead to increased proportions of mature DC and DCleu, but reduced proportions of viable and overall, as well as TLR4- and TLR9-expressing DC. 2. MLC: PINDs increased early (CD8+) T-cell activation (CD69+), but reduced proportions of effector-T-cells after MLC 3. AF: Presence of PINDs in DC- and MLC-cultures reduced T-cells' as well as innate cells' antileukemic functionality. 4. Cytokine-release profile: Supernatants from PIND-treated DC- and MLC-cultures resembled an inhibitory microenvironment, correlating with impaired blast lysis. CONCLUSIONS: Our data shows that addition of PINDs to DC-cultures and MLC result in a "blast-protective-capacity" leading to impaired AF, likely due to changes in the composition of T-/innate effector cells and the induction of an inhibitory microenvironment. PINDs might be promising in treating infectious diseases, but cannot be recommended for the treatment of AML-patients due to their inhibitory influence on antileukemic functionality.

The influence of glucocorticoid receptor single nucleotide polymorphisms on outcome after haematopoietic stem cell transplantation.

Haematopoietic stem cell transplantation (HSCT) remains the only cure for most haematological malignancies, however, the mortality rate remains high. Complications after HSCT include relapse, graft versus host disease (GvHD), graft rejection and infection. Over the last few years several groups, have demonstrated that non-HLA gene polymorphisms can be predictive of outcome after HSCT. Since the glucocorticoid cortisol is pivotal in the regulation of the immune system, we decided to examine single nucleotide polymorphisms (SNPs; rs6198, rs33388 and rs33389) within the glucocorticoid receptor (GR) and correlate with HSCT outcome. The training set consisted of patients (n = 458) who underwent HSCT for acute leukaemia between 1983 and 2005. In the recipients, the absence of the ACT haplotype and absence of the T allele of rs33388 were associated with decreased OS and the absence of the ACT haplotype, the absence of the T allele of rs33388 and the presence of the ATA haplotype were associated with increased risk of relapse. In addition, the presence of the ACT haplotype in the recipient showed a trend to be associated with increased risk of chronic graft versus host disease (cGvHD). The patients in this cohort received mainly myeloablative conditioning (n = 327). The SNPs in the glucocorticoid receptor were then investigated in a validation set (n = 251) of HSCT patients transplanted for acute leukaemia from 2006. This cohort contained significantly more patients that had received reduced intensity conditioning (RIC). Some of the results could be validated in these patients. However, contrary to the training set, the absence of the haplotype ACT in the donor in this cohort was associated with increased risk of cGvHD. Differences in the conditioning were shown to influence the results. These results are the first to associate GR SNPs with HSCT outcome and demonstrate the inherent problems of replicating SNP association studies in HSCT, due to different pre-transplant regimens.

Splenic irradiation before hematopoietic stem cell transplantation for chronic myeloid leukemia: long-term follow-up of a prospective randomized study.

In the context of discussions on the reproducibility of clinical studies, we reanalyzed a prospective randomized study on the role of splenic irradiation as adjunct to the conditioning for hematopoietic stem cell transplantation (HSCT) for chronic myeloid leukemia (CML). Between 1986 and 1989, a total of 229 patients with CML were randomized; of these, 225 (98 %; 112 with, 113 without splenic irradiation) could be identified in the database and their survival updated. Results confirmed the early findings with no significant differences in all measured endpoints (overall survival at 25 years: 42.7 %, 32.0-52.4 % vs 52.9 %, 43.2-62.6 %; p = 0.355, log rank test). Additional splenic irradiation failed to reduce relapse incidence. It did not increase non-relapse mortality nor the risk of late secondary malignancies. Comforting are the long-term results from this predefined consecutive cohort of patients: more than 60 % were alive at plus 25 years when they were transplanted with a low European Society for Blood and Marrow Transplantation (EBMT) risk sore. This needs to be considered today when treatment options are discussed for patients who failed initial tyrosine kinase inhibitor therapy and have an available low risk HLA-identical donor.

Mast cells and GVHD: old cells with a new role.

In this issue of Blood, Leveson-Gower et al describe an immunomodulatory role of mast cells in graft-versus-host-disease (GVHD).

Virus infection in HLA-haploidentical hematopoietic stem cell transplantation: incidence in the context of immune recovery in two different transplantation settings.

We retrospectively compared the incidence of virus infections and outcome in the context of immune reconstitution in two different HLA-haploidentical transplantation (haplo-HSCT) settings. The first was a combined T-cell-replete and T-cell-deplete approach using antithymocyte globulin (ATG) prior to transplantation in patients with hematological diseases (cTCR/TCD group, 28 patients; median age 31 years). The second was a T-cell-replete (TCR) approach using high-dose posttransplantation cyclophosphamide (TCR/PTCY group, 27 patients; median age 43 years). The incidence of herpesvirus infection was markedly lower in the TCR/PTCY (22 %) than in the cTCR/TCD group (93 %). Recovery of CD4+ T cells on day +100 was faster in the TCR/PTCY group. CMV reactivation was 30 % in the TCR/PTCY compared to 57 % in the cTCR/TCD group, and control with antiviral treatment was superior after TCR/PTCY transplantation (100 vs 50 % cTCR/TCD). Twenty-five percent of the patients in the cTCR/TCD group but no patient in the TCR/PTCY group developed PTLD. While 1-year OS was not different (TCR/PTCY 59 % vs cTCR/TCD 39 %; p = 0.28), virus infection-related mortality (VIRM) was significantly lower after TCR/PTCY transplantation (1-year VIRM, 0 % TCR/PTCY vs 29 % cTCR/TCD; p = 0.009). On day +100, predictors of better OS were lymphocytes >300/µl, CD3+ T cells >200/µl, and CD4+ T cells >150/µl, whereas the application of steroids >1 mg/kg was correlated with worse outcome. Our results suggest that by presumably preserving antiviral immunity and allowing fast immune recovery of CD4+ T cells, the TCR approach using posttransplantation cyclophosphamide is well suited to handle the important issue of herpesvirus infection after haplo-HSCT.

Younger patients with chronic myeloid leukemia do well in spite of poor prognostic indicators: results from the randomized CML study IV.

Since the advent of tyrosine kinase inhibitors, the impact of age on outcome of chronic myeloid leukemia (CML) patients has changed. We therefore analyzed patients from the randomized CML study IV to investigate disease manifestations and outcome in different age groups. One thousand five hundred twenty-four patients with BCR-ABL-positive chronic phase CML were divided into four age groups: (1) 16-29 years, n = 120; (2) 30-44 years, n = 383; (3) 45-59 years, n = 495; and (4) ≥60 years, n = 526. Group 1 (adolescents and young adults (AYAs)) presented with more aggressive disease features (larger spleen size, more frequent symptoms of organomegaly, higher white blood count, higher percentage of peripheral blasts and lower hemoglobin levels) than the other age groups. In addition, a higher rate of patients with BCR-ABL transcript levels >10 % on the international scale (IS) at 3 months was observed. After a median observation time of 67.5 months, no inferior survival and no differences in cytogenetic and molecular remissions or progression rates were observed. We conclude that AYAs show more aggressive features and poor prognostic indicators possibly indicating differences in disease biology. This, however, does not affect outcome.

Anti-leukaemic activity of a novel haploidentical-transplantation approach employing unmanipulated bone marrow followed by CD6-depleted peripheral blood stem cells in children with refractory/relapsed acute leukaemia.

The treatment outcome of children with refractory acute leukaemia or relapse post-stem cell transplantation is dismal. We report 10 children (non-remission n = 7) who underwent a new haploidentical transplant approach utilizing unmanipulated bone marrow followed by CD6-depleted peripheral blood stem cells. Nine patients had successful engraftment and no evidence of leukaemia. Acute and chronic graft-versus-host-disease was observed in five and three patients, respectively; two patients died of treatment-related toxicity. Seven patients relapsed after 7 (range 3-34) months, however two patients are alive at 6·5 and 7·0 years. This approach provides anti-leukaemic activity even in heavily pre-treated children but long-term disease control requires further intervention.

Immunotherapy with FBTA05 (Bi20), a trifunctional bispecific anti-CD3 x anti-CD20 antibody and donor lymphocyte infusion (DLI) in relapsed or refractory B-cell lymphoma after allogeneic stem cell transplantation: study protocol of an investigator-driven, open-label, non-randomized, uncontrolled, dose-escalating Phase I/II-trial.

BACKGROUND: Patients with B cell malignancies refractory to allogeneic stem cell transplantation (SCT) can be treated by subsequent immunotherapy with donor lymphocyte infusions (DLI). But unlike myeloid leukemia, B cell leukemia and lymphoma are less sensitive to allogeneic adoptive immunotherapy. Moreover, the beneficial graft-versus-lymphoma (GVL) effect may be associated with moderate to severe graft-versus-host disease (GVHD). Thus, novel therapeutic approaches augmenting the anti-tumor efficacy of DLI and dissociating the GVL effect from GVHD are needed. The anti-CD20 x anti-CD3 trifunctional bispecific antibody (trAb) FBTA05 may improve the targeting of tumor cells by redirecting immune allogeneic effector cells while reducing the risk of undesirable reactivity against normal host cells. Hence, FBTA05 may maximize GVL effects by simultaneously decreasing the incidence and severity of GVHD. METHODS/DESIGN: Based on this underlying treatment concept and on promising data taken from preclinical results and a small pilot study, an open-label, non-randomized, uncontrolled, dose-escalating phase I/II-study is conducted to evaluate safety and preliminary efficacy of the investigational antibody FBTA05 in combination with DLI for patients suffering from rituximab- and/or alemtuzumab-refractory, CD20-positive low- or high-grade lymphoma after allogeneic SCT. During the first trial phase with emphasis on dose escalation a maximum of 24 patients distributed into 4 cohorts will be enrolled. For the evaluation of preliminary efficacy data a maximum of 12 patients (6 patients with low-grade lymphoma and/or Chronic Lymphocytic Leukemia (CLL) / 6 patients with high-grade or aggressive lymphoma) will attend the second phase of this clinical trial. DISCUSSION: Promising data (e.g. induction of cellular immunity; GVL predominance over GVHD; achievement of partial or complete responses; prolongation of time-to-progression) obtained from this phase I/II trial would represent the first milestone in the clinical evaluation of a novel immunotherapeutic concept for treatment-resistant low- and high-grade lymphoma and NHL patients in relapse. TRIAL REGISTRATION: NCT01138579.

Chronic graft-versus-host disease: long-term results from a randomized trial on graft-versus-host disease prophylaxis with or without anti-T-cell globulin ATG-Fresenius.

Previous randomized graft-versus-host disease (GVHD)-prophylaxis trials have failed to demonstrate reduced incidence and severity of chronic GVHD (cGVHD). Here we reanalyzed and updated a randomized phase 3 trial comparing standard GVHD prophylaxis with or without pretransplantation ATG-Fresenius (ATG-F) in 201 adult patients receiving myeloablative conditioning before transplantation from unrelated donors. The cumulative incidence of extensive cGVHD after 3 years was 12.2% in the ATG-F group versus 45.0% in the control group (P < .0001). The 3-year cumulative incidence of relapse and of nonrelapse mortality was 32.6% and 19.4% in the ATG-F group and 28.2% and 33.5% in the control group (hazard ratio [HR] = 1.21, P = .47, and HR = 0.68, P = .18), respectively. This nonsignificant reduction in nonrelapse mortality without increased relapse risk led to an overall survival rate after 3 years of 55.2% in the ATG-F group and 43.3% in the control group (HR = 0.84, P = .39, nonsignificant). The HR for receiving immunosuppressive therapy (IST) was 0.31 after ATG-F (P < .0001), and the 3-year probability of survival free of IST was 52.9% and 16.9% in the ATG-F versus control, respectively. The addition of ATG-F to standard cyclosporine, methotrexate GVHD prophylaxis lowers the incidence and severity of cGVHD, and the risk of receiving IST without raising the relapse rate. ATG-F prophylaxis reduces cGVHD morbidity.

Influence of molecular subgroups on outcome of acute myeloid leukemia with normal karyotype in 141 patients undergoing salvage allogeneic stem cell transplantation in primary induction failure or beyond first relapse.

Based on molecular aberrations, in particular the NPM1 mutation (NPM1(mut)) and the FLT3 internal tandem duplication (Flt3-ITD), prognostic subgroups have been defined among patients with acute myeloid leukemia with normal karyotype. Whereas these subgroups are known to play an important role in outcome in first complete remission, and also in the indication for allogeneic stem cell transplantation, data are limited on their role after transplantation in advanced disease. To evaluate the role of molecular subgroups of acute myeloid leukemia with normal karyotype after allogeneic stem cell transplantation beyond first complete remission, we analyzed the data from 141 consecutive adults (median age: 51.0 years, range 18.4-69.3 years) who had received an allogeneic transplant either in primary induction failure or beyond first complete remission. A sequential regimen of cytoreductive chemotherapy (fludarabine, high-dose AraC, amsacrine) followed by reduced intensity conditioning (FLAMSA-RIC), was uniformly used for conditioning. After a median follow up of three years, overall survival from transplantation was 64 ± 4%, 53 ± 4% and 44 ± 5% at one, two and four years, respectively. Forty patients transplanted in primary induction failure achieved an encouraging 2-year survival of 69%. Among 101 patients transplanted beyond first complete remission, 2-year survival was 81% among patients with the NPM1(mut)/FLT3(wt) genotype in contrast to 43% in other genotypes. Higher numbers of transfused CD34(+) cells (hazard ratio 2.155, 95% confidence interval 0.263-0.964, P=0.039) and favorable genotype (hazard ratio 0.142, 95% confidence interval: 0.19-0.898, P=0.048) were associated with superior overall survival in multivariate analysis. In conclusion, patients with acute myeloid leukemia with normal karyotype can frequently be rescued after primary induction failure by allogeneic transplantation following FLAMSA-RIC. The prognostic role of NPM1(mut)/FLT3-ITD based subgroups was carried through after allogeneic stem cell transplantation beyond first complete remission.

Cognitive functioning in allogeneic hematopoietic stem cell transplantation recipients and its medical correlates: a prospective multicenter study.

BACKGROUND: Owing to its neurotoxicity, allogeneic hematopoietic stem cell transplantation (HSCT) carries risks for cognitive impairment. In this multicenter study, we prospectively evaluated cognitive functioning and its medical and demographic correlates in patients undergoing allogeneic HSCT. METHODS: A total of 102 patients were consecutively assessed prior to (T0 ), 100 ± 20 days (T1 ) after, and 12 ± 1 months (T2 ) after HSCT (61% men, 41% acute myeloid leukemia). A comprehensive neuropsychological test battery was applied to evaluate attention, memory, executive function, and fine motor function, summing up into 14 test scores. RESULTS: Before and after HSCT, patients performed below test norms in up to 50% of the test scores. Patients were mostly impaired on word fluency (24%, T0 ), fine motor function, and verbal delayed recall (19% each, T2 ). Impairment on ≥ 1/5 cognitive domains occurred in 47% (T0 ) and 41% (T2 ) of the patients. Performance (mean z-scores) partially improved over time (i.e., visual span forward, verbal learning, and word fluency). However, from baseline to T2 , 16% of the patients showed reliable decline on ≥ 3/14 test scores (reliable change index method). For the majority of neuropsychological subtests, no associations with conditioning intensity, total body irradiation, graft-versus-host disease, cyclosporine treatment, and length of hospital stay were found. Age and premorbid intelligence level were consistently associated with cognition. CONCLUSIONS: Below average cognitive performance is common in this patient group. In addition, a subgroup shows reliable cognitive decline after allogeneic HSCT. Healthcare professionals should be aware of these treatment-related cognitive side effects.

Effective and long-term control of EBV PTLD after transfer of peptide-selected T cells.

Posttransplantation lymphoproliferative disease (PTLD) associated with Epstein-Barr virus (EBV) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation. PTLD is efficiently prevented by adoptive transfer of EBV-specific T cells from the donor. To make EBV-specific T cells available in urgent clinical situations, we developed a rapid protocol for their isolation by overnight stimulation of donor blood cells with peptides derived from 11 EBV antigens, interferon-gamma surface capture, and immunomagnetic separation. Six patients with PTLD received 1 transfusion of EBV-specific T cells. No response was seen in 3 patients who had late-stage disease with multiorgan dysfunction at the time of T-cell transfer. In 3 patients who received T cells at an earlier stage of disease, we observed complete and stable remission of PTLD. Two patients have remained free from EBV-associated disease for more than 2 years. CD8(+) T cells specific for EBV early antigens rapidly expanded after T-cell transfer, temporarily constituted greater than 20% of all peripheral blood lymphocytes, and were maintained throughout the observation period. Thus, a rapid and sustained reconstitution of a protective EBV-specific T-cell memory occurred after the infusion of small numbers of directly isolated EBV-specific T cells.

Allogeneic hematopoietic stem cell transplantation (allo SCT) for chronic myeloid leukemia in the imatinib era: evaluation of its impact within a subgroup of the randomized German CML Study IV.

The role of allogeneic stem cell transplantation in chronic myeloid leukemia is being reevaluated. Whereas drug treatment has been shown to be superior in first-line treatment, data on allogeneic hematopoietic stem cell transplantation (allo SCT) as second-line therapy after imatinib failure are scarce. Using an interim safety analysis of the randomized German CML Study IV designed to optimize imatinib therapy by combination, dose escalation, and transplantation, we here report on 84 patients who underwent consecutive transplantation according to predefined criteria (low European Group for Blood and Marrow Transplantation [EBMT] score, imatinib failure, and advanced disease). Three-year survival after transplantation of 56 patients in chronic phase was 91% (median follow-up: 30 months). Transplantation-related mortality was 8%. In a matched pair comparison of patients who received a transplant and those who did not, survival was not different. Three-year survival after transplantation of 28 patients in advanced phase was 59%. Eighty-eight percent of patients who received a transplant achieved complete molecular remissions. We conclude that allo SCT could become the preferred second-line option after imatinib failure for suitable patients with a donor. The study is registered at the National Institutes of Health, http://clinicaltrials.gov: NCT00055874.

Clofarabine-containing conditioning regimen for allo-SCT in AML/ALL patients: a survey from the Acute Leukemia Working Party of EBMT.

Clofarabine (CLO), a second-generation purine analogue, has demonstrated an efficient anti-leukemia activity while showing a favorable toxicity profile. This retrospective multicenter report assessed the outcome of 90 patients who received a CLO-containing conditioning regimen before allo-SCT for AML (n = 69) or ALL (n = 21). Median age was 42 yr at transplant. The majority of cases (n = 66) presented with an active disease at transplant while 38 patients had received previous transplantation(s). A total of 88 and two patients received a reduced-intensity conditioning or a myeloablative regimen, respectively. Engraftment was achieved in 97% of evaluable patients. With a median follow-up of 14 months (range, 1-45), the 2-year OS, LFS, relapse, and NRM rates were 28 ± 5%, 23 ± 5%, 41 ± 6%, and 35 ± 5%, respectively. When comparing AML and ALL patients, OS and LFS were significantly higher for AML (OS, 35 ± 6% vs. 0%, P < 0.0001); LFS: 30 ± 6% vs. 0%, P < 0.0001). In a Cox multivariate analysis, an AML diagnosis was the only factor associated with a better LFS (HR = 0.37; 95%CI, 0.21-0.66; P = 0.001). We conclude that a CLO-containing conditioning regimen prior to allo-SCT might be an effective treatment. Prospective studies are needed to evaluate the potential role of CLO as part of conditioning regimens in acute leukemias.

Surveillance of megakaryocytic function by measurement of CD61-exposing microparticles in allogeneic hematopoietic stem cell recipients.

Increasing evidence suggests that circulating microparticles (MP) exposing CD61 originate predominantly from megakaryocytes. Dramatic changes in megakaryocytic homeostasis are regularly observed following allogeneic hematopoietic stem cell transplantation (HSCT) and associated with transplantation-associated complications. We studied MP plasma levels prospectively in healthy subjects (n = 10) and allogeneic HSCT recipients (n = 19) twice weekly from the start of conditioning therapy up to day 30. A total of 224 measurement points were evaluated. MP were isolated, double-stained with annexin V and anti-CD61, and analyzed by flow cytometry. In uncomplicated HSCT, we found a correlation between platelet and CD61-exposing MP count, which resulted in a constant ratio of MP per platelet. The ratio was increased in patients with active hematological malignancies before transplantation and normalized during conditioning therapy. After take, the MP ratio increased, whereas infections and microangiopathic hemolytic anemia did not affect the ratio. In patients with GvHD, a decreased MP ratio was observed depending on the grade of GvHD, possibly indicating megakaryocytic damage. The MP ratio was able to discriminate between toxic, septic, and GvHD-induced hyperbilirubinemia. We first describe CD61+ MP levels during allogeneic HSCT and postulate that the MP ratio might be a useful biomarker for the surveillance of megakaryocytes during HSCT.

Canine embryo-derived stem cells and models for human diseases.

Embryonic stem (ES) cells are pluripotent and permanent cell lines which can differentiate into cell types of all the three germ layers. These features imply multiple opportunities for clinical applications in tissue engineering and regenerative medicine. Most of our knowledge on the biology and technology of ES cells is derived from studies with mouse ES cells. While appropriate for proof-of-principle studies, the mouse model has limitations in its application in translational, pre-clinical studies. This is particularly true for studies evaluating the safety and efficacy of stem cell therapies. For this purpose, large animal models more closely mimicking important aspects of human anatomy, physiology and pathology than mouse models are urgently needed. In this context, the dog is an excellent candidate: the plethora of different dog breeds offer a large phenotypic and genetic variability, which can be exploited increasingly well due to the advanced status of the dog genome project and the rapidly growing box of genomic tools. Recently, the first pluripotent canine embryo-derived stem cells have been described, further increasing the potential of the dog as a model system for regenerative medicine. Although these cells express alkaline phosphatase, NANOG and OCT4, and can be differentiated in vitro towards endoderm-, mesoderm- and ectoderm-lineages (typical features of human and mouse ES cells), their in vivo differentiation capability, i.e. formation of teratomas in immunodeficient mice or contribution to chimeric animals, remains to be demonstrated. Here, we discuss the features of reported canine embryo-derived cells and their potential applications in basic and translational biomedical research.