Targeting GD2 after allogeneic SCT: effector cell composition defines the optimal use of ch14.18 and the bispecific antibody construct NG-CU (GD2-CD3).

We investigated whether T cell-recruiting bispecific anti-CD3/GD2 antibody NG-CU might be an alternative to therapeutic anti-GD2 monoclonal antibody (mAb) ch14.18, mediating complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC) through natural killer (NK) cells for immunotherapy in high-risk/relapsed neuroblastoma after autologous/allogeneic stem cell transplantation (auto/alloSCT). Different antibody concentrations and effector-to-target ratios (E:T) were evaluated using xCELLigence RTCA system, peripheral blood mononuclear cells (PBMCs) (healthy donors and patients after alloSCT), and neuroblastoma cell lines (LS/LAN-1). Mean specific lysis of LS cells utilizing PBMCs from healthy donors and ch14.18 (1 µg/ml) was 40/66/75% after 12/24/48 h compared to 66/93/100% in the presence of NG-CU (100 ng/ml). NG-CU showed enhanced cytotoxicity compared to ch14.18, even at lower concentrations and E:T ratios, and completely eradicated LS cells after 72 h. To decipher the influence of effector cell subsets on lysis, different ratios of T and NK cells were tested. At a ratio of 1:1, ch14.18 was more effective than NG-CU. Using patient PBMCs taken at different time points posttransplant, significant lysis with both constructs was detectable depending on percentages and total numbers of T and NK cells; in the early posttransplant phase, NK cells were predominant and ch14.18 was superior, whereas later on, T cells represented the majority of immune cells and NG-CU was more effective. Our study highlights the importance of analyzing effector cell subsets in patients before initiating antibody-based therapy. Consequently, we propose an adjusted administration of both antibody constructs, considering the state of posttransplant immune recovery, to optimize anti-tumor activity.

Monocytes show immunoregulatory capacity on CD4+ T cells in a human in-vitro model of extracorporeal photopheresis.

Extracorporeal photopheresis (ECP) is a widely used immunomodulatory therapy for the treatment of various T cell-mediated disorders such as cutaneous T cell lymphoma (CTCL), graft-versus-host disease (GvHD) or systemic sclerosis. Although clinical benefits of ECP are already well described, the underlying mechanism of action of ECP is not yet fully understood. Knowledge on the fate of CD14+ monocytes in the context of ECP is particularly limited and controversial. Here, we investigated the immunoregulatory function of ECP treated monocytes on T cells in an in-vitro ECP model. We show that ECP-treated monocytes significantly induce proinflammatory T cell types in co-cultured T cells, while anti-inflammatory T cells remain unaffected. Furthermore, we found significantly reduced proliferation rates of T cells after co-culture with ECP-treated monocytes. Both changes in interleukin secretion and proliferation were dependent on cell-contact between monocytes and T cells. Interestingly, blocking interactions of programmed death ligand 1 (PD-L1) to programmed death 1 (PD-1) in the in-vitro model led to a significant recovery of T cell proliferation. These results set the base for further studies on the mechanism of ECP, especially the regulatory role of ECP-treated monocytes.

Pediatric Langerhans cell histiocytosis: the impact of mutational profile on clinical progression and late sequelae.

Langerhans cell histiocytosis (LCH) is a clonal histiocytic disorder with recurrent mutations of BRAF and MAP2K1, but data on the impact of genetic features on progression and long-term sequelae are sparse. Cases of pediatric LCH with long-term follow-up from our institution were analyzed for mutations in BRAFV600 and MAP2K1 exons 2 and 3 by immunostaining with mutation-specific VE1 antibody, as well as allele-specific PCR and sequencing, respectively. Clinical and follow-up data were obtained from our files and a questionnaire sent to all former patients. Sixteen of 37 (43%) evaluable cases showed BRAFV600E, one case a BRAFV600D and eleven (30%) a MAP2K1 mutation. Nine cases were unmutated for both genes. All cases with risk organ involvement showed either BRAFV600 or MAP2K1 mutation. Patients with BRAFV600 mutation excluding Hashimoto-Pritzker cases had a significantly higher risk for relapses (p = 0.02). Long-term sequelae were present in 19/46 (41%) patients (median follow-up 12.5 years, range 1.0 to 30.8) with a trend for higher rates in mutated cases (mutated = 9/17, 53% versus non-BRAFV600/MAP2K1 mutated = 2/7, 29%). In addition, 8/9 cases with skin involvement including all Hashimoto-Pritzker cases (n = 3) were positive for BRAFV600E. Infants below 2 years more frequently had BRAFV600 mutations (p = 0.013). Despite favorable prognosis, pediatric LCH shows a high frequency of relapses and long-term medical sequelae.

Antifungal prophylaxis with posaconazole vs. fluconazole or itraconazole in pediatric patients with neutropenia.

Pediatric patients with hemato-oncological malignancies and neutropenia resulting from chemotherapy have a high risk of acquiring invasive fungal infections. Oral antifungal prophylaxis with azoles, such as fluconazole or itraconazole, is preferentially used in pediatric patients after chemotherapy. During this retrospective analysis, posaconazole was administered based on favorable results from studies in adult patients with neutropenia and after allogeneic hematopoietic stem cell transplantation. Retrospectively, safety, feasibility, and initial data on the efficacy of posaconazole were compared to fluconazole and itraconazole in pediatric and adolescent patients during neutropenia. Ninety-three pediatric patients with hemato-oncological malignancies with a median age of 12 years (range 9 months to 17.7 years) that had prolonged neutropenia (>5 days) after chemotherapy or due to their underlying disease, and who received fluconazole, itraconazole, or posaconazole as antifungal prophylaxis, were analyzed in this retrospective single-center survey. The incidence of invasive fungal infections in pediatric patients was low under each of the azoles. One case of proven aspergillosis occurred in each group. In addition, there were a few cases of possible invasive fungal infection under fluconazole (n = 1) and itraconazole (n = 2). However, no such cases were observed under posaconazole. The rates of potentially clinical drug-related adverse events were higher in the fluconazole (n = 4) and itraconazole (n = 5) groups compared to patients receiving posaconazole (n = 3). Posaconazole, fluconazole, and itraconazole are comparably effective in preventing invasive fungal infections in pediatric patients. Defining dose recommendations in these patients requires larger studies.

Consensus of German transplant centers on hematopoietic stem cell transplantation in Fanconi anemia.

Allogeneic hematopoietic stem cell transplantation (HSCT) is currently the only curative therapy for the severe hematopoietic complications associated with Fanconi anemia (FA). In Germany, it is estimated that 10-15 transplants are performed annually for FA. However, because FA is a DNA repair disorder, standard conditioning regimens confer a high risk of excessive regimen-related toxicities and mortality, and reduced intensity regimens are linked with graft failure in some FA patients. Moreover, development of graft-versus-host disease is a major contributing factor for secondary solid tumors. The relative rarity of the disorder limits HSCT experience at any single center. Consensus meetings were convened to develop a national approach for HSCT in FA. This manuscript outlines current experience and knowledge about HSCT in FA and, based on this analysis, general recommendations reached at these meetings.

Comparison of itraconazole, voriconazole, and posaconazole as oral antifungal prophylaxis in pediatric patients following allogeneic hematopoietic stem cell transplantation.

Oral antifungal prophylaxis with extended-spectra azoles is widely used in pediatric patients after allogeneic hematopoietic stem cell transplantation (HSCT), while controlled studies for oral antifungal prophylaxis after bone marrow transplantation in children are not available. This survey analyzed patients who had received either itraconazole, voriconazole, or posaconazole. We focused on the safety, feasibility, and initial data of efficacy in a cohort of pediatric patients and adolescents after high-dose chemotherapy and HSCT. Fifty consecutive pediatric patients received itraconazole, 50 received voriconazole, and 50 pediatric patients received posaconazole after HSCT as oral antifungal prophylaxis. The observation period lasted from the start of oral prophylactic treatment with itraconazole, voriconazole, or posaconazole until two weeks after terminating the oral antifungal prophylaxis. No incidences of proven or probable invasive mycosis were observed during itraconazole, voriconazole, or posaconazole treatment. A total of five possible invasive fungal infections occurred, two in the itraconazole group (4%) and three in the voriconazole group (6%). The percentage of patients with adverse events potentially related to clinical drugs were 14% in the voriconazole group, 12% in the itraconazole group, and 8% in the posaconazole group. Itraconazole, voriconazole, and posaconazole showed comparable efficacy as antifungal prophylaxis in pediatric patients after allogeneic HSCT.

Differential expression of THELPER 1 cytokines upon antigen stimulation predicts ex vivo proliferative potential and cytokine production of virus-specific T cells following re-stimulation.

INTRODUCTION: Cytomegalovirus (CMV) and human adenovirus (ADV) infections are causes of morbidity after stem cell transplantation. Antigen (Ag)-specific T cells are essential for the control of viral infections. However, in vivo expansion potential of T-cell subpopulations is hardly predictable in humans. Furthermore, ex vivo identification of human T cells with repopulating capacity for adoptive T-cell transfer has been difficult. METHODS: We analyzed Ag-specific T-cell populations, subdivided according to the expression of different THELPER- 1 (Th1) cytokines. Isolation by flow cytometry was based on interferon-gamma (IFN)-γ, interleukin (IL)-2, or tumor necrosis factor-alpha (TNF-α) secretion of T cells after ex vivo stimulation with the Ags hexon (for ADV) and pp65 (for CMV). Isolated T cells were expanded and examined for functional characteristics, expansion/differentiation potential, and naïve, effector memory, central memory, and late effector phenotypes. RESULTS: Isolation based on IFN-γ production provides a T-cell population with a mixture of early, central memory, and effector memory T cells, high expansion potential, and effective cytokine production. Selection of T cells with Ag-specific expression of IL-2 or TNF-α, however, results in a T-cell population with reduced proliferation and lower effector potential after expansion. CONCLUSION: We conclude that the exclusive secretion of IFN-γ in the human antiviral T-cell responses preferentially leads to higher repopulation capacities of antiviral T cells, compared to IL-2 or TNF-α secreting T-cell populations.

Children with relapsed or refractory nephroblastoma: favorable long-term survival after high-dose chemotherapy and autologous stem cell transplantation.

BACKGROUND: High-dose chemotherapy (HDC) with autologous stem-cell rescue (ASCR) is a treatment option for pediatric patients with relapsed nephroblastoma. We present long term results of 9 patients treated between 1993 and 2013 at our center. PROCEDURE: Reinduction therapy was carried out according to GPOH and SIOP recommendations. The conditioning regimen consisted of carboplatin (1 200 mg/m²), etoposide (800 mg/m² or 40 mg/kg) and melphalan (180 mg/m²). Purging of the grafts with immunomagnetic CD34 positive selection was performed in 5 patients. RESULTS: 8 of 9 Patients (90%) are alive without evidence of disease after a median follow-up of 8.5 years. Leukocyte engraftment occurred after a median of 10 days (range 8-12). Median numbers of 667/µl CD3+, 329/µl CD4+, 369/µl CD8+T cells and 949/µl B cells were reached after 180 days. No negative impact of CD34 selection was observed. No transplantation-related death occurred. Acute toxicity comprised mucositis III°-IV° in all and veno-occlusive disease in one patient. Long term effects probably related to treatment occurred in 3/7 evaluable patients and comprised hearing impairment, reduced renal phosphate reabsorption, mild creatinine elevation and hypothyroidism (n=1, each). CONCLUSION: Thus, in our experience HDC with ASCR is an effective treatment of recurrent or refractory nephroblastoma with acceptable side effects. However, a randomized trial proving its efficiency with a high level of evidence is needed.

Neutrophilic myeloid-derived suppressor cells in cord blood modulate innate and adaptive immune responses.

Neonates show an impaired anti-microbial host defence, but the underlying immune mechanisms are not understood fully. Myeloid-derived suppressor cells (MDSCs) represent an innate immune cell subset characterized by their capacity to suppress T cell immunity. In this study we demonstrate that a distinct MDSC subset with a neutrophilic/granulocytic phenotype (Gr-MDSCs) is highly increased in cord blood compared to peripheral blood of children and adults. Functionally, cord blood isolated Gr-MDSCs suppressed T cell proliferation efficiently as well as T helper type 1 (Th1), Th2 and Th17 cytokine secretion. Beyond T cells, cord blood Gr-MDSCs controlled natural killer (NK) cell cytotoxicity in a cell contact-dependent manner. These studies establish neutrophilic Gr-MDSCs as a novel immunosuppressive cell subset that controls innate (NK) and adaptive (T cell) immune responses in neonates. Increased MDSC activity in cord blood might serve as key fetomaternal immunosuppressive mechanism impairing neonatal host defence. Gr-MDSCs in cord blood might therefore represent a therapeutic target in neonatal infections.

Stem cell transplantation.

Stem cell transplantation in pediatric patients with leukemia has been a matter of debate since the first successful transplantation in a child with aplastic anemia in Germany in 1975. Since then, there has been a long way to implement fully stem cell transplantation strategies into the treatment studies organized within BFM Groups for first line or second line treatment of acute and chronic leukemias and myelodysplastic syndrome. The role of different risk groups, different donors, stem cell sources and alternative approaches as haploidentical transplantation as well have been studied as the impact of chimerism and minimal residual disease. Finally, for all leukemias and myelodysplastic syndromes integrated treatment pathways have been developed, which integrate stem cell transplantation on an evidence base into the treatment of the patient.

Human leukocyte antigen distribution in German Caucasians with advanced Ewing's sarcoma.

BACKGROUND: Risk stratification criteria for patients with Ewing's sarcoma family of tumors (ESFT) are still limited. We hypothesized divergent human leukocyte antigen (HLA) patterns in ESFT patients and compared HLA-A, -B and -DR phenotype frequencies of patients with advanced ESFT with those of healthy controls. PATIENTS: HLA types of all German Caucasian patients with advanced ESFT and available HLA-A, -B and -DR data registered in the European Group for Blood and Marrow Transplantation, Paediatric Registry for Stem Cell Transplantation and the MetaEICESS data bases (study group, n=30) were retrospectively compared with HLA types of healthy German stem cell donors (control group, n=8 862 for single HLA frequencies and n=8 839 for allele combinations). Study group patients had been immuno-typed due to eligibility for allogeneic stem cell transplantation for high risk of treatment failure, and thus constituted a selected subgroup of ESFT patients. RESULTS: After Bonferroni correction for multiple testing (PC), phenotype frequencies of HLA-A24 remained significantly higher in the study group compared to controls (PC<0.05). Furthermore, several HLA combinations were significantly more frequent in the study group compared to controls (all PC<0.05). CONCLUSION: We report an increased incidence of circumscribed HLA patterns in German Caucasians with advanced ESFT. The possible clinical significance of this observation has to be re-assessed in prospective trials comprising larger ESFT patient numbers of all risk groups.

Nephron sparing surgery for synchronous bilateral nephroblastoma involving the renal hilus.

PURPOSE: Bilateral nephroblastoma involving the renal hilus represents a significant surgical challenge. Different operative strategies have been proposed for this condition. We analyzed the outcome of simultaneous bilateral partial nephrectomy for complex stage V nephroblastoma. MATERIALS AND METHODS: We retrospectively analyzed patients with bilateral nephroblastoma involving the renal hilus operated on at our institution between 2002 and 2008. We assessed patient data and surgical and oncologic outcomes. RESULTS: We analyzed data from 5 patients with a median age of 27 months at surgery (range 13 to 58). Two children had additional pulmonary metastases. Patients were treated according to the International Society of Pediatric Oncology 2001/German Society of Pediatric Oncology and Hematology protocol. All children underwent synchronous bilateral nephron sparing surgery (longitudinal partial nephrectomy or enucleation) of the central tumors. Median operating time was 182 minutes (range 129 to 291), with vascular exclusion performed in 4 patients (7 to 25 minutes). Complications consisted of urinary leakage in 2 cases. Postoperative renal function was unimpaired in 4 patients and 1 patient had Wilms tumor/aniridia/genitourinary malformations/retardation syndrome with glomerulopathy. One patient with pulmonary metastases and blastemal histology had multiple pulmonary relapses and died due to pulmonary progressive disease. Four patients are alive without evidence of disease at a median followup of 45 months (range 44 to 73). CONCLUSIONS: Surgery for central stage V nephroblastoma is possible with good functional and oncologic outcomes. The single stage approach is safe, provided that operating and treating physicians have sufficient expertise with such conditions. The ultimate goal is to avoid tumor nephrectomy.

No difference in survival after HLA mismatched versus HLA matched allogeneic stem cell transplantation in Ewing sarcoma patients with advanced disease.

Patients with advanced Ewing sarcoma (AES) carry a poor prognosis. Retrospectively, we analyzed 66 AES patients treated with allogeneic stem cell transplantation (allo-SCT) receiving HLA-mismatched (group A, n = 39) versus HLA-matched grafts (group B, n = 27). Median age at diagnosis was 13 years, and 15 years (range 3-49 years) at allo-SCT. The two groups did not differ statistically in distribution of gender, age, remission status/number of relapses at allo-SCT, or risk stratum. 9/39 (23%) group A versus 2/27 (7%) group B patients developed severe acute graft versus host disease (GvHD). Of patients alive at day 100, 7/34 (21%) group A versus 9/19 (47%) group B patients had developed chronic GvHD. In group A, 33/39 (85%) versus 20/27 (74%) group B patients died of disease and 1/39 (3%) versus 1/27 (4%) patients died of complications, respectively. Altogether 12/66 (18%) patients survived in CR. Median EFS 24 months after allo-SCT was 20% in both groups, median OS was 27% (group A) versus 17% (group B), respectively. There was no difference in EFS and OS in AES patients transplanted with HLA-mismatched versus HLA-matched graft in univariate and multivariate analyses. In this analysis, CR at allo-SCT is a condition for survival (p < 0.02).

Successful autologous stem cell transplantation in two patients with juvenile dermatomyositis.

Juvenile dermatomyositis (JDM) is a chronic inflammatory disorder of unknown aetiology that affects muscle and skin. We report on two patients with severe progressive JDM who developed contractures and were wheelchair dependent despite therapy including methotrexate (MTX), steroids, immunoglobulins, cyclosporin A, and rituximab. On account of the refractory disease, autologous stem cell transplantation (ASCT) was performed using a CD3/CD19-depleted graft after immunoablative conditioning with fludarabine, cyclophosphamide, and anti-thymocyte globulin. This induced a dramatic improvement and sustained remission of the disease in both patients. We demonstrate that ASCT is a therapeutic option with low toxicity for patients with severe, refractory JDM.

Identification and selective depletion of alloreactive T-cells for adoptive immunotherapy.

BACKGROUND: T-cell-depleted allografts may exhibit delayed T-cell recovery, severe infections, and relapse after haploidentical hematopoietic stem cell transplantation (HSCT). Required donor lymphocyte infusions containing nonalloreactive cells may transfer immune function without causing graft-versus-host disease. METHODS: We developed an ex vivo approach for the immunomagnetic depletion of alloreactive CD25+, CD69+, and HLA-DR+ T-cells. To achieve highest rates of alloantigen expression, we cocultured peripheral blood mononuclear cells (PBMNCs) with PBMNCs (A/B*), dendritic cells (A/B* DCs), or cytokine-pretreated PBMNCs (A/B* cyt cells). Functional analyses were performed after depletion. RESULTS: After coculture with PBMNCs (A/B* cells), 29% of T-cells became CD25+, CD69+, and HLA-DR+. In modified mixed lymphocyte reactions (MLR) (A/B* cyt cells and A/B* DCs), 35% and 37% of T-cells became CD25+, CD69+, and HLA-DR+. Alloactivation was confirmed by interferon gamma release and proliferation. Immuno-magnetic depletion produced <1% alloactivated cells. Furthermore, this depletion strategy was allospecific and hardly impaired the immune function of the retained cells. DISCUSSION: The efficiency of immunomagnetic depletion depended on the stimulatory capacity of stimulator cells and was improved by using cytokine-pretreated PBMNCs for alloactivation. Overall, this approach might be a promising strategy for restoration of the immune system, particularly after haploidentical HSCT.

Basic research and clinical applications of non-hematopoietic stem cells, 4-5 April 2008, Tubingen, Germany.

From 4 to 5 April 2008, international experts met for the second time in Tubingen, Germany, to present and discuss the latest proceedings in research on non-hematopoietic stem cells (NHSC). This report presents issues of basic research including characterization, isolation, good manufacturing practice (GMP)-like production and imaging as well as clinical applications focusing on the regenerative and immunomodulatory capacities of NHSC.

Cellular immune reconstitution after haploidentical transplantation in children.

Delayed immune reconstitution is 1 of the major contributions to the morbidity and mortality after haploidentical transplantation. Patients with a slow recovery of the innate and especially of the adaptive immune system are at high risk for severe and often lethal infections. The reason for delayed immune reconstitution after haploidentical transplantation include the T cell depletion (TCD) of the graft, the thymic dysfunction induced by pretransplant chemotherapies and by the conditioning regimens, and the occurrence of graft-versus-host disease (GVHD) and its treatment. The detailed analysis, understanding, and manipulation of the reconstitution of the cellular immune system will be of utmost importance to overcome the posttransplant immunodefcient status, and should result in a reduced risk of severe and overwhelming infections and hopefully also to a reduced risk of relapse through better immunological control of residual malignant cells.

The history and future prospective of haplo-identical stem cell transplantation.

Initial attempts at haplo-identical transplantation with T-cell replete bone marrow (BM) were associated with a high transplant-related mortality (TRM), mainly caused by severe graft-versus-host disease (GvHD), and previous efforts to prevent GvHD by ex vivo T-cell depletion of haplo-identical BM were associated with a high risk of graft failure and other complications. Improvements in large-scale T-cell depletion techniques of haplo-identical peripheral mobilized stem cells (PBSC) have overcome the human leukocyte antigen (HLA) barrier by using megadose numbers of stem cells obtained by either highly purified CD34(+) selection or negative depletion of T cells. In addition, recent insights into the role of graft-facilitating and anti-leukemic alloreactive natural killer (NK) cells, the permanent availability of the haplo-identical donor post-transplant and continuous improvements in graft-engineering techniques for the generation of effector cells for post-transplant adoptive transfer, have facilitated the development of strategies to decrease regimen-related toxicity through the use of less intensive preparative regimens, prevent severe infections by rebuilding the immune system and decrease the risk of relapse by exploiting the alloreactivity of donor NK cells and other donor-derived effector cells.

A large-scale method for the selective depletion of alphabeta T lymphocytes from PBSC for allogeneic transplantation.

BACKGROUND: We sought to develop a method for the clinical large-scale depletion of alphabeta T lymphocytes from mobilized peripheral stem cells, which would allow the allogeneic transplantation of a graft enriched for stem cells, natural killer (NK) cells and gammadelta T lymphocytes. METHODS: Therefore, we obtained mononuclear cells from either mobilized or non-mobilized healthy adult volunteer donors and incubated the cells with a biotinylated anti-alphabeta T-cell Ab and subsequently with an anti-biotin Ab conjugated with magnetic microbeads. The depletion was then performed using a CliniMACS device. RESULTS: The median T-cell depletion was 3.9 log (range 3.5-4.1 log). The recovery of the gammadelta and NK cells was 92% and 80%, respectively. The recovery of CD34+ stem cells from the mobilized donors was 66%. DISCUSSION: This method had no negative influence on the in vitro colony formation of stem cells, and transplantation of alphabeta-depleted cells into NOD-SCID IL-2 common gamma chain knockout (NOD-scid IL2r (null)) mice resulted in a rapid engraftment of human myeloid and lymphoid cells. This method will allow large-scale depletion of alphabeta T cells from mobilized peripheral blood in clinical trials.

Flow cytometry with anti HLA-antibodies: a simple but highly sensitive method for monitoring chimerism and minimal residual disease after HLA-mismatched stem cell transplantation.

Transplantation of HLA-mismatched stem cells may allow determination of chimerism status of single cells by differential expression of HLA molecules. Monoclonal antibodies against HLA antigens can be used to determine the HLA type of sub-populations by standard flow cytometry. Blood samples from 23 patients transplanted from HLA-mismatched family donors were monitored using HLA-specific antibodies. Suitable antibodies could be found for all donor recipient pairs by using differences in HLA Bw4 and Bw6 groups or other serological antigens. Pretransplant controls of donor and recipient were used to correct for variable fluorescence intensities of the antibodies and sub-populations. Owing to the high sensitivity, cell populations with a minimum frequency of 0.1% were detectable. Flow-cytometric analysis was confirmed by chimerism analysis of immunomagnetically isolated T cells by standard PCR technique. In addition to chimerism evaluation, HLA antibodies improved the detection of leukemic cells after transplantation with aberrant phenotype. In conclusion, flow cytometry using antibodies against HLA antigens is an interesting tool for determination of chimerism and minimal residual disease after HLA-mismatched transplantation. Information about the chimerism status is given on a single-cell level and allows fast and convenient analysis of sub-populations.