Benjamin N. Ostendorf

Myeloid-derived suppressor cells in human peripheral blood: optimized quantification in healthy donors and patients with metastatic renal cell carcinoma

Induction of myeloid-derived suppressor cells is an important mechanism leading to tolerance against tumors. Phenotypic characterization of MDSC has been established and heterogeneous populations with monocytic or granulocytic features have been characterized. Increased levels of MDSC have been described in metastatic renal cell carcinoma and seem to correlate with an adverse outcome. As MDSC constitute only small populations in peripheral blood of cancer patients, it is highly important to achieve technically optimized conditions for quantification. Different cell preparation techniques--besides freezing and thawing--are potential sources of substantial variation. Our study was focused on an optimized quantification of MDSC in pB of healthy donors and patients with mRCC, in whom major technical sources of variation were analyzed. Whole blood and peripheral blood mononuclear cells were used for the flow cytometric quantification of MDSC in the pB of mRCC patients and healthy donors. We compared (1) analysis in whole blood vs. PBMC after Ficoll gradient centrifugation and (2) immediate analysis after blood drawing vs. analysis one day later. Finally, in order to evaluate our optimized technical approach, pB of 15 patients with histologically confirmed mRCC under treatment with either sunitinib or sorafenib was analyzed. No difference in the number of MDSC was observed after analysis in whole blood vs. PBMC. In contrast, the time point of analysis was a source of substantial variation (one day later vs. immediate analysis after blood drawing). In conclusion, for optimal analysis of MDSC, immediate analysis of whole blood after blood drawing rather than one day later seems to be most appropriate under the aspect of practical feasibility and reliability. Using this method, we were able to confirm both (a) increased numbers of MDSC in patients with mRCC and (b) a decrease of MDSC under sunitinib therapy.

A Novel Domain Regulating Degradation of the Glomerular Slit Diaphragm Protein Podocin in Cell Culture Systems

Mutations in the gene NPHS2 are the most common cause of hereditary steroid-resistant nephrotic syndrome. Its gene product, the stomatin family member protein podocin represents a core component of the slit diaphragm, a unique structure that bridges the space between adjacent podocyte foot processes in the kidney glomerulus. Dislocation and misexpression of slit diaphragm components have been described in the pathogenesis of acquired and hereditary nephrotic syndrome. However, little is known about mechanisms regulating cellular trafficking and turnover of podocin. Here, we discover a three amino acids-comprising motif regulating intracellular localization of podocin in cell culture systems. Mutations of this motif led to markedly reduced degradation of podocin. These findings give novel insight into the molecular biology of the slit diaphragm protein podocin, enabling future research to establish the biological relevance of podocin turnover and localization.

Association between low uric acid levels and acute graft-versus-host disease

Endogenous danger signals are increasingly recognized in the pathogenesis of graft-versus-host disease (GVHD). Uric acid (UA) is a known danger signal and is released from injured cells during conditioning for allogeneic hematopoietic stem cell transplantation (HSCT), but its role in GVHD is unclear. Here, we retrospectively analyze 228 consecutive patients with malignant diseases undergoing HSCT from 10/10-HLA-matched donors. Low UA levels at the time of HSCT (day 0) were significantly associated with acute GVHD grades II–IV in univariate (HR 0.836, p = 0.0072) and multivariate analyses (HR 0.815, p = 0.0047). There was no significant association between UA levels and overall survival, non-relapse mortality, and relapse. This is the first report demonstrating a negative association between UA levels and acute GVHD. Due to the easy assessment and established pharmaceutical modification of UA, our findings are potentially clinically relevant. Confirmation in independent cohorts and further investigations into underlying mechanisms, such as reduced antioxidative capacity in hypouricemia, are warranted.

Severe radiotoxicity in an allogeneic transplant recipient with a heterozygous ATM mutation

Patients receiving radiotherapy often experience toxicity of the skin and mucous membranes. While radiotherapy is a mainstay of myeloablative conditioning for allogeneic hematopoietic stem cell transplantation (ASCT), no risk factors for radiotoxicity have been identified in this setting. Here, we report on a patient with excessive radiation‐induced toxicity after ASCT who carried a heterozygous mutation in the Ataxia telangiectasia mutated (ATM) gene. This is the first case to suggest a genetic basis for increased radiotoxicity after myeloablative ASCT.

Synchronous tuberculosis, Epstein-Barr virus-associated lymphoproliferative disorder and cytomegalovirus infection in an allogeneic transplant recipient: a case report

BackgroundAllogeneic stem cell transplant recipients are prone to infections by various organisms. Tuberculosis (TB) represents a rare infectious complication, especially in countries non-endemic for TB.Case reportHere, we report the case of a German patient with exposure to TB decades before he was diagnosed with disseminated TB as well as synchronous Epstein-Barr virus associated lymphoproliferative disorder and cytomegalovirus infection after allogeneic stem cell transplantation for refractory acute myeloid leukemia. Tuberculostatic and virostatic therapy was administered and the patient could be discharged with no apparent signs of infection two weeks after initiation of therapy.ConclusionThis case illustrates the need for awareness of mycobacterial infections in patients from non-endemic regions undergoing stem cell transplantation even if other reasons for fever are present.

Phenotypic characterization of aberrant stem and progenitor cell populations in myelodysplastic syndromes

Recent reports have revealed myelodysplastic syndromes (MDS) to arise from cancer stem cells phenotypically similar to physiological hematopoietic stem cells. Myelodysplastic hematopoiesis maintains a hierarchical organization, but the proportion of several hematopoietic compartments is skewed and multiple surface markers are aberrantly expressed. These aberrant antigen expression patterns hold diagnostic and therapeutic promise. However, eradication of MDS requires targeting of early myelodysplasia propagating stem cells. This warrants an exact assessment of the differentiation stage at which aberrant expression occurs in transformed hematopoiesis. Here, we report results on the prospective and extensive dissection of the hematopoietic hierarchy in 20 patients with either low-risk MDS or MDS with excess blasts and compare it to hematopoiesis in patients with non-malignancy-associated cytopenia or B cell lymphoma without bone marrow infiltration. We found patients with MDS with excess blasts to exhibit characteristic expansions of specific immature progenitor compartments. We also identified the aberrant expression of several markers including ALDH, CLL-1, CD44, and CD47 to be specific features of hematopoiesis in MDS with excess blasts. We show that amongst these, aberrant CLL-1 expression manifested at the early uncommitted hematopoietic stem cell level, suggesting a potential role as a therapeutic target.

BCR-ABL Mutation-Guided Therapy for CML Blast Crisis: A Case Report

The management of patients with chronic myeloid leukemia (CML) in advanced phases is challenging and requires the consideration of different treatment approaches, including targeted therapy with tyrosine kinase inhibitors, cytotoxic chemotherapy, and allogeneic stem cell transplantation. Here, we present the case of a patient with CML in mixed phenotype blast phase illustrating the integration of these strategies and demonstrating the need for close monitoring of treatment response in order to individually adjust treatment regimens.