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Immunotherapy with allogeneic natural killer (NK) cells offers therapeutic perspectives for multiple myeloma patients. Here, we aimed to refine NK cell therapy by evaluation of the relevance of HLA-class I and HLA-E for NK anti-myeloma reactivity. We show that HLA-class I was strongly expressed on the surface of patient-derived myeloma cells and on myeloma cell lines. HLA-E was highly expressed by primary myeloma cells but only marginally by cell lines. HLA-Elow expression on U266 cells observed in vitro was strongly upregulated after in vivo (bone marrow) growth in RAG-2−/−γc−/− mice, suggesting that in vitro HLA-E levels poorly predict the in vivo situation. Concurrent analysis of inhibitory receptors (KIR2DL1, KIR2DL2/3, KIR3DL1 and NKG2A) and NK cell degranulation upon co-culture with myeloma cells revealed that KIR–ligand-mismatched NK cells degranulate more than matched subsets and that HLA-E abrogates degranulation of NKG2A+ subsets. Inhibition by HLA-class I and HLA-E was also observed with IL-2-activated NK cells and at low oxygen levels (0.6 %) mimicking hypoxic bone marrow niches where myeloma cells preferentially reside. Our study demonstrates that NKG2A-negative, KIR–ligand-mismatched NK cells are the most potent subset for clinical application. We envision that infusion of high numbers of this subclass will enhance clinical efficacy. Electronic supplementary material The online version of this article (doi:10.1007/s00262-015-1694-4) contains supplementary material, which is available to authorized users.

Purpose: Novel therapeutic agents have significantly improved the survival of patients with multiple myeloma. Nonetheless, the prognosis of patients with multiple myeloma who become refractory to the novel agents lenalidomide and bortezomib is very poor, indicating the urgent need for new therapeutic options for these patients. The human CD38 monoclonal antibody daratumumab is being evaluated as a novel therapy for multiple myeloma. Prompted with the encouraging results of ongoing clinical phase I/II trials, we now addressed the potential value of daratumumab alone or in combination with lenalidomide or bortezomib for the treatment of lenalidomide- and bortezomib-refractory patients. Experimental Design: In ex vivo assays, mainly evaluating antibody-dependent cell-mediated cytotoxicity, and in an in vivo xenograft mouse model, we evaluated daratumumab alone or in combination with lenalidomide or bortezomib as a potential therapy for lenalidomide- and bortezomib-refractory multiple myeloma patients. Results: Daratumumab induced significant lysis of lenalidomide/bortezomib-resistant multiple myeloma cell lines and of primary multiple myeloma cells in the bone marrow mononuclear cells derived from lenalidomide- and/or bortezomib-refractory patients. In these assays, lenalidomide but not bortezomib, synergistically enhanced daratumumab-mediated multiple myeloma lysis through activation of natural killer cells. Finally, in an in vivo xenograft model, only the combination of daratumumab with lenalidomide effectively reduced the tumorigenic growth of primary multiple myeloma cells from a lenalidomide- and bortezomib-refractory patient. Conclusions: Our results provide the first preclinical evidence for the benefit of daratumumab plus lenalidomide combination for lenalidomide- and bortezomib-refractory patients. Clin Cancer Res; 21(12); 2802–10. ©2014 AACR. See related commentary by Laubach and Richardson, p. 2660

To begin to understand the mechanisms that regulate self-renewal, differentiation, and transformation of human hematopoietic stem cells or to evaluate the efficacy of novel treatment modalities, stem cells need to be studied in their own species-specific microenvironment. By implanting ceramic scaffolds coated with human mesenchymal stromal cells into immune-deficient mice, we were able to mimic the human bone marrow niche. Thus, we have established a human leukemia xenograft mouse model in which a large cohort of patient samples successfully engrafted, which covered all of the important genetic and risk subgroups. We found that by providing a humanized environment, stem cell self-renewal properties were better maintained as determined by serial transplantation assays and genome-wide transcriptome studies, and less clonal drift was observed as determined by exome sequencing. The human leukemia xenograft mouse models that we have established here will serve as an excellent resource for future studies aimed at exploring novel therapeutic approaches.

Large animal models are an important preclinical tool for the evaluation of new interventions and their translation into clinical practice. The pig is a widely used animal model in multiple clinical fields, such as cardiology and orthopedics, and has been at the forefront of testing new therapeutics, including cell-based therapies. In the clinic, mesenchymal stem cells (MSCs) are used autologously, therefore isolated, and administrated into the same patient. For successful clinical translation of autologous approaches, the porcine model needs to test MSC in a similar manner. Since a limited number of MSCs can be isolated directly from the bone marrow, culturing techniques are needed to expand the population in vitro prior to therapeutic application. Here, we describe a protocol specifically tailored for the isolation and propagation of porcine-derived bone marrow MSCs.

Interactions within the hematopoietic niche in the BM microenvironment are essential for maintenance of the stem cell pool. In addition, this niche is thought to serve as a sanctuary site for malignant progenitors during chemotherapy. Therapy resistance induced by interactions with the BM microenvironment is a major drawback in the treatment of hematologic malignancies and bone-metastasizing solid tumors. To date, studying these interactions was hampered by the lack of adequate in vivo models that simulate the human situation. In the present study, we describe a unique human-mouse hybrid model that allows engraftment and outgrowth of normal and malignant hematopoietic progenitors by implementing a technology for generating a human bone environment. Using luciferase gene marking of patient-derived multiple myeloma cells and bioluminescent imaging, we were able to follow pMM cells outgrowth and to visualize the effect of treatment. Therapeutic interventions in this model resulted in equivalent drug responses as observed in the corresponding patients. This novel human-mouse hybrid model creates unprecedented opportunities to investigate species-specific microenvironmental influences on normal and malignant hematopoietic development, and to develop and personalize cancer treatment strategies.

Although mesenchymal stromal cells (MSCs) have been applied clinically to treat cardiac diseases, it is unclear how and to which extent transplanted MSCs exert their beneficial effects. To address these questions, pre-clinical MSC administrations are needed for which pigs appear to be the species of choice. This requires the use of porcine cells to prevent immune rejection. However, it is currently unknown to what extent porcine MSCs (pMSCs) resemble human MSCs (hMSCs). Aim of this study was to compare MSC from porcine bone marrow (BM) with human cells for phenotype, multi-lineage differentiation potential, immune-modulatory capacity and the effect on cardiac function after transplantation in a mouse model of myocardial infarction. Flow cytometric analysis revealed that pMSC expressed surface antigens also found on hMSC, including CD90, MSCA-1 (TNAP/W8B2 antigen), CD44, CD29 and SLA class I. Clonogenic outgrowth was significantly enriched following selection of CD271+ cells from BM of human and pig (129 ± 29 and 1961 ± 485 fold, respectively). hMSC and pMSC differentiated comparably into the adipogenic, osteogenic or chondrogenic lineages, although pMSC formed fat much faster than hMSC. Immuno-modulation, an important feature of hMSC, was clearly demonstrated for pMSC when co-cultured with porcine peripheral blood cells stimulated with PMA and pIL-2. Finally, pMSC transplantation after myocardial infarction attenuated adverse remodelling to a similar extent as hMSC when compared to control saline injection. These findings demonstrate that pMSCs have comparable characteristics and functionality with hMSCs, making reliable extrapolation of pre-clinical pMSC studies into a clinical setting very well possible.

Previously, we have reported that our human bone marrow (BM)-like scaffold xenograft model allows the engraftment and outgrowth of normal and malignant hematopoiesis (e.g. multiple myeloma (MM), acute myelocytic/lymphocytic leukemia (AML/ALL) and MDS (Groen et al. Blood 2012; Gutierrez et al. JCI 2014 and data not shown). Whereas the presence of osteoblasts and bone of human origin mimics a human BM-like niche more closely than the murine BM in standard xenotransplant models (e.g. NOD-SCID/NSG mice), still some essential components of the human BM niche, i.e. human blood vessels, are missing. To this end, in addition to human mesenchymal stromal cells we now incorporated cord blood-derived endothelial progenitor cells (CB-EPCs) in the hybrid scaffold production process, to create a multi-tissue compartment that "maximally humanizes" the BM-like niche of our scaffolds. Towards successful implementation of a human vascular system we compared: i) scaffold material composition (biphasic calcium phosphate (BCP) vs. tricalcium phosphate (TCP)); ii) scaffold shape (particles vs. tubes); iii) different types of matrigel for CB-EPC embedding. Histological analysis of the humanized scaffolds, eight weeks after implantation in mice, showed a large number of functional human blood vessels, as indicated by hCD31+ staining and the presence of erythrocytes within. Comparison of the composition and the shapes of the scaffolds indicated superiority of TCP and tube-shaped scaffolds in supporting the formation of vessels. Further analysis of scaffolds for CD44, CD146, LEPR and nestin-positive cells, revealed the presence of other stromal niche cells besides human osteoblasts and endothelial cells. Irradiation of mice carrying these humanized implants did not have a significant deleterious effect on the established human vessels, allowing their further functional evaluation in xenotransplantation. Additionally, mice carrying tubes with and without human CB-EPC derived vessels (on either flank) were subsequently inoculated with adult BM-derived CD34-positive cells by intracardiac injection. Upon analysis 12 weeks later, all tubes showed multi-lineage hematopoietic outgrowth. Interestingly, CB-EPC embedment resulted in increased numbers of CD45+ (2-fold), CD13+ (4-fold) and CD7+ (2-fold), while CD19+ cell numbers were equal. In contrast, in mouse BM almost only CD19+ cells could be detected. Moreover, we observed that the use of CB-EPCs in our scaffolds provides faster kinetics of in vivo engraftment and growth of both patient-derived MM or AML cells. With the addition of both human CB-EPCs and human BM stromal cells, our scaffold systems now simulate both human endosteal and vascular niches of the BM, thereby more closely recapitulating the human hematopoietic niche. Disclosures Yuan: Xpand Biotechnology BV: Employment. de Bruijn:Xpand Biotechnology BV: Employment. Mitsiades:TEVA: Research Funding; Janssen/Johnson & Johnson: Research Funding; Novartis: Research Funding. Martens:Johnson & Johnson: Research Funding. Groen:Johnson & Johnson: Research Funding.

Purpose of review For heart failure patients, the urgent need for heart transplantation exceeds the availability of donor hearts. Therefore, cell transplantation has emerged as an interesting and potential solution. This review will focus on the capability of different types of stem cells to regenerate the heart. Moreover, the mechanism for success will be addressed, focusing on the specific (and indispensable?) role of the cells. Recent findings In recent years, many types of stem cells have been described as a possible source for cell transplantation in failing hearts, with mixed outcomes. Cell transplantation is hampered by suboptimal delivery techniques, limited survival of cells, and reduced proliferation and differentiation rates in vivo. Interestingly, the number of injected cells that engrafted the heart successfully cannot explain the observed beneficial effects and, therefore, paracrine effects are suggested for the success in cell therapy. Summary This review summarizes the current types of stem or progenitor cells used in cardiac cell therapy and beneficial effects on heart function and morphology in preclinical studies. Currently, the observed effects suggest that paracrine effects might be responsible, thereby triggering mobilization and activation of resident (stem) cells, which challenges the classical concept and true regenerative capacity of cell therapy at this point.

Heart failure emerges with a net loss of viable cardiomyocytes, and there is no current therapy to reverse this process to improve long-term cardiac function. Due to a change in viewpoint, that the human heart cannot be considered a terminally differentiated postmitotic organ, incapable of myocardial regeneration, a belief in a new approach for therapy evolved: regenerating the heart. Finding stem cells in the heart capable of replenishing lost cardiomyocytes became a holy grail for research. Heart stem cells were isolated and characterized, originally derived from in- or outside of the heart. Since the endogenous repair potential of the heart following injury is not sufficient, cellular therapy has been performed after myocardial infarction in clinical settings. Clinical therapies performed with autologous skeletal myoblasts, cardiomyocytes, and bone marrow, as well as the animal studies, showed improvements in cardiac function, although the clinical effects are still limited. These findings have stimulated optimism that progression of heart failure might be prevented or even reversed with cell-based therapy. For future research, it will be a challenge to isolate the most potent therapeutic cell with an intrinsic capacity to stimulate regeneration in the heart, by direct participation or by producing paracrine factors.

Daratumumab is an anti-CD38 monoclonal antibody with lytic activity against multiple myeloma (MM) cells, including ADCC (antibody-dependent cellular cytotoxicity) and CDC (complement-dependent cytotoxicity). Owing to a marked heterogeneity of response to daratumumab therapy in MM, we investigated determinants of the sensitivity of MM cells toward daratumumab-mediated ADCC and CDC. In bone marrow samples from 144 MM patients, we observed no difference in daratumumab-mediated lysis between newly diagnosed or relapsed/refractory patients. However, we discovered, next to an expected effect of effector (natural killer cells/monocytes) to target (MM cells) ratio on ADCC, a significant association between CD38 expression and daratumumab-mediated ADCC (127 patients), as well as CDC (56 patients). Similarly, experiments with isogenic MM cell lines expressing different levels of CD38 revealed that the level of CD38 expression is an important determinant of daratumumab-mediated ADCC and CDC. Importantly, all-trans retinoic acid (ATRA) increased CD38 expression levels but also reduced expression of the complement-inhibitory proteins CD55 and CD59 in both cell lines and primary MM samples. This resulted in a significant enhancement of the activity of daratumumab in vitro and in a humanized MM mouse model as well. Our results provide the preclinical rationale for further evaluation of daratumumab combined with ATRA in MM patients.

For more than 10 years umbilical cord blood (UCB) has been used as an alternative source of hematopoietic stem cells for allogeneic transplantation. Although the clinical results are encouraging, UCB is associated with delayed engraftment. To address these issues we have used the NOD/SCID mouse model to study the engraftment potential of cord blood cells in more detail, to assess the engraftment potential of expanded megakaryocytic progenitor cells, and to study the effect of co-transplantation of mesenchymal stem cells on engraftment.

Objective Umbilical cord blood (UCB) is considered as an attractive alternative source of hematopoietic stem cells for allogeneic stem cell transplantations in patients who lack human leukocyte antigen (HLA)-matched donors. However, the low cell dose adversely affects hematopoietic recovery and therefore limits application of UCB transplantation in adults. Transplantation of multiple UCB units could be a strategy to overcome cell dose limitations. Materials and Methods To investigate the effect of double cord transplantation, nonobese diabetic/severe combined immunodeficient mice were transplanted with human hematopoietic progenitor cells (CD34 + ) derived from two UCB units with HLA disparity. Human cell engraftment and donor origin was determined by flow cytometry. Results Double CB transplantation resulted in increased engraftment levels in the bone marrow and peripheral blood in comparison with recipients of a single unit. Because this effect could be due to the higher cell dose (2.10 5 vs 1.10 5 cells), double CB transplantation was compared with single units containing equal cell numbers (2.10 5 ). In some cases, engraftment levels in recipients of single units containing 2.10 5 cells were significantly higher than after transplantation of 1.10 5 cells. These engraftment levels were similar to those observed after double CB transplantation. Chimerism analysis indicated that increased engraftment in recipients of two units was predominantly derived from one unit, whereas in other cases the contribution of the two units was similar. Conclusion These results indicate that engraftment may be enhanced by addition of a second unrelated CB that might be attributed to a cell dose effect or due to a graft-facilitating effect.

An increase in the number of circulating endothelial cells (CEC) and of bone marrow-derived endothelial progenitor cells (EPC) in the peripheral blood is associated with vascular injury, repair and neovascularization. The phenotype and number of CEC may serve as diagnostic or prognostic parameters of vascular injury and tumour growth. An increase in the number of EPC may reflect repair of ischaemic vascular injury, a finding which has resulted in the initiation of clinical cardiovascular pilot trials using cell therapy. However, there is no consensus on the exact phenotype of the EPC and haematopoietic stem cells (HSC) and therefore the best candidate cell for transplant has not been established. Although the use of peripheral blood stem cells following mobilization, or of ex vivo-expanded cells,. may improve EPC-mediated vascular graft endothelialization or tissue vascularization, sustained EPC-induced neovascularization still needs to be proven. Flow cytometric characterization, in combination with functional assays, will further elucidate the phenotype of the CEC and EPC, thereby providing reliable detection to appreciate their role in vascular diseases and cancer and to evaluate and, if possible, improve their therapeutic potential

Objective Mesenchymal stem cells (MSC) have been implicated as playing an important role in hematopoietic stem cell engraftment. We identified and characterized a new population of MSC derived from human fetal lung. In cotransplantation experiments, we examined the homing of MSC as well as the effect on engraftment of human umbilical cord blood (UCB)-derived CD34 + cells in NOD/SCID mice. Materials and Methods Culture-expanded fetal lung-derived CD34 + cells were characterized by immune phenotyping and cultured under conditions promoting differentiation to osteoblasts or adipocytes. Irradiated (3.5 Gy) NOD/SCID mice (n = 51) were transplanted intravenously with 0.03 to 1.0 × 10 6 UCB CD34 + cells in the presence or absence of 1 × 10 6 culture-expanded fetal lung-derived MSC, irradiated CD34 − cells, B cells, or with cultured MSC only. Results Culture-expanded fetal lung CD34 + cells were identified as MSC based on phenotype (CD105 + , SH3 + , SH4 + , CD160 + ) and their multilineage potential. Cotransplantation of low doses of UCB CD34 + cells and MSC resulted in a three-fold to four-fold increase in bone marrow engraftment after 6 weeks, whereas no such effect was observed after cotransplantation of irradiated CD34 − or B cells. Homing experiments indicated the presence of MSC in the lung, but not in the bone marrow, of NOD/SCID mice. Conclusions We identified a population of MSC derived from human fetal lung. Upon cotransplantation, MSC, but not irradiated CD34 − or B cells, promote engraftment of UCB CD34 + cells in bone marrow, spleen, and blood by mechanisms that may not require homing of MSC to the bone marrow.

It was hypothesized that during mammalian development, the extensive need for hematopoietic cells requires equal contribution to blood cell production from both quiescent and cycling hematopoietic stem cells (HSCs) while maintaining the stem cell pool. To investigate this hypothesis, the engraftment potential of umbilical cord blood (UCB) CD34+ cells residing in either G0(G0CD34+ cells) or G1(G1CD34+ cells) phases of the cell cycle was assessed in nonobese diabetic/severe combined immune-deficient (NOD/SCID) mice. Whereas the level of chimerism in mice transplanted with UCB G0CD34+ cells was 69.9% ± 24.0%, mice receiving equal numbers of G1CD34+ cells harbored 46.7% ± 21.3% human cells 8 weeks posttransplantation. Both groups of cells sustained multilineage differentiation and the production of CD34+cells in recipient animals. The relationship between the number of transplanted G0CD34+ or G1CD34+ cells and the level of chimerism was analyzed by a general linear models procedure. Although the initial level of chimerism following transplantation of G0CD34+ cells was higher than that sustained by G1CD34+ cells, the increment in the degree of chimerism obtained with each additional 103 cells of either phenotype was identical, suggesting that the reconstitution potential of these 2 types of cells was similar. Of interest is that human cells recovered from primary recipients of both G0CD34+ and G1CD34+cells engrafted in secondary NOD/SCID recipients, albeit at a substantially lower level, confirming the primitive nature of UCB CD34+ cells residing in G1.

Aim: One of the main limitations for an effective cell therapy for the heart is the poor cell engraftment after implantation, which is partly due to a large percentage of cell death in the hostile myocardium. In the present study, we investigated the utilization of Necrostatin-1 (Nec-1) as a possible attenuator of cell death in Sca-1+ cardiac progenitor cells (CPCs). Methods and Results: Under oxidative stress conditions in vitro, Nec-1 pretreatment reduced necrotic cell death in Sca-1+ CPCs. In a mouse model of myocardial infarction, survival of CPCs 3 days after intra-myocardial injection was 39% higher (BLI signal, 71,665 ± 11,165 vs 117,138 ± 18,567 ph/s/cm2/sr) in cells pretreated with the Nec-1 compound. However, the increase in cell number did not translate into improved cardiac function at one month follow-up (EF %, 20.6±2.1 vs 21.4±2.5 for vehicle and Nec-1 treated CPC, respectively). We extensively investigated, but did not find, alternative effects to the pro-survival properties of the compound on the CPCs. Furthermore, CPCs rescued by Nec-1 remained functionally competent. Conclusion: A pharmacological pretreatment approach to solely enhance cell survival on the short-term does not seem to be effective strategy to improve cardiac cell therapy with Sca-1+ CPCs. Since the initial cell retention directly after injection is low (~10%), survival strategies could conceivably be more useful in a tissue engineering setting, in which they can exert their effects on larger number of cells.

Aims One of the main limitations for an effective cell therapy for the heart is the poor cell engraftment after implantation, which is partly due to a large percentage of cell death in the hostile myocardium. In the present study, we investigated the utilization of necrostatin-1 (Nec-1) as a possible attenuator of cell death in cardiomyocyte progenitor cells (CMPCs). Methods and results In a mouse model of myocardial infarction, survival of CMPCs 3 days after intra-myocardial injection was 39 ± 9% higher in cells pretreated with the Nec-1 compound. However, the increase in cell number was not sustained over 28 days, and did not translate into improved cardiac function (ejection fraction %, 20.6 ± 2.1 vs. 21.4 ± 2.5 for vehicle and Nec-1-treated CMPC, respectively). Nonetheless, Nec-1 rescued CMPCs remained functionally competent. Conclusion A pharmacological pretreatment approach to solely enhance cell survival on the short term does not seem to be effective strategy to improve cardiac cell therapy with CMPCs.

Analysis of T cell subsets in the spleen during graft-versus-host (GVH) reactions in a fully allogeneic mouse strain combination demonstrated that first CD4+ T cells become activated, and initiate the GVH reaction. Subsequently, CD8+ T cells become involved. Here we show that anti-CD8 treatment on day +3 resulted in a significant increase in survival, while early treatment (day -1 or day +1) did not. Acute GVH reactions were induced (day 0) in lethally irradiated (C57BL/6 x CBA/J)F1 (H-2b/k) mice by intravenous injection of BALB/c (H-2d) spleen and lymph node cells (3.6 x 10(7)) within 24 h after irradiation. Mice were treated intraperitoneally with a single optimally depleting dose of rat anti-CD8 (YTS 169.4) or untreated. Symptoms of GVHD became obvious 6 days after reconstitution, and mortality started at day 8. The mutual influence of CD4+ and CD8+ T cells in the development of GVHD becomes apparent from our data, and demonstrates that GVHD lethality can be caused by CD8+ T cells as well as by CD4+ T cells.

Objective To determine prostanoid levels (prostaglandin E 2 , prostaglandin F 2α , 6-keto-prostaglandin F 1α , and thromboxane B 2 [TXB 2 ]) in embryo culture medium containing inactivated maternal serum and their correlation with the clinical outcome of IVF-ET. Design Prostanoid levels were measured in blank control medium and in medium containing an embryo or nonfertilized oocyte with a high-pressure liquid chromatography (HPLC-RIA) method. Comparison of HPLC-RIA, Seppak C 18 -RIA, and RIA directly in the medium demonstrated identical results for TXB 2 , allowing the use of direct RIA in the large investigation of 129 media. Setting Leiden University Hospital, The Netherlands. Patients Patients with (n=12) and without (n=15) an ongoing pregnancy after IVF-ET. Main Outcome Measures Prostanoid levels in embryo culture medium and relationship between prostanoid levels and successful implantation. Results Thromboxane B 2 is the only prostanoid consistently found in these media. In both groups there was no difference in TXB 2 levels between control media, media containing a nonfertilized oocyte, and media containing an embryo. There was no difference in TXB 2 levels between media that had harbored the beginning of a successful pregnancy and those that had not produced a pregnancy. Conclusion Thromboxane B 2 in the embryo culture medium originates from maternal serum and bears no relationship with the likelihood of fertilization and implantation.

Patients suffering from heart failure as a result of myocardial infarction are in need of heart transplantation. Unfortunately the number of donor hearts is very low and therefore new therapies are subject of investigation. Cell transplantation therapy upon myocardial infarction is a very promising strategy to replace the dead myocardium with viable cardiomyocytes, smooth muscle cells and endothelial cells, thereby reducing scarring and improving cardiac performance. Despite promising results, resulting in reduced infarct size and improved cardiac function on short term, only a few cells survive the ischemic milieu and are retained in the heart, thereby minimizing long-term effects. Although new capillaries and cardiomyocytes are formed around the infarcted area, only a small percentage of the transplanted cells can be detected months after myocardial infarction. This suggests the stimulation of an endogenous regenerative capacity of the heart upon cell transplantation, resulting from release of growth factor, cytokine and other paracrine molecules by the progenitor cells – the so-called paracrine hypothesis. Here, we focus on a relative new component of paracrine signalling, i.e. exosomes. We are interested in the release and function of exosomes derived from cardiac progenitor cells and studied their effects on the migratory capacity of endothelial cells.

We have recently demonstrated that corticotropin releasing hormone (CRH) potentiates the contractile response to oxytocin of human gestational myometrium, using a high flow microsuperfusion system and electrical field stimulation. We now report this potentiation to be equivalent to that of 1 nM prostaglandin F2 alpha (PGF2 alpha), while 10 nM PGF2 alpha did not potentiate the response to oxytocin. Prostaglandin E2 (PGE2) also showed no augmentation of the contraction force of the myometrium in response to oxytocin. The CRH potentiated response was inhibited by the lipoxygenase and cyclooxygenase inhibitor BW755C (1 microM) and by indomethacin (0.1 microM), but not by the lipoxygenase inhibitor BW4C (1 microM). Measurements of prostaglandins in the superfusate showed no significant trends. It is concluded that the potentiation of contraction force to oxytocin by CRH is dependent on prostaglandins, probably PGF2 alpha and that leukotrienes, generated via the lipoxygenase pathway are not involved.

Aims: Clinical trials showed contradictory results in functional recovery after intracoronary infusion of autologous mononuclear (bone marrow) cells in patients with acute myocardial infarction. A recent study suggests that this might be related to the isolation protocol used. In The Netherlands, a comparable randomised multicentre trial (HEBE) was designed. To validate the isolation method of bone marrow and peripheral blood-derived mononuclear cells, we compared our processing protocol with methods comparable to the ASTAMI (no beneficial effect) and the REPAIR-AMI study (beneficial effect). Methods and results: The effect of several factors (density gradient, washing buffer and centrifugation speed) has been studied on recovery and function (migration and clonogenic capacity) of mononuclear cells. Significantly lower cell recoveries were found at a centrifugation speed of 250 g, compared to 600 or 800 g, respectively. Furthermore, washing buffer without supplemented human serum albumin and heparin resulted in significantly lower cell recovery and functional impairment as measured by clonogenic capacity. Conclusions: The results of our study justify the cell-processing protocol as applied in the HEBE trial (600 g, human serum albumin supplemented washing buffer). This protocol results in viable and functional cells of which the quantity and quality is at least comparable to a successful study like the REPAIR-AMI.

Interactions with the hematopoietic niche in the bone marrow (BM) microenvironment are essential for hematopoietic stem cell (HSC) self-renewal. In addition, this niche is considered to serve as a sanctuary site for leukemic stem cells during chemotherapy, and contributes to disease relapse. Although many advances have been made in understanding how the niche regulates HSC self-renewal and confers therapy resistance, most of this knowledge is based on genetically engineered murine models. Given the need for models that more closely resemble the human niche, we developed a humanized model in which a scaffold seeded with human BM stromal cells generates a bone microenvironment. Inoculation of these mice with human CD34+-progenitor cells resulted in homing to the human bone environment and the generation of hematopoietic cells of distinct lineages as well as the engraftment of CD34+ cells themselves. The functionality of these humanized niches was further investigated with primary samples obtained from patients diagnosed with MDS, AML, T-ALL and MM, malignancies of which the tumor cells are highly dependent on the BM microenvironment for survival and growth. In addition, by gene-marking MM and T-ALL cells with luciferase and using bioluminescent imaging, we were able to follow tumor burden over time as well as response to therapy. Importantly, in this model, the response of primary MM cells to established anti-MM agents correlates with clinical responses of the respective patients. Moreover, this model allows us to study bidirectional interactions between MM cells and stromal cells and the resulting impact. By analyzing gene expression in human BM stromal cells (CD73+ CD90+ CD105+) that we cultured from scaffolds containing MM tumors, we identified potential novel markers for osteogenesis in MM (e.g. OGN, OMD and ASPN), as well as adhesion molecules (e.g. ITGA2) and extracellular matrix proteins (e.g. STC1 and TGM2). Hence, our model allows to investigate essential interactions within the human BM microenvironment for the development of normal and malignant hematopoiesis and thus for therapy development. This abstract is also presented as Poster B41. Citation Format: Jessica Sigmans, Willy Noort, Coleman Lindsley, Li Pan, Linda Aalders, Megan Bariteau, Benjamin Ebert, Jon Aster, Uli Steidl, Jan Schuringa, Huipin Yuan, Joost de Bruijn, Reinier Raymakers, Henk Lokhorst, Tuna Mutis, Anton Martens, Constantine Mitsiades, Richard Groen. Biological insights into tumor-bone marrow microenvironment interactions derived from a humanized murine model. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr PR12. doi:10.1158/1538-7445.CHTME14-PR12

Chimeric Antigen Receptors (CARs) are engineered constructs consisting of an antibody-derived antigen recognition domain linked to intracellular T cell signaling domains. Cytotoxic T cells transduced to express tumor-reactive CARs are highly promising tools for immunotherapy of cancer. The CD38 molecule, with its high and homogenous expression on Multiple Myeloma (MM) tumor cells, is considered a suitable target for antibody therapy of MM. Prompted by this, we evaluated the feasibility and efficacy of targeting MM cells with CD38-CAR-transduced T cells (CD38-CAR T cells). To this end, we generated three different retroviral CAR constructs based on human CD38 antibodies as antigen recognition domain, CD3zeta and 41BB (CD137) as signaling domains and transduced them into PBMCs of a healthy donor. After in vitro selection and expansion, all CD38-CAR T cells, either unsorted or CD4/CD8 sorted, effectively lysed MM cell lines in a dose-, and CD38 expression-dependent manner, with a better efficacy for the CD8+ fraction. CD38-CAR T cells also effectively eradicated primary MM cells in the bone marrow mononuclear cells derived from MM patients, indicating their clinical relevancy. Although CD38-CAR T cells also displayed cytotoxic activity against the CD38+ fraction of mature monocytes and NK cells and to a lesser extent CD38+ B and T cells, they did not affect the outgrowth of CD34+ cells into various myeloid lineages. In addition,CD38-CAR T cell activity was effectively controllable by transducing them with a caspase 9-based inducible suicide gene. More interestingly, we discovered that the CD38-CAR T cells were themselves devoid of CD38 surface expression, indicating that CD38 was not essential for T cell expansion and function. Finally, in a novel in vivo xenotransplant model (UM9 cell line), in which myeloma cells were grown in a humanized bone marrow microenvironment, i.v. as well as intra tumor administration of CD38-CAR T cells established significant anti-tumor effects, proving that CD38-CAR endowed cytotoxic T lymphocytes, even with no CD38 expression, can efficiently migrate, infiltrate and eliminate human MM tumors growing in their natural niche. These results demonstrate the feasibility and potency of CAR mediated targeting of CD38+ MM cells. Optimization of CD38-CAR and suicide-gene control of CD38 CAR T cellsmay provide next steps towards safe clinical implementation of CD38-CAR T cell immune therapy. Disclosures Drent: Genmab BV: Guest employee (unpaid) Other. Lammerts van Bueren:Genmab : Employment. Parren:Genmab: Employment, Equity Ownership. van de Donk:Genmab BV: Research Funding; J&J: Research Funding; Celgene: Research Funding. Martens:Genmab BV: Research Funding; J&J: Research Funding; Celgene: Research Funding. Lokhorst:Celgene: Research Funding; J&J: Research Funding; Genmab: Research Funding. Mutis:Celgene: Research Funding; J&J: Research Funding; Genmab BV: Research Funding.

Objective Previously, we have found that human culture-expanded fetal lung–derived mesenchymal stem cells (MSC) promote the engraftment of umbilical cord blood (UCB)-derived CD34 + cells. The high frequency of MSC in fetal lung allowed us to study whether this represented a biological feature of these cells or a property that was acquired during expansion in culture. Materials and methods Irradiated NOD/SCID mice (n=80) were transplanted with 0.1×10 6 UCB CD34 + cells in the presence or absence of 10 6 primary nonexpanded or culture-expanded fetal lung, liver, or BM CD45 − cells, or with nonexpanded fetal lung liver or BM CD45 − cells only. Results In comparison with transplantation of UCB CD34 + cells only, cotransplantation of UCB CD34 + cells and primary fetal lung or BM CD45 − cells resulted in a significantly higher level of engraftment (% hCD45 + cells) in BM, PB, and spleen. In addition, primary mesenchymal cells derived from adult BM had a similar promoting effect. The engraftment-enhancing effect was similar to that of culture-expanded fetal lung and BM MSC. Primary mesenchymal cells, but not culture-expanded MSC, were detected in recipient mice, suggesting that the primary cells were able to home and that this capacity was lost after expansion. Conclusion These results show that primary mesenchymal cells from fetal lung and BM promote the engraftment of UCB-derived CD34 + cells to a similar degree as culture-expanded MSC, indicating that it reflects a biological property of primary MSC that is preserved during expansion in culture.

We previously found that human fetal lung is a rich source of mesenchymal stem cells (MSC). Here we characterize and analyze the frequency and function of MSC in other second-trimester fetal tissues.Single cell suspensions of fetal bone marrow (BM), liver, lung, and spleen were made and analyzed by flow cytometry for the expression of CD90, CD105, CD166, SH3, SH4, HLA-ABC, HLA-DR, CD34 and CD45. We assessed the frequency of MSC by limiting dilution assay.The frequency of MSC in BM was significantly higher than in liver, lung, and spleen (p0.05). On primary non-expanded cells from fetal liver, lung and spleen the number of cells positive for mesenchymal markers was significantly higher within the CD34 positive population than within the CD34 negative population. The phenotype of the culture-expanded MSC was similar for all fetal tissues, i.e. CD90, CD105, CD166, SH3, SH4 and HLA-ABC positive and CD34, CD45 and HLA-DR negative. Culture-expanded cells from all tissues were able to differentiate along adipogenic and osteogenic pathways. However, adipogenic differentiation was less in MSC derived from spleen, and osteogenic differentiation was reduced in liver-derived MSC (p0.05).Our results indicate that culture-expanded MSC derived from second-trimester fetal tissues, although phenotypically similar, exhibit heterogeneity in differentiating potential. We speculate that these differences may be relevant for the clinical application of MSC.

Human mesenchymal stem cells (MSCs) are multipotent stem cells, able to differentiate into multiple mesenchymal lineages.[1][1]-[3][2] Previously, we have shown that human fetal lung–derived MSCs enhance the engraftment of human umbilical cord blood (UCB)–derived CD34+ hematopoietic cells in

Techniques have recently beome available to isolate and grow mesenchymal progenitors and to manipulate their growth under defined in vitro culture conditions. As a result mesenchymal stem cells can be rapidly expanded to numbers that are required for clinical application. This has allowed the clinical testing of culture-expanded MSCs in the context of hematopoietic stem cell transplantation. In this paper we discuss the role of MSCs in hematopoietic engraftment after transplantation.

Umbilical cord blood (UCB), bone marrow (BM) and mobilized peripheral blood (mPB) are used as sources of hematopoietic stem cells for transplantation. The NOD/SCID mouse model was used to compare the lineage-specific repopulating potential of CD34(+) cells derived from these sources. Six to 8 weeks after transplantation, blood, BM, spleen, liver and thymus, were harvested, and analyzed by flow cytometry using CD34, CD45, myeloid, and lymphoid lineage-specific antibodies. Fifty percent engraftment of human cells in bone marrow of mice was estimated to be reached with 0.55 x 10(6) CD34(+) UCB cells or with 7.9 x 10(6) CD34(+) cells from adult sources, illustrating a 10-fold superiority of UCB CD34(+) cells to engraft NOD/SCID mice. Lineage-specific characterization of engrafted human cells showed that the high engraftment potential of CD34(+) cells from UCB was due to a preferential B cell development (2-81%). In contrast, comparable percentages of myeloid cells were found following transplantation of CD34(+) cells from UCB, BM and mPB (1-38%), and occurred at significant levels only at relatively high doses. Since the CD34 content of UCB transplants is usually at least one log lower than of transplant from adult sources, these results correspond to the clinical findings with UCB transplantation showing a relatively high overall engraftment, but delayed myeloid recovery.

Multiple myeloma (MM), a B-cell neoplasm characterized by a clonal expansion of malignant plasma cells in the bone marrow (BM), is accompanied by osteolytic lesions and/or diffuse osteopenia in up to 90% of the patients. Even after successful treatment, these MM-induced bone lesions do not normalize. We hypothesized that this might be caused by MM-induced irreversible impairment of the osteoblast function in the BM microenvironment. To study this bone remodeling processes in MM we used a recently developed, humanized mouse model of MM that allows engraftment and outgrowth of patient MM (pMM) cells in a humanized BM niche. To this end, ceramic scaffolds are seeded with culture-expanded human mesenchymal stromal cells (MSCs) from human BM, differentiated in vitro to osteoblasts for 1 week, then implanted subcutaneously in immune-deficient RAG2-/-gc-/--mice and after 6-8 weeks a layer of human bone is deposited on the surface of the scaffolds. Following the injection of luciferase-GFP gene marked primary MM cells (pMM), this results in homing and outgrowth of pMM in the scaffolds (Groen et al., Blood 2012). Here we describe a modification of this in vivo model, by co-implanting MSC loaded scaffolds, with pMM cells adhered to the hybrid scaffolds, at one side of the mouse, and with hybrid scaffolds only (without pMM) at the other side of the mouse. At this contra-lateral location bone formation can take place undisturbed (i.e., not affected by the presence of MM) and serves as an internal control for the osteogenic potential of the osteoblasts. Thus this model allows us to study bidirectional interactions between pMM cells and the osteoblast and the resulting inhibition of osteogenesis. Here we report that outgrowth pMM cells indeed resulted in on average 50-75% decrease in bone formation, and, using bioluminescence imaging, we found an inverse correlation between the size of the tumor and the amount of bone formation: with increasing tumor size, the amount of bone formed was less. Human AML growing in the scaffolds (serving as control) does not influence the bone forming process. At the end of the experiment when we analyzed gene expression in the human stromal cells (CD73+ CD90+ CD105+) that we cultured from scaffolds containing pMM tumors, we found a significant reduction in expression of transcripts for alkaline phosphatase (ALP), collagen1A1 (colA1), osteoglycin (OGN), osteomodulin (OMD), and abnormal spindle-like microcephaly associated (ASPM), genes that have been implicated in osteogenesis. These data suggest that pMM cells interfere with the osteogenic differentiation of MSCs in the context of an in vivo biocompatible scaffold engineered to simulate the human BM microenvironment. Taken together, our data show that co-implanting MSCs together with the pMM cells can serve as a model to study the effect of pMM cells on osteogenesis, which provides a tool to unravel the mutual interaction between MM cells and the bone marrow microenvironment. Disclosures: No relevant conflicts of interest to declare.

Multiple myeloma (MM) remains an incurable malignancy of clonal plasma cells. Although the new generation of immunomodulatory agents, such as lenalidomide (LEN), and the potent proteasome inhibitor bortezomib (BORT) have significantly improved the overall survival of MM patients, all chemotherapy strategies are eventually hampered by the development of drug-resistance. The outcome of patients who are refractory to thalidomide, lenalidomide (LEN) and bortezomib (BORT) is very poor. Set out with the idea that targeted immunotherapy with human antibodies may offer new perspectives for MM patients, we have recently developed daratumumab (DARA), a CD38 human antibody with broad-spectrum killing activity, mainly via ADCC (antibody dependent cellular cytotoxicity) and CDC (complement dependent cytotoxicity). In our previous preclinical studies and in current clinical phase I/II trials, DARA induces marked anti-MM activity. Based on these encouraging results, we now explored the potential activity of DARA for patients who are refractory to LEN- and/or BORT. In a recently developed human-mouse hybrid model that allows the in vivo engraftment and outgrowth of patient-derived primary myeloma cells in immune deficient Rag2-/-gc-/- mice, single dose DARA treatment appeared to effectively inhibit the malignant expansion of primary MM cells derived from a LEN- and BORT-refractory patient, indicating the potential efficacy of DARA even in LEN/BORT refractory patients. To substantiate the conclusions of these in vivo data, we conducted in vitro assays, in which full BM-MNCs from LEN (n=11) and LEN/BORT (n=8) refractory patients were treated with DARA alone or the combination of DARA with LEN or BORT to induce MM cell lysis. As expected, LEN alone induced no or little lysis of MM cells in the LEN-refractory patients and also BORT was not able to induce any lysis in the BORT-refractory patients. On the contrary, DARA induced substantial levels of MM cell lysis in all LEN and LEN/BORT-refractory patients. This lysis was significantly enhanced by combination with LEN or BORT. The combination of DARA and BORT improved MM lysis by additive mechanisms. However, LEN improved DARA-mediated lysis of MM cells in a synergistic manner through the activation of effector cells involved in DARA-mediated ADCC. In conclusion, our results demonstrate that DARA is also effective against multiple myeloma cells derived from LEN- and BORT-refractory patients. Especially LEN seems to improve responses in a synergistic manner. Our results provide a rationale for clinical evaluation of DARA in combination with LEN to achieve more effective results in LEN- and BORT-refractory patients. Disclosures: Lammerts van Bueren: Genmab: Employment. Bakker:Genmab: Employment. Parren:Genmab: Employment. van de Donk:Celgene: Research Funding. Lokhorst:Genmab A/S: Consultancy, Research Funding; Celgene: Honoraria; Johnson-Cilag: Honoraria; Mudipharma: Honoraria.

Abstract 940 The evolution of multiple myeloma (MM) is a multi-step process during which mature B cells acquire genetic mutations in multiple genes, which typically takes place in the bone marrow (BM) microenvironment. This, together with the difficulty to culture MM in vitro or to grow MM in vivo in animal models has been the main reason during past decades for poor progress in preclinical research with patient-derived myeloma (pMM) cells. Recently, we developed a unique human-mouse hybrid model that allows engraftment and outgrowth of pMM cells by implementing a technology that is based on first generating a human bone environment in immune deficient mice (Groen et al. 2012) and that is subsequently capable of supporting growth of injected pMM cells. The model offers the opportunity (1) to study the pathobiology of myeloma, and (2) to evaluate, preclinically, new therapeutics for MM treatment, including antibody testing against pMM cells, obtained from patients who acquired resistance to conventional and novel drugs. Daratumumab (DARA) is a human CD38 antibody with broad-spectrum killing activity. Daratumumab induces effective killing of MM tumor cells via complement dependent cytolysis (CDC), ADCC (antibody dependent cellular cytolysis) and ADCP (antibody-dependent phagocytosis). DARA represents a novel promising treatment for MM and other hematological malignancies and is currently tested in Phase I/II clinical trials. In these clinical studies the adverse events have been manageable and marked reductions in paraprotein and bone marrow plasma cells have been observed. In the current study, we asked whether DARA was able to inhibit growth of refractory tumor cells in our human-mouse hybrid model. To this end, immune-deficient RAG2−/−gc−/−-mice were implanted subcutaneously with biphasic calcium phosphate (BCP) particles (2–3 mm) loaded with culture expanded human mesenchymal stromal cells (MSCs). Eight weeks later, the humanized scaffolds in mice (n=45) were injected with 0.5–5×106 pMM cells obtained from different refractory, MM patients. The pMM cells were gene-marked with a GFP-luciferase lentiviral construct for imaging of viable tumor cells. Bioluminescent imaging (BLI) was used to follow myeloma outgrowth in time and to visualize the effect of treatment. The pMM cells were obtained from patients at diagnosis (type 1); at end stage disease, after a history of MPT (melphalan, prednisone, thalidomide, type 2); or from a patient refractory to chemotherapy with bortezomib (BORT), adriamycine and dexamethasone (DEX) (type 3). Mice carrying the pMM cells received similar treatment as the patients or were treated with DARA in a dose range of 1x 50 μg (low dose (LD)) or 2 to 3x 200 μg/mouse (high dose (HD)). BLI showed that the type 1 pMM-bearing mice responded well to all treatments, including DARA; type 2-bearing pMM mice showed no reduction in tumor growth after chemotherapy, but DARA treatment (LD) resulted in an almost complete elimination of circulating MM cells, as assessed with a CD138 antibody, in blood and BM. In a second experiment, type 2-pMM bearing mice were treated with a high DARA dose early (day 34, 50 and 72, 3 times HD, tumor size/BLI signal 8000 cpm/cm2). A significant reduction of overall tumor load, as measured with BLI was observed, which interestingly did not differ between the high and low tumor load group. A reduction of circulating tumor cells (CD138+) was observed for both conditions, which was most obvious in the early treated mice and in agreement with the observations in the first experiment. Type 3 (resistant) pMM-bearing mice showed only a minor response to DEX and BORT, but were highly sensitive to melphalan. When DEX- and BORT-treated mice were treated with a single injection of DARA, this resulted in a complete remission in 3 out of 4 mice and a reduction of the tumor load by 50% in the fourth BORT-treated mouse. In conclusion, our results demonstrate that DARA is effective against multiple myeloma cells derived from therapy- naïve or -refractory patients grafted in a humanized mouse model. In addition, this humanized MM model can be used to study the potential and mechanism of action of DARA in vivo. This novel MM model might be used to predict responsiveness of myeloma patients to particular treatments. Disclosures: Groen: Genmab BV: Research Funding. Raymakers:Novartis: Consultancy. Lammerts van Bueren:Genmab BV: Employment. Parren:genmab: Employment. Mutis:genmab: Research Funding. Martens:Genmab BV: Research Funding.

Abstract 1834 During progression of Multiple Myeloma (MM), the disease spreads to multiple sites in the bone marrow (BM) and towards terminal stages also to extra-medullary sites. If spreading of MM cells via the circulation could be prevented, it would reduce subsequent sites of MM growth and prevent additional bone lesions. To study this hypothesis an animal model that truly mimics human disease is essential. Recently, we described a novel human-mouse hybrid model of MM, based on the generation of a human bone microenvironment (BME) in RAG2−/−gc−/− mice by combining a ceramic scaffold with culture-expanded mesenchymal stromal cells (MSCs). This BME acts as a hematopoietic niche and supports outgrowth of patient-derived MM cells (pMM) (Groen et al, Blood 2012). By marking pMM cells with the luciferase gene and using bioluminescent imaging (BLI), we were able to monitor pMM outgrowth in time in humanized scaffolds and visualize effects of treatment. pMM cells, injected in scaffolds located at one side of the mice showed local outgrowth to MM tumors but were also found to migrate to non-injected scaffolds at the contralateral side. pMM cells circulated in a low numbers in mouse blood and were found to colonize mouse BM. These combined phenomena provided us with the ideal MM model to study therapeutic agent(s) not only targeting the pMM tumors, but also to study targeting of circulating pMM cells and thus inhibit spreading to secondary locations, i.e. to humanized scaffolds located contra-lateral or to mouse BM. One such novel agent is daratumumab (DARA), which is in clinical development for MM. DARA is a human CD38 antibody with broad-spectrum killing activity. DARA exerts its effects via complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity and phagocytosis (ADCC/ADCP). In clinical studies DARA showed marked reductions in paraprotein and BM plasma cells and adverse events were manageable. To study whether DARA could prevent spreading of disease to other sites, mice carrying humanized scaffolds, in which luciferase marked pMM cells that were refractory to chemotherapy were growing, were treated with DARA at early (day 34, 50 and 72) or late (day 50 and 72) stage disease. Parallel groups of mice were treated with melphalan, bortezomib or dexamethason. Growth of scaffold-injected pMM cells and response to DARA- or chemo -therapy, was monitored with BLI. Animals were treated early (small tumors) or late (large tumors) during disease progression with different dose levels of DARA, i.e. 1× 50 μg, or 2 or 3 × 200 μg/mouse. The 50 μg dose of late stage disease, strongly reduced the number of circulating CD138+ MM cells in blood and, interestingly, also in BM. Treatment at late stage with melphalan, bortezomib or dexamethasone resulted in only a marginal effect on the outgrowth of pMM grafts in scaffolds. 200 μg DARA at early stage (day 35, 50, 72) resulted in a strong anti-pMM effect with complete elimination of the CD38+ fraction from the scaffolds, as analyzed by immunohistochemistry and FACS. Late treatment (day 50,72) with 200 μg DARA also resulted in a strong anti-pMM effect, but the surviving MM tumors had a mixed phenotype, consisting of 4 subpopulations, being CD38/CD138 positive and negative cells. In the blood a low percentage of circulating tumor cells (CD38+/CD138+) was observed before treatment (day 34: 0.06%). This stayed low in the early treatment group; on day 70, (∼40-fold lower) as compared to controls. On day 90 it reached 4%, but consisted only of CD38− cells. In the late treatment group the number of circulating tumor cells was ∼3–6 fold lower at day 70, as compared to controls. As DARA plasma levels were very low in late treatment groups, suggesting target-mediated clearance of DARA by the pMM tumors. This also suggests that DARA dosing may be increased to optimize treatment. In summary, whilst conventional drug treatment did not effectively inhibit growth of scaffold-grafted multiple-drug refractory pMM tumors, low dose DARA was already able to reduce pMM plasma cells in the circulation and to reduce spreading to other medullary sites, e.g. mouse BM. At a high dose level, treatment at an early time point induced elimination of CD38+ cells from blood, with only CD38− cells surviving in scaffolds. Treatment with high dose DARA at a late time point temporarily reduced tumor growth but the optimal dose levels in this animal model did not seem to be reached. This requires further investigation. Disclosures: Groen: Genmab: Research Funding. Raymakers:Novartis: Consultancy. Parren:genmab: Employment. Lokhorst:Celgene: Honoraria. Mutis:genmab: Research Funding. Martens:Genmab: Research Funding.

Abstract 3412 Interactions with the hematopoietic niche in the bone marrow (BM) microenvironment are essential for hematopoietic stem cell (HSC) self-renewal. In addition, in hematological malignancies this niche is considered to serve as a sanctuary site for leukemic stem cells during chemotherapy, and to contribute to disease relapse. Although many advances have been made in understanding how the niche regulates HSC self-renewal and confers therapy resistance, most of this knowledge is based on genetic loss- or gain-of-function murine models. Since these models do not recapitulate the human physiology, there is a need for models that more closely resemble the human niche. Here, we describe a unique humanized model, which implements a novel scaffold-based technology for generating a human bone environment in RAG2−/−gc−/−-mice. Inoculation of these mice with normal human CD34+ hematopoietic progenitor cells, isolated from umbilical cord blood, resulted in homing to the human bone environment and the generation of human hematopoietic cells of distinct lineages, but more importantly also the engraftment of CD34+ cells themselves. In a next series of experiments the supportive nature of the humanized niche was further investigated with patient-derived acute myeloid leukemia (pAML) and multiple myeloma (pMM) cells, two hematopoietic malignancies that are highly dependent on the BM microenvironment for survival and growth. Inoculation of the humanized mice with pAML cells, obtained from a poor-risk patient (M1; complex karyotype) or cells from a good risk AML patient (M4; inv(16)) revealed the ability of the reconstructed human bone environment to support outgrowth of the leukemia with the cells having a similar phenotype as those from the patient sample. Interestingly, engraftment of good risk AML samples, including inv(16), has been reported to be very difficult in the NOD/SCID-based AML xenotransplant model. The humanized model that we developed was further substantiated by the ability to support the outgrowth of pMM from 7 out of 7 patients. MM is a hematological malignancy that fails to grow in mouse tissues without extra support, e.g. fetal human bone chips. Moreover, the outgrowth of pMM in our humanized model is accompanied by an increase in osteoclast activity, indicating the presence of bone resorption, one of the most relevant clinical sequelae of MM. In addition, by gene-marking pMM cells with luciferase and using bioluminescent imaging, we were able to follow myeloma outgrowth in time. Treatment of pMM-bearing mice with identical drugs as given to the patients showed that the pMM cells growing in the humanized environment in the mice responded similar as the MM patients. Hence, our model allows, for the first time, to investigate essential interactions within the human BM microenvironment for the development of normal and malignant hematopoiesis and thus for therapy development. Disclosures: de Bruijn: Xpand Biotechnology BV: Employment. Weers:Genmab BV: Employment. Parren:Genmab BV: Employment.

The effects of treatment with the synthetic long-acting somatostatin analogue SMS-201-995 were studied in a patient with a fluid and electrolyte secreting villous adenoma of the rectum. The effects of SMS-201-995 on rectal fluid volume and electrolyte loss, and local and general prostanoid production were compared with those of treatment with indomethacin. During treatment with the somatostatin analogue iso-osmolar rectal fluid production increased about 25%; the quantity of prostaglandin E2 in the rectal fluid rose almost 20-fold. Prostaglandin F2 alpha, 6-keto-prostaglandin F1 alpha and 13,14-dihydro-15-keto-prostaglandin F2 alpha output showed similar, though less impressive increments during somatostatin treatment. The somatostatin analogue did not affect urinary prostanoid excretion except for levels of 2,3-dinor-thromboxane B2, which doubled. With indomethacin treatment diurnal rectal fluid production dropped by about 50% and all prostanoids measured in urine and rectal fluid decreased below control values. It appears that the somatostatin analogue SMS-201-995 has a marked stimulatory effect on the in vivo prostanoid production by the villous adenoma. Perhaps this stimulation is not confined to the tumor only, but also affects thromboxane synthesis.

It is thought that adult mesenchymal stromal cells (MSC) are important for tissue repair and maintenance. Crucial in these processes is the presence of MSC at the site of injury, however the recruitment and migration of MSC towards their destiny is poorly understood. With respect to future cell therapy, we are studying the process of migration of various human mesenchymal stem cell sources, and hypothesize that only a subpopulation of ex vivo expanded mesenchymal stem cells is capable of specific homing. For this purpose, MSC from different sources i.e. fetal lung (FL), fetal bone marrow (FBM), adult bone marrow (ABM) and adult adipose tissue (AT) were derived by plastic adherence and subsequently expanded. All MSC sources were characterized as CD73+, CD90+, CD105+, CD34− and CD45−. MSC (P4-9) were allowed to migrate for 4h towards SDF-1a, PDGF-BB, HGF, bFGF or FCS over fibronectin-coated 12 mm pore size transwell plates. FL-MSC migrated significantly better towards SDF-1a as compared to ABM-MSC or AT-MSC. This enhanced migration capacity towards SDF-1a is specific for FL-MSC since AT-MSC migrated better towards FCS as compared to FL-MSC. Even ABM-MSC responded better to FCS than FL-MSC. This suggests that MSC originating from all sources are able to migrate but require different triggers to induce migration. In order to elucidate whether the observed differences in migration potential were due to developmental stage, cultured MSC derived from fetal bone marrow were tested as well. No significant differences in migration capacity were observed between adult and fetal BM- MSC for any of the (chemotactic) stimuli evaluated. Interestingly, FL-MSC had a significant increased migration capacity as compared to FBM-MSC towards SDF-1a, PDGF-BB and HGF, suggesting that the origin of tissue may determine migration capacity of ex vivo expanded MSC. Since it was observed that only a small percentage of the cultured MSC were able to migrate towards the various stimuli, checkerboard migration was performed to elucidate whether a synergistic effect could be observed. No synergistic effect was observed between SDF and PDGF, SDF and FCS or PDGF and FCS in FL-MSC, suggesting that there may be one subpopulation of MSC that possesses migratory capacities. When studying the SDF-1-induced migratory subpopulation in more detail, it was observed that, after migration, migratory MSC originating from all tissue sources maintain their proliferation and differentiation capacity and express CXCR4 at a higher level than MSC that did not migrate. To be able to migrate, cells have to rearrange their actin cytoskeleton and focal adhesions. These processes can be initiated by various chemokines and growth factors. In response to SDF or FCS, morphological changes were observed in ABM-MSC by confocal microscopy. Cells became smaller and membrane protrusions appeared, whereas this was absent in the control. Furthermore, upon stimulation with SDF, PDGF and FCS, tyrosine-phosphorylation of the adapter protein paxillin that links the actin cytoskeleton to focal adhesions was increased. In conclusion, our results suggest that migration potential of ex vivo expanded MSC derived from various adult and fetal tissues have different migratory capacity towards growth factor and chemokine stimuli and may involve paxillin phosphorylation. Our data indicate that further studies on the migratory subpopulation(s) within the heterogeneous population of culture expanded MSC will contribute to unravel how and which MSC will be of interest for future cellular therapies.

Urinary TXB2 and 6-keto-PGF1 alpha were measured by high pressure liquid chromatography combined with radioimmunoassay, in order to determine whether or not urinary excretion of 6-keto-PGF1 alpha and TXB2 followed a same pattern in pregnancy and labor. The excretion of 6-keto-PGF1 alpha was higher than that of TXB2 in both non-pregnant and pregnant women, but the ratio between them increased in pregnancy. The urinary excretion of both 6-keto-PGF1 alpha and TXB2 excretion was significantly increased (p less than 0.001) in pregnancy. Labor was associated with a much wider inter-individual variation in the excretion of 6-keto-PGF1 alpha and TXB2 than observed in pregnancy and in non-pregnant women. Also, the ratio between the two compounds varied more in labor than in pregnancy. The data indicate that the urinary levels of these two compounds do not follow a single well-determined pattern in pregnancy and labor.

Solvent extraction of 6-keto-PGF1 alpha from aqueous solutions with ethyl acetate was found to result in variable and irreproducible elution patterns, when the extracts were subjected to high pressure liquid chromatography. These problems could not be resolved satisfactorily by using ethyl acetate from different suppliers, nor by changing acids or pH for acidification. After a number of unsuccessful attempts to resolve this problem, we found that variable and irreproducible elution patterns could be avoided by using methyl t-butyl ether as extraction solvent.

Since endothelial progenitor cells (EPC) were found in adult blood, active interferences of vascular diseases by cellular therapy with EPC were initiated. However, controversies exist on the identity of the EPC, e.g. concerning phenotype before and after culture, in vitro and in vivo behavior, as well as on quantities and differentiation. EPC can be quantified in vitro by culturing CFU-EC. In order to clarify which cells are essential and which are facilitating the formation of CFU-EC, we determined the contribution of several cell types to the formation of colonies. Peripheral blood mononuclear cells were isolated and were either positively selected or depleted for several cell populations (CD34+/KDR+/CD146+, CD3+, CD14+, CD19+ or CD56+). Subsequently the cells were labeled with PKH2 or irradiated (40Gy) to determine the contribution to colony formation. The purity of the cell populations was determined by flow cytometry. From these cell populations, CFU-EC were cultured on fibronectin-coated tissue culture plates, in endothelial selective medium EndoCultTM (Stem Cell Technologies). After 2 days of culture, non-adherent cells were subsequently cultured for an additional 3 days to form colonies. To determine the contribution of soluble factors to colony formation, transwells (0.8 μm pore size) were used to separate the cell populations during culture. CFU-EC are not derived from mature endothelial cells nor from immature EPC, as similar number of colonies per well were found when the starting population was depleted for CD146+/CD34+/KDR+ cells (18±9 vs. 20±14 in controls; n=4). In contrast, when CD14+ cells were depleted from the starting population, no CFU-EC were formed (0±0 vs. 29±23 in controls; n=7, p95% CD14+ fraction. This resulted in an increase in colony formation (>95% monocytes: 2±1; with insert: 10±9, n=2). In conclusion, CFU-EC are derived from CD14+ cells, but need the presence of CD14− cells, which is in part due to paracrine factors secreted by CD14− cells. This study further clarifies the identity of the EPC as determined by CFU-EC, and may give more insight to the role of several cell populations in vascular repair.

Different engraftment kinetics have been observed after transplantation of bone marrow (BM), G-CSF-mobilized peripheral blood (mPB) and umbilical cord blood (UCB). This may not only result from qualitative but also from qualitative differences in these grafts. We studied the repopulating potential of increasing numbers of CD34 + cells from UCB, BM, and mPB in NOD/SCID mice. CD34 + cells were selected by immunomagnetic cell selection (93 ± 5% purity within life gate). Mice (n = 66) were sublethally irradiated (3.5 Gy) and transplanted with increasing numbers (0.1–4 × 10 6 ) of CD34 + cells isolated from UCB, BM or mPB. After 6–8 weeks the mice were sacrificed and blood, BM, and organs were harvested. Single cell suspensions were made and analyzed by flow cytometry with anti-human CD45, CD34, CD2, CD4, CD8, CD19, CD20, CD14, CD15 and CD33. After transplantation of 0.1-0.3-0.5-0.7 × 10 6 CD34 + BM or mPB cells no engraftment was observed. In contrast, after transplantation of a relatively low dose (0.3 × 10 6 ) of UCB CD34 + cells, 40-85% of cells in the BM of recipient mice were of human origin. Grafts containing more than 1 × 10 6 BM or mPB CD34 + cells resulted in measurable engraftment of human cells (CD45 + ) in the BM. Human cells found in BM of the NOD/SCID mice transplanted with 6 UCB CD34 + cells were mainly of B cell origin (81–97%). After transplantation of ≥1 × 10 6 CD34 + UCB cells, the percentage of B cells in the bone marrow was significantly lower (45–85%) concommittant with an increase in the percentage of myeloid cells (20–55%). A similar ratio between lymphoid and myeloid cells in the bone marrow was observed after transplantation of ≥ 1 × 10 6 CD34 + cells derived from BM or mPB. We suggest that 1). The frequency of early progenitor cells preferentially developing into B cells, is higher in UCB CD34 + transplants than in BM or mPB grafts. 2) The frequency of progenitor cells developing into myeloid cells is similar in CD34 + cell population derived from UCB, BM and mPB.

Urinary TXB2 excretion was measured during pregnancy and labor using high pressure liquid chromatography and radioimmunoassay. From the first trimester onwards TXB2 levels in urine of pregnant women (n = 60) were significantly (p less than 0.001) higher than in non-pregnant women (n = 12) and they increased, albeit not significantly, with advancing gestation. Labor was associated with a two-fold increase in urinary TXB2 excretion. Levels in established labor were significantly higher than at any other time in pregnancy (p less than 0.001), but the levels in incipient labor showed considerable overlap with these in late pregnancy. Thus urinary TXB2, while not necessarily originating from the pregnant uterus, appears to reflect the uterine activity of labor and may be the expression of a general stimulation of prostanoid production during parturition.

To study the possibility that changes in fetal surfactant composition depend on the availability of inositol, we isolated surfactant material from lungs of fetal and neonatal rats and estimated their plasma inositol concentration. During the 18- to 22-day gestational period the amount of surfactant increases from 0.17 to 3.10 µmol phospholipids/g wet lung. From day 20 onward, 70% or more of the phospholipids is phosphatidylcholine. In this period the relatively high percentage of phosphatidylinositol (8%) in the lung surfactant decreases to 4% whereas the percentage of phosphatidylglycerol increases from 2 to 8% at parturition. During gestation the phospholipid/protein ratio of the surfactant material increase from 3 to 11 and the highest ratio is found immediately after birth. It decreases again 24 h after birth to values characteristic for surfactant from adult rats. The plasma inositol concentration drops during the 18- to 22-day period from 0.81 to 0.26 mmol/liter and a similar decrease in inositol concentration occurs in amniotic fluids. The phosphatidylglyercol/phosphatidylinositol ratio of surfactant correlated negatively with the fetal plasma inositol concentration. It is most likely that the reduction in the level of fetal plasma inositol resulting from a declining production and an increasing metabolism, causes the decrease in phosphatidylinositol and increase in PG content of the surfactant of the fetal rat.

Plasma levels of 6-keto-PGF1α and 13, 14-dihydro-15-keto-PGF2α (PGF2α were measured by high pressure liquid chromatography and radioimmunoassay during and up to 48 hours after term labor. PGFM levels increased during labor to reach values which at full dilatation, at delivery of the fetal head and at placental separation were each time higher than levels obtained earlier. In all women (n = 10) PGFM levels reached their maximum and started to decline within 10 min. after placental separation. Levels decreasd to prelabor values within 2 to 3 hours after delivery and no temporary increases were observed within the first 2 days. Levels of 6-keto-PGF1α on the other hand, showed no consistent trends throughout labor and the early puerperium. The observed changes are believed to be of relevance for ensuring adequate hemostatis after birth.

Urinary excretion of 6-keto-PGF1 alpha was measured by high pressure liquid chromatography and radioimmunoassay at various stages of pregnancy and labor. In the first trimester of pregnancy, urinary 6-keto-PGF1 alpha concentrations were not different from those measured before pregnancy, but they showed a significant increase in the second trimester of pregnancy (p less than 0.001). The levels rose further in the third trimester, although this increase was not statistically significant when compared to levels obtained in the second trimester. There was no evidence for a significant change in 6-keto-PGF1 alpha excretion with the onset of labor. During well-established, progressive labor mean values of 6-keto-PGF1 alpha excretion were about twice as high as before the onset of labor, but the range of values during labor was so wide that there was no statistical difference with values obtained in the second half of pregnancy. It is concluded that the increase in the urinary excretion of 6-keto-PGF1 alpha occurs later in pregnancy than the increase in TXB2 excretion and that labor at term is not associated with marked changes in 6-keto-PGF1 alpha excretion.