Establishing human leukemia xenograft mouse models by implanting human bone marrow-like scaffold-based niches.

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.

Pre-clinical evaluation of CD38 chimeric antigen receptor engineered T cells for the treatment of multiple myeloma.

Adoptive transfer of chimeric antigen receptor-transduced T cells is a promising strategy for cancer immunotherapy. The CD38 molecule, with its high expression on multiple myeloma cells, appears a suitable target for antibody therapy. Prompted by this, we used three different CD38 antibody sequences to generate second-generation retroviral CD38-chimeric antigen receptor constructs with which we transduced T cells from healthy donors and multiple myeloma patients. We then evaluated the preclinical efficacy and safety of the transduced T cells. Irrespective of the donor and antibody sequence, CD38-chimeric antigen receptor-transduced T cells proliferated, produced inflammatory cytokines and effectively lysed malignant cell lines and primary malignant cells from patients with acute myeloid leukemia and multi-drug resistant multiple myeloma in a cell-dose, and CD38-dependent manner, despite becoming CD38-negative during culture. CD38-chimeric antigen receptor-transduced T cells also displayed significant anti-tumor effects in a xenotransplant model, in which multiple myeloma tumors were grown in a human bone marrow-like microenvironment. CD38-chimeric antigen receptor-transduced T cells also appeared to lyse the CD38(+) fractions of CD34(+) hematopoietic progenitor cells, monocytes, natural killer cells, and to a lesser extent T and B cells but did not inhibit the outgrowth of progenitor cells into various myeloid lineages and, furthermore, were effectively controllable with a caspase-9-based suicide gene. These results signify the potential importance of CD38-chimeric antigen receptor-transduced T cells as therapeutic tools for CD38(+) malignancies and warrant further efforts to diminish the undesired effects of this immunotherapy using appropriate strategies.

Preclinical Evidence for the Therapeutic Potential of CD38-Targeted Immuno-Chemotherapy in Multiple Myeloma Patients Refractory to Lenalidomide and Bortezomib.

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.

Reconstructing the human hematopoietic niche in immunodeficient mice: opportunities for studying primary multiple myeloma.

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.

Cell cycle and tissue of origin contribute to the migratory behaviour of human fetal and adult mesenchymal stromal cells.

Mesenchymal stromal cells (MSC) are potential cells for cellular therapies, in which the recruitment and migration of MSC towards injured tissue is crucial. Our data show that culture-expanded MSC from fetal lung and bone marrow, adult bone marrow and adipose tissue contained a small percentage of migrating cells in vitro, but the optimal stimulus was different. Overall, fetal lung-MSC had the highest migratory capacity. As fetal bone marrow-MSC had lower migratory potential than fetal lung-MSC, the tissue of origin may determine the migratory capacity of MSC. No additive effect in migration towards combined stimuli was observed, which suggests only one migratory MSC fraction. Interestingly, actin rearrangement and increased paxillin phosphorylation were observed in most MSC upon stromal cell-derived factor-1alpha or platelet-derived growth factor-BB stimulation, indicating that this mechanism involved in responding to migratory cues is not restricted to migratory MSC. Migratory MSC maintained differentiation and migration potential, and contained significantly less cells in S- and G2/M-phase than their non-migrating counterpart. In conclusion, our results suggest that MSC from various sources have different migratory capacities, depending on the tissue of origin. Similar to haematopoietic stem cells, cell cycle contributes to MSC migration, which offers perspectives for modulation of MSC to enhance efficacy of future cellular therapies.

Stem cells from in- or outside of the heart: isolation, characterization, and potential for myocardial tissue regeneration.

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.

Recovery and functional activity of mononuclear bone marrow and peripheral blood cells after different cell isolation protocols used in clinical trials for cell therapy after acute myocardial infarction.

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.

The presence of activated CD4(+) T cells is essential for the formation of colony-forming unit-endothelial cells by CD14(+) cells.

The number of colony forming unit-endothelial cells (CFU-EC) in human peripheral blood was found to be a biological marker for several vascular diseases. In this study, the heterogeneous composition of immune cells in the CFU-ECs was investigated. We confirmed that monocytes are essential for the formation of CFU-ECs. Also, however, CD4(+) T cells were found to be indispensable for the induction of CFU-EC colonies, mainly through cell-cell contact. By blocking or activating CD3 receptors on CD4(+) T cells or blocking MHC class II molecules on monocytes, it was shown that TCR-MHCII interactions are required for induction of CFU-EC colonies. Because the supernatant from preactivated T cells could also induce colony formation from purified monocytes, the T cell support turned out to be cytokine mediated. Gene expression analysis of the endothelial-like colonies formed by CD14(+) cells showed that colony formation is a proangiogenic differentiation and might reflect the ability of monocytes to facilitate vascularization. This in vitro study is the first to reveal the role of TCR-MHC class II interactions between T cells and monocytes and the subsequent inflammatory response as stimulus of monocytic properties that are associated with vascularization.

Enhanced engraftment of umbilical cord blood-derived stem cells in NOD/SCID mice by cotransplantation of a second unrelated cord blood unit.

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.

Nonexpanded primary lung and bone marrow-derived mesenchymal cells promote the engraftment of umbilical cord blood-derived CD34(+) cells in NOD/SCID mice.

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 0.1x10(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. CONCLUSIONS: 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.

Mesenchymal stem cells in human second-trimester bone marrow, liver, lung, and spleen exhibit a similar immunophenotype but a heterogeneous multilineage differentiation potential.

BACKGROUND AND OBJECTIVES: 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. DESIGN AND METHODS: 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. RESULTS: The frequency of MSC in BM was significantly higher than in liver, lung, and spleen (p<0.05). 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 (p<0.05). INTERPRETATION AND CONCLUSIONS: 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.

Mesenchymal stem cells and hematopoietic stem cell transplantation.

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.

Mesenchymal stem cells promote engraftment of human umbilical cord blood-derived CD34(+) cells in NOD/SCID mice.

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 x 10(6) UCB CD34(+) cells in the presence or absence of 1 x 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.