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.

A Rational Strategy for Reducing On-Target Off-Tumor Effects of CD38-Chimeric Antigen Receptors by Affinity Optimization.

Chimeric antigen receptors (CARs) can effectively redirect cytotoxic T cells toward highly expressed surface antigens on tumor cells. The low expression of several tumor-associated antigens (TAAs) on normal tissues, however, hinders their safe targeting by CAR T cells due to on-target/off-tumor effects. Using the multiple myeloma (MM)-associated CD38 antigen as a model system, here, we present a rational approach for effective and tumor-selective targeting of such TAAs. Using "light-chain exchange" technology, we combined the heavy chains of two high-affinity CD38 antibodies with 176 germline light chains and generated ∼124 new antibodies with 10- to >1,000-fold lower affinities to CD38. After categorizing them into three distinct affinity classes, we incorporated the single-chain variable fragments of eight antibodies from each class into new CARs. T cells carrying these CD38-CARs were extensively evaluated for their on-tumor/off-tumor cytotoxicity as well as CD38-dependent proliferation and cytokine production. We identified CD38-CAR T cells of ∼1,000- fold reduced affinity, which optimally proliferated, produced Th1-like cytokines, and effectively lysed CD382+ MM cells, but spared CD38+ healthy hematopoietic cells in vitro and in vivo. Thus, this systematic approach is highly suitable for the generation of optimal CARs for effective and selective targeting of TAAs.

A Mussel-Inspired Conductive, Self-Adhesive, and Self-Healable Tough Hydrogel as Cell Stimulators and Implantable Bioelectronics.

A graphene oxide conductive hydrogel is reported that simultaneously possesses high toughness, self-healability, and self-adhesiveness. Inspired by the adhesion behaviors of mussels, our conductive hydrogel shows self-adhesiveness on various surfaces and soft tissues. The hydrogel can be used as self-adhesive bioelectronics, such as electrical stimulators to regulate cell activity and implantable electrodes for recording in vivo signals.

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.

Evaluation of novel resorbable membranes for bone augmentation in a rat model.

OBJECTIVES: Our study compared two novel, biodegradable poly(trimethylene carbonate) (PTMC) barrier membranes to clinically applied barrier membranes in maintaining volume of block autologous bone grafts in a rat mandible model. MATERIAL AND METHODS: Two hundred and forty rats were included in this study. Block autologous bone grafts of 5 mm in diameter were harvested from the mandibular angles and transplanted onto the contralateral side. The bone grafts were either covered with a membrane or left uncovered. The applied membranes included pure PTMC membranes, biphasic calcium phosphate (BCP) incorporated PTMC composite membranes, expanded poly(tetrafluoroethylene) (e-PTFE) membranes (Tex) and collagen membranes (Geistlich Bio-Gide). After 2, 4 and 12 weeks, the rat mandibles were retrieved and analysed by histological evaluation and µCT quantification. RESULTS: The histological evaluation revealed that in time the block autologous bone graft was well integrated to the recipient bone via gradually maturing newly formed bone and did not show signs of resorption, independent of membrane coverage or types of membrane. µCT quantification showed the volume of the bone graft and recipient bone together was maintained by new bone formation and recipient bone resorption. CONCLUSIONS: Our study showed that the use of PTMC membranes and PTMC-BCP composite membranes resulted in similar bone remodelling to the collagen membranes and e-PTFE membranes and that the use of barrier membranes did not interfere with bone remodelling of the bone grafts and recipient bones. However, the used barrier membranes seemed not to contribute in maintaining the volume of block autologous bone grafts.

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.

Osteoinductive ceramics as a synthetic alternative to autologous bone grafting.

Biomaterials can be endowed with biologically instructive properties by changing basic parameters such as elasticity and surface texture. However, translation from in vitro proof of concept to clinical application is largely missing. Porous calcium phosphate ceramics are used to treat small bone defects but in general do not induce stem cell differentiation, which is essential for regenerating large bone defects. Here, we prepared calcium phosphate ceramics with varying physicochemical and structural characteristics. Microporosity correlated to their propensity to stimulate osteogenic differentiation of stem cells in vitro and bone induction in vivo. Implantation in a large bone defect in sheep unequivocally demonstrated that osteoinductive ceramics are equally efficient in bone repair as autologous bone grafts. Our results provide proof of concept for the clinical application of "smart" biomaterials.

Mimicking the Graded Wavy Structure of the Anterior Cruciate Ligament.

Anterior cruciate ligament (ACL) is the connective tissue providing mechanical stability to the knee joint. ACL reconstruction upon rupture remains a clinical challenge due to the high mechanical properties required for proper functioning. ACL owes its outstanding mechanical properties to the arrangement of the extracellular matrix (ECM) and to the cells with distinct phenotypes present along the length of the tissue. Tissue regeneration appears as an ideal alternative. In this study, a tri-phasic fibrous scaffold that mimics the structure of collagen in the native ECM is developed, presenting a wavy intermediate zone and two aligned uncurled extremes. The mechanical properties of the wavy scaffolds present a toe region, characteristic of the native ACL, and an extended yield and ultimate strain compared to aligned scaffolds. The presentation of a wavy fiber arrangement affects cell organization and the deposition of a specific ECM characteristic of fibrocartilage. Cells cultured in wavy scaffolds grow in aggregates, deposit an abundant ECM rich in fibronectin and collagen II, and express higher amounts of collagen II, X, and tenomodulin as compared to aligned scaffolds. In vivo implantation in rabbits shows a high cellular infiltration and the formation of an oriented ECM compared to aligned scaffolds.

Genesis of osteoclasts on calcium phosphate ceramics and their role in material-induced bone formation.

Innate immune responses play important roles in material-induced bone formation and such roles were further explored in the current study with an emphasis on M2 macrophages and osteoclastogenesis. With the presence of M-CSF and RANKL, M0 macrophages from FVB mouse bone marrow-derived monocytes (BMMs) fused to osteoclasts with both M2 marker and osteoclast marker at day 5, and such osteoclast formation at day 5 was enhanced when the cells were treated with IL-4 at day 3. With IL-4 treatment alone for 24 h, M0 polarized into M2 macrophages. Conditioned medium of M2 macrophages enhanced osteogenic differentiation of MC3T3-E1 (pre-osteoblasts) while osteoclast conditioned medium enhanced osteogenic differentiation of CRL-12424 (osteogenic precursors). TCPs (a typical osteoinductive material) supported M2 macrophage polarization at day 4 and osteoclast formation at day 5, while TCPb (a typical non-osteoinductive material) was less effective. Moreover, osteoclasts formed on TCPs produced osteogenic factors including S1P, Wnt10B and BMP-6, resulting osteogenic differentiation of CRL-12424 cells. Similar to in vitro testing, TCPs favored M2 macrophage polarization followed by the formation of osteoclasts in vivo, as compared to TCPb. The overall data provided evidence of a coupling between M2 macrophages, osteoclasts and material-induced bone formation: osteoclasts formed from M2 macrophages secrete osteogenic cytokines to induce osteogenic differentiation of osteogenic precursor cells to finally form bone. The current findings outlined a biological mechanism of material-induced bone formation and further rationalized the use of osteoinductive materials for bone regeneration. STATEMENT OF SIGNIFICANCE: This paper provides evidence for finding out the relationship between M2 macrophages, osteoclasts and osteogenesis in material-induced bone formation. It suggested that osteoinductive materials enhanced macrophage polarization to M2 macrophages which fuses to osteoclasts, osteoclasts subsequently secret osteogenic cytokines to differentiate finally osteogenic precursors to form bone in osteoinductive materials. The data supports scientifically the superiority of osteoinductive materials for bone regeneration in clinics.

Hypoxia Drives Material-Induced Heterotopic Bone Formation by Enhancing Osteoclastogenesis via M2/Lipid-Loaded Macrophage Axis.

Heterotopic ossification (HO) is a double-edged sword. Pathological HO presents as an undesired clinical complication, whereas controlled heterotopic bone formation by synthetic osteoinductive materials shows promising therapeutic potentials for bone regeneration. However, the mechanism of material-induced heterotopic bone formation remains largely unknown. Early acquired HO being usually accompanied by severe tissue hypoxia prompts the hypothesis that hypoxia caused by the implantation coordinates serial cellular events and ultimately induces heterotopic bone formation in osteoinductive materials. The data presented herein shows a link between hypoxia, macrophage polarization to M2, osteoclastogenesis, and material-induced bone formation. Hypoxia inducible factor-1α (HIF-1α), a crucial mediator of cellular responses to hypoxia, is highly expressed in an osteoinductive calcium phosphate ceramic (CaP) during the early phase of implantation, while pharmacological inhibition of HIF-1α significantly inhibits M2 macrophage, subsequent osteoclast, and material-induced bone formation. Similarly, in vitro, hypoxia enhances M2 macrophage and osteoclast formation. Osteoclast-conditioned medium enhances osteogenic differentiation of mesenchymal stem cells, such enhancement disappears with the presence of HIF-1α inhibitor. Furthermore, metabolomics analysis reveals that hypoxia enhances osteoclastogenesis via the axis of M2/lipid-loaded macrophages. The current findings shed new light on the mechanism of HO and favor the design of more potent osteoinductive materials for bone regeneration.

The genetic background determines material-induced bone formation through the macrophage-osteoclast axis.

Osteoinductive materials are characterized by their ability to induce bone formation in ectopic sites. Thus, osteoinductive materials hold promising potential for repairing bone defects. However, the mechanism of material-induced bone formation remains unknown, which limits the design of highly potent osteoinductive materials. Here, we demonstrated a genetic background link among macrophage polarization, osteoclastogenesis and material-induced bone formation. The intramuscular implantation of an osteoinductive material in FVB/NCrl (FVB) mice resulted in more M2 macrophages at week 1, more osteoclasts at week 2 and increased bone formation after week 4 compared with the results obtained in C57BL/6JOlaHsd (C57) mice. Similarly, in vitro, with a greater potential to form M2 macrophages, monocytes derived from FVB mice formed more osteoclasts than those derived from C57 mice. A transcriptomic analysis identified Csf1, Cxcr4 and Tgfbr2 as the main genes controlling macrophage-osteoclast coupling, which were further confirmed by related inhibitors. With such coupling, macrophage polarization and osteoclast formation of monocytes in vitro successfully predicted in vivo bone formation in four other mouse strains. Considering material-induced bone formation as an example of acquired heterotopic bone formation, the current findings shed a light on precision medicine for both bone regeneration and the treatment of pathological heterotopic bone formation.

Specific Targeting of Multiple Myeloma by Dual Split-signaling Chimeric Antigen Receptor T cells Directed against CD38 and CD138.

PURPOSE: The success of B-cell maturation antigen (BCMA)-specific chimeric antigen receptor (CAR) T cells illustrates the potential of this novel therapy for multiple myeloma. Nonetheless, broadening CAR T-cell therapy beyond BCMA requires inventive strategies as there are only a few multiple myeloma- or plasma cell-specific target antigens. We investigated the feasibility of achieving multiple myeloma specificity by dual-split CD38/CD138 CAR targeting, whereby the stimulatory and costimulatory signals for T-cell activation are split into two separate stimulatory (sCAR) and costimulatory CARs (cCAR). EXPERIMENTAL DESIGN: Using various combinations of CD38 and CD138 sCARs and cCARs with different affinities, we generated several dual-split CAR T cells and analyzed them for multiple myeloma-specific effector functions in vitro. The best-functioning CAR T cells were tested in vivo in a murine xenograft model. RESULTS: We found optimal designs of both CD38sCAR/CD138cCAR and CD138sCAR/CD38cCAR combinations, that effectively lysed multiple myeloma cells but spared single CD38- or CD138-positive healthy hematopoietic cells. While the CD38sCAR/CD138cCAR T cells achieved multiple myeloma-specific activity solely due to the low affinity of the CD38sCARs, the multiple myeloma-specific cytotoxicity, cytokine release, and proliferation of CD138sCAR/CD38cCAR T cells were established through a true combinatorial stimulatory and costimulatory effect. The most optimal combination comprised a low-affinity CD138sCAR combined with a high-affinity CD38cCAR. These CD138sCAR/CD38cCAR T cells also showed dual-antigen specific anti-multiple myeloma effects in vivo. Importantly, they were also effective against multiple myeloma cells from daratumumab pretreated patients with decreased CD38 expression levels. CONCLUSIONS: We demonstrate the possibility to specifically target multiple myeloma cells, even after CD38 targeted therapy, with carefully-designed dual-split CARs directed against CD38 and CD138.

An off-the-shelf decellularized and sterilized human bone-ACL-bone allograft for anterior cruciate ligament reconstruction.

Approximately 1% of active individuals participating in sports rupture their anterior cruciate ligaments (ACL) every year, which is currently reconstructed using tendon autografts. Upon reconstruction, clinical issues of concern are ACL graft rupture, persistent knee instability, limited return to sports, and early onset of osteoarthritis (OA). This happens because tendon autografts do not have the same compositional, structural, and mechanical properties as a native ACL. To overcome these problems, we propose to use decellularized bone-ACL-bone allografts in ACL reconstruction (ACLR) as a mechanically robust, biocompatible, and immunologically safe alternative to autografts. Here, a decellularization protocol combined with sterilization using supercritical carbon dioxide (scCO2) was used to thoroughly decellularize porcine and human ACLs attached to tibial and femoral bone blocks. The specimens were named ultrACLean and their compositional, structural, and mechanical properties were determined. Our results indicate that: 1) decellularization of ultrACLean allografts leads to the removal of nearly 97% of donor cells, 2) ultrACLean has mechanical properties which are not different to native ACL, 3) ultrACLean maintained similar collagen content and decreased GAG content compared to native ACL, and 4) ultrACLean is not cytotoxic to seeded tendon-derived cells in vitro. Results from an in vivo pilot experiment showed that ultrACLean is biocompatible and elicits a moderate immunological response. In summary, ultrACLean has proven to be a mechanically competent and biocompatible graft with the potential to be used in ACLR surgery.

Osteoinductive biomaterials: current knowledge of properties, experimental models and biological mechanisms.

In the past thirty years, a number of biomaterials have shown the ability to induce bone formation when implanted at heterotopic sites, an ability known as osteoinduction. Such biomaterials--osteoinductive biomaterials--hold great potential for the development of new therapies in bone regeneration. Although a variety of well characterised osteoinductive biomaterials have so far been reported in the literature, scientists still lack fundamental understanding of the biological mechanism underlying the phenomenon by which they induce bone formation. This is further complicated by the observations that larger animal models are required for research, since limited, if any, bone induction by biomaterials is observed in smaller animals, including particularly rodents. Besides interspecies variation, variations among individuals of the same species have been observed. Furthermore, comparing different studies and drawing general conclusions is challenging, as these usually differ not only in the physico-chemical and structural properties of the biomaterials, but also in animal model, implantation site and duration of the study. Despite these limitations, the knowledge of material properties relevant for osteoinduction to occur has tremendously increased in the past decades. Here we review the properties of osteoinductive biomaterials, in the light of the model and the conditions under which they were tested. Furthermore, we give an insight into the biological processes governing osteoinduction by biomaterials and our view on the future perspectives in this research field.

Serial cellular events in bone formation initiated by calcium phosphate ceramics.

To better understand the biological mechanisms triggered by osteoinductive materials in vivo, we evaluated the timeline of cellular responses to osteoinductive materials subcutaneously implanted in FVB mice. More F4/80-positive macrophages were present in osteoinductive tri-CaP ceramic (TCP) with submicron surface topography (TCPs) than non-osteoinductive TCP with micron surface topography (TCPb) at week 1. Moreover, TCPs (but not TCPb) significantly enhanced osteoclastogenesis, and induced macrophages to polarize from M1 to M2 in the first week. The time sequence and relevance of macrophages and osteoclasts responses involved in bone formation was then evaluated through peri-implant injection of specific chemicals in mice implanted with osteoinductive TCPs. Day-1 injection of clodronate liposomes (LipClod) depleted macrophages, inhibited macrophage polarization to M2, blocked osteoclastogenesis and bone formation, while the day-6 injection was less effective. Anti-RANKL antibody (aRANKL) did not affect macrophage colonization but inhibited osteoclastogenesis. Injection of aRANKL before week 2 aborted bone formation in TCPs, while injection at week 4 partially inhibited bone formation. The overall data show that following ectopic implantation, osteoinductive materials allow macrophage colonization in hours to days, macrophage polarization to M2 in days (within 7 days), osteoclastogenesis in weeks (e.g. in 2 weeks) and bone formation thereafter (after 4 weeks). The serial cellular events verified herein bring a new insight on material-induced bone formation and pave the way to further explore the mechanisms triggered by osteoinductive materials. STATEMENT OF SIGNIFICANCE: A series of key cellular events triggered by osteoinductive calcium phosphate ceramic was revealed: macrophages colonized within hours to days, polarization of M2 macrophages occurred within 7 days, osteoclastogenesis mainly occurred in weeks (e.g. in 2 weeks) and bone formation finally arose thereafter (after 4 weeks). Moreover, such time sequence of cellular events was confirmed with specific chemicals (clodronate liposomes and anti-RANKL antibody). The findings verified herein bring a new insight on material-induced bone formation and pave the way to further explore the mechanisms triggered by osteoinductive materials.

Coupling between macrophage phenotype, angiogenesis and bone formation by calcium phosphates.

The ability of calcium phosphate (CaP) materials to induce bone formation varies with their physicochemical properties, with surface topography as one of the most crucial triggers. In view of the natural wound healing processes (e.g., inflammation, angiogenesis, tissue formation and remodeling) initiated after surgical implantation, we here comparatively investigated the biological cascades occurring upon ectopic implantation of a tricalcium phosphate with submicron surface topography (TCP-S, osteoinductive) and a tricalcium phosphate with micron-scale topography (TCP-B, non-osteoinductive). In vitro, TCP-S facilitated M2 polarization of macrophages derived from a human leukemic cell line (THP-1) as shown by the enhanced secretion of TGF-ß and CCL18. Interestingly, the conditioned media of polarized M2 macrophages on TCP-S enhanced tube formation by human umbilical vein endothelial cells (HUVECs), while had no influence on the osteogenic differentiation of human bone marrow stromal cells (HBMSCs). Following an intramuscular implantation in canines, TCP-S locally increased typical M2 macrophage markers (e.g., IL-10) at week 1 to 3 and enhanced blood vessel formation after week 3 as compared to TCP-B. Bone formation was observed histologically in TCP-S 6 weeks after implantation, and bone formation was inhibited when an angiogenesis inhibitor (KRN633) was loaded onto TCP-S. No bone formation was observed for TCP-B. The data presented herein suggest strong links between macrophage polarization, angiogenesis and CaP-induced bone formation. STATEMENT OF SIGNIFICANCE: The ability of calcium phosphate (CaP) materials to induce bone formation varies with their physicochemical properties, and the key physicochemical properties relevant to CaP-induced bone formation have been outlined in the last two decades. However, the biological mechanism underlying this material-driven osteoinduction remains largely unknown. This manuscript presented demonstrates strong links between surface topography, macrophage polarization, angiogenesis and bone formation in CaP materials implanted in non-osseous sites. The finding may provide new clues for further exploring the possible mechanism underlying osteoinduction by CaP materials.

CD38-specific Chimeric Antigen Receptor Expressing Natural Killer KHYG-1 Cells: A Proof of Concept for an "Off the Shelf" Therapy for Multiple Myeloma.

Chimeric antigen receptor (CAR) T cells are highly successful in the treatment of hematologic malignancies. We recently generated affinity-optimized CD38CAR T cells, which effectively eliminate multiple myeloma (MM) cells with little or no toxicities against nonmalignant hematopoietic cells. The lack of universal donors and long manufacturing times however limit the broad application of CAR T cell therapies. Natural killer (NK) cells generated from third party individuals may represent a viable source of "off the shelf" CAR-based products, as they are not associated with graft-versus-host disease unlike allogeneic T cells. We therefore explored the preclinical anti-MM efficacy and potential toxicity of the CD38CAR NK concept by expressing affinity-optimized CD38CARs in KHYG-1 cells, an immortal NK cell line with excellent expansion properties. KHYG-1 cells retrovirally transduced with the affinity-optimized CD38CARs expanded vigorously and mediated effective CD38-dependent cytotoxicity towards CD38high MM cell lines as well as primary MM cells ex vivo. Importantly, the intermediate affinity CD38CAR transduced KHYG-1 cells spared CD38neg or CD38int nonmalignant hematopoietic cells, indicating an optimal tumor nontumor discrimination. Irradiated, short living CD38CAR KHYG-1 cells also showed significant anti-MM effects in a xenograft model with a humanized bone marrow-like niche. Finally, CD38CAR KHYG-1 cells effectively eliminated primary MM cells derived from patients who are refractory to CD38 antibody daratumumab. Taken together, the results of this proof-of-principle study demonstrate the potential value of engineering affinity-optimized CD38CARs in NK cells to establish effective anti-MM effects, with an excellent safety profile, even in patients who failed to response to most advanced registered myeloma therapies, such as daratumumab.