Hyaluronan as a Novel Marker for Rapid Selection of Connective Tissue Progenitors

Patient Age and Cell Concentration Influence Prevalence and Concentration of Progenitors in Bone Marrow Aspirates: An Analysis of 436 Patients

BACKGROUND

Connective tissue progenitors (CTPs) resident in native tissues serve as biological building blocks in tissue repair and remodeling processes. Methods for analysis and reporting on CTP quantity and quality are essential for defining optimal cell sources and donor characteristics and the impact of cell processing methods for cell therapy applications. The present study examines the influence of donor characteristics and cell concentration (nucleated cells/mL) on CTP prevalence (CTPs/million nucleated cells) and CTP concentration (CTPs/mL) in bone marrow aspirates (BMAs).

METHODS

Iliac crest bone marrow was aspirated from 436 patients during elective total knee or hip arthroplasty. Bone marrow-derived nucleated cells were plated at a density of 1.19 × 105 cells/cm2. Colony-forming unit analysis was performed on day 6.

RESULTS

Large variation was seen between donors. Age (p < 0.05) and cell concentration (p < 0.001) significantly influenced CTP prevalence and CTP concentration. For every 1-year increase in age, the odds of having at least an average CTP prevalence and CTP concentration decreased by 1.5% and 1.6%, respectively. For every 1 million cells/mL increase in cell concentration, the odds of having at least an average CTP prevalence and CTP concentration increased by 2.2% and 7.9%, respectively. Sex, race, body mass index (BMI), and the presence of osteoporosis did not influence CTP prevalence or CTP concentration.

CONCLUSIONS

BMA-derived CTPs were obtained from all patient groups. CTP prevalence and CTP concentration decreased with age. Cell concentration decreased with age and positively correlated with total CTP prevalence and CTP concentration. The mean CTP concentration in patients >60 years of age was a third of the CTP concentration in patients <30 years of age.

CLINICAL RELEVANCE

Proper BMA techniques are necessary to obtain a high-quality yield and composition of cells and CTPs. The reduced CTP concentration and CTP prevalence in the elderly may be mitigated by the use of cell processing methods that increase CTP concentration and CTP prevalence (e.g., by removing red blood cells, serum, and non-CTPs or by increasing aspirate volumes). Cell concentration in the BMA can be measured at the point of care and is an appropriate initial assessment of the quality of BMA.

Modifying MSC Phenotype to Facilitate Bone Healing: Biological Approaches

Healing of fractures and bone defects normally follows an orderly series of events including formation of a hematoma and an initial stage of inflammation, development of soft callus, formation of hard callus, and finally the stage of bone remodeling. In cases of severe musculoskeletal injury due to trauma, infection, irradiation and other adverse stimuli, deficient healing may lead to delayed or non-union; this results in a residual bone defect with instability, pain and loss of function. Modern methods of mechanical stabilization and autologous bone grafting are often successful in achieving fracture union and healing of bone defects; however, in some cases, this treatment is unsuccessful because of inadequate biological factors. Specifically, the systemic and local microenvironment may not be conducive to bone healing because of a loss of the progenitor cell population for bone and vascular lineage cells. Autologous bone grafting can provide the necessary scaffold, progenitor and differentiated lineage cells, and biological cues for bone reconstruction, however, autologous bone graft may be limited in quantity or quality. These unfavorable circumstances are magnified in systemic conditions with chronic inflammation, including obesity, diabetes, chronic renal disease, aging and others. Recently, strategies have been devised to both mitigate the necessity for, and complications from, open procedures for harvesting of autologous bone by using minimally invasive aspiration techniques and concentration of iliac crest bone cells, followed by local injection into the defect site. More elaborate strategies (not yet approved by the U.S. Food and Drug Administration-FDA) include isolation and expansion of subpopulations of the harvested cells, preconditioning of these cells or inserting specific genes to modulate or facilitate bone healing. We review the literature pertinent to the subject of modifying autologous harvested cells including MSCs to facilitate bone healing. Although many of these techniques and technologies are still in the preclinical stage and not yet approved for use in humans by the FDA, novel approaches to accelerate bone healing by modifying cells has great potential to mitigate the physical, economic and social burden of non-healing fractures and bone defects.

The biological basis for concentrated iliac crest aspirate to enhance core decompression in the treatment of osteonecrosis

Core decompression is a surgical procedure that is capable of salvaging the patient's own natural joint, if the operation is performed in the early stages of osteonecrosis, in which the articular surface has not collapsed. The addition of concentrated cells, aspirated from the iliac crest, to the core tract has been shown to enhance the viability of the femoral head, although large, prospective, randomized, blinded multicentre studies are lacking. The rationale for adding these cells to the core decompression tract is to provide osteoprogenitor and vascular progenitor cells to the area of decompressed dead bone, in order to facilitate tissue regeneration and repair. It has become increasingly evident that vast discrepancies exist in different series in regard to the criteria for patient selection, the surgical technique of core decompression, the methods for harvesting, processing, and injecting the cells, and the methodology for determining success or failure in a specific patient cohort. This paper reviews the salient points relevant to the treatment of osteonecrosis by core decompression with addition of concentrated iliac crest aspirates and poses important questions regarding the future successful application of this technique.

Variation in primary and culture-expanded cells derived from connective tissue progenitors in human bone marrow space, bone trabecular surface and adipose tissue

BACKGROUND AIMS

Connective tissue progenitors (CTPs) embody the heterogeneous stem and progenitor cell populations present in native tissue. CTPs are essential to the formation and remodeling of connective tissue and represent key targets for tissue-engineering and cell-based therapies. To better understand and characterize CTPs, we aimed to compare the (i) concentration and prevalence, (ii) early in vitro biological behavior and (iii) expression of surface-markers and transcription factors among cells derived from marrow space (MS), trabecular surface (TS), and adipose tissues (AT).

METHODS

Cancellous-bone and subcutaneous-adipose tissues were collected from 8 patients. Cells were isolated and cultured. Colony formation was assayed using Colonyze software based on ASTM standards. Cell concentration ([Cell]), CTP concentration ([CTP]) and CTP prevalence (P_CTP) were determined. Attributes of culture-expanded cells were compared based on (i) effective proliferation rate and (ii) expression of surface-markers CD73, CD90, CD105, SSEA-4, SSEA-3, SSEA-1/CD15, Cripto-1, E-Cadherin/CD324, Ep-CAM/CD326, CD146, hyaluronan and transcription factors Oct3/4, Sox-2 and Nanog using flow cytometry.

RESULTS

Mean [Cell], [CTP] and P_CTP were significantly different between MS and TS samples (P = 0.03, P = 0.008 and P= 0.0003), respectively. AT-derived cells generated the highest mean total cell yield at day 6 of culture-4-fold greater than TS and more than 40-fold greater than MS per million cells plated. TS colonies grew with higher mean density than MS colonies (290 ± 11 versus 150 ± 11 cell per mm²; P = 0.0002). Expression of classical-mesenchymal stromal cell (MSC) markers was consistently recorded (>95%) from all tissue sources, whereas all the other markers were highly variable.

CONCLUSIONS

The prevalence and biological potential of CTPs are different between patients and tissue sources and lack variation in classical MSC markers. Other markers are more likely to discriminate differences between cell populations in biological performance. Understanding the underlying reasons for variation in the concentration, prevalence, marker expression and biological potential of CTPs between patients and source tissues and determining the means of managing this variation will contribute to the rational development of cell-based clinical diagnostics and targeted cell-based therapies.

The CD45lowCD271high Cell Prevalence in Bone Marrow Samples May Provide a Useful Measurement of the Bone Marrow Quality for Cartilage and Bone Regenerative Therapy

BACKGROUND

Bone marrow aspirates and concentrates are increasingly being used for musculoskeletal regenerative therapies, providing bone and cartilage progenitors. However, the quality of these bone marrow samples remains imprecise within clinical settings. As there is a need for the development of these therapies, a method of counting CD45CD271 cells was optimized and tested as an indicator of bone marrow sample quality.

METHODS

Bone marrow aspirates were collected from 54 donors (28 male and 26 female; median age of 48 years). The reagent concentrations were optimized for fast staining, and an acoustic-focusing flow cytometer (Attune) was used to enable automated CD45CD271 cell counting in bone marrow aspirates, bone marrow concentrates, and samples loaded onto a collagen scaffold. The CD45CD271 cell counts were compared with those obtained using another flow-cytometry-based method (LSR II) and with connective tissue progenitor (CTP) counts quantified using a colony forming unit-fibroblast (CFU-F) assay.

RESULTS

The optimized method enabled the counting of CD45CD271 cells within only 15 minutes. The quantified cell counts (median, 1,520; range, 96 to 20,992 cells/mL of bone marrow) were positively correlated with the CTP counts (p < 0.0001; r = 0.7237). In agreement with CFU-F and LSR II-based assays, the CD45CD271 cell counts quantified using the Attune-based method decreased with age in the samples from female but not male donors (p = 0.0015 and p = 0.3877, respectively). A significant increase in CD45CD271 cell counts was detected following bone marrow concentration (mean, 5-fold; 95% confidence interval [CI], 3.6 to 7.2-fold). Additionally, the number of CD45CD271 cells attached to the collagen scaffold was positively correlated with the number of progenitor cells that survived on the scaffold after 2-week culture (p = 0.0348).

CONCLUSIONS

An assay for counting CD45CD271 cells may provide a useful measurement of bone marrow quality. While the specificity of this measurement of CD45CD271 cells remained low in our experimental conditions, CD45CD271 cell counts were positively and modestly correlated with the prevalence of CTPs.

CLINICAL RELEVANCE

A fast and automated assessment of bone marrow aspirate/concentrate quality using CD45CD271 cell counting may be a useful tool for improving the quality of regenerative therapy.

Assessment of Methods for Rapid Intraoperative Concentration and Selection of Marrow-Derived Connective Tissue Progenitors for Bone Regeneration Using the Canine Femoral Multidefect Model

Treatment of large bone defects remains an unsolved clinical challenge, despite a wide array of existing bone graft materials and strategies. Local deficiency in osteogenic connective tissue progenitors (CTP-Os) due to tissue loss is one of the central biological barriers to bone regeneration. Density separation (DS) and selective retention (SR) represent two promising methods that can be used intraoperatively to rapidly concentrate cells and potentially select CTP-Os. This project was designed to compare DS and SR using the canine femoral multidefect (CFMD) model. Mineralized cancellous allograft (MCA) was used as a standardized scaffold for cell transplantation. Two experiments were performed using a cohort of six animals in each comparison. In Cohort I, unprocessed bone marrow aspirate (BMA) clot was compared to DS processing. MCA combined with raw BMA or DS processed cells produced a robust and advanced stage of bone regeneration throughout the defect in 4 weeks with reconstitution of hematopoietic marrow. However, the retention of DS processed cells and CTP-Os in the MCA matrix was low compared to BMA clot. In Cohort II, MCA with DS-T cells (addition of calcium chloride thrombin to induce clotting and enhance cell and CTP-O retention) was compared to MCA with SR cells. A mean of 276 ± 86 million nucleated cells and 29,030 ± 10,510 CTP-Os were implanted per defect in the DS-T group. A mean of 76 ± 42 million nucleated cells and 30,266 ± 15,850 CTP-Os were implanted in the SR group. Bone formation was robust and not different between treatments. Histologically, both groups demonstrated regeneration of hematopoietic marrow tissue. However, SR sites contained more hematopoietic vascular tissues, less fibrosis, and less residual allograft, particularly in the intramedullary cavity, suggesting a more advanced stage of remodeling (p = 0.04). These data demonstrate excellent overall performance of DS and SR processing methods. Both methods achieve a bone regeneration response that approaches the limits of performance that can be achieved in the CFMD model. Further advancement and comparison of these intraoperative bone marrow cell processing methods will require use of a larger and more biologically compromised defect site to guide the next steps of preclinical development and optimization.

Uncovering the dual role of RHAMM as an HA receptor and a regulator of CD44 expression in RHAMM-expressing mesenchymal progenitor cells

The interaction of hyaluronan (HA) with mesenchymal progenitor cells impacts trafficking and fate after tissue colonization during wound repair and these events contribute to diseases such as cancer. How this interaction occurs is poorly understood. Using 10T½ cells as a mesenchymal progenitor model and fluorescent (F-HA) or gold-labeled HA (G-HA) polymers, we studied the role of two HA receptors, RHAMM and CD44, in HA binding and uptake in non-adherent and adherent mesenchymal progenitor (10T½) cells to mimic aspects of cell trafficking and tissue colonization. We show that fluorescent labeled HA (F-HA) binding/uptake was high in non-adherent cells but dropped over time as cells became increasingly adherent. Non-adherent cells displayed both CD44 and RHAMM but only function-blocking anti-RHAMM and not anti-CD44 antibodies significantly reduced F-HA binding/uptake. Adherent cells, which also expressed CD44 and RHAMM, primarily utilized CD44 to bind to F-HA since anti-CD44 but not anti-RHAMM antibodies blocked F-HA uptake. RHAMM overexpression in adherent 10T½ cells led to increased F-HA uptake but this increased binding remained CD44 dependent. Further studies showed that RHAMM-transfection increased CD44 mRNA and protein expression while blocking RHAMM function reduced expression. Collectively, these results suggest that cellular microenvironments in which these receptors function as HA binding proteins differ significantly, and that RHAMM plays at least two roles in F-HA binding by acting as an HA receptor in non-attached cells and by regulating CD44 expression and display in attached cells. Our findings demonstrate adhesion-dependent mechanisms governing HA binding/ uptake that may impact development of new mesenchymal cell-based therapies.

Circular Halbach array for fast magnetic separation of hyaluronan-expressing tissue progenitors

Connective tissue progenitors (CTPs) are a promising therapeutic agent for bone repair. Hyaluronan, a high molecular mass glycosaminoglycan, has been shown by us to be a suitable biomarker for magnetic separation of CTPs from bone marrow aspirates in a canine model. For the therapy to be applicable in humans, the magnetic separation process requires scale-up without compromising the viability of the cells. The scaled-up device presented here utilizes a circular Halbach array of diametrically magnetized, cylindrical permanent magnets. This allows precise control of the magnetic field gradient driving the separation, with theoretical analysis favoring a hexapole field. The separation vessel has the external diameter of a 50 mL conical centrifuge tube and has an internal rod that excludes cells from around the central axis. The magnet and separation vessel (collectively dubbed the hexapole magnet separator or HMS) was tested on four human and four canine bone marrow aspirates. Each CTP-enriched cell product was tested using cell culture bioassays as surrogates for in vivo engraftment quality. The magnetically enriched cell fractions showed statistically significant, superior performance compared to the unenriched and depleted cell fractions for all parameters tested, including CTP prevalence (CTPs per 10(6) nucleated cells), proliferation by colony forming unit (CFU) counts, and differentiation by staining for the presence of osteogenic and chondrogenic cells. The simplicity and speed of the HMS operation could allow both CTP isolation and engraftment during a single surgical procedure, minimizing trauma to patients and lowering cost to health care providers.

Hyaluronan in the healthy and malignant hematopoietic microenvironment

The fate of both endogenous and transplanted stem cells is dependent on the functional status of the regulatory local microenvironment, which is compromised by disease and therapeutic intervention. The glycosaminoglycan hyaluronan (HA) is a critical component of the hematopoietic microenvironment. We summarize recent advances in our understanding of the role of HA in regulating mesenchymal stem cells, osteoblasts, fibroblasts, macrophages, and endothelium in bone marrow (BM) and their crosstalk within the hematopoietic microenvironment. HA not only determines the volume, hydration, and microfluidics of the BM interstitial space, but also, via interactions with specific receptors, regulates multiple cell functions including differentiation, migration, and production of regulatory factors. The effects of HA are dependent on the polymer size and are influenced by the formation of complexes with other molecules. In healthy BM, HA synthases and hyaluronidases form a molecular network that maintains extracellular HA levels within a discrete physiological window, but HA homeostasis is often perturbed in pathological conditions, including hematological malignancies. Recent studies have suggested that HA synthases may have functions beyond HA production and contribute to the intracellular regulatory machinery. We discuss a possible role for HA synthases, intracellular and extracellular HA in the malignant BM microenvironment, and resistance to therapy.

In vivo transplantation of autogenous marrow-derived cells following rapid intraoperative magnetic separation based on hyaluronan to augment bone regeneration

INTRODUCTION

This project was designed to test the hypothesis that rapid intraoperative processing of bone marrow based on hyaluronan (HA) could be used to improve the outcome of local bone regeneration if the concentration and prevalence of marrow-derived connective tissue progenitors (CTPs) could be increased and nonprogenitors depleted before implantation.

METHODS

HA was used as a marker for positive selection of marrow-derived CTPs using magnetic separation (MS) to obtain a population of HA-positive cells with an increased CTP prevalence. Mineralized cancellous allograft (MCA) was used as an osteoconductive carrier scaffold for loading of HA-positive cells. The canine femoral multidefect model was used and four cylindrical defects measuring 10 mm in diameter and 15 mm in length were grafted with MCA combined with unprocessed marrow or with MS processed marrow that was enriched in HA(+) CTPs and depleted in red blood cells and nonprogenitors. Outcome was assessed at 4 weeks using quantitative 3D microcomputed tomography (micro-CT) analysis of bone formation and histomorphological assessment.

RESULTS

Histomorphological assessment showed a significant increase in new bone formation and in the vascular sinus area in the MS-processed defects. Robust bone formation was found throughout the defect area in both groups (defects grafted with unprocessed marrow or with MS processed marrow.) Percent bone volume in the defects, as assessed by micro-CT, was greater in defects engrafted with MS processed cells, but the difference was not statistically significant.

CONCLUSION

Rapid intraoperative MS processing to enrich CTPs based on HA as a surface marker can be used to increase the concentration and prevalence of CTPs. MCA grafts supplemented with heparinized bone marrow or MS processed cells resulted in a robust and advanced stage of bone regeneration at 4 weeks. A greater new bone formation and vascular sinus area was found in defects grafted with MS processed cells. These data suggest that MS processing may be used to enhance the performance of marrow-derived CTPs in clinical bone regeneration procedures. Further assessment in a more stringent bone defect model is proposed.