Complex electrophysiological remodeling in postinfarction ischemic heart failure.

Heart failure (HF) following myocardial infarction (MI) is associated with high incidence of cardiac arrhythmias. Development of therapeutic strategy requires detailed understanding of electrophysiological remodeling. However, changes of ionic currents in ischemic HF remain incompletely understood, especially in translational large-animal models. Here, we systematically measure the major ionic currents in ventricular myocytes from the infarct border and remote zones in a porcine model of post-MI HF. We recorded eight ionic currents during the cell's action potential (AP) under physiologically relevant conditions using selfAP-clamp sequential dissection. Compared with healthy controls, HF-remote zone myocytes exhibited increased late Na+ current, Ca2+-activated K+ current, Ca2+-activated Cl- current, decreased rapid delayed rectifier K+ current, and altered Na+/Ca2+ exchange current profile. In HF-border zone myocytes, the above changes also occurred but with additional decrease of L-type Ca2+ current, decrease of inward rectifier K+ current, and Ca2+ release-dependent delayed after-depolarizations. Our data reveal that the changes in any individual current are relatively small, but the integrated impacts shift the balance between the inward and outward currents to shorten AP in the border zone but prolong AP in the remote zone. This differential remodeling in post-MI HF increases the inhomogeneity of AP repolarization, which may enhance the arrhythmogenic substrate. Our comprehensive findings provide a mechanistic framework for understanding why single-channel blockers may fail to suppress arrhythmias, and highlight the need to consider the rich tableau and integration of many ionic currents in designing therapeutic strategies for treating arrhythmias in HF.

Prevascularization of self-organizing engineered heart tissue by human umbilical vein endothelial cells abrogates contractile performance.

Establishing vascularization is a critical obstacle to the generation of engineered heart tissue (EHT) of substantial thickness. Addition of endothelial cells to the formative stages of EHT has been demonstrated to result in prevascularization, or the formation of capillary-like structures. The detailed study of the effects of prevascularization on EHT contractile function is lacking. Here, we evaluated the functional impact of prevascularization by human umbilical vein endothelial cells (HUVECs) in self-organizing EHT. EHT fibers were generated by the self-organization of neonatal rat cardiac cells on a fibrin hydrogel scaffold with or without HUVECs. Contractile function was measured and force-length relationship and rate of force production were assessed. Immunofluorescent studies were used to evaluate arrangement and distribution of HUVECs within the EHT fibers. RT-PCR was used to assess the transcript levels of hypoxia inducible factor-1a (Hif-1α). EHT with HUVECs manifested tubule-like structures at the periphery during fiber formation. After fiber formation, HUVECs were heterogeneously located throughout the EHT fiber and human CD31+ tubule-like structures were identified. The expression level of Hif-1α did not change with the addition of HUVECs. However, maximal force and rate of force generation were not improved in HUVECs containing EHT as compared to control EHT fibers. The addition of HUVECs may result in sparse microvascularization of EHT. However, this perceived benefit is overshadowed by a significant decrease in contractile function and highlights the need for perfused vascularization strategies in order to generate EHT that approaches clinically relevant dimensions.

Effects on proliferation and differentiation of multipotent bone marrow stromal cells engineered to express growth factors for combined cell and gene therapy.

A key mechanism for mesenchymal stem cells/bone marrow stromal cells (MSCs) to promote tissue repair is by secretion of soluble growth factors (GFs). Therefore, clinical application could be optimized by a combination of cell and gene therapies, where MSCs are genetically modified to express higher levels of a specific factor. However, it remains unknown how this overexpression may alter the fate of the MSCs. Here, we show effects of overexpressing the growth factors, such as basic fibroblast growth factor (bFGF), platelet derived growth factor B (PDGF-BB), transforming growth factor ß(1) (TGF-ß(1) ), and vascular endothelial growth factor (VEGF), in human bone marrow-derived MSCs. Ectopic expression of bFGF or PDGF-B lead to highly proliferating MSCs and lead to a robust increase in osteogenesis. In contrast, adipogenesis was strongly inhibited in MSCs overexpressing PDGF-B and only mildly affected in MSCs overexpressing bFGF. Overexpression of TGF-ß(1) blocked both osteogenic and adipogenic differentiation while inducing the formation of stress fibers and increasing the expression of the smooth muscle marker calponin-1 and the chondrogenic marker collagen type II. In contrast, MSCs overexpressing VEGF did not vary from control MSCs in any parameters, likely due to the lack of VEGF receptor expression on MSCs. MSCs engineered to overexpress VEGF strongly induced the migration of endothelial cells and enhanced blood flow restoration in a xenograft model of hind limb ischemia. These data support the rationale for genetically modifying MSCs to enhance their therapeutically relevant trophic signals, when safety and efficacy can be demonstrated, and when it can be shown that there are no unwanted effects on their proliferation and differentiation.

Human cord blood progenitors with high aldehyde dehydrogenase activity improve vascular density in a model of acute myocardial infarction.

UNLABELLED: Human stem cells from adult sources have been shown to contribute to the regeneration of muscle, liver, heart, and vasculature. The mechanisms by which this is accomplished are, however, still not well understood. We tested the engraftment and regenerative potential of human umbilical cord blood-derived ALDH(hi)Lin(-), and ALDH(lo)Lin(-) cells following transplantation to NOD/SCID or NOD/SCID beta2m null mice with experimentally induced acute myocardial infarction. We used combined nanoparticle labeling and whole organ fluorescent imaging to detect human cells in multiple organs 48 hours post transplantation. Engraftment and regenerative effects of cell treatment were assessed four weeks post transplantation. We found that ALDH(hi)Lin(-) stem cells specifically located to the site of injury 48 hours post transplantation and engrafted the infarcted heart at higher frequencies than ALDH(lo)Lin(-) committed progenitor cells four weeks post transplantation. We found no donor derived cardiomyocytes and few endothelial cells of donor origin. Cell treatment was not associated with any detectable functional improvement at the four week endpoint. There was, however, a significant increase in vascular density in the central infarct zone of ALDH(hi)Lin(-) cell-treated mice, as compared to PBS and ALDH(lo)Lin(-) cell-treated mice. CONCLUSIONS: Our data indicate that adult human stem cells do not become a significant part of the regenerating tissue, but rapidly home to and persist only temporarily at the site of hypoxic injury to exert trophic effects on tissue repair thereby enhancing vascular recovery.

Smooth muscle cells healing atherosclerotic plaque disruptions are of local, not blood, origin in apolipoprotein E knockout mice.

BACKGROUND: Signs of preceding episodes of plaque rupture and smooth muscle cell (SMC)-mediated healing are common in atherosclerotic plaques, but the source of the healing SMCs is unknown. Recent studies suggest that activated platelets adhering to sites of injury recruit neointimal SMCs from circulating bone marrow-derived progenitor cells. Here, we analyzed the contribution of this mechanism to plaque healing after spontaneous and mechanical plaque disruption in apolipoprotein E knockout (apoE-/-) mice. METHODS AND RESULTS: To determine the origin of SMCs after spontaneous plaque disruption, irradiated 18-month-old apoE-/- mice were reconstituted with bone marrow cells from enhanced green fluorescent protein (eGFP) transgenic apoE-/- mice and examined when they died up to 9 months later. Plaque hemorrhage, indicating previous plaque disruption, was widely present, but no bone marrow-derived eGFP+ SMCs were detected. To examine the origin of healing SMCs in a model that recapitulates more features of human plaque rupture and healing, we developed a mechanical technique that produced consistent plaque disruption, superimposed thrombosis, and SMC-mediated plaque healing in apoE-/- mice. Mechanical plaque disruption was produced in irradiated apoE-/- mice reconstituted with eGFP+ apoE-/- bone marrow cells and in carotid bifurcations cross-grafted between apoE-/- and eGFP+ apoE-/- mice. Apart from few non-graft-derived SMCs near the anastomosis site in 1 transplanted carotid bifurcation, no SMCs originating from outside the local arterial segment were detected in healed plaques. CONCLUSIONS: Healing SMCs after atherosclerotic plaque disruption are derived entirely from the local arterial wall and not circulating progenitor cells in apoE-/- mice.

Preclinical in Vitro and in Vivo Assessment of Linear and Branched l-Valine-Based Poly(ester urea)s for Soft Tissue Applications.

New polymers are needed to address the shortcomings of commercially available materials for soft tissue repair. Herein, we investigated a series of l-valine-based poly(ester urea)s (PEUs) that vary in monomer composition and the extent of branching as candidate materials for soft tissue repair. The preimplantation Young's moduli (105 ± 30 to 269 ± 12 MPa) for all the PEUs are comparable to those of polypropylene (165 ± 5 MPa) materials currently employed in hernia-mesh repair. The 2% branched poly(1-VAL-8) maintained the highest Young's modulus following 3 months of in vivo implantation (78 ± 34 MPa) when compared to other PEU analogues (20 ± 6-45 ± 5 MPa). Neither the linear or branched PEUs elicited a significant inflammatory response in vivo as noted by less fibrous capsule formation after 3 months of implantation (80 ± 38 to 103 ± 33 µm) relative to polypropylene controls (126 ± 34 µm). Mechanical degradation in vivo over three months, coupled with limited inflammatory response, suggests that l-valine-based PEUs are translationally relevant materials for soft tissue applications.

Amino acid-based Poly(ester urea) copolymer films for hernia-repair applications.

The use of degradable materials is required to address current performance and functionality shortcomings from biologically-derived tissues and non-resorbable synthetic materials used for hernia mesh repair applications. Herein a series of degradable l-valine-co-l-phenylalanine poly(ester urea) (PEU) copolymers were investigated for soft-tissue repair. Poly[(1-VAL-8)0.7-co-(1-PHE-6)0.3] showed the highest uniaxial mechanical properties (332.5 ±â€¯3.5 MPa). Additionally, l-valine-co-l-phenylalanine poly(ester urea)s were blade coated on small intestine submucosa extracellular matrix (SIS-ECM) and found to enhance the burst test mechanical properties of SIS-ECM in composite films (force at break between 102.6 ±â€¯6.5-151.4 ±â€¯11.3 N). Free standing films of l-valine-co-l-phenylalanine PEUs were found to have superior extension at break when compared to SIS-ECM (averages between 1.2 and 1.9 cm and 1.2 cm respectively). Fibroblast (L-929) spreading, proliferation, and improved attachment over control were observed without toxicity in vitro, while a reduced inflammatory response at both 7 and 14 days post-implant was observed for poly[(1-VAL-8)⁠0.7-co-(1-PHE-6)⁠0.3] when compared to polypropylene in an in vivo rat hernia model. These results support the use of PEU copolymers as free-standing films or as composite materials in soft-tissue applications for hernia-repair.

Smooth muscle cells in atherosclerosis originate from the local vessel wall and not circulating progenitor cells in ApoE knockout mice.

OBJECTIVE: Recent studies of bone marrow (BM)-transplanted apoE knockout (apoE-/-) mice have concluded that a substantial fraction of smooth muscle cells (SMCs) in atherosclerosis arise from circulating progenitor cells of hematopoietic origin. This pathway, however, remains controversial. In the present study, we reexamined the origin of plaque SMCs in apoE-/- mice by a series of BM transplantations and in a novel model of atherosclerosis induced in surgically transferred arterial segments. METHODS AND RESULTS: We analyzed plaques in lethally irradiated apoE-/- mice reconstituted with sex-mismatched BM cells from eGFP+ apoE-/- mice, which ubiquitously express enhanced green fluorescent protein (eGFP), but did not find a single SMC of donor BM origin among approximately 10,000 SMC profiles analyzed. We then transplanted arterial segments between eGFP+ apoE-/- and apoE-/- mice (isotransplantation except for the eGFP transgene) and induced atherosclerosis focally within the graft by a recently invented collar technique. No eGFP+ SMCs were found in plaques that developed in apoE-/- artery segments grafted into eGFP+ apoE-/- mice. Concordantly, 96% of SMCs were eGFP+ in plaques induced in eGFP+ apoE-/- artery segments grafted into apoE-/- mice. CONCLUSIONS: These experiments show that SMCs in atherosclerotic plaques are exclusively derived from the local vessel wall in apoE-/- mice.

Mesenchymal Stem Cell Seeding of Porcine Small Intestinal Submucosal Extracellular Matrix for Cardiovascular Applications.

In this study, we investigate the translational potential of a novel combined construct using an FDA-approved decellularized porcine small intestinal submucosa extracellular matrix (SIS-ECM) seeded with human or porcine mesenchymal stem cells (MSCs) for cardiovascular indications. With the emerging success of individual component in various clinical applications, the combination of SIS-ECM with MSCs could provide additional therapeutic potential compared to individual components alone for cardiovascular repair. We tested the in vitro effects of MSC-seeding on SIS-ECM on resultant construct structure/function properties and MSC phenotypes. Additionally, we evaluated the ability of porcine MSCs to modulate recipient graft-specific response towards SIS-ECM in a porcine cardiac patch in vivo model. Specifically, we determined: 1) in vitro loading-capacity of human MSCs on SIS-ECM, 2) effect of cell seeding on SIS-ECM structure, compositions and mechanical properties, 3) effect of SIS-ECM seeding on human MSC phenotypes and differentiation potential, and 4) optimal orientation and dose of porcine MSCs seeded SIS-ECM for an in vivo cardiac application. In this study, histological structure, biochemical compositions and mechanical properties of the FDA-approved SIS-ECM biomaterial were retained following MSCs repopulation in vitro. Similarly, the cellular phenotypes and differentiation potential of MSCs were preserved following seeding on SIS-ECM. In a porcine in vivo patch study, the presence of porcine MSCs on SIS-ECM significantly reduced adaptive T cell response regardless of cell dose and orientation compared to SIS-ECM alone. These findings substantiate the clinical translational potential of combined SIS-ECM seeded with MSCs as a promising therapeutic candidate for cardiac applications.

Small intestinal submucosa-derived extracellular matrix bioscaffold significantly enhances angiogenic factor secretion from human mesenchymal stromal cells.

INTRODUCTION: The in vivo therapeutic effect of mesenchymal stromal cells (MSCs) is currently believed to be tightly linked to their paracrine secretion ability. However, insufficient or imprecise cell delivery, low cell survival and retention post-transplant, along with harsh donor site microenvironments, are major barriers to the clinical success of MSC therapies. Here we tested a small intestinal submucosa (SIS)-derived extracellular matrix (ECM) bioscaffold augmented with MSCs, with the hypothesis that they will facilitate the precise delivery of increased numbers of MSCs therefore improving cell viability and retention. METHODS: In this study, we evaluated the secretion of angiogenic factors from three human MSC lines cultured on SIS ECM. We used human antibody array and enzyme-linked immunosorbent assay to measure the level of angiogenic factors released from MSCs when cultured on SIS ECM or regular tissue culture plastic. We tested MSCs cultured for three different time points. RESULTS: We found that the SIS ECM culture environment can significantly enhance the release of several angiogenic factors when compared to MSCs cultured on standard tissue culture plastic. Specifically, vascular endothelial growth factor and interleukin-8 secretion was significantly increased at 24, 48 and 72 hours postseeding onto SIS ECM whereas vascular endothelial growth factor release for cells cultured on plastic surface remained the same during these time points. We also observed significant donor to donor variation in cytokine production. CONCLUSIONS: This study demonstrates that MSCs transplanted onto a SIS ECM may greatly increase their therapeutic potential through an increase in pro-angiogenic cytokine release.

Lysophosphatidic acid enhances stromal cell-directed angiogenesis.

Ischemic diseases such as peripheral vascular disease (PVD) affect more than 15% of the general population and in severe cases result in ulcers, necrosis, and limb loss. While the therapeutic delivery of growth factors to promote angiogenesis has been widely investigated, large-scale implementation is limited by strategies to effectively deliver costly recombinant proteins. Multipotent adipose-derived stromal cells (ASC) and progenitor cells from other tissue compartments secrete bioactive concentrations of angiogenic molecules, making cell-based strategies for in situ delivery of angiogenic cytokines an exciting alternative to the use of recombinant proteins. Here, we show that the phospholipid lysophosphatidic acid (LPA) synergistically improves the proangiogenic effects of ASC in ischemia. We found that LPA upregulates angiogenic growth factor production by ASC under two- and three-dimensional in vitro models of serum deprivation and hypoxia (SD/H), and that these factors significantly enhance endothelial cell migration. The concurrent delivery of LPA and ASC in fibrin gels significantly improves vascularization in a murine critical hindlimb ischemia model compared to LPA or ASC alone, thus exhibiting the translational potential of this method. Furthermore, these results are achieved using an inexpensive lipid molecule, which is orders-of-magnitude less costly than recombinant growth factors that are under investigation for similar use. Our results demonstrate a novel strategy for enhancing cell-based strategies for therapeutic angiogenesis, with significant applications for treating ischemic diseases.

Computational analysis of contractility in engineered heart tissue.

Engineered heart tissue (EHT) is a potential therapy for heart failure and the basis of functional in vitro assays of novel cardiovascular treatments. Self-organizing EHT can be generated in fiber form, which makes the assessment of contractile function convenient with a force transducer. Contractile function is a key parameter of EHT performance. Analysis of EHT force data is often performed manually; however, this approach is time consuming, incomplete and subjective. Therefore, the purpose of this study was to develop a computer algorithm to efficiently and objectively analyze EHT force data. This algorithm incorporates data filtering, individual contraction detection and validation, inter/intracontractile analysis and intersample analysis. We found the algorithm to be accurate in contraction detection, validation and magnitude measurement as compared to human operators. The algorithm was efficient in processing hundreds of data acquisitions and was able to determine force-length curves, force-frequency relationships and compare various contractile parameters such as peak systolic force generation. We conclude that this computer algorithm is a key adjunct to the objective and efficient assessment of EHT contractile function.

Contractile and electrophysiologic characterization of optimized self-organizing engineered heart tissue.

BACKGROUND: Engineered heart tissue (EHT) is being developed for clinical implantation in heart failure or congenital heart disease and therefore requires a comprehensive functional characterization and scale-up of EHT. Here we explored the effects of scale-up of self-organizing EHT and present detailed electrophysiologic and contractile functional characterization. METHODS: Fibers from EHT were generated from self-organizing neonatal rat cardiac cells (0.5×10(6) to 3×10(6)/fiber) on fibrin. We characterized contractile patterns and measured contractile function using a force transducer, and assessed force-length relationship, maximal force generation, and rate of force generation. Action potential and conduction velocity of EHT were measured with optical mapping, and transcript levels of myosin heavy chain beta were measured by reverse transcriptase-polymerase chain reaction. RESULTS: Increasing the cell number per construct resulted in an increase in fiber volume. The force-length relationship was negatively impacted by increasing cell number. Maximal force generation and rate of force generation were also abrogated with increasing cell number. This decrease was not likely attributable to a selective expansion of noncontractile cells as myosin heavy chain beta levels were stable. Irregular contractile behavior was more prevalent in constructs with more cells. Engineered heart tissue (1×10(6)/construct) had an action potential duration of 140.2 milliseconds and a conduction velocity of 23.2 cm/s. CONCLUSIONS: Engineered heart tissue displays physiologically relevant features shared with native myocardium. Engineered heart tissue scale-up by increasing cell number abrogates contractile function, possibly as a result of suboptimal cardiomyocyte performance in the absence of vasculature. Finally, conduction velocity approaches that of native myocardium without any electrical or mechanical conditioning, suggesting that the self-organizing method may be superior to other rigid scaffold-based EHT.

Nonviral transfection of leukemic primary cells and cells lines by siRNA-a direct comparison between Nucleofection and Accell delivery.

Transient downregulation of genes in vitro employing short interfering RNA (siRNA) is a time-honored approach to study gene function. A crucial prerequisite to obtain a downregulation is an efficient and nontoxic delivery of the siRNA into the target cells. However, this has proven difficult to accomplish, particular in cells in suspension. Thus, there is a need for a systematic evaluation of different methodologies to identify the most suitable protocol. We compared Nucleofection with Accell, a novel nonviral-based delivery system in the setting of leukemic blasts from patients with myeloid leukemias. Two cell surface proteins, human inhibitory C-type lectin-like receptor and CD96, both believed to be associated with leukemic stem cells, were chosen as target genes. Accell not only yielded higher transfection rates, but also retained superior cell viabilities for both cell lines and primary leukemic cells. Thus, transfection efficiencies in primary cells after Accell delivery was 85% (range, 71-97%) compared to 38% (23-65%) using Nucleofection for siRNA delivery. Preliminary studies of clonal growth of primary acute myeloid leukemia cells indicated growth inhibition after siRNA transfection. Our results reveal that Accell delivery is suitable for nonviral transfection of cells in suspension, including primary leukemic cells. These data should provide a platform for further studies of genes involved in early leukemogenesis.

Characterization and in vivo testing of mesenchymal stem cells derived from human embryonic stem cells.

Mesenchymal stem cells (MSCs) have been shown to contribute to the recovery of tissues through homing to injured areas, especially to hypoxic, apoptotic, or inflamed areas and releasing factors that hasten endogenous repair. In some cases genetic engineering of the MSC is desired, since they are excellent delivery vehicles. We have derived MSCs from the human embryonic stem cell (hESC) line H9 (H9-MSCs). They expressed CD105, CD90, CD73, and CD146, and lacked expression of CD45, CD34, CD14, CD31, and HLA-DR, the hESC pluripotency markers SSEA-4 and Tra-1-81, and the hESC early differentiation marker SSEA-1. Marrow-derived MSCs showed a similar phenotype. H9-MSCs did not form teratoma in our initial studies, whereas the parent H9 line did so robustly. H9-MSCs differentiated into bone, cartilage, and adipocytes in vitro, and displayed increased migration under hypoxic conditions. Finally, using a hindlimb ischemia model, H9-MSCs were shown to home to the hypoxic muscle, but not the contralateral limb, by 48 h after IV injection. In summary, we have defined methods for differentiation of hESCs into MSCs and have defined their characteristics and in vivo migratory properties.

Human thymus mesenchymal stromal cells augment force production in self-organized cardiac tissue.

BACKGROUND: Mesenchymal stromal cells have been recently isolated from thymus gland tissue discarded after surgical procedures. The role of this novel cell type in heart regeneration has yet to be defined. The purpose of this study was to evaluate the therapeutic potential of human thymus-derived mesenchymal stromal cells using self-organized cardiac tissue as an in vitro platform for quantitative assessment. METHODS: Mesenchymal stromal cells were isolated from discarded thymus tissue from neonates undergoing heart surgery and were incubated in differentiation media to demonstrate multipotency. Neonatal rat cardiomyocytes self-organized into cardiac tissue fibers in a custom culture dish either alone or in combination with varying numbers of mesenchymal stromal cells. A transducer measured force generated by spontaneously contracting self-organized cardiac tissue fibers. Work and power outputs were calculated from force tracings. Immunofluorescence was performed to determine the fate of the thymus-derived mesenchymal stromal cells. RESULTS: Mesenchymal stromal cells were successfully isolated from discarded thymus tissue. After incubation in differentiation media, mesenchymal stromal cells attained the expected phenotypes. Although mesenchymal stromal cells did not differentiate into mature cardiomyocytes, addition of these cells increased the rate of fiber formation, force production, and work and power outputs. Self-organized cardiac tissue containing mesenchymal stromal cells acquired a defined microscopic architecture. CONCLUSIONS: Discarded thymus tissue contains mesenchymal stromal cells, which can augment force production and work and power outputs of self-organized cardiac tissue fibers by several-fold. These findings indicate the potential utility of mesenchymal stromal cells in treating heart failure.

Minimal engraftment of human CD34+ cells mobilized from healthy donors in the infarcted heart of athymic nude rats.

Cell-based regenerative therapy may be useful for treatment of acute myocardial infarction (AMI). Animal xenograft models are ideally suited for preclinical studies evaluating prospective treatment regimes, identifying candidate human cell populations, and gaining mechanistic insight. Here we address whether the athymic nude rat is suitable as a xenograft model for the study of human CD34+ mobilized peripheral blood stem cells (M-PBSCs) in the repair of AMI. We injected human donor cells into the infarct border of athymic nude rats with surgically induced AMI and evaluated engraftment and functional improvement. We found no human engraftment by immunofluorescence staining at 14 days after transplantation or functional improvement at days 2 and 14 compared to controls. The lack of long-term human engraftment was furthermore confirmed in a time series study analyzing animals at 0, 24, 48, 72, and 96 h after transplantation. Although we found fluorescent microbeads coinjected with human CD34+ M-PBSCs at all time points, the number of donor cells rapidly declined and became undetectable at 96 h. CD34+ M-PBSCs from the same donor used to treat athymic nude rat hearts engrafted the bone marrow of nonobese diabetic/severe combined immunodeficient mice 8-10 weeks after transplantation. In conclusion, human CD34+ M-PBSCs with confirmed hematopoietic engraftment potential rapidly disappeared from the site of injury following intramyocardial transplantation in the athymic nude rat AMI model.

Preloading potential of retroviral vectors is packaging cell clone dependent and centrifugation onto CH-296 ensures highest transduction efficiency.

Retroviral vector-mediated gene transfer has been used successfully in clinical gene therapy. Cells of the hematopoietic lineages, however, remain difficult to transduce, although precoating of culture vessels with the fibronectin fragment CH-296 may improve transduction efficiency. Alternatively, low-speed centrifugation of vector-containing supernatant onto culture vessels may improve transduction efficiency in the absence of CH-296 preloading. Using the NIH/3T3-derived Moloney murine leukemia virus-based packaging cell lines PG13, PA317, and PT67, we here show that preloading by low-speed centrifugation improves transduction efficiency in a packaging cell subclone-dependent manner. Preloading by centrifugation, however, cannot generally replace CH-296 and we obtained the overall highest transduction levels when combining centrifugation and CH-296 precoating. We found, moreover, that the factor responsible for high susceptibility to preloading in our PG13-derived vector supernatant was transferable to a PA317-derived vector supernatant with low susceptibility to preloading. Furthermore, our PA317, PG13, and PT67 subclones shed into their supernatants variable amounts of fibronectin. This soluble fibronectin formed aggregates of various sizes and generated complexes with vector particles. The fibronectin-vector complexes readily sedimented onto culture vessels and copurified after fibronectin-specific affinity purification of vector-containing supernatants. Finally, vector supernatant from 293T cells, which barely produce fibronectin, was not susceptible to preloading. The susceptibility to preloading by centrifugation thus appears to be dependent both on the specific packaging cell line and on the association of vector particles and packaging cell-produced fibronectin. Rigorous screening of individual vector-containing supernatants is therefore required to identify optimal transduction conditions for retroviral gene transfer.