[show abstract][hide abstract] ABSTRACT: Mesenchymal stem cells (MSCs) spontaneously fuse with somatic cells in vivo, albeit rarely, and the fusion products are capable of tissue-specific function (mature trait) or proliferation (immature trait), depending on the microenvironment. That stem cells can be programmed, or somatic cells reprogrammed, in this fashion suggests that stem cell fusion holds promise as a therapeutic approach for the repair of damaged tissues, especially tissues not readily capable of functional regeneration, such as the myocardium. In an attempt to increase the frequency of stem cell fusion and, in so doing, increase the potential for cardiac tissue repair, we expressed the fusogen of the vesicular stomatitis virus (VSV-G) in human MSCs. We found VSV-G expressing MSCs (vMSCs) fused with cardiomyocytes (CMs) and these fusion products adopted a CM-like phenotype and morphology in vitro. In vivo, vMSCs delivered to damaged mouse myocardium via a collagen patch were able to home to the myocardium and fuse to cells within the infarct and peri-infarct region of the myocardium. This study provides a basis for the investigation of the biological impact of fusion of stem cells with CMs in vivo and illustrates how viral fusion proteins might better enable such studies.
[show abstract][hide abstract] ABSTRACT: The ability of two or more cells of the same type to fuse has been utilized in metazoans throughout evolution to form many complex organs, including skeletal muscle, bone and placenta. Contemporary studies demonstrate fusion of cells of the same type confers enhanced function. For example, when the trophoblast cells of the placenta fuse to form the syncytiotrophoblast, the syncytiotrophoblast is better able to transport nutrients and hormones across the maternal-fetal barrier than unfused trophoblasts(1-4). More recent studies demonstrate fusion of cells of different types can direct cell fate. The "reversion" or modification of cell fate by fusion was once thought to be limited to cell culture systems. But the advent of stem cell transplantation led to the discovery by us and others that stem cells can fuse with somatic cells in vivo and that fusion facilitates stem cell differentiation(5-7). Thus, cell fusion is a regulated process capable of promoting cell survival and differentiation and thus could be of central importance for development, repair of tissues and even the pathogenesis of disease. Limiting the study of cell fusion, is lack of appropriate technology to 1) accurately identify fusion products and to 2) track fusion products over time. Here we present a novel approach to address both limitations via induction of bioluminescence upon fusion (Figure 1); bioluminescence can be detected with high sensitivity in vivo(8-15). We utilize a construct encoding the firefly luciferase (Photinus pyralis) gene placed adjacent to a stop codon flanked by LoxP sequences. When cells expressing this gene fuse with cells expressing the Cre recombinase protein, the LoxP sites are cleaved and the stop signal is excised allowing transcription of luciferase. Because the signal is inducible, the incidence of false-positive signals is very low. Unlike existing methods which utilize the Cre/LoxP system(16, 17), we have incorporated a "living" detection signal and thereby afford for the first time the opportunity to track the kinetics of cell fusion in vivo. To demonstrate the approach, mice ubiquitously expressing Cre recombinase served as recipients of stem cells transfected with a construct to express luciferase downstream of a floxed stop codon. Stem cells were transplanted via intramyocardial injection and after transplantation intravital image analysis was conducted to track the presence of fusion products in the heart and surrounding tissues over time. This approach could be adapted to analyze cell fusion in any tissue type at any stage of development, disease or adult tissue repair.
[show abstract][hide abstract] ABSTRACT: Rationale: Cost-effectiveness studies comparing spinal surgery with conservative treatment and studies comparing different techniques of spinal fusion have been carried out previously. The studies comparing different techniques of spinal fusion have been limited by not being able to compare stochastic costs and outcomes at the patient-level. Objective: To determine the cost-effectiveness of titanium cage (new intervention) versus femoral ring allograft (standard intervention) in circumferential lumbar spinal fusion. A secondary aim was to assess whether using different methods of dealing with missing utility data changed the study conclusion reached. Methods: An economic evaluation was undertaken alongside a prospective controlled trial of 78 participants randomised to titanium cage (TC) (n=41) or femoral ring allograft (FRA) (n=37) surgery between 1998 and 2002 from a secondary care NHS perspective. Five others were excluded from randomisation due to technical infringements. The timeframe for the economic evaluation was 2 years. NHS resources relating to the surgery and any revision surgery needed during the trial period were record in clinical records and costed using local unit costs where available or published national unit costs where not. The Short Form-6D (SF-6D) (11 questions from the Short Form-36 patient questionnaire) was administered preoperatively and at 6, 12 and 24 months in order to elicit patient utility from which to derive Quality-Adjusted Life Years (QALYs) for the trial period. Bootstrapped mean differences in costs and benefits were generated in order to explore the cost-effectiveness of TC and FRA implants in circumferential fusion of the lumbar spine. Missing utility data was imputed using linear interpolation in the base case but in sensitivity analysis complete case analysis, available case analysis, and multiple imputation were undertaken. Results: A significant mean cost saving of £1,942 (95% confidence interval £849 to £3,145) was associated with FRA (UK£2005/6). Mean QALYs per patient over the 24 month trial period were 0.0522 (SD 0.0326) in the TC group and 0.1914 (SD 0.0398) in the FRA group, producing a significant difference of -0.1392 (95% confidence interval 0.2349 to 0.0436). There was no missing cost data. However, a proportion of utility scores were missing at each time point (FRA: 5% at baseline, 30% at 6 months, 19% at 12 months and 5% at 24 months, TC: 10% at baseline, 29% at 6 months, 19% at 12 months and 24% at 24 months). The discounted mean difference in QALYs between TC and FRA was highest in the base case using linear interpolation. Multiple imputation resulted in a mean difference of -0.1367 compared to -0.0675 using available case analysis and -0.0518 using complete case analysis. Conclusion: From a secondary care NHS perspective, the trial data show that TC is not cost-effective in circumferential lumbar fusion compared to the FRA. The use of FRA was both cheaper and generated greater QALY gains. Although the FRA was always less costly and more effective than the TC, in the complete case analysis and available case analysis the mean effect was calculated to be half that of the base case.