Muscle stem cells can act as antigen-presenting cells: implication for gene therapy

Muscle stem cells as immunomodulator during regeneration

The skeletal muscle is well known for its remarkable ability to regenerate after injuries. The regeneration is a complex and dynamic process that involves muscle stem cells (also called muscle satellite cells, MuSCs), fibro-adipogenic progenitors (FAPs), immune cells, and other muscle-resident cell populations. The MuSCs are the myogenic cell populaiton that contribute nuclei directly to the regenerated myofibers, while the other cell types collaboratively establish a microenvironment that facilitates myogenesis of MuSCs. The myogenic process includes activation, proliferation and differentiationof MuSCs, and subsequent fusion their descendent mononuclear myocytes into multinuclear myotubes. While the contributions of FAPs and immune cells to this microenvironment have been well studied, the influence of MuSCs on other cell types remains poorly understood. This review explores recent evidence supporting the potential role of MuSCs as immunomodulators during muscle regeneration, either through cytokine production or ligand-receptor interactions.

Blood Transcriptome Profiling Links Immunity to Disease Severity in Myotonic Dystrophy Type 1 (DM1)

The blood transcriptome was examined in relation to disease severity in type I myotonic dystrophy (DM1) patients who participated in the Observational Prolonged Trial In DM1 to Improve QoL- Standards (OPTIMISTIC) study. This sought to (a) ascertain if transcriptome changes were associated with increasing disease severity, as measured by the muscle impairment rating scale (MIRS), and (b) establish if these changes in mRNA expression and associated biological pathways were also observed in the Dystrophia Myotonica Biomarker Discovery Initiative (DMBDI) microarray dataset in blood (with equivalent MIRS/DMPK repeat length). The changes in gene expression were compared using a number of complementary pathways, gene ontology and upstream regulator analyses, which suggested that symptom severity in DM1 was linked to transcriptomic alterations in innate and adaptive immunity associated with muscle-wasting. Future studies should explore the role of immunity in DM1 in more detail to assess its relevance to DM1.

Temporal Dynamics and Heterogeneity of Cell Populations during Skeletal Muscle Regeneration

Mammalian skeletal muscle possesses a unique ability to regenerate, which is primarily mediated by a population of resident muscle stem cells (MuSCs) and requires a concerted response from other supporting cell populations. Previous targeted analysis has described the involvement of various specific populations in regeneration, but an unbiased and simultaneous evaluation of all cell populations has been limited. Therefore, we used single-cell RNA-sequencing to uncover gene expression signatures of over 53,000 individual cells during skeletal muscle regeneration. Cells clustered into 25 populations and subpopulations, including a subpopulation of immune gene enriched myoblasts (immunomyoblasts) and subpopulations of fibro-adipogenic progenitors. Our analyses also uncovered striking spatiotemporal dynamics in gene expression, population composition, and cell-cell interaction during muscle regeneration. These findings provide insights into the cellular and molecular underpinning of skeletal muscle regeneration.

Immune checkpoint failures in inflammatory myopathies: An overview

Dermatomyositis (DM), polymyositis (PM), inclusion body myositis (IBM), immune mediated necrotizing myopathy (IMNM) and overlap myositis (OM) are classified as inflammatory myopathies (IM) with involvement of autoimmune features such as autoreactive lymphocytes and autoantibodies. Autoimmunity can be defined as a loss in self-tolerance and attack of autoantigens by the immune system. Self-tolerance is achieved by a group of immune mechanisms occurring in central and periphal lymphoid organs and tissues, called immune checkpoints, that work in synergy to protect the body from harmful immune reactions. Autoimmune disorders appear when immune checkpoints fail. In this review, the different immune checkpoint failures are discussed in DM, PM, IBM and IMNM. Exploring research contribution in each of these immune checkpoints might help to highlight research perspectives in the field and obtain a more complete picture of IM disease pathology.

Schwann cells promote post-traumatic nerve inflammation and neuropathic pain through MHC class II

The activation of T helper cells requires antigens to be exposed on the surface of antigen presenting cells (APCs) via MHC class II (MHC-II) molecules. Expression of MHC-II is generally limited to professional APCs, but other cell types can express MHC-II under inflammatory conditions. However, the importance of these conditional APCs is unknown. We and others have previously shown that Schwann cells are potentially conditional APCs, but the functional relevance of MHC-II expression by Schwann cells has not been studied in vivo. Here, we conditionally deleted the MHC-II β-chain from myelinating Schwann cells in mice and investigated how this influenced post-traumatic intraneural inflammation and neuropathic pain using the chronic constriction injury (CCI) model. We demonstrate that deletion of MHC-II in myelinating Schwann cells reduces thermal hyperalgesia and, to a lesser extent, also diminishes mechanical allodynia in CCI in female mice. This was accompanied by a reduction of intraneural CD4+ T cells and greater preservation of preferentially large-caliber axons. Activation of T helper cells by MHC-II on Schwann cells thus promotes post-traumatic axonal loss and neuropathic pain. Hence, we provide experimental evidence that Schwann cells gain antigen-presenting function in vivo and modulate local immune responses and diseases in the peripheral nerves.

Effects of APC De-targeting and GAr modification on the duration of luciferase expression from plasmid DNA delivered to skeletal muscle

Immune responses to expressed foreign transgenes continue to hamper progress of gene therapy development. Translated foreign proteins with intracellular location are generally less accessible to the immune system, nevertheless they can be presented to the immune system through both MHC Class I and Class II pathways. When the foreign protein luciferase was expressed following intramuscular delivery of plasmid DNA in outbred mice, expression rapidly declined over 4 weeks. Through modifications to the expression plasmid and the luciferase transgene we examined the effect of detargeting expression away from antigen-presenting cells (APCs), targeting expression to skeletal muscle and fusion with glycine-alanine repeats (GAr) that block MHC-Class I presentation on the duration of luciferase expression. De-targeting expression from APCs with miR142-3p target sequences incorporated into the luciferase 3'UTR reduced the humoral immune response to both native and luciferase modified with a short GAr sequence but did not prolong the duration of expression. When a skeletal muscle specific promoter was combined with the miR target sequences the humoral immune response was dampened and luciferase expression persisted at higher levels for longer. Interestingly, fusion of luciferase with a longer GAr sequence promoted the decline in luciferase expression and increased the humoral immune response to luciferase. These studies demonstrate that expression elements and transgene modifications can alter the duration of transgene expression but other factors will need to overcome before foreign transgenes expressed in skeletal muscle are immunologically silent.

Transgene expression and local tissue distribution of naked and polymer-condensed plasmid DNA after intradermal administration in mice

DNA vaccination using cationic polymers as carriers has the potential to be a very powerful method of immunotherapy, but typical immune responses generated have been less than robust. To better understand the details of DNA vaccine delivery in vivo, we prepared polymer/DNA complexes using three structurally distinct cationic polymers and fluorescently labeled plasmid DNA and injected them intradermally into mice. We analyzed transgene expression (luciferase) and the local tissue distribution of the labeled plasmid at the injection site at various time points (from hours to days). Comparable numbers of luciferase expressing cells were observed in the skin of mice receiving naked plasmid or polyplexes one day after transfection. At day 4, however, the polyplexes appeared to result in more transfected skin cells than naked plasmid. Live animal imaging revealed that naked plasmid dispersed quickly in the skin of mice after injection and had a wider distribution than any of the three types of polyplexes. However, naked plasmid level dropped to below detection limit after 24h, whereas polyplexes persisted for up to 2 weeks. The PEGylated polyplexes had a significantly wider distribution in the tissue than the nonPEGylated polyplexes. PEGylated polyplexes also distributed more broadly among dermal fibroblasts and allowed greater interaction with antigen-presenting cells (APCs) (dendritic cells and macrophages) starting at around 24h post-injection. By day 4, co-localization of polyplexes with APCs was observed at the injection site regardless of polymer structure, whereas small amounts of polyplexes were found in the draining lymph nodes. These in vivo findings demonstrate the superior stability of PEGylated polyplexes in physiological milieu and provide important insight on how cationic polymers could be optimized for DNA vaccine delivery.

Polymer-mediated DNA vaccine delivery via bystander cells requires a proper balance between transfection efficiency and cytotoxicity

Direct targeting of dendritic cells is an ideal goal for DNA vaccine delivery in order to stimulate both arms of the immune system. However, dendritic cells are often difficult to transfect using nonviral polyplexes. Here we show that transfecting bystander cells such as fibroblasts with PEI/DNA complexes leads to efficient cross-presentation of a model antigen by dendritic cells and subsequent activation of antigen-specific CD8(+) T cells. Maturation of dendritic cells is also stimulated after co-culture with transfected fibroblasts. Such outcomes depend on a proper balance between transfection efficiency and polyplex-induced cytotoxicity in the fibroblasts. In fact, substantial cytotoxicity is desirable and even necessary for cross-presentation and cross-priming of T cells. This study illustrates a new pathway of polymer-based DNA vaccine delivery via bystander cells without direct targeting of antigen-presenting cells and highlights the importance of exploiting polymer-induced cytotoxicity for the benefit of immune activation.

miRNA-mediated silencing in hepatocytes can increase adaptive immune responses to adenovirus vector-delivered transgenic antigens

Adenovirus vectors based on human serotype 5 can induce potent CD8 T cell responses to vector-encoded transgenic antigens. However, the individual contribution of different cell types expressing antigen upon adenovirus vector injection to the generation of antigen-directed adaptive immune responses is poorly understood so far. We investigated the role of hepatocytes, skeletal muscle, and hematopoietic cells for the induction of cellular and humoral immune responses by miRNA-mediated tissue-specific silencing of antigen expression. Using hepatitis B small surface antigen (HBsAg) as the vector-encoded transgene we show that adenovirus vector dissemination from an intramuscular (i.m.) injection site into the liver followed by HBsAg expression in hepatocytes can limit early priming of CD8 T cells and the generation of anti-HBsAg antibody responses. However, hepatocyte-specific miRNA122a-mediated silencing of HBsAg expression overcame these limitations. Early clonal expansion of K(b)/S(190-197)-specific CD8 T cells was significantly enhanced and improved polyfunctionality of CD8 T cells was found. Furthermore, miRNA122a-mediated antigen silencing induced significantly higher anti-HBsAg antibody titers allowing an up to 100-fold vector dose reduction. These results indicate that miRNA-mediated regulation of antigen expression in the context of adenovirus vectors can significantly improve transgene product-directed immune responses. This finding could be of interest for future adenovirus vaccine vector development.

Liver-restricted expression of the canine factor VIII gene facilitates prevention of inhibitor formation in factor VIII-deficient mice

BACKGROUND

Gene therapy for hemophilia A with adeno-associated virus (AAV) vectors involves difficulties in the efficient expression of factor VIII (FVIII) and in antibody formation against transgene-derived FVIII.

METHODS

AAV8 vectors carrying the canine B domain deleted FVIII (cFVIII) gene under the control of the ubiquitous beta-actin promoter, the liver-specific human alpha1 anti-trypsin promoter (HAAT) and the liver-specific hepatic control region (HCR) enhancer/human alpha1 anti-trypsin promoter complex (HCRHAAT) were used for the expression of cFVIII in FVIII deficient (fviii(-/-)) mice.

RESULTS

Addition of the hepatic control region enhancer element to the HAAT promoter successfully augmented HAAT promoter activity without loss of liver-specificity in vivo. Using this enhancer/promoter complex, a high cFVIII transgene expression was achieved, resulting in increased blood cFVIII activities to more than 100% of the normal canine FVIII levels in fviii(-/-) mice at a 1 : 10 lower dose of the AAV8 vector carrying the cFVIII gene driven by the HAAT promoter. Under short-term immunosuppression, neutralizing antibodies against cFVIII developed in only one out of six mice when the HAAT promoter was used for cFVIII expression, whereas all the mice developed neutralizing antibodies against cFVIII when the beta-actin promoter was used for cFVIII expression. No neutralizing antibodies against cFVIII developed in fviii(-/-) mice that received the AAV8 vector carrying the cFVIII gene driven by the HCRHAAT enhancer/promoter complex without immunosuppression.

CONCLUSIONS

These data suggest that AAV8 vector-mediated liver-restricted cFVIII gene expression is sufficient for immune hypo-responsiveness to transgene-derived cFVIII in fviii(-/-) mice.

Effect of tissue-specific promoters and microRNA recognition elements on stability of transgene expression after hydrodynamic naked plasmid DNA delivery

Intravenous hydrodynamic injections into the liver and skeletal muscle have increased the efficacy of naked DNA delivery to a level that makes therapeutically relevant gene transfer attainable. Although there are no concerns about the immunogenicity of the delivered DNA itself, transgene products that are foreign to the host can trigger an immune response and hamper the therapeutic effect. Our goal was to determine whether and to what extent some known preventive measures are applicable to these delivery methods in order to achieve longterm expression of foreign proteins in immunocompetent mice. We designed plasmid DNA vectors that expressed a marker gene under the control of either a ubiquitous or a tissue-specific promoter. We also included microRNA (miR) target sites in the transcripts in order to silence expression in antigen-presenting cells (APCs). The constructs were delivered either into muscle or liver, using outbred ICR and inbred C57BL=6 mice. The data suggest that firefly luciferase, a potent immunogen, triggered a uniform immune response only in outbred ICR mice, and only when expressed from a ubiquitous promoter. This response could not be prevented by including APC-specific miR target sites in the transcript. In contrast, the probability of immune rejection in ICR mice could be significantly diminished by using tissue-specific promoters, and under these circumstances, the silencing of transgene expression in APCs did confer some benefits. After a single hydrodynamic injection, inbred mice did not reject luciferase under any of the tested conditions for at least 8 weeks. To test whether they became tolerized, they were challenged with a second boost of a cytomegalovirus promoter-driven luciferase construct. This triggered a strong immune response, suggesting that luciferase-reactive cells from the animals' T and B cell repertoire had not been eliminated. This secondary reaction could not be prevented by silencing expression in APCs. In conclusion, for the clinical application of hydrodynamic naked DNA delivery the use of tissue-specific promoters in combination with silencing expression in APCs will increase the probability of long-term expression, but the most desirable outcome, the establishment of transgene tolerance, appears unlikely to be achieved by any of these measures.

Fracture healing and bone repair: an update

Bone healing represents a physiological process of repair and restoration of function. Recent advances in a variety of medical disciplines have enabled scientists and clinicians to characterise this phenomenon at the molecular level. A number of molecular mediators and cells interact utilising different pathways. Despite the involvement of many local and systemic factors failure of the naturally occurring mechanisms can occur leading to either delayed union or non-union. This review article is focused on the recent understanding of the mechanisms governing the bone repair process.

Polymeric Materials for Gene Delivery and DNA Vaccination

Gene delivery holds great potential for the treatment of many different diseases. Vaccination with DNA holds particular promise, and may provide a solution to many technical challenges that hinder traditional vaccine systems including rapid development and production and induction of robust cell-mediated immune responses. However, few candidate DNA vaccines have progressed past preclinical development and none have been approved for human use. This Review focuses on the recent progress and challenges facing materials design for nonviral DNA vaccine drug delivery systems. In particular, we highlight work on new polymeric materials and their effects on protective immune activation, gene delivery, and current efforts to optimize polymeric delivery systems for DNA vaccination.

Gene therapy with an improved doxycycline-regulated plasmid encoding a tumour necrosis factor-alpha inhibitor in experimental arthritis

Inhibition of tumour necrosis factor (TNF)-alpha with biological molecules has proven an effective treatment for rheumatoid arthritis, achieving a 20% improvement in American College of Rheumatology score in up to 65% of patients. The main drawback to these and many other biological treatments has been their expense, which has precluded their widespread application. Biological molecules could alternatively be delivered by gene therapy as the encoding DNA. We have developed novel plasmid vectors termed pGTLMIK and pGTTMIK, from which luciferase and a dimeric TNF receptor II (dTNFR) are respectively expressed in a doxycycline (Dox)-regulated manner. Regulated expression of luciferase from the self-contained plasmid pGTLMIK was examined in vitro in a variety of cell lines and in vivo following intramuscular delivery with electroporation in DBA/1 mice. Dox-regulated expression of luciferase from pGTLMIK of approximately 1,000-fold was demonstrated in vitro, and efficient regulation was observed in vivo. The vector pGTTMIK encoding dTNFR was delivered by the same route with and without administration of Dox to mice with collagen-induced arthritis. When pGTTMIK was delivered after the onset of arthritis, progression of the disease in terms of both paw thickness and clinical score was inhibited when Dox was also administered. Vectors with similar regulation characteristics may be suitable for clinical application.

Noninvasive evaluation of liver repopulation by transplanted hepatocytes using 31P MRS imaging in mice

Hepatocyte transplantation (HT) is being explored as a substitute for liver transplantation for the treatment of liver diseases. For the clinical application of HT, a preparative regimen that allows preferential proliferation of transplanted cells in the host liver and a noninvasive method to monitor donor cell engraftment, proliferation, and immune rejection would be useful. We describe an imaging method that employs the creatine kinase (CK) gene as a marker of donor hepatocytes. Creatine kinase is unique among marker genes, because it is normally expressed in brain and muscle tissues and is therefore not immunogenic. Preferential proliferation of transplanted CK-expressing hepatocytes was induced by preparative hepatic irradiation and expression of hepatocyte growth factor using a recombinant adenoviral vector. CK is normally not expressed in mouse liver and its expression by the donor cells led to the production of phosphocreatine in the host liver, permitting (31)P magnetic resonance spectroscopic imaging of liver repopulation by engrafted hepatocytes. In conclusion, this study combined a noninvasive imaging technique to assess donor hepatocyte proliferation with a preparative regimen of partial liver irradiation that allowed regional repopulation of the host liver. Our results provide groundwork for future development of clinical protocols for HT.

Comparison of promoter region constructs for in vivo intramuscular expression

BACKGROUND

High transgene expression is generally expected after gene transfer. However, different level, kinetics and localization of expression might be needed for relevant therapeutic applications. Former studies have compared various promoter regions driving gene expression leading to conflicting results. In the present work, two promoter families have been compared using the efficient in vivo intramuscular electrotransfer technique.

METHODS

Three promoter regions were constructed by associating the strong ubiquitous cytomegalovirus (CMV) enhancer-promoter to its homologous intron A or to a heterologous intron, or to a hybrid intron. Promoter regions derived from the muscle creatine kinase (MCK) promoter were also studied. The expression of the same transgene (SeAP or neurotrophin-3) under control of these different promoters was compared after plasmid electrotransfer in mouse tibialis-cranialis skeletal muscle.

RESULTS

Heterologous intron association to the CMV promoter did not modify gene expression kinetics nor increase gene expression level. Usefulness of intron A or hybrid intron association to the CMV promoter depended on the gene. The various MCK promoters drove efficient gene expression but lower than that obtained with the CMV promoter. Furthermore, peak value was reached earlier with MCK promoter regions (14 days).

CONCLUSION

For applications of gene transfer restricted to skeletal muscle, the MCK promoter or a MCK promoter variant would be a promising alternative to the CMV promoter. Indeed, it has been demonstrated that the use of MCK promoter limits humoral and cell-mediated immune responses. Furthermore, the MCK promoter decreases the initial expression peak that may be detrimental, drives a sustained gene expression, and improves gene transfer safety.

In Vivo Liver Electroporation: Optimization and Demonstration of Therapeutic Efficacy

Adverse effects (death and leukemogenesis) from viral vector-mediated gene therapy have renewed interest in plasmids as safer, more scalable, simple, and cost-effective vectors. Electroporation and hydrodynamic delivery are two techniques that improve the efficiency of plasmid-mediated gene transfer. The liver is a good tissue platform for targeted transfer of therapeutically relevant genes for correction of metabolic disorders, for example, hemophilia A. However, in vivo electroporation of liver has not yet been shown to achieve therapeutic efficacy of systemically active, secreted transgenic proteins. We have investigated the effect of field strength, pulse duration, pulse number, electrical waveforms, electrode contact area, plasmid administration routes, and injection technique on the efficiency of in vivo electrotransfer of naked plasmid to liver. Plasmid injection into a systemic vein was superior to intrahepatic injection. Unlike in vivo muscle electroporation, high-voltage pulses and microsecond pulses offered no advantage. Optimal electroporation conditions were 8-10 uni- or bipolar pulses of 20 msec, each at 250 V/cm. Using a nonhydrodynamic technique that greatly enhanced electrotransfer efficiency with minimal tissue injury, we demonstrate for the first time that liverdirected in vivo electroporation of factor VIII cDNA achieved significant phenotypic correction in hemophilic mice.

Phenotype correction of hemophilia A mice with adeno-associated virus vectors carrying the B domain-deleted canine factor VIII gene

Adeno-associated virus (AAV) vectors carrying the B domain-deleted canine FVIII (BDD cFVIII) gene utilizing the beta-actin minimum promoter (167b) pseudotyped with serotype 1 (AAV1-beta-actin-cFVIII) and serotype 8 (AAV8-beta-actin-cFVIII) were developed to express cFVIII in hemophilia A mice. FVIII clotting activities measured by the APTT method increased in hemophilia A mice with intramuscular injection of AAV1-beta-actin-cFVIII in a dose-dependent manner. Therapeutic FVIII levels (2.9+/-1.0%) in hemophilia A mice with the AAV1-beta-actin-cFVIII dose of 1 x 10(12) gc/body were achieved, suggesting partial correction of the phenotype with AAV1-beta-actin-cFVIII vectors. FVIII clotting activity levels in hemophilia A mice with intravenous injection of AAV8-beta-actin-cFVIII also were increased dose-dependently, achieving therapeutic FVIII levels (5-90%) in hemophilia A mice with the AAV8-beta-actin-cFVIII doses of 1-3 x 10(11) gc/body and supernormal FVIII levels (180-670%) in hemophilia A mice with the AAV8-beta-actin-cFVIII dose of 1 x 10(12) gc/body. Transduction of the liver with AAV8-beta-actin-cFVIII is superior to transduction of skeletal muscles with AAV1cFVIII regarding the FVIII production and antibody formation. These data suggested that both AAV1 and AAV8 vectors carrying the FVIII gene utilizing a minimum promoter have a potential for hemophilia A gene therapy.

Kinetic of transgene expression after electrotransfer into skeletal muscle: Importance of promoter origin/strength

We determined over a 3-week period some of the factors that may influence the kinetic of gene expression following in vivo gene electrotransfer. Histochemical analysis of beta-galactosidase and biochemical analysis of luciferase expressions were used to determine reporter gene activity in the Tibialis anterior muscles of young Sprague-Dawley male rats. Transfection efficiency peaked 5 days after gene electrotransfer and then exponentially decreased to reach non-detectable levels at day 28. Reduction of muscle damage by decreasing the amount of DNA injected or the cumulated pulse duration did not improve the kinetic of gene expression. Electrotransfer of luciferase expression plasmids driven either by viral or mammalian promoters rather show that most of the decrease in transgene expression was related to promoter origin/strength. By regulating the amount of transgene expression, the promoter origin/strength could modulate the immune response triggered against the foreign protein and ultimately the kinetic of transgene expression.