Successful histocompatible myoblast transplantation in dystrophin-deficient mdx mouse despite the production of antibodies against dystrophin

Myoblast transplantation in non-dystrophic dog

Dog myoblasts obtained from muscle biopsies were infected in vitro with a defective retroviral vector containing a cytoplasmic beta-galactosidase (beta-Gal) gene. These myoblasts were initially transplanted in the irradiated muscles of SCID mice and beta-Gal positive muscle fibers were observed. beta-Gal myoblasts were also transplanted back either in the donor dogs (autotransplantation model) or in unrelated recipient dogs (allotransplantation model). Following these myoblast injections, a rapid inflammatory reaction developed within the muscle as indicated by an expression of P-selectin and of pro-inflammatory cytokine mRNAs (interleukin 6 (IL-6) and transforming growth factor beta (TGF-beta), and by a neutrophil infiltration. Following either auto- or allotransplantation in inadequately or non-immunosuppressed dogs, a specific immune reaction also developed within 2 weeks as indicated by the infiltration of CD4+ and of CD8+ lymphocytes, the increased expression of IL-10 and granzyme B mRNAs and the presence of antibodies reacting with the injected cells. Some dogs were immunosuppressed with several combinations of FK506, cyclosporine (CsA) and RS-61443. In dogs immunosuppressed with CsA combined with RS-61443, only a few myoblasts and myotubes expressing beta-Gal were observed 1-2 weeks after the transplantation, but no muscle fibers expressing beta-Gal were observed after 4 weeks, and antibodies against the injected cells were formed. In dogs immunosuppressed with FK506 alone, although no antibodies against the injected cells were produced, there were no small cells and no muscle fibers expressing beta-Gal 1 month after the transplantation. However, FK506 triggered diarrhea and vomiting in dogs. When the dogs were immunosuppressed with FK506 combined with CsA and RS-61443, muscle fibers expressing beta-Gal were present 4 weeks after the transplantation and no antibodies reacting with donor myoblasts were detected. These results indicate that the combination of three immunosuppressive agents (i.e., FK506, CsA and RS-61443) is effective in controlling the specific immune reactions following myoblast transplantation in dogs and they underline that the outcome of myoblast transplantation is dependent in part on an adequate immunosuppression. These results obtained here in normal dogs may justify myoblast transplantation in dystrophic dogs despite the side effects of FK506.

Anti-inflammatory effect of transforming growth factor-beta1 in myoblast transplantation

BACKGROUND

The inflammatory reaction that occurs during the 5 days after transplantation led at 3 days to the death of 70% of injected myoblasts. Use of anti-inflammatory agents appeared to be a possible way to increase myoblast survival. The application of gene transfer techniques to cell transplantation offers the potential for the prevention of inflammatory reaction.

METHODS

In this study, transforming growth factor-beta1 (TGF-beta1) gene was introduced in myoblasts with a retroviral vector to permit the secretion of this anti-inflammatory cytokine. Survival of (1) infected myoblasts expressing TGF-beta1 or (2) normal myoblasts transplanted with genetically modified cloned myoblasts was compared with survival of normal myoblasts.

RESULTS

Expression of TGF-beta1 by myoblasts or by cotransplanted cells decreased myoblast mortality after 3 days by roughly 20% (66.0+/-3.0% in control vs. 46.3+/-4.2% and 46.2+/-5.9%). The increase of myoblast survival by TGF-beta1 expression was correlated with a lower polymorphonuclear cell and macrophage infiltration in muscles compared with control. In addition, cytotoxicity of neutrophils against myoblasts was assayed in vitro. The oxidation of myoblasts by activated neutrophils was decreased after infection of the myoblasts with the TGF-beta1 retroviral vector.

CONCLUSIONS

These data demonstrate that the insertion of TGF-beta1 decreases inflammatory reaction observed after myoblast transplantation and thus prolongs their survival.

High-level dystrophin expression after adenovirus-mediated dystrophin minigene transfer to skeletal muscle of dystrophic dogs: prolongation of expression with immunosuppression

Replication-deficient adenovirus vectors (AdV) have been successfully used to transfer a truncated human dystrophin cDNA to skeletal muscle of dystrophin-deficient mdx mice. A dystrophin-deficient golden retriever dog model (GRMD) has been identified, which, unlike the mouse model, leads to a clinicopathological phenotype similar to that of Duchenne muscular dystrophy (DMD). We show for the first time that high-level dystrophin expression in skeletal muscle of GRMD dogs can be achieved by AdV-mediated gene transfer. However, a humoral and cellular immune response of the host against antigens of viral and transgene origin (similar to that occurring in mdx mice after AdV-mediated dystrophin gene transfer) leads to a decline of dystrophin expression over a 2-month period. Immunosuppression by cyclosporin significantly prolonged transgene expression. The GRMD model may help to solve the open questions pertaining to dystrophin gene transfer such as systemic delivery and improvement of muscle function before human trials for gene replacement therapy in DMD may be considered.

Transplantation of myoblasts from a transgenic mouse overexpressing dystrophin prduced only a relatively small increase of dystrophin-positive membrane

Myoblast cultures from normal and Tg-MDA (transgenic mouse overexpressing dystrophin 50-fold) mice were transplanted into dystrophin-deficient mdx mouse muscles. Four weeks after transplantation, dystrophin-positive fibers were observed four times more frequently in cross sections of muscles injected with Tg-MDA. Myoblasts from Tg-MDA mice also expressing the beta-gal transgene (Tg-MDA/beta-gal) and myoblasts from beta-gal transgenic mice containing one normal dystrophin gene (normal/beta-gal) were also transplanted into mdx mouse muscles. Four weeks after transplantation, the fiber length positive for dystrophin (nuclear domain) was shorter (439 +/- 326 microm) than the beta-gal nuclear domain (1466 +/- 713 microm) of the same fiber when normal/beta-gal myoblasts were transplanted, but increased (1302 +/- 487 microm) when Tg-MDA/beta-gal myoblasts were used. These experiments show that despite the presence in Tg-MDA myoblasts of constructions which lead in vivo in transgenic mice to an overexpression of dystrophin 50-fold, the membrane area over which dystrophin was expressed was increased only threefold. This observation is also expected for vector-mediated gene therapy.

Muscle fibers of mdx mice are more vulnerable to exercise than those of normal mice

It is well known that eccentric exercise induces muscle damage by disrupting the sarcolemma. The aim of this study was to analyze the effects of downhill running on several locomotor and respiratory muscles of normal and mdx mice. Degenerating muscle fibers in the skeletal muscles of mice were visualized by in vivo staining with Evans blue. This dye injected intravenously stained only degenerating muscle fibers which were visible as blue fibers macroscopically and could also be seen as red fluorescent fibers microscopically. Evans blue-stained muscle fibers were either hypercontracted or degenerating. Without exercise no muscle fibers were labeled with Evans blue in the normal mice, indicating that their membranes were intact. However, even without exercise, the percentage of fibers permeable to Evans blue varied from 2% to 15% in various muscles of the mdx mice. Our downhill running protocol (i.e., running down a treadmill with a 15 degrees slope at 10 m/min) produced in normal mice only a slight (0-3%) increase in percentage of muscle fibers which were permeable to the dye compared with up to 31% in some mdx muscles.

Chemotaxis of skeletal muscle satellite cells

Migration of myogenic cells occurs extensively during both embryogenesis and regeneration of skeletal muscle and is important in myoblast gene therapy, but little is known about factors that promote chemotaxis of these cells. We have used satellite cells from adult rats purified by Percoll density gradient centrifugation to test growth factors and wound fluids for chemotactic activity in blind-well Boyden chambers. Of a variety of growth factors tested only hepatocyte growth factor (HGF) and transforming growth factor-beta (TGF-beta) exhibited significant chemotactic activity. The dose-response curves for both of these factors was bell-shaped with maximum activity in the 1-10 ng/ml range. Checkerboard analysis of TGF-beta showed that chemotaxis occurred only in response to a positive concentration gradient. An extract of rat platelets also exhibited chemotactic activity for satellite cells. Half-maximal activity of this material was about 3 micrograms/ml, and there was no evidence of inhibition of migration at high concentrations. Checkerboard analysis of platelet extract exhibited evidence of both chemotaxis and chemokinesis, or increase in random motility of cells. Inhibition experiments showed that most, but not all, of the chemotactic activity in platelet extract could be blocked with a neutralizing antibody to TGF-beta. A saline extract of crushed muscle was found to contain both mitogenic and motogenic factors for satellite cells. The two activities were present in different fractions after heparin affinity chromatography. We propose that the proliferation and migration of satellite cells during regeneration is regulated by overlapping gradients of several effector molecules released at the site of muscle injury. These molecules may also be useful for enhancing the dispersion of injected myoblasts during gene therapy.

Role of non-major histocompatibility complex antigens in the rejection of transplanted myoblasts

Myoblasts obtained from donors histoincompatible for several non-major histocompatibility complex antigens (i.e., including minor histocompatibility antigens) and from syngeneic donors were transplanted without any immunosuppression into the muscles of male dystrophic C57BL/10J mdx/mdx mice. Myoblasts from syngeneic mice resulted in the formation of a high percentage of dystrophin-positive fibers 16 weeks after the transplantation. There was no evidence of a cellular immune reaction against the donor myoblasts, i.e., no infiltration by CD4 or CD8 lymphocytes and no increased expression of granzyme B and interferon-gamma mRNAs. Transplantation of myoblasts obtained from donors histoincompatible only for non- major histocompatibility complex antigens produced a transient increase of dystrophin-positive fibers at 4 weeks after transplantation for some donor strains but not for others. For donor strains that did produce an increase at 4 weeks, the number of dystrophin-positive fibers was reduced 16 weeks after the transplantation. There was evidence of a cellular immune reaction-infiltration by CD4 and by CD8 lymphocytes and increased expression of granzyme B and interferon-gamma mRNAs. Transplantation of myoblasts obtained from male C57BL/10J +/+ mice into female C57BL/10J mdx/mdx mice also led to the presence of only a few dystrophin-positive fibers with the same signs of cellular immune reaction. In this later case, the cellular immune response was attributed to the H-Y minor antigens. Finally, antibodies against fetal calf serum were detected after both syngeneic and nonsyngeneic transplantations, indicating that the culture medium may also be a source of antigens. In mice, the presence of these antibodies against culture medium did not reduce the success of a first syngeneic transplantation.

LacZ gene transfer to skeletal muscle using a replication-defective herpes simplex virus type 1 mutant vector

Herpes simplex virus type 1 (HSV-1) represents a promising new viral vector capable of efficient transduction of myofibers in vivo. Here we report on the use of a replication-defective HSV-1 mutant vector (DZ) deleted for the essential immediate early (IE) gene ICP4 for studies of reporter gene transfer and expression following direct inoculation of mouse skeletal muscle. The recombinant vector was engineered to contain the Escherichia coli lacZ gene under transcriptional control of the strong human cytomegalovirus (HCMV) IE promoter. The effect of vector cytotoxicity on the durability of transgene expression following infection of muscle cells in culture and myofibers in vivo revealed that this first-generation HSV vector was cytopathic, limiting the persistence of vector-transduced cells. UV irradiation of vector preparations reduced viral cytotoxicity for myoblasts in culture without reducing significantly beta-galactosidase production. Moreover, muscle cell viability and the durability of transgene expression was enhanced by several days following UV inactivated-vector infection in vivo. Nevertheless, the viral DNA was subsequently lost from vector-inoculated muscle tissue within 2 weeks. This observation indicated that vector toxicity alone did not account for the lack of persistent transgene expression. Longer-term vector transduction and transgene expression was observed, however, following inoculation of immunodeficient SCID mice, indicating that host immunocompetence played an important role in determining the duration of transgene expression in animals. To support this hypothesis, cells expressing CD4 and CD8 antigens have been found in the HSV-1 injected muscle of immunocompetent mice. These data demonstrated that both vector toxicity and vector-induced immunity are significant obstacles to the use of HSV-1 vectors for muscle gene transfer. These impediments must be overcome to further develop HSV vectors for muscle gene therapy applications.

[Molecular pathogenesis of muscular diseases]

Recent advances in the field of molecular myology have provided significant insight into the pathological mechanisms underlying a variety of neuromuscular disorders. Genetic abnormalities can now be linked to primary and secondary pathophysiological changes in muscle fibres which compromise structural, metabolic, regulatory or contractile mechanisms. Ion channel myopathies such as paramyotonia congenita, hyper- and hypokalaemic periodic paralysis, myotonia congenita, episodic ataxia and malignant hyperthermia were established as linked to mutations in genes encoding the sodium channel, dihydropyridine receptor, chloride channel, potassium channel and the ryanodine receptor calcium release channel, respectively. Metabolic disorders affecting skeletal muscle were found to be due to deficiencies in a variety of enzymes. Identification of defects in components belonging to the gigantic dystrophin-glycoprotein complex led to the discovery of the molecular pathogenesis of Duchenne muscular dystrophy and related disorders. Based on these molecular findings, it is now feasible to design and evaluate new techniques such as gene and myoblast transfer therapy in order to replace defective components in diseased muscle fibres.

Prevention of immune reactions triggered by first-generation adenoviral vectors by monoclonal antibodies and CTLA4Ig

The therapeutic potential of adenovirus-mediated gene transfer using first-generation vectors is severely limited by the fact that only transient expression is achievable in immunocompetent animals. The loss in transgene expression can be attributed at least in part to the appearance of detrimental immune responses directed toward vector and/or transgene-encoded determinants. FK506 and cyclosporin A both reduced these immune responses. These immunosuppressants, however, may induce many severe side effects during prolonged use. An alternative strategy has been developed to overcome these problems following in vivo transfection of muscles of adult immunocompetent mice with a delta E1/E3a adenoviral vector encoding a beta-galactosidase (beta-Gal) expression cassette. YTS 177 (an anti-CD4 monoclonal antibody) as well as CTLA4Ig, a recombinant protein, partially controlled the immune responses. They were indeed able to reduce the muscle infiltration by CD4+ and CD8+ cells but they failed to repress the humoral response. Co-administration of YTS 191 (an anti-CD4), YTS 169 (an anti-CD8), and TIB 213 (an anti-CD11a) was, however, very efficient in blocking both cellular and humoral immune reactions. This combination of monoclonal antibodies allowed strong and stable transgene expression over 1 month. These data underline the potential of monoclonal antibodies as immunosuppressive adjunct treatment for adenovirus-mediated gene transfer.

Partial laminin alpha2 chain restoration in alpha2 chain-deficient dy/dy mouse by primary muscle cell culture transplantation

Laminin-2 is a component of skeletal and cardiac basal lamina expressed in normal mouse and human. Laminin alpha2 chain (LAMA2), however, is absent from muscles of some congenital muscular dystrophy patients and the dystrophia muscularis (dy/dy) mouse model. LAMA2 restoration was investigated following cell transplantation in vivo in dy/dy mouse. Allogeneic primary muscle cell cultures expressing the beta-galactosidase transgene under control of a muscular promoter, or histocompatible primary muscle cell cultures, were transplanted into dy/dy mouse muscles. FK506 immunosuppression was used in noncompatible models. All transplanted animals expressed LAMA2 in these immunologically-controlled models, and the degrees of LAMA2 restoration were shown to depend on the age of the animal at transplantation, on muscle pretreatment, and on duration time after transplantation in some cases. LAMA2 did not always colocalize with new or hybrid muscle fibers formed by the fusion of donor myoblasts. LAMA2 deposition around muscle fibers was often segmental and seemed to radiate from the center to the periphery of the injection site. Allogeneic conditionally immortalized pure myogenic cells expressing the beta-galactosidase transgene were characterized in vitro and in vivo. When injected into FK506-immunosuppressed dy/dy mice, these cells formed new or hybrid muscle fibers but essentially did not express LAMA2 in vivo. These data show that partial LAMA2 restoration is achieved in LAMA2-deficient dy/dy mouse by primary muscle cell culture transplantation. However, not all myoblasts, or myoblasts alone, or the muscle fibers they form are capable of LAMA2 secretion and deposition in vivo.