Coenen, Michael J.

When long bones fracture, healing occurs spontaneously in about 90% of cases, while the remaining 10% result in non-union, presenting significant clinical challenges. The standard treatment for non-unions is autologous bone grafting, but this approach has limitations, including high complication rates, donor site morbidity, and limited graft availability. An alternative strategy involves using growth factors to promote bone regeneration, with recombinant bone morphogenetic protein-2 (rBMP-2) being the most common. Although effective, rBMP-2 requires supra-physiological doses that cause inflammation, poor bone quality, and severe side effects. Our previous work suggests that genetic delivery of BMP-2 may offer more controlled healing. We aim to develop a more effective therapy for non-unions using adeno-associated viral vectors. By lyophilizing the vector onto a scaffold, we also aim to increase treatment potency, reduce leakage, and improve transduction using cryoprotectant buffers.AAV6-GFP-Luciferase was used to compare the activity of AAV6 stored at −80°C versus lyophilized in cryoprotectant buffer. A rat critical-sized defect model was employed, as described in [1]. For standard storage, AAV was added to the collagen sponge before implantation into a 5mm defect. For lyophilization, AAV was mixed with cryoprotectant, loaded onto the sponge, and lyophilized. Rats were imaged at 7- and 10-days using IVIS. To assess therapeutic relevance, the experiment was repeated with AAV6-BMP2-IL1Ra, implanted into 5mm femoral defects on collagen sponges, with healing monitored by X-ray every 4 weeks (continuing through 12-weeks post-operation).The reporter and therapeutic vectors showed improved transduction efficiency with lyophilization. The reporter vector exhibited higher transgene expression at days 7 and 10. This boost in expression either remained significant through 4 weeks or continued to show better signal at that time, correlating with improved healing seen in the X-rays (Fig. 2).Preliminary data suggest that lyophilization could reduce the therapeutic dose of AAV needed for treating osseous nonunion with a bicistronic vector. Lyophilization offers various benefits: enhanced transduction efficiency, improved stability of the gene product at logistically feasible conditions, and reduced off-target effects due to less AAV leakage from the implantation site. While in vivo experiments with AAV6-BMP2-IL1Ra are ongoing, these findings warrant further investigation into lyophilized AAV therapies for this application.For any figures or tables, please contact the authors directly.

Osteoarthritis (OA) is a major global health problem with no disease-modifying therapies. Interleukin-1 (IL-1) is a critical cytokine associated with the pathophysiology of OA and can be inhibited by IL-1 receptor antagonist (IL-1Ra). Here, we tested the delivery of a gene therapeutic encoding the human IL-1Ra to the knee in a phase 1, open-label clinical trial that enrolled nine patients with radiographic knee OA. The IL-1Ra gene was delivered by a self-complementary (sc)–recombinant adeno-associated virus (rAAV) serotype 2.5 (sc-rAAV2.5IL-1Ra) by intra-articular injection into an index knee at one of three doses: low [1 × 10 11 viral genomes (vg)], mid (1 × 10 12 vg), or high (1 × 10 13 vg). The primary outcome was safety. There were no serious adverse events (AEs) related to sc-rAAV2.5IL-1Ra. Two AEs occurred that were possibly related to the vector. Both were effusions with increased pain and resolved with conservative treatment. sc-rAAV2.5IL-1Ra did not cause changes in vital signs, physical findings, or clinical laboratory measures. Less than 1% of the injected dose of sc-rAAV2.5IL-1Ra vg was detected in circulation after 1 day and was cleared within a week. Titers of neutralizing antibodies to AAV2.5 rose in serum and synovial fluid. In all cases, IL-1Ra concentration increased in the synovial fluid, and IL-1Ra concentrations remained elevated after 1 year. Baseline pain and function scores improved during the study. Therefore, we found that intra-articular gene therapy with sc-rAAV2.5IL-1Ra was safe. The sustained increase in local IL-1Ra in human knee joints supports the further clinical examination of this therapy to provide therapeutic benefit in OA.

AbstractThis study defined and compared the course of native, impaired and growth factor‐stimulated bone regeneration in a rat femoral defect model. A mid‐diaphyseal defect with rigid internal fixation was surgically created in the right femur of male Fischer rats and serially analyzed over 36 weeks. Native bone regeneration was modeled using a sub‐critical, 1 mm size defect, which healed uneventfully. Critical size defects of 5 mm were used to analyze impaired bone regeneration. In a third group, the 5 mm defects were filled with 11 µg of recombinant human bone morphogenetic protein 2 (rhBMP2) impregnated onto an absorbable collagen sponge, modeling its clinical use. Native bone regeneration was characterized by endochondral ossification with progressive remodeling to ultimately resemble intact femora. An endochondral response was also observed under conditions of impaired bone regeneration, but by week 8 medullary capping occurred with fibrofatty consolidation of the tissue within the defect, resembling an atrophic non‐union. rhBMP2 treatment was associated with prolonged inflammatory cytokine expression and rapid intramembranous bone formation occurring with reduced expression of cartilage‐associated collagens. Between weeks 4 and 36, rhBMP2‐treated bones demonstrated decreased trabecular number and increased trabecular separation, which resulted in inferior mechanical properties compared with bones that healed naturally. Clinical Significance: Recombinant human bone morphogenetic protein 2 (rhBMP2) is used clinically to promote healing of long bones. Our data suggest that it drives intramembraneous ossification producing an inferior regenerate that deteriorates with time. Clinical outcomes would be improved by technologies favoring endochondral regenerative ossification.

The use of multiphasic scaffolds to treat injured tendon-to-bone entheses has shown promising results in vitro. Here, we used two versions of a biphasic silk fibroin scaffold to treat an enthesis defect created in a rat patellar model in vivo. One version presented a mixed transition between the bony and the tendon end of the construct (S-MT) while this transition was abrupt in the second version (S-AT). At 12 weeks after surgery, the S-MT scaffold promoted better healing of the injured enthesis, with minimal undesired ossification of the insertion area. The expression of tenogenic and chondrogenic markers was sustained for longer in the S-MT-treated group and the tangent modulus of the S-MT-treated samples was similar to the native tissue at 12 weeks while that of the S-AT-treated enthesis was lower. Our study highlights the important role of the transition zone of multiphasic scaffolds in the treatment of complex interphase tissues such as the tendon-to-bone enthesis.

Large segmental osseous defects heal poorly. Recombinant, human bone morphogenetic protein-2 (rhBMP-2) is used clinically to promote bone healing, but it is applied at very high doses that cause adverse side effects and raise costs while providing only incremental benefit. We describe a previously unexplored, alternative approach to bone regeneration using chemically modified messenger RNA (cmRNA). An optimized cmRNA encoding BMP-2 was delivered to critical-sized femoral osteotomies in rats. The cmRNA remained orthotopically localized and generated BMP locally for several days. Defects healed at doses ≥25 μg of BMP-2 cmRNA. By 4 weeks, all animals treated with 50 μg of BMP-2 cmRNA had bridged bone defects without forming the massive callus seen with rhBMP-2. Moreover, such defects recovered normal mechanical strength quicker and initiated bone remodeling faster. cmRNA regenerated bone via endochondral ossification, whereas rhBMP-2 drove intramembranous osteogenesis; cmRNA provides an innovative, safe, and highly translatable technology for bone healing.

Collagen has a major role in the structural organization of tendons. Picrosirius red (PSR) staining viewed under polarized light microscopy is the standard method to evaluate the organization of collagen fibers in tissues. It is also used to distinguish between type I and type III collagen in tissue sections. However, accurate analysis and interpretation of PSR images are challenging because of technical factors and historical misconceptions. The aim of this study was to clarify whether collagen types I and III can be distinguished by PSR staining in rat Achilles tendons, using double immunohistochemistry as the positive control. Our findings showed that PSR staining viewed with polarized light microscopy was suitable for qualitative and quantitative assessment of total collagen but was not able to distinguish collagen types. We found it critical to use a polarizing microscope equipped with a rotating stage; tendon section orientation at 45° with respect to crossed polarizers was optimal for the qualitative and quantitative assessment of collagen organization. Immunohistochemistry was superior to PSR staining for detection of collagen type III. We also compared formalin and Bouin solution as fixatives. Both produced similar birefringence, but formalin-fixed tendons provided higher quality histological detail with both hematoxylin–eosin and immunostaining: