Despite the clinical relevance of back pain and intervertebral disc herniation, the lack of reliable models has strained their molecular understanding. We characterized the lumbar spinal phenotype of C57BL/6 and SM/J mice during aging. Interestingly, old SM/J lumbar discs evidenced accelerated degeneration, associated with high rates of disc herniation. SM/J AF's and degenerative human's AF transcriptomic profiles showed altered immune cell, inflammation, and p53 pathways. Old SM/J mice presented increased neuronal markers in herniated discs, thicker subchondral bone, and higher sensitization to pain. Dorsal root ganglia transcriptomic studies and spinal cord analysis exhibited increased pain and neuroinflammatory markers associated with altered extracellular matrix regulation. Immune system single-cell and tissue level analysis showed distinctive T-cell and B-cell modulation and negative correlation between mechanical allodynia and INF-α, IL-1β, IL2, and IL4, respectively. This study underscores the multisystemic network behind back pain and highlights the role of genetic background and the immune system in disc herniation disease. Acknowledgments: This study is supported by grants from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) R01AR055655, R01AR064733, R01AR074813 to MVR

Bone regeneration is a complex but very well organized process in which the immune system has a decisive role. The adaptive immune system and its experience level (percentage of effector and memory T cells) has been proven to influence the healing cascade especially in the early healing phases. This opens the possibility of an early intervention to enhance bone healing during the primary clinical treatment. Patients stratified for possible delayed bone healing could benefit from immunomodulatory treatment approaches. In pre-clinical studies cells and signaling molecules have been identified that could represent promising candidates to help patients in need

An estimated 10% of patients have problems with fracture healing. Initial studies have revealed that it is likely that both the innate and specific immune systems play a role in fracture repair, but this has not been attributed to particular components, cells or their products. It is known that the functionality of the immune system is impaired with age and this may account for the higher rate of delayed union in elderly patients. We used a validated mouse model of a reproducible closed tibial fracture. In order to prevent any foreign body inflammatory/immune response no artificial internal fracture fixation was used and instead external support was provided using a Plaster of Paris cast. The role of the specific immune system was studied using an immunodeficient Balb/c SCID (Severe Combined Immuno Deficient) mutant mouse. The SCID mice were matched for age, sex (all males) and weight to the control, wild type Balb/c mice. Mechanical (4 point bending) and radiographic (Radiographs scanned and calculations of callus area, index and density made with image analysis software) measures were used to assess fracture repair at 21 days. Mechanical measurements revealed an enhancement of fracture healing in the SCID mouse strain compared to the control strain, with stress at yield and Young’s modulus higher in SCID mice than controls. (Stress at yield: 4.2 +/− 0.23MPa in Controls, 7.1 =/− 0.6MPa in SCIDs, P< 0.01; Young’ Modulus: 22.1 +/− 2.99MPa in Controls, 60+/− 9.9MPa in SCIDs P< 0.01). There were no significant differences seen in mechanical properties of unfractured bone between the two strains. Radiographic analysis revealed no significant differences in callus area or index (both measurements of callus size) but callus density was significantly higher (P< 0.01) in the SCID subjects compared to controls (2.6 +/− 0.06E5 Greyscale in SCIDs vs. 2.2 +/− 0.09E5 in controls). We conclude that an abnormality of the immune system due to either lack of the specific immune system (T and B cells) or an enhancement of the innate system results in increased mineralization, stiffness and strength of fracture healing, and that further investigation might result in novel therapies directed toward avoidance of non/delayed-union

There is evidence that fracture healing is impaired in patients with chronic immune disorders the reasons remaining unclear so far. To further elucidate the role of the immune system in bone healing, this study investigated the hypothesis that fracture healing would be considerably disturbed in a mouse model with severe defects of the innate as well as adaptive immune system. Immune deficient Nod-scidIL2Rγ. null. and immune competent BALBcByJ mice were used (12 weeks, male, each n=24). The mice received a femur osteotomy stabilized by an external fixator and were sacrificed at d 21, 28, and 35. The calli were evaluated by three-point-bending testing, μCT and histomorphometry. The flexural rigidity of the callus did not significantly differ between both genotypes after 21 and 28 days but was significantly lower in Nod-scidIL2Rγ. null. mice after 35 days (31%). The maximum moment of inertia was significantly increased after 21 days (by 34%), and the callus cross section area after 21, 28 and 35 days in Nod-scidIL2Rγ. null. mice. BV/TV of the callus of Nod-scidIL2Rγ. null. mice was significantly decreased after 28 and 35 days (by 32% and 41%). The histological evaluation showed a significantly enhanced amount of cartilage in the fracture gap of Nod-scidIL2Rγ. null. mice. These data indicate an only moderate delay in fracture healing in Nod-scidIL2Rγ. null. mice suffering on severe defects in innate and adaptive immune response

Introduction: Metal on Metal articulations produce Cobalt Chromium nanoparticles (CoCrNP) which seems to affect the adaptive immune system, as evident from the perivascular infiltrate of lymphocytes & plasma cells found around some implants, and the reduced CD8+ count described with hip resurfacing. We therefore analyzed effects of CoCrNP on Dendritic Cells, T cells & B cells. Methods: CoCrNP were produced by repetitive short spark discharges between electrodes of prosthetic CoCr alloy. Electron micrography & BET both confirmed nanoparticle size. Dendritic Cells were cultured from mouse bone marrow and incubated with CoCrNP of varying concentrations, for 24hrs, or lipopolysaccharide as a positive control. Activation status was then characterized by CD40 expression on FACS analysis. Cells from mouse lymph nodes were incubated with CoCrNP in varying concentrations. At 48hrs, Propidium Iodide (PI) was added & % PI+ve determined on FACS analysis. Cells from mouse lymph nodes were cultured in medium without phenol red and incubated with ∝CD3, ∝CD3 + CoCrNP, ∝CD3 + ∝CD28 or ∝CD3 + ∝CD28 + CoCrNP. At 48hrs, Almar Blue was added & difference in light absorbance at 570nm & 600nm was then used to determine T cell proliferation at 72hrs. Cells from lymph nodes of an MD4 mouse (only able to mount a b cell response to Hen egg Lysozyme (HEL)) were incubated with CoCrNP, HEL (positive control) or CoCrNP + HEL. B cell regulation at 48hrs was characterized by CD40 and CD86 expression on FACS analysis. Results: CoCrNP did not significantly increase CD 40 expression on DCs or Cd 40/ Cd 86 expression on B cells. At subletal concentrations, CoCrNP inhibited ∝CD3 & ∝CD28 dependent T-cell proliferation. Discussion: CoCrNP reduces both signal 1 & signal 2 dependent T cell proliferation, which may explain the observed reduction in CD 8+ count with hip resurfacing

Harnessing the potential of mesenchymal stem cell (MSC) mediated endochondral ossification for the repair of large bone defects represents a promising avenue of investigation as an alternative option to autologous bone transplantation. To date, it has been shown that undifferentiated MSCs are somewhat immune-privileged. In order to induce bone formation from MSCs by endochondral ossification it is usually necessary to first differentiate these cells chondrogenically. However, the status of differentiated cells is less clear than that of undifferentiated MSCs. Furthermore, the fate of implanted bone forming constructs in an allogeneic setting is not known. The potential to use allogeneic MSCs for large bone defect repair would offer opportunities to researchers to develop new therapies using more potent MSC sources and in a more readily available manner with regard to the patient. I will present our research investigating the interactions between chondrogenically primed MSCs and immune cell subsets, namely T cells and dendritic cells. Furthermore, I will discuss the ability of human paediatric MSCs to form bone in the in vivo allogeneic setting.

Background: Increased use of metal on metal (MOM) hip replacements has stimulated interest in immunological effects of chronic CoCr elevation. Unlike metal-on-polyethelylene, MOM implants are associated with a perivascular infiltrate of lymphocytes & plasma cells. This may be the mode of failure of MOM implants. A reduction in CD8+ T lymphocyte counts associated with MOM implants has previously been described. CoCr therefore seems to affect the adaptive immune response even though it is not a proteinous antigen.

We therefore analyzed the effects of CoCr particles on T cells & B cells. We also analyzed it effects on dendritic cells, which are the key antigen presenting cells to T helper cells.

Methods: CoCr nano particles were produced by repetitive short spark discharges between electrodes of prosthetic CoCr alloy. Electron micrography & BET both confirmed nanoparticle size.

Dendritic cells (DCs) were harvested from mouse bone marrow & cultured in medium supplemented with GM-CSF for 6 days, generating DCs typically 80–90% CD11c+. These were incubated with CoCr in concentrations of 25, 10 & 2.5 μg/ml, for 24 hours, or lipopolysaccharide 1 μg/ml as a positive control. Following incubation, activation status of CD11c+ DCs was characterized by MHC Class II, CD40, CD80 & CD86 expression by FACS analysis.

T-Lymphocytes were harvested from mouse lymph nodes & cultured in medium without phenol red. These were incubated at 5 ×105 cells/well with either CoCr, conA (positive control) or CoCr + conA & repeated using 2.5 ×105 cells/well. Other positive controls (CD3 & CD 28) were studied in repeating the experiment. At 48 hours Almar Blue was added & further incubation for 24 hrs. Light absorbance at 570nm & 600nm was then used to determine T cell proliferation

B-Lymphocytes were harvested from the lymph nodes of mice which were only able to mount a B-cell reaction to Hen egg Lysozyme (HEL). These were incubated with medium with CoCr, HEL (positive control) or CoCr+ HEL. The concentration of the CoCr was varied between 25, 10 & 2.5 μg/ml. FACS analysis for markers of B cell regulation was performed after 48 hours incubation..

Results: CoCr did not significantly increase CD 40 expression on DCs, although such expression was increased significantly by lipopolysaccaride CoCr did not significantly up or down regulate B cells as compared to the effects of HEL. CoCr did inhibit proliferation of T-cells & this was more pronounced where the ratio of CoCr/cell density was higher.

Conclusion: Both dendritic & B cells are unaffected by CoCr in vitro. However, CoCr inhibited T cell proliferation. This demonstrates the observed reduction in CD + T cells are probably due to a direct effect of CoCr, & not mediated through another cell type. The perivascular response to MOM implants on the other hand probably requires cell interaction in an in vivo environment.

A growing number of recent investigations on the human genome, gut microbiome, and proteomics suggests that the loss of mucosal barrier function, particularly in the gastrointestinal tract, may substantially affect antigen trafficking, ultimately influencing the close bidirectional interaction between the gut microbiome and the immune system. This cross-talk is highly influential in shaping the host immune system and ultimately clinical infections. The hypothesis of the current study was that a change in microbiome and/or breach in GI epithelial barrier could be partially responsible for development of periprosthetic joint infections (PJI). Multiple biomarkers of gut barrier disruption were tested in parallel in plasma samples collected as part of a prospective cohort study of patients undergoing revision arthroplasty for aseptic failures or PJI (As defined by the 2018 ICM criteria). All blood samples were collected before any antibiotic was administered. Samples were tested for Zonulin, soluble CD14 (sCD14), and lipopolysaccharide (LPS) using commercially available enzyme-linked immunosorbent assays. Statistical analysis consisted of descriptive statistics, Mann-Whitney t-test, and Kruskal-Wallis test. A total of 134 patients were consented and included in the study. 44 were classified as PJI (30 chronic and 14 acute), and 90 as aseptic failures (26 primaries and 64 aseptic revisions). Both Zonulin and sCD14, but not LPS, were found to be significantly increased in the PJI group compared to non-infected cases (p<0.001; p=0.003). Higher levels of Zonulin were found in acute infections compared to chronic PJI (p=0.005. This prospective ongoing study reveals a possible link between gut permeability and the ‘gut-immune-joint axis’ in PJI. If this association continues to be born out with larger cohort recruitment and more in-depth analysis, it would have an immense implication in managing patients with PJI. In addition to administering antimicrobials, patients with PJI and other orthopedic infections may require gastrointestinal modulators such as pro and prebiotics

Aims. Biofilm infections are among the most challenging complications in orthopaedics, as bacteria within the biofilms are protected from the host immune system and many antibiotics. Halicin exhibits broad-spectrum activity against many planktonic bacteria, and previous studies have demonstrated that halicin is also effective against Staphylococcus aureus biofilms grown on polystyrene or polypropylene substrates. However, the effectiveness of many antibiotics can be substantially altered depending on which orthopaedically relevant substrates the biofilms grow. This study, therefore, evaluated the activity of halicin against less mature and more mature S. aureus biofilms grown on titanium alloy, cobalt-chrome, ultra-high molecular weight polyethylene (UHMWPE), devitalized muscle, or devitalized bone. Methods. S. aureus-Xen36 biofilms were grown on the various substrates for 24 hours or seven days. Biofilms were incubated with various concentrations of halicin or vancomycin and then allowed to recover without antibiotics. Minimal biofilm eradication concentrations (MBECs) were defined by CFU counting and resazurin reduction assays, and were compared with the planktonic minimal inhibitory concentrations (MICs). Results. Halicin continued to exert significantly (p < 0.01) more antibacterial activity against biofilms grown on all tested orthopaedically relevant substrates than vancomycin, an antibiotic known to be affected by biofilm maturity. For example, halicin MBECs against both less mature and more mature biofilms were ten-fold to 40-fold higher than its MIC. In contrast, vancomycin MBECs against the less mature biofilms were 50-fold to 200-fold higher than its MIC, and 100-fold to 400-fold higher against the more mature biofilms. Conclusion. Halicin is a promising antibiotic that should be tested in animal models of orthopaedic infection. Cite this article: Bone Joint Res 2024;13(3):101–109

Aim. A growing number of recent investigations on the human genome, gut microbiome, and proteomics suggests that the loss of mucosal barrier function, particularly in the gastrointestinal tract, may substantially affect antigen trafficking, ultimately influencing the close bidirectional interaction between the gut microbiome and the immune system. This cross-talk is highly influential in shaping the host immune system function and ultimately shifting genetic predisposition to clinical outcome. Therefore, we hypothesized that a similar interaction could affect the occurrence of acute and chronic periprosthetic joint infections (PJI). Method. Multiple biomarkers of gut barrier disruption were tested in parallel in plasma samples collected as part of a prospective cohort study of patients undergoing revision arthroplasty for aseptic or PJI (As defined by the 2018 ICM criteria). All blood samples were collected before any antibiotic was administered. Samples were tested for Zonulin, soluble CD14 (sCD14), and lipopolysaccharide (LPS) using commercially available enzyme-linked immunosorbent assays. Statistical analysis consisted of descriptive statistics and ANOVA. Results. A total of 96 patients were consented and included in the study. 32 were classified as PJI (23 chronic and 9 acute), and 64 as aseptic. Both Zonulin and LPS were found to be increased in the acute PJI group 8.448 ± 7.726 ng/mL and 4.106 ± 4.260 u/mL, compared to chronic PJI (p<0.001) and aseptic revisions (p=0.025). sCD14 was found to be increased in both chronic (0.463 ± 0.168 ug/mL) and acute PJI (0.463 ± 0.389 ug/mL) compared to aseptic revisions (p<0.001). Conclusions. This prospective ongoing study reveals a possible link between gut permeability and the ‘gut-immune-joint axis’ in PJI. If this association continues to be born out with larger cohort recruitment, it would have a massive implication in managing patients with PJI. In addition to the administration of antimicrobials, patients with PJI and other orthopedic infections may require gastrointestinal modulators such as pro and prebiotics

Aims. Trained immunity confers non-specific protection against various types of infectious diseases, including bone and joint infection. Platelets are active participants in the immune response to pathogens and foreign substances, but their role in trained immunity remains elusive. Methods. We first trained the innate immune system of C57BL/6 mice via intravenous injection of two toll-like receptor agonists (zymosan and lipopolysaccharide). Two, four, and eight weeks later, we isolated platelets from immunity-trained and control mice, and then assessed whether immunity training altered platelet releasate. To better understand the role of immunity-trained platelets in bone and joint infection development, we transfused platelets from immunity-trained mice into naïve mice, and then challenged the recipient mice with Staphylococcus aureus or Escherichia coli. Results. After immunity training, the levels of pro-inflammatory cytokines (tumour necrosis factor alpha (TNF-α), interleukin (IL)-17A) and chemokines (CCL5, CXCL4, CXCL5, CXCL7, CXCL12) increased significantly in platelet releasate, while the levels of anti-inflammatory cytokines (IL-4, IL-13) decreased. Other platelet-secreted factors (e.g. platelet-derived growth factor (PDGF)-AA, PDGF-AB, PDGF-BB, cathepsin D, serotonin, and histamine) were statistically indistinguishable between the two groups. Transfusion of platelets from trained mice into naïve mice reduced infection risk and bacterial burden after local or systemic challenge with either S. aureus or E. coli. Conclusion. Immunity training altered platelet releasate by increasing the levels of inflammatory cytokines/chemokines and decreasing the levels of anti-inflammatory cytokines. Transfusion of platelets from immunity-trained mice conferred protection against bone and joint infection, suggesting that alteration of platelet releasate might be an important mechanism underlying trained immunity and may have clinical implications. Cite this article: Bone Joint Res 2022;11(2):73–81

Rheumatoid arthritis (RA) is an autoimmune disease that involves T and B cells and their reciprocal immune interactions with proinflammatory cytokines. T cells, an essential part of the immune system, play an important role in RA. T helper 1 (Th1) cells induce interferon-γ (IFN-γ), tumour necrosis factor-α (TNF-α), and interleukin (IL)-2, which are proinflammatory cytokines, leading to cartilage destruction and bone erosion. Th2 cells primarily secrete IL-4, IL-5, and IL-13, which exert anti-inflammatory and anti-osteoclastogenic effects in inflammatory arthritis models. IL-22 secreted by Th17 cells promotes the proliferation of synovial fibroblasts through induction of the chemokine C-C chemokine ligand 2 (CCL2). T follicular helper (Tfh) cells produce IL-21, which is key for B cell stimulation by the C-X-C chemokine receptor 5 (CXCR5) and coexpression with programmed cell death-1 (PD-1) and/or inducible T cell costimulator (ICOS). PD-1 inhibits T cell proliferation and cytokine production. In addition, there are many immunomodulatory agents that promote or inhibit the immunomodulatory role of T helper cells in RA to alleviate disease progression. These findings help to elucidate the aetiology and treatment of RA and point us toward the next steps. Cite this article: Bone Joint Res 2022;11(7):426–438

Aims. Staphylococcus aureus is a major cause of septic arthritis, and in vitro studies suggest α haemolysin (Hla) is responsible for chondrocyte death. We used an in vivo murine joint model to compare inoculation with wild type S. aureus 8325-4 with a Hla-deficient strain DU1090 on chondrocyte viability, tissue histology, and joint biomechanics. The aim was to compare the actions of S. aureus Hla alone with those of the animal’s immune response to infection. Methods. Adult male C57Bl/6 mice (n = 75) were randomized into three groups to receive 1.0 to 1.4 × 10. 7. colony-forming units (CFUs)/ml of 8325-4, DU1090, or saline into the right stifle joint. Chondrocyte death was assessed by confocal microscopy. Histological changes to inoculated joints were graded for inflammatory responses along with gait, weight changes, and limb swelling. Results. Chondrocyte death was greater with 8325-4 (96.2% (SD 5.5%); p < 0.001) than DU1090 (28.9% (SD 16.0%); p = 0.009) and both were higher than controls (3.8% (SD 1.2%)). Histology revealed cartilage/bone damage with 8325-4 or DU1090 compared to controls (p = 0.010). Both infected groups lost weight (p = 0.006 for both) and experienced limb swelling (p = 0.043 and p = 0.018, respectively). Joints inoculated with bacteria showed significant alterations in gait cycle with a decreased stance phase, increased swing phase, and a corresponding decrease in swing speed. Conclusion. Murine joints inoculated with Hla-producing 8325-4 experienced significantly more chondrocyte death than those with DU1090, which lack the toxin. This was despite similar immune responses, indicating that Hla was the major cause of chondrocyte death. Hla-deficient DU1090 also elevated chondrocyte death compared to controls, suggesting a smaller additional deleterious role of the immune system on cartilage. Cite this article: Bone Joint Res 2022;11(9):669–678

Aim. “Implant associated Staphylococcus aureus or S. epidermidis infections are often difficult to treat due to the formation of biofilms on prosthetic material. Biofilms are bacterial communities adhered to a surface with a self-made extracellular polymeric substance that surrounds resident bacteria. In contrast to planktonic bacteria, bacteria in a biofilm are in an adherent, dormant state and are insensitive to most antibiotics. In addition, bacteria in a biofilm are protected from phagocytic cells of the immune system. Therefore, complete surgical removal and replacement of the prosthetic implant is often necessary to treat this type of infections. Neutrophils play a crucial role in clearing bacterial pathogens. They recognize planktonic bacteria via immunoglobulin (Ig) and complement opsonisation. In this project, we aim to evaluate the role of IgG and complement in the recognition and clearance of staphylococcal biofilms by human neutrophils. Furthermore, we evaluate if monoclonal antibodies (mAbs) targeting biofilm structures can enhance recognition and clearance of staphylococcal biofilms by the human immune system.”. Method. “We produced a set of 20 recombinant mAbs specific for staphylococcal antigens. Using flow cytometry and ELISA-based methods we determined the binding of these mAbs to planktonic staphylococci and in vitro staphylococcal biofilms. Following incubation with IgG/IgM depleted human serum we determined whether mAbs can react with the human complement system after binding to biofilm. Confocal microscopy was used to visualize the location of antibody binding in the biofilm 3D structure.”. Results. “We show that mAbs directed against several staphylococcal surface targets such as wall teichoic acid (a glycopolymer on the S. aureus/S. epidermidis cell wall) and polymeric-N-acetyl-glucosamine (major constituent of the S. epidermidis biofilm extracellular matrix) bind biofilms in a dose-dependent manner. This interaction was specific since no binding was observed for control antibodies (recognizing the hapten DNP). Furthermore we show that these antibodies can penetrate the complete 3D structure of an in vitro biofilm. Products of complement activation via the classical pathway were detected upon incubation with human serum and the biofilm binding mAbs.”. Conclusions. “Having established that our mAbs can bind biofilms and induce complement opsonisation via C3b deposition, we will now study if we can engineer these antibodies to enhance complement deposition. A combination of enhanced complement and antibody opsonisation may improve recognition and clearance of biofilms by phagocytic immune cells. These mAbs could be used to boost the immune system to clear implant associated infections, without the need to replace the implant via invasive surgical procedures.”

Macrophages play a critical role in innate immunity by promoting or inhibiting tissue inflammation and repair. Classically, macrophages can differentiate into either pro-inflammatory (M1) or pro-reparative (M2) phenotypes in response to various stimuli. Therefore, this study aimed to address how extracellular vesicles (EVs) derived from polarized macrophages can affect the inflammatory response of tendon cells. For that purpose, human THP-1 cells were stimulated with lipopolysaccharide (LPS), and interleukins -4 and -13 (IL- 4, IL-13), to induce macrophages polarization into M1, M2, and hybrid M1/M2 phenotypes. Subsequently, the EVs were isolated from the culture medium by ultracentrifugation. The impact of these nanovesicles on the inflammation and injury scenarios of human tendon-derived cells (hTDCs), which had previously been stimulated with interleukin- 1 beta (IL-1ß) to mimic an inflammatory scenario, was assessed. We were able to isolate three different nanovesicles populations, showing the typical shape, size and surface markers of EVs. By extensively analyzing the proteomic expression profiles of M1, M2, and M1/M2, distinct proteins that were upregulated in each type of macrophage-derived EVs were identified. Notably, most of the detected pro- inflammatory cytokines and chemokines had higher expression levels in M1-derived EVs and were mostly absent in M2-derived EVs. Hence, by acting as a biological cue, we observed that M2 macrophage-derived EVs increased the expression of the tendon-related marker tenomodulin (TNMD) and tended to reduce the presence of pro-inflammatory markers in hTDCs. Overall, these preliminary results show that EVs derived from polarized macrophages might be a potential tool to modulate the immune system responses becoming a valuable asset in the tendon repair and regeneration fields worthy to be further explored

Anatomically, bone consists of building blocks called osteons, which in turn comprise a central canal that contains nerves and blood vessels. This indicates that bone is a highly innervated and vascularized tissue. The function of vascularization in bone (development) is well-established: providing oxygen and nutrients that are necessary for the formation, maintenance, and healing. As a result, in the field of bone tissue engineering many research efforts take vascularization into account, focusing on engineering vascularized bone. In contrast, while bone anatomy indicates that the role of innervation in bone is equally important, the role of innervation in bone tissue engineering has often been disregarded. For many years, the role of innervation in bone was mostly clear in physiology, where innervation of a skeleton is responsible for sensing pain and other sensory stimuli. Unraveling its role on a cellular level is far more complex, yet more recent research efforts have unveiled that innervation has an influence on osteoblast and osteoclast activity. Such innervation activities have an important role in the regulation of bone homeostasis, stimulating bone formation and inhibiting resorption. Furthermore, due to their anatomical proximity, skeletal nerves and blood vessels interact and influence each other, which is also demonstrated by pathways cross-over and joint responses to stimuli. Besides those closely connected sytems, the immune system plays also a pivotal role in bone regeneration. Certain cytokines are important to attract osteogenic cells and (partially) inhibit bone resorption. Several leukocytes also play a role in the bone regeneration process. Overall, bone interacts with several systems. Aberrations in those systems affect the bone and are important to understand in the context of bone regeneration. This crosstalk has become more evident and is taken more into consideration. This leads to more complex tissue regeneration, but may recapitulate better physiological situations

In orthopedic surgery, implant infections are a serious issue and difficult to treat. The aim of this study was to use superparamagnetic nanoporous silica nanoparticles (MNPSNP) as candidates for directed drug delivery. Currently, short blood circulation half-life due to interactions with the host's immune system hinder nanoparticles in general from being clinically used. PEGylation is an approach to reduce these interactions and to enhance blood circulation time. The effect of PEGylation of the used . 68. Ga-labelled MNPSNP on the distribution and implant accumulation was examined by PET/CT imaging and gamma counting in an implant mouse model. Female Balb/c mice (n=24) received a magnetic implant subcutaneously on the left and a titanium implant on the right hind leg. On day one, 12 of these mice received an additional clodronate®-injection for macrophage depletion. On the second postoperative day, mice were anaesthetized and MNPSNP (native or PEGylated) injected intravenously, followed by a dynamic PET-scan over 60 minutes, a CT- and a static PET-scan at 120 min. As control, 12 mice received only . 68. Ga-MNPSNP (native or PEGylated). Gamma counting of inner organs, urine, blood and implant area was performed as further final analysis. Although PEGylation of the nanoparticles already resulted in lower liver uptakes, both variants of . 68. Ga-labeled MNPSNP accumulated in liver and spleen. Combination of PEGylation with clodronate®-injection led to a highly significant effect whereas clodronate®-injection alone could not reveal significant differences. In gamma counting, a significantly higher %I.D./g was found for the tissue surrounding the magnetic implants compared to the titanium control, although in a low range. PEGylation and/or clodronate®-injection revealed no significant differences regarding nanoparticle accumulation at the implantation site. PEGylation increases circulation time, but MNPSNP accumulation at the implant site was still insufficient for treatment of infections. Additional efforts have to further increase circulation time and local accumulation. Acknowledgements: This work is funded by the German Research Foundation (DFG, project number 280642759)

Aim. Antimicrobial peptides occur naturally in our intrinsic immune system. PLG0206 is a novel, engineered, 24-amino acid peptide which has broad-spectrum antimicrobial activity, including in biofilm and against multi-drug resistant pathogens (1,2). This is the first clinical study to evaluate the safety and tolerability of PLG0206 when administered via an irrigation solution in patients with periprosthetic joint infections (PJI) following total knee arthroplasty (TKA) during debridement, antibiotics, and implant retention (DAIR). Secondary objectives were to evaluate pharmacokinetics (PK), biomarkers and initial clinical efficacy at one year post-DAIR procedure. Method. This prospective, multicenter, open-label, interventional study assessed two dose levels of PLG0206. Fourteen patients underwent revision for PJI after TKA. At the end of debridement, they received a single intra-articular irrigation of PLG0206 into the wound cavity lasting 15 minutes at concentrations of 3 mg/mL (n=7) or 10 mg/mL (n=7). Patients received post-operative care and intravenous/oral antimicrobial therapy as per their institutional guidelines. Patients were monitored for safety and signs of relapse or persistent infection for 12 months post study drug administration and PK and blood biomarkers were assessed. Results. All patients completed their final study assessment at Day 365. Over the 1-year follow-up, only one recurrence (7%) was noted at Day 169 in the low-dose cohort. Following dosing, nine patients (64.3%) had limited systemic exposure; maximum plasma concentration occurred 1-hour post-administration and declined rapidly to undetectable levels by 24 hours following treatment in all patients. The incidence of drug related treatment-emergent adverse events (TEAEs) was low. Two patients, both in the higher dose cohort, experienced a transient drug related TEAE; one of hypertransaminasaemia and one of neuralgia. Both events were moderate in severity and resolved within two weeks of onset. Conclusions. A single 15-minute irrigation of PLG0206 into the wound cavity of patients undergoing a DAIR procedure for PJI following TKA, is safe and well tolerated by patients. This new antimicrobial peptide offers a promising therapeutic option in musculoskeletal infection. The initial clinical efficacy is encouraging but now needs to be investigated in a much larger clinical trial

Biphasic calcium phosphate (BCP) with a characteristic needle-shaped submicron surface topography (MagnetOs) has attracted much attention due to its unique bone-forming ability which is essential for repairing critical-size bone defects such as those found in the posterolateral spine. Previous in vitro and ex-vivo data performed by van Dijk LA and Yuan H demonstrated that these specific surface characteristics drive a favorable response from the innate immune system. This study aimed to evaluate and compare the in vivo performance of three commercially-available synthetic bone grafts, (1) i-FACTOR Putty. ®. , (2) OssDsign. ®. Catalyst Putty and (3) FIBERGRAFT. ®. BG Matrix, with that of a novel synthetic bone graft in a clinically-relevant instrumented sheep posterolateral lumbar spine fusion (PLF) model. The novel synthetic bone graft comprised of BCP granules with a needle-shaped submicron surface topography (MagnetOs) embedded in a highly porous and fibrillar collagen matrix (MagnetOs Flex Matrix). Four synthetic bone grafts were implanted as standalone in an instrumented sheep PLF model for 12 weeks (n=3 bilateral levels per group; levels L2/3 & L4/5), after which spinal fusion was determined by manual palpation, radiograph and µCT imaging (based on the Lenke scale), range-of-motion mechanical testing, and histological and histomorphological evaluation. Radiographic fusion assessment determined bilateral robust bone bridging (Lenke scale A) in 3/3 levels for MagnetOs Flex Matrix compared to 1/3 for all other groups. For µCT, bilateral fusion (Lenke scale A) was found in 2/3 levels for MagnetOs Flex Matrix, compared to 0/3 for i-FACTOR Putty. ®. , 1/3 for OssDsign. ®. Catalyst Putty and 0/3 for FIBERGRAFT. ®. BG Matrix. Fusion assessment for MagnetOs Flex Matrix was further substantiated by histology which revealed significant graft resorption complemented by abundant bone tissue and continuous bony bridging between vertebral transverse processes resulting in bilateral spinal fusion in 3/3 implants. These results show that MagnetOs Flex Matrix achieved better fusion rates compared to three commercially-available synthetic bone grafts when used as a standalone in a clinically-relevant instrumented sheep PLF model

Aim. Infections represent a serious threat to the successful utilization of implants in modern medicine. Implant-associated infections are difficult to treat, because they involve biofilms that protect bacteria from the immune system and harbour antibiotic-tolerant persister cells. In this work, we developed an antibody-drug conjugate (ADC) containing the anti-neoplastic drug mitomycin C (MMC) as a novel treatment paradigm for implant-associated infections. MMC was chosen as it is a potent antimicrobial against biofilms and its synthesis into an ADC was chosen to alleviate toxicity. Following development and synthesis of the ADC, stability and release of MMC was measured. We then used the ADC to kill bacteria in suspension and in biofilms, in vitro and in vivo. Method. Mitomycin C was conjugated to a commercially available antibody against S. aureus via a disulfide linkage, with a drug release occurred via thiol-disulfide exchange. ADC as tested against S. aureus under various growth conditions (planktonic, persisters and biofilm). In vitro toxicity of ADC vs MMC was measured using a human cell line (MOLT-4). Finally, two independent in vivo experiments were performed in a murine implant-associated osteomyelitis model. In experiment one ADC treatment was compared NaCl, vancomycin and vancomycin + ADC (n=10 for all groups). Subsequently, ADC was compared to NaCl, the antibody used in the ADC construction, MMC and a novel ADC constructed with a non-S. aureus antibody (n=10 for all groups). All treatments were started day 7 post inoculation and were administered for 3 days. CFU enumeration was done following sonication to quantify bacterial load. Results. Drug release could be triggered on demand with N-acetyl cysteine and release occurred, once in contact with free thiols on S. aureus cell surface. The ADCs exhibited a concentration-dependent antimicrobial effect against S. aureus with doses exceeding 0.5 mg/l reducing amount of CFU to below detection limit (p< 0.001). 15 minutes exposure to ADC resulted in an approx. 2 log CFU/ml reduction compared to untreated biofilms (p < 0.01). In vivo ADC treatment was effective compared to NaCl treatment and the vancomycin treatment (p≤ 0.001). Further ADC and MMC treatment were comparable in efficacy, but both were superior than NaCl, pure antibody and the non-specific ADC (p≤ 0.05). Finally, in vitro cytotoxicity was significantly lower for ADC than MMC. Conclusions. In this study we have demonstrated that ADCs can be a novel treatment approach to combat implant-associated infections caused by S. aureus