Dmitriy Sheyn

Bone metastasis can be facilitated by systemic remodeling, yet the tumor‐derived signals that influence the bone marrow microenvironment remain incompletely understood. Large oncosomes (LOs) are atypically large (> 1 µm), tumor‐derived extracellular vesicles shed by amoeboid cancer cells. Here, we demonstrate that LOs function as systemic mediators of metastatic niche formation by activating innate immune sensing in bone marrow mesenchymal stem cells (BM‐MSCs). Systemic administration of LOs to immunocompetent tumor‐bearing mice did not affect primary tumor growth but increased metastatic burden. LOs induced a robust, dose‐dependent interferon‐driven inflammatory program, characterized by interferon‐stimulated genes and neutrophil chemokines. Mechanistically, this response was driven by LO‐associated nucleic acids activating convergent cytosolic DNA‐ and RNA‐sensing pathways in recipient stromal cells. LO‐conditioned BM‐MSCs promoted the accumulation and polarization of neutrophils toward an immunosuppressive, polymorphonuclear myeloid‐derived suppressor cell (PMN‐MDSC)‐like phenotype. In vivo, genetic suppression of LO shedding in tumor cells reduced PMN‐MDSC accumulation in the bone marrow, which was reversed by systemic LO administration. Together, these findings support a model in which LO‐associated signals reprogram the bone marrow microenvironment to support metastatic colonization, identifying a previously unrecognized mechanism linking tumor vesiculation to immune remodeling at distant sites.

In the US, 33 million musculoskeletal injuries have been reported per year, with 50% involving tendons and ligaments in both athletic and aging populations. Tendon repair often results in the formation of biomechanically inferior scar tissue rather than functional regeneration. Local cell therapy is garnering significant interest in tendon repair because it provides a targeted means to repopulate defects with potent therapeutic cells. Here, we developed a porcine tendon-derived thermoresponsive extracellular matrix hydrogel (TG) as an injectable, bio-instructive carrier for scleraxis-overexpressing induced mesenchymal stem cell–derived tenocytes (iTenocytes), with the goal of improving cell retention and overall transplantation success. TG was compositionally distinct from purified collagen (PC, from rat tail type 1 collagen) and exhibited favorable material properties for a minimally invasive percutaneous strategy, including thermoresponsive gelation, shear-thinning injectability, retention at the injection site, and controlled biodegradation. In vitro , TG supported three-dimensional cell residence, promoted cell interconnectivity and redistribution at the matrix interface, and increased collagen type I release from iTenocytes compared to those embedded in PC. Transcriptomic and proteomic analyses further showed that TG enhanced programs associated with tenogenic maturation, extracellular matrix assembly, focal adhesion, mechano-transduction, and remodeling. In a rat Achilles tendon partial defect model, both optical imaging and histological analyses demonstrated retention of iTenocytes at the injection site. Additionally, confocal imaging demonstrated retention of iTenocytes within the defect site for up to 10 days. Together, these findings identify TG as a biofunctional injectable carrier that supports the tenogenic characteristics of iTenocytes and enhances their local persistence after transplantation.

Background: Low back pain remains the leading cause of disability worldwide, with intervertebral disc degeneration representing a major biological contributor. Although cell‐based therapies have shown promise in preclinical models, clinical translation has yielded modest and inconsistent outcomes. Accumulating evidence suggests that therapeutic failure reflects not only limitations in cell source or differentiation potential, but also the hostile biochemical and biomechanical microenvironment of the degenerative disc. Hypoxia, nutrient deprivation, acidity, lactate accumulation, fibrosis, senescence, inflammation, and abnormal mechanical loading collectively impair cell survival, integration, and long‐term function. Method: We performed a comprehensive review of the literature using PubMed, Web of Science, and Google Scholar, with emphasis on studies published between 2020 and 2026. Evidence was critically evaluated to examine advances in cell‐based therapies for IVDD, including cell sources, mechanisms of repair, biomaterial‐assisted delivery systems, microenvironment‐targeted strategies, translational studies, and emerging technologies that enhance regenerative efficacy. Discussion: Current evidence indicates that successful disc regeneration depends not only on selecting an appropriate therapeutic cell source but also on overcoming the biological constraints imposed by the degenerative niche. We critically compare the regenerative potential of mesenchymal stromal cells, nucleus pulposus cells, and induced pluripotent stem cell‐derived therapies, highlighting their respective advantages and limitations. We further discuss how biomaterial carriers, extracellular vesicles, developmental biology‐guided differentiation, genetic engineering, preconditioning approaches, and smart delivery platforms are being integrated to improve cell survival, phenotype stability, extracellular matrix restoration, and functional repair. Conclusion: Future success in intervertebral disc regeneration will require integrated therapeutic strategies that combine optimized cell sources with biomaterial‐assisted delivery, microenvironment modulation, and precision bioengineering. Advancing these complementary approaches will be essential for achieving durable biological repair, restoring disc structure and function, and translating regenerative therapies into effective clinical treatments for patients with degenerative disc disease.

Tendon injuries often result in fibrosis, compromising function and predisposing to re-injury. Here, we used a full-width, non-repair Achilles tendon transection model in young (3 weeks old) and adult (18-20 weeks) rats to elucidate the cellular mechanisms governing regenerative versus fibrotic healing. Functional and biomechanical analyses revealed that young tendons recovered motion and load-bearing capacity more rapidly but exhibited more fibrotic early healing. Single-nuclei RNA sequencing identified seven major cell populations within the connective tissue compartment. Adult tendons maintained a synthetic fibroblast population marked by upregulated ECM synthesis, reduced stress-related gene expression, whereas young tendons favored expansion of Cxcl12+/Lrp6+/Gas6+; fibrotic fibroblasts linked to oxidative and pro-angiogenic signaling. The young group showed sustained activation of Nox4-Gas6 pathways driving a self-reinforcing fibrotic circuit. These findings define a fibroblast lineage bifurcation that dictates oxidative stress signaling as a key regulator of fibrotic remodeling, highlighting potential therapeutic targets to promote regenerative tendon repair.

Background: Lower back pain (LBP) is one of the most common causes of disability, with up to 40% of LBP cases attributed to intervertebral disc (IVD) degeneration. While small animal models are widely used to study IVD degeneration and LBP, the small size of their IVDs limits translational and biological relevance. Large animal models more accurately emulate human disease; however, methods of measuring LBP are not well established. The porcine model has been questioned for LBP research, due to notochordal cells (NCs) persistence through life, unlike humans. Here, we developed a comprehensive porcine model with quantitative measures of discogenic pain via biobehavioral testing (BBT), MRI, and multi‐omics tissue analyses of the IVD and DRGs. Methods: Utilizing a previously established porcine annular injury model of IVD degeneration, pigs underwent longitudinal MRI and biobehavioral testing to monitor degenerative changes in the IVD and pain development. At the study endpoint, IVD and dorsal root ganglia (DRG) tissues were collected for multi‐omic analysis. Results: MRI demonstrated the progression of IVD degeneration beginning at 4 weeks post‐injury. BBTs showed the development of significant pain responses as early as week 2 post‐injury, supported by transcriptomics of injury‐matched DRGs. Single‐cell transcriptomics, trajectory, and cell–cell communication analyses suggest that, with injury, NCs are differentiating to nucleus pulposus cells (NPCs). Furthermore, NPCs showed upregulation of cellular stress, neural outgrowth, and inflammation pathways, consistent with pain‐inducing distress signals found in human samples. Conclusions: This study establishes novel MRI and BBT‐based methods for quantifying LBP in pigs and supports its translational relevance to human discogenic LBP. The identification of LBP‐associated clusters mirrors our previous findings in humans. Moreover, the shift of NC to NPC phenotype further supports that the porcine model is relevant to human pathology, as the injury induced accelerated aging and loss of NCs with IVD degeneration and discogenic pain.

Post-traumatic osteoarthritis (PTOA) is a common long-term consequence of joint injury and a major cause of chronic pain and disability, yet no disease-modifying therapies are currently available. A central barrier to effective intervention is the persistence of maladaptive synovial inflammation, driven in part by macrophage-mediated signaling that sustains tissue degeneration and pain. Here, we developed a scalable, chemically defined platform to generate human induced pluripotent stem cell (iPSC)-derived anti-inflammatory macrophages (iMac-M2) as an off-the-shelf cell therapy designed to restore joint immune homeostasis after injury. These cells maintained a stable anti-inflammatory phenotype and function under osteoarthritis-relevant inflammatory conditions and suppressed inflammatory and catabolic responses in human joint cell co-culture systems. In a preclinical model of PTOA, intra-articular delivery of iMac-M2 after injury improved functional and structural outcomes while modulating synovial inflammatory and pain-associated transcriptional programs. Treatment was well tolerated, with no evidence of systemic immune activation or ectopic tissue formation. Together, these findings support iPSC-derived macrophage therapy as a clinically translatable immunomodulatory strategy to interrupt early inflammatory drivers of PTOA and preserve joint health following injury.

During vertebrate embryogenesis, axial tendons develop from the paraxial mesoderm and differentiate through specific developmental stages to reach the syndetome stage. While the main roles of signaling pathways in the earlier stages of differentiation have been well established, pathway nuances in syndetome specification from the sclerotome stage have yet to be explored. Here, stepwise differentiation of human induced pluripotent stem cells to the syndetome stage is shown, using chemically defined media and small molecules that were modified based on single-cell RNA-sequencing and pathway analysis. A significant population of branching off-target cells differentiating toward a neural phenotype overexpressing Wnt was identified. Further transcriptomics post-addition of a WNT inhibitor at the somite stage and onwards revealed not only total removal of the neural off-target cells, but also increased syndetome induction efficiency. Fine-tuning tendon differentiation in vitro is essential to address the current challenges in developing a successful cell-based tendon therapy.

Background: Current treatments for osteoarthritis (OA) include physical therapy, nonsteroidal anti-inflammatory drugs, and joint arthroplasty, which aim to address symptoms rather than modify disease progression. Autologous platelet-rich plasma (PRP) and other biologics administered in the affected joint are widely used as alternatives that are believed to alleviate symptoms. However, PRP's effectiveness in reducing knee OA pain is inconsistent across the literature, and the specific therapeutic components remain unclear. Purpose: To identify whether specific cellular and protein biomarkers correlate with patient-reported outcomes and can therefore serve as predictive biomarkers for PRP effectiveness. Study Design: Case series; Level of evidence, 4. Methods: PRP samples from 30 patients (30 knees) with knee OA (Kellgren & Lawrence grades 2-3) who were undergoing PRP treatment were analyzed to identify biomarkers associated with response. Blood samples were drawn, and 2 identical PRP samples were prepared, with one set used for therapy and the other for analysis. Component analysis included cell counts, immune cell, and platelet characterization via mass cytometry, along with proteomic analysis using mass spectrometry. Clinical outcomes were assessed using the Knee injury and Osteoarthritis Outcome Score (KOOS) and Patient-Reported Outcomes Measurement Information System patient reported outcomes at baseline and up to 6 months postinjection. Results: PRP therapy improved pain in 19 of 30 patients at 6 weeks postinjection (mean ± SD age, 56.04 ± 10.56 years): Several distinct immune cell clusters (T helper 1 CD4 T cells ( r = 0.44; P < .05), Central memory CD4 T cells ( r = 0.46; P < .05), Effector memory CD4 T cells ( r = 0.52; P < .05), and CD8 T cells ( r = 0.44; P < .05) positively correlated with ΔKOOS ( P < .05). Proteomic analysis showed that differentially expressed proteins integrin-linked kinase ( r = −0.50; P < .05), and glutathione peroxidase 1 ( r = −0.55; P < .01) negatively correlated with ΔKOOS Pain ( P < .05), whereas cathepsin G ( r = 0.51; P < .05), and calprotectin subunit ( r = 0.65; P < .01) were positively correlated with ΔKOOS Pain ( P < .05) (* P < .05, ** P < 0.01). Conclusion: These findings suggest that some cellular and protein biomarkers may potentially be used as therapeutic targets and predictive markers for PRP success, guiding personalized therapeutic strategies. However, these targets must be further validated for knee OA in future studies.

Lower back pain (LBP) is one of the most common causes of disability, with up to 40% of LBP cases attributed to intervertebral disc (IVD) degeneration. While small animal models are widely used to study IVD and LBP, the small size of their IVDs limits translational and biological relevance. Large animal models more accurately emulate human disease; however, methods of measuring LBP are not well established. Pigs were also considered unfit for LBP research, due to notochordal cells (NCs) persistence through life, unlike humans. We developed a comprehensive porcine model with quantitative measure of discogenic pain via biobehavioral testing (BBT), MRI, and multi-omics tissue analysis of IVD and DRGs. MRI demonstrated the progression of IVD degeneration beginning at 4 weeks post-injury. BBTs showed the development of significant pain responses by week 4 post-injury, supported by transcriptomics of injury matched DRGs. Single cell transcriptomics, trajectory and cell-cell communication analyses suggest that, with injury, NCs are differentiating to nucleus pulposus cells (NPCs). Furthermore, NPCs showed upregulation of cellular stress, neural outgrowth, and inflammation pathway, consistent with pain-inducing distress signals found in human samples. This study establishes novel MRI and BBT-based methods for quantifying LBP in pigs and supports its translational relevance to human discogenic LBP. The identification of LBP-associated clusters mirrors our previous finding in humans. Moreover, the shift of NC to NPC phenotype further supports that the porcine model is relevant to human pathology, as the injury induced accelerated aging and loss of NCs with IVD degeneration and discogenic pain.