Mesenchymal Stem Cell-conjugated Tumor Necrosis Factor α Inhibitor For Synergistic Therapy Of Rheumatoid Arthritis

Rheumatoid arthritis（RA）is an autoimmune system disease of unknown origin,characterized by cartilage destruction,bone loss and inflammatory synovial heterogeneity.It is generally believed that the progression state of RA is positively correlated with production of matrix metalloproteinases（MMPs）,chemokines,and proinflammatory cytokines.MMPs are a family of endopeptidases that are widely distributed in most tissues in the body and have metal ion dependence such as Mg²⁺,Ca²⁺,and Zn²⁺.MMPs have multiple functionally distinct domains,and each domain cooperates with each other,playing an important role in the degradation of extracellular matrix,immunity,and connective tissue remodeling under physiological conditions.At the same time,many studies have reported that MMPs are also involved in a variety of pathological processes such as atherosclerosis,inflammation,tumor growth and metastasis.Among the more than 20 MMPs,the two most well-known,MMP-2 and MMP-9,are overproduced in the joints of RA patients,play an important role in the mechanism of RA cartilage damage by stimulating angiogenesis and degrading the cartilage matrix directly.In addition,increased production of proinflammatory cytokines,such as tumor necrosis factor alpha（TNF-α）,IL-6,and IL-1βalso play a critical role in the immunopathogenesis of RA.Among the many pro-inflammatory cytokines,TNF-αis one of the key cytokines that cause RA inflammation and induce other inflammatory cytokines.Blocking TNF-αwith inhibitors biological agent can reduce the production of IL-1,IL-6,IL-8,and granulocyte colony-stimulating factor,reflecting its leading role in rheumatoid synovitis.In the past two decades,great achievements in RA treatment have been made.Classic therapeutic approaches include glucocorticoids,disease modifying antirheumatic drugs（DMARDs）,nonsteroidal anti-inflammatory drugs（NSAIDs）,and so on.In addition,some biological DMARDs（bDMARDs）,such as TNF-inhibitors,have been approved for clinical treatment of RA.And in recent years,the first targeted synthetic DMARDs（tsDMARDs）,Janus kinase（Jak）inhibitors has been approved for sale in many countries,and more DMARDs are under development.bDMARDs and tsDMARDs have achieved significant therapeutic effects in the treatment of RA,especially in patients who are ineffective or tolerated after treatment with conventional synthetic DMARDs.Despite great progress,there are still many side effects,such as skin cancer,immune system abnormality,and infections,etc.,which limit its clinical application.Therefore,how to achieve more precise targeting of drugs to local inflammation,increase local drug concentration,and minimize drug toxicity,is one of the hotspots of current research.At the same time,researchers have used bone marrow mesenchymal stem cells（BMSCs）for the treatment of RA by transplantation.BMSC are a cell type with the potential to give rise to multiple distinct lineages.BMSCs can differentiate into a range of tissue types including bone,cartilage,myocardial tissue,and nervous tissue in response to specific stimuli in vitro or in vivo.BMSC has made great achievements in many fields of tissue engineering,and many researchers are looking forward to the application of BMSC in the treatment of RA.BMSC has shown superior functions in regulating immune responses,including inhibiting the proliferation of T lymphocytes and inhibiting inflammatory mediators,which has attracted widespread attention in recent years.In our previous study,a cartilage defect model was established based on the rat CIA model,and BMSCs were transplanted into the joint.It was confirmed that local transplantation of BMSCs in the joint cavity can regulate the local immune microenvironment,effectively inhibit the inflammation around the joint tissue and promote the repair of articular cartilage damage,which has a good therapeutic effect on RA.Also,studies have shown that BMSCs can accumulate in specific tissues,particularly in tumors,damaged tissues,and sites of inflammation owing to their ability to home to these sites.The exact mechanisms underlying this migration are unclear,although studies to date suggest that it is related to the expression of specific ligands and/or receptors in inflamed or damaged tissues that allow for cellular recruitment,much as inflammation normally facilitates leukocyte recruitment.Such homing has been leveraged in the context of cancer to target the tumors themselves.In this study,a new drug-loading system based on BMSC targeted delivery was designed.Etanercept（ETA）,a biological agent can bind to TNF-αthus preventing its proinflammatory actions,were linked to the surface of BMSC by using PLGLAG,a MMP-2 sensitive short peptides.In this way,ETA can reach inflammatory site with the assist of BMSC homing ability.Subsequently,PLGLAG will be cleaved in affected joints by the overexpressed MMP-2 between glycine and leucine residues as predicted,releasing drugs to realize targeted decrease of inflammation.With this strategy,ETA provides a suitable immune microenvironment for BMSCs,and also,the selectivity of ETA toward inflammation site is enhanced.In addition,the synergistic effect and mechanisms of the combined applications of BMSCs and ETA are investigated.The project provides a new idea for the immunotherapy of RA.