What’s New in Biologics

At the turn of the twenty-first century, biologics were anticipated to herald substantial advances that could reduce reliance on orthopaedic surgery to treat both acute and chronic musculoskeletal problems. For example, the use of biologics in the form of tumor necrosis factor-alpha (TNF-α) blockers reduced symptoms and joint damage in a sufficient proportion of patients with rheumatoid arthritis to significantly reduce their need for major joint replacements1. However, clinically proven biologics that have symptom and disease-modifying effects for common musculoskeletal conditions or that accelerate healing from orthopaedic injuries remain limited. Increased emphasis on evidence-based practice is needed for biologics to reach its full potential in solving some of the most prevalent and disabling conditions that have large negative global impacts on mobility and public health. What Is a Biologic? The broad definition of biologics is “substances made from a living organism or its products.”2 These substances include genes, cells, and proteins, with antibodies, enzymes, and inhibitors representing common types of proteins. Under this definition, insulin was reclassified by the U.S. Food and Drug Administration (FDA) from a drug to a biologic in 20203, making it one of the first biologic therapies. Other biologics commonly used clinically include vaccines and monoclonal antibodies. Gene therapy has been approved by the FDA for a few indications, such as the treatment of sickle cell disease and Duchenne muscular dystrophy4. Cell therapy refers to the introduction of cells without a structural biomaterial carrier, through injection either intravenously or into the target site (e.g., intra-articularly or intradiscally). In this regard, cells may potentially have been modified (i.e., expanded or genetically reprogrammed) before being injected into the body. Successful cell therapies include hematopoietic stem cell transplantation (HSCT), autologous chondrocyte implantation5, and chimeric antigen receptor T-cell (CAR-T) therapy6, which is a heavily manipulated genetically engineered cell product. The term “tissue engineering” refers to the regeneration of tissues and organs through combinations of cells, biomaterial scaffolds, and environmental regulators (e.g., growth factors and mechanical bioreactors). “Orthobiologics” is a relatively new term that encompasses the various biologic approaches used to enhance tissue healing and restoration within the musculoskeletal system7. The most commonly used orthobiologic is autologous platelet-rich plasma (PRP). Cell therapies currently in clinical use to treat musculoskeletal conditions include the FDA-approved matrix-associated chondrocyte implantation (MACI) technique for the treatment of chondral defects and autologous cells derived from bone marrow that meet the FDA 361 pathway requirements. The FDA 361 pathway was enacted to regulate human cell and tissue products that may be used clinically, such as bone grafts or allograft tissues, but do not pose a risk to public health and thus qualify for minimal FDA oversight. The requirements include autologous, minimally manipulated tissues for homologous use that are not combined with other substances except water or storage agents and that will not have systemic effects. Thus, mechanically disrupted fat meets these criteria, whereas the enzymatic or mechanical separation of fat into cellular or stromal vascular fractions does not. For 361 pathway biologics, there are also additional regulatory requirements such as registration and listing of the clinical performance site with the FDA, adhering to Current Good Tissue Practice (CGTP), reporting adverse events, and prohibiting making therapeutic claims8. Many Current Orthobiologic Treatments Are Considered Unproven Indiscriminate use of the 361 pathway prior to 2021 hampered evidence-based practice for orthobiologics. This circumstance, in which unproven treatments that had not been reviewed or approved by the FDA were marketed to patients as regenerative therapies9,10, reduced the perceived need for high-quality clinical trials to support efficacy claims. In 2017, the FDA finalized guidance to clarify the 361 pathway, particularly regarding minimal manipulation and homologous use11. Enforcement discretion regarding the tighter guidelines was extended through May 2021, after which the majority of products marketed as stem cell therapies such as umbilical cord products and adipose stromal vascular fraction were no longer allowed through the 361 pathway. Phased clinical trials take time to complete. Although there have been a few recent studies showing promising results with culture-expanded adipose-derived cells12 and umbilical cord-derived products13, none have yet gained FDA approval for marketing in the United States. Clinical evidence showing efficacy is needed to support therapeutic claims. Major roadblocks to assessing clinical effects of PRP and minimally manipulated FDA 361 pathway-eligible biologics include the high variability between and within patients in the composition and bioactivity of these products14. Coupling product variability with differing patient indications and responsiveness15 yields a situation in which it is difficult to conduct rigorous, reproducible, and meaningful human clinical trials. In essence, when there are a multitude of ever-changing variables, any therapeutic effects that occur in individual patients will be diluted by data from those who are nonresponsive because of different disease states or bioactive pathways. For these reasons, high-quality randomized controlled trials have failed to show efficacy of PRP and minimally manipulated cell therapies for common indications such as for the treatment of knee osteoarthritis16,17. Minimally manipulated orthobiologics are currently the mainstay of clinical care and are likely to retain a substantial role in the future. In a collaborative conference funded by the American Academy of Orthopaedic Surgeons (AAOS) and the National Institutes of Health (NIH), participants from academia and government (FDA), clinicians, patients, and international experts determined that registries have the potential to provide basic information on outcomes and complications following the use of minimally manipulated biologics for different demographic populations and indications9. Furthermore, the AAOS-NIH U13 meeting9 highlighted that registry-linked biorepositories similar to what had been established at the VA Palo Alto to determine predictors of responsiveness to PRP injections for knee osteoarthritis had the potential to provide real-world evidence18. The Biologics Alliance (BA), which formed after this meeting, then developed a multisite network to collect platelet counts and biospecimens for analyses against patient-reported outcomes. In collaboration with this alliance, the AAOS recently initiated an Orthobiologics Registry to implement a pilot program measuring clinical outcomes for the PRP treatment of knee osteoarthritis19. Similar registries can be established for quality and post-market assessment of cell therapies. Although registries can provide important information on large effect outcomes and safety, particularly for post-market monitoring, they are limited by variable inputs, missing data, and insufficient commitment and resources for effective implementation. Advancing the therapeutic potential of orthobiologics, particularly cell therapies, toward effective clinical treatment of musculoskeletal conditions likely requires moving beyond minimally manipulated autologous preparations. This is because the composition and bioactivity of the biologic needs to be matched with the mechanistic need in order for clinical trials to determine efficacy. For example, insulin accomplishes the therapeutic goal of lowering blood sugar by the mechanistic action of instructing cellular transporters to bring blood glucose into cells. Consequently, new insulins can be assessed on the basis of clinical outcomes (blood glucose levels) and mechanistic outcomes (glucose transport activity). A musculoskeletal example would be autologous chondrocyte implantation, discussed later. Defining mechanisms of action and therapeutic goals of a biologic is key to addressing and assessing efficacy in preclinical and clinical trials20. The known uncontrolled variability of minimally manipulated autologous preparations means that processing will be needed to screen, enrich, and enhance the properties that support the mechanistic action needed to achieve the desired therapeutic goal. Minimal manipulation means that the biologic is left almost completely in the native state, which may be inadequate to achieve therapeutic goals. Beyond Minimal Manipulation Efficacy has been proven and FDA approvals have been obtained for gene therapy to treat Duchenne muscular dystrophy and for a cell therapy to treat chondral defects, both with and without matrix scaffold5,21. FDA oversight, policies, and regulations apply to all biologics, whether cellular or acellular. Acellular biologic products such as exosomes, peptides, and gene therapies, although more complex than traditional chemically synthesized drugs with highly predictable structures, are extracted and purified through processes that can be reproduced to defined standards. Because biologics arise from living systems and may have greater variability with a higher potential for immunogenicity and unintended effects than small-molecule drugs, proof of clinical safety and efficacy will be needed for evidence-based practice. Cells represent the metabolic engines for numerous paracrine signaling and extracellular matrix synthesis functions. Cell therapies, particularly stem cell therapies, have therefore captured intense scientific and public interest. However, minimally manipulated autologous cell preparations are uncharacterized and heterogeneous. These properties make clinical trials to determine efficacy of minimally manipulated products for specific indications largely unworkable. Increased cellular homogeneity can be achieved via ex vivo characterization of cells, cell sorting, and culture expansion of desired cells capable of effecting the therapeutic goal. For example, chondrocytes have the ability to form cartilage. Although the cells eventually de-differentiate, the chondrogenic potential is retained in early passages. Following preclinical studies, autologous chondrocyte implantation, which involves isolation and culture expansion of chondrocytes from a cartilage biopsy taken from the patient5, was shown in clinical trials to repair cartilage defects and was approved by the FDA in 1997. Supported by a Phase-3 randomized controlled trial showing improved patient-reported outcomes compared with microfracture21, MACI in which autologous culture-expanded chondrocytes are delivered on a scaffold was approved by the FDA in 2016. Although there are new cell therapies in clinical trials, the autologous chondrocyte products are the only FDA-approved cell therapies for musculoskeletal treatment at the time of this writing. This situation is likely to change with increased emphasis on early collaboration with the FDA to accelerate the translation of new treatments for serious conditions such as osteoarthritis into clinical practice. In September 2025, the FDA issued new draft guidance, including “Expedited Programs for Regenerative Medicine Therapies for Serious Conditions.”22 Mesenchymal Stem Cells Imprecise terminology has also contributed to slow progress in harnessing the potential of cell therapies to advance orthopaedic care. “Mesenchymal stem cell” (MSC) was a term originally coined by Arnold Caplan to represent cells that were isolated from human and mammalian bone marrow and expanded, and retained the in vitro capacity to differentiate into multiple mesodermal tissues such as bone, cartilage, and fat23,24. Due to uncertainty whether these cells adequately meet accepted definitions of stem cells by being capable of multipotent differentiation, having self-renewal, and being able to recreate functional tissues25, MSCs have also been called different names, such as “mesenchymal stromal cells” and “multipotent stromal cells.”26 The International Society for Cell & Gene Therapy (ISCT) officially described MSCs as being multipotent mesenchymal stromal cells27,28. Nevertheless, by all definitions, MSCs required isolation, culture expansion, and further manipulation to demonstrate pluripotency, typically by differentiation in vitro into cells exhibiting bone, cartilage, and fat phenotypes. When bone marrow aspirate concentrate, micronized fat, adipose stromal vascular fraction, and other minimally manipulated preparations started being referred to as MSCs and stem cells by the industry and the lay press and in scientific articles, patients began to believe that these mixed cell preparations had regenerative effects. The successful clinical translation of such “stem cell” therapies has been further clouded by a dearth of randomized, controlled, and prospective clinical trials29 coupled with poor trial reporting30 and has been exacerbated by the expanded presence of “rogue” stem cell clinics that make unwarranted claims or perform risky procedures, in the United States and worldwide10. Around the same time, Caplan advocated rebranding MSCs as “medicinal signaling cells,” in part to better align terminology with potential mechanisms of action24. Most studies of MSCs have shown little, if any, homing or engraftment to injury or inflammatory sites to enhance repair, and nearly all such cell injections result in cell death or clearing within days of injection31,32. Thus, it has been postulated that MSCs may offer therapeutic benefit via a paracrine phenomenon in which cell-cell communication produces a signal to induce changes in nearby cells or in the microenvironment to support regenerative and immunomodulatory effects. Evidence to support a paracrine effect includes that implantation of muscle-derived MSCs induced tissue repair primarily mediated through the involvement of host cells that were chemoattracted by the implanted cells33,34. Paracrine signaling factors released by MSCs include growth factors and cytokines as well as exosomes and extracellular vesicles that transfer proteins, lipids, microRNA, and other genetic material to recipient cells35. Allogenic Cells Allogenic cells have been evaluated for orthopaedic applications13,36. They can be obtained from a variety of sources, including bone marrow, adipose tissue, and umbilical cord blood. Furthermore, they can be sourced from a younger, healthier donor, which may result in higher-quality cells. Also, allogenic cells can be stored in cell banks and can be readily available to reduce time and costs. Cell banking requires tests of cell viability, purity, contamination (mycoplasma, sterility, endotoxins), phenotypic stability, and biomarkers for the lot release37. When the mechanism of action of the injected cells relies on paracrine factors released by the injected cells and does not require the cells to integrate into the host tissue, the use of allogenic cells is more accepted. With the advent of a multitude of new methods for cellular engineering, a new generation of orthobiologic cell therapies will emerge that can provide functional tissue replacements as well as exogenous or even self-regulating capabilities for therapeutic delivery. The potential for rejection and adverse responses to allogenic cells likely varies with treatment route, location, and the recipient’s immune system. Being avascular, articular cartilage may have a lower immune response to allogenic cells than highly vascularized tissues. A human study using 10% autologous chondrons (chondrocytes surrounded by their territorial matrix) and 90% banked allogenic MSCs to treat chondral defects in 35 patients showed improved clinical outcomes and defect fills on magnetic resonance imaging at 1 year38 with a lack of serious events over 5 years, suggesting that allogenic cells can play a role in cartilage repair39. However, this study contained no control group for comparison, and, therefore, conclusions about the clinical efficacy of this procedure could not be made. A randomized controlled but nonblinded study performed in the Republic of Korea showed improved cartilage repair after treatment with allogenic umbilical cord-derived MSC compared with microfracture at 48 weeks and improved clinical outcomes at 3 to 5 years40. A small Phase-I safety study has been completed in the United States13. Optimization of Autologous Products Optimizing patient biology has the potential to improve the bioactivity of autologous blood and tissue-derived biologics. The bioactive properties of autologous products reflect the biologic state of the patient at the time the blood or tissue was extracted. Age, sex, stress, diet, and other patient factors influence PRP composition14,15. Modifiable factors generally accepted as improving the biologic state include diet, exercise, adequate sleep, and stress reduction. Patient actions to improve these aspects of their life may positively influence the biologic profile of autologous products, albeit to varying degrees depending on individual physiology, biologic need, and effort. Senescence is a driving mechanism for MSC dysfunction with advancing age and also with the passage of even young MSCs in culture. Often characterized by increased reactive oxygen species, senescence-associated heterochromatin foci, inflammatory cytokine secretion, and reduced proliferative capacity, senescence directly inhibits the efficacy of MSCs as a therapeutic agent for musculoskeletal regeneration41. Furthermore, autologous delivery of senescent MSCs can further induce disease and aging progression through the secretion of the senescence-associated secretory phenotype and mitigate the regenerative potential of MSCs. Recent studies have shown that the senolytic agent fisetin can reduce markers of senescence within culture-expanded adipose-derived MSC (AD-MSC) populations while maintaining the differentiation potential of the expanded AD-MSCs41. Alternatively, studies are underway investigating whether treating patients with senolytic agents prior to adipose cell isolation may reduce senescent cell burden in the endogenous fat. This strategy may reduce aging-related effects on autologous products. Engineering Cells to Maximize Therapeutic Benefit The advancement of cell-based orthobiologics may benefit from recent advances in gene and tissue to enhance factors such as homing and cell or immunomodulatory signaling to therapeutic mesenchymal cells can be genetically modified to therapeutic a living drug delivery for growth or signaling in the of or In the of therapies, cells that have been to cytokines or inhibitors of can enhance healing as cell-based therapies or exogenous control of these delivery other approaches have and genetic into stem cells and engineered recent advances in and in with new approaches are being developed for control of cellular in response to environmental These approaches can be used to new of cells with and as well as gene that provide for drug In studies have used genetic of endogenous to the of therapeutic for self-regulating gene by gene using the of the has the ability for of cells, the for This has been used to induced stem cells that have responses to inflammatory and cytokines such as and growth gene has been used to that gene that are and to regulate the of biologic These were engineered to form self-regulating tissue that have shown promising efficacy in various in vivo of inflammatory cells have the potential to with the therapeutic delivery of biologic drugs, as well as in cell homing and has been shown for additional regulatory systems such as a gene that produces biologic in response to mechanical or a gene that target on a program on the to these into preclinical and clinical trial are Orthobiologics has largely minimally manipulated products that have the of the defined or cellular treatments shown in or in vitro studies to have regenerative and therapeutic effects. and cell therapies can potentially the most musculoskeletal whether or With the advent of a multitude of new methods for cellular engineering, a new generation of orthobiologic cell therapies will emerge that can provide functional tissue replacements as well as exogenous or even self-regulating capabilities for therapeutic delivery. advance orthobiologics toward therapeutic need to beyond minimal manipulation to and biologics in to mechanisms of and clinical trials can then be performed to well the biologic the effects and whether this positively clinical outcomes. This will require collaboration clinicians, and the emphasis on and products on biologic need and defined mechanisms of effect will orthobiologics to the most conditions to musculoskeletal injury and