Harnessing Adult Mesenchymal Stem Cells as Next-Generation Therapeutics to Combat Antimicrobial Resistance: A One Health Perspective

Abstract

Antimicrobial resistance (AMR) is one of the most pressing current global health challenges, threatening human and animal health, food security, and environmental sustainability. The extensive use and misuse of antibiotics in human medicine and livestock production system have accelerated the emergence of multidrug-resistant (MDR) pathogens, necessitating the development of innovative alternatives to conventional antibiotics. While there are several areas of innovative alternatives are currently being pursued globally to mitigate MDR, adult mesenchymal stem cells (MSCs) have emerged as one of the most promising candidates owing to their regenerative, immunomodulatory, and especially intrinsic antimicrobial properties. Increasing evidence demonstrates that MSCs secrete a broad spectrum of antimicrobial peptides (AMPs), cytokines, chemokines, extracellular vesicles (EVs), and other bioactive molecules that directly inhibit pathogens while enhancing host immune responses. Unlike conventional antibiotics, MSC-derived products exert multifaceted actions by simultaneously promoting microbial clearance, reducing inflammation, and facilitating tissue repair, thereby minimizing the risk of resistance development. From a One Health perspective, MSC-based therapeutics offer an attractive strategy to reduce antibiotic use in livestock, improve animal health, and limit the spread of resistant pathogens across humans, animals, and the environment. Here we highlights the antimicrobial mechanisms of adult MSCs, their potential applications in veterinary medicine, and emerging opportunities for transcriptomics-guided discovery of novel MSC-derived antimicrobial peptides as well as application of artificial intelligence for sustainable animal production. Keywords: Mesenchymal stem cells, MDR pathogens, antimicrobial resistance, antimicrobial peptides (AMP), One Health. Introduction AMR has become a major global public health concern, compromising the effectiveness of antibiotics that have transformed medicine over the past century. The inappropriate use of antimicrobials in humans, food-producing animals, and agriculture has accelerated the emergence of multidrug-resistant (MDR) organisms. Resistant pathogens and resistance genes spread through direct animal contact, food products, waste-water, soil, and wildlife, emphasizing the interconnected nature of human, animal, and environmental health. Consequently, the One Health approach advocates integrated strategies to reduce antimicrobial use while developing safe and effective alternatives. Among emerging alternatives, adult mesenchymal stem cells (MSCs) have attracted considerable attention because they combine regenerative medicine with innate immune defense. Initially recognized for their ability to differentiate into mesodermal tissues, MSCs are now known to function primarily through paracrine signaling. Their secretome, comprising antimicrobial peptides (AMPs), cytokines, growth factors, extracellular vesicles, and immunomodulatory proteins, contributes significantly to tissue repair and antimicrobial defense. Antimicrobial peptides (AMPs) in combating antimicrobial resistance AMPs are evolutionary conserved gene encoded, short, positively charged host defense peptides found in all walks of life from microorganisms to humans (Zhang et al., 2016). Many AMPs are encoded in clusters in the genome and are expressed either constitutively or induced by specific external stimulators like infection or inflammatory condition. Constitutively expressed AMPs are primarily stored as inactive precursors in granules and are released locally at the site of infection or inflammation, whereas the induced expression of AMPs are stimulated by pathogen-associated molecular patterns (PAMPs) or cytokines (Hancock and Diamond, 2000). AMPs belong to the innate immune system which provides first line of protection against microbial infection. The anti microbial activity of AMP was demonstrated against gram positive as well as gram negative bacteria, viruses, fungi and protozoa (Hancock et al., 2000). AMPs exert its action through disturbing the cell membrane integrity, hindering the protein, DNA and RNA synthesis, interfering with protein folding and targeting the intracellular components (Nguyen et al., 2011). The swift action of AMP over the bacterial membrane is brought out by translocation across the membrane by disrupting the physical integrity of the cell and further target the intracellular components (Hancock and Sahl, 2006). The hydrophobic region of the peptides anchored in the hydrophobic lipid bilayer of the membrane. In another mechanism, disruption of the electrostatic forces between the cationic peptides and the negative charge of the bacterial surface occurs. In addition to the antimicrobial activity, AMPs possess immunomodulatory property and beneficial biological effects that supplement the antimicrobial action. They have been identified in various bodily surfaces such as skin, eyes, ears, mouth, airways, lung, intestines, and the urinary tract. Till date more than 3000 AMPs have been isolated and characterized in different species according to the online Antimicrobial Peptide Database (APD). As of 2020, there are 363 AMPs from bacteria (bacteriocins/antibiotics), 5 from archaea, 8 from protists, 21 from fungi, 360 from plants, and 2406 from animals have been reported and the list is ever growing. Apart from particular antimicrobial activity, AMPs also demonstrated the multiple other properties like anti cancer, anti diabetic, wound healing, anti-inflammatory, spermicidal, insecticidal, ion channel inhibitors, protease inhibitors and anti-oxidant (http://aps.unmc.edu/AP/main.php). Antimicrobial Properties of Adult Mesenchymal Stem Cells Recent in vitro and in vivo studies have demonstrated that MSCs, derived from various tissue sources, along with their conditioned media (CM), exhibit potent antimicrobial effects. These effects include activity against multidrug-resistant (MDR) pathogens and a reduction in chronic biofilm formation, mediated through both direct and indirect mechanisms (Sung et al. 2016; Gupta et al. 2012; Krasnodembskaya et al. 2012; Alcayaga-Miranda et al. 2015; Sutton et al. 2016; Tehrani et al. 2017; Johnson et al. 2017; Chow et al. 2020). Similar antimicrobial properties of MSCs and their CM have also been reported in veterinary species, including equine, bovine, and canine models (Harman et al, 2017; Johnson et al, 2017;Cortes-Araya et al. 2018; Humenik et al. 2019; Lange-Consiglio. 2019; Bujňáková et al. 2020; Marx et al., 2020, Camelia et al 2026). These antimicrobial effects of MSCs have been attributed to expression of a variety of AMPs (Balan et al. 2014; Gupta et al. 2012; Krasnodembskaya et al. 2010). Emerging evidence indicates that MSCs from different tissue origins vary in their antibacterial properties (Raicevic et al. 2011). For example, CM collected from equine bone marrow-derived MSCs (BM-MSCs), adipose tissue-derived MSCs (AT-MSCs), and endometrial MSCs (EM-MSCs) has demonstrated antibacterial activity, with AT-MSCs and EM-MSCs exhibiting greater efficacy than BM-MSCs. Interestingly, AT-MSCs express lower levels of immunomodulatory genes compared to BM-MSCs and EM-MSCs, yet demonstrate stronger antimicrobial effects, suggesting a complex interplay between immunomodulation and antimicrobial activity (Cortés-Araya et al. 2018). Furthermore, Chow et al. (2020) reported that human BM-MSC derived CM achieved a significantly higher bacterial killing rate—up to 69%—when combined with antibiotics, compared to either treatment alone. Other studies suggest that while BM-MSCs provide partial protection in infections such as sepsis, menstrual blood-derived MSCs (MenSCs) may more effectively improve survival rates. This enhanced efficacy is likely due to MenSCs’ higher frequency of mesenchymal progenitors and greater proliferative capacity (Gonzalez-Rey et al. 2009; Nemeth et al. 2009). These findings support the potential of allogeneic MSC therapy as a preferred approach, enabling rapid administration of ready-to-use cell products during acute infection onset, such as in sepsis. Expression of MSCs derived AMPs: current status including species variations The expression of AMPs by MSCs varies widely depending on species and tissue sources. For instance, murine BM-MSCs and AT-MSCs express cathelin-related antimicrobial peptide (CRAMP) and LL-37, respectively (Johnson et al. 2017), while lipocalin-2 (Lcn 2) is also produced by murine BM-MSCs (Gupta et al. 2012). Interestingly, mouse AT-MSCs exhibit antimicrobial activity in the presence of Ophiophagus hannah L-amino acid oxidase (oh-LAAO), even in the absence of detectable endogenous AMP expression (Mot et al., 2017). In human MSCs, antimicrobial functionality is linked to the expression of several AMPs and immunomodulatory genes. These include Indoleamine 2,3-dioxygenase-1 (IDO-1) and Indoleamine 2,3-dioxygenase-2 (IDO-2), which are upregulated under IFN-γ stimulation (Müller et al. 2009; Croitoru-Lamoury et al. 2011), as well as Cathelicidin-2 (CATHL2) (Sutton et al. 2016). Human MenSCs express hepcidin, contributing to direct antimicrobial activity against bacteria, fungi, and viruses (Alcayaga-Miranda et al. 2015). LL-37 and beta-defensins have been identified in human BM-MSCs, AT-MSCs, and UC-MSCs, further supporting their broad antimicrobial repertoire (Moeinabadi-Bidgoli et al. 2022). Higher expression of cathelicidin, ERK (Extracellular signal-regulated kinase), MyD88 (Myeloid Differentiation primary response gene 88), and TLR-9 (Toll-like receptors 9) are observed in the blood of women in the pre-pregnancy, pregnancy, and their infant cord blood (Madanchi et al. 2022). Veterinary species also demonstrate diverse AMP expression profiles. Bovine BM-MSCs and AT-MSCs express bBD4A, while NK1 is specific to AT-MSCs (Cahuascanco et al. 2019). Equine p