ABSTRACT: The immunomodulatory potential of mesenchymal stromal cells (MSCs) has led to their widespread exploration in treating various inflammatory conditions. MSCs sourced from adult tissues such as bone marrow, Wharton’s jelly, and adipose tissue are multipotent and exhibit strong stemness characteristics. According to the International Society for Cell and Gene Therapy, MSCs are defined by their plastic-adherent, fibroblast-like morphology, expression of surface markers CD90, CD105, and CD73 (positive), absence of markers like CD34, CD45, and HLA-DR (negative), and their ability to differentiate into multiple lineages in vitro. Despite promising therapeutic outcomes, the clinical application of MSCs faces several obstacles. These include limitations associated with autologous stem cell efficiency, the invasiveness of administration procedures, risks of immune rejection, and the high costs associated with cell isolation, maintenance, and storage. Additionally, ensuring consistent cell viability, preventing spontaneous differentiation, and maintaining quality control contribute further to the financial and logistical challenges, limiting broader clinical accessibility. In recent years, the MSC-derived secretome has emerged as a compelling alternative in regenerative medicine. As MSCs exert many of their therapeutic effects via paracrine signaling rather than direct tissue integration, the secretome—a complex mix of cytokines, growth factors, extracellular vesicles (EVs), and microRNAs—offers a cell-free therapeutic option. However, the composition of the secretome is highly variable and influenced by factors such as tissue source, donor variability, culture conditions, passage number, and environmental cues. The MSC secretome contains a diverse range of biologically active molecules, including anti-inflammatory, pro-angiogenic, and signaling factors. Key components include growth factors like VEGF, TGF, FGF, HGF, and IGF; chemokines such as CCL-2, CCL-5, CCL-10, and CCL-20; and microRNAs like miR-27a, miR-133, miR-196a, miR-206, miR-15a/b, and miR-125b-5p. Additionally, anti-apoptotic and immunoregulatory molecules such as Indoleamine 2,3-dioxygenase (IDO) and Interleukin-10 (IL-10), as well as ECM-related proteins, are present. The functional plasticity of the MSC secretome can be enhanced by altering culture conditions—for instance, hypoxic environments, 3D culture systems, or exposure to specific stimulants. These strategies influence the secretome’s role in immunomodulation, extracellular matrix (ECM) remodeling, and angiogenesis. Notably, MSCs exposed to inflammatory stimuli adopt a more immunosuppressive phenotype, promoting the release of anti-inflammatory factors. Our study investigates the impact of priming MSCs with a defined protein cocktail on the composition of their secretome.
Raviraja Seetharam 
