Composition of allogeneic equine orthobiologics and their repeated intra‐articular administrations

Background Orthobiologics such as platelet‐rich plasma (PRP) and alpha‐2‐macroglobulin (A2MG) are increasingly used for equine musculoskeletal injuries. However, their composition and safety with repeated allogeneic intra‐articular administration remain poorly investigated. Objectives To characterise orthobiological preparations with or without 1 h incubation at 37°C (PRP, PRP + Inc, A2MG, A2MG + Inc) and evaluate immunological safety following repeated intra‐articular administration (autologous and allogeneic) of PRP combined with A2MG + Inc in healthy horses. Study Design In vivo experiments. Methods This was a two‐phase study with biochemical characterisation followed by repeated intra‐articular injections in four healthy horses. Blood was processed to produce PRP or A2MG, with or without incubation, and characterised using haematology, biochemistry and enzyme‐linked immunosorbent assay. For immunogenic assessment, healthy horses received three intra‐articular injections of combined PRP and A2MG + Inc at 2‐week intervals (Days 0, 14 and 28) (allogeneic n = 3, autologous n = 1). Blood and synovial fluid were collected on Days 0, 14, 28 and 42. Blood was analysed for haematology, biochemistry, CD4/CD8 ratio and SAA, while synovial fluid was analysed for leukocyte counts and immunoglobulins. Results Biochemical characterisation demonstrated effective removal of blood cells from all orthobiologics. PRP‐based formulations were enriched in platelets and growth factors, whereas A2MG preparations had higher alpha‐2‐macroglobulin and lower growth factor levels. Repeated intra‐articular administration of PRP and A2MG + Inc caused no clinically relevant changes in systemic or synovial immune cells, lymphocyte subsets, or acute‐phase markers, indicating no immunological activation. Main Limitations Small sample sizes, the limited scope of characterised compositions and the use of combined PRP and A2MG + Inc for which only individual components were characterised. Conclusions PRP may promote repair via growth factors, and A2MG is proposed to modulate immunity and catabolism. Repeated intra‐articular injections of PRP with A2MG + Inc caused no systemic or synovial immune response, with no differences between autologous and allogeneic use.