Allogeneic major histocompatibility complex‐mismatched equine bone marrow‐derived mesenchymal stem cells are targeted for death by cytotoxic anti‐major histocompatibility complex antibodies

Abstract

Summary Background Allogeneic mesenchymal stem cells (MSCs) are a promising cell source for treating musculoskeletal injuries in horses. Controversy exists, however, over whether major histocompatibility complex (MHC)-mismatched MSCs are recognised by the recipient immune system and targeted for death by a cytotoxic antibody response. Objectives To determine if cytotoxic anti-MHC antibodies generated in vivo following MHC-mismatched MSC injections are capable of initiating complement-dependent cytotoxicity of MSCs. Study design Experimental controlled study. Methods Antisera previously collected at Days 0, 7, 14 and 21 post-injection from 4 horses injected with donor MHC-mismatched equine leucocyte antigen (ELA)-A2 haplotype MSCs and one control horse injected with donor MHC-matched ELA-A2 MSCs were utilised in this study. Antisera were incubated with ELA-A2 MSCs before adding complement in microcytotoxicity assays and cell death was analysed via eosin dye exclusion. ELA-A2 peripheral blood leucocytes (PBLs) were used in the assays as a positive control. Results Antisera from all 4 horses injected with MHC-mismatched MSCs contained antibodies that caused the death of ELA-A2 haplotype MSCs in the microcytotoxicity assays. In 2 of the 4 horses, antibodies were present as early as Day 7 post-injection. MSC death was consistently equivalent to that of ELA-A2 haplotype PBL death at all time points and antisera dilutions. Antisera from the control horse that was injected with MHC-matched MSCs did not contain cytotoxic ELA-A2 antibodies at any of the time points examined. Main limitations This study examined MSC death in vitro only and utilized antisera from a small number of horses. Conclusions The cytotoxic antibody response induced in recipient horses following injection with donor MHC-mismatched MSCs is capable of killing donor MSCs in vitro. These results suggest that the use of allogeneic MHC-mismatched MSCs must be cautioned against, not only for potential adverse events, but also for reduced therapeutic efficacy due to targeted MSC death.

Tenogenically Induced Allogeneic Peripheral Blood Mesenchymal Stem Cells in Allogeneic Platelet-Rich Plasma: 2-Year Follow-up after Tendon or Ligament Treatment in Horses

“…Currently, the significance of these antibodies is unknown and warrants further research in case of repeated injections ( 39 ). In addition, an in vitro study described a cytotoxic antibody response in recipient horses after the injection of allogeneic MHC-mismatched BM-derived MSCs ( 40 ). This indicates that MHC levels are crucial for allogeneic transplantations and warrant analyses before clinical use in horses.…”

Mammalian MSC from selected species: Features and applications

“…Similarly, cross‐species immunotolerance was obtained using human placenta‐derived MSC to treat myelomeningocele in utero in a fetal ovine model , or canine placenta‐derived MSC to treat neurological disorders in dogs . Horses, however, which were transplanted with allogeneic MHC‐mismatched MSC, contained antibodies that killed donor MSC in an in vitro cytotoxicity assay indicating that MHC compatibility seemed required for acceptance of MSC transplants . In line, MSC injection into healthy horses caused a mild increase of blood CD8 T‐cells and regulatory T cells in the spleen, which might indicate a cytotoxic response to the allogeneic cell transplants.…”

The Potential of Mesenchymal Stem Cells to Treat Systemic Inflammation in Horses

“…Despite the development of antibodies, no adverse clinical signs were reported. Development of cytotoxic ELA-A2 antibodies in vivo following incubation with allogeneic bone marrow derived MSCs has been reported (132). Evidence also exists that differentiation has an influence on equine MSC immunogenicity.…”