Speaker
Description
Introduction
In recent years, there has been growing evidence that mesenchymal stem cells (MSCs) are not truly immune-privileged but immune-evasive, and thus, their recognition and elimination by the immune system in the allogeneic setting should be considered. In this regard, antibody production after MSC allogeneic administration MSCs has been demonstrated in several species, including the horse, which is highly relevant both as patient and as translational model. The development of immune memory mechanisms could impact MSC clinical application and potentially limit their repeated administration. Proinflammatory priming of MSCs can potentiate their regulatory ability in vivo but increased expression of the major histocompatibility complex (MHC) might also increase their immunogenicity. Moreover, MSC differentiation may influence both their immunomodulation and immunogenicity.
This study will assess the humoral immune response to equine MSCs, unmanipulated (MSC-naïve), pro-inflammatory stimulated (MSC-primed) and chondrogeneically differentiated (MSC-chondro) by evaluating the production of cytotoxic allo-antibodies directed against donor’s equine leukocyte antigen (ELA) after autologous and allogeneic MHC-matched and mismatched administration.
Methodology
Three animals homozygous for specific MHC haplotypes were selected as MSC donors. Equine MSC-naïve, MSC-primed or MSC-chondro were obtained and encapsulated in alginate hydrogels, and subcutaneously placed in either the donor horses (autologous) or in MHC-matched or MHC-mismatched recipient horses. Each animal received three MSC implants with the same type of MSCs on one neck side. The implants were removed after 1, 3 and 6 weeks. One month after removing the last implant, each animal was re-exposed to the same MSCs by repeating the whole procedure in the contralateral neck side to assess the possible development of immune memory mechanisms.
Peripheral blood from each horse was collected before implant placement and serially at each time-point of removal. The sera were harvested and used to assess the humoral immune response over time and under the different conditions by using microcytotoxicity assays, in which sera were exposed to MSCs from the corresponding donor. This methodology has been previously described to detect the presence of cytotoxic allo-antibodies after MSCs administration in the horse. MSC targeting was assessed using the scoring system previously described: score 1 < 10%; score 2, 10–19%; score 4, 20–49%; score 6, 50–80%; score 8, 81–100% of dead cells.
Results
According to previous results, autologous and allogeneic MHC-matched recipients did not develop antibodies against the ELA of the MSC donor, regardless of having received MSC-naïve, MSC-primed or MSC-chondro. All the samples of these animals were scored as 1 or 2, which reflects non-significant presence of allo-antibodies in sera.
However, higher scores were observed in sera from animals receiving MHC-mismatched MSCs in the tree conditions, reflecting recognition by the recipient's immune system and the production of allo-antibodies.
Conclusion
The compatibility between donor and recipient is a key point to consider in order to avoiding the production of immune memory mechanisms against allogeneic MSCs, including antibody formation against donor’s MHC. The immune response elicited against equine allogeneic MSCs and the factors influencing it must be further studied to develop more effective and safer cell therapies.
