Humoral immune response to equine mesenchymal stem/stromal cells (MSCs): MHC compatibility has more influence than inflammatory priming or chondrogenic differentiation.

Overview

• This study investigated how the immune system of horses responds to repeated administration of different types of mesenchymal stem/stromal cells (MSCs) from donors with varying degrees of genetic compatibility.
• It found that the genetic compatibility at the major histocompatibility complex (MHC) between donor and recipient is the key factor affecting immune responses, outweighing impacts from cell inflammation priming or differentiation.

Background

• Mesenchymal stem/stromal cells (MSCs): These cells have promising therapeutic potential for regenerative medicine and immune modulation.
• Allogeneic therapies: Using donor-derived MSCs rather than the recipient’s own cells enables off-the-shelf treatments but risks immune recognition and rejection.
• Immune response concerns: When the recipient’s immune system recognizes donor MSCs as foreign, it can produce antibodies (humoral response) that reduce therapy effectiveness or cause adverse effects.
• Equine model: Horses serve both as veterinary patients and as models to study human-related MSC immunology due to similarities in immune system dynamics.

Research Aims

• To evaluate how repeated injections of differentially treated equine MSCs influence the humoral immune response based on MHC compatibility.
• To determine the relative importance of MHC compatibility versus inflammatory priming and chondrogenic differentiation in eliciting allo-antibody production.

Methodology

• MSC Preparation:
  • MSC-naïve: Untreated, basal state.
  • MSC-primed: Treated with pro-inflammatory agents to activate them before implantation.
  • MSC-chondro: Induced to partially differentiate towards cartilage-producing cells (chondrogenic differentiation).
• Scaffold embedding: MSCs were placed into alginate scaffolds to enhance localized delivery and retention in tissue.
• Recipient types:
  • Autologous recipients (self MSCs)
  • MHC-matched allogeneic recipients (genetically compatible donors)
  • MHC-mismatched allogeneic recipients (genetically different donors)
• Repeated subcutaneous implantation: Scaffolded MSCs were implanted multiple times over weeks.
• Serum analysis: Collected before and at intervals after each administration (1, 3, 6 weeks) and tested in various dilutions using two-stage microcytotoxicity assays to detect cytotoxic allo-antibodies against donor MHC.

Key Findings

• No antibody production in autologous and MHC-matched recipients: Neither baseline MSCs, primed MSCs, nor chondrogenically differentiated MSCs triggered humoral responses when donor and recipient shared MHC.
• Allo-antibody generation in MHC-mismatched recipients: Immune recognition occurred after the first MSC administration and increased markedly after the second.
• MSC type impact on immune strength: Although all MSC types triggered antibodies, MSC-chondro caused the strongest humoral immune response in mismatched individuals.

Conclusions and Implications

• MHC matching is crucial: Compatibility between donor and recipient at the MHC locus plays a dominant role in preventing immune responses to allogeneic MSC-based therapies.
• Inflammatory priming and differentiation have limited effect: While these modifications can influence cell behavior, they do not significantly alter the humoral immune response if MHC mismatch exists.
• Clinical relevance for equine and potentially human therapies:
  • Careful donor-recipient MHC matching may allow safe repeated MSC administrations without antibody development.
  • Supports the design of MSC treatments with consideration of genetic compatibility to enhance safety and efficacy.