Figure 2

Cytotoxic antibody responses to allogeneic (major histocompatibility complex class I and class II mismatched) donor ELA-A2 mesenchymal stromal/stem cells by recipient horses A to F. The cytotoxic antibody titer was determined by the highest dilution (N) of each recipient serum sample that resulted in killing of at least 80% of donor peripheral blood leukocytes (PBLs). Ab, antibodies detected by the presence of donor PBL death, but with donor PBL death below the cutoff value of 80%; No Ab, no antibodies detected (no donor PBL death). As shown, four recipient horses (Horses B, C, E, and F) had strong anti-ELA-A2 antibody responses which persisted for the duration of the experiment, while two recipient horses (Horses A and D) had weak responses. ^∨Both weak responders A and D received a second injection of donor mesenchymal stromal/stem cells at 5 weeks (35 days). ELA-A2, equine leukocyte antigen haplotype.