Effect of cryopreservation and HLA-DR matching on the cellular immunogenicity of human cardiac valve allografts.

The cellular immunogenicity of fresh and cryopreserved human cardiac valve leaflets was measured in a lymphocyte proliferation assay. One fresh leaflet and a cryopreserved leaflet derived from the same valve were cut into 2 mm diameter pieces and incubated with responder peripheral blood mononuclear cells, matched or mismatched for HLA-DR. The tritiated thymidine incorporation into the lymphocytes measured after 7 days, was expressed as stimulation index. Fresh, HLA-mismatched valve pieces induced high stimulation index in all cases (median 9, range 4 to 117). The cryopreservation procedure resulted in a significantly lower stimulation index (p = 0.002, Wilcoxon), with a median stimulation index of 2 (range 0 to 9). In the instances where HLA-DR matched combinations were studied, cryopreservation was also associated with lower stimulation index. HLA matching itself was able to reduce the stimulation index both with cryopreserved and fresh valve pieces as stimulator, resulting in a median stimulation index of 4 (range 2 to 117) for the HLA-DR-mismatched and 1 (range 0 to 5) for the matched lymphocytes (p = 0.006, Wilcoxon). In conclusion, human cardiac valves are able to stimulate immune competent cells in vitro, even after cryopreservation. The cellular allogeneic response in vitro could be an explanation for valve allograft degeneration observed in the clinic. Matching for HLA-DR may reduce these effects.