In vitro assessment of parathyroid immunogenicity: the effect of cryopreservation.

Post-parathyroidectomy hypoparathyroidism, although fortunately uncommon, is a disorder of major inconvenience and potential morbidity. Attempts at modifying parathyroid tissue to facilitate allotransplantation without host immunosuppression are warranted. Cryopreservation has been reported to improve survival of canine parathyroid allografts. We employed a modification of the mixed lymphocyte culture to study the effect in vitro of cryopreservation on human parathyroid tissue. Dispersed parathyroid cells from fresh and previously cryopreserved tissue from 10 patients were incubated with unrelated mononuclear cells for 6 days, and incorporation of tritiated thymidine was measured after a 1-day pulse. Studies with irradiated mononuclear cells and parathyroid cells confirmed the model as a one-way test in which mononuclear cells respond to parathyroid cells but not vice versa. An antigenicity index was computed to express mononuclear cell tritiated thymidine incorporation for similar numbers of viable parathyroid cells. Although absolute values of the antigenicity index varied from patient to patient, there were no consistent differences in the antigenicity index of patients' fresh compared with cryopreserved tissue. In an attempt to identify the cells responsible for immunogenicity, we incubated cytocentrifuged parathyroid cell suspensions with antiserum directed at leukocyte common antigen, a marker of lymphoid tissue. Cell suspensions of parathyroid tissue demonstrated leukocyte common antigen-positive cells (median, 2.7% positive; range, 0% to 16%). There were no consistent differences in the number of leukocyte common antigen-positive cells in fresh compared with cryopreserved tissue, and the number of leukocyte common antigen-positive cells did not correlate with the antigenicity index.