Development of monoclonal antibodies against parathyroid hormone: genetic control of the immune response to human PTH

Parathyroid Hormone Monitoring during Total Parathyroidectomy for Renal Hyperparathyroidism: Pilot Study of the Impact of Renal Function and Assay Specificity

Background: Commonly used assays for intact parathyroid hormone (iPTH) detect not only the biologically active 84–amino acid hormone [PTH(1–84)], but cross-react with an N-terminal–truncated fragment. Because iPTH assays often fail to predict success of parathyroidectomy in patients with renal hyperparathyroidism (rHPT), we compared results of a 3rd-generation PTH(1–84) assay (Bio-iPTH; Nichols Institute Diagnostics) with two 2nd-generation iPTH assays (from Nichols and Roche Diagnostics) by evaluating the PTH clearance kinetics during surgical treatment.

Methods: We collected blood samples in short time intervals from 35 consecutive surgical patients with rHPT. Three patients had to be excluded from further calculations; the remainder were grouped according to kidney function and postoperative outcome. All samples were analyzed with the 3 automated PTH assays, which have different specificities.

Results: Twenty minutes after removal of the last gland, the PTH(1–84) values decreased to within the reference intervals in all patients with total and subtotal resection; however, iPTH concentrations normalized in only one half of these patients. In patients with poor renal function, the half-life of PTH(1–84) was shorter than the half-lives obtained with the iPTH assays.

Conclusions: The accuracy of PTH monitoring during surgery for rHPT depends on renal function and assay specificity. All assays tested showed similar effectiveness in detecting missed glands, but the assay for PTH(1–84) gave more reliable results than the iPTH assays, which overestimated the concentration of PTH and hampered the intrasurgical diagnosis of resection sufficiency.

Production and characterisation of monoclonal antibodies to parathyroid hormone (1-34)

Monoclonal antibodies to the biologically active N terminal region of parathyroid hormone (PTH) suitable for use in the measurement of circulating PTH concentrations have proved difficult to produce. In this study, no serum PTH antibody titres could be detected in mice using synthetic human PTH (1-34) (free or coupled to albumin) or PTH (1-10) (coupled to keyhole limpet haemocyanin) as immunogen. A consistent response to PTH (1-34) peptide was obtained in DA rats. We have produced five monoclonal antibodies to PTH (1-34) derived from the fusion of DA rat spleen cells and the mouse myeloma line X63 Ag.8.653. Bulk production of the antibodies was achieved using congenitally athymic mice for ascites production. Antibody assessment studies revealed the antibodies to be sensitive to the oxidation state of the methionine residues in PTH (1-34). Two of the antibodies, 3B3 and 6E3, were shown to be of potential use in measuring circulating PTH (1-84) when used in combination with available antibodies to C terminal PTH. A third antibody, 4G3, which failed to recognise PTH (1-84) when used in combination with 3B3, formed the basis of a specific assay for PTH (1-34).

Monoclonal antibodies to human parathyroid hormone (1-34) and their use in the immunocytochemical detection of parathyroid tumours

Monoclonal antibodies against the biologically active N-terminal fragment of human parathyroid hormone, hPTH (1-34), were produced. The procedure included the use of novel secondary immunization in vitro of mouse spleen cell cultures. Dissociated spleen cells from primary immunized Balb/c mice, were cultured for five days in the presence of thymocyte conditioned media (TCM) and synthetic hPTH (1-34). Contrary to previous findings by other workers, in our hands Balb/c mice responded well. Following immunization the spleen cells were fused with NSl myeloma cells and cultured for eleven days before screening for antibody. Using an enzyme linked immunosorbent assay (ELISA) a number of positive clones were detected. Positive cells were cloned by limiting dilution and fifteen specific monoclonal hybridomas were produced. The immunoglobulin class of the different monoclonal antibodies was found to be IgGl. The immunocytochemical reaction was tested with chief cell carcinoma tissue and found to be clearly positive.