Control of hypercalcaemia of parathyroid carcinoma by immunisation

Patients with parathyroid tumours can develop extreme hypercalcaemia and osteitis fibrosa cystica. Clinical features result from the action of parathyroid hormone (PTH) on bone receptors. Because this hormone is produced in microgram quantities, inhibition of its metabolic effects with potent PTH antibodies should be possible. We tested whether an immunisation with synthetic human and bovine PTH peptides could stimulate autoantibodies against PTH.

A patient with metastatic parathyroid carcinoma in the lungs and pleura developed severe bone disease and extreme hypercalcaemia that proved resistant to conventional therapy. She was immunised with 200 microg human and bovine PTH peptides and 50 microg human PTH. Booster doses were also given at 4 weeks and 11 weeks. The patient was then seen every week.

Antibodies against PTH were produced within 4 weeks of initial immunisation and titres increased with repeated doses of immunogens. Total serum calcium concentrations, which had ranged from 3.5 mmol/L to 4.2 mmol/L over the previous 18 months, fell to between 2.5 mmol/L and 3.0 mmol/L over 6 months of therapy. This fall was accompanied by striking clinical improvement.

We believe this is the first use of immunotherapy to control remote, non-metastatic complications of malignant disease. B-cell tolerance to human PTH was broken by immunisation with PTH peptides in adjuvant. This therapeutic approach could be used to control excess hormone production in several types of endocrine tumour and may have applications in other diseases.