Calcium-sensing receptor autoantibody-mediated hypoparathyroidism associated with immune checkpoint inhibitor therapy: diagnosis and long-term follow-up

Figures

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  Figure 1. Time course of biochemical tests. The results of biochemical tests are shown for corrected calcium (normal range: 8.4–10.2 mg/dL), phosphate (normal range: 2.5–4.5 mg/dL), ionized calcium (normal range: 1.13–1.32 mmol/L), magnesium (normal range: 1.8–2.9 mg/dL), and intact parathyroid hormone (PTH) (normal range: 15–65 pg/mL) from the start of acute hypocalcemia to the most recent follow-up visit.

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  Figure 2. Response of the patient to ipilimumab plus nivolumab treatment. Positron emission tomography (PET) scans showing the patient prior to treatment (left-hand panel) and the complete response to treatment (right-hand panel) with disappearance of all the patient’s cancer lesions 2 years after the start of immune checkpoint inhibitor (ICI) therapy.

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  Figure 3. Calcium-sensing receptor (Casr) and NACHT leucine-rich repeat protein 5 (NALP5) antibody tests. The upper limit of healthy control sera in the CaSR antibody assay was a CaSR antibody index of 2.69. The upper limit of healthy control sera in the NALP5 antibody assay was an NALP5 antibody index of 1.73. The upper limit for each assay is shown by a dotted line.

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  Figure 4. Characterization of the patient’s calcium-sensing receptor (CaSR) antibodies. (A) Epitope identification. Patient post-treatment serum samples and sera from 10 healthy controls were evaluated at a dilution of 1:100 in ELISAs for antibodies against CaSR peptides 41–69, 75–115, 114–126, 138–170, 171–195, 214–238, 260–340, 344–358, and 374–391. The CaSR antibody index (mean±SD) is shown for three experiments. (B) Effect of the patient’s CaSR antibodies on CaSR activity. Changes in inositol-1-phosphate (IP1) accumulation were measured in response to Ca2+ in human embryonic kidney 293 cells expressing the receptor (HEK293-CaSR) cells preincubated with the patient’s purified CaSR antibody against CaSR peptide 114–126 at a 1:100 dilution prior to stimulation with Ca2+ at a final concentration of 1.5 mM. HEK293-CaSR cells without preincubation with antibody and preincubated with IgG from a healthy individual were included as controls. Intracellular IP1 accumulation was measured using a IP-One ELISA. The mean (±SD) IP1 accumulation is shown for three experiments.