Phosphodiesterase 10A IgG: A novel biomarker of paraneoplastic neurologic autoimmunity

Abstract

Objective: To describe a novel antibody biomarker of neurologic paraneoplastic autoimmunity specific for phosphodiesterase 10A (PDE10A), a striatum-enriched phosphodiesterase, and to characterize the clinical phenotype of patients with PDE10A immunoglobulin G (IgG).

Methods: We describe 7 patients with autoantibodies specific for PDE10A identified in the Mayo Clinic Neuroimmunology Laboratory. Patient specimens (sera, 7; CSF, 4) produced identical basal ganglia-predominant synaptic staining of murine brain tissue by indirect immunofluorescence. The autoantigen was identified by immunoprecipitation and mass spectrometry as PDE10A, and confirmed by antigen-specific recombinant Western blot and cell-based assays, and immune absorption experiments.

Results: The median patient age was 70 years (range 66-76); 4 were men. Four patients with clinical information available had movement disorders (hyperkinetic in 3 [chorea, ballismus, dystonia] and parkinsonism in 1). All patients but one had cancer (lung [adenocarcinoma 1, squamous cell carcinoma 1, poorly differentiated mesenchymal carcinoma 1], renal adenocarcinoma 2, and pancreatic adenocarcinoma 1). Two of the 7 patients developed hyperkinetic movement disorders during treatment with immune checkpoint inhibitors (nivolumab and pembrolizumab), though none of 26 cancer control patients treated with immune checkpoint inhibitors harbored PDE10A IgG in their serum. MRIs from those 2 patients with hyperkinetic movement disorders demonstrated fluid-attenuated inversion recovery/T2 basal ganglia hyperintensities, and their CSF harbored unique oligoclonal bands. One of those 2 patients had substantial improvement after corticosteroids. One patient's renal adenocarcinoma expressed PDE10A by immunohistochemistry.

Conclusions: PDE10A IgG defines a novel rare neurologic autoimmune syndrome and expands the spectrum of diagnosable paraneoplastic CNS disorders. The intracellular location of PDE10A suggests a T-cell-mediated pathology targeting cells displaying MHC1-bound PDE10A peptides.

Figure 1. Detection of the patients with phosphodiesterase 10A autoantibody

Indirect immunofluorescence assay performed on murine tissue with patient serum demonstrates synaptic staining of the basal ganglia (A), more prominent than the hippocampus (B) and to a lesser extent the granular layer of the cerebellum (C). (D) Western blot probing of lysed membrane fraction of pig basal ganglia with serum immunoglobulin G (IgG) of 3 patients identified an immunoreactive band ∼75 kDa and another >200 kDa that were not seen with normal control serum IgG. Elution of patient 1's IgG from the corresponding 75 kDa excised nitrocellulose band reproduced the original tissue staining pattern when applied to mouse brain as the patient's serum (E), while an IgG elution from a control band (∼150 kDa) did not (not shown). (F) T2 fluid-attenuated inversion recovery MRI of patient 4 with bilateral basal ganglial hyperintensities. GL = granular layer; GP = globus pallidus; Hi = hippocampus; ML = molecular layer; SN = substantia nigra; Str = striatum.

Figure 2. Antigen characterization

(A) Rabbit phosphodiesterase 10A (PDE10A) immunoglobulin G (IgG) (green) colocalizes with patient serum IgG (red) by confocal indirect immunofluorescence imaging on murine basal ganglia (merged images; yellow). Nuclei are blue (DAPI stained). (B) Recombinant PDE10A Western blot (WB) of 5 patients (6 sera; patient 4 had sera from 2 timepoints) and normal controls. The 2 patients whose serum lacked 75 kDa reactivity in WB testing with pig basal ganglia extracts (figure 1D) were positive by recombinant WB but yielded a less intense signal than the other patients' sera. (C) Cell-based indirect immunofluorescence, commercial PDE10A IgG (green), patient's serum (red), and merged images (yellow); nuclear staining in blue (DAPI). (D) Immune absorption of PDE10A-IgG-positive patient's serum with 2 μg of recombinant PDE10A protein eliminates the basal ganglia staining by indirect immunofluorescence while the control Purkinje-cell cytoplasmic antibody 1 (PCA1)–IgG-positive serum's staining in the perikarya of cerebellar Purkinje neurons is unchanged when absorbed with the same amount of recombinant PDE10A protein.

Figure 3. Immunohistochemistry of renal cell carcinoma (patient 4)

(A, B) Phosphodiesterase 10A (PDE10A) immunohistochemistry in normal control human kidney tissue. The high power image (B) indicates the collecting tubular epithelium with marked expression of PDE10A. The kidney carcinoma tissue of patient 4 shows foci of variable PDE10A immunoreactivity: moderate expression (C, D) or scant PDE10A expression (E, F) in different parts of the tumor. Scale bars in A, C, and E = 100 μm. Scale bars in B, D, and F = 20 μm.