Pathologic findings in retinal pigment epithelial cell implantation for Parkinson disease

Abstract

Background: Attempts at cell-based dopamine replacement therapy in Parkinson disease (PD) have included surgical implantation of adrenal medullary, fetal mesencephalic, and cultured human mesencephalic tissue grafts. Trials involving putamenal implantation of human retinal pigment epithelial (RPE) cells in PD have also been performed. Neuropathologic findings in humans undergoing RPE cell implantation have not heretofore been reported. We describe the brain autopsy findings from a subject enrolled in a clinical trial of RPE cells in gelatin microcarriers for treatment of PD, and suggest factors which may have impacted cell survival.

Methods: A 68-year-old man underwent bilateral surgical implantation of 325,000 RPE cells in gelatin microcarriers (Spheramine) but died 6 months after surgery. The left cerebral hemisphere was examined. Routine postmortem formalin fixation was performed and standard, as well as immunohistochemical methods used to highlight senile plaque and Lewy body pathologic changes, iron deposition, cellular inflammation, and reactive astrocytosis in implant regions. Manual cell counts were done of RPE cells.

Results: Hematoxylin-eosin and alpha-synuclein immunostains confirmed the diagnosis of PD. Needle tracts with matrix material and RPE cells were observed in the context of local inflammatory and astrocytic reactive change. A total of 118 cells were counted (estimated 0.036% survival).

Conclusions: Retinal pigment epithelial cells are seen in human brain 6 months postimplantation, but overall survival of implanted cells appeared poor.

Figure 1 Parkinson disease neuropathology Hematoxylin-eosin (H-E) stained frozen section of substantia nigra (SN) (A) and H-E stained paraffin section of locus ceruleus (LC) (B) showing severe pigmented neuron loss in SN and Lewy bodies in residual LC neurons (arrows). α-Synuclein immunostaining highlights rare immunoreactive neuron in frontal cortex (C).

Figure 2 Representative tract lesions and associated findings (A) Low power view of 2 tract sites, with upper lesion containing cluster of hemosiderin-containing cells shown in higher power in (B), and stained with Perl's iron in (E). (C) Linear tract lesion in internal capsule (arrow). (D) Tract focus containing matrix material without retinal pigment epithelial (RPE) cells. (F) Perl's iron stain of another tract site with matrix material and dense aggregate of likely hemosiderin-containing macrophages. (G–K) Hematoxylin-eosin stain of tract sites showing basophilic matrix material with representative RPE cell neuromelanin profiles. (L) Matrix material within Virchow-Robin space and abutting small artery in inferior putamen. Scale bar: A, C 200 μm; B 50 μm; D–F 30 μm; G 20 μm; H–K 30 μm; L 150 μm.

Figure 3 Representative immunostaining results (A) CD68 immunostain of tract lesion demonstrating inflammatory cell infiltration. (B) Glial fibrillary acidic protein immunostain shows rare immunoreactive astrocytes encroaching on matrix, with retinal pigment epithelial (RPE) cell within matrix lattice (arrow). (C) RPE 65 immunostain of normal human retina highlights RPE cells. (D) RPE 65 immunostain of matrix-containing tract site showing absence of immunoreactivity. Scale bar: 20 μm.