Measuring neuroinflammation in hemiparkinsonian rhesus treated with iPSC-derived dopaminergic neuronal grafts using [18F]FEPPA PET

182 Background: Cell replacement with induced pluripotent stem cell-derived midbrain dopaminergic neuronal grafts (iPSC-mDA) is a promising therapeutic strategy for Parkinson’s disease (PD). Without the aid of immunosuppression, use of allogeneic iPSC-mDA (obtained from a donor) in therapy may trigger an immune response leading to increased neuroinflammation at the site of the grafts. Compared to allogeneic iPSC-mDA, cell replacement with autologous iPSC-mDA (obtained from the same individual) should not trigger this response. Objectives: The purpose of this study was to assess in vivo using the PET TSPO radiotracer, [18F]FEPPA, whether rhesus subjects treated with autologous or allogeneic iPSC-mDA show increased microglial activation (a biomarker for neuroinflammation) at the graft sites. Methods: The present study was performed in strict accordance with the recommendations in the NIH Guide for the Care and Use of Laboratory Animals. Experimental procedures were approved by the IACUC of the University of Wisconsin-Madison. Ten adult male rhesus macaques received a unilateral (right) intracarotid artery injection of the neurotoxin MPTP under sterile surgical conditions and isoflurane anesthesia. Six to eight months later, four primates received autologous iPSC-mDA and six primates received allogeneic iPSC-mDA to the ipsilateral (right) putamen. Cell delivery was performed using real-time intraoperative MRI (IMRI) in a 3-T GE SIGNA MRI scanner. Twenty four months following surgery, the primates underwent 120-minute dynamic [18F]FEPPA scans in a microPET Focus 220 scanner. Region of interest (ROI) masks were generated for each iPSC-mDA graft site through segmentation of the IMRI data (Figure 1). ROIs for the left putamen (control region) and cerebellum (unaffected by surgery) were generated from an in-house rhesus atlas. The ROIs were registered to the [18F]FEPPA PET data to extract time-activity curves, and 90-120 minute summed PET frames were used to generate an asymmetry index (L-R)/(L+R)/2 for the ROIs to assess hemispheric differences of [18F]FEPPA uptake. Results: Average time-activity curves (Figure 2) for primates with allogeneic and autologous iPSC-mDA grafts reveal disparity in the uptake of [18F]FEPPA at the site of the grafts between groups. On average, primates with allogeneic grafts show increased uptake at the graft sites relative to the control, whereas no difference is observed with the autologous grafts. Table 1 displays the asymmetry indices for the putamen and cerebellum. From the asymmetry analysis, primates with allogeneic grafts show significant asymmetry of [18F]FEPPA uptake in the putamen compared to primates with autologous grafts (two-sample t-test: p Conclusions: Our results demonstrate that [18F]FEPPA PET can be used as an in vivo biomarker of neuroinflammation after autologous or allogeneic iPSC-mDA intracerebral grafts. Post mortem analysis of the brains, including evaluation of CD68 immunoreactivity as a marker of microglia recruitment, is currently underway to validate the PET data.