In Vivo Tracking of Transplanted Progenitor Cells after Photocoagulation Using Multimodal Photoacoustic Microscopy, OCT, and Fluorescence Imaging

Abstract

Purpose : Stem cell therapy offers a great promise for retinal degenerations which have no current effective treatments, including age-related macular degeneration and retinal pigmentosa. To achieve optimized treatment outcome, it is important to utilize non-invasive imaging technology to track the behaviors of stem cells after transplantation. This study describes a multimodal photoacoustic microscopy (PAM), optical coherence tomography (OCT), and fluorescence imaging for noninvasive and real-time monitoring of stem cells delivered into the subretinal space and follows their biodistribution, survival, migration, and differentiation longitudinally for up to 3 months.

Methods : A precursor human retinal pigment epithelial cell (ARPE-19) were labeled with ultrapure chain-like clusters gold nanoparticle (CGNP) conjugated with indocyanine green and RGD peptide at 100 µg/mL for 24 h. PAM images were acquired at 578 nm and 650 nm were overlaid on the same image plane and on the OCT image. Rabbits were treated with retinal laser photocoagulation to induce RPE injury and received subretinal injection of 30 µL (10⁶ cells/ µL) labeled cells into the subretinal space and monitored before and at 1, 3, 7, 14, 21, 28 days, 2 and 3 months after transplantation. All animal studies were approved by the UM IACUC.

Results : PAM images obtained at 578 nm show hemoglobin in retinal vasculature with high contrast. PAM images acquired at 650 show the distribution of ARPE-19 cells in the subretinal space due to strong absorption of the internalized CGNPs inside the cells and minimal absorption of hemoglobin at 650nm. ICG fluorescence imaging correlated well with the 650nm PAM images initially but rapidly lost fluorescent signal after only 1 week. The transplanted cells localized to areas of photocoagulation injury by day 7 post-injection. Subretinal injection of labeled ARPE-19 cells enhanced fluorescent intensity by 39-fold post-injection, PA signal by 30-fold post-injection, and OCT intensity by 180% post-injection. Immunofluorescentanalysis indicated that ARPE-19 cells were effectively localized to areas of damage corresponding to multimodal in vivo imaging.

Conclusions : This study represents an advanced technique for long-term tracking of the transplanted cells using multimodal PAM, OCT, and fluorescence imaging with the assistance of CGNP.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.