Intravenous indocyanine green dye is insufficient for robust immune cell labelling in the human retina

Abstract

It is not currently possible to reliably visualise and track immune cells in the human central nervous system or eye. Previous work demonstrated that indocyanine green (ICG) dye could label immune cells and be imaged after a delay during disease in the mouse retina. We report a pilot study investigating if ICG can similarly label immune cells within the human retina. Twelve adult participants receiving ICG angiography as part of routine standard of care were recruited. Baseline retinal images were obtained prior to ICG administration then repeated over a period ranging from 2 hours to 9 days. Matched peripheral blood samples were obtained to examine systemic immune cell labelling and activation from ICG by flow cytometry with human macrophage cultures as positive controls. Differences between the delayed near infrared ICG imaging and 488 nm autofluorescence was observed across pathologies, likely arising from the retinal pigment epithelium (RPE). Only one subject demonstrated ICG signal on peripheral blood myeloid cells and only three distinct cell-sized signals appeared over time within the retina of three participants. No significant increase in immune cell activation markers were detected after ICG administration. ICG accumulated in the endosomes of macrophage cultures and was detectable above a minimum concentration, suggesting cell labelling is possible. ICG can label RPE and may be used as an additional biomarker for RPE health across a range of retinal disorders. Standard clinical doses of intravenous ICG do not lead to robust immune cell labelling in human blood or retina and further optimisation in dose and route are required.

Indocyanine Green-Labeled Platelets for Survival and Recovery Studies

“…This may indicate successful ICG platelet-labeling stability in survival and recovery studies in vivo. ICG stability in serum and its non-targetability are commonly described challenges and are required to be tested in vivo [45,46]. Here, we present a successful and stable ICG labeling of platelets in WB ex vivo as a proof of concept for clinical trials.…”

ICG‐based laser treatments for ophthalmic diseases: Toward their safe and rapid strategy

“…The combination of light guidance and molecular targeting for precise drug delivery may have unexpected surprises. For instance, we noticed a clinical trial that tries to label immune cell in the human retina [71], meaning that specific cell therapy based on PS might be possible. In clinical practice, a class of PS drugs represented by ICG is mainly used for clinical diagnosis, such as surgical navigation of liver cancer.…”

Triazole-derivatized near-infrared cyanine dyes enable local functional fluorescent imaging of ocular inflammation

“…There is proof of concept in mouse that infiltrating cells can be actively imaged with ICG (Sim et al, 2015) however, imaging immune cells in deeper retinal layers or the heavily pigmented choroid will necessitate the use of fluorescent labels. Previous studies have demonstrated that ICG could label infiltrating leukocytes in a laser-induced CNV mouse model of age-related macular degeneration (AMD) after depot administration (Sim et al, 2015), but intravenous ICG was insufficient to detect immune cell labelling in the human eye (Bell et al, 2020).…”