Quantifying specificity of stem cell delivery to the trabecular meshwork

Abstract

Purpose : Cell therapy to functionalize the trabecular meshwork (TM) has promise for IOP control in glaucoma, but off-target cell delivery is undesirable. Here we introduce a novel method of magnetically-steered cell delivery to the TM and quantify its performance.

Methods : 11 eyes of 3-4 mo wild-type C57BL/6J mice were intracamerally injected with human adipose-derived mesenchymal stem cells doubly labeled with superparamagnetic nanoparticles (enabling magnetic cell steering) and a fluorophore (enabling cell localization). Cell delivery to the TM used 1 of 3 methods:
1. No Magnet: cells were transported passively by aqueous humor flow (n = 3)
2. Ring: a ring magnet (ID = 2 mm) was placed over the eye at the limbus to attract cells to TM (n = 4)
3. Point: The tip of a thin stainless steel rod attached to a small cube magnet was moved circumferentially adjacent to the limbus during cell injection to steer cells to the TM (n = 4).
The No Magnet and Ring methods have been used previously. Eyes were enucleated 48 hrs after injection, fixed in formalin and sagittaly cryosectioned. TM specificity of cell distribution in each section was quantified by an "off-target index (OTI)”:
Off-target Index: ∑ AB
A = (distance of pixel from TM measured along iris) / (total length of iris)
B = (fluorescent intensity) / ∑fluorescent intensity
where both sums are over all pixels in the image (Fig 1). Lower OTI values indicate more TM-specific delivery. At least 2 quadrants were analyzed/eye.

Results : OTI values for No Magnet and Ring were similar (0.36 ± 0.10 vs. 0.37± 0.13, respectively; mean ± SD; p = 0.84, linear mixed-effect model), but Point delivered the cells closer to the TM, with a significantly (p < 10^-10) lower OTI value (0.07 ± 0.07; Fig 2).

Conclusions : A novel magnetic technique for steering magnetically responsive stem cells to the TM was much more efficient vs. other methods and can potentially increase the therapeutic benefits of TM cell therapy in glaucoma, especially in larger human eyes.
Support: NIH grant R01 EY030071 (CRE, SYE, MHK) and the Georgia Research Alliance (CRE).

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Figure 1. Fluorescently labeled cells (red) delivered to the anterior chamber of mouse eyes using different methods. Insets: magnified views of cell-containing regions.

 

Figure 2. OTI (see text) for different delivery methods. Each dot is one sagittal section, grouped by color for each eye. * p < 10^-10.