Abstract
Background:
It is well established that the mesenchymal stromal cell (MSC) therapeutic potency can be enhanced by cytokine pre-activation or licensing. However, its effects on therapeutic efficacy of small extracellular vesicles (MSC-sEV) have not yet been well established. Here we report on two different cytokine licensing strategies, using either a pro-inflammatory or anti-inflammatory cytokine and evaluate their therapeutic potency in vitro and in a preclinical model of corneal chemical burn.
Methods:
BALB/c MSCs were cultured with no supplement, recombinant IFNγ, or recombinant TGFβ1 for 72 h. sEV, sEVIFNγ, and sEVTGFβ were then isolated from conditioned medium of parental cells by a combination of ultrafiltration and size exclusion chromatography. Following isolation MSC-sEV were thoroughly characterized for size, marker expression and therapeutic efficacy. To evaluate their immunomodulatory capacity, both naïve and licensed MSC-sEV were tested in in vitro macrophage and T cell assays and in a preclinical corneal injury model.
Results:
Relative to unlicensed sEV, sEVIFNγ exhibited increased expression of MHC I and PD-L1 on their surface, whereas sEVTGFβ expressed higher levels of CD44, CD29, and CD73. For immunomodulatory capacity, only sEVTGFβ was found to reduce macrophage expression of MHC II and CD80 and induced the secretion of anti-inflammatory macrophage cytokines. sEVTGFβ were also found to increase Treg expansion and FOXP3 expression. Given the superior efficacy observed of sEVTGFβ in vitro, this product was evaluated in a preclinical mouse model of corneal chemical burn. sEVTGFβ were applied either topically (day 0, 1, and 3) or subconjunctivally (day 0, and 3), and mice were monitored for 14 days. sEVTGFβ ameliorated burn-induced structural damage and accelerated restoration of normal corneal thickness, compared to PBS-treated controls. sEVTGFβ also resulted in reduced inflammatory mediators (IL-1β, iNOS) and minimised levels of fibrosis-associated collagen in the cornea. Mice that received subconjunctival, but not topical, administration of sEVTGFβ exhibited regulatory immune cell profiles with reduced pro-inflammatory- macrophages, increased anti-inflammatory macrophages, and restored Treg function and balance of the Treg/Th17 axis.
Conclusions:
Overall, IFNγ and TGFβ licensing strategies were found to yield unique MSC-sEV phenotypes that can modulate inflammation differentially in vitro and in a corneal chemical burn model. This work found sEVTGFβ to represent a promising cell-free therapy for the treatment of corneal chemical burns.