Development of cell-free approaches to the treatment of limbal stem cell deficiency

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Title: Development of cell-free approaches to the treatment of limbal stem cell deficiency PROJECT SUMMARY/ABSTRACT Limbal stem cells (LSCs) give rise to the entire corneal epithelium and are known to reside in the border area between the cornea and conjunctiva called limbus. Loss of LSCs or destruction of the LSC niche can result in Limbal Stem Cell Deficiency (LSCD) – a common cause of vision loss in the world. While transplantation of the autologous limbal tissues removed from the contralateral eye can cure patients with unilateral LSCD, bilateral LSCD patients have no autologous limbal tissues available. These patients often require transplantation of allogeneic donor limbal grafts; however, their success is highly variable. Moreover, the worldwide corneal donor shortage poses significant challenges for the availability of allogeneic LSCs for the treatment of bilateral LSCD patients. Thus, the overarching goal of this project is to develop cell-free LSCD therapies through the discovery of novel mechanisms of LSC maintenance and regeneration. Our lab has discovered an ATP-binding cassette (ABC) superfamily member B5 (ABCB5) as a novel LSC marker. ABCB5-positive LSCs isolated from human donors were capable of the long-term corneal restoration in pre-clinical LSCD models. Clinical trials are currently on the way to address the therapeutic potential of this stem cell population in human patients. Our most recent studies aimed to explore the cellular hierarchy within ABCB5-positive LSCs using single-cell RNA- sequencing revealed a novel LSC subpopulation that could be differentiated from the other LSC clusters by low expression levels of the cornea-specific genes. Here we hypothesized that this subpopulation possesses the most primitive stem cell characteristics with the highest regenerative potential. Further in-depth analyses revealed that these cells preferentially expressed the molecules involved in FGF, BMP, and AXL signaling cascades. We posit that these molecular pathways are essential for the maintenance of the undifferentiated LSC phenotype and can be employed for de-novo LSC induction and restoration of the LSC niche in the setting of bilateral LSCD. The two Aims of this proposal will: mechanistically dissect the role of FGF7, BMP2 and AXL in the LSC maintenance using murine and human genetically engineered experimental models (Aim 1) and will test the therapeutic potential of targeting these pathways for the treatment of LSCD in pre-clinical murine disease models (Aim 2). Successful completion of this study will further advance our understanding of LSC development, maintenance, and regulation with significant implications for clinical translation. Building on the PI’s training in regenerative medicine, the PI will gain extensive experience in corneal stem cell biology under the mentorship of Dr. Frank, a world-class leader in the fields of LSC biology and ABC transporters, and a member of Harvard Stem Cell Institute. Furthermore, this research will provide an important career guidance on his path of becoming an independent investigator.