Gamm Lab

David Gamm

David Gamm, MD, PhD’s lab studies inherited and acquired eye diseases that culminate in the degeneration of photoreceptors and retinal pigment epithelium (RPE), a significant cause of visual morbidity.

The expansion and targeted differentiation of human stem and progenitor cells in vitro provide an essential source of biological material for modeling retinal development and potential cell-based treatments for these debilitating diseases. The aims of the Gamm Laboratory are to 1) investigate cellular and molecular events that occur during retinogenesis and 2) provide cells for use in rescue or replacement therapies for retinal degenerative diseases.

To meet these goals, Dr. Gamm utilizes a variety of cell types. Human embryonic stem cells (hESCs) are used to delineate the genetic “checkpoints” necessary to produce a particular retinal cell type and serve as a model system for studying human retinal development. Lastly, the Gamm laboratory has directed induced pluripotent stem cells (iPS) towards a retinal lineage in a manner similar to hESCs, allowing for the creation of cell-based models for human retinal degenerative diseases. By understanding the behavior of these cell types in vitro and in vivo, the Gamm lab hopes to optimize strategies to delay or reverse the effects of inherited and acquired eye diseases such as retinitis pigmentosa and macular degeneration.

Inherited and acquired diseases of the neural retina (NR) and/or retinal pigment epithelium (RPE) are a significant issue in human health and quality of life. Stepwise retinal differentiation of human pluripotent stem cells (hPSCs) can provide a model system to study human retinal development and supply cells for the potential treatment of debilitating retinal diseases. We have shown that two types of hPSCs, human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), can differentiate along the retinal lineage in a manner that closely parallels normal human retinogenesis. Our long-term mission is to use hPSCS to define molecular mechanisms of retinal cell fate determination and differentiation, to develop models of retinal diseases processes in vitro from patient-derived iPSCs, and to apply this knowledge to the study and treatment of human developmental and degenerative retinal disorders.

Current Research Projects

Mechanisms of Retinogenesis in Human Stem Cells
An important step in vertebrate retinogenesis occurs during the optic vesicle (OV) stage, when cells make the seminal decision to develop either as a neural retinal progenitor cell (NRPC) or an RPE cell. VSX2 is the earliest known marker of NRPCs and is hypothesized to pattern the naive OV into the NR and RPE domains by repressing expression of the early RPE-associated gene MITF. Disruption of Vsx2 expression in animal models by various means causes severe defects of the eye and retina, and humans with mutations in this gene exhibit microphthalmia and malformed retinas. Despite the critical roles attributed to VSX2 during retinal development, there is scant information available on its mechanisms of action and regulation in humans. Our unique capability to culture human cell populations from the earliest stages of retinogenesis and to isolate OV- like structures provides a pertinent in vitro model system to study VSX2 function in human retinal cell development. The primary objectives are to a) determine the purpose and necessity of VSX2 in the initial production of retinal cell types from hPSCs and b) identify endogenous hPSC signaling mechanisms that control VSX2 expression during differentiation.

Finding Elusive RP Genes
The purpose of this project is to utilize whole genome sequencing analysis and human iPS cell-based approaches to develop technique(s) for the discovery of retinitis pigmentosa-causing gene mutations that escape standard methods of detection.

Co-Culture and Analysis of Neural Retina and RPE Derived from GMP Super Donor Human iPSC Lines
A number of retinal degenerative diseases result in combined RPE and photoreceptor (PR) loss in their later stages. This scenario poses a particular challenge for cell replacement therapy since it requires reconstruction of two essential retinal layers, one of which – the RPE- plays an important role in maintaining the retina’s status as an immune privileged site. Therefore, donor cells introduced into the barren subretinal space are at risk of rejection, with repeated transplants likely to incite even greater immune responses. To address these major issues, we propose to use human iPSCs as cell sources to work on 1) the manufacture and testing of implantable, bilayered outer retinal patches consisting of mature, functional RPE monolayers grown on a biocompatible scaffold overlaid with photoreceptor (PR)-enriched neural retinal cells, and 2) the generation of clinical-grade iPSCs from a pre-identified group of “super donors.” As part of this effort, we will develop iPSC tools to isolate and test pure PR populations with RPE scaffolds as well. Super donor iPSC lines will be produced from individuals with immune profiles that favorably match significant segments of the U.S. population, thus decreasing the odds of rejection.

Production and Characterization of Patient-Specific iPS Cell Models of Best Disease for Therapeutic Testing
Best disease (BD) is a degenerative disorder of the human macula that results in progressive and irreversible central vision loss. It is most often caused by autosomal dominant (ad) mutations in the RPE gene BEST1, which ultimately lead to the accumulation of subretinal fluid and waste products and secondary photoreceptor death. We recently developed a hiPSC-RPE model-in-a-dish of adBD from iPSCs reprogrammed from skin biopsies of two BD patients (harboring either the N296H or A146K mutations in BEST1). To expand upon our previous findings, improve our understanding of BD, and apply new knowledge toward the development of custom therapies for BD, we propose the specific aims: 1) Produce and characterize hiPSC-RPE derived from an individual harboring a adBD (R218C)BEST1 mutation and up to two patients with arBD mutations and compare findings to our previously described adBD hiPSC lines. 2) Apply our improved understanding of the molecular events and intracellular pathways involved in patient-specific cases of BD to identify and test drugs that may counteract the deleterious effects of BEST1 mutations on RPE.