Within certain anatomical sites (eye, brain, testis, and the maternal-fetal interface), foreign tissue survives for an extended period of time and escapes from normal immune-mediated rejection. The failure of immune effector mechanisms to eliminate foreign tissue from privileged sites is due to the induction of a highly regulated immune response in which non-specific inflammation is reduced via several different mechanisms. One mechanism eliminates Fas receptor positive lymphocytes that infiltrate into the eye. Fas Ligand, which triggers the Fas receptor and activates a signaling pathway that results in apoptosis, is constitutively expressed on tissues within the eye.
Dr. Ksander’s current research is directed at understanding the mechanisms by which Fas Ligand contributes to establishing and maintaining immune privilege within the eye and also determining how this mechanism fails to protect the eye during ocular disease (uveitis and cornea allograft rejection).
Immunity to Cornea Allografts
One of the best examples of immune privilege in the eye is the exceptionally high acceptance rate of corneal allografts. Unlike other types of foreign allografts that are only accepted if donor and recipient are matched at the major histocompatibility loci, corneal allografts are accepted at a high rate, regardless of whether the donor and recipient are matched. One reason for this phenomenon is that the major transplantation antigens are less important than the minor transplantation antigens in corneal allograft survival.
However, further research in the role of minor transplantation antigens has been hampered by a lack of information on minor antigens. Dr. Ksander’s research is directed at studying the role of minor transplantation antigens in the survival of corneal allografts. Dr. Ksander is currently using a genetically defined group of minor transplantation antigens.
Immunity to Ocular Tumors
Melanomas that develop within the eye are treated with a variety of methods that, in general, successfully control primary tumor growth. However, all of these treatments fail to alter the incidence of metastatic disease, which is unusually high. There is currently no successful treatment available for patients with metastatic melanomas derived from ocular tumors.
Dr. Ksander’s previous studies indicate that ocular melanomas are immunogenic tumors that express tumor antigens recognized by specific T cells. In order to successfully activate specific T cells, we propose to use a form of gene therapy that increases the immunogenicity of primary ocular melanoma cells. The ultimate goal of this research is to develop a tumor cell vaccine that protects ocular melanoma patients from developing metastatic tumors. Protection is achieved by using primary tumor cells to stimulate tumor-specific T cells that eliminate metastatic tumor cells.
Dr. Ksander hypothesizes that primary tumor cells genetically engineered to express the costimulatory molecules CD80 and Class II will stimulate tumor-specific helper and cytotoxic T cells among the patient's peripheral blood lymphocytes. These lymphocytes may possess the ability to eliminate metastatic tumor cells.
- Function of inflammation during the development of glaucoma
- Function of microglia and infiltrating macrophages in the development of age related macular degeneration
- Restoration of the corneal epithelium using limbal stem cells
Glaucoma is a neurodegenerative disease that destroys only the retinal ganglion cells. However, the exact mechanisms by which these neurons are destroyed are still unclear. We demonstrated that a protein called Fas Ligand is expressed in the retina during the development of glaucoma. Fas Ligand exists in two forms that have opposite functions: the membrane form triggers inflammation and death of retinal neurons (neurotoxic function); while the soluble form prevents inflammation and neuronal death (neuroprotective function).
Therefore, regulating the ratio of the different forms of Fas Ligand can determine the extent of damage and vision loss during glaucoma. This discovery provides many new opportunities for therapeutic intervention for treating glaucoma.
Age-Related Macular Degeneration (AMD)
AMD is also a neurodegenerative disease that destroys photoreceptor cells within the macula, a specific area of the retina. The loss of photoreceptor cells is preceded by the development of deposits (called drusen) beneath the retina.
We discovered that at the site of drusen deposition in AMD patients the surrounding cells (called RPE cells) express a gene called NALP3 that is an important regulator of inflammation. NALP3 is important in the activation of a protein complex called the “inflammasome” that is a critical first step in the amplification of local inflammation. This data suggest that inflammation is an important early trigger in the development of AMD and also suggest a variety of new therapeutic targets that could be used to stop disease progression.
We are also studying the function of microglia and infiltrating macrophages in the laserinduced mouse model of CNV (choroidal neovascularization). We observed a significant loss of microglia during CNV that coincided with a dramatic increase in the number of infiltrating macrophages. Nanostring gene expression analysis indicate that microglia are neuroprotective, and infiltrating macrophages are neurotoxic.
Restoration of the Corneal Epithelium
Many mammalian organs (skin, stomach, intestines, colon, and eye) possess a source of adult stem cells that continually replenishes their rapidly self-renewing epithelial surfaces. One important challenge in regenerative medicine is replacing these stem cells when they are eliminated after an injury or disease. Patients with a limbal stem cell deficiency are unable to regenerate the corneal epithelium, resulting ultimately in blindness due to an irreversibly opaque cornea.
Several approaches have been used to replace limbal stem cells by transplanting tissue or cells harvested from the limbus. However, success of these procedures is severely limited by the inability to purify stem cells from the limbus.
We discovered that the ABCB5 gene—a new member of the ATP-binding cassette (ABC) superfamily of active transporters—is expressed on adult limbal stem cells that are capable of regenerating corneal epithelium. Importantly, ABCB5 is a cell surface protein that can be used to purify ABCB5+ cells from the limbus. This provides us with a unique opportunity to study the regenerative mechanisms of adult limbal stem cells and develop new methods to restore the specialized epithelium of the cornea in eyes with a limbal stem cell deficiency.