Grants Awarded

Date of Award
December 2015

Amount of Award
$50,000

Layperson Summary
The immune system utilizes Lymphocytes as the main line of defense to detect and destroy tumor cells. Lymphocytes are a type of white cells that circulate in the blood stream searching for abnormal cells or pathogens. They contain highly toxic proteins and substances stored in little closed-sack or vesicles known as lytic granules (LG), which upon recognition of foreign proteins on the outside of these invaders, are released and trigger cell death. Subjects carrying genetic defects that affect these processes manifest with Familial Hemophagocytic Lymphohisticytosis (FHL), a life threatening inflammatory disorder mainly affecting children. Currently, our understanding of the molecular and cellular basis of FHL is incomplete, and targeted therapies are lacking. As a result, patients are often treated with generalized immunosuppressive medications, which while effective, are associated with significant toxicity. Hematopoietic Stem Cell Transplantation (HSCT) result in permanent control of the disease, but unfortunately transplant mortality and with secondary effects is high. To improve theoutcome for patients with HLH, it is imperative that we better understand the processes of lytic granule transport and release in normal and pathological conditions. By probing the mechanisms of interaction and function of key proteins affected in FHL patients and how their functions are impaired in FHL, these studies will shed light on the pathophysiology of the disease and provide insights into how defects in granule release can be bypassed or corrected in a therapeutically relevant manner. Additionally, by identifying key signature defects in the lytic granule transport may lead to the development of novel tests for rapid diagnostics complementing the existing one. The long-term goal of this proposal is to utilize these functional systems as a springboard to establish whether mutations in FHL patients directly impair membrane fusion and to provide a flexible read-out system for studying additional proteins, which are also involved in granule exocytosis in immune cells.

Twelve Month Report
Familial Hemophagocytic Lymphohisticytosis (FHL) is a life threatening inflammatory disorder mainly affecting children. Normal Immune cells when recognize a virally infected or cancer cell try to eliminate them by releasing the toxic components stored in sack-like compartments called cytolytic granules. FHL subjects harboring mutations in the genes encoding Munc13-4, Syntaxin 11 and Syntaxin Binding Protein 2 display abnormal Cytotoxic T-lymphocytes (CTL) and Natural Killer (NK) cell activity owing to an impaired cytolytic granule release. Currently, understanding of the molecular and cellular basis of FHL is incomplete, and targeted therapies are lacking. As a result, patients are often treated with generalized immunosuppressive medications, which while effective, are associated with significant toxicity. Hematopoietic Stem Cell Transplantation (HSCT) result in permanent control of the disease, but unfortunately transplant mortality and with secondary effects is high. Results from our studies provided new insights into how the processes of cytolytic granule transport and release occur in normal and pathological conditions. By probing the mechanisms of interaction and function of key proteins affected in FHL patients, such as STX11 and STXBP2, we have identified that they need to associate with other proteins such as SNAP23 and Vamp8 in order to accomplish their function. Additionally, we have identified that certain mutations in STX11 and STXBP2 found in FHL patients, hinder these association and thus alter CTL cytotoxic functions. These studies have been published in the Proceeding of the National Academy of Science (P.N.A.S.- 2017 in press). Moreover, we have developed a novel assay to systematically test the biological significance of novel mutations identified in FHL patients. Now, we can utilize these functional systems as a springboard to establish whether mutations in FHL patients directly impair membrane fusion or not and to provide a flexible read-out system for studying additional proteins, which are also involved in granule exocytosis in immune cells.