Grants Awarded

Date of Award
December 2014

Amount of Award
$50,000

Layperson Summary
Familial hemophagocytic lymphohistiocytosis (FHL) is a devastating inherited disease affecting mainly infants and young children. It causes fever, enlarged liver and spleen, as well as reduced numbers of white blood cells. Without treatment FHL is invariably fatal. With the HLH-94 treatment protocol, based on chemotherapy and immunotherapy followed by bone marrow transplantation, the survival has increased to approximately 60%. Transplantation is the only curative curative treatment of FHL, but is associated with considerable risks. However, delay of treatment and transplantation can increase the risk of neurological dysfunction in FHL patients. Thus, rapid and accurate diagnosis of FHL is imperative.

The symptoms in FHL are caused by mutations in proteins that facilitate killing of target cells by specialized immune cells termed cytotoxic lymphocytes. When cytotoxic lymphocytes are unable to kill target cells, an infection can trigger an uncontrolled accumulation and activation of immune cells, mainly T cells and macrophages that infiltrate tissues and cause the symptoms associated with FHL. Mutations in genes encoding perforin, Munc13-4, syntaxin-11, and Munc18-2 have been associated with development of FHL. We and others have demonstrated that these proteins are implicated in release of cytotoxic granules. However, how these proteins interact to facilitate release of granules for target cell killing is not clear. In addition, several other molecular components remain elusive. Our research aims at gaining insights into the mechanisms of lymphocyte cytotoxicity.

Further insights into the molecular mechanisms underlying FHL and better means of diagnosis are called for to assist in decisions concerning treatment of FHL patients and our research can thus help patients in several ways. First, understanding the molecular mechanisms of FHL can help explain the biological effect of specific mutations. Second, identification of new genes associated with FHL through studies of the molecular mechanism of granule trafficking and release can explain disease in FHL patients not identified by current methods. In this setting, a genetic diagnosis can aid in rapidly providing adequate treatment. Moreover, this can aid genetic counseling or, if desired, prenatal diagnostics. Finally, biological studies of the molecular pathways and proteins involved in granule trafficking and release, together with analyses of genotype and clinical phenotype can facilitate the establishment of functional criteria that can offer very rapid diagnosis andstratification of HLH patients. Such studies may in the future provide important platforms for decisions concerning treatment of diverse FHL patients and increase our understanding of patients with symptoms but as yet no clear diagnosis.

Twelve Month Report
My laboratory received a grant amounting to 50 000 USD for a project entitled “Gaining Insights into the Mechanisms of Lymphocyte Cytotoxicity Underlying Hemophagocytic Lymphohistiocytosis” for 2015.

Familial hemophagocytic lymphohistiocytosis (FHL) is a devastating inherited disease affecting mainly infants and young children. The symptoms in FHL are caused by mutations in proteins that facilitate killing of target cells by specialized immune cells termed cytotoxic lymphocytes. When cytotoxic lymphocytes are unable to kill target cells, an infection can trigger an uncontrolled accumulation and activation of immune cells, mainly T cells and macrophages that infiltrate tissues and cause the symptoms associated with FHL. Mutations in genes encoding perforin, Munc13-4, syntaxin-11, and Munc18-2 have been associated with development of FHL. We and others have demonstrated that these proteins are implicated in release of cytotoxic granules. However, how these proteins interact to facilitate release of granules for target cell killing is not clear. In addition, several other molecular components remain elusive. Our research aims at gaining insights into the mechanisms of lymphocyte cytotoxicity.

With support of the Histiocytosis Association, we have made new discoveries that change the view of how cytotoxic lymphocytes kill target cells. Upon encountering an infected target cell, cytotoxic lymphocytes release the contents of large secretory vesicles, so called cytotoxic granules, at sites of interaction between the two cells. Cytotoxic granules contain proteins specialized for penetrating membranes and inducing death in target cells. Previously, this process has been thought to involve a direct recruitment and fusion of cytotoxic granules with the cytotoxic lymphocyte’s cell surface. We have now demonstrated that this process is more stringently regulated that previously appreciated (Marshall et al. J Cell Biol 2015). We find that smaller, more numerous vesicles termed recycling endosomes initially traffic to the site of contact with a target cell, fusing with the cytotoxic lymphocyte’s cell surface and thereby depositing molecules required for the subsequent cytotoxic granule content release and target cell killing. As such, we provide new insights to how the localization and function of proteins associated to FHL are regulated and a further level of understanding of the cellular machinery required for target cell killing and proper immune function. Moreover, these novel insights may provide new views of how other cell types in the body may work.