Mechanistic regulation of HLA binding receptors during human natural killer cell development

About This Grant

PROJECT SUMMARY Natural killer (NK) cells are innate lymphocytes that regulate multiple components of the innate and adaptive immune systems and have direct cytotoxic function against pathogen-infected cells and cancer cells. NK cells complement T cell immune surveillance and can mediate an important graft-versus-leukemia effect following allogeneic hematopoietic stem cell transplantation for acute leukemia. During pregnancy, maternal NK cells are unique mediators in the carefully orchestrated processes of implantation, placentation, and fetal growth; and they are also poised to rapidly respond to infection. In these and other settings, NK cells rely on their expression of inhibitory and activating cell surface receptors to sense their environment and communicate with other cells. Killer immunoglobulin-like receptors (KIRs) comprise a large family of receptors that bind human leukocyte antigen (HLA) molecules and enable NK cells to distinguish healthy from diseased cells. Despite their central importance to NK cell function, it is not yet known how KIR expression is regulated during NK cell development. For over 20 years we have worked to identify and characterize NK cell developmental intermediates (NKDIs) in human tissues and to determine how their differentiation and maturation are regulated. Although KIR acquisition occurs during late stages of NK cell maturation, we now have preliminary data to indicate that prior to this developmental window, early stage NKDIs require a conducive microenvironment to become primed for subsequent development into KIR+ NK cells. Moreover, our findings have uncovered a paradoxical inhibitory role of the NK cell growth factor, interleukin (IL)-15, during the priming phase of human NK cell development, thus challenging current dogma and raising important clinical implications for NK cell mediated therapies. The central goal of this proposal is to elucidate the mechanisms regulating KIR acquisition during human NK cell development. Our specific aims are: 1) To determine how the microenvironment regulates NKDI priming for KIR acquisition; and 2) To elucidate cell intrinsic mechanisms of NKDI priming and its suppression by IL-15. We hypothesize that specific hematopoietic helper cells support NKDI priming by triggering activating receptors through a critical developmental synapse, in turn leading to MEK/ERK/AP-1 signaling and subsequent induction of sense transcription at KIR gene loci. Further, we hypothesize that these critical priming steps are abrogated in the setting of early-stage exposure to IL-15, at least in part through dysregulated STAT5- and mTOR-dependent sense and antisense expression at KIR promoters. In Aim 1 we propose a series of experiments to determine how soluble factors and cell-cell interactions in the microenvironment mediate NKDI priming. In Aim 2 we will investigate NKDI cell intrinsic mechanisms to determine how priming affects KIR promoter expression and how IL-15 subverts NK cell priming and subsequent KIR acquisition. Our overarching goal is to gain a comprehensive understanding of the processes that regulate KIR acquisition during human NK cell development to best understand how NK cell functions can be enhanced in the face of human disease.