analysis-of-human-natural-killer-cell-metabolism

Analysis of Human Natural Killer Cell Metabolism

Natural Killer (NK) cells mediate mainly innate anti-tumor and anti-viral immune responses and respond to a variety of cytokines and other stimuli to ...

National Institutes of Health

IL-15 bound to the IL-15Rα-chain (IL-15Rα) is presented in trans to cells bearing the IL-2Rβ-chain and common γ-chain. As IL-15 transpresentation occurs in the context of cell-to-cell contacts, it has the potential for regulation by and of other receptor-ligand interactions. In this study, human NK cells were tested for the sensitivity of IL-15 transpresentation to inhibitory receptors. Human cells expressing HLA class I ligands for inhibitory receptors KIR2DL1, KIR2DL2/3, or CD94-NKG2A were transfected with IL-15Rα. Proliferation of primary NK cells in response to transpresented IL-15 was reduced by engagement of either KIR2DL1 or KIR2DL2/3 by cognate HLA-C ligands. Inhibitory KIR-HLA-C interactions did not reduce the proliferation induced by soluble IL-15. Therefore, transpresentation of IL-15 is subject to downregulation by MHC class I-specific inhibitory receptors. Similarly, proliferation of the NKG2A(+) cell line NKL induced by IL-15 transpresentation was inhibited by HLA-E. Coengagement of inhibitory receptors, either KIR2DL1 or CD94-NKG2A, did not inhibit phosphorylation of Stat5 but inhibited selectively phosphorylation of Akt and S6 ribosomal protein. IL-15Rα was not excluded from, but was evenly distributed across, inhibitory synapses. These findings demonstrate a novel mechanism to attenuate IL-15-dependent NK cell proliferation and suggest that inhibitory NK cell receptors contribute to NK cell homeostasis. 

NK Cell Proliferation Induced by IL-15 Transpresentation Is Negatively Regulated by Inhibitory Receptors.

The goal of cancer immunotherapy is to stimulate the host immune system to attack malignant cells. Antibody-dependent cellular cytotoxicity (ADCC) is a pivotal mechanism of antitumor action of clinically employed antitumor antibodies. IL-15 administered to patients with metastatic malignancy by continuous i.v. infusion at 2 μg/kg/d for 10 days was associated with a 38-fold increase in the number and activation status of circulating natural killer (NK) cells and activation of macrophages which together are ADCC effectors. We investigated combination therapy of IL-15 with rituximab in a syngeneic mouse model of lymphoma transfected with human CD20 and with alemtuzumab (Campath-1H) in a xenograft model of human adult T cell leukemia (ATL). IL-15 greatly enhanced the therapeutic efficacy of both rituximab and alemtuzumab in tumor models. The additivity/synergy was shown to be associated with augmented ADCC. Both NK cells and macrophages were critical elements in the chain of interacting effectors involved in optimal therapeutic responses mediated by rituximab with IL-15. We provide evidence supporting the hypothesis that NK cells interact with macrophages to augment the NK-cell activation and expression of FcγRIV and the capacity of these cells to become effectors of ADCC. The present study supports clinical trials of IL-15 combined with tumor-directed monoclonal antibodies.

IL-15 enhanced antibody-dependent cellular cytotoxicity mediated by NK cells and macrophages.

Interleukin 15 (IL-15) is an essential cytokine for the survival and proliferation of natural killer (NK) cells. IL-15 activates signaling by the β and common γ (γ) chain heterodimer of the IL-2 receptor through -presentation by cells expressing IL-15 bound to the α chain of the IL-15 receptor (IL-15Rα). We show here that membrane-associated IL-15Rα-IL-15 complexes are transferred from presenting cells to NK cells through -endocytosis and contribute to the phosphorylation of ribosomal protein S6 and NK cell proliferation. NK cell interaction with soluble or surface-bound IL-15Rα-IL-15 complex resulted in Stat5 phosphorylation and NK cell survival at a concentration or density of the complex much lower than required to stimulate S6 phosphorylation. Despite this efficient response, Stat5 phosphorylation was reduced after inhibition of metalloprotease-induced IL-15Rα-IL-15 shedding from -presenting cells, whereas S6 phosphorylation was unaffected. Conversely, inhibition of -endocytosis by silencing of the small GTPase TC21 or expression of a dominant-negative TC21 reduced S6 phosphorylation but not Stat5 phosphorylation. Thus, -endocytosis of membrane-associated IL-15Rα-IL-15 provides a mode of regulating NK cells that is not afforded to IL-2 and is distinct from activation by soluble IL-15. These results may explain the strict IL-15 dependence of NK cells and illustrate how the cellular compartment in which receptor-ligand interaction occurs can influence functional outcome.

Olga M. Anton

Lymphoid Malignancies Branch,
Center for Cancer Research,
National Cancer Institute,
Lymphoid Malignancies Branch, Center for Cancer Research, National Cancer Institute

National Institutes of Health

Analysis of Human Natural Killer Cell Metabolism

Olga M. Anton

Lymphoid Malignancies Branch,Center for Cancer Research,National Cancer Institute,Lymphoid Malignancies Branch, Center for Cancer Research, National Cancer Institute

National Institutes of Health

Analysis of Human Natural Killer Cell Metabolism

Lymphoid Malignancies Branch,
Center for Cancer Research,
National Cancer Institute,
Lymphoid Malignancies Branch, Center for Cancer Research, National Cancer Institute