The Krüppel-Like Factor 4 (KLF4) Modulates Survival and Tissue Distribution of Natural Killer Cells.

Abstract 282

Natural Killer (NK) cells are important mediators of the innate immune system that could be targeted therapeutically to treat hematologic malignancies and to prevent graft-versus-host disease. Hence, a better understanding of NK cell survival and tissue trafficking at steady state is vital to develop cell-based therapies. Genes that control proliferation are often involved in tissue distribution of lymphocytes, such as KLF2 in T cells. KLF4, another member of the Krüppel-like factor family, can activate and repress genes involved in diverse cellular processes. We recently reported that KLF4 is part of a novel inhibitory pathway that prevents proliferation of naïve T cells during homeostasis and retain memory T cells in lymph nodes (Yamada et al., Nature Immunology, 2009). In this work, we studied the role of KLF4 in the development and maintenance of NK cells by deleting Klf4-floxed gene (fl/fl) using the Mx1-Cre system. The percentage of NK1.1+TCR- cells is significantly reduced in peripheral blood of Klf4-deficient (▪/▪) mice (fl/fl: 3.4±1.1 versus ▪/▪: 1.2±0.1, n=9) and also absolute numbers in spleen (▪/▪: 1.1±1.3 ×106, n=6) due to increased percentage of Annexin V positive cells (fl/fl: 9.2±3.2 versus ▪/▪: 22.9±15.5, n=15). The number of CD49d+TCR- cells was also significantly reduced in peripheral blood and spleen of Klf4-deficient mice. In contrast, the number of NK cells in bone marrow and lymph nodes of Klf4-deficient mice was similar to controls. Deletion of Klf4 gene led to reduced numbers of NK1.1+TCR-CD27+CD11b+ and NK1.1+TCR-CD27-CD11b+ cells, which correlated with increasing apoptosis of these subsets. Yet, the percentages of these NK cell subsets were normal in bone marrow ruling out a developmental defect in this tissue. Transplant of wild type and Klf4-deficient bone marrow cells into wild type mice suggested environmental rather than cell intrinsic defects. NK cells (NK1.1+TCR-) isolated from spleen of Klf4-deficient mice showed to be functional in a cytotoxicity assay using a mixture of differentially CFSE-labeled RMA-S (target) and EL4 (control). In summary, KLF4 plays a key role in the maintenance of mature NK cells in peripheral blood and spleen.