Role of NKG2D in Cytokine-Induced Killer (CIK) Cells Against Multiple Myeloma Cells

Abstract 5119

Cytokine-induced killer (CIK) cells are T lymphocytes enriched in CD3⁺CD56⁺ cells, which can be easily and rapidly expanded in vitro from human peripheral blood, bone marrow or cord blood mononuclear cells with the sequential addition of interferon (IFN)-{gamma}, OKT-3 and high doses of interleukin (IL)-2. The cytokine-induced killer (CIK) cells have been reported to have potent cytotoxicity against a variety of tumor cells including multiple myleoma (MM) cells. The mechanism of CIK cell recognizing MM cells remains unknow. Recent studies indicated that ligation of NKG2D on immunological cells directiy induce cytotoxicity. We suspect whether NKG2D receptor induction on CIK cells by cytokines is responsible for the killing of MM cells by CIK. We expended CIK cells from healthy controlswith interferon (IFN)-γ, CD3 monoclonal antibodies (mAb) and IL-2, and checked expression of NK cell receptors on CIK cells by flow cytometry. We found higher expression of NKG2D receptor and lower other NK receptors, such as CD158a,CD158b and NCRs on expanded CIK. These CIK cells showed higer cytotoxicity to multiple myleoma cell line U266 expressing NKG2D ligands. Interestingly, when cocultured with U266 cells, only NKG2D expressing CIK cells released IFN-γ detected by flow cytometry. We next analyzed NKG2D ligands expression on primary plasma cells in 22 MM patients by flow cytometry, the primary plasma cells in 16/22 (72.7%) MM patients expressed different levels of ULBPs or MICA/B on the cell surface. CIK cells showed higher cytotoxicity (12.5%) to NKG2D ligands expressing primary plasma cells compared to those did not express NKG2D ligands. The killing of CIK against MM cells were partially blocked by treatment of CIK with anti-NKG2D antibody. We conclude that NKG2D-NKG2D ligangd interaction may be one of the mechanisms by which CIK cells kill MM cells.