Irradiation of breast cancer cells enhances CXCL16 ligand expression and induces the migration of natural killer cells expressing the CXCR6 receptor.

BACKGROUND AIMS: Few studies have examined the migration pattern of natural killer (NK) cells, especially after radiation treatment for cancer. We investigated whether irradiation can modulate the expression of chemokines in cancer cells and the migration of NK cells to irradiated tumor cells. METHODS: The expression of chemokine receptors (CXCR3, CXCR4 and CXCR6) on interleukin-2 (IL-2)/IL-15-activated NK cells was assessed using flow cytometry. Related chemokine ligands (CXCL11, CXCL12 and CXCL16) in human breast cancer cell lines (MCF7, SKBR3 and MDA-MB231) irradiated at various doses were assessed using reverse transcription-polymerase chain reaction (RT-PCR), fluorescence-activated cell sorting (FACS) and enzyme-linked immunosorbent assay (ELISA). The cell-free culture supernatant was collected 96 h after irradiation of breast cancer cell lines for migration and blocking assays. RESULTS: The activated NK cells expressed CXCR6. Expression of the CXCR6 ligand CXCL16 increased in a time- and dose-dependent manner in all analyzed cancer cell lines. CXCL16 expression was statistically significantly enhanced in all breast cancer cell lines on day 3 after 20 Gy irradiation. Activated NK cells migration correlated with CXCL16 concentration (R2 = 0.91; P <0.0001). Significantly enhanced migration of NK cells to irradiated cancer cells was observed for a dose of 20 Gy in MCF7 (P = 0.043) and SKBR3 (P = 0.043) cells, but not in MDA-MB231 (P = 0.225) cells. A blocking assay using a CXCR6 antibody showed a significant decrease in the migration of activated NK cells in all cancer cell lines. CONCLUSIONS: Our data indicate that irradiation induces CXCL16 chemokine expression in cancer cells and enhances the migration of activated NK cells expressing CXCR6 to irradiated breast cancer cells. These results suggest that radiation would improve the anti-tumor effect of NK cells through enhanced migration of NK cells to tumor site for the treatment of patients with breast cancer.

Effect of exposure to interleukin-21 at various time points on human natural killer cell culture.

BACKGROUND AIMS: Interleukin-21 (IL-21) can enhance the effector function of natural killer (NK) cells but also limits their proliferation when continuously combined with IL-2/IL-15. Paradoxically, membrane-bound (mb)-IL-21 has been shown to improve human NK cell proliferation when cultured with IL-2/mb-IL-15. To clarify the role of IL-21, we investigated the effect of the timing of IL-21 addition to NK cell culture. METHODS: IL-2/IL-15-activated NK cells were additionally treated with IL-21 according to the following schedules; (i) control (without IL-21); (ii) first week (day 0 to day 7); (iii) intermittent (the first 3 days of each week for 7 weeks); (iv) after 1 week (day 8 to day 14); and (v) continuous (day 0 to day 49). The expression of NK receptors, granzyme B, perforin, CD107a, interferon-γ, telomere length and NK cell death were measured by flow cytometry. RESULTS: Compared with the control (2004.2-fold; n = 10 healthy donors) and intermittent groups (2063.9-fold), a strong proliferative response of the NK cells on day 42 was identified in the "first week" group (3743.8-fold) (P < 0.05). NK cells treated with IL-21 in the "first week" group showed cytotoxicity similar to that in control cells. On day 28, there was a significant increase in cytotoxicity of "first week" NK cells that received IL-21 treatment for an additional 2 days compared with the "first week" NK cells (P < 0.05). CONCLUSIONS: These data suggest that controlling temporal exposure of IL-21 during NK cell proliferation can be a critical consideration to improve the yields and cytotoxicity of NK cells.

Overnight storage of blood in ACD tubes at 4{degrees}C increases NK cell fraction in peripheral blood mononuclear cells.

A considerable variabilility in the effects of sample handling on NK cytotoxicity has been observed. Using flow cytometry, NK cytotoxicity assays and lymphocyte subset analysis of Ficoll-Hypaque-separated peripheral blood mononuclear cells (PBMCs) isolated from whole blood stored under various conditions were performed. The NK cytotoxicity of samples in heparin tubes stored overnight at 4 and 22°C, as well as at 22°C in acid citrate dextrose (ACD) tubes, was lower than that of a fresh sample. However, the NK cytotoxicity of samples in an ACD tube stored at 4°C was similar to that of a fresh sample. Based on lymphocyte subset analysis, samples in an ACD tube stored at 4°C showed a lower percentage of CD3+ T cells and a higher percentage of CD16/56+ NK cells compared to samples stored under other conditions. The NK cytotoxicity of fresh samples and samples in ACD tubes stored in a Styrofoam cooler box did not differ significantly; however, the differences were inconsistent. Overnight storage of peripheral blood in ACD tubes at 4°C is optimum for retention of NK cytotoxicity, the level of which is similar to that of fresh blood. This may be associated with an increased NK-cell fraction in Ficoll-Hypaque-separated PBMCs after overnight storage.

Ex vivo expansion of canine cytotoxic large granular lymphocytes exhibiting characteristics of natural killer cells.

Canine NK cells still are not well-characterized due to the lack of information concerning specific NK cell markers and the fact that NK cells are not an abundant cell population. In this study, we selectively expanded the canine cytotoxic large granular lymphocytes (CLGLs) that exhibit morphologic, genetic, and functional characteristics of NK cells from normal donor PBMCs. The cultured CLGLs were characterized by a high proportion of CD5(dim) expressing cells, of which the majority of cells co-expressed CD3 and CD8, but did not express TCRαß and TCRγδ. The phenotype of the majority of the CLGLs was CD5(dim)CD3(+)CD8(+) TCRαß(-)TCRγδ(-)CD4(-)CD21(-)CD11c(+/-)CD11d(+/-)CD44(+). The expression of mRNAs for NK cell-associated receptors (NKG2D, NKp30, NKp44, Ly49, perforin, and granzyme B) were highly upregulated in cultured CLGLs. Specifically, NKp46 was remarkably upregulated in the cultured CLGLs compared to PBMCs. The mRNAs for the NKT-associated iTCRα gene in CLGLs was present at a basal level. The cytotoxic activity of the CLGLs against canine NK cell-sensitive CTAC cells was remarkably elevated in a dose-dependent manner, and the CLGLs produced large amounts of IFN-γ. The antitumor activity of CLGLs extended to different types of canine tumor cells (CF41.Mg and K9TCC-pu-AXC) without specific antigen recognition. These results are consistent with prior reports, and strongly suggest that the selectively expanded CLGLs represent a population of canine NK cells. The results of this study will contribute to future research on canine NK cells as well as NK cell-based immunotherapy.

An improved flow cytometry-based natural killer cytotoxicity assay involving calcein AM staining of effector cells.

Several flow cytometric methods for measuring natural killer cell activity have been developed. Commonly used protocols involve the staining of target cells with various fluorescent dyes. However, these protocols are not applicable to certain experimental settings. Therefore, we used Calcein AM (CAM), which has been reported to be the most suitable dye for use in target cell staining protocols, as a means of developing an improved flow cytometry-based NK cytotoxicity assay involving effector cell staining. Peripheral blood mononuclear cells (PBMCs) isolated by gradient density centrifugation and expanded NK cells were used as effector cells. Cytotoxicity against K562 cells and several hematologic cancer cell lines was measured by a flow cytometry-based method using CAM and propidium iodide. The new assay was compared with a standard (51)Cr release assay (CRA) in terms of its ability to measure the cytotoxicity of NK cells in PBMCs and expanded NK cells against K562 cells. The optimal concentration of CAM for staining effector cells was 0.05 µM, and CAM fluorescence intensity in effector cells was maintained for 4 hours. CAM staining had no significant effect on NK cell activity in human PBMCs or expanded NK cells. Comparison of the CRA and this new assay using K562 cells revealed a good correlation (PBMCs, r = 0.894; expanded NK cells, r = 0.887). Distinct separation between target tumor cells (Daudi, Raji, RPMI8226, U266, U937, and K562 cells) and CAM-stained PBMCs (E:T ratio, 12.5:1 to 50:1) or expanded NK cells (E:T ratio, 0.5 to 4:1) was observed after incubation for 1 or 4 hours. In summary, we successfully developed an effective flow cytometry-based assay for assessing the activity of NK cells in PBMCs and expanded NK cells against K562 cells and various types of hematologic cancer cells.