A multi-step isolation scheme for obtaining CD16+ human natural killer cells

Flow cytometry-based assessment of direct-targeting anti-cancer antibody immune effector functions

Monoclonal antibody-based therapies are increasingly being used to treat cancer. Some mediate their therapeutic effects through modifying the function of immune cells globally, while others bind directly to tumor cells and can recruit immune effector cells through their Fc regions. As new direct-binding agents are developed, having the ability to test their Fc-mediated functions in a high-throughput manner is important for selecting antibodies with immune effector properties. Here, using monoclonal anti-CD20 antibody (rituximab) as an example and the CD20⁺ Raji cell line as tumor target, we describe flow cytometry-based assays for determining an antibody's capacity for mediating antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP) and complement-dependent cytotoxicity (CDC). These assays are sensitive, reliable, affordable and avoid the use of radioactivity.

A new human natural killer leukemia cell line, IMC-1. A complex chromosomal rearrangement defined by spectral karyotyping: functional and cytogenetic characterization

A new human IL-2 dependent leukemic cell line with a natural killer (NK) cell phenotype, IMC-1, was established from an adult patient with aggressive NK cell leukemia. The IMC-1 cell line expresses the CD56, CD2, CD11a, CD38 and HLA-DR cell surface antigens, whereas the CD16 and CD8 antigens expressed on the primary leukemic blasts from which the cell line was derived were lost after 7 and 28 weeks of culture, respectively. The IMC-1 cell line displays functional NK cytotoxicity and lyses target cells in a non-MHC restricted, antibody-independent manner with equal or superior efficiency to freshly isolated NK cells. Cytogenetic analysis at presentation and after 55 weeks in culture revealed complex structural and numerical abnormalities, defined by classic G-banding and by spectral karyotyping (SKY). Three apparently intact copies of chromosome 8 occurred in the diagnostic bone marrow specimen; the cell line also contains three copies of chromosome 8 but each was structurally altered. The development and detailed characterization of this new NK leukemic cell line will facilitate biologic and functional studies of NK cells and chromosomal aberrations potentially important in leukemic transformation.

Inhibition of a phosphodiesterase III in the lysis-sensitive target-induced elevation of cyclic AMP (cAMP) in human natural killer cells

Natural killer (NK) cells are lymphocytes that are capable of destroying tumor cells and virally infected cells (cytolysis) without prior sensitization. When cyclic AMP (cAMP) is elevated artificially in NK cells, it is a potent inhibitor of their cytolytic function. Recently, we have shown that when NK cells are exposed to a range of lysis-sensitive (LS) tumor target cells, there is an increase in intracellular cAMP levels in the NK cells over a 60-min period. There is no increase in NK-cell cAMP in response to lysis-resistant (LR) tumor target cells. We determined that this cAMP elevation is due, in part, to an LS target-induced activation of adenylyl cyclase (AC), and that the AC-activation component appears to require a protein tyrosine kinase (PTK) activity. In the present study, we demonstrated that an LS target-induced inhibition of phosphodiesterase (PDE) is also contributing to the overall elevation of cAMP. Direct measurement of PDE activity showed an inhibition in lymphocytes that were exposed to LS targets but not in those exposed to LR targets. The inhibition of PDE activity was maximal by 30 min. Lymphocytes were exposed to targets and then lysed, so that PDE activity could be measured. Addition of class-selective inhibitors of PDE (at levels sufficient to completely block that class of PDE) to the lysate focused the measurement of PDE activity on those classes of PDE that were unaffected by the selective inhibitor. Using the PDE IV selective inhibitor rolipram and the PDE III selective inhibitors trequinsin and milrinone, we showed that a PDE III is being inhibited in lymphocytes by exposure to LS targets. As PDE III is known to be inhibited by elevated cyclic GMP (cGMP) levels, increased cGMP in NK cells following exposure to LS targets was a possible mechanism by which a PDE III in NK cells might be inhibited. However, when we measured cGMP levels in control and LS target-stimulated lymphocytes, we saw no change.

Lysis-sensitive targets stimulate an elevation of cAMP in human natural killer cells

Natural killer (NK) cells are lymphocytes that are capable of destroying tumour cells and virally infected cells (cytolysis) without prior sensitization. When cAMP is artificially elevated in NK cells, it is a potent inhibitor of their cytolytic function. We investigated whether NK-cell cAMP levels are modulated in response to tumour target cells to determine the potential of cAMP as a physiological regulator of NK cytotoxic function. When NK cells are exposed to a range of lysis-sensitive (LS) tumour-target cells there is an increase in intracellular cAMP levels in the NK cells over a 60-min period. The peak increase in cAMP (200-400% above control) occurs at 30 min for all LS targets tested. There is no increase in NK-cell cAMP in response to lysis-resistant (LR) tumour-target cells. The cAMP elevation may be dependent on both LS-target-stimulated adenylyl cyclase (AC) activation and LS-target-stimulated phosphodiesterase (PDE) inhibition. When the NK cells are pretreated with the protein tyrosine kinase (PTK) inhibitor, genistein (30 micrograms/ml), the AC-activation component of the cAMP elevation is abolished. Thus, the AC-activation component appears to require PTK activation. When NK cells are pretreated with the protein kinase C (PKC) inhibitor, chelerythrine chloride (10 microM) the cAMP elevation in response to LS targets was not diminished. This indicates that neither the AC-activation component nor any PDE-inhibition component require PKC activation.

Human natural killer cells: a convenient purification procedure and the influence of cryopreservation on cytotoxic activity

The recognition of natural killer cells as a lymphoid subpopulation with a distinct set of surface markers has led to the development of a variety of antibody-based purification methods. In this paper we describe a rapid, three-step negative selection protocol for the purification of human natural killer (NK) cells from the mononuclear cell fraction, which is obtained by the centrifugation of peripheral blood on Ficoll-Paque. Subsequently, monocytes and B lymphocytes are removed by adherence to nylon wool and T lymphocytes by panning with anti-CD3. With this procedure, CD3-, CD16/56+ NK cells are purified about five-fold, from 12 +/- 3% in the starting population to a final purity of 61 +/- 11%. A further increase to > or = 70% is obtained, if an extra Ficoll centrifugation step is included. The recovery of NK cells (50%) is significantly higher than is usually achieved by previously described procedures. Furthermore, we show that activation of cytotoxicity, with concomitant changes in target specificity, occurs when frozen/thawed NK effector cells are kept in culture in order to regain their pre-freezing cytotoxicity levels.

Acetylsalicylic acid has no effects on various isolated immune cells in vitro

In addition to the well known biological effects of acetylsalicylic acid (ASA), its stimulating effect on the immune system has recently been described. In the present study, therefore, the influence of ASA on isolated leucocytes was investigated in vitro. Various concentrations of ASA, representing therapeutic concentrations, had neither an inhibitory nor a stimulating influence on the cytotoxicity of CD16-positive cells. The phytohaemagglutinin-induced proliferation of lymphocytes and the phagocytosis activity of monocytes and neutrophilic granulocytes was similarly unaffected. These results would indicate that the immunostimulating effects already described for ASA cannot be examined in isolated leucocytes in vitro and should be attributed to an interaction of various effector cells in vivo.

Enhanced capacity of females for early interferon-gamma production by natural killer-like cells following stimulation by staphylococcal enterotoxin A

Staphylococcal enterotoxin A (SEA) induced the production of interferon-gamma (IFN-gamma) by spleen cells from ICR Swiss mice during the first 24 h of culture. Splenocytes from females produced higher levels of IFN-gamma than did those from males at 8, 12, and 16 h. By 20 h after SEA stimulation, IFN-gamma production by spleen cells from males was similar to that of females. The cell types involved in IFN-gamma production in this SEA/spleen cell system were analyzed by depletion studies. Removal of Thy-1+ cells by panning prevented production of IFN-gamma in the 24 h after SEA stimulation. In vivo depletion of asialo GM1+ (AGM1+) cells prevented production of IFN-gamma through 16 h of culture with SEA, but permitted a modest IFN-gamma response at 20 h that was similar in magnitude in both sexes. Following removal of L3T4+ and Lyt-2+ cells by panning, IFN-gamma production was detected at 12 h after SEA stimulation and maintained through 24 h of culture with cells from females producing higher levels of IFN-gamma. These data suggest that male ICR Swiss mice are deficient in the activity of Thy-1+, AGM1+, L3T4-, and Lyt-2- cells in the early (8-16 h) production of IFN-gamma following SEA stimulation of spleen cells.

AGM1+ spleen cells contain gamma interferon (IFN-gamma) gene transcripts in the early, sex-dependent production of IFN-gamma after picornavirus infection

Encephalomyocarditis D variant (EMCV-D)-infected spleen cell cultures prepared from diabetes-resistant ICR Swiss female mice produce more gamma interferon (IFN-gamma) activity over a 24-h period than do spleen cell cultures from diabetes-susceptible male mice of this strain. Pretreatment of mice with anti-asialo GM1 eliminates early in vitro IFN-gamma production from 4 to 16 h postinfection (p.i.) and reduces IFN-gamma production from 16 to 24 h p.i. In this study, depletion of spleen cells with anti-Thy-1 by panning greatly reduced IFN-gamma activity in EMCV-D-infected spleen cell cultures throughout a 24-h period. Populations of asialo GM1 (AGM1), L3T4, and Lyt-2-positive cells were isolated from cells harvested at 9 h p.i. from EMCV-D-infected spleen cell cultures by a modified panning technique on polystyrene microscope slides. By in situ hybridization with a [35S]dATP-labeled IFN-gamma cDNA probe, only the AGM1-bearing cells were found to contain detectable IFN-gamma gene transcripts. An AGM1+, Thy-1+ natural killer-like cell is the probable producer of the early, sex-dependent IFN-gamma activity in this system.