Interleukin-2-dependent long-term cultures of low-density lymphocytes allow the proliferation of lymphokine-activated killer cells with natural killer, Ti gamma/delta or TNK phenotype

Lipopolysaccharide stimulates the proliferation of human CD56+CD3- NK cells: a regulatory role of monocytes and IL-10

NK cells recognize and kill tumor cells and normal cells, and these play an important role in immune defense in cancer, infectious disease, and autoimmunity. NK killing is regulated by positive or negative signals derived from the interaction of surface receptors with ligands on the target cells. However, the mechanisms controlling the proliferation and maintenance of NK cells in normal human individuals are less clearly defined. In this study, using an entirely autologous system, we demonstrate that human peripheral blood CD3-CD56+, killer cell-inhibitory receptor (KIR)-expressing cells proliferate and expand in response to LPS. These responses are enhanced in the presence of anti-IL-10 receptor-blocking Abs or on the removal of CD14+ cells from the cultures. This enhancement is also reflected in substantial increases in cytolytic activity and IFN-gamma production. The negative effect of CD14+ cells may also be IL-10 mediated, IL-10 being lost from the culture supernatants of CD14-depleted PBMC and rIL-10 reversing the effect of this depletion. On the other hand, mRNA for the p35 and p40 subunits of IL-12 is still induced in CD14-depleted cultures. The expansion of CD3-CD56+ cells was also inhibited by CTLA4-Ig, indicating a role for CD80/86. B lymphocytes were not required for the expansion of CD3-CD56+ cells, whereas removal of MHC class II+ cells from CD14-depleted cultures resulted in a complete abrogation of these responses. Expansion of CD3-CD56+ cells was reconstituted in MHC class II-depleted cell cultures by adding back monocyte-derived dendritic cells. These results indicate that the responses of CD3-CD56+ NK cells to LPS may be driven by a MHC class II+ B7+ CD14- peripheral population, most likely blood dendritic cells.

Cytokine-induced cytotoxic function expressed by lymphocytes of the innate immune system: distinguishing characteristics of NK and LAK based on functional and molecular markers

Several molecular events are now identifiable during the activation, recognition, and killing by natural killer (NK) cells that are distinct from those differentiated in response to cytokines during the generation of lymphokine-activated killer (LAK) cells or during lymphocyte proliferation. Because LAK and MHC-unrestricted killing activities also include the prototypic NK targets as part of their broad recognition spectra, accurate identification of the complete function being studied is critical. In many publications, past and present, only NK-sensitive target cells were used (K562, Molt-4, others), and, therefore, the results do not necessarily indicate whether the effectors are NK or have differentiated into LAK cells. Such a consideration becomes critical when the effectors are grown in interleukin-2 (IL-2), and an attempt is made to define receptor recognition, signal transduction pathways, and specificity at the molecular level. In some instances, effector cells are likely to have stopped, therefore merely expressing NK activity, and have also acquired LAK function. The identified receptors may not have been unique to NK cells or NK function. Not until the targets employed are also confirmed to be NK sensitive, and the effectors do not kill NK-resistant targets can the results of molecular studies be proposed to represent aspects unique to NK. Reports of the use of IL-2-expanded NK clones are most likely providing data concerning the biology of LAK and not of classic NK. The classic NK activity surveying our blood apparently performs an important function, including the ability to respond rapidly to certain cytokines and to acquire additional functions and receptors for use in destroying a vast array of target cells. It is critical for scientists to appreciate the functional distinctions and to identify the molecules and pathways unique to each of these curious cytolytic systems.

Augmentative effects of phytohemagglutinin-P on proliferation and cytotoxicity of interleukin-2-activated canine peripheral blood lymphocytes

Canine peripheral blood lymphocytes (PBL) were simulated with recombinant human interleukin-2 (rhIL-2) alone, or with phytohemagglutinin-P (PHA) and subsequent rhIL-2 in order to obtain large numbers of lymphokine-activated killer (LAK) cells. Incubation of PBL with rhIL-2 alone allowed proliferation of large granular lymphocyte (LGL)-like lymphocytes, and the cytotoxic activity of the lymphocytes against canine transmissible venereal sarcoma cells was detected 5-7 days after the culture onset. However, the lymphocytes died within 2 weeks of culture, resulting in limited generation of functional LAK cells. Thus, PBL pretreated with PHA are subjected to rhIL-2-dependent culture. Small- or middle-sized lymphocytes predominantly proliferated in response to rhIL-2, and proliferation of the lymphocytes was sustained for longer than 30 days by repeated stimulations with PHA and subsequent rhIL-2. Cytotoxicity reached significant levels from 2 weeks after the culture onset and thereafter remained almost constant for at least 2 weeks, leading to large-scale production of the LAK cells. Pretreatment of PBL and PHA seems to enhance the LAK cell functions through modification of the precursors of the effector LAK cells.

Development of four donor-specific phenotypes in human long-term lymphokine-activated killer cell cultures

A series of 62 lymphokine-activated killer cell (LAK) cultures from 44 different donors was investigated for the distribution of various CD markers during a cultivation period of 3 weeks. Great differences in the phenotypic pattern were found between different donors, but similar changes of the subset pattern of various donors allowed a classification of the LAK cultures into four distinct LAK types. LAK type 1 was characterised by low numbers of CD3+ cells and high values for CD56+ cells. In LAK type 2 cultures gamma/delta TCR+ cells extensively proliferated, whereas in LAK type 3 cultures the CD57 and CD8 values increased considerably. LAK type 4 cultures did not show any of these characteristics. The resulting phenotype of a LAK culture was donor-specific, as LAK cultures established from the same peripheral blood mononuclear cells (PBMC), fresh or after cryopreservation, or from PBMC obtained from the same donor at different venous punctures, always developed the same phenotype. A clear correlation between phenotype and killing activity could only be found for LAK type 1 cultures, which always developed high lytic activity. Long-term IL-2 stimulation induced high levels of perforin-positive cells in LAK cultures but the perforin content did not correlate with the cytotoxicity. The transcription pattern for various cytokines only varied slightly between the cultures. Messenger RNA for granulocyte/macrophage- colony-stimulating factor, interferon gamma, tumour necrosis factor alpha, interleukin-4 (IL-4) and IL-5 were found in almost all cultures during the entire cultivation period, whereas mRNA for IL-2 was never detected. Most variations in the transcription pattern were observed for IL-6 and IL-7. However, no correlation could be found between the endogenous cytokine production and the phenotype or lytic activity of the LAK cultures. Further studies are required to determine the factors that cause lymphocyte subsets from a specific donor to proliferate preferentially under long-term IL-2 stimulation.

Induction of lymphokine-activated killer cells with low-dose interleukin 2 and interferon-gamma in oral cancer patients

Lymphokine-activated killer (LAK) cells were induced with low-dose recombinant interleukin 2 (rIL-2) and recombinant interferon-gamma (IFN-gamma) in 28 oral carcinoma patients. The patients received daily intravenous injections of rIL-2 (1.2 x 10(5) U/m2) and rIFN-gamma (7.0 x 10(4) U/m2), and both natural killer (NK) and LAK activities were periodically examined. A significant increase in CD16+CD57+ and CD16+CD57- NK subsets was observed after the induction. An increase in the T-cell population was also found, with a significant increase in CD3+HLA-DR+, CD8+Leu8-, and CD4+Leu8- cells. Significant increases in NK activity, from the original level of 32.0 +/- 13.7 to 49.9 +/- 15.2%, and LAK activity, from 4.8 +/- 3.5 to 11.0 +/- 6.1%, at Day 7 were observed. Both activities were maintained at high levels during the cytokine injections, but greater enhancement of the killing activities could not be obtained subsequently. When NK and LAK activities were investigated in each subpopulation of CD3- and CD16- cells, no remarkable cytotoxic activity could be observed before induction in any subset without NK activity in CD3- cells (31.1 +/- 14.3%). At Day 7, NK activity of CD16- cells increased up to 21.4 +/- 14.9%, accompanied by an increase in CD3(-)-cell activity (54.5 +/- 20.6%). LAK activities of both subsets were also enhanced, with activity at Day 7 of 6.5 +/- 5.6 and 9.4 +/- 6.6% in CD16- and CD3- cells, respectively. These increased activities were maintained at the same level during the induction. Phorbol myristate acetate-induced polymorphonuclear leukocyte (PMNL) O2-generation was significantly increased, from the original 81.1 +/- 28.1 to 95.6 +/- 34.9 pmol/min/10(4) cells, after 1 week of treatment. Protein kinase C activity in the cytosol decreased, and the activity in the membrane fraction conversely increased. No remarkable adverse effects except for mild fever were observed. Together with LAK induction ability and PMNL enhancement, with scarce toxicity, a combination of low-dose rIL-2 and rIFN-gamma is thought to be useful in cancer treatments.

Differential lysis of tumor target cells displayed by lymphokine activated killer (LAK) cell clones

Lymphokine-activated killer (LAK) cells exhibit major histocompatibility complex (MHC) unrestricted cytolysis against a wide variety of fresh and cultured tumor cells. Because previous work from our laboratory suggested that trypsin treatment of unseparated populations of LAK cells had a differential effect on lysis of different tumors, in this report we analyzed the lytic specificity of LAK cell clones against a panel of three different targets: MCA, B16 and YAC-1. We found that 21 out of the 24 analyzed murine spleen and bone marrow clones killed a combination of two, but not all three, of these tumor cells. Determinations of the phenotype of 10 LAK cell clones showed six with rearrangements for the T cell receptor (TCR) beta chain gene, suggesting a T cell origin, and four with germ line configurations for the TCR beta and delta chain genes, a result consistent with a non-T cell lineage. This cloning procedure provided an experimental tool to develop new procedures of adaptive immunotherapy.

High release of tumor necrosis factor alpha, interferon gamma and interleukin-6 by adherent lymphokine-activated killer cells phenotypically derived from T cells

Adherent lymphokine-activated killer cells (A-LAK) are highly potent cytotoxic cells, which are shown to be derived not only from natural killer (NK)/K cells but phenotypically also from T cells. The generation and phenotypical and functional characterisation of these T-cell-derived A-LAK are described. In contrast to non-adherent cells (NA-LAK) and unseparated LAK (UN-LAK), these mostly CD3+ CD56+ CD8+ cells display a high degree of expansion following initial interleukin-2 (rIL-2) activation and further culturing in autologous conditioned medium. A comparison of cytotoxic activities of cultured cells reveals a significantly higher oncolytic ability of A-LAK cells against both K562 and Daudi cells than that of cultured controls of NA-LAK and UN-LAK. In addition, A-LAK are characterised by a marked endogenous cytokine release of interferon gamma, tumour necrosis factor alpha and IL-6 as well as by their shedding of p55 IL-2 receptor after exposure to IL-2. The results demonstrate A-LAK to be the lymphocyte subpopulation with the most cytotoxic activity and endogenous cytokine release after exposure to IL-2. The improvement of techniques for long-term cultures may be of interest for future therapeutic approaches.

Expression of perforin and serine esterases by human gamma/delta T cells

gamma/delta T cells have recently been described in association with a number of disorders, including autoimmune diseases. gamma/delta T cells are thought to play a cytotoxic role, but their mechanism of action is not known. Several granule mediators of cytotoxicity, including a pore-forming protein (perforin), and a family of serine esterases, have been isolated from cytotoxic T lymphocytes (CTL), lymphokine-activated killer (LAK) cells, and natural killer (NK) cells. We demonstrate here that gamma/delta T cells also express these mediators. Northern blots show that gamma/delta T cells express perforin, serine esterase 1 (SE 1), and SE 2. Three polyclonal antisera - raised against murine perforin, a peptide composed of amino acids 1-34 of human perforin, and human peforin expressed in bacteria - all reacted with a 70-kD protein in gamma/delta T cells on Western blots. Immunostaining with antiperforin antisera shows that primary gamma/delta T cells also contain perforin. Electron microscopy reveals that the granules of gamma/delta T cells resemble those of CTL, LAK, and NK cells. Gamma/delta T cells also resemble LAK cells in possessing inclusion bodies in their nuclei. These results imply that gamma/delta T cells resemble other cytolytic lymphocytes in their mechanism of action.