Cytotoxic studies in human newborns: lessened allogeneic cell-induced (augmented) cytotoxicity but strong lymphokine-activated cytotoxicity of cord mononuclear cells

Nonspecific cytotoxic responses such as natural killer activity can be increased in vitro by incubating effector cells with soluble factors or allogeneic cells. We sought to determine if newborn cells, known to be deficient in most cytotoxic responses, including resting NK activity, could develop enhanced cytotoxic responses following incubation with allogeneic cells (augmented cytotoxicity) or with lymphokines (lymphokine-activated cytotoxicity). Cord whole mononuclear cells (WMC) incubated with irradiated Raji cells for 5 days develop lower levels of cytotoxicity toward K562 targets at both a 20:1 effector:target (E:T) ratio (39 +/- 2.7% vs 49 +/- 3.6%) and a 10:1 E:T ratio (29 +/- 2.6% vs 40 +/- 3.6%) than do adult cells. Lessened specific cytotoxicity of cord cells developed toward the sensitizing Raji cells was also observed at both E:T ratios. Attempts to enhance the induced cytotoxicity by incubation with interferon or isoprinosine were unsuccessful. In contrast, lymphokine (i.e., interleukin 2)-activated killer (LAK) cytotoxicity is not deficient in cord WMC. Indeed, the level of LAK cytotoxicity is equivalent to that observed with similarly treated adult cells despite a lower baseline level of cytotoxicity toward the target cells. In the presence of purified IL-2 for 5 days, cord WMC cytotoxicity against K562 cells increased from 12 +/- 2.6 to 71 +/- 4.2% and against Raji cells increased from 9.6 +/- 2.5 to 48 +/- 6.7%. Similarly treated adult cells increased their killing against K562 from 23 +/- 4.2 to 61 +/- 4.5% and against Raji from 12 +/- 3.0 to 36 +/- 5.3%. This substantial lymphokine-activated cytotoxicity of newborn cells suggests the possibility of therapeutic intervention with purified lymphokines in neonatal infections or neoplasms.     

Heterogeneity of human NK cells: comparison of effectors that lyse HSV-1-infected fibroblasts and K562 erythroleukemia targets

In this study, we compared the natural killer (NK) cells that lyse HSV-1-infected NK(HSV-1) or uninfected [NK-(FS)] fibroblasts to those that lyse K562 erythroleukemia cells [NK(K562)]. Activity against all three targets was found in Percoll gradient fractions enriched for large granular lymphocytes, which suggests that these effector cells have a common morphology. In competition studies between 51Cr-labeled targets and unlabeled targets, both the infected and the uninfected fibroblasts competed for lysis of NK(HSV-1) and NK(FS) activity, whereas K562 cells competed poorly. In contrast, when 51Cr-labeled K562 cells were used, the unlabeled K562 cells competed well, but HSV-1-infected and uninfected fibroblasts competed poorly. Panning studies and complement elimination experiments using monoclonal antibodies were performed to describe cell surface markers on the NK cell populations. Treatment with an antibody to an la framework antigen reduced NK(HSV-1) but not NK(K562) activity. In contrast, the majority of NK(K562) effectors were recognized by antibodies to the E-rosette receptor (Lyt-3 and OKT11A), whereas NK(HSV-1) activity was much less sensitive to this antibody. OKM1, OKT10, and Leu-7 (HNK-1) markers were found on a portion, but not all, of the cells that lysed both the HSV-FS and K562 targets, while treatment with HLA plus complement totally abrogated both NK activities. Taken together, these data are consistent with the concept that human NK cells are heterogeneous and that we are dealing with at least three subpopulations of effector cells--one that kills the infected or uninfected fibroblasts; one that kills K562 cells; and a third population that may be able to kill all three targets. Patient studies provide additional evidence for heterogeneity within the NK cells that lyse the fibroblasts and K562 cells. We have studied a number of individuals who have normal NK activity with one target (HSV-FS or K562) but have low or no activity against the other. These patients provide strong evidence not only that NK cells are heterogeneous but also that these NK subpopulations can be regulated independently of each other in vivo.     

Killing activity of human umbilical cord blood-derived TCRValpha24<Superscript>+</Superscript> NKT cells against normal and malignant hematological cells in vitro: a comparative study with NK cells or OKT3 activated T lymphocytes or with adult peripheral blood NKT cells

PURPOSE: We aimed to determine the effects of human umbilical cord blood (UCB)-derived natural killer T (NKT) cells as immunological effectors against hematological malignancies, as well as auto- or allo-dendritic cells (DCs) or EB transformed cell lines (EBCLs). MATERIALS: TCRValpha24(+) Vbeta11(+) UCB- or PB-NKT cells were isolated by sorting and activated by alpha-galactosylceramide-pulsed autologous DCs. UCB-NK cells were induced from CD34(+) cells by stem cell factor plus IL-15. UCB-T cells were primarily activated by anti-CD3 monoclonal antibody. All those effectors were cultured with IL-2 (100 U/ml), and their cytotoxic activities were evaluated by (51)Cr-release assay. UCB-NKT cells were cultured with IL-12, IL-18 or higher dose of IL-2 (1000 U/ml), and again tested for the cytotoxicity against selected targets. RESULTS: UCB-NKT cells exhibited a pattern of killing activity against various hematological malignancies similar to that of UCB-NK cells, but could not kill K562, which was a vulnerable target for NK cells. The level of activity was quite similar to that of PB-NKT cells. In contrast, OKT-3-activated UCB-T lymphocytes showed a stronger and wider spectrum of killing compared with UCB-NK or NKT cells. IL-12, IL-18 or a higher dose of IL-2 upregulated the activity; however several targets, including fresh leukemic cells, still remained resistant. NKT cells killed auto- or allo-DCs at a level similar to that of T cells, but could not kill allo-EBCLs, which were efficiently killed by T cells. While NK cells showed only marginal or no killing against DC or EBCLs. DISCUSSION: The anti-cancer activity of human NKT cells depends on the concentrations or the combination of Th1-cytokines. Basically, those cells might not be contributing to the immune surveillance of hematological malignancies, as shown by a relatively low cytotoxicity against malignant cells, together with the quite strong killing against auto-DCs.     

Expansion of NK cells by engineered K562 cells co-expressing 4-1BBL and mMICA,combined with soluble IL-21

NK cells hold promise for protecting hosts from cancer and pathogen infection through direct killing and expressing immune-regulatory cytokines. In our study, a genetically modified K562 cell line with surface expression of 4-1BBL and MICA was constructed to expand functional NK cells in vitro for further adoptive immunotherapy against cancer. After a long-term up to 21 day co-culture with newly isolated peripheral blood mononuclear cells (PBMCs) in the presence of soluble IL-21 (sIL-21), notable increase in proportion of expanded NK cells was observed, especially the CD56^brightCD16⁺ subset. Apparent up-regulation of activating receptors CD38, CD69 and NKG2D was detected on expanded NK cells, so did inhibitory receptor CD94; the cytotoxicity of expanded NK cells against target tumor cells exceeded that of NK cells within fresh PBMCs. The intracellular staining showed expanded NK cells produced immune-regulatory IFN-γ. Taken together, we expanded NK cells with significant up-regulation of activating NKG2D and moderate enhancement of cytotoxicity, with IFN-γ producing ability and a more heterogeneous population of NK cells. These findings provide a novel perspective on expanding NK cells in vitro for further biology study and adoptive immunotherapy of NK cells against cancer.     

Mode of in vitro augmentation of natural killer cell activity by recombinant human interleukin 2: a comparative study of Leu-11+ and Leu-11- cell populations in cord blood and adult peripheral blood

Human newborn natural killer (NK) cell activity against K562 target cells was observed to be low compared with adult controls. Although Leu-7 (HNK-1)+ cells were negligible in cord blood, the proportions of Leu-11+ cells were equal to those of adult peripheral blood. Leu-11+ cells sorted from cord blood lymphocytes, as well as from adult lymphocytes exhibited the morphology of granular lymphocytes. In this study, we have investigated the phenotypic characterization of recombinant interleukin 2 (rIL 2)-induced cytotoxic lymphocytes against K562 cells by using anti-Leu-11 monoclonal antibody. Spontaneous cytotoxicity of lymphocytes was restricted to Leu-11+ cells in cord blood, as well as in adult blood, but this activity was low in cord blood Leu-11+ cells as compared with that of adult ones. NK cell activity of adult Leu-11+ cells could not be additionally enhanced after an 18-hr incubation with rIL 2(25 U/ml), whereas rIL 2 could potentiate the cytotoxicity of cord blood Leu-11+ cells approximately to the adult levels. It should be noted that cytotoxic activity of both Leu-11- cells from cord blood and adult blood that had no basal NK cells activity could be significantly potentiated by rIL 2. On the other hand, lymphokine-activated killer cells cytotoxic for HL-60 cell line could not be generated, and no proliferation of the lymphocytes was detected after an 18-hr incubation with rIL 2. It was shown that rIL 2 could not enhance the ability to bind to target cells in Leu-11+ and Leu-11- cells by means of a single cell conjugate assay, but the rate of target lysis of Leu-11+ cells from cord blood was significantly enhanced by rIL 2. These results suggested that rIL 2-induced cytotoxic effector cells were heterogeneous, and rIL 2 might potentiate the cytotoxicity of functionally immature NK cells or NK precursor cells.     

Killer cells of feline leukemia virus- and feline sarcoma virus-infected transformed cells: the role of NK, ADCC, and in vitro generated cytotoxic cells

Feline white blood cells (WBC) manifested a primary in vitro mixed lymphocyte tumor cell culture (MLTC) proliferative response to feline leukemia virus-feline sarcoma virus (FeLV-FeSV)-infected transformed target cells, which reached a peak at Day 15. Furthermore, primary in vitro MLTC cultures generated cytotoxic killer cells capable of killing a variety of targets in non-major histocompatibility gene complex restricted fashion, and effector cells were capable of killing targets introduced repeatedly into cultures over a 49-day period. The presence of feline fibrosarcoma (f-sarc) stimulators was the primary driving force for proliferation and generation of killing because exogenous IL-2 conditioned medium did not appreciably increase the yield of killer cells generated in vitro. WBC cultured without f-sarc stimulators with or without IL-2 supplementation also generated killer (K) cells but at a low level. The killer cell population was composed of approximately 50% lymphocytes and 50% monocytes. Cats had K cells functional in antibody-dependent cell-mediated cytotoxicity against FeLV-coated chicken red blood cells but not against any FeLV-FeSV-infected transformed targets tested. Natural killer (NK) cell activity to any targets tested was not found. Although no evidence was found for K or NK cell activity against FeLV-FeSV-infected transformed cells, feline WBC were readily able to generate killer cells in vitro and it is probable that this cell-mediated immune potential is functionally important in vivo.     

In vivo administration of low-dose human interleukin-2 induces lymphokine-activated killer cells for enhanced cytolysis in vitro

We have examined the effect of the intradermal administration of IL-2 on the generation of natural killer (NK) cell and lymphokine-activated killer (LAK) cell activity. Peripheral blood mononuclear cells (PBMC) obtained from borderline lepromatous (BL) and lepromatous leprosy (LL) patients and normal volunteers prior to and after IL-2 injection were stimulated in vitro with IL-2 and their cytolytic activities compared against 51Cr labeled target K562 cells, Daudi cells, and monocytes. Before IL-2 administration, PBMC obtained from BL/LL patients and normal volunteers possessed similar levels of NK cell activity indicating that the NK cell activity of the BL/LL patients was intact. LAK cell activity was induced with IL-2 in vitro in both BL/LL patients and in normal volunteers. The level of LAK cell activity in BL/LL patients was, however, suboptimal. A single intradermal dose of 25 micrograms IL-2 had no effect on the phenotype of circulating mononuclear cells in either patients or normal volunteers. However, 6-12 days after IL-2 injection and subsequent restimulation of the PBMC with IL-2 in vitro, cytolytic activity of LAK cells obtained from the BL/LL patients was enhanced while cells from normal volunteers expressed the same high levels of activity as observed before IL-2 injection.     

Natural killer cell activity correlates with the amount of beta 2-microglobulin on human peripheral blood lymphocytes

Two cytotoxic assays, lectin-dependent cytotoxicity and natural killer (NK) cytotoxicity, were used to assess the competence of cord blood and neonatal peripheral blood mononuclear cell (PBMC) and T-cell cytotoxic reactions. The effect of exogenous interferon was also studied. Results were compared with cytotoxic capabilities of adult cells and cells from patients with primary immunodeficiency syndromes. Lectin-dependent cytotoxicity (LDCC), a property of both T and non-T cells, was assessed by lysis of chromium-labeled EL4 tumor target cells in the presence or absence of exogenous fibroblast interferon (IFN-β). Natural killer cytotoxicity was assessed by lysis of two different chromium-labeled tumor target cells, Molt 4f and K562 in the presence or absence of IFN-β. Lectin-dependent cytotoxicity (LDCC) of PBMC of cord blood (32 ± 4% SEM) and adult cells (36 ± 2% SEM) were equivalent but neonatal cells had slightly decreased LDCC (22 ± 3% lysis). T-depleted cells from cord or neonatal blood had increased LDCC but T-enriched (>95% sheep erythrocyte rosette-forming cells) from both cord (22 ± 3%) and neonatal blood (18 ± 5%) had significantly reduced LDCC compared to 55 ± 2% for adult T cells. This deficiency corrects with age and is near normal after age 2. Preincubation with IFN-β did not enhance LDCC of newborn or adult cells. The LDCC of some cord T cells was markedly reduced and was in the same low range as patients with severe combined immunodeficiency. Natural killer (NK) cytotoxicity of PBMC from cord and adult cells was equivalent at three effector:target ratios against the Molt 4f target but against the K562 target, cord PBMC had significantly less NK activity (22 ± 11 SD) compared to adult NK activity (50.5 ± 22.2 SD) at a 50:1 effector:target ratio. Similar differences were noted at 25:1 and 10:1 target:effector ratios. NK cytotoxicity against Molt 4f targets of adult cells was significantly enhanced by preincubation with IFN-β but NK of cord cells was only variably enhanced. By contrast, IFN-β enhanced NK against K562 targets of both adult and cord cells, adult greater (67.7 ± 20) than cord cells (37.8 ± 2.0). These T-cell effector deficiencies are in marked contrast to the vigorous proliferative responses of newborn T cells, and parallel deficiencies of certain neonatal lymphokines. These defects may explain the newborns' enhanced susceptibility to intracellular viruses and to congenital viral infections.     

Target cell-directed inactivation and IL-2-dependent reactivation of LAK cells

In a previous study, we demonstrated that human natural killer cells (NK) lost their lytic activity after interaction with a sensitive target. The loss of NK activity also led to the loss of antibody-dependent cellular cytotoxicity (ADCC), prompting us to postulate that NK and ADCC activities may result from a common lytic mechanism. In this study, we examined whether nonadherent lymphocytes cultured 7 days in the presence of IL-2 (lymphokine-activated killer (LAK) cells) could also be inactivated and, subsequently, be reactivated in the presence of IL-2. We tested three populations of effector cells (EC): cells isolated from freshly drawn blood and tested immediately, cells cultured with IL-2 for 18 hr, and LAK cells. Once they have interacted with K562, all three cell populations lost greater than 90% of their NK-like lytic activity (NK-CMC) but only 80% of ADCC. However, when we treated the three cell types with antibody-coated K562, they lost 90-99% of NK-CMC and 90-97% of ADCC. In these inactivated effector cells we also observed: (i) a reduction in membrane expression of C-reactive protein; and (ii) a decrease in the expression of Leu-11a when EC were inactivated with antibody-coated K562. The loss of lytic activity against K562 was accompanied by a concomitant loss of activity against other LAK-sensitive targets as well as against antibody-coated targets (ADCC). In competitive inhibition experiments the inactivated effector cells failed to inhibit normal NK-CMC and ADCC activities mediated by fresh NK cells. As we have shown previously, this target-directed inactivation was not due to cell death or to lack of conjugate formation. Inactivated LAK cells regained their lytic potential when cultured with IL-2 and this effect was time dependent. By 72 hr, LAK cells inactivated with K562 regained 99% NK-CMC and 82% ADCC, whereas LAK cells inactivated with antibody-coated K562 regained only 80% NK-CMC and 70% ADCC. When we treated the effector cells with emetine, a potent inhibitor of protein synthesis, we could still inactivate the effector cells with K562 and with antibody-coated K562 but could not reactivate them with IL-2.     

Comparison of the effect of IL-2 and IL-6 on the lytic activity of purified human peripheral blood large granular lymphocytes

The effects of IL-6 and IL-2 on highly purified, human peripheral blood large granular lymphocytes (LGL) were investigated and compared. IL-6 enhanced LGL NK activity in a dose-dependent manner against K562, however IL-2 was a more potent stimulus of LGL NK function. Neither IL-2 nor IL-6 increased LGL cytotoxic potential in a parallel estimation of heteroconjugated antibody (anti-CD16 x anti-nitrophenyl mAb)-dependent cytotoxicity against nitrophenyl-modified YAC. Unlike IL-2, IL-6 did not significantly induce LGL lymphokine-activated killer activity, LGL proliferation, or LGL lymphokine production. In particular, IL-6 did not stimulate detectable LGL IL-2 production or IL-2R modulation, and mAb to the p75 IL-2R had no effect on IL-6 induction of LGL NK activity. Therefore, in the absence of T cells, IL-6 provided an IL-2-independent signal to LGL that resulted in augmentation of their NK activity without stimulating their proliferation or other LGL functions.     

Role of interferon in natural kill of HSV-1-infected fibroblasts

The production of interferon during natural killer (NK) assays against HSV-1-infected fibroblasts (NK(HSV-1)) was studied to determine whether this interferon was responsible for inducing the preferential lysis of herpes-virus-infected target cells over uninfected target cells. The interferon produced during NK(HSV-1) assays was analyzed and found to have the properties of HU-IFN-alpha. Little or no IFN was produced during NK assays against uninfected fibroblasts (NK(FS)) or K562 (NK(K562)) cells. Although the appearance of interferon in the culture supernatants seemed to parallel the development of cytotoxicity during NK(HSV-1) assays, the levels of cytotoxicity and IFN generated did not correlate, arguing against a strict quantitative dependence of cytotoxicity upon IFN production. NK(K562) and NK(FS) cytotoxicity developed with little or no production of IFN. When IFN-pretreated effector cells were used, there was still a preferential lysis of infected over uninfected target cells. This preferential lysis by IFN-treated effector cells of infected over uninfected targets was seen as early as 2 hr into the assay. Anti-IFN antibodies added to the NK assays, although neutralizing all the IFN produced during the assays, had no effect on NK(FS) or NK(K562) cytotoxic activity and caused a slightly reduction of NK(HSV-1) activity only in one of three experiments. We conclude that although IFN is generated during NK(HSV-1) assays, this IFN cannot solely account for the increased lysis of infected over uninfected cells and that NK(HSV-1) activity is in some other way dependent on the virus infection.     

Human trophoblast and JEG choriocarcinoma cells are sensitive to lysis by IL-2-stimulated decidual NK cells.

Freshly isolated decidual large granular lymphocytes (LGL) show natural killer (NK) activity against K562 cells but not against normal human trophoblast. We now show that these decidual LGL proliferate in vitro in response to recombinant interleukin-2 (rIL-2) and that these rIL-2-stimulated cells acquire a broad cytolytic potential that is characteristic of lymphokine-activated killer (LAK) cells. Both fetal fibroblasts and JEG-3 choriocarcinoma cells are resistant to lysis by freshly isolated decidual effectors but are readily killed by IL-2-stimulated decidual LGL. The ability to kill these target cells is acquired after only 18 hr exposure to rIL-2. rIL-2-activated decidual LGL also kill cultured normal trophoblast cells but much lower levels of cytolysis were seen even after the effectors had been stimulated with rIL-2 for 4-6 days. The preferential killing of malignant over normal human trophoblast cells raises questions about the potential role of IL-2-activated decidual LGL in the control of unduly invasive or malignant trophoblast populations in vivo.     

Innate immune response of the human host to exposure with herpes simplex virus type 1: in vitro control of the virus infection by enhanced natural killer activity via interleukin-15 induction

Infections with herpes simplex virus type 1 (HSV-1) in humans and in animal models are accompanied by enhanced natural killer (NK) activity. In vitro, HSV-1 also enhances the NK activity of human peripheral blood mononuclear cells (PBMC). The molecular basis of this enhanced NK activity, however, is not well characterized. We investigated the role of human interleukin-15 (IL-15) in this phenomenon and report here that HSV-1-mediated enhanced NK activity was abrogated by neutralizing antibodies for IL-15 but not for other cytokines (i.e., IL-2, IL-12, gamma interferon [IFN-gamma], tumor necrosis factor alpha, or IFN-alpha). Anti-CD122 antibodies which block signaling through IL-2 receptor beta chain, and therefore neutralize the effects of IL-15 (and IL-2), also abrogated this enhancement. Furthermore, HSV-1 increased the levels of IL-15 mRNA and the production of IL-15 in HSV-1-infected PBMC cultures. The neutralization of IL-15 in cocultures of PBMC with HSV-1-infected cells significantly increased HSV-1 production. These results strongly suggest a role for IL-15 in the HSV-1-mediated in vitro enhancement of NK activity and in the PBMC-mediated suppression of HSV-1 replication.     

Radiosensitivity of human natural killer cells: binding and cytotoxic activities of natural killer cell subsets

The sensitivity of human natural killer (NK) cell activities (both binding and killing) after exposure of peripheral blood mononuclear cells to different doses of gamma radiation was studied. A panel of monoclonal antibodies was used to identify the NK and T-lymphocyte subsets and to evaluate their radiosensitivity. Peripheral blood mononuclear cells were irradiated with low (2-6 Gy) and high (10-30 Gy) doses and NK cell binding and cytotoxic activity against K562 target cells were studied after 3 h and 48 h in culture. The primary damage to NK cell activity was identified at the postbinding level and affected mainly the lytic machinery. After 48 h culture postirradiation, an overall depression of cytotoxic activity was observed, but ionizing radiation produced either a selection of the more cytotoxic NK cell subsets, which therefore might be considered more resistant to radiation damage than the less cytotoxic NK cells, or a long-term stimulation of cytotoxic activity in surviving cells.     

Interleukin (IL)-15 in combination with IL-2, fms-like tyrosine kinase-3 ligand and anti-CD3 significantly enhances umbilical cord blood natural killer (NK) cell and NK-cell subset expansion and NK function

Background aimsInterleukin (IL)-15 and fms-like tyrosine kinase-3 (FLT-3) are crucial factors for the development of human and murine natural killer (NK) cells. Previously, we have demonstrated significant ex vivo expansion and activation of unrelated cord blood (UCB) NK cells with an antibody/cytokine cocktail consisting of anti-CD3 + IL-2 + IL-12 + IL-7 and anti-CD3 + IL-2 + IL-12 + IL-18.MethodsIn the current experiments, we investigated the effects of short-term culture with anti-CD3 + IL-2 + FLT-3 + IL-15 on cord blood (CB) NK cell and NK-cell subset expansion and function. CB mononuclear cells were cultured for 48 h in AIM-V media or AIM-V + IL-2 (5 ng/mL) + anti-CD3 (50 ng/mL) + FLT-3 (50 ng/mL) ± escalating doses of IL-15 (1, 10 or 100 ng/mL). Flow cytometric analysis was performed using various fluorescent-conjugated monoclonal antibodies. In vitro cytotoxicity was determined with a standard europium assay against K562 and Daudi cells.ResultsThere was a 4.8-fold significant increase in NK-cell population (CD3^?/16⁺/56⁺; P < 0.03), 21-fold significant increase in CD3^?/56⁺/158a⁺ (KIR2DL1/S1; P < 0.002), 46-fold significant increase in CD3^?/56⁺/158b⁺ (KIR2DL1/S2; P < 0.002) and 11.5-fold significant increase in CD3^?/56⁺/NKB1⁺ (KIR3DL1; P < 0.01). We also noted a significant increase in both NK and lymphokine-activated killer (LAK) cytotoxicity with IL-2 + anti-CD3 + FLT-3 + IL-15 (100 ng/mL) compared with IL-2 + anti-CD3 + FLT-3 and media alone against K562 (P < 0.01) and Daudi (P < 0.001), respectively.ConclusionsWe have demonstrated a significant increase in UCB NK cells and NK cells expressing a variety of killer immunoglobulin-like receptor (KIR) receptors after short-term culture with anti-CD3, IL-2, FLT-3 and IL-15. Furthermore, there was a significant increase in in vitro NK/LAK cell cytotoxicity.     

Fibroblasts from human spleen regulate NK cell differentiation from blood CD34(+) progenitors via cell surface IL-15

Besides a structural role in tissue architecture, fibroblasts have been shown to regulate the proliferation and differentiation of other neighboring specialized cell types, but differently according to the anatomic site and pathologic status of their tissue of origin. In this study we report a novel regulatory function of human spleen-derived fibroblasts in the development of NK cells from adult resting blood progenitors. When CD34(+) cells were cocultured with spleen-derived fibroblasts in monolayers, nonadherent CD56(+)CD3(-) NK cells were predominantly produced after 2-3 wk of culture in the absence of exogenous cytokines. Most NK cells expressed class I-recognizing CD94 and NK p46, p44, and p30 receptors as well as perforin and granzyme lytic granules. Moreover, these cells demonstrated spontaneous killing activity. Cell surface immunophenotyping of spleen-derived fibroblasts revealed a low and consistent expression of IL-15, Flt3 ligand, and c-kit ligand. Additionally, low picogram amounts of the three cytokines were produced extracellularly. Neutralizing Abs to IL-15, but not the other two ligands, blocked NK cell development. Additionally, suppressing direct contacts of CD34(+) progenitors and fibroblasts by microporous membrane abrogated NK cell production. We conclude that stromal fibroblasts within the human spleen are involved via constitutive cell surface expression of bioactive IL-15 in the development of functional activated NK cells under physiologic conditions.     

Natural killer (NK)-resistant human lung cancer cells are lysed by recombinant interleukin-2-activated NK cells

Natural killer (NK) cells are active in host defence against tumors. In order to determine if NK cells have the capacity to lyse human lung cancer cells, we evaluated blood NK cell activity against human lung carcinoma lines representing each of the commonest histological types of lung cancer, NCI-H157 (large cell), LICM107 and NCI-H146 (small cell), NCI-H226 (squamous cell), and LICM26 (adeno), and compared the results to their activity against a standard NK-sensitive target, K562, using a 16-hr 51Cr-release assay. At effector to target (E:T) ratios up to 50:1, NK activity was very low against each of the lung cancer cell lines compared to the K562 cells (NCI-H157 10 +/- 2%, LICM107 12 +/- 2%, NCI-H146 14 +/- 5%, NCI-H226 8 +/- 5%, and LICM26 7 +/- 3%, compared to K562 60 +/- 3%, P less than 0.001, for each compared to K562 cells). Recombinant interleukin 2 (IL-2) produced a dose-dependent augmentation of NK activity against each of the lung cancer cell lines, with doses as low as 0.25 U/ml being effective. The highest level of boosting was seen against NCI-H157 cells where NK activity (E:T, 50:1, IL-2, 250 U/ml) increased from 9 +/- 2 to 56 +/- 7%, P less than 0.001). Only brief exposure to IL-2 was necessary for augmentation to occur, with as little as 5 min being required for activation, although increased exposure times produced increased levels of augmentation. NK cells appeared to be the IL-2-responsive lytic cell population in these experiments as Leu 11b-depleted lymphocytes expressed little IL-2-mediated augmentation of activity against these target cells, and most of this IL-2-mediated augmentation of activity was located in the large granular lymphocyte-enriched fraction of the lymphocyte population. We conclude that normal blood NK cell activity against human lung cancer cell lines is low but that this activity can be markedly augmented by brief exposure of NK cells to low doses of recombinant IL-2, suggesting a potential role for IL-2 in the immunotherapy of human lung cancer.     

Cytokine production and killer activity of NK/T-NK cells derived with IL-2, IL-15, or the combination of IL-12 and IL-18

NK cell populations were derived from murine splenocytes stimulated by IL-2, IL-15, or the combination of IL-12 and IL-18. Whereas NK cells derived with the latter cytokines consisted of an homogeneous population of NK cells (DX5+CD3-), those derived with IL-2 or IL-15 belonged to two different populations, namely NK cells (DX5+CD3-) and T-NK cells (DX5+CD3+). Among NK cells, only those derived with IL-12/IL-18 produced detectable levels of cytokines, namely IFN-gamma, IL-10, and IL-13 (with the exception of IL-13 production by NK cells derived with IL-2). As for T-NK cells, IL-2-stimulated cells produced a wide range of cytokines, including IL-4, IL-5, IL-9, IL-10, and IL-13, but no IFN-gamma, whereas IL-15-derived T-NK cells failed to produce any cytokine. Switch-culture experiments indicated that T-NK cells derived in IL-2 and further stimulated with IL-12/IL-18 produced IFN-gamma and higher IL-13 levels. Next, we observed that NK/T-NK cell populations exerted distinct effects on Ig production by autologous splenocytes according to the cytokines with which they were derived. Thus, addition of NK cells derived in IL-12/IL-18 inhibited Ig production and induced strong cytotoxicity against splenocytes, whereas addition of NK or T-NK cells grown in IL-2 or IL-15 did not. Experiments performed in IFN-gammaR knockout mice demonstrated that IFN-gamma was not involved in the killer activity of IL-12/IL-18-derived NK cells. The hypothesis that their cytotoxic activity was related to the induction of target apoptosis was confirmed on murine A20 lymphoma cells. Experiments performed in MRL/lpr mice indicated that IL-12/IL-18-derived NK cells displayed their distinct killer activity through a Fas-independent pathway. Finally, perforin was much more expressed in IL-12/IL-18-derived NK cells as compared with IL-2- or IL-15-derived NK cells, an observation that might explain their unique cytotoxicity.     

Association of decreased natural and antibody-dependent cellular cytotoxicity and production of natural killer cytotoxic factor and interferon in neonates

Cord blood lymphocytes (CBL) were compared with adult peripheral blood lymphocytes (a-PBL) for their: (i) natural killer (NK) and antibody-dependent cellular cytotoxic (ADCC) activities, (ii) target-binding capacity, (iii) ability to induce soluble natural killer cytotoxic factor (NKCF), (iv) interferon (IFN)-, interleukin 2 (IL-2)-, and lectin-induced augmentation of NK activity, and (v) ability to produce IFN against tumor targets in vitro. CBL depleted of adherent cells and Percoll-separated, NK-enriched subpopulations demonstrated significantly lower NK, ADCC, and target-binding activities compared to a-PBL. CBL produced significantly lower levels of NKCF directed against K562 tumor targets in comparison with a-PBL. Although the NK activity of CBL was not stimulated by either IFN or IL-2 to the same levels shown by a-PBL, the percentage enhancement of cytotoxicity of CBL by IFN and IL-2 was greater than that of a-PBL. Lectin-induced enhancement of cytotoxicity was significantly greater for CBL in comparison with a-PBL. Further, the ability of CBL lymphocytes to produce IFN-gamma in vitro against K562 target cells was significantly lower than that of adult PBL. These studies suggest an association between decreased NK, ADCC, and target-binding activities, induction of NKCF and IFN production by CBL, and increased susceptibility of neonates to infection.