Lymphokine-activated killer cells in rats. III. A simple method for the purification of large granular lymphocytes and their rapid expansion and conversion into lymphokine-activated killer cells.

A simple method for the purification and rapid expansion of large granular lymphocytes into cells with efficient broad antitumor cytotoxicity after stimulation by human rIL-2 is described. Nylon-wool nonadherent splenic mononuclear leukocytes from Fischer 344 rats were cultured in medium containing 1,000 U/ml rIL-2. The initial response of a small subpopulation of cells (less than 2%) to rIL-2 was their adherence to the plastic surface. This response was noted as soon as 2 h after addition of rIL-2. 2-h rIL-2-activated plastic adherent lymphocytes were 90-98% LGL, expressed surface markers characteristic of rat NK cells (OX8 [CD8]+, asialo GM1, laminin+, OX19 [CD5]-, R1-3B3 [CD5]-, W3/25 [CD4]-, OX39 [CD25]-, Ia-, and Ig-), and expressed very high levels of cytotoxicity against YAC-1 target cells. In addition to the above markers, plastic-adherent LGLs obtained at 24, 48, or 72 h progressively expressed Ia surface antigens, but were not phagocytic and contained less than 1% monocytes/macrophages by morphology. When 24- or 48-h plastic-adherent LGL/NK cells were cultured over 3-4 d in rIL-2, the cells expanded between 30- and 100-fold, reaching densities between 2-3 X 10(6) cells/ml. These rapidly expanding LGL/NK cells also generated very high levels of LAK activity (including lysis of fresh NK-resistant solid tumor cells), expressed a phenotype characteristic of activated rat NK/LAK cells, and incorporated [3H]TdR into DNA. This technique not only provides a novel method for the purification of LGL/NK cells for in vitro studies but also provides a means for the rapid expansion of highly purified cells with high levels of broad antitumor (LAK) cytotoxicity.

Monoclonal antibody to a triggering structure expressed on rat natural killer cells and adherent lymphokine-activated killer cells.

To study the cellular structures involved in NK and lymphokine-activated killer (LAK) cell function, we have produced a panel of mAbs that modulate the cytolytic function of a population of cells with LAK activity that derive from large granular lymphocyte (LGL)/NK cells (adherent LAK [A-LAK] cells). In this report, we describe an mAb (3.2.3; IgG1k) that recognizes a triggering structure that is expressed on rat LGL/NK cells and A-LAK cells. This epitope is also expressed on polymorphonuclear leukocytes (PMN). The expression of the epitope identified by mAb 3.2.3 increased progressively on A-LAK cells after culture in the presence of rIL-2. mAb 3.2.3 enhanced the cytolytic activity of NK and A-LAK cells against FcR+ target cells, but not FcR- target cells. However, this effect was not induced by F(ab')2 fragments of 3.2.3. This antibody also induced the release of N-alpha-benzyloxycarbonyl-L-lysine thiobenzy esteresterase by A-LAK cells. These data suggest that the epitope identified by mAb 3.2.3 is on a triggering structure expressed on rat NK cells and A-LAK cells. The expression of the epitope recognized by mAb 3.2.3 on LGL/NK cells and PMN suggests that this structure may be analogous to that identified by the anti-CD16 (-FcR) mAbs. However, the molecule immunoprecipitated by mAb 3.2.3 was a 60-kD dimer composed of two 30-kD chains. These data suggest that mAb 3.2.3 recognizes a unique triggering structure. As mAb 3.2.3 is the first antibody recognizing a determinant with functional significance, selectively expressed on both rat NK cells and A-LAK cells, it will be a useful tool for the study of NK cell ontogeny and function, and the development of cells with LAK activity from the NK cell compartment.

Lymphokine-activated killer cells in rats: analysis of tissue and strain distribution, ontogeny, and target specificity.

The coculture of lymphoid cells from Fischer 344 rats with recombinant human interleukin 2 (rIL-2) resulted in the generation of lymphokine-activated killer (LAK) cells. Maximal LAK activity was obtained between 200 and 1000 units/ml rIL-2. Lymphoid cells from spleen, thymus, bone marrow, peripheral blood, and lymph nodes were able to generate LAK activity although the kinetics and magnitudes of the responses were appreciably different among these tissues. Thus, while spleen and blood lymphocytes responded quickly (by day 3) and gave the highest level of LAK activity in response to rIL-2, bone marrow and thymus cells responded only by 7 to 9 days in culture. LAK activity could be generated from a variety of rat strains regardless of whether there were high or low levels of endogenous splenic natural killer (NK) activity, but the early (day 3) response was lower in the strains with low levels of NK activity. Cells with LAK activity could lyse a variety of tumor targets including fresh ascites or fresh syngeneic solid tumor explants but could not lyse fresh normal cells including syngeneic fibroblasts, peripheral blood lymphocytes, bone marrow cells, thymocytes, or T,B blasts. The generation of LAK activity required a concomitant proliferative response and could be completely abrogated by mitomycin C, actinomycin D, or X-irradiation above 500 rads. These treatments, however, did not affect natural killer activity or short-term (4 h) IL-2-boosted NK activity. LAK activity could be generated from spleen cells obtained from rats as early as 10 days of age but could not be generated from unfractionated neonatal spleen, neonatal liver, or peritoneal macrophages. The ontogeny of the development of splenic LAK activity correlated closely to the development of concurrent natural killer activity. When mixed with an NK-resistant mammary adenocarcinoma (MADB106) and adoptively transferred to normal syngeneic recipients in standard Winn-type assays, LAK cells were effective at inducing complete tumor inhibition.

Enhanced antimetastatic activity of lymphokine-activated killer cells purified and expanded by their adherence to plastic.

We have recently reported a simple and reproducible technique for the purification and rapid expansion of homogeneous populations of large granular lymphocytes expressing a natural killer cell phenotype and high levels of broad antitumor cytotoxic activity [lymphokine-activated killer (LAK) activity]. This technique exploits the observation that, in the presence of recombinant interleukin 2 (rIL-2), large granular lymphocytes/natural killer cells become adherent to plastic surfaces, actively proliferate, and acquire high levels of LAK activity. Because of their adherent properties these cells have been termed adherent LAK or A-LAK cells. The present studies investigate the antimetastatic effects of A-LAK cells in a syngeneic rat model of experimental pulmonary and hepatic metastases. For pulmonary metastases, F344 rats received i.v. injections with a natural killer-resistant mammary adenocarcinoma, MADB106, and, for hepatic metastases, animals received an intrasplenic injection of MADB106 tumor cells followed by surgical splenectomy. Three days later, the animals were treated with A-LAK cells alone, A-LAK cells plus rIL-2, or rIL-2 alone. These treatments were compared to immunotherapy using standard cultures of LAK cells (unfractionated spleen cells) and rIL-2. The results indicate that the administration of unfractionated LAK cells plus interleukin 2 (IL-2) was effective in reducing established lung or liver metastases in this rat model. However, the results also indicate that purified populations of A-LAK cells in combination with rIL-2 demonstrate dramatic and superior antimetastatic effects when compared to LAK cells cultured under standard conditions. The antimetastatic effects of standard LAK cells or A-LAK cells plus IL-2 translated into significant survival benefits compared to animals receiving no therapy or IL-2 therapy alone. Survival after therapy with A-LAK cells plus IL-2 was significantly prolonged compared to treatment with standard LAK cells. These data suggest that purified populations of LAK cells (derived from natural killer cells) may prove superior for adoptive immunotherapy in the clinical setting.

Elimination of established liver metastases by human interleukin 2-activated natural killer cells after locoregional or systemic adoptive transfer.

An in vivo model of liver metastasis induced by human gastric carcinoma was established in nude mice and used for locoregional or systemic immunotherapy with a subset of human A-natural killer (NK) cells defined previously. A single intrasplenic (i.s.) delivery of A-NK cells (1 x 10(7)) and interleukin 2 (IL-2; 60,000 international units, twice a day for 5 days, i.p.) to animals with 3-day established liver metastases, but not IL-2 alone, resulted in rapid (within 24 h) elimination of the majority of metastases and significantly improved survival. A single i.s. or i.v. transfer of these effector cells and IL-2 significantly prolonged survival of the mice with 3-day established metastases (P < 0.03 and P < 0.02, respectively) compared with untreated mice. Using 51Cr-labeled A-NK cells, it was determined that, at best, 75% of 1 x 10(7) cells delivered i.s., and up to 50% of those delivered i.v. were found in the liver 30 min-4 h later. Using image analysis with Di-O dye-labeled A-NK cells, 60-100% of A-NK cells delivered i.s. or i.v. were detected in the liver 24 h later. By light microscopy, 3-day liver metastases were mostly intravascular, but some had already begun to spread into liver tissue. When rhodamine- or Di-O dye-labeled A-NK cells were injected i.s. or i.v. to study their distribution in the liver, they were detectable by confocal fluorescence microscopy in tumor-free tissue and in association with tumor cells 12-24 h after transfer. No evidence for selective localization of A-NK cells to liver metastases was obtained; many A-NK cells were randomly distributed in tissue and not associated with visible metastases. However, confocal fluorescence and electron microscopy showed some A-NK cells to be in cell-to-cell contact with tumor cells, both in the blood vessel and liver tissue. These results indicate that a majority of human A-NK cells transferred i.s. or i.v. to mice with liver metastases have the capacity to migrate to the liver and to enter liver tissue and tumor metastases in vivo. The presence of these effector cells even in a modest number in the liver leads to elimination of most, but not all, metastases and to significantly prolonged survival of animals treated with A-NK cells and IL-2.

Immunotherapy of liver metastases of human gastric carcinoma with interleukin 2-activated natural killer cells.

To better understand the events occurring during immunotherapy of liver metastases with effector cells, we have developed a clinically relevant animal model in which both effector-tumor cell interactions and survival can be evaluated. A cell line of human gastric carcinoma (HR) metastatic to the liver has been established from a patient's liver biopsy. HR cells (10 x 10(6)) injected intrasplenically metastasize into the liver of immunosuppressed nude mice, with micrometastases detectable histologically by day 4 and macrometastases by day 7. The animals subsequently develop ascites and die between days 30 and 40 after tumor injection. To investigate early metastatic events in the liver, HR cells were transduced with a plasmid containing both the lacZ gene under the control of the CMV promoter and NeoR gene. Transfectants selected for neomycin resistance were lacZ gene positive and stained blue in the presence of a beta-galactosidase substrate, 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal). These transfectants (HRLZ) remained lacZ gene positive for at least 25 passages in vitro. Injected intrasplenically, an HRLZ clone grew invasively in nude mice and formed liver metastases comparably to parental tumor cells. The number and localization of blue X-Gal-positive tumor cells were followed in liver tissues of animals sacrificed at various times, from 1 h to 28 days postinjection of HRLZ cells. HRLZ cells were seen in liver blood vessels and sinusoids within 1 h after injection, and the progressive growth of micrometastases and macrometastases could be followed with precision by X-Gal staining. On day 3 after injection of HRLZ cells, numerous micrometastases were established containing 12-16 tumor cells. When these 3-day established HRLZ micrometastases were treated by the intrasplenic infusion of interleukin 2 (IL2)-activated human natural killer (NK) cells selected by IL2-induced adherence to plastic (A-NK) and systemic IL2, nearly all liver micrometastases were eliminated within 24 h after a single transfer of A-NK cells (P < 0.001). This xenogeneic model was also used for adoptive immunotherapy of 7-day established liver macrometastases with human A-NK cells injected intrasplenically and exogenous IL2 given i.p. A significant decrease in the number of hepatic metastases and the weight of livers (P < 0.003) in comparison with those of control mice was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

A new approach to generating antitumor effectors for adoptive immunotherapy using human adherent lymphokine-activated killer cells.

Lymphocytes from human peripheral blood incubated with interleukin-2 (IL2) develop lymphokine-activated killer (LAK) activity with the ability to kill a wide variety of tumor cells in a non-major histocompatibility complex-restricted manner. Adoptive immunotherapy with LAK cells and IL2 has been reported to lead to a regression of solid tumors in some patients with advanced malignancies. Aiming to improve the effectiveness of clinical adoptive immunotherapy, we developed a procedure for selective enrichment from human blood mononuclear cells (MNC) of IL2-activated antitumor effector cells. These cells, termed adherent LAK (A-LAK) cells because of their characteristic property of adherence to plastic, demonstrated both higher proliferative potential and greater antitumor cytotoxicity than unseparated MNC. Human A-LAK cells represented only 1 to 4% of IL2-activated MNC at 24 h but expanded from 130- to 1100-fold in 20 days. They comprised a population highly enriched in CD3-Leu19+ effector cells with antitumor activity against fresh human solid tumor cells and established cell lines. A-LAK cells retained antitumor activity for up to 14 days when cultured in the presence of IL2. They also mediated antibody-dependent cytotoxicity. Large-scale generation of A-LAK cells from the blood of patients with cancer proved feasible and should yield populations that are effective in vivo at lower doses than those required with unseparated LAK cells. This offers the potential for improving the antitumor effects, reducing the toxicity, and facilitating the administration of adoptive immunotherapy in humans. A Phase I/II clinical trial utilizing A-LAK cells and IL2 in patients with melanoma and renal cell carcinoma is now in progress.

Lymphokine-activated killer cells in rats: analysis of progenitor and effector cell phenotype and relationship to natural killer cells.

The progenitor and effector cell phenotype of lymphokine-activated killer (LAK) cells generated in F344 rats by recombinant human interleukin 2 (IL-2) (rIL-2) were analyzed. Highly purified populations of peripheral blood large granular lymphocytes (LGL) exhaustively depleted of T-cells were fully capable of generating high levels of LAK activity by 3 to 5 days in culture while purified populations of resting T-cells devoid of LGL could not generate LAK activity. This pure population of LGL expressed surface markers characteristic of rat natural killer (NK) cells [i.e., OX8+, asialomonoganglioside (asialo-GM1+), laminin+, OX19-, R1-3B3-, W3/25-, Ia-, surface immunoglobulin negative (SIg-)]. Further evidence that NK cells were the progenitors of cells with LAK activity was obtained by treatment of spleen or peripheral blood lymphocytes with anti-laminin or anti-asialo-GM1 antibodies plus complement or with the lysosomotropic agent L-leucine methyl ester. These treatments effectively depleted LGL/NK cell activity and the subsequent generation of rIL-2-induced LAK activity. Analysis of the LAK effector phenotype by cell sorting demonstrated that the majority of cells with LAK activity were OX8+, asialo-GM1+, laminin+, OX6+, OX19-, R1-3B3-, W3/25-, and SIg-. Furthermore, treatment of LAK cells with L-leucine methyl ester also significantly reduced their cytolytic activity. Thus, the LAK effector cells were also LGL and expressed surface marker characteristic of activated NK cells and not those of mature T- or B-cells. The proliferative response of rat spleen or blood lymphocytes to rIL-2 appeared to be primarily associated with LGL/NK cells since depletion of NK cells by anti-asialo-GM1 or anti-laminin antibody plus complement or by L-leucine methyl ester significantly (P less than 0.001) reduced the incorporation of [3H]thymidine into DNA. In contrast, depletion of T-cells (by anti-T-cell antibody plus complement) did not significantly affect rIL-2-induced proliferation. Similarly, T-cell-depleted, highly purified populations of LGL gave substantial proliferative responses to rIL-2. These studies clearly indicate that in the rat, the major cell population activated by rIL-2 is the LGL/NK cell and these cells appear to represent the major population of cells in blood or spleen which generate broad antitumor (LAK) cytotoxicity.

Natural killer cells and tumor therapy.

Evidence has been reviewed which indicates that NK cells play a role in the control of metastasis dissemination. Both activation of endogenous NK cells in a tumor-bearing host and adoptive transfer of ex vivo activated NK cells may be therapeutically beneficial. The small number of phase I/II clinical trials of AIT with A-NK cells performed in patients with cancer so far does not allow firm conclusions, except to ascertain the feasibility and a lack of toxicity of this form of therapy. Although numerous trials have been performed with BRMs, many of which are known to upregulate NK activity in vivo, a general lack of correlations between clinical responses or survival and upregulated NK activity in the peripheral blood has dampened enthusiasm for biological therapies. However, these clinical trials have been confined largely to patients with advanced metastatic disease. It is highly likely that tumor-induced immunosuppression plays a crucial role in neutralizing the benefits of BRM therapy, and that levels of effector cell activation sufficient for metastasis elimination are seldom achieved in this clinical setting. On the other hand, administration of BRMs in the adjuvant setting could be more effective and when combined with monitoring for effector cell functions might perhaps provide a better guide for achieving the levels of endogenous NK activity necessary for elimination of remaining or occult metastases. An improved understanding of NK cell biology in cancer patients is likely to serve as a positive reinforcement for design of a new generation of clinical trials incorporating novel approaches to NK cell mediated cancer therapy.

Human tumor antigen-specific T lymphocytes and interleukin-2-activated natural killer cells: comparisons of antitumor effects in vitro and in vivo.

Human antitumor effector cells include class I major histocompatibility complex (MHC)-restricted T cells and non-MHC-restricted natural killer (NK) cells. These two types of effector cells have not been directly compared for the ability to eliminate tumor cell targets. Here, we compare in vitro and in vivo antitumor functions of two human T-cell lines specific for a shared tumor antigen to the antitumor functions of A-NK cells, a subset of IL-2-activated NK cells. Human squamous cell carcinoma of the head and neck cell lines cultured in suspensions or as spheroids or tumor xenografts established in nude mice were used to evaluate antitumor functions of IL-2-activated and expanded T and NK effector cells in various assays, both in vitro and in vivo. Both tumor cell targets, PCI-13 and OSC-19, expressed class I and II MHC antigens after IFN-gamma pretreatment, gave rise to tumors upon injection into immunosuppressed nude mice, and were resistant to lysis by resting NK cells but sensitive to lysis mediated by A-NK cells or HLA-A2-restricted T-cell lines specific for a shared squamous cell carcinoma of the head and neck antigen. No significant differences were observed in the ability of A-NK cells or tumor-specific T cells to bind to tumor cell monolayers or to enter into spheroids. However, A-NK cells mediated significantly higher killing than tumor-specific CD8+ T cells in 4-h 51Cr-release assays (a measure of cell membrane damage and necrosis), 1-h [3H]thymidine-release assays (a measure of DNA fragmentation and apoptosis), and in terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assays (a measure of apoptosis). In contrast, CD8+ T cells were consistently more effective than A-NK cells in inducing growth inhibition of tumor cells in 24-h MTT assays. In the presence of tumor-specific antibodies, A-NK cell binding, entry into spheroids, and infiltration into tumor in vivo were significantly increased. In vivo perilesional delivery of effector cells to mice with established tumors indicated that human A-NK cells exert antitumor effects as potent as those of tumor-specific T cells. However, in contrast to tumor-specific T cells, A-NK cells are readily available for cancer therapy, expand rapidly in culture without prior sensitization, and can be armed with antitumor antibodies to increase localization of effector cells to the tumor.

Measurement of NK activity by the microcytotoxicity assay (MCA): a new application for an old assay.

Natural killer (NK) cells are spontaneously cytotoxic immune effector cells with the ability to selectively destroy tumor cells without harming normal cells. To perform this function, NK cells utilize two main cytotoxicity pathways, the well known perforin/granzyme-mediated secretory/necrotic killing and the recently defined TNF family ligand-mediated non-secretory/apoptotic killing. The former mechanism is manifested mainly against a few cultured leukemia cell targets, while the latter mediates killing against a large variety of tumor cell targets. Therefore, the biological role and significance of these mechanisms might be different. The NK cell-mediated necrotic killing has been reliably and selectively measured in humans by the standard 4-h 51Cr release assay (CRA) against K562 myeloid leukemia cell targets. However, no standardized high throughput assay is available for testing the NK cell-mediated apoptotic killing. Here, we introduce the modified MCA as a convenient method for measuring perforin/granzyme-independent NK cell-mediated apoptotic killing. The assay is performed in microwells of Terasaki tissue culture microtest plates, using adherent tumor cell targets, which are selectively susceptible to non-secretory/apoptotic killing and resistant to secretory/necrotic killing mediated by NK cells. Target cells are plated in microwells and incubated overnight to adhere to the plastic surface and to regenerate cell surface-bound TNF family receptors. Following this adherence, target cells are co-incubated with freshly isolated human peripheral blood mononuclear leukocytes (PBMNL) or purified subpopulations of immune cells for 24 h in various effector/target (E/T) ratios. During this incubation, dead target cells become non-adherent and are removed by washing the wells. Remaining adherent (viable) target cells are fixed, stained and optically counted. A notable dose-dependent (peak at 200:1 E/T ratio), time-dependent (peak at 24 h of incubation) and donor-dependent killing of tumor cells was consistently and reproducibly induced by PBMNL of normal donors. Using purified subpopulations of immune cells, it was demonstrated that among PBMNL, CD3(-)CD56(+)CD16(+) mature NK cells are the only mediators of tumor cell killing in MCA, as well as in CRA. Comparative studies of NK activity detected by MCA and CRA, performed with PBMNL from normal individuals and breast cancer patients, showed no significant correlation between the cytotoxicities measured in the two assays. In addition, while NK activity measured in CRA was normal in most breast cancer patients, NK activity assessed in MCA was decreased in a large majority of the patients. Thus, MCA is a sensitive NK assay, which is biologically different from CRA, and may be clinically relevant. MCA has also a higher throughput, and is more practical and economical than CRA.

Role of TNF family ligands in antitumor activity of natural killer cells.

NK cells have the ability to destroy tumor cells by two main cytotoxic pathways, the well-known perforin/granzyme-mediated secretory/necrotic killing and the newly defined TNF family ligand-mediated apoptotic killing. The former mechanism is operative mainly against a few cultured leukemia cell targets, while the latter mediates substantial activity against most tumor cell targets. It also appears from emerging data that the apoptotic mechanism is the main antitumor pathway in vito. This review is focused on the apoptotic mechanism of killing, the molecules and cell signaling pathways involved in this process, and its potential biologic significance along with its relation to the secretory/necrotic cytolytic pathway.

Blood monocytes and tumor-associated macrophages in human cancer: differences in activation levels.

This study was performed to investigate functional properties of mononuclear phagocytes isolated from ascitic fluid in patients with peritoneal carcinomatosis (PC), and potential immunomodulatory effects of soluble factors produced or induced by human metastatic malignant cells. Phagocytic activity and nitric oxide production of peripheral blood monocytes (PBMo) and tumor-associated macrophages (TAM) or peritoneal macrophages (PEM) were synchronously examined in cancer patients and control individuals. Our results showed that contrary to peripheral blood monocytes, where phagocytic activity was not altered, TAM had impaired phagocytic activity. Moreover, dilutions of crude supernatant from short-term cultures of the peritoneal cells obtained from ascitic fluid of patient with PC, cause a significant, dose dependent inhibition of control PBMo and PEM phagocytosis, comparable to those in TAM, indicating that a soluble factor(s) plays a prominent role in this alteration. Next, we investigated the potential of cancer patients mononuclear phagocytes to produce nitric oxide (NO). It was found that TAM produce fourfold lower levels of NO than PEM from control subject, whereas monocytes produce NO at levels comparable to those of corresponding controls. These data support the hypothesis that depressed TAM function may contribute to the mechanisms of tumor escape from immune destruction.

Inhibition of apoptosis in human tumour cells by the tumour-associated serpin, SCC antigen-1.

The squamous cell carcinoma antigen (SCC Ag) is a tumour-associated protein and a member of the serine protease inhibitor (serpin) family. The SCC Ag has been used as a serologic tumour marker for SCC progression, and its elevated serum levels are a risk factor for disease relapse. However, the biologic significance of this intracytoplasmic protein in cancer cells remains unknown. In this report, we demonstrated that apoptosis induced by 7-ethyl-10-hydroxycamptothecin, tumour necrosis factor-alpha (TNF-alpha) or interleukin (IL)-2-activated natural killer (NK) cells was significantly inhibited in tumour cells transduced with the SCC Ag-1 cDNA, as compared to control cells in vitro. Also, inhibition of the SCC Ag-1 expression in tumour cells by transfection of antisense SCC Ag-1 cDNA was accompanied by significantly increased sensitivity of these cells to apoptosis induced by etoposide or TNF-alpha. The mechanism of protection of tumour cells from apoptosis involved inhibition of caspase-3 activity and/or upstream proteases. In vivo, tumour cells overexpressing the SCC Ag-1 formed significantly larger tumours in nude mice than the SCC Ag-1-negative controls. Thus, overexpression of the SCC Ag-1, a member of the serpin family, in human cancer cells contributed to their survival by mediating protection from drug-, cytokine- or effector cell-induced apoptosis.

Nonsecretory apoptotic killing by human NK cells.

We defined a novel constitutive mechanism of cell-mediated cytotoxicity, utilized by nonactivated human peripheral blood NK cells against a variety of tumor cell targets resistant to secretory (i.e., perforin/granzyme-mediated) NK cell killing. Untreated NK cells rapidly induced membrane damage and necrosis in K562 target cells (as determined by 51Cr release assay and confirmed by transmission electron microscopy; TEM), in the absence of DNA fragmentation and apoptosis (as assessed by [3H]thymidine release assay and TEM). Chelation of extracellular Ca2+ or paraformaldehyde fixation completely abrogated NK cell secretory activity and necrotic killing. In contrast, NK cells with either normal or impaired secretion consistently exhibited cytotoxicity against a wide variety of solid tumor cell lines in 1-h [3H]thymidine release, but not in 4-h 51Cr release, assays. Thus, the cytotoxicity was attributable to a nonsecretory, cell membrane-mediated mechanism. It appeared to selectively induce DNA fragmentation and apoptosis without plasma membrane damage and necrosis. This was further demonstrated by a terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay and confirmed by TEM. Among defined populations of immune cells, only NK cells showed an inherent ability to rapidly induce apoptotic death in solid tissue-derived malignant cells. This study demonstrates that NK cells are unique immune cells constitutively endowed with multiple mechanisms of destroying abnormal cells.

Absence of B7.1-CD28/CTLA-4-mediated co-stimulation in human NK cells.

Recent studies have suggested that B7-CD28 interactions provide co-stimulatory signals for activation of NK cells. Transduction of the B7.1 (CD80) gene into tumor cells has been shown to trigger proliferation and cytotoxicity of murine NK cells and a human NK cell line, YT2C2. Therefore, transduction of the B7.1 gene into CD80-negative human squamous cell carcinomas of the head and neck (SCCHN) and its stable expression was expected to upregulate proliferation and cytotoxic activities of human NK cells. However, expression of the B7.1 receptors, CD28 and CTLA-4, could not be demonstrated on the surface or in the cytoplasm of normal human NK cells, irrespective of the state of their activation. In proliferation experiments or various cytotoxicity assays, utilizing highly purified human NK cells as responder or effector cells, no enhancement of NK cell generation or activity, respectively, by B7.1+ SCCHN was observed relative to non-transduced or LacZ gene-transduced SCCHN. In contrast, co-incubation of B7.1+ SCCHN targets with human NK cells induced significant inhibition of NK cell growth. Thus, the B7.1-CD28/CTLA-4 pathway is not involved in triggering of human adult NK cells.

In vivo distribution and tissue localization of highly purified rat lymphokine-activated killer (LAK) cells.

A highly purified population of effector lymphokine-activated killer (LAK) cells was generated by culturing nylon-wool column nonadherent rat splenocytes in the presence of interleukin 2 (IL-2), and the cells which became adherent to the plastic flasks were separated and maintained in culture for a total of 5 days. More than 95% of these cells had the morphology of large granular lymphocytes (LGL), expressed surface phenotypes characteristic of rat natural killer (NK) cells, and were able to kill NK-sensitive and NK-resistant tumor target cells. 51Cr-labeled purified A-LAK cells injected intravenously into syngeneic F344 rats localized primarily in the lungs 2 hr after injection but then redistributed to the liver and the spleen by 24 hr after injection. The effects of various immunological manipulations on the distribution pattern of the isolated LAK cells were evaluated. Treatment of the host with 500 rad total body X-irradiation 24 hr before cell injection resulted in an early uptake of LAK cells into the liver and the spleen, whereas treatment with cyclophosphamide 1 day before cell injection, resulted in an early uptake of LAK cells into the liver but not into the spleen. Treatment of the recipient rats with up to 120,000 units recombinant interleukin-2 intraperitoneally did not result in the accumulation of LAK cells at the site of IL-2 injection, nor did it result in a modulation of the overall distribution pattern or total recovery of radiolabeled LAK cells. Rather, the administration of IL-2 was necessary to maintain the cytotoxic activity of the injected LAK cells isolated from the liver and spleen.

Constitutive expression and role of the TNF family ligands in apoptotic killing of tumor cells by human NK cells.

Natural killer cells mediate spontaneously secretory/necrotic killing against rare leukemia cell lines and a nonsecretory/apoptotic killing against a large variety of tumor cell lines. The molecules involved in nonsecretory/apoptotic killing are largely undefined. In the present study, freshly isolated, nonactivated, human NK cells were shown to express TNF, lymphotoxin (LT)-alpha, LT-beta, Fas ligand (L), CD27L, CD30L, OX40L, 4-1BBL, and TNF-related apoptosis-inducing ligand (TRAIL), but not CD40L or nerve growth factor. Complementary receptors were demonstrated to be expressed on the cell surface of solid tumor cell lines susceptible to apoptotic killing mediated by NK cells. Individually applied, antagonists of TNF, LT-alpha1beta2, or FasL fully inhibited NK cell-mediated apoptotic killing of tumor cells. On the other hand, recombinant TNF, LT-alpha1beta2, or FasL applied individually or as pairs were not cytotoxic. In contrast, a mixture of the three ligands mediated significant apoptosis in tumor cells. These findings demonstrate that human NK cells constitutively express several of the TNF family ligands and induce apoptosis in tumor cells by simultaneous engagement of at least three of these cytotoxic molecules.

Lymphokine-activated killer cells in rats. IV. Developmental relationships among large agranular lymphocytes, large granular lymphocytes, and lymphokine-activated killer cells.

The developmental relationships among large agranular lymphocytes (LAL) large granular lymphocytes (LGL) and the activation of these cells into lymphokine-activated killer (LAK) cells by rIL-2 was investigated. Highly enriched populations of LAL were isolated from Fischer 344 spleen cells by a combination of nylon-wool filtration (to remove B cells and macrophages), treatment with a pan T cell antibody plus complement (to remove T cells) and incubation in L-leucine methyl ester (to remove LGL). The resultant cells were highly enriched in morphologically identifiable LAL which expressed asialo GM1 and partially expressed the OX8 surface marker. The enriched LAL did not contain detectable NK cytotoxic activity, did not express pan T cell (OX19), Ia, Ig, or laminin surface markers and contained less than 0.2% LGL. Incubation of LAL in a low dose of rIL-2 (100 U/ml) induced the generation of LGL having NK activity within 24 h of culture. Longer culture periods (48 h) resulted in a continued increase in the percentage of LGL and higher levels of NK activity. However, with this low dose of rIL-2, little or no LAK activity (i.e., reactivity against NK-resistant target cells) was generated. With a high dose of rIL-2 (500 U/ml), LAL responded by first generating LGL with NK activity (within 24 h), with subsequent generation of LAK activity by 48 h. Evidence that the development of granular lymphocytes from LAL was responsible first for NK activity and then LAK activity was demonstrated by depletion of the generated granular NK or LAK effector cells by second treatments with L-leucine methyl ester. Concomitant with the induction of LGL with NK or LAK activity, rIL-2 also caused LGL to proliferate and expand four- to five-fold in 48 h. This occurred in the presence of high or low dose rIL-2. These results indicate that LAL are the precursors of LGL/NK cells, that LAL, LGL/NK cells and LAK cells appear to represent sequential developmental or activation stages and that LAL may comprise major source of LAK progenitors in lymphoid populations having few LGL or mature active NK cells.