The heterogeneity of target recognition by lymphokine-activated killer precursor cells

Lymphokine-activated killer (LAK) cells were generated from peripheral blood lymphocytes (PBL) that were depleted of mature cytotoxic natural killer (NK) cells. PBL NK activity was abolished by pretreatment of effector cells with the toxic lysosomotropic agent L-leucine methyl ester (LME) or by depletion of effector cells by K562 monolayer absorption (MA). Both treatments markedly reduced the proportion of cells expressing NK-associated markers such as CD 16 (Leu 11b, B73.1), Leu 7, and NKH-1 (Leu 19), whereas these treatments had minimal effects on cells expressing T cell markers (CD 3, CD 4, and CD 8). LME and MA also drastically decreased the proportion of K562 target-binding lymphocytes. LAK activity against NK-sensitive and NK-resistant targets can be generated from the NK cell-depleted PBL by incubation with interleukin-2. Peak LAK activity generated from MA-treated PBL was later than the peak of LAK activity generated from either untreated or LME-treated PBL. Although MA of PBL on NK-resistant S4 sarcoma targets had little effect on NK activity, LAK activity against both K562 and S4 targets was reduced. These results suggest that there are at least three LAK precursor subpopulations in PBL: mature NK cells that can bind and kill K562 targets (LME-sensitive and MA-sensitive); "pre-NK" cells that can bind but cannot kill (LME-resistant and MA-sensitive); and non-NK cells that cannot bind and cannot kill K562 targets (MA-resistant).     

The Heterogeneity of Target Recognition by Lymphokine-activated Killer Precursor Cells

Lymphokine-activated killer (LAK) cells were generated from peripheral blood lymphocytes (PBL) that were depleted of mature cytotoxic natural killer (NK) cells. PBL NK activity was abolished by pretreatment of effector cells with the toxic lysosomotropic agent l -leucine methyl ester (LME) or by depletion of effector cells by K562 monolayer absorption (MA). Both treatments markedly reduced the proportion of cells expressing NK-associated markers such as CD 16 (Leu 11b, B73.1), Leu 7, and NKH-1 (Leu 19), whereas these treatments had minimal effects on cells expressing T cell markers (CD 3, CD 4, and CD 8). LME and MA also drastically decreased the proportion of K562 target-binding lymphocytes. LAK activity against NK-sensitive and NK-resistant targets can be generated from the NK cell-depleted PBL by incubation with interleukin-2. Peak LAK activity generated from MA-treated PBL was later than the peak of LAK activity generated from either untreated or LME-treated PBL. Although MA of PBL on NK-resistant S4 sarcoma targets had little effect on NK activity, LAK activity against both K562 and S4 targets was reduced. These results suggest that there are at least three LAK precursor subpopulations in PBL: mature NK cells that can bind and kill K562 targets (LME-sensitive and MA-sensitive); "pre-NK"cells that can bind but cannot kill (LME-resistant and MA-sensitive); and non-NK cells that cannot bind and cannot kill K562 targets (MA-resistant).     

健康人和骨肉瘤病人来源的LAK细胞体外抗瘤作用

采用５１Ｃｒ释放试验对健康人和骨肉瘤病人外周血单个核细胞（ＰＢＭ）在重组白细胞介素－２（ｒＩＬ－２）条件下，ＬＡＫ细胞的诱导形成及对４种传代瘤细胞的体外杀伤活性进行探讨。实验结果表明：２种来源ＬＡＫ细胞对Ｋ５６２（人慢性髓样红白血病细胞系）、ＳＭＭＣ７７２１（人肝癌细胞系）、ＬＡＸ（人肺腺癌细胞系）的杀伤活性均在５５％以上（按效靶比例５０：１），而对ＯＳ细胞（人骨肉瘤细胞系）的活性普遍低下，杀伤率低于３５％。结果证实：１）健康人和骨肉瘤病人的ＰＢＭ均能在ｒＩＬ－２条件下诱导形成具有广谱抗瘤活性的ＬＡＫ细胞群，二者的杀伤格局和效力相近。２）骨肉瘤细胞本身对ＬＡＫ细胞的杀伤作用存在强烈抗性。     

Preparation of NK-enriched LAK cells--their potential cytotoxic and ADCC activities

We examined several culture methods to induce proliferation of natural killer (NK) cells from peripheral blood mononuclear cells (PBMC). In the presence of IL-2, a remarkable proliferation of NK cells was observed when PBMC were co-cultured with MMC-treated K562, which is known as a highly sensitive in vitro target cell for the NK assay. Addition of OK-432 or TNF-alpha and IL-1 beta also induced marked NK proliferation in a dose dependent manner. These NK-enriched lymphokine activated killer (LAK) cells showed highly cytotoxic activities against various MHC class I positive or negative tumor cells. They also showed potent ADCC activities against Herceptin-coated SK-BR-3, a HER2/neu positive breast cancer cell line. These results indicated that NK-enriched LAK cells are potent effector cells, and suggested novel therapeutic strategies for nonspecific immunotherapy as well as target immunotherapy in combination with anticancer antibodies, such as Herceptin.     

Preparation and Bioactivity Assay of CD3AK Cell from Lmbilical Cord Blood：—Clinic Report of 10 Tumor Cases

Objective To study the anti-tumor effect of CD3AK cell prepared from umbilical blood,to explore the short-term curative effect on tumor cases and seek better immune index for biotherapy.Methods IL-2 and IL-2 CD3Ab were used to induce LAK cells and CD3AK cells isolated from umbilical blood mononuclear cells(UBMC).The expanding number and bioactivity of LAK cells and CD3AK cells were examined at different time points after culture,the NK activity of peripheral blood mononuclear cells(PBMC)of 10 cases of malignant tumor were determined before and after CD3AK cell adopting immune therapy as well.Results The number and bioactivity(NK killing K562 cell)of LAK and CD3AK cells reached their peaks on 11 th day.The number of LAK and CD3AK cells were 18 folds and 24 folds of that before culture;The NK activities of LAK and CD3AK against K562 were 2.6 folds and 3.2 folds of those before culture respectively.The nK activity for killing K562 cells of malignant tumor patient‘s PBMC was increased from 63%-81% by CD3AK cell transfusing,rising mean 28%.Conclusion (1)The UBMC is a potential and better source of predecessor for LAK and CD3AK;(2)The NK activity of LAK and CD3AK cells from UBMC reached their peaks at 11 th day after culture,and the NK aftivity of CD3AK cells in much greater than that of LAK cells;(3)The NK activity of malignant tumor patient‘s PBMC can be obviously elevated by transfusing CD3AK cell(4)The test of NK activity of PBMC of malignant tumor patient may become an objective immune index for tumor biotherapy.     

Inhibition of colony formation of drug-resistant human tumor cell lines by combinations of interleukin-2-activated killer cells and antitumor drugs

The cytotoxicity of interleukin-2-activated killer (LAK) cells with or without anticancer drugs against cell lines with acquired drug resistance was evaluated in vitro by colony assay. Human non-small cell lung cancer cell lines, PC-9 and PC-14, human leukemia cell line, K-562, and their sublines resistant to cisplatin (CDDP), PC-9/CDDP and PC-14/CDDP, and to adriamycin (ADM), K-562/ADM, were used as target cells. PC-9/CDDP demonstrated a marked increase in susceptibility to killing by both peripheral blood lymphocytes (PBL) and LAK cells, as compared to the parental cell line, PC-9. The cytotoxicity of PBL and LAK cells against PC-14/CDDP and K-562/ADM was similar to that against their parental cell lines. Moreover, the combination of LAK and CDDP had a synergistic effect on PC-14 and PC-14/CDDP.     

Inhibition of Colony Formation of Drug-resistant Human Tumor Cell Lines by Combinations of Interleukin-2-activated Killer Cells and Antitumor Drugs

The cytotoxicity of interleukin-2-activated killer (LAK) cells with or without anticancer drugs against cell lines with acquired drug resistance was evaluated in vitro by colony assay. Human non-small cell lung cancer cell lines, PC-9 and PC-14, human leukemia cell line, K-562, and their sublines resistant to cisplatin (CDDP), PC-9/CDDP and PC-14/CDDP, and to adriamycin (ADM), K-562/ADM, were used as target cells. PC-9/CDDP demonstrated a marked increase in susceptibility to killing by both peripheral blood lymphocytes (PBL) and LAK cells, as compared to the parental cell line, PC-9. The cytotoxicity of PBL and LAK cells against PC-14/CDDP and K-562/ADM was similar to that against their parental cell lines. Moreover, the combination of LAK and CDDP had a synergistic effect on PC-14 and PC-14/CDDP.     

Increased cytotoxicity against B-chronic lymphocytic leukemia by cellular manipulations: potentials for therapeutic use

B-cell chronic lymphocytic leukemia (CLL) is characterized by profound immune dysfunction and a marked resistance to apoptosis. Understanding the cellular biology of immune effector cells from CLL patients as well as leukemic target cells is essential to developing immune mediated therapeutic strategies for CLL. In this study, an immortal CLL cell line called WSU-CLL has been used to study the characteristics of B-cell CLL as a tumor target for natural killer (NK), activated natural killer, and lymphokine activated killer (LAK) cells. The WSU-CLL cells were significantly less (p<0.001) susceptible to NK cell mediated cytotoxicity compared to K562, a standard tumor target cell line. In vitro activation of effector cells with either short term, low dose IL-2 or long term, high dose IL-2 significantly increased the susceptibility of CLL cells for cell mediated killing. The addition of CD1a+/CD3-/CD4+/CD80+/CD83+ dendritic cells derived from human umbilical cord blood increased the cytotoxicity of LAK cells against WSU-CLL. There is an increased expression of Bcl-2 and decreased expression of Fas on WSU-CLL cells as determined by RT-PCR techniques indicating possible roles for these genes in exerting resistance to immune cell mediated lysis. When Bcl-2 expression was downregulated in WSU-CLL cells using gene specific antisense oligonucleotides, the susceptibility of WSU-CLL cells to the cytotoxicity of chemotherapeutic agent Fludarabine was increased. Thus, our results suggest that in vitro activation with cytokines, addition of accessory cell populations such as dendritic cells and/or manipulation of key gene expression i.e. down regulation of Bcl-2 might be potential strategies to increase the antitumor cytotoxicity against CLL cells.     

Tumour necrosis factor-alpha enhances the cytolytic and cytostatic capacity of interleukin-2 activated killer cells

The cytotoxic and cytostatic responses of peripheral blood lymphocytes from eight cancer patients and splenocytes from four patients activated with rIL2 and a combination of rIL2 and rTNF-alpha were tested against two tumour cell lines. The cytotoxic response of rIL2-activated lymphocytes did not exceed the natural killer cytotoxicity values in all patients tested. In fact the killing capacity of some PBL deteriorated after rIL2 activation. The combined use of rIL2 and rTNF-alpha reversed this detrimental effect and enhanced the cytotoxic capacity of all PBL tested. In instances where high levels of killing were already achieved by rIL2 alone additional rTNF-alpha did not induce a significant change. This indicates that the role of rTNF-alpha may be to promote the response to rIL2 of PBL which react suboptimally to this lymphokine. rTNF-alpha did not only enhance cytotoxic capacity but also conferred cytostatic capacity to rIL2-activated LAK cells which were cytotoxic but unable to inhibit the growth of the surviving target cells. Natural killer cell selected K562 target cells which were less susceptible to killing by untreated lymphocytes than the parent K562 tumour cell line were killed more aggressively by rIL2 + rTNF-alpha LAK cells than by rIL2-LAK cells. No phenotypic differences were detected in these two cultures of LAK cells which indicates that the increased cytotoxic and cytostatic capacity of rIL2 + rTNF-alpha-LAK cells may be due to a higher state of activation of these cells or due to their capacity to recognise a broader spectrum of targets than rIL2-LAK cells.     

Reversible inhibition of lymphokine-activated killer cell activity by lipoxygenase-pathway inhibitors

Natural killer (NK) cells and lymphokine-activated killer (LAK) cells are anomalous cytotoxic cells which are potentially important in host defense against cancer. Several studies have demonstrated that natural killer (NK) cell activity can be suppressed by chemical inhibitors of the lipoxygenase pathway through inhibition of the production of leukotriene B4 (LTB4). The present study investigated the effects of the lipoxygenase inhibitors BW755C and nordihydroguaiaretic acid (NDGA) on NK and LAK cell activity. NK cell function of fresh peripheral blood mononuclear cells (PBMC) was determined via a standard chromium release assay employing K562 as the tumor target. The LAK cell activity of PBMC which had been stimulated with 10 IU of interleukin-2 for 72 hr was determined against the NK-resistant cell line Daudi. Both BW755C and NDGA inhibited NK and LAK cell function at a variety of concentrations. Indomethacin, a prostaglandin synthesis inhibitor, did not bring about an appreciable diminution in NK or LAK cell activity. Inhibition of NK and LAK cell activities by BW755C and NDGA could be reversed by washing the effector cell suspensions prior to the cytotoxic assay or by adding LTB4 (10(-11)-10(-8) M) directly to the effector:target suspensions. These data indicate that certain arachidonic acid oxidation products of the lipoxygenase pathway are essential for the function of LAK cells.     

Ewing's sarcoma: ex vivo sensitivity towards natural and lymphokine-activated killing

We studied the ex vivo cell-mediated cytotoxicity of natural killer (NK) and lymphokine-activated killer (LAK) cells against continuously cultured Ewing's sarcoma cells from 3 different patients. Target cell lysis was measured in a 4-hour 51Cr radioisotope release assay. At an effector to target (E:T) ratio of 50:1, the mean (+/- 1 SD) cytolysis by fresh purified large granular lymphocytes (NK cells) was 20 +/- 8, 25 +/- 2, and 21 +/- 3% in Ewing's sarcoma cell lines 6647, 5838, and A4573, respectively. Under identical conditions, NK cells lysed 56 +/- 7% of K562 (a standard NK target), and 3 +/- 3% of Daudi (a standard NK-resistant LAK target). When compared to fresh unseparated peripheral blood mononuclear cells (PBMC), purified NK cells did not exhibit an enhanced cytotoxic reactivity against either Ewing's sarcoma target. In contrast, LAK cells (i.e., PBMC that were preincubated for 4 days in the presence of rIL-2) were highly cytotoxic against all three Ewing's sarcoma targets. LAK activity was dependent on the concentration of rIL-2 used in PBMC cultures. Optimum cell-mediated toxicity against the standard LAK target Daudi (99 +/- 10% cytolysis at 50:1 E:T ratio) was achieved at rIL-2 concentrations of 1,000 u/ml. LAK cells grown under these conditions were also effective against Ewing's sarcoma cells. At an E:T ratio of 50:1, 86 +/- 16, 85 +/- 16, and 67 +/- 13% inhibition was observed in 6647, 5838, and A4573 cells, respectively, as compared to 17 +/- 10, 19 +/- 15, and 29 +/- 11% cytolysis by fresh uninduced PBMC. In summary, our results suggest that rIL-2-induced LAK-type immune effector cells may be of some therapeutic value in the treatment of poor prognosis Ewing's sarcoma.     

Glycoproteic nature of surface molecules of effector cells with lymphokine-activated killer (LAK) activity. Evidence that T11, T8 or T3 molecules are not involved in tumor-cell lysis by LAK effector T cells

Human peripheral blood mononuclear cells cultured in the presence of interleukin-2 (IL-2) acquire the capability of lysing NK-resistant fresh tumor target cells. In an attempt to delineate the surface structure(s) present on the effector cells, the latter were first treated with different amounts of pronase and neuraminidase. The effect of the enzymes on cytolytic activity against fresh melanoma cells was evaluated and compared with the NK-like activity against K562 target cells of the same effector population. At a pronase concentration of 0.01 mg/ml, no inhibition of NK-like activity was detected, whereas LAK activity was inhibited by more than 75%. In addition, neuraminidase had no effect on NK-like activity, even at 1 U/ml, whereas as little as 0.03 U/ml inhibited LAK activity by more than 75%. Metabolic inhibition of N-linked glycosylation with Tunicamycin prevented the generation of LAK activity, even when added late (18 hr before termination of the culture). Tunicamycin, on the other hand, had no effect on the boost of NK activity induced by IL-2. Provided that LAK activity can also be generated in T-cell (E-rosetting) populations, in the presence of adherent cells, we analyzed the inhibitory activity of monoclonal antibodies (MAbs) to T11, T3 and T8 molecules. While all these MAbs strongly inhibited the specific target cell lysis by alloreactive CTLs, they had no effect on the LAK activity.     

Infiltrative and cytolytic activities of lymphokine-activated killer cells against a human glioma spheroid model

In the present study, we investigated not only the cytotoxic effects of lymphokine-activated killer (LAK) cells on a tumor mass but also the ultrastructural cell-to-cell interaction between LAK effector cells and tumor cells during the cytolytic process within a three-dimensional solid tumor. A multicellular tumor spheroid of a human glioma cell line (U-251MG) was utilized as a solid tumor model. LAK cells were generated from peripheral blood lymphocytes of a healthy donor after stimulation by interleukin 2. Multicellular tumor spheroids with diameters of 500 microns were cocultivated with either LAK cells or nonactivated peripheral blood lymphocytes at the effector:target cell ratio of 20:1, and then time-sequential kinetic, morphological, and ultrastructural analyses were carried out. Morphological and kinetic studies showed that LAK cells directly infiltrated toward the inner areas of multicellular tumor spheroids and caused a progressive tumor destruction. In contrast, peripheral blood lymphocytes hardly exhibited such activities. Ultrastructurally, it was found that the infiltrating LAK effector cells were composed of heterogeneous subpopulations, T-like cells, and large granular lymphocyte-like cells. Both types of lymphocytes tightly adhered to the tumor cells and showed typical morphological features of killing them.     

Cytolysis of mammary tumor targets by resting, interleukin-2 stimulated and in vitro cultured peripheral blood lymphocytes from breast cancer patients

The cytotoxic capacity of resting, interleukin-2 (IL-2)-stimulated and in vitro cultured (3-5 days in 10 U/ml IL-2 containing media) peripheral blood lymphocytes (PBLs) from breast cancer patients to a panel of established mammary tumor cell lines was ascertained. Significant cytolysis (ranging from 7.8 to 12.4%, at an effector: target ratio of 20:1) of all mammary tumor targets (MCF-7, 734B, ZR-75-1, ZR-75-30, BT-20 and Hs578T) by PBLs was demonstrable in 18 h chromium release assays. Natural killer (NK) cytotoxicity was distinct from IL-2 stimulated (5 U/ml) and in vitro cultured PBL cytotoxicity in that resting PBLs were not cytolytic to RAJI cells, normal breast epithelia (Hs578Bst) and fibroblasts. Basal NK activity against mammary tumor targets was significantly reduced in patients receiving chemotherapy when compared to both untreated patients and normal controls. In criss-cross cold target inhibition studies, ZR-75-1 and K562 targets were not mutually competitive in NK cell assays (using resting PBLs) but were mutually competitive in lymphokine-activated killer (LAK) assays (using in vitro cultured PBLs). In eleven independent experiments, basal NK activity of ZR-75-1 cells was increased by a cold target excess of K562 (8.2 +/- 2.4% vs 30.5 +/- 5.2%, mean +/- SE, p greater than 0.01, cold:hot target ratio = 10:1). Interestingly, no such parallel increase of cytolysis of 734B targets by K562 cells was observed. Basal cytotoxicity against ZR-75-1 and K562 targets was serologically depleted using antibodies to natural killer cells HNK-1 and Leu 11b. Thus mammary tumor cell lines parallel autologous tumor cells, yet show features that are distinct from NK-resistant and sensitive lymphoid cell lines in their susceptibility to natural resistant cytolytic mechanisms.     

Natural cytotoxicity in humans: susceptibility of freshly isolatd tumor cells to lysis

The cytotoxic potential of blood lymphocyters from healthy donors was tested against freshly isolated lung cancer cells and the erythroleukemia K562 cell line in short-term 51Cr release assays conducted at an effector:target ratio of 50:1. Most donors exhibited significant activity against K6-562 cells. By contrast, fresh tumor cells were refractory, only 6 of 30 showing significant cytotoxicity. The low susceptibility of these tumor cells was confirmed in third-party cold inhibition assays in which they interfered minimally with killing of K562 targets under conditions in which unlabeled K562 cells efficiently blocked cytotoxicity. Cells prepared from normal lung tissue and Raji cells also failed to inhibit killing. Although in comparison to the K562 cell line freshly isolated tumor cells were resistant, their susceptibility may not be so low as to be biologically irrelevant, inasmuch as boosting of natural killing activity by interferon induced levels of cytotoxicity against both types of target cell that were unattainable by unstimulated effectors. Interferon-boosted killers were lytic for "normal" lung cells and the Raji cell line.     

Synergistic action of a plant rhamnogalacturonan enhancing antitumor cytotoxicity of human natural killer and lymphokine-activated killer cells: chemical specificity of target cell recognition.

The spontaneous natural killer (NK) and lymphokine-activated killer (LAK) cytotoxicity of highly purified CD56+CD3- NK cells (90 to 95%) against NK-sensitive and NK-insensitive target cells was drastically enhanced when a rhamnogalacturonan contained in a commercially available Viscum album extract was present during 4-h cytotoxicity assays. This enhancement correlated strictly with an increased formation of NK cell or LAK cell/tumor cell conjugate formation. Information on the chemical specificity of NK cell and LAK cell interaction with target cells and with the rhamnogalacturonan was obtained from inhibition studies. The most efficient inhibitors (100% inhibition at 5 mg/ml) were acetylated D-mannose and acetylated L-mannonic acid gamma-lactone. They specifically inhibited in a dose-dependent manner: (a) the cytotoxicity of NK cells against K562 cells and the formation of NK cell/K562 cell conjugates; (b) the cytotoxicity of LAK cells against K562 cells and Daudi cells as well as the formation of LAK cell/K562 cell and of LAK cell/Daudi cell conjugates; and (c) the synergistic effects of the rhamnogalacturonan in the cytotoxicity assays and the target cell-conjugate formation assays with NK cells and LAK cells. The inhibitory effects observed after pretreatment of NK cells or LAK cells with acetylated mannose were completely reversible, but that obtained with acetylated mannonic acid gamma-lactone was only partly reversible, and the degree of reversibility depended on the inhibitor concentration applied during pretreatment. Nonacetylated mannose or mannose derivatives up to concentrations of 20 mmol showed no inhibitory effects. A mechanistic model representing the interaction of NK cells and LAK cells with target cells and with rhamnogalacturonan is proposed.     

脐血CD3AK细胞治疗恶性肿瘤的临床应用研究

目的:研究用脐血单个核细胞制备CD3AK细胞的抗肿瘤作用,探讨肿瘤生物治疗近期疗效的免疫指标.方法:分离脐血单个核细胞,分别用IL-2和IL-2 CD3Ab诱导LAK和CD3AK细胞,并测其扩增数量和对K562细胞的杀伤活性;测定肿瘤患者用CD3AK细胞治疗前后外周血T淋巴细胞亚群绝对计数的变化情况和外周血单核细胞(PBMC)的NK杀伤活性.结果:脐血LAK细胞和脐血CD3AK细胞均于培养后11天时扩增倍数最高,分别是培养前的18倍、24倍,对K562的杀伤活性分别是培养前的2.6倍和3.2倍;肿瘤患者输注CD3AK细胞一疗程后,其外周血T淋巴细胞亚群绝对计数有明显升高:总T升高66.0%,Th升高68.0%,Ts升高58.0%;其PBMC的NK杀伤活性由63.0%升高到81.0%,平均升高28.0%.结论:1)脐血单个核细胞是LAK细胞和CD3AK细胞良好的前体细胞.2)LAK和CD3AK细胞的数量和杀伤能力在培养的11天时达高峰,而且CD3AK细胞数量和杀伤活性明显优于LAK细胞.3)CD3AK细胞输注能明显提高肿瘤患者外周血T淋巴细胞亚群绝对计数和PBMC的NK活性.4)肿瘤患者的外周血T淋巴细胞计数和PBMC的NK活性测定可望成为肿瘤生物治疗的一个近期疗效参数.     

Recombinant interleukin-2 activates peripheral blood lymphocytes from children with acute leukemia to kill autologous leukemic cells

In order to determine if recombinant interleukin-2 (rIL-2) can induce lymphokine-activated killer (LAK) cells able to lyse autologous leukemic cells, we incubated peripheral blood (PB) mononuclear cells from children with acute leukemia with 50 U/ml rIL-2 for 5 days. These PB effector cells were then tested for their ability to lyse autologous leukemic cells in a 51CR release assay. The PB cells before incubation with rIL-2 showed little or no cytotoxicity for autologous blasts (range, 0 to 12%; mean, 2%). However, after incubation with rIL-2, PB cells from four of five children with acute lymphoblastic leukemia (ALL) at diagnosis or in relapse, and from six of eight children with ALL in remission were able to lyse autologous blasts. The percent lysis (range) was 0 to 69% (mean, 37%) for the former group, and 0 to 113% (mean, 43%) for the latter group. The PB cells from three patients (one in relapse and two in remission) failed to develop LAK activity after incubation with rIL-2. However, in each case cytotoxicity versus K562 was increased after incubation with rIL-2. Furthermore, in a Phase I study of rIL-2 for the treatment of refractory leukemia, a patient was treated with rIL-2 for 3 weeks (nine injections of 3 x 10(6) U/m2 each). Her fresh PB mononuclear cells developed a low level of cytotoxicity (11% lysis) against her autologous blasts during this time. The finding that rIL-2 in vitro and in vivo induces LAK cells with cytotoxicity against autologous leukemic cells provides the rationale for the clinical trial of this agent in the treatment of children with ALL.     

Lymphokine-activated killer cells can kill target cells not only by early killing but also by late killing,and the late killing level against autotumor cell line

Generally, lymphokine-activated killer (LAK) cells kill target cells early after the LAK cells adhere to them. In this study, we describe that LAK cells can also kill at a later time, such as 24-96 h. LAK cells were generated from a cancer patient and healthy volunteers. As target cells, the patient's autotumor cell line H41 was used. When LAK cells were added to the target cells in a culture well, the LAK cells killed the target cells by cell-cell adhesion within 1-4 h (early killing), but not all cells were killed. The LAK cells were then removed. However, the remaining cells ultimately died 24-96 h later (late killing). The late killing was different from the early killing because numerous granules and vacuoles appeared in the cytoplasm. The late killing was not induced by adding supernatant of the LAK cell culture, suggesting that LAK-target cell contact may be necessary for the killing. The cell injury was inhibited by 3-methyladenine (lysosome inhibitor). It suggests that the vacuoles may be caused by activated lysosome. The patient's LAK cells induced late killing at high levels. There was a high percentage of CD8(+)CD16(+) cells in the peripheral blood lymphocytes (PBL). This subset induced late killing more effectively than the CD8(-)CD16(+) subset. Killing was more conspicuous against H41 than against allogeneic cell line T98G. This type of killing is noteworthy for understanding of killing mechanism of LAK cells.