Generation and characterization of lymphokine-activated killer cells against fresh human leukemia cells

Lymphokine-activated killer (LAK) cells generated from 15 acute leukemia patients in remission showed significant levels of cytotoxicity against Daudi 1A4, a natural killer-resistant cell line. This indicates that lymphocytes of leukemia patients in remission could respond to interleukin-2 to generate conventional LAK cells. However, LAK cells caused lysis of autologous leukemia cells at considerably lower levels in seven out of the 15 patients, with the exception of one case (48.6% cytolysis). None of the remaining eight patients exhibited LAK activity against autologous leukemia cells. On the other hand, patients' LAK could lyse allogeneic leukemia cells including those resistant to autologous LAK. Thus, patients' LAK seem not to be defective in lysis of leukemia cells. In the cold target competition analysis, the binding of patients' LAK to leukemia cells could be inhibited by autologous and allogeneic leukemia cell competitors, implying that almost all leukemia cells could be recognized by patients' LAK. Most LAK cells from normal donors showed significant lysis of allogeneic leukemia cells, but some leukemia cells were found to be resistant to lysis. LAK cells against both leukemia cells and Daudi 1A4 were phenotypically heterogenous, and were predominantly observed in the T3- fraction in the precursor phase. In the effector phase, whereas LAK activity against leukemia cells was also predominantly shown in the T cell-depleted fraction, similar levels of LAK activity against Daudi 1A4 were found in both the T cell-depleted and -enriched fractions.     

Increased susceptibility to lymphokine activated killer (LAK) lysis of relapsing vs. newly diagnosed acute leukemic cells without changes in drug resistance or in the expression of adhesion molecules.

The NK and LAK activity of peripheral blood lymphocytes of leukemic patients as well as the susceptibility of their acute myeloid (AML) and lymphoblastic (ALL) leukemia cells to autologous and allogeneic LAKs were examined. In addition, neoplastic cells at diagnosis and at relapse were compared in the same patients for several features, including in vitro susceptibility to LAKs and to the drugs used in the induction phase, expression of MDR phenotype and of adhesion molecules, and differentiation markers. The NK activity of patients' LAK cells on K562 was significantly lower than that of a group of healthy donors whereas no differences were found in LAK activity as evaluated on Daudi cells. Three of 5 AML and 3 of 4 ALL were significantly more susceptible to autologous and allogeneic LAK lysis when blasts obtained at relapse were compared with leukemic cells of the same patients at diagnosis. This different lysability was not associated with in vitro modified sensitivity to drugs used in induction treatment. Moreover, no elevation in the expression of the multidrug-resistance (MDR)-related P170 glycoprotein was noted in relapsing leukemic cells. Even the expression of adhesion molecules and differentiation markers did not correlate with lysability of leukemic cells. These data demonstrate that relapsing leukemic blasts can be significantly lysed by LAK cells and suggest a rationale for adoptive immunotherapy with IL-2 and LAK cells in the treatment of acute leukemic patients.     

Cytotoxic Activity of Various LAK Cells against Autologous Lung Cancer, K-562 and Daudi Cells

Comparative cytotoxic activity and specificity studies of lymphokineactivated killer (LAK) cells from different sources and preparationswere carried out. Cytotoxic studies of lymphocytes from regionallymph nodes (Rn-LAK), peripheral blood (Pb-LAK) and those stimulatedby autologous tumor cells and then activated by recombinantinterleukine 2 (St-LAK) against autologous lung cancer cells,were conducted using the ⁵¹Cr-releasing test. The cytotoxicactivities of these three LAK cells against autologous fibroblasts,allogeneic tumor cells, K-562 and Daudi cells were also compared.A time course experiment disclosed that the cytotoxic activityof Pb-LAK cells against autologous tumor cells reached a maximumon day 3 and declined shortly after the peak while that of Rn-LAKcells gradually increased to a maximum on day 7 and remainedat a high titer for at least two weeks. The cytotoxic activityof Rn-LAK cells was significantly higher than that of Pb-LAKcells in seven out of 10 individual experiemnts and that ofstimulated LAK (St LAK) cells was higher than the cytotoxicactivities of the other LAK cells in eight out of nine experiments.A specificity study showed that Rn-LAK cells possessed a highercytotoxic activi ty against autologous tumor cells and a lowercytotoxic activity against autologous fibroblasts and allogeneictumor cells than Pb-LAK cells. A comparative study of cytotoxicactivities against K-562, Daudi cells and autologous tumor cellsbetween St- and Rn-LAK cells demonstrated that although therewas no difference in natural killer activity, cytotoxic activityagainst autologous tumor cells as well as the LAK activity ofSt-LAK cells were higher than that of Rn-LAK cells. These resultsindicate that the activities and specificities of LAK cellsdiffer according to their source and preparation.     

Lysis of autologous melanoma cells by tumor-infiltrating lymphocytes: association with clinical response

Tumor-infiltrating lymphocytes (TILs) can be grown in vitro in medium containing interleukin-2 (IL-2). In clinical trials at the Surgery Branch of the National Cancer Institute, patients with metastatic malignant melanomas were treated with IL-2 plus the adoptive transfer of autologous TILs. At the time of treatment, TILs were assayed for in vitro lysis of fresh autologous and allogeneic melanoma cells and Daudi cells. Patients were evaluated for clinical response 4-8 weeks later. Lysis of autologous tumor cells by TILs was significantly higher for responding than for nonresponding patients. Tumor cells from responding and nonresponding patients were equally sensitive to lysis by allogeneic lymphokine-activated killer (LAK) cells. There was no difference between TILs from responding and nonresponding patients for lysis of LAK-sensitive Daudi cells, which was low in most cases and demonstrated that TIL lysis of autologous tumor cells was not due to LAK cells. The observed association of autologous tumor cell lysis by TILs with clinical response suggests that the development of culture methods to optimize lysis of autologous tumors may lead to increased response rates using this TIL treatment regimen.     

Alpha-interferon and lymphokine-activated killer cells in hairy cell leukemia

Lymphokine-activated killer (LAK) cell activity generated from peripheral blood was tested in 6 patients with typical hairy cell leukemia, 3 not on treatment with alpha-interferon (alpha-IFN) and 3 receiving therapy. In all cases, substantial killing of the LAK-sensitive target Daudi was observed, but hairy cells, whether or not they had been pretreated with alpha-IFN, were uniformly resistant to LAK lysis. The hairy cells were also resistant to LAK cell killing generated from normal peripheral blood mononuclear cells. alpha-IFN added at various times during LAK generation had little or no effect on LAK activity. It is concluded that LAK cells are not important in mediating the beneficial effects of alpha-IFN in hairy cell leukemia.     

Functional analysis of cytotoxic cells in patients with acute nonlymphoblastic leukemia in complete remission

In the current study, we investigated the cytotoxic ability of peripheral blood mononuclear cells (PBMC) recovered from patients with acute nonlymphoblastic leukemia (ANLL) in complete remission (CR) against natural killer (NK)-sensitive, NK-resistant, autologous and allogeneic leukemic target cells taken at diagnosis. Our purpose was to define the role played by cytotoxic mechanisms in the control of leukemic cell growth in ANLL. Experiments were carried out at resting conditions and after in vitro activation with recombinant interleukin-2 (rIL-2) and anti-CD3 monoclonal antibody (moAb). At resting conditions, PBMC recovered from ANLL patients displayed a NK function that was not significantly different from controls (mean +/- standard error of the mean [SEM]: 21.9% +/- 3.9% versus control values of 27.5% +/- 2.9%; the P value was not significant [NS]), but they were unable to show cytotoxic activity against autologous and allogeneic leukemic cells. After in vitro boosting with rIL-2, PBMC were able to generate lymphokine activated killer (LAK) cells, as demonstrated by an increased killing of NK-resistant Daudi targets (16.3% +/- 2.7%). Although LAK activity was quantitatively lower than in control subjects (mean +/- SEM: 16.3% +/- 2.7% versus control values of 79.8% +/- 3.1%; P less than 0.001), it still exerted a cytotoxic effect against autologous and allogeneic leukemic cells. Similar results were obtained when anti-CD3 moAb was used as a stimulus in vitro. Our data suggest that nonspecific cytotoxic cells may be triggered to exert an in vitro cytotoxic effect on leukemic cells, which could possibly play a key role in vivo in the control of leukemic cell growth regulation.     

Susceptibility of acute myelogenous leukemia blasts to lysis by lymphokine-activated killer (LAK) cells and its clinical relevance.

To help understanding host-tumor relationships in acute myelogenous leukemia (AML) and better define indications for interleukin 2 (IL-2) therapy in this disease, we studied the relationship between the susceptibility of leukemic cells of 44 AML patients to lysis by autologous (26 cases) and/or allogeneic (41 cases) lymphokine-activated killer (LAK) cells and characteristics of the leukemia. Lymphocytes were activated in the presence of 1000 u/ml recombinant IL-2 for 5 days. Lysis of AML cells was studied by 51Cr release. Average lysis of AML cells by autologous LAK cells was 9 +/- 13% and by allogeneic LAK cells 10 +/- 9% with a significant correlation between lyses by both effectors (p = 0.01). Autologous (p = 0.005) and allogeneic (p = 0.004) lyses were higher in patients with initial infection. Allogeneic lysis was correlated with initial WBC count (p = 0.009), serum lactic-dehydrogenase level (p = 0.05), and expression of CD13 (p = 0.01). Autologous lysis was inversely correlated with expression of CD34 (p = 0.003). Expression of adhesion molecules CD54 (ICAM-1) and CD58 (LFA-3) by the leukemic cells did not correlate with their lysis by LAK cells. Susceptibility of leukemic cells to lysis by LAK cells did not correlate with prognosis of the leukemia.     

Resistance of chronic lymphocytic leukaemia cells to interferon-alpha generated lymphokine activated killer cells.

Recent studies have shown that, when used in early stage disease, interferon-alpha (IFN-alpha) can produce a fall in the number of malignant cells in the peripheral blood of patients with B-CLL. In this study, we investigated the effect of IFN-alpha on natural killer (NK) cell and lymphokine-activated cell (LAK) activity in patients with B-CLL. In vitro, IFN-alpha (500 U/ml for 18 hours) induced LAK activity in patients with B-CLL (27.7 +/- 9.9%, n = 20), and IL-2 (500 U/ml for 5 days) produced similar activity (35.9 +/- 8.8%, n = 7). Despite the induction of LAK activity by IFN-alpha and IL2 in patients with B-CLL, the malignant cells remained resistant to both allogeneic and autologous LAK effectors. NK activity in patients with B-CLL is also low (23.1 +/- 7.2%, n = 20), and B-CLL cells were resistant to NK cell activity. In cold target competition assays, CLL cells did not compete with labelled K562 or Daudi targets in the NK and LAK assays, suggesting that the malignant cells are not recognised by the effector cells, and this may be related to low level of expression of the adhesion receptors, LFA-1 and ICAM-1. Finally, CLL cells were also resistant to antibody dependent cell mediated cytotoxicity, but were susceptible to antibody dependent complement mediated lysis. These results suggest that it is unlikely that the effects of IFN-alpha in B-CLL are due to the enhancement of NK or LAK activity.     

Lymphokine activated killing of fresh human leukaemias

The relative susceptibility of 10 human leukaemias comprising acute phase leucocytes from 5 acute myeloid and 5 lymphoid neoplasms, and 2 immunoblastic lymphomas to killing by peripheral blood mononuclear cells (PBMC), before and after target cell treatment with phytohaemagglutinin (PHA), and by interleukin-2 (IL-2) activated peripheral blood lymphocytes (PBL) was investigated in short term 51Cr release assays using effector cells from 10 allogeneic donors. Optimal lectin-dependent cellular cytotoxicity (LDCC) was verified against K562 and L1210 cells and lymphokine-activated killing (LAK) against K562 and Daudi cells. Under these conditions, the majority of the leukaemias tested revealed only a finite sensitivity to any of the cytotoxic mechanisms, which was dependent on the donor origin of the effectors. The leukaemias were more consistently susceptible to LDCC than LAK and removal of adherent cells to enrich for the latter activity in effector populations, was ineffective. Lymphocytes from a patient in long term (greater than 5 yr) remission exhibited LAK against the autologous target E84, a natural killer (NK)-sensitive acute myelomonocytic leukaemia. These cells failed to cross-compete for lysis of K562 by LAK cells, suggesting the existence of different recognition structure(s) on the two targets.     

Susceptibility of adult acute lymphoblastic leukemia blasts to lysis by lymphokine-activated killer cells

To help understand host-tumor relationships in adult acute lymphoblastic leukemia (ALL) and to better define potential indications for interleukin-2 (IL-2) treatment in this disease, the relationship between the susceptibility of leukemia cells of 22 patients with ALL to lysis by allogeneic lymphokine-activated killer (LAK) cells and characteristics of the leukemia was studied. Lymphocytes were activated in the presence of 1000 U/ml recombinant IL-2 for 5 days. The lysis of ALL cells was studied by the release of 51Cr. The average lysis of ALL cells by control, unactivated lymphocytes was 1.2 +/- 2.4% and by LAK cells 8.9 +/- 8.6%. The susceptibility of leukemic cells to lysis did not correlate with the expression of lymphoid or myeloid differentiation markers or expression of the adhesion molecules CD54 (ICAM-1) and CD58 (LFA-3). Leukemic cells of the FAB I2 subtype were significantly more resistant to lysis than those of the other subtypes (average lysis 1.4 +/- 3.0% versus 12.3 +/- 8.2%, p = 0.003). The susceptibility to lysis did not correlate with the other initial characteristics of the leukemia. The 11 patients in whom 8% or more of leukemic cells were lysed by allogeneic LAK cells survived significantly longer than the 11 patients whose blast cells were less susceptible to lysis (p = 0.04). It is concluded that IL-2 treatment might be of benefit in adult ALL, particularly in non-L2 FAB subtypes and during complete remission to possibly delay relapse and prolong survival.     

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.     

肺癌肿瘤全溶物脉冲自体树突状细胞体外诱生T细胞抗肿瘤反应的研究

目的　探讨非小细胞肺癌 (NSCLC)患者全瘤溶解物 (WTL)冲击的自体树突状细胞 (DCs)瘤苗体外诱生T细胞介导的抗肿瘤反应。方法　在含重组人粒细胞 巨噬细胞 集落刺激因子 (rhGM CSF)和重组人白细胞介素 4 (rhIL 4 )的培养条件下 ,以 10例患者的贴壁外周血单核细胞 (PBMCs)衍生不成熟的树突状细胞 (imDCs) ,分别添加肿瘤坏死因子 (TNFα)、自体WTL或WTL TNFα诱导成熟 ,即分别为DCs/TNF、DCs/WTL和 DCs/WTL ,用流式细胞仪和混合淋巴细胞反应 (MLR) ,检测细胞表面分子的表达变化及其刺激异基因或同基因的T细胞增殖能力。将 DCs/WTL和自体T细胞共培养1～ 2周 ,以诱导细胞毒性T淋巴细胞 (CTL) ,用计数γ 干扰素 (IFN γ)释放的酶联免疫斑点 (ELISPOT)试验和乳酸脱氢酶 (LDH)释放的细胞毒试验 ,分别检测该CTL中识别自体肿瘤细胞释放特异性IFN γ的T细胞数和溶瘤活性。结果　以 30 μg/ml蛋白的WTL体外冲击自体 10 6imDCs,可导致上调DC表型 ,包括CD1a、CD83和CD86以及HLA DR的分子表达 ,与常规TNFα诱导成熟的DCs表型相似。虽然两者均能显著刺激异基因T细胞的增殖 ,但其刺激自体T淋巴细胞的增殖能力 ,DCs/WTL却显著高于DCs/TNF(P <0 .0 5 )。将体外与 DCs/WTL共培养的自体T细胞作为反应或效应细胞 ,再次     

Interleukin-2-inducible Killer Activity and Its Regulation by Blood Monocytes from Autologous Lymphocytes of Lung Cancer Patients

The ability of blood lymphocytes of newly diagnosed lung cancer patients to respond to interleukin 2 (IL-2) to become IL-2-activated killer (LAK) cells and its regulation by autologous monocytes were examined. LAK activity was measured by ³¹Cr release assay. The abilities of lymphocytes among blood mononuclear cells (MNC) of subjects of different ages without malignancies to generate LAK activity against NK-cell resistant Daudi cells and lung adenocarcinoma (PC-9) cells were very similar. The LAK activity of blood MNC of lung cancer patients was also nearly the same as that of blood MNC of control subjects. There was no significant difference in IL-2-inducible LAK activity between MNC of patients with small cell lung cancer (SCLC) and those of patients with non-SCLC. Monocytes and lymphocytes were separated from blood MNC on a one-step Percoll gradient. Monocytes of lung cancer patients were found to augment in vitro induction of LAK activity by IL-2 of autologous blood lymphocytes. In contrast, endotoxin-stimulated monocytes suppressed LAK induction of autologous lymphocytes of cancer patients. These findings suggest that administration of IL-2 and LAK cells induced in vitro may be of benefit in the treatment of lung cancer.     

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。     

Interleukin-2-inducible killer activity and its regulation by blood monocytes from autologous lymphocytes of lung cancer patients.

The ability of blood lymphocytes of newly diagnosed lung cancer patients to respond to interleukin 2 (IL-2) to become IL-2-activated killer (LAK) cells and its regulation by autologous monocytes were examined. LAK activity was measured by 51Cr release assay. The abilities of lymphocytes among blood mononuclear cells (MNC) of subjects of different ages without malignancies to generate LAK activity against NK-cell resistant Daudi cells and lung adenocarcinoma (PC-9) cells were very similar. The LAK activity of blood MNC of lung cancer patients was also nearly the same as that of blood MNC of control subjects. There was no significant difference in IL-2-inducible LAK activity between MNC of patients with small cell lung cancer (SCLC) and those of patients with non-SCLC. Monocytes and lymphocytes were separated from blood MNC on a one-step Percoll gradient. Monocytes of lung cancer patients were found to augment in vitro induction of LAK activity by IL-2 of autologous blood lymphocytes. In contrast, endotoxin-stimulated monocytes suppressed LAK induction of autologous lymphocytes of cancer patients. These findings suggest that administration of IL-2 and LAK cells induced in vitro may be of benefit in the treatment of lung cancer.     

Isolation of human lymphocyte antigens class I-restricted cytotoxic T lymphocytes against autologous myeloma cells.

Peripheral blood T cells from a patient with multiple myeloma in complete remission were selected in vitro against an autologous myeloma cell line (SBN-1), using a protocol designed for the selection of relatively rare precursor cytotoxic T cells (pCTL). Delayed addition (2 weeks) of interleukin 2 induced T-cell proliferation, and a bulk culture (T-cell line) was obtained 2 days later. This T-cell line displayed cytotoxicity against SBN-1. A CD8+ CD4- cytotoxic T-cell clone (CT5) was then obtained that recognized SBN-1 but not autologous EBV+ B-lymphoblastoid cells, autologous T PHA-blasts, or Daudi, Raji, K562, and 11 allogeneic myeloma cell lines. Moreover, CT5 cytotoxic activity against SBN-1 was blocked by monoclonal antibodies recognizing human lymphocyte antigen class I molecules. This seems to be the first demonstration of myeloma-specific pCTL in peripheral blood T cells of patients with multiple myeloma.     

Local administration of autologous lymphokine-activated killer cells and recombinant interleukin 2 to patients with malignant brain tumors

Lymphokine-activated killer cells (LAK cells) were induced from lymphocytes from patients with malignant glioma by using interleukin 2 (IL-2), and their killing activity was examined. Their LAK activity against Daudi cells was 66.2 +/- 13.1% and 48.7 +/- 12.7% against self glioma cells, 54.4 +/- 10.1% against K562 cells, 43.1 +/- 7.9% against Raji cells, and 33.5 +/- 16.2% against allogeneic glioma cells. The phenotype of these LAK cells was Leu 1 (++), 2a (+/-), 3a (++), 7 (+), and 11 (++). The phenotype of precursor LAK cells, on the other hand, was Leu 1 (-), 2a (-), 3a (+), 7 (-), and 11 (++). Other activated killer cells, including LAK cells, phytohemagglutinin-activated killer cells, autoactivated killer cells, and their precursor LAK cells, were studied serologically in order to identify their phenotypic characteristics. From these data, the LAK cell populations were considered to be polyclonal. Using these LAK cells plus IL-2, local adoptive immunotherapy was undertaken in 23 patients with recurrent malignant glioma. We injected, that is, autologous LAK cells plus IL-2 directly into the cavities of the brain tumors; 1.2 to 324 x 10(8) LAK cells per ml and 0.8 to 5.4 x 10(3) units of IL-2 were directly injected into the brain tumor by using an Ommaya reservoir. Definite tumor regression, improvement of some clinical symptoms, and continuous remission over 6 mo or more were observed in six, nine, and three patients, respectively. There were no marked side effects, except for slight fever and chill, in eight and three patients, respectively. These results suggested the possibility of induction of a sufficient number of LAK cells from the lymphocytes of the patients with recurrent malignant glioma, indicating that local adoptive immunotherapy by direct injections of LAK cells and IL-2 into the brain tumor will prove to be an effective means of immunotherapy. Additional follow-up of the patients will be required before its therapeutic value can be established.     

Cytotoxicity of Cytokine-Induced Killer Cells Coated with Bispecific Antibody Against Acute Myeloid Leukemia Cells

Various types of cytokines have been used in in vitro experiments to generate cytokine-induced killer (CIK) cells that are reactive to patient acute myeloid leukemia (AML) cells. Of these CIK cells, interleukin-2 (IL-2)-activated peripheral blood mononuclear cells, i.e., lymphokine-activated killer (LAK) cells, with the initial addition of the anti-CD3 monoclonal antibody (T3 LAK cells), are the most potent cytotoxic lymphocytes, and have marked proliferative capacity. The cytotoxicity of such T3 LAK cells against CD13⁺ AML cells is further enhanced by the addition of anti-CD3 x anti-CD 13 bispecific antibody (BsAb) during the cytotoxicity assay. The combined use of T3 LAK cells and the BsAb can be used for ex vivo purging of CD13⁺ AML cells in autologous bone marrow transplantation. Other cytokines, such as IL-7 or IL-7 in combination with IL-2, or newly identified cytokines, will also be tested in attempts to obtain more specific and more potent effector cells. Studies of methods to increase the susceptibility of AML cells to CIK are also required.     

Effect of Cytotoxic Cells on Minimal Residual Leukemia

The presence of minimal residual disease is indicated by the high frequency of relapses after twin bone marrow transplants and after allogeneic bone marrow transplants without graft versus host disease (up to 75% and 45% of cases, respectively). The graft versus leukemia effect may be mediated by IL-2 activation of natural killer cells (CD16 +, CD56 +, CD3-, CD8+/-) or cytotoxic T cells (CD3 +, CD56+/-). These activated killer cells can bind to targets and cause their lysis, and then recirculate to kill other targets. Killing can be blocked by anti-perforin antibodies and enhanced by protein kinase C-activation of effectors

There are several studies indicating that a high percentage of leukemic cells can be killed by LAK-cells. However even in the most sensitive cases, lysis of all the cells cannot be achieved. The finding that leukemic clonogenic cells are generally sensitive to both NK and LAK cytotoxicity provides a more hopeful possibility

The lack of tumor specific antigents, leukemic cell-immunoheterogeneity and maturation asynchrony explains why antigen dependent T-cell mediated cytotoxicity is only partly effective in eradicating residual leukemic cells. Future work should therefore include more studies of the mechanism of resistance to LAK cells, possibilities of further enchancing cytotoxicity and the mechanism of graft-versus-leukemia effect     

Augmentation of the Susceptibility of Human Leukemia to Lymphokine-Activated Killer (LAK) Cells by Exposure of the Leukemic Target Cells to Cytotoxic Drugs in Vitro and in Vivo

Experimental studies have shown that interleukin-2-induced lymphokine-activated killer (LAK) cells are able to lyse fresh noncultured leukemia cells and that human leukemia cells have a distinct susceptibility to LAK-cell-mediated cytolysis. Cytolysis is considerably lower with fresh noncultured leukemia cells than with the leukemia cell lines K562 and Daudi. For therapeutic considerations it would be desirable to achieve as much cytolysis as possible. The current study revealed that incubating leukemia cells with cytotoxic drugs in vitro significantly augments their susceptibility to the lytic effect of LAK cells and, more importantly that exposing leukemia cells to anticancer agents in vivo during induction chemotherapy also increases their sensitivity to LAK-cell-mediated cytolysis. These results support a possible benefit from combining chemotherapy with immunotherapeutic approaches in leukemia treatment.