Lymphokine-activated killer (LAK) cells inhibit the clonogenic growth of human leukemic stem cells

Influence of malignant cell clonogenic capacities and position along the maturation pathway on their susceptibility to lymphokine-activated killer cell cytotoxicity

In order to investigate the sensitivity of malignant target cells to lysis by LAK cells according to their clonogenic capacities and their position along the maturation pathway, we compared clonogenic and chromium release cytotoxicity assays performed on human hematopoietic cell lines using Effector: Target ratios of 1:1, 3:1, 6:1, 12:1, 24:1, 48:1 and 96:1, and studied the sensitivity of HL-60 and U937 human cell lines after exposure to different factors including GM-CSF, SCF, IFN, Retinoic acid (RA), DMSO, and TPA which are able to recruit cells into the cell cycle or to induce cell differentiation. There was a good correlation between the lysis of the target cells using 51Cr release and the growth inhibition in semisolid medium. The degree of inhibition was significantly higher using the colony growth assay (p = 0.006). Regarding the effects of culturing cell lines with proliferating and differentiating agents on the sensitivity of these cell lines to LAK cytolysis, a correlation was noted between the proliferative response of the U937 cell line and susceptibility to LAK cell lysis (p = 0.01), while results appeared close to significance with HL-60. The most significant effects were a decreased sensitivity of HL-60 to LAK lysis with RA (p < 0.001) and TPA (p < 0.001), and an increased susceptibility of U937 to LAK lysis with GM-CSF (p < 0.0001). In studies planned to investigate whether susceptibility of treated cells to LAK activity was a consequence of a downregulation of adhesion molecules expressed on target cell surface, the proportion of cells expressing adhesion molecules was not significantly changed, except for CD54 expression on HL-60 cells which showed a higher expression, after cells were treated with RA or DMSO. We conclude that clonogenic cells are more sensitive to LAK cell lysis and that cell line sensitivity to LAK cytolysis can be modulated by a variety of agents of potential therapeutic use. The poor correlation between adhesion molecules expression and sensitivity to LAK lysis suggests that molecules other than CD54, CD56, CD58, and CD106 may possibly be more central to the processes involved.

Cellular immunotherapy and autologous transplantation for hematologic malignancy

The success of allogeneic transplantation is in part due to the immunotherapeutic effect mediated by the graft. Autologous transplantation is hampered by the absence of this effect, leading to a higher relapse rate. We have conducted a series of studies designed to augment the immunologic activity of the graft after autologous transplant with a view towards introducing an autologous graft-versus-tumor effect that could decrease the rate of relapse after autologous transplant. These studies have included IL-2 activation of marrow followed by post-transplant infusional IL-2, the development of a novel protocol for the generation of highly efficient cytotoxic effector cells, termed cytokine-induced killer (CIK) cells, with broad and potent antitumor activity. In order to determine the potential for generating peptide-specific cytolytic T cells, studies have been conducted upon transducing antigen-presenting cells (APC) with AAV vector-mediated gene transfer, a vector capable of transducing non-proliferating target cells. Transduction of human monocytes and macrophages resulted in high expression of the transduced gene. This latter study forms the basis for determining whether genetic modification of APC can potentiate specific immune responses to tumor-specific gene products. Taken together, these strategies will hopefully increase the therapeutic efficacy of autologous transplantation.

The biological therapy of acute and chronic leukemia

With the increasing knowledge of the mechanisms of immune-mediated cytotoxicity, immunotherapeutic strategies are rapidly being incorporated into chemotherapy treatment schemes for acute and chronic leukemias. This includes the use of mAbs, immunotoxins, tumor-specific T cells, and, most recently, vaccines. Much of the new information is derived from bone marrow transplant data, where immune enhancement from IL-2 and donor T-cell infusions are being studied. Trials using humanized mAbs that permit prolonged and repeated dosing will allow better evaluation of the effectiveness of mAb therapy. More sophisticated molecular tests have been developed, allowing the detection of minimal residual disease to a greater degree. It is likely that biological and immunological therapy of leukemia will have its greatest impact here.

Potentiation of lysis of leukaemia cells by a bispecific antibody to CD33 and CD16 (Fc gamma RIII) expressed by human natural killer (NK) cells

Bispecific antibodies recognizing tumour-associated antigens and trigger molecules expressed on immune effector cells have been shown to redirect cytotoxicity of several types of peripheral blood cells against relevant tumour targets. Among various effector cells, natural killer (NK) cells appear to play a role in defence against leukaemia. Here we report the successful chemical conjugation of monoclonal antibodies to CD33 and CD16 to create a bispecific antibody (BsAb 251 x 3G8). This bispecific antibody is capable of augmenting the killing of otherwise resistant leukaemia cells by peripheral blood lymphocytes (PBL), purified resting NK (R-NK) cells, and activated NK (A-NK) cells. BsAb 251 x 3G8 may play a role in the therapy of acute myeloid leukaemia (AML) through redirecting the cytotoxic activity of endogenous or adoptively transferred NK cells.

Polyethylene glycolated interleukin-2 as maintenance therapy for acute myelogenous leukemia in second remission

Seven patients in second complete remission of acute myeloid leukemia (AML) aged 19-65 years were treated with polyethylene glycolated interleukin-2 (PEG IL-2), 1 x 10(6) U/M2 IV weekly as the sole postremission therapy. Second remission duration was in the range of 4-49+ months, and three patients had a second remission duration substantially longer than their first (6, 21+, and 42+ months). The results suggest that PEG IL-2 may prolong second remission duration in AML and that a prospective randomized study designed to test that idea is warranted.

Interleukin-2 and gene therapy in the management of acute lymphoblastic leukaemia

The overall unfavourable prognosis of adult acute leukaemia patients has prompted the search for alternative therapeutic strategies. Probably the most sought challenge, which over the years has been met by consistent disillusion, has been immunotherapy. With little doubt the goal of stimulating the immune system of the host in the hope of controlling or eradicating residual disease following more conventional ablative regimens, remains conceptually a highly desirable approach. During the last few years an innovative strategy, based on the in vitro demonstration that IL2 is capable of inducing a previously unrecognized cytotoxic function directed against primary tumours and named LAK, has been applied with some success in solid tumour patients. Here, we shall review the pre-clinical data which indicate that IL2-based immunotherapy may be employed also in the management of patients with acute leukaemia. Clinical data which support a possible in vivo antileukaemic effect of IL2 are presented. The clinicohaematological modifications, as well as the biological modulations induced in the patients following the administration of IL2 are also discussed. In view of the recent demonstration that the IL2 gene can be successfully transduced into human neoplastic cells, we finally discuss the rationale of gene transfer approaches in an attempt to overcome some of the limitations associated with the administration of high doses of exogenous IL2.

Agar capillary clonogenic microassays for cellular immunocytotoxic activities in human leukaemia and lymphoma

Current concepts of immunotherapeutic approaches in leukemias and lymphomas using activated cytotoxic lymphocytes and macrophages are briefly reviewed. Defective cellular immunocytotoxic activities and effects of interleukins and chemotherapeutic drugs thereupon are discussed. In vitro assays to measure lymphokine-activated killer (LAK) and natural killer (NK) cell activities suffer from various problems, depending on the quality of the endpoints. Our clonogenic microassay for LAK cell activity, using agar-containing glass capillaries, avoids some of the potential artifacts and offers several advantages that are discussed. As an example the stimulatory effect of low mafosfamide concentrations on the LAK cell activity versus K562 human myeloid leukemia cells is demonstrated. Thus, our clonogenic LAK microassay provides a valid tool for preclinical screening of immunomodulatory agents.

IL2 treatment for cancer: from biology to gene therapy

In this review we shall discuss the biological rationale and the clinical findings obtained using Interleukin 2 (IL2)-based immunotherapy in the management of cancer patients. Objective and long-lived clinical responses have been documented in a proportion of cases, particularly renal cell carcinoma, melanoma and acute myeloid leukaemia. Though encouraging, the clinical use of IL2 has so far been limited by toxicity, as well as by the heterogeneous and unpredictable responses and by the lack of specific anti-tumour effect. These considerations have led to the belief that more sophisticated technologies aimed at introducing the IL2 gene into the neoplastic cells may potentially overcome some of the limitations coupled to the in vivo infusion of high doses of IL2. The data accumulated in animal models and, more recently, also with human tumour cells indicate that the IL2 gene may be successfully inserted into neoplastic cells. The constitutive secretion of IL2 by the tumour cells leads to a reduced or abrogated tumorigenicity in several different tumour models. The evidence that in some experimental tumours the transduction of the IL2 gene into the neoplastic cells may elicit a specific cytotoxic response and confer anti-tumour memory, suggests that vaccination protocols based on this innovative strategy may represent a potential new tool in the management of cancer patients.

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.

Generation of adherent lymphokine activated killer (A-LAK) cells from patients with acute myelogenous leukaemia

Successful generation of adherent lymphokine-activated killer (A-LAK) cells, highly-enriched in CD3-CD56+ antitumour effector cells, from the peripheral blood of ten patients with acute myelogenous leukaemia (AML) is described. The AML patients were either untreated or in remission. In vitro proliferation of A-LAK cells in patients with AML was generally poor, unless the cells were cocultured with irradiated concanavalin A (ConA)--prestimulated allogeneic PBL or selected lymphoblastoid cell lines (LCL) as feeder cells. Using this method, the median fold proliferation was 290 for A-LAK cells cultured with ConA-activated feeders and 291 for those grown with LCL, both significantly higher (both P less than 0.001) than the median of 2-fold expansion observed in cultures without feeders. A-LAK cultures generated in the presence of feeders consistently showed good enrichment (up to 90%) in CD3-CD56+ NK cells. Although NK activity was not significantly increased on a per cell basis in A-LAK cells grown with feeder cells, total lytic activities against both NK-sensitive target, K562, and NK-resistant target, Daudi, were significantly greater (P less than 0.02 for ConA-PBL feeders and P less than 0.005 for LCL feeders) as compared to those in paired cultures without feeders. In the presence of irradiated allogeneic feeder cells, 7/10 AML patients generated A-LAK cultures characterised by good proliferation and increased purity as well as cytotoxic activity.

Continuous intravenous infusion of high-dose recombinant interleukin-2 for acute myeloid leukaemia--a phase II study

A group of 13 patients with acute myeloid leukaemia of differing disease status were treated with continuous intravenous infusion of high-dose recombinant interleukin-2 (rIL-2). There was up-regulation of the cellular cytotoxic functions in all these patients following the rIL-2 therapy, with increase in the natural killer (NK) activity, lectin-dependent cellular cytotoxicity, induction of cytotoxicity-linked cytoplasmic serine esterase and lymphocyte activation. However, the clinical response to rIL-2 in these patients was disappointing, especially in patients treated in frank relapse. Although 1 patient treated in early second relapse achieved a third complete remission, the duration of the remission was brief and lasted only 6 months. Adverse reactions among these patients were common. Whether or not lymphokine-activated killer cells are needed to improve the response rate over rIL-2 alone in these patients deserves further investigation.

Treatment of acute myeloid leukaemia patients with recombinant interleukin 2: a pilot study

Twelve patients with acute myeloid leukaemia (AML) with evidence of resistant disease were treated with recombinant interleukin 2 (rIL2) given intravenously by continuous infusion. No objective response to rIL2 alone was documented in the seven patients with advanced disease (20-90% resistant blasts in the marrow), except for a partial response to rIL2 plus chemotherapy in one. Of the five patients with limited disease (8-15% marrow blasts), three obtained a complete disappearance of the blasts following two to four 5d courses of rIL2 alone. One patient persists in fourth complete remission (CR) 30 months later, another obtained a third CR for 4 months, and the last remained in third CR for 9 months before relapsing. This latter patient achieved a fourth CR with low-dose cytarabine. The remissions have been maintained with low-dose monthly courses of rIL2 given on an out-patient basis. Two AML did not respond to rIL2 alone; one, however, obtained a fourth CR with chemotherapy and rIL2. Administration of rIL2 was accompanied by organomegaly and leucocytosis, with a frequent lymphocytosis and increase in eosinophils and large granular lymphocytes, both in the blood and in the marrow. Side effects, though often severe, were controllable using a daily dose escalating protocol and never required intensive care treatment. The results of this pilot study indicate that treatment of AML patients with rIL2 is feasible and may result in the disappearance of chemotherapy-resistant blasts in patients with limited but detectable disease. Further controlled trials in AML in CR appear warranted.

Inducibility of lymphokine activated killer (LAK) cells in patients with acute myelogenous leukaemia in complete remission and its clinical relevance

Peripheral blood mononuclear cells (PBMC) from 42 patients with acute myelogenous leukaemia (AML) in complete remission (CR) and from normal donors were activated into LAK cells in the presence of 1000 U/ml of recombinant interleukin-2 (rIL-2). Cytotoxicity of LAK cells was assayed against K562, Daudi, and Raji cell lines, and autologous and/or allogeneic thawed leukaemic blasts. Fresh unactivated PBMC from normal donors and AML patients served as controls. Mean +/- standard deviation (SD) percentage lysis of the different targets by patient LAK cells were: K562 61 +/- 20%, Daudi 62 +/- 23%, Raji 48 +/- 24%, autologous blast cells 12 +/- 16% and allogeneic blast cells 13 +/- 10%. Lysis of the different targets by LAK cells from normal donors was similar to that achieved with LAK cells from AML patients. Overall there was a good correlation between the lysis of the different targets. There was no significant difference between the percentage lysis of autologous and allogeneic thawed blast cells, although LAK cells from seven out of the 18 patients tested were unable to lyse autologous leukaemic cells. Activity of patient LAK cells did not correlate with the initial characteristics of the patient nor with the time spent in CR before harvesting PBMC for activation. At the time of analysis, 32 patients were in continuing CR and 10 had relapsed. Multivariant analysis for prognostic factors showed that patients whose LAK cells had more lytic activity on K562 (P = 0.005) and fresh blast cell (P = 0.02) targets had significantly less risk of relapse than patients with little inducible LAK cell activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin 2 does not promote the in vitro and in vivo proliferation and growth of human acute leukaemia cells of myeloid and lymphoid origin

The effect of recombinant interleukin 2 (IL2) on the in vitro and in vivo proliferation and growth of human acute leukaemia cells of both myeloid and lymphoid origin was investigated. In none of the 25 primary samples tested could a continuously in vitro growing cell line be obtained by adding IL2 to the culture medium. Although IL2 induced a proliferative signal in three of the 31 acute leukaemias analysed, the overall 3H-thymidine uptake of the neoplastic cells was significantly reduced (P less than 0.05) in the presence of IL2. The unlikelihood of an important proliferative signal triggered by IL2 was confirmed in a semisolid clonogenic assay, which failed to document an increased colony growth in the 26 samples studied. Furthermore, using a colorimetric assay as a test for cell proliferation and survival, in seven of the 11 fresh acute leukaemia samples tested a 22-40% reduction in viability was observed in the presence of IL2, while in the remaining four, IL2 was ineffective. In order to investigate the effect of IL2 in an in vivo setting, an experimental model in heavily immunosuppressed nu/nu mice was established. In no case did IL2 promote the in vivo proliferation and growth of human myeloid and lymphoid acute leukaemia cells injected in the mice. On the contrary, with seven of the eight leukaemic cell lines which gave rise spontaneously to leukaemic masses, this could be prevented when the mice received locally 300 U of IL2 three times daily for 90 d. IL2 also blocked the growth in vivo of three fresh acute leukaemia samples (two myeloid and one lymphoid). Co-culture experiments using leukaemic cell lines and increasing numbers of normal lymphocytes suggest that the inhibitory effect of IL2 is probably exerted via an indirect mechanism. These findings, coupled to the well-documented ability of IL2 to generate lymphokine activated killer cells cytolytic against leukaemic blasts, further point to the potential role of immunotherapy with IL2 in the management of patients with haematological malignancies.