Lymphokine-activated killer cell phenomenon. II. Precursor phenotype is serologically distinct from peripheral T lymphocytes, memory cytotoxic thymus-derived lymphocytes, and natural killer cells

The Immunogenomic Landscape of Peripheral High-Dose IL-2 Pharmacodynamics in Patients with Metastatic Renal Cell Carcinoma: A Benchmark for Next-Generation IL-2-Based Immunotherapies

High-dose (HD) IL-2 was the first immuno-oncology agent approved for treating advanced renal cell carcinoma and metastatic melanoma, but its use was limited because of substantial toxicities. Multiple next-generation IL-2 agents are being developed to improve tolerability. However, a knowledge gap still exists for the genomic markers that define the target pharmacology for HD IL-2 itself. In this retrospective observational study, we collected PBMC samples from 23 patients with metastatic renal cell carcinoma who were treated with HD IL-2 between 2009 and 2015. We previously reported the results of flow cytometry analyses. In this study, we report the results of our RNA-sequencing immunogenomic survey, which was performed on bulk PBMC samples from immediately before (day 1), during (day 3), and after treatment (day 5) in cycle 1 and/or cycle 2 of the first course of HD IL-2. As part of a detailed analysis of immunogenomic response to HD IL-2 treatment, we analyzed the changes in individual genes and immune gene signatures. By day 3, most lymphoid cell types had transiently decreased, whereas myeloid transcripts increased. Although most genes and/or signatures generally returned to pretreatment expression levels by day 5, certain ones representative of B cell, NK cell, and T cell proliferation and effector functions continued to increase, along with B cell (but not T cell) oligoclonal expansion. Regulatory T cells progressively expanded during and after treatment. They showed strong negative correlation with myeloid effector cells. This detailed RNA-sequencing immunogenomic survey of IL-2 pharmacology complements results of prior flow cytometry analyses. These data provide valuable pharmacological context for assessing PBMC gene expression data from patients dosed with IL-2-related compounds that are currently in development.

Adoptive immunotherapy with cells from tumor-draining lymph nodes activated and expanded in vitro

Tumor-draining lymph nodes (tumor-DLNs) provide a rich source of tumor-reactive lymphocytes which can be used in adoptive immunotherapy (AIT) and that circumvent the need to resect autologous tumor, without the challenges and shortcomings associated with using autologous tumor or anti-CD3 monoclonal antibody. Bryostatin/Ionomycin (Bryo/Io) provide a useful method of activating tumor-DLNs such that they can readily be expanded to sufficient numbers to be used in AIT, and growing the tumor-DLN lymphocytes in the gamma chain cytokines IL-7 plus IL-15 is superior to IL-2 in terms of T cell numbers and phenotype. AIT with these cells induces tumor regression and provides protection against metastases and future tumor challenge. Here, we provide a stepwise protocol to sensitize tumor-DLN cells in donor mice, activate tumor-DLN T cells ex vivo using Bryo/Io, expansion of these cells in gamma chain cytokines and adoptive transfer of the expanded cells back into tumor-bearing hosts. Methods relevant to these experiments, such as injecting tumor cells intravenously and monitoring for pulmonary metastases, tumor volume measurement and resection, and use of luciferase-expressing tumor cells to monitor for metastases following resection, are described in detail. The methods outlined herein can be easily adapted to suit similar experiments across multiple tumor cell lines and syngeneic mouse models.

Distinct Predictive Immunogenomic Profiles of Response to Immune Checkpoint Inhibitors and IL2: A Real-world Evidence Study of Patients with Advanced Renal Cancer

Recombinant human high-dose IL2 (HD-IL2; aldesleukin) was one of the first approved immune-oncology agents based upon clinical activity in renal cell carcinoma (RCC) and metastatic melanoma but use was limited due to severe toxicity. Next-generation IL2 agents designed to improve tolerability are in development, increasing the need for future identification of genomic markers of clinical benefit and/or clinical response. In this retrospective study, we report clinical and tumor molecular profiling from patients with metastatic RCC (mRCC) treated with HD-IL2 and compare findings with patients with RCC treated with anti-PD-1 therapy. Genomic characteristics common and unique to IL2 and/or anti-PD-1 therapy response are presented, with insight into rational combination strategies for these agents. Residual pretreatment formalin-fixed paraffin embedded tumor samples from n = 36 patients with HD-IL2 mRCC underwent RNA-sequencing and corresponding clinical data were collected. A de novo 40-gene nearest centroid IL2 treatment response classifier and individual gene and/or immune marker signature differences were correlated to clinical response and placed into context with a separate dataset of n = 35 patients with anti-PD-1 mRCC. Immune signatures and genes, comprising suppressor and effector cells, were increased in patients with HD-IL2 clinical benefit. The 40-gene response classifier was also highly enriched for immune genes. While several effector immune signatures and genes were common between IL2 and anti-PD-1 treated patients, multiple inflammatory and/or immunosuppressive genes, previously reported to predict poor response to anti-PD-L1 immunotherapy, were only increased in IL2-responsive tumors. These findings suggest that common and distinct immune-related response markers for IL2 and anti-PD-1 therapy may help guide their use, either alone or in combination.

Significance

Next-generation IL2 agents, designed for improved tolerability over traditional HD-IL2 (aldesleukin), are in clinical development. Retrospective molecular tumor profiling of patients treated with HD-IL2 or anti-PD-1 therapy provides insights into genomic characteristics of therapy response. This study revealed common and distinct immune-related predictive response markers for IL2 and anti-PD-1 therapy which may play a role in therapy guidance, and rational combination strategies for these agents.

Arming Immune Cells for Battle: A Brief Journey through the Advancements of T and NK Cell Immunotherapy

Simple Summary

This review is intended to provide an overview on the history and recent advances of T cell and natural killer (NK) cell-based immunotherapy. While the thymus was discovered as the origin of T cells in the 1960s, and NK cells were first described in 1975, the clinical application of adoptive cell therapies (ACT) only began in the early 1980s with the first lymphokine activated killer (LAK) cell product for the treatment of cancer patients. Over the past decades, further immunotherapies have been developed, including ACT using cytokine-induced killer (CIK) cells, products based on the NK cell line NK-92 as well as specific T and NK cell preparations. Recent advances have successfully improved the effectiveness of T, NK, CIK or NK-92 cells towards tumor-targeting antigens generated by genetic engineering of the immune cells. Herein, we summarize the promising development of ACT over the past decades in the fight against cancer.

Abstract

The promising development of adoptive immunotherapy over the last four decades has revealed numerous therapeutic approaches in which dedicated immune cells are modified and administered to eliminate malignant cells. Starting in the early 1980s, lymphokine activated killer (LAK) cells were the first ex vivo generated NK cell-enriched products utilized for adoptive immunotherapy. Over the past decades, various immunotherapies have been developed, including cytokine-induced killer (CIK) cells, as a peripheral blood mononuclear cells (PBMCs)-based therapeutic product, the adoptive transfer of specific T and NK cell products, and the NK cell line NK-92. In addition to allogeneic NK cells, NK-92 cell products represent a possible “off-the-shelf” therapeutic concept. Recent approaches have successfully enhanced the specificity and cytotoxicity of T, NK, CIK or NK-92 cells towards tumor-specific or associated target antigens generated by genetic engineering of the immune cells, e.g., to express a chimeric antigen receptor (CAR). Here, we will look into the history and recent developments of T and NK cell-based immunotherapy.

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Pregnancy Zone Protein (PZP) is significantly upregulated in the decidua of recurrent and spontaneous miscarriage and negatively correlated to Glycodelin A (GdA)

BACKGROUND

Pregnancy Zone Protein (PZP) is an immunosuppressive protein that is expressed by the placenta and has also been identified in immune cells. When PZP and Glycodelin A (GdA) are combined, they act synergistically to inhibit Th-1 immune response. Little is known about its combined expression and role in normal and disturbed first trimester pregnancy.

PATIENTS AND METHODS

We investigated the expression of PZP and GdA in placental tissue obtained from spontaneous miscarriage (SM) (n = 19) and recurrent miscarriage (RM) (n = 17) at gestational weeks 6-13 by immunohistochemistry and on mRNA-level by either TaqMan PCR or in situ hybridization. Placental tissue from legal terminations of healthy pregnancies (n = 15) served as control group. Immunofluorescence double staining was used to analyse the combined expression of PZP and GdA in decidual tissue.

RESULTS

The protein level of PZP was significantly increased in decidual stroma of SM samples compared to the decidua of control specimens and also significantly upregulated in the decidual stroma cells in the RM group. Concerning GdA, the decidual stroma revealed a significantly decreased protein level in the group with spontaneous abortions than in the group with healthy pregnancies. There was also a significant downregulation of GdA in the decidual stroma of RM samples compared to the control group. We observed a significant negative correlation of PZP and GdA in decidual stromal tissue of recurrent abortion. We could confirm the staining results for PZP as well as for GdA on mRNA level. Both proteins are co-localized in decidual stroma as analysed by immunofluorescence double staining.

CONCLUSION

A balanced expression of GdA and its carrier protein PZP in the decidua seems crucial for a successful ongoing pregnancy. According to our data, these immunosuppressive proteins are co-localized in the decidual tissue and show a negative correlation only in patients suffering from recurrent abortion.

Antigen-independent killer cells prepared for adoptive immunotherapy: One source, divergent protocols, diverse nomenclature

Adoptive cell therapy (ACT) using tumor antigen-independent killer cells has been widely used in clinical trials of cancer treatment. Circumventing the need for identification of a particular tumor-associated antigen on tumor cells, the approach has opened possibilities for the extension of ACT immunotherapy to patients with a wide variety of cancer types. Namely, Natural Killer (NK), Lymphokine-activated Killer (LAK) cells and Cytokine-induced killer (CIK) cells are the most commonly used cell types in antigen-independent adoptive immunotherapy of cancer. They all originate from peripheral blood mononuclear cells and share several common features in their killing mechanisms. However, despite broad application in clinical settings, the boundaries between these cell types are not very clearly defined. The current study aims to review different aspects of these cell populations in terms of phenotypical characteristic and preparation media, to clarify how the boundaries are set.

Prospects of IL-2 in Cancer Immunotherapy

IL-2 is a powerful immune growth factor and it plays important role in sustaining T cell response. The potential of IL-2 in expanding T cells without loss of functionality has led to its early use in cancer immunotherapy. IL-2 has been reported to induce complete and durable regressions in cancer patients but immune related adverse effects have been reported (irAE). The present review discusses the prospects of IL-2 in immunotherapy for cancer.

Peripheral Blood Lymphocyte Response to Exogenous Interleukin 2 by PHA-Prestimulated and Non-PHA-Prestimulated Cells in Patients with Cancer

The study aims were 1) to assess the response of peripheral blood lymphocytes (PBL) of cancer patients to exogenous Interleukin 2 (IL 2) either by PHA-prestimulated or non PHA-prestimulated PBL, and 2) to carry out preliminary experiments for a direct quantitative evaluation of endogenous IL 2 production by PBL cultures of cancer patients in order to define the actual role of IL 2 in the disease. Analysis of PBL subsets was also carried out with monoclonal antibodies in a selected group of patients. A total of 134 patients entered the study. Cancer sites were: larynx 32, breast 36, lung (NSC) 24, colorectal 17 and gynecologic 25. In the former 3 cancer sites staging showed localized or only locally advanced disease, and in the last 2 sites disseminated disease. Our results provided evidence that cancer patients exhibit a T-cell functional immunodepression, which progresses during tumor growth, so that the localized disease shows a low-grade defect, and advanced disease a high-grade defect. Our data also clearly suggested that the factor involved with a primary role in this functional immune impairment is the IL 2 deficiency. A perspective may be drawn on the therapeutic administration in vivo of IL 2 and IL 2-activated lymphokine-activated killer cells in controlled clinical trials of selected groups of cancer patients.

Targeting tumor tolerance: A new hope for pancreatic cancer therapy?

With a 5-year survival rate of just 8%, pancreatic cancer (PC) is projected to be the second leading cause of cancer deaths by 2030. Most PC patients are not eligible for surgery with curative intent upon diagnosis, emphasizing a need for more effective therapies. However, PC is notoriously resistant to chemoradiation regimens. As an alternative, immune modulating strategies have recently achieved success in melanoma, prompting their application to other solid tumors. For such therapeutic approaches to succeed, a state of immunologic tolerance must be reversed in the tumor microenvironment and that has been especially challenging in PC. Nonetheless, knowledge of the PC immune microenvironment has advanced considerably over the past decade, yielding new insights and perspectives to guide multimodal therapies. In this review, we catalog the historical groundwork and discuss the evolution of the cancer immunology field to its present state with a specific focus on PC. Strategies currently employing immune modulation in PC are reviewed, specifically highlighting 66 clinical trials across the United States and Europe.

'Nonspecific' MHC-unrestricted killer cells and their receptors

The receptors involved in apparently nonspecific, MHC- unrestricted effector cell-target cell interaction and lysis continue to raise controversy. They bind to distinct ligands on their target cells and activate diverse cellular functions such as gene expression, lymphokine production, proliferation and/or cytolytic activity by the effector cells. Several distinct receptors may mediate MHC-unrestricted cytotoxicity. Here, Peter Hersey and Reinder Bolhuis review evidence that the four main receptors involved in triggering this form of lytic activity are the CD2 molecule (the sheep red cell receptor), CD3-associated αβ chain T-cell receptor (TCR), the γδ chain TCR-CD3 complex and the CD16 molecule (the IgG0Fc receptor). The apparent non-specificity specificity of killing is a reflection of the widespread expression of natural ligands for these receptors on target cells.

IL-2: the first effective immunotherapy for human cancer

The ability of IL-2 to expand T cells with maintenance of functional activity has been translated into the first reproducible effective human cancer immunotherapies. The administration of IL-2 can lead to durable, complete, and apparently curative regressions in patients with metastatic melanoma and renal cancer. The growth of large numbers of tumor-infiltrating lymphocytes with in vitro anti-cancer activity in IL-2 has led to the development of cell transfer therapies that are highly effective in patients with melanoma. The genetic modification of T cells with genes encoding αβ TCRs or chimeric Ag receptors and the administration of these cells after expansion in IL-2 have extended effective cell transfer therapy to other cancer types.

Targeting therapy for glioma by LAK cells coupled with bispecific antibodies

Targeting of T cells or natural killer (NK) cells to tumours by using bispecific antibodies has attracted increasing interest in the past few years. We treated 31 patients with malignant glioma using adoptive transfer of lymphokine-activated killer (LAK) cells coupled to a bispecific antibody (anti-CD3+anti-glioma) as post-operative adjuvant therapy. Although this study excluded patients with deeply-seated tumours or a poor performance status, approximately 50% of the patients remained alive after 3 years, and 40% were free of recurrence. Serial CT scans revealed disappearance of remnant tumours in some patients. In addition, CT-guided stereotactic biopsy of the tumour in 3 patients showed extensive necrosis and degeneration after specific targeting therapy (STT). Five patients developed acute infection, and one of them died of bacterial meningitis. Our results suggest that antibody-targeted LAK therapy can achieve a higher response rate in patients with standard LAK therapy or any type of conventional treatment.

Cigarette smoking is associated with the reduction of lymphokine-activated killer cell and natural killer cell activities

Lymphokine-activated killer (LAK) cell and natural killer (NK) cell activities were determined in a group of healthy individuals with differing smoking habits. The study population consisted of 54 Japanese males, including 23 smokers, 8 ex-smokers and 23 non-smokers. Peripheral blood mononuclear cells (PBMC) were isolated and used as effector cells. LAK cells were generated by incubation of PBMC with interleukin-2 for 72 h. LAK cell activity against NK-resistant Raji cells and NK cell activity against NK-sensitive K562 cells were examined by 4-h51Cr-release assay. LAK cell activity in the smokers was significantly lower than that in the nonsmokers. The smokers showed significantly lower NK cell activity than the nonsmokers, whereas NK cell activity of the ex-smokers was comparable to that of the non-smokers. The proportion of NK cells (CD3-16+56-, CD3-16-56+, or CD3-16+56+ cells) in the smokers was significantly lower than that in the nonsmokers. The present study demonstrates for the first time that cigarette smokers have lower LAK cell activity than nonsmokers.

Pulsing with blast cell lysate or blast-derived total RNA reverses the dendritic cell-mediated cytotoxic activity of cytokine-induced killer cells against allogeneic acute myelogenous leukemia cells

Immunotherapeutic strategies may be a treatment option in patients with refractory acute myelogenous leukemia (AML) or, in cases of complete remission after conventional therapy regimens, may help to reduce disease recurrence or delay time to progression. Evidence suggests a key role of dendritic cells (DCs) in cancer immunotherapy due to their capacity to present tumour antigens to effector cells. We generated cytokine-induced killer (CIK) cells from healthy donors and examined their responses in vitro in an LDH release assay against three cell lines and allogeneic HLA non-matched blasts from three patients with de novo AML after coincubation with autologous peripheral blood monocyte-derived DCs. Although DCs were unable to enhance CIK cell effects against all three cell lines tested, the cytotoxic activity against the patients’ AML cells increased after coculture with mature DCs, which was significant in two of three patients. However, neither prior pulsing of the DCs with blast cell lysates nor with leukemic cell-derived total RNA further enhanced the lytic capacity of the CIK cells. On the contrary, pulsing reduced or even reversed the cytotoxic activity of the effector cells. This decrease of allogeneic cytotoxicity led us to conclude that monocyte-derived DCs may be useful in autologous or allogeneic vaccine strategies for the treatment of AML or in priming donor lymphocytes in vitro, but unfractionated antigens as pulsing agents may have inhibitory effects on T cell efficiency and their employment in immunotherapeutic strategies for AML seems questionable.

Biologic and clinical significance of cytokine production in B-cell malignancies

Cytokines are a group of polypeptide hormones endowed with pleiotropic biological properties. Normal B lymphocytes produce a number of these factors that subserve important regulatory functions in the combined processes of proliferation and differentiation. Also neoplastic B cells can release cytokines and, simultaneously, respond to the same factors in an autocrine circuit that supports their malignant growth. In addition, tumor cells can make use of the factors released by normal cells, either spontaneously or under the influence of inductive signals from the neoplastic cells. Inappropriate or excessive release of cytokines may have an important role in the pathophysiology of some clinical features. Thus, neutralization of cytokine biologic activity in vivo could be a therapeutic strategy for treatment of human B-cell neoplasias.

The regulation and activation of CD44 by natural killer (NK) cells and its role in the production of IFN-gamma

Natural killer (NK) cells can express high levels of CD44, and signaling through CD44 has been shown to enhance NK cell cytotoxic activity. However, little is known about the factors that regulate CD44-mediated activation of NK cells. The studies reported here reveal that resting NK cells constitutively express CD44 that is in an inactive form that does not bind to hyaluronan (HA), the principal known ligand for CD44. After infection of mice with the intracellular parasite Toxoplasma gondii, however, a population of NK cells that expressed activated CD44 emerged. To determine how expression and activation of CD44 by resting NK cells were regulated, the role of cytokines in these events was assessed. These studies revealed that whereas stimulation of resting NK cells with interleukin-12 (IL-12) or IL-18 caused increased expression of CD44, only IL-2 or IL-15 led to the upregulation and activation of CD44. The cytokine-induced upregulation and activation of CD44 was independent of NK cell proliferation. To determine the functional consequences of CD44 activation, the effects of low molecular weight HA (LMWHA) on the production of interferon-gamma (IFN-gamma) by IL-2-activated NK cells were assessed. These studies showed that HA alone had little effect on the production of IFN-gamma, but when used in combination with IL-2, IL-12, or IL-18, LMWHA was a potent enhancer of IFN-gamma production. Together, these studies indicate an important role for proinflammatory cytokines in the activation of CD44 on NK cells and identify a novel pathway to enhance the ability of activated NK cells to produce IFN-gamma.

Aging of innate immunity: functional comparisons of NK/LAK cells obtained from bulk cultures of young and aged mouse spleen cells in high concentrations of interleukin-2

The technique of bulk cultivation of aged mouse spleen cells in high concentration of IL-2 was employed to obtain NK/LAK cells in sufficient number and enrichment for studies on the effects of aging on their functions. The yield and enrichment were equivalent to that of young mouse spleen cells. The aged and young mouse NK/LAK cells were equivalent also in their functional competence to proliferate, kill target cells and produce IFNgamma; i.e. they did not display age-associated defects typical of freshly-isolated NK/LAK cells. In two respects, however, the NK/LAK cells derived from aged mouse spleen were altered: (a) in the efficiency of nuclear translocation of transcription factors STAT 5A and 5B, and (b) in the deficiency in production of mRNA transcripts representing several chemokines. We recommend caution in the use of bulk cultivation in IL-2 to obtain NK/LAK cells for studies on aging. However, it does appear from this study that aging may severely affect chemokine production, at least in the case of NK/LAK cells.

Direct killing of xenograft cells by CD8+ T cells of discordant xenograft recipients

BACKGROUND

Long-term pig xenografts in monkeys demonstrated the infiltration of CD8 T cells into pig cartilage xenografts, transplanted into monkeys. The objective of the present study was to determine in an experimental animal model whether CD8 T cells in pig xenograft recipients exert any direct cytotoxic effect on pig cells.

METHODS

The killing of xenograft cells by CD8 T cells, obtained from xenograft recipients, was studied in alpha1,3galactosyltransferase knockout mice that were repeatedly injected intraperitoneally with pig kidney membranes. The pig kidney cell line PK15, which shares many antigens with pig kidney membranes, served as a model for xenograft target cells in cytotoxicity assays. Cell lines from other species were also studied as target cells.

RESULTS

Lymphocytes obtained freshly from spleens of mice immunized with pig kidney membranes failed to display significant cytotoxic activity against pig cells. However, incubation of these lymphocytes with irradiated PK15 cells and addition of recombinant interleukin (IL)-2 (100 U/mL), on the third day of incubation, resulted in extensive proliferation and expansion of CD8 cytotoxic T lymphocytes (CTL). These CTL, obtained after 12 days of incubation, killed nonspecifically pig, human, and mouse normal and malignant cells. These CTL were not generated in cultures in the absence of stimulatory pig cells or in the absence of IL-2. These CTL could not be generated in cultures of lymphocytes from naive mice that were incubated with PK15 cells and IL-2.

CONCLUSIONS

The data obtained imply that CD8 T cells from xenograft recipients can be stimulated in vitro by xenoantigens and IL-2 to differentiate into highly reactive nonspecific CTL that are capable of killing a large variety of xenogeneic and syngeneic cells. Similar in vivo microenvironmental conditions within the xenograft may induce the local differentiation of infiltrating CD8 T cells into CTL that can destroy nonspecifically adjacent xenograft cells. Such cells may not be active outside the xenograft because of the absence of IL-2 in sufficiently high concentrations.

Therapeutic activity of NK cells against tumors

While it is generally accepted that natural killer (NK) cells, by killing tumor cells in the circulation, represent a first line of defense against metastases, their therapeutic activity against established tumors has been limited. In this review, we describe studies to improve the therapeutic effectiveness of activated NK cells in both animal models and clinical trials to better understand the biological problems that limit their effectiveness.

Immunotherapy of disseminated fibrosarcoma in mice using IL-2-producing tumor cells: studies on its mechanism and specificity

Genetically modified, IL-2-producing tumor cells have been shown to regress in vivo and immunize mice against subsequent challenge with parental tumor. We investigated whether IL-2-producing tumor cells may serve as immunotherapy of established tumors in mice. MCA 205 and MCA 203, weakly immunogenic murine sarcomas of B6 origin, were transfected with the pBMGNeo-mIL-2 vector containing the murine IL-2 cDNA. Mice receiving intraperitoneal injections of the parental sarcoma cells developed ascites and died within 4 weeks. The intraperitoneal injection of IL-2-producing tumor cells significantly prolonged survival and, moreover, significantly reduced the number of established pulmonary metastases. The specificity of this effect was indicated by the unaltered course of disease in mice that were injected with unrelated IL-2-producing tumor cells. FACS analysis of peritoneal cells obtained from treated mice showed a predominance of Vbeta3-positive cells. In a 4 h 51Cr release assay, these Vbeta3-positive cells exhibited tumor-specific cytotoxicity and also nonspecific effector cells are shown to be involved in tumor rejection.

Immunocytokines: a promising approach to cancer immunotherapy

Recombinant antibody-cytokine fusion proteins are immunocytokines that achieve high cytokine concentrations in the tumor microenvironment and thereby effectively stimulate cellular immune responses against malignancies. The activation and expansion of immune effector cells, such as CD8+ T lymphocytes, by interleukin-2 immunocytokines resulted in the eradication of established pulmonary and hepatic metastases of murine melanoma and colorectal carcinoma in syngeneic mouse models. These immunocytokines were equally effective in eliminating established bone marrow and liver metastases of murine neuroblastoma by activating natural killer cells. The effective eradication of metastases by immunocytokines resulted in significant prolongation in life span of mice over that of controls receiving equivalent mixtures of antibody and interleukin-2, which failed to reduce the growth of disseminated metastases. Proof of concept was established, indicating that immunocytokine-induced activation and expansion of immune effector cells in the tumor microenvironment can effectively eradicate established tumor metastases. This promising new approach to cancer immunotherapy may lead to clinical applications that improve treatment of cancer patients with minimal residual disease in an adjuvant setting.

Lymphokine-activated killer (LAK) cell anti-HIV-1 ADCC reactivity: a potential strategy for reduction of virus-infected cellular reservoirs

Lymphocytes from HIV-1-seropositive and -seronegative individuals were examined to determine whether HIV-1 infection interfered with the ability to generate a lymphokine-activated killer (LAK) cell response. Following a 3-day ex vivo incubation in the presence of 1000 U/ml of recombinant interleukin-2, lymphocytes from seropositive individuals exhibited a LAK cell response which was equivalent to or greater than that of seronegative controls as measured against Daudi cell targets. LAK cells from seropositive and seronegative donors showed no specific cytolytic activity against gp120-coated or HIV-1-infected targets. However, in the presence of patient sera, significant levels of virus-specific LAK cell-mediated antibody-dependent cellular cytotoxicity (ADCC) were observed. The level of this specific LAK cell-mediated ADCC was greater than that mediated under similar conditions by freshly isolated peripheral blood mononuclear cells. The greatest improvement in ADCC over baseline activity was seen with lymphocytes from AIDS patients after the 3-day ex vivo activation, suggesting that this patient population might benefit the most from adaptive LAK cell therapy.

Natural Killer Cell–Mediated Eradication of Neuroblastoma Metastases to Bone Marrow by Targeted Interleukin-2 Therapy

Targeted interleukin-2 (IL-2) therapy with a genetically engineered antidisialoganglioside GD2 antibody–IL-2 fusion protein induced a cell-mediated antitumor response that effectively eradicated established bone marrow and liver metastases in a syngeneic model of neuroblastoma. The mechanism involved is exclusively natural killer (NK) cell–dependent, because NK-cell deficiency abrogated the antitumor effect. In contrast, the fusion protein remained completely effective in the T-cell–deficient mice or immunocompetent mice depleted of CD8+ T cells in vivo. A strong stimulation of NK-cell activity was also shown in vitro. Immunohistology of the leukocytic infiltrate of livers from treated mice revealed a strong staining for NK cells but not for CD8+ T cells. The therapeutic effect of the fusion protein was increased when combined with NK-cell–stimulating agents, such as poly I:C or recombinant mouse interferon-γ. In conclusion, these data show that targeted delivery of cytokines to the tumor microenvironment offers a new strategy to elicit an effective cellular immune response mediated by NK cells against metastatic neuroblastoma. This therapeutic effect may have general clinical implications for the treatment of patients with minimal residual disease who suffer from T-cell suppression after high-dose chemotherapy but are not deficient in NK cells.

Natural Killer Cell–Mediated Eradication of Neuroblastoma Metastases to Bone Marrow by Targeted Interleukin-2 Therapy

Targeted interleukin-2 (IL-2) therapy with a genetically engineered antidisialoganglioside GD2 antibody–IL-2 fusion protein induced a cell-mediated antitumor response that effectively eradicated established bone marrow and liver metastases in a syngeneic model of neuroblastoma. The mechanism involved is exclusively natural killer (NK) cell–dependent, because NK-cell deficiency abrogated the antitumor effect. In contrast, the fusion protein remained completely effective in the T-cell–deficient mice or immunocompetent mice depleted of CD8+ T cells in vivo. A strong stimulation of NK-cell activity was also shown in vitro. Immunohistology of the leukocytic infiltrate of livers from treated mice revealed a strong staining for NK cells but not for CD8+ T cells. The therapeutic effect of the fusion protein was increased when combined with NK-cell–stimulating agents, such as poly I:C or recombinant mouse interferon-γ. In conclusion, these data show that targeted delivery of cytokines to the tumor microenvironment offers a new strategy to elicit an effective cellular immune response mediated by NK cells against metastatic neuroblastoma. This therapeutic effect may have general clinical implications for the treatment of patients with minimal residual disease who suffer from T-cell suppression after high-dose chemotherapy but are not deficient in NK cells.

Targeted interleukin-2 therapy for spontaneous neuroblastoma metastases to bone marrow

BACKGROUND

Advanced (stage 4) cases of neuroblastoma, a childhood cancer of the nervous system, are associated with high relapse rates, even after intensive chemotherapy, radiotherapy, and autologous bone marrow transplantation. Therefore, the use of monoclonal antibodies directed against the neuroblastoma tumor marker disialoganglioside GD2 (GD2), in combination with recombinant human interleukin 2 (rhIL-2), is under clinical investigation. We hypothesize that targeted cytokine immunotherapy with a recombinant anti-GD2 antibody-interleukin 2 fusion protein (ch14.18-IL-2) is superior to a combination of ch14.18 and rhIL-2. Our purpose was as follows: 1) to develop a syngeneic model for murine neuroblastoma that expresses GD2 and features both experimental and spontaneous metastases to bone marrow and liver, and 2) to assess anti-GD2-targeted IL-2 therapy in this mode.

METHODS

A hybrid neuroblastoma cell line was used to generate the GD2-positive NXS2 cell line. Bone marrow and liver metastases were quantified by reverse transcription-polymerase chain reaction for tyrosine hydroxylase and by organ weight or counts of macroscopic tumor foci, respectively. All P values reported are two-sided.

RESULTS

Injection of NXS2 cells resulted in disseminated bone marrow and liver metastases exhibiting stable, but heterogeneous expression of GD2. Treatment with fusion protein (10 microg/day for 6 days) effectively suppressed growth of both experimental and spontaneous metastases to bone marrow and liver (P<.001). In contrast, a mixture of rhIL-2 and ch14.18 at equivalent dose levels was inefficient. Only mice treated with ch14.18-IL-2 showed a twofold prolongation in life span (P<.001).

CONCLUSION

Targeted IL-2 therapy with a ch14.18-IL-2 fusion protein elicits an effective antitumor response. Our data suggest that a study of ch14.18-IL-2 as an adjuvant treatment in patients with minimal residual disease may be of value.

Apoptotic and necrotic cytolytic processes induced by membrane associated proteins of LAK cells

Cytolytic processes induced by membrane-associated proteins of human lymphokine-activated killer (LAK) cells with different phenotypes (CD3+, CD16-, CD8+ and CD16+, CD8+, CD3-) were studied using L929 and K562 types of target cells. Independently of the phenotype of effector cells and the type of target cells, total fractions of membrane proteins induced several different cytolytic processes occurring with different rates and involving different mechanisms of genome fragmentation. The membrane fraction induced, irrespective of the phenotype of LAK cells, mostly apoptotic processes in the L929 line. At the same time, cytolytic processes induced in K562 line differed by the mechanisms of DNA fragmentation. An inhibitor of lysosome activation, NH4Cl, and a Ca(2+)-binding reagent, ethylene glycol bis-(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA), induced partial inhibition of short-term cytolytic processes (developing within 1-5 h) but did not affect the development of long-term cytolytic processes requiring more than 6-8 h for their development.

CC chemokines induce the generation of killer cells from CD56+ cells

We describe here that members of the CC chemokines exhibit biological activities other than chemotaxis. Macrophage inflammatory protein (MIP)-1 alpha, MIP-1 beta, monocyte chemoattractant protein-1 and RANTES, but not interleukin (IL)-8, induce the generation of cytolytic cells, designated here as CHAK (CC chemokine-activated killer) cells to distinguish them from IL-2-activated (LAK) cells. Like IL-2, CC chemokines can induce the proliferation and activation of killer cells. While incubating CC chemokines with CD4+ or CD8+ cells did not generate CHAK activity, all CC chemokines were capable of inducing CHAK activity upon incubating with CD56+ cells, suggesting that the primary effectors are NK cells. However, the presence of other cell types, such as CD4+ or CD8+, are necessary to induce the proliferation of CD56+ cells. Confirming the involvement of T cell-derived factors in inducing the proliferation of these cells, anti-IL-2 and anti-interferon-gamma, but not anti-IL-1 beta, anti-tumor necrosis factor-alpha, anti-IL-8, or anti-granulocyte/monocyte-colony-stimulating factor inhibited RANTES-induced proliferation of nylon wool column-nonadherent cells. Our results may have important clinical applications for the utilization of CHAK cells in the treatment of cancer and immunodeficient patients.

Differential inhibition of lymphokine-activated killing, proliferation, and cytokine secretion by humanized antibodies against the low- and intermediate-affinity interleukin-2 receptors. A novel model for activation of human peripheral blood mononuclear cells by interleukin 2

Human PBMCs generate LAK, proliferate, and secrete secondary cytokines in response to IL-2. We assessed the roles of the various receptor complexes in these responses to IL-2 using antibodies that block the interaction of IL-2 with the intermediate-affinity IL-2R (humanized Mik beta 1) and high- and low-affinity interactions (HTac). The HTac antibody produced dramatic reductions in proliferation (27%) and in the secretion of cytokines (TNF)-alpha and -beta and IFN-gamma inhibited 68%, 72%, and 80%, respectively) with no decrease in LAK. HMik inhibited LAK activation by 65% and proliferation by 60% but had little effect on cytokine secretion. The combination of the two antibodies completely inhibited all proliferative, cytolytic, and secretory activity. These data suggest a novel model for the activation of human PBMCs by IL-2. Whereas induction of LAK activity is mediated through the intermediate-affinity IL-2R and cytokine secretion is mediated through the high-affinity complex, interaction between IL-2 and both of these receptor complexes is required for the induction and maintenance of proliferative activities in human PBMCs.

Lymphokine-activated killer cytotoxicity and lymphocyte subpopulations in patients with acute leukemia

In this report we investigated lymphokine-activated killer (LAK) cytotoxicity and lymphocyte subpopulations of peripheral blood mononuclear cells (PBMCs) of patients with acute leukemia in complete remission after chemotherapy or autologous bone marrow transplantation (ABMT) and of normal donors. A positive linear correlation was found between the percentage of spontaneous LAK activity and that of lymphocyte subpopulations with phenotypes CD56+, CD3-CD8+ CD3-CD56+ and CD3-CD57+ in both groups of patients. A 3-day culture with IL-2 produced an up-regulation in the expression of the CD25, CD69, and HLA-DR markers proportional to the LAK cytotoxicity levels generated in the culture. Determination of percentages of spontaneous and in vitro generated LAK activity as well as of the above mentioned phenotypic markers contribute to the analysis of the process of LAK activation in patients with acute leukemia and may also be useful in those cases in which immunotherapy with IL-2 and/or LAK cells is anticipated.

Development of four donor-specific phenotypes in human long-term lymphokine-activated killer cell cultures

A series of 62 lymphokine-activated killer cell (LAK) cultures from 44 different donors was investigated for the distribution of various CD markers during a cultivation period of 3 weeks. Great differences in the phenotypic pattern were found between different donors, but similar changes of the subset pattern of various donors allowed a classification of the LAK cultures into four distinct LAK types. LAK type 1 was characterised by low numbers of CD3+ cells and high values for CD56+ cells. In LAK type 2 cultures gamma/delta TCR+ cells extensively proliferated, whereas in LAK type 3 cultures the CD57 and CD8 values increased considerably. LAK type 4 cultures did not show any of these characteristics. The resulting phenotype of a LAK culture was donor-specific, as LAK cultures established from the same peripheral blood mononuclear cells (PBMC), fresh or after cryopreservation, or from PBMC obtained from the same donor at different venous punctures, always developed the same phenotype. A clear correlation between phenotype and killing activity could only be found for LAK type 1 cultures, which always developed high lytic activity. Long-term IL-2 stimulation induced high levels of perforin-positive cells in LAK cultures but the perforin content did not correlate with the cytotoxicity. The transcription pattern for various cytokines only varied slightly between the cultures. Messenger RNA for granulocyte/macrophage- colony-stimulating factor, interferon gamma, tumour necrosis factor alpha, interleukin-4 (IL-4) and IL-5 were found in almost all cultures during the entire cultivation period, whereas mRNA for IL-2 was never detected. Most variations in the transcription pattern were observed for IL-6 and IL-7. However, no correlation could be found between the endogenous cytokine production and the phenotype or lytic activity of the LAK cultures. Further studies are required to determine the factors that cause lymphocyte subsets from a specific donor to proliferate preferentially under long-term IL-2 stimulation.

Immunohistochemical expression of CD68 antigen in human peripheral blood T cells

CD68 antigen is expressed by tissue macrophages and cells of myeloid/mononuclear lineage. CD68 is recognized by many monoclonal antibodies (mAbs), including KP1, EMB11, Y1/82A, Y2/131, Ki-M6, and Ki-M7. Using the labeled strept-avidin-biotin (LSAB) immunoperoxidase technique, we examined CD68 antigen expression in human peripheral blood T cells. The anti-CD68 mAbs KP1 and EMB11 stained virtually all fresh isolated gamma/delta T cells and CD3-CD56+ natural killer (NK) cells in a granular cytoplasmic pattern. In contrast, fresh isolated CD4+ and CD8+ T lymphocytes showed no detectable reactivity with these two anti-CD68 mAbs. However, in vitro stimulation with T-cell mitogen or recombinant interleukin-2 (rIL-2) induced expression of CD68 antigen in activated CD4+ and CD8+ T lymphocytes. Similarly, the lymphokine-activated killer (LAK) cells generated after long-term (14 to 21 days) culture of peripheral blood mononuclear cells (PBMC) in rIL-2 also showed strong granular cytoplasmic staining by the anti-CD68 antibodies. This study shows that the CD68 antigen is constitutively expressed in NK cells and gamma/delta T cells and that its expression is strongly induced in activated CD4+ and CD8+ T lymphocytes as well as LAK cells.

Behaviorally conditioned modulation of natural killer cell activity: enhancement of baseline and activated natural killer cell activity

Natural killer (NK) cells comprise a sub-population of lymphocytes functionally defined by their ability to spontaneously lyse select tumor and virally infected cells. NK cell lytic function is sensitive to modulation by cytokines and neuroendocrine mediators. Behavioral conditioning trains an animal to cognitively associate a novel environmental cue (i.e. odor) with a physiologically active agent (i.e. Polylnosinic:PolyCytidilic acid, Poly I:C). Poly I:C induces interferon production resulting in activation of NK cells and enhanced NK cell lytic activity. Subsequent to behavioral conditioning, independent presentation of the odor should elicit similar responses (enhanced NK cell activity). We have shown that animals pre-exposed to the conditioning apparatus or manual restraint prior to behavioral conditioning demonstrate enhanced baseline NK cell activity or no effects respectively. To assess the influence of NK cell activation in conjunction with behavioral conditioning, we have re-presented the odor to animals with activated or baseline NK activity. Lymphocytes were then incubated for five days with IL-2 and cellular cytotoxic activity re-assessed. Behavioral conditioning significantly enhanced baseline and activated NK cell activity in animals previously exposed to the conditioning apparatus. No differences in lytic activity versus NK sensitive targets were observed following IL-2 activation. In contrast, animals manually restrained prior to conditioning showed no differences in baseline or in vivo activated NK activity, but previously non-activated lymphocytes stimulated with IL-2 demonstrated significantly higher lytic activity in conditioned animals re-presented with the odor. These results demonstrate central nervous system (CNS) modulation of NK cell activity and the presence of an interplay between cytokine activation and responsiveness to CNS immunoregulatory signals.

Correlation of serum cytokine and acute phase reactant levels with alterations in weight and serum albumin in patients receiving immunotherapy with recombinant IL-2

Recombinant IL-2 (rIL-2) has been used alone or in combination with other chemotherapeutic agents to enhance host defences against cancer. Prolonged administration of high doses, required for clinical efficacy, may precipitate serious dose-limiting toxicity. rIL-2-induced 'vascular leak syndrome' leads to hypotension, renal insufficiency, respiratory disturbances and other organ dysfunctions. Serial measurements of serum cytokines and the acute phase protein C-reactive protein (CRP) were performed on nine patients who received high-dose i.v. continuous therapy with rIL-2. The influence of these immunological parameters upon alterations in patients' weight and serum albumin, as indicators of toxicity, was assessed. All patients experienced weight increases during the cycle (3-11% of total body weight). The serum levels of tumour necrosis factor (TNF-alpha) and CRP were highly predictive of alterations in patients' weight (both P < 0.001), while no correlation was found with IL-6 and weight change. Serum albumin fell linearly throughout the infusion cycle, but this showed no correlation with variations in serum levels of IL-6, TNF-alpha, or CRP. The complement components C3 and C4 were significantly reduced at the end of the infusion, suggesting a possible role for this cascade system in mediating these clinical changes. The strong association between serum TNF-alpha and weight change, not previously documented, further supports the hypothesis that TNF-alpha is a key mediator in the pathogenesis of the 'vascular leak syndrome'.

Suramin inhibits tumor cell cytotoxicity mediated through natural killer cells, lymphokine-activated killer cells, monocytes, and tumor necrosis factor

Suramin, a polysulfonated naphthylurea, is an antitrypanosomal and antifilarial drug. Because of its anti-reverse transcriptase activity and antiproliferative activity, suramin is also used for the treatment of acquired immunodeficiency syndrome and cancer. In spite of these uses, very little is known about its effects on the immune system. In this report, we investigated the effects of suramin on peripheral blood mononuclear cells. We found that natural killer (NK) cell-mediated cytotoxicity against human erythroblastoid cell line K562 was completely inhibited by suramin in a dose-dependent manner. It also completely blocked lymphokine-activated killer (LAK) cell-mediated cytotoxicity against the human B lymphoblastoid cell lines Raji and Daudi. The cytotoxicity against the human melanoma tumor cell line A-375 mediated by unstimulated and stimulated monocytes was also suppressed by suramin. Maximum inhibition of monocyte-mediated cytotoxicity was observed when suramin was present during both the activation and the effector phases of cytotoxicity. Besides its effects on cell-mediated cytotoxicity, suramin also inhibited the cytotoxic effects of tumor necrosis factor (TNF) against different tumor cell lines. Furthermore, we found that suramin interferes with the binding of TNF with its receptor. Thus our results indicate that suramin overall downregulates the immune system by inhibiting cell-mediated and TNF-mediated cytotoxicity against different tumor cells.

The role of apoptotic and necrotic processes in cytolysis mediated by LAK cells with different phenotypes

The role of necrotic and apoptotic pathways in cytolysis mediated by LAK cells was studied. The contribution of necrotic and apoptotic processes to cytolysis depends both on the LAK cells' phenotype and the type of target cells. CD16+/CD8+/CD3- LAK cells induced necrosis of K562 and L929 target cells. The cell death induced by CD3+/CD8+/CD16- LAK cells was found to include features of apoptotic and necrotic processes.

T cells and monocytes regulate the generation and functional activity of natural killer-derived lymphokine-activated killer cells

The lymphokine-activated killer (LAK) phenomenon is generally referred to as nonspecific, i.e., major histocompatibility complex (MHC)-unrestricted cytotoxicity against tumor cells generated by ex vivo culture of human peripheral blood lymphocytes with interleukin 2 (IL-2). In this study, we selectively purified and depleted cell subpopulations such as natural killer (NK) cells, T-lymphocytes and monocytes from fresh human peripheral blood by negative selection. While highly purified NK cells could be induced to acquire potent LAK activity in five-day culture with IL-2, the presence of T-lymphocytes and monocytes in NK cultures was needed in order to induce a significant expansion of cytotoxic effector cells over the culture period. Neither T cells nor monocytes by themselves were able to generate LAK cells in a standard five-day IL-2 culture. However, when added to highly purified NK cells prior to IL-2 incubation, a proportion of CD3+ T-lymphocytes was found to gain LAK-like killing activity. Monocytes, when cultured with IL-2 in the presence of NK cells and T-lymphocytes, did not appear to acquire LAK activity but were able to induce a dramatic increase in cytotoxic lymphocyte recovery after five days with IL-2. In summary, we could demonstrate that peripheral blood T-lymphocytes and monocytes are potent regulators of NK-dependent lymphokine (IL-2)-activated killing.

Interleukin-2. A review of its pharmacological properties and therapeutic use in patients with cancer

Recombinant interleukin-2 (IL-2) products (e.g. aldesleukin, teceleukin) are nonglycosylated, modified forms of the endogenous compound. IL-2 acts as a pleiotropic mediator within the immune system, having a variety of effects via specific cell surface receptors. The interaction of IL-2 with the IL-2 receptor induces proliferation and differentiation of a number of T lymphocyte subsets, and stimulates a cytokine cascade that includes various interleukins, interferons and tumour necrosis factors. Antitumour effects of IL-2 appear to be mediated by its effects on natural killer, lymphokine-activated killer (LAK) and other cytotoxic cells. In vivo and in vitro effects of IL-2 seem to be dependent to a large extent on the environment; many studies have reported conflicting results, perhaps due to diverse populations of effector cells, the availability of other cytokines that have synergistic or inhibitory influences, and the dosage regimens used. The recombinant products appear to be biologically indistinguishable from native IL-2 in vitro and in vivo; the former induce minor antibody formation but this does not appear to alter functional properties. In patients with metastatic renal cell carcinoma, IL-2 therapy achieves average objective response rates of 20% (range 0 to 40%), with a complete response rate of about 5% (range 0 to 19%). Response duration varies considerably but can be durable (lasting for > 12 months), with some patients remaining in complete response for > 60 months. It is unclear at present whether higher dosage regimens improve clinical response, or whether combination therapy with other agents and/or adoptive therapy is beneficial. Survival duration may depend on the risk factors present, with poorer performance status and more than one site of metastases associated with shorter survival times. Patients with metastatic malignant melanoma receiving IL-2 as monotherapy show an average objective response rate of 13% (range 3 to 24%); however, objective response rate averages 30% (range 4 to 59%) when IL-2 is used in combination with other agents. Overall median survival appears to be about 10 months. Preliminary data indicate that IL-2 produces a lower response rate in patients with refractory colorectal carcinoma, ovarian cancer, bladder cancer, acute myeloid leukemia or non-Hodgkin's lymphoma. Adverse effects accompanying high dose, intravenous IL-2 therapy can be severe, with cardiovascular, pulmonary, haematological, hepatic, neurological, endocrine, renal and/or dermatological complications frequently requiring doses to be withheld.(ABSTRACT TRUNCATED AT 400 WORDS)

Time-dependent changes of LAK cell phenotypes correlate with the secretion of different cytotoxic proteins

Human lymphokine-activated killer (LAK) cells were generated from peripheral blood lymphocytes (PBL) of normal volunteers by interleukin-2 (IL-2) stimulation for 1-8 days. During the first 3 days the surface marker CD16 characteristic for natural killer (NK) cells was expressed and later the CD3 marker characteristic for cytotoxic T cells became predominant. The conditioned media of LAK cells collected after interaction of LAK cells with K562 target cells was chromatographically separated into two cytotoxic fractions: F1 and F2. It was demonstrated that fraction F1 contained cytotoxic proteins having molecular weights of 30 and 40 kDa, and fraction F2 contained cytotoxic proteins having molecular weights of 22, 38 and 75 kDa. The presence of the proteins in each of these two fractions correlated with the phenotype changes of LAK cells: the F2 cytotoxic proteins were characteristic for NK-like cells, and the F1 proteins for cytotoxic T-lymphocyte (CTL)-like phenotypes.

Interferon--a major regulator of natural killer cell-mediated cytotoxicity

Natural killer (NK) cells probably function as an early defense line against viruses because of their ability to kill virus-infected cells as well as a variety of tumor cells. In both cases, the killing is major histocompatibility complex (MHC)-unrestricted. NK cells exhibit spontaneous activity but they are positively regulated by interferons (IFNs) or indirectly by such IFN inducers as viruses, bacterial products, poly(rI):(rC), and mitogens. In addition to their "positive" regulation on NK activity, IFNs often act as "negative signals" for NK and lymphokine-activated killer (LAK) cell-mediated cytotoxicity. If NK susceptible target cells are exposed to IFN prior to NK cells, their sensitivity to NK activity is often markedly diminished. The mechanism by which IFNs (IFN-alpha, -beta, and -gamma) affect the sensitivity of target cells to NK activity remains unknown, but it is clear that this function is not shared by other cell-mediated killing processes. The protective effect induced by IFN against NK activity is dependent on new mRNA and protein synthesis and can be abolished when target cells are incubated with a combination of IFN and metabolic inhibitors or by chemotherapeutic purine or pyrimidine analogs. IFN treatment neither affects the conjugate formation between NK cell and target cell nor the susceptibility of target cells to NK cytotoxic factor (NKCF), released by effector cells. However, IFN reduces the capacity of target cells to induce activation of conjugated NK cells. Because IFN has the ability to induce or increase class I MHC antigen expression (on NK target cells), it has been suggested that class I MHC antigens act as "negative signals" or NK-mediated cytotoxicity. Although many studies support this hypothesis, others present evidence for a lack of involvement of class I MHC antigens in mediating sensitivity to NK activity. This review summarizes and discusses the dual effect of IFNs in the regulation of NK activity, the relationship between the expression of class I MHC antigens on target cell surface and sensitivity to NK activity following treatment with IFNs, and the possible clinical relevance of the dual effect of IFN.

Heterogeneous binding and killing behaviour of human gamma/delta-TCR+ lymphokine-activated killer cells against K562 and Daudi cells

Effector-target conjugates, formed by coincubation of lymphokine-activated killer (LAK) cells with either K562 or Daudi cells, were separated from single cells by Percoll sedimentation. The occurrence of various CD molecules (CD3, CD56, CD57, CD16, gamma/delta-TCR) was compared in both fractions. Only LAK cells expressing the gamma/delta T cell receptor (TCR) were found in a significantly increased percentage in fractions containing conjugates indicating that gamma/delta-TCR+ LAK cells were preferably bound to target cells at the time of separation. In order to determine whether gamma/delta-TCR+ LAK cells also show a preferred killing activity against the targets, cultures enriched with or depleted of gamma/delta-TCR+ cells were established. Against K562 cells, gamma/delta-TCR(+)-enriched cultures showed a greatly reduced killing activity compared to LAK bulk cultures or cultures depleted of gamma/delta-TCR+ cells. Using Daudi cells as targets the enriched fraction revealed a slightly increased killing activity compared to bulk cultures or depleted fractions. Preincubation of gamma/delta-TCR+ LAK cells with anti-gamma/delta or anti-CD3 mAb resulted in a distinct increase of the killing activity against K562 cells, but in only a slightly enhanced activity against Daudi cells. It is postulated that gamma/delta-TCR+ LAK cells use the same adhesion mechanism for both targets but that only Daudi cells express a specific ligand for the gamma/delta-TCR. Occupation of the gamma/delta-TCR/CD3 complex by mAb, however, seems to substitute for the absent epitope on K562 cells by eliciting stimulatory signals in gamma/delta-TCR+LAK cells which, in combination with the binding stimulus, trigger cytolytic activity.