Two unique human leukemic T-cell lines endowed with a stable cytotoxic function and a different spectrum of target reactivity analysis and modulation of their lytic mechanisms

Enabling continuous immune cell recirculation on a microfluidic array to study immunotherapeutic interactions in a recapitulated tumour microenvironment

The effects of immunotherapeutics on interactions between immune and cancer cells are modulated by multiple components in the tumour microenvironment (TME), including endothelium and tumour stroma, which provide both a physical barrier and immunosuppressive stimuli. Herein, we report a recirculating chip to enable continuous immune cell recirculation through a microfluidic cell array to include these crucial players. This system consists of a three-layered cell array (μFCA) spatially emulating the TME, with tailored fluidic circuits establishing T cell recirculation. This platform enables the study of dynamics among the TME, immune cells in a circulatory system and cancer cell responses thereof. Through this system, we found that tumour endothelium hindered T cell infiltration into the reconstructed breast cancer tumour compartment. This negative effect was alleviated when treated with anti-human PD-L1 (programmed cell death ligand 1) antibody. Another key stromal component - cancer associated fibroblasts - attenuated T cell infiltration, compared against normal fibroblasts, and led to reduced apoptotic activity in cancer cells. These results confirm the capability of our tumour-on-a-chip system in identifying some key axes to target in overcoming barriers to immunotherapy by recapitulating immune cell interactions with the reconstructed TME. Our results also attest to the feasibility of scaling up this system for high-throughput cancer immunotherapeutic screening.

Different glycosylation profiles of cystatin F alter the cytotoxic potential of natural killer cells

Cystatin F, a cysteine peptidase inhibitor, is a potent modulator of NK cytotoxicity. By inhibiting granule-mediated cytotoxicity pathway, cystatin F induces formation of non-functional NK cell stage, called split-anergy. We show that N-glycosylation determines the localization and cellular function of cystatin F. Cystatin F mostly exhibited high-mannose glycosylation in U-937 cells, both high-mannose and complex glycosylation in NK-92 and primary NKs, and predominantly complex glycosylation in super-charged NKs. Manipulating N-glycosylation with kifunensine increased high-mannose glycosylation of cystatin F and lysosome localisation, which decreased cathepsin C activity and reduced NK cytotoxicity. Mannose-6-phosphate could significantly reduce the internalization of extracellular cystatin F. By comparing NK cells with different cytotoxic potentials, we found that high-mannose cystatin F was strongly associated with lysosomes and cathepsin C in NK-92 cell line. In contrast, in highly cytotoxic super-charged NKs, cystatin F with complex glycosylation was associated with the secretory pathway and less prone to inhibit cathepsin C. Modulating glycosylation to alter cystatin F localisation could increase the cytotoxicity of NK cells, thereby enhancing their therapeutic potential for treating cancer patients.

Cytotoxic immune cells do not affect TDP-43 and p62 sarcoplasmic aggregation but influence TDP-43 localisation

Sporadic inclusion body myositis (sIBM) is an idiopathic inflammatory myopathy with invasion of CD8 T cells in muscle and aggregation of proteins in the sarcoplasm. TDP-43 and p62 are two proteins that aggregate in affected muscle, and have been suggested as specific markers for sIBM over other inflammatory myopathies. TDP-43 is also mislocalised from the nucleus to the sarcoplasm in sIBM. It is not clear if inflammation precedes protein aggregation in sIBM. This study investigated if exposure to cytotoxic inflammatory cells caused TDP-43 and p62 aggregation or TDP-43 mislocalisation in cultured myotubes. TALL-104 coculture was highly cytotoxic to myotubes after 24 h. Secretion of IFNγ and TNFα were higher in cocultures compared to monocultured TALL-104 cells, indicating activation. TALL-104 cells attached to and infiltrated myotubes. There was no effect of TALL-104 coculture on TDP-43 or p62 sarcoplasmic aggregate size or frequency. However, there was decreased localisation of TDP-43 to the nucleus with TALL-104 coculture compared to control. In an in vitro setting, cytotoxic immune cells did not cause TDP-43 or p62 sarcoplasmic aggregation, suggesting cellular cytotoxicity may not trigger aggregation of these proteins. However TALL-104 coculture influenced TDP-43 localisation, suggesting cytotoxic immune cells may contribute to TDP-43 localisation shifts which is observed in sIBM.

A phenotypic screen for compounds that reverse cAMP-mediated suppression of T cell functions

The solid tumor microenvironment (TME) suppresses immune responses. Three alterations in the TME converge on a pathway triggered by elevated cyclic AMP (cAMP) that suppresses T cell receptor (TCR) signaling. We developed a phenotypic assay to screen for small molecules that interfere with this pathway using TALL-104 human leukemic cytotoxic T lymphocytes pretreated with prostaglandin E2 to elevate cAMP. Beads coated with anti-CD3 antibodies stimulate lytic granule exocytosis, which is detected via binding of an antibody against lysosome associated membrane protein 1 (LAMP-1) measured with flow cytometry. Confirming that the assay can find compounds with desired activity, treating cells with a phorbol ester restores exocytosis. The assay behaves well in 96-well format and we screened a collection of compounds expected to have effects on epigenetic regulatory proteins. Compounds in this collection affected lytic granule exocytosis after 24-hour treatment, but none prevented cAMP from suppressing lytic granule exocytosis. We used a fully automated 384-well version of the assay to screen the Prestwick Compound Library but obtained no confirmed hits. Analyzing this assay's performance reveals two points of interest. First, cytometry offers multiple ways to quantify signals. Z' was higher using percent positive cells than mean fluorescence because the relationship between the two measures saturates, but using percent positive could make it harder to find hits in some assays. Second, variance was higher in positive controls than in negative controls in this assay, which degrades assay performance less than if variance was higher in negative controls.

CD4 T-cell immune stimulation of HER2 + breast cancer cells alters response to trastuzumab in vitro

Introduction

The HER2 + tumor immune microenvironment is composed of macrophages, natural killer cells, and tumor infiltrating lymphocytes, which produce pro-inflammatory cytokines. Determining the effect of T-cells on HER2 + cancer cells during therapy could guide immunogenic therapies that trigger antibody-dependent cellular cytotoxicity. This study utilized longitudinal in vitro time-resolved microscopy to measure T-cell influence on trastuzumab in HER2 + breast cancer.

Methods

Fluorescently-labeled breast cancer cells (BT474, SKBR3, MDA-MB-453, and MDA-MB-231) were co-cultured with CD4 + T-cells (Jurkat cell line) and longitudinally imaged to quantify cancer cell viability when treated with or without trastuzumab (10, 25, 50 and 100 μg/mL). The presence and timing of T-cell co-culturing was manipulated to determine immune stimulation of trastuzumab-treated HER2 + breast cancer. HER2 and TNF-α expression were evaluated with western blot and ELISA, respectively. Significance was calculated using a two-tailed parametric t-test.

Results

The viability of HER2 + cancer cells significantly decreased when exposed to 25 μg/mL trastuzumab and T-cells, compared to cancer cells exposed to trastuzumab without T-cells (p = 0.01). The presence of T-cells significantly increased TNF-α expression in trastuzumab-treated cancer cells (p = 0.02). Conversely, cancer cells treated with TNF-α and trastuzumab had a similar decrease in viability as trastuzumab-treated cancer cells co-cultured with T-cells (p = 0.32).

Conclusions

The presence of T-cells significantly increases the efficacy of targeted therapies and suggests trastuzumab may trigger immune mediated cytotoxicity. Increased TNF-α receptor expression suggest cytokines may interact with trastuzumab to create a state of enhanced response to therapy in HER2 + breast cancer, which has potential to reducing tumor burden.

Increased cystatin F levels correlate with decreased cytotoxicity of cytotoxic T cells

Background Cystatin F is a protein inhibitor of cysteine peptidases, expressed predominantly in immune cells and localised in endosomal/lysosomal compartments. In cytotoxic immune cells cystatin F inhibits both the major pro-granzyme convertases, cathepsins C and H that activate granzymes, and cathepsin L, that acts as perforin activator. Since perforin and granzymes are crucial molecules for target cell killing by cytotoxic lymphocytes, defects in the activation of either granzymes or perforin can affect their cytotoxic potential. Materials and methods Levels of cystatin F were assessed by western blot and interactions of cystatin F with cathepsins C, H and L were analysed by immunoprecipitation and confocal microscopy. In TALL-104 cells specific activities of the cathepsins and granzyme B were determined using peptide substrates. Results Two models of reduced T cell cytotoxicity of TALL-104 cell line were established, either by treatment by ionomycin or by immunosuppressive transforming growth factor beta. Reduced cytotoxicity correlated with increased levels of cystatin F and with attenuated activities of cathepsins C, H and L and of granzyme B. Co-localisation of cystatin F and cathepsins C, H and L and interactions between cystatin F and cathepsins C and H were demonstrated. Conclusions Cystatin F is designated as a possible regulator of T cell cytotoxicity, similar to its role in natural killer cells.

A high-throughput phenotypic screen of cytotoxic T lymphocyte lytic granule exocytosis reveals candidate immunosuppressants

We screened the National Institutes of Health's Molecular Libraries Small Molecule Repository for inhibitors of cytotoxic T lymphocyte (CTL) lytic granule exocytosis by measuring binding of an antibody in the extracellular solution to a lysosomal membrane protein (LAMP-1) that is transferred to the plasma membrane by exocytosis. We used TALL-104 human leukemic CTLs stimulated with soluble chemicals. Using high-throughput cluster cytometry to screen 364,202 compounds in a 1536-well plate format, we identified 2404 initial hits: 161 were confirmed on retesting, and dose-response measurements were performed. Seventy-five of those compounds were obtained, and 48 were confirmed active. Experiments were conducted to determine the molecular mechanism of action (MMOA) of the active compounds. Fifteen blocked increases in intracellular calcium >50%. Seven blocked phosphorylation of extracellular signal-regulated kinase (ERK) by upstream mitogen-activated protein kinase kinases >50%. One completely blocked the activity of the calcium-dependent phosphatase calcineurin. None blocked ERK catalytic activity. Eight blocked more than one pathway. For 8 compounds, we were unable to determine an MMOA. The activity of 1 of these compounds was confirmed from powder resupply. We conclude that a screen based on antibody binding to CTLs is a good means of identifying novel candidate immunosuppressants with either known or unknown MMOAs.

Effect of the disintegrin eristostatin on melanoma-natural killer cell interactions

Malignant melanoma is difficult to treat due to its resistance to chemotherapeutic regimens. Discovery of new pharmaceuticals with inhibitory potential can be helpful in the development of novel treatments. The snake venom disintegrin eristostatin, from the viper Eristicophis macmahoni, caused immunodeficient mice to be significantly protected from development of lung colonization when melanoma cells and the disintegrin were co-injected in vivo into the lateral tail vein compared to vehicle controls. Cytotoxicity assays suggested that eristostatin makes the melanoma cells a better target for lysis by human natural killer cells. Direct binding assays using atomic force microscopy showed eristostatin does specifically bind the surface of the six melanoma cell lines tested. Eristostatin binding was partially inhibited by the addition of soluble RGDS peptide, suggesting an integrin as one likely, but not the sole, binding partner. Studies done with melanoma cells on a culture dish and natural killer cells attached to a cantilever tip in atomic force microscopy showed four major populations of interactions which exhibited altered frequency and unbinding strength in the presence of eristostatin.

CD16+ gammadelta T cells mediate antibody dependent cellular cytotoxicity: potential mechanism in the pathogenesis of multiple sclerosis

Our overall objective is to understand the role of gammadelta T cells in the pathogenesis of the central nervous system (CNS) autoimmune disease multiple sclerosis (MS). We have demonstrated that gammadelta T cells are directly cytotoxic to CNS cells in vitro. Although the exact mechanism of damage in MS is unknown, recent evidence suggests a role for B cells and antibodies to myelin. We were therefore interested in examining whether gammadelta T cells can injure CNS cells via an indirect mechanism involving antibody dependent cellular cytotoxicity. To study this we developed an in vitro flow cytometric cellular cytotoxicity assay (called "FC(3)A") to quantitate the amount of cytotoxicity. We utilized known target cells (Burkitt's B lymphoma) that express CD20, together with a monoclonal antibody (mAb) to CD20, rituximab, that is being studied as a potential treatment for MS. Target cells are first coated with rituximab followed by co-culture with gammadelta T cells derived from patients with MS. Specific lysis of target cells was determined by quantitation of 7-AAD (which increases only upon nuclear disruption indicating cell death). We determined that this lysis was due to gammadelta T cells that express CD16 (Fc gamma receptor) and were therefore capable of binding the rituximab and mediating cytolysis via ADCC. This specific cell lysis correlated with rituximab concentration, E:T ratio, and the surface expression of CD16 on gammadelta T cells. These findings provide a new perspective with regards to the role of gammadelta T cells in the immunopathogenesis of MS and an insight into one of the potential therapeutic effects of rituximab in the treatment of MS. In addition, this new FC(3)A method we developed could readily be adapted to study other types of immune cells suspected of ADCC-type killing.

Calcineurin activation is only one calcium-dependent step in cytotoxic T lymphocyte granule exocytosis

We have tested the idea that calcineurin, a calcium-dependent phosphatase that is critical for activating cytokine gene expression in helper T cells, plays a role in lytic granule exocytosis in cytotoxic T lymphocytes (CTLs). We used TALL-104 human leukemic CTLs as a model. Our results confirm an earlier report (Dutz, J. P., Fruman, D. A., Burakoff, S. J., and Bierer, B. E. (1993) J. Immunol. 150, 2591-2598) that immunosuppressive drugs inhibit exocytosis in CTLs stimulated either via the T cell receptor (TCR) or via TCR-independent soluble agents. Of the two recently reported alternate targets of immunosuppressive drugs (Matsuda, S., Shibasaki, F., Takehana, K., Mori, H., Nishida, E., and Koyasu, S. (2000) EMBO Rep. 1, 428-434 and Matsuda, S., and Koyasu, S. (2000) Immunopharmacology 47, 119-125), JNK is not required for lytic granule exocytosis, but we were not able to exclude a role for P38. Exocytosis could be inhibited by expressing GFP fused to a C-terminal fragment of CAIN (cabin 1), but not by expressing VIVIT-GFP. Finally, expressing either full-length or truncated constitutively active mutant calcineurin A enhanced lytic granule exocytosis. However, the mutant calcineurin was unable to support exocytosis when cells were stimulated in the absence of Ca2+ influx. Taken together, our results support the idea that activation of calcineurin is required for lytic granule exocytosis but suggest that it is not the sole Ca2+-dependent step.

Protein kinase C activity is required for cytotoxic T cell lytic granule exocytosis, but the theta isoform does not play a preferential role

CTLs kill virus-infected, tumor, and transplanted targets via secretion of lytic agents including perforin and granzymes. Knowledge of the signals controlling this important process remains vague. We have tested the idea that protein kinase C (PKC)theta, a member of the novel PKC (nPKC) family, which has been shown to play a preferential role in critical Th cell functions, plays a similar, preferential role in CTL lytic granule exocytosis using T acute lymphoblastic leukemia-104 (TALL-104) human leukemic CTLs as a model. We provide evidence consistent with the idea that PKC activity is important for the degranulation step of lytic granule exocytosis, as opposed to upstream events. In contrast with previous work, our results with pharmacological agents suggest that conventional PKCs (cPKCs) and nPKCs may participate. Our results suggest that stimulation with soluble agents that bypass the TCR and trigger granule exocytosis activates PKCalpha and PKCtheta, which can both accumulate at the site of contact with a target cell, although PKCtheta did so more often. Finally, using a novel assay that detects granule exocytosis specifically in transfected, viable cells, we find that overexpression of constitutively active mutants of PKCalpha or PKCtheta can synergize with increases in intracellular [Ca(2+)] to promote granule exocytosis. Taken together, our results lend support for the idea that PKCtheta does not play a preferential role in CTL granule exocytosis.

Exocytic responses of single leukaemic human cytotoxic T lymphocytes stimulated by agents that bypass the T cell receptor

Cytotoxic T lymphocytes kill targets via secretion of lytic agents including perforin and granzymes. Recently, new methods have been developed to monitor cytotoxic T lymphocyte degranulation. These include detecting the appearance of lysosome-associated membrane protein on the cell's surface, and monitoring decreases in cellular perforin content. We have combined these methods with microscopy and flow cytometry to provide the first analysis of how single cytotoxic T cells degranulate. We used TALL-104 human leukaemic cytotoxic T cells as a model system, and stimulated them with thapsigargin and PMA, soluble agents that mimic the two major signalling pathways activated by T cell receptor cross-linking. Our results indicate that essentially every TALL-104 cell responds to maximal stimulation by releasing about half of its lytic granule complement. This reflects complete release of the contents of half the cell's granules, rather than partial release of the contents of all of the granules. Sub-maximal stimulation reduces both the fraction of cells that respond and the magnitude of single cell responses. We find that individual cells respond to maximal stimulation with a variable latency, and provide evidence that, once it starts, degranulation is a slow process taking tens of minutes.

Receptors and lytic mediators regulating anti-tumor activity by the leukemic killer T cell line TALL-104

The major histocompatibility complex nonrestricted cytotoxic leukemic T cell line T acute lymphoblastic leukemia (TALL)-104 is being pursued as a therapeutic agent for cancer. However, the receptors and effector mechanisms responsible for its broad tumoricidal function remain undefined. Here, we examined the roles played by natural cytotoxicity receptors (NCR), killer cell immunoglobulin-like receptors, cytolytic granule components, and tumor necrosis factor (TNF) family members in tumor recognition and lysis by TALL-104 cells. The perforin-granzyme pathway, TNF-related apoptosis-inducing ligand (TRAIL), and Fas were each involved in the lysis of particular tumor targets by TALL-104. Furthermore, phorbol 12-myristate 13-acetate/ionomycin treatment induced surface expression of Fas-L and TRAIL. In addition, supernatants from CD3-stimulated TALL-104 cultures exhibited antiproliferative activity, which was blocked 50-90% by anti-TNF-alpha monoclonal antibody (mAb). Although negative for the NCR natural killer (NK)p44, this cell line was found to express NKp46. An anti-NKp46 antibody strongly blocked TALL-104-mediated lysis of certain targets and directly induced cytokine production, granule release, and redirected lysis responses. Anti-NKG2D and anti-2B4 also stimulated redirected cytotoxicity by TALL-104. By contrast, anti-NKG2A mAb did not stain the cells or inhibit killing responses. Alternatively, KIR3DL2 was detected on TALL-104, and expression of its reported ligand, human leukocyte antigen (HLA)-A, on target cells provided protection from cytotoxicity. Thus, NKp46, NKG2D, and 2B4 are activating receptors, and KIR3DL2 is an inhibitory receptor on TALL-104. The data demonstrate the ability of TALL-104 cells to recognize a wide variety of tumors with NK cell receptors and kill them with a broad arsenal of cytolytic effector mechanisms, including cytolytic granules and TNF family ligands.

Evaluating the cytotoxicity of innate immune effector cells using the GrB ELISPOT assay

Background

This study assessed the Granzyme B (GrB) ELISPOT as a viable alternative to the ⁵¹Cr-release assay for measuring cytotoxic activity of innate immune effector cells. We strategically selected the GrB ELISPOT assay because GrB is a hallmark effector molecule of cell-mediated destruction of target cells.

Methods

We optimized the GrB ELISPOT assay using the human-derived TALL-104 cytotoxic cell line as effectors against K562 target cells. Titration studies were performed to assess whether the ELISPOT assay could accurately enumerate the number of GrB-secreting effector cells. TALL-104 were treated with various secretion inhibitors and utilized in the GrB ELISPOT to determine if GrB measured in the ELISPOT was due to degranulation of effector cells. Additionally, CD107a expression on effector cells after effector-target interaction was utilized to further confirm the mechanism of GrB release by TALL-104 and lymphokine-activated killer (LAK) cells. Direct comparisons between the GrB ELISPOT, the IFN-γ ELISPOT and the standard ⁵¹Cr-release assays were made using human LAK cells.

Results

Titration studies demonstrated a strong correlation between the number of TALL-104 and LAK effector cells and the number of GrB spots per well. GrB secretion was detectable within 10 min of effector-target contact with optimal secretion observed at 3–4 h; in contrast, optimal IFN-γ secretion was not observed until 24 h. The protein secretion inhibitor, brefeldin A, did not inhibit the release of GrB but did abrogate IFN-γ production by TALL-104 cells. GrB secretion was abrogated by BAPTA-AM (1,2-bis-(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid tetra(acetoxymethyl) ester), which sequesters intracellular Ca²⁺, thereby preventing degranulation. The number of effector cells expressing the degranulation associated glycoprotein CD107a increased after interaction with target cells and correlated with the stimulated release of GrB measured in the ELISPOT assay.

Conclusions

Because of its high sensitivity and ability to estimate cytotoxic effector cell frequency, the GrB ELISPOT assay is a viable alternative to the ⁵¹Cr-release assay to measure MHC non-restricted cytotoxic activity of innate immune cells. Compared to the IFN-γ ELISPOT assay, the GrB ELISPOT may be a more direct measure of cytotoxic cell activity. Because GrB is one of the primary effector molecules in natural killer (NK) cell-mediated killing, detection and enumeration of GrB secreting effector cells can provide valuable insight with regards to innate immunological responses.

Interactions of the allogeneic effector leukemic T cell line, TALL-104, with human malignant brain tumors

TALL-104 is a human leukemic T cell line that expresses markers characteristic of both cytotoxic T lymphocytes and natural killer cells. TALL-104 cells are potent tumor killers, and the use of lethally irradiated TALL-104 as cellular therapy for a variety of tumors has been explored. We investigated the interactions of TALL-104 cells with human brain tumor cells. TALL-104 cells mediated increased lysis of a panel of brain tumor cells at low effector-to-target ratios over time. We obtained evidence that TALL-104 cells injured glioma cells by both apoptotic and necrotic pathways. A 7-amino actinomycin D flow cytometry assay revealed that the percentages of both apoptotic and necrotic glioma cells increased after TALL-104 cell/glioma cell coincubations. Fluorescent microscopy studies and a quantitative morphologic assay confirmed that TALL-104 cell/glioma cell interactions resulted in tumor cell apoptosis. Cytokines are secreted when TALL-104 cells are coincubated with brain tumor cells; however, morphologic analysis assays revealed that the soluble factors contained within clarified supernates obtained from 4 h coincubates added back to brain tumor cell cultures did not trigger the glioma apoptosis. TALL-104 cells do not express Fas ligand, even upon coincubation with glioma targets, which suggests that the Fas/Fas ligand apoptotic pathway is not likely responsible for the cell injury observed. We obtained evidence that cell injury is calcium dependent and that lytic granule exocytosis is triggered by contact of TALL-104 cells with human glioma cells, suggesting that this pathway mediates glioma cell apoptosis and necrosis.

Cross-talk with Ca2+ Influx Does Not Underlie the Role of Extracellular Signal-regulated Kinases in Cytotoxic T Lymphocyte Lytic Granule Exocytosis

One important mechanism cytotoxic T lymphocytes use to kill target cells is exocytosis of lytic granules that contain cytotoxic agents such as perforin and granzyme. Ca(2+) influx and activation of protein kinase C have been known for many years to be key signals for granule exocytosis. Recent work has suggested that activation of extracellular signal-regulated kinases (ERK), members of the mitogen-activated protein kinase (MAP kinase) family, may be a third required signal. We surmised that the involvement of ERK in lytic granule exocytosis could be mediated through cross-talk with Ca(2+) influx, rather than constituting an independent signal. We tested this idea using TALL-104 human leukemic CTLs as a model system and discovered the following. 1) ERK inhibition caused a modest decrease in the amplitude of increases in intracellular Ca(2+) concentration, but this effect cannot account for the profound inhibition of granule exocytosis. 2) Ca(2+) influx can activate ERK in TALL-104 cells, but this effect does not contribute to ERK activation stimulated by solid phase anti-CD3 monoclonal antibodies. We conclude that cross-talk between ERK signaling and Ca(2+) does not mediate the role of ERK in CTL lytic granule exocytosis.

The actin cytoskeleton and cytotoxic T lymphocytes: evidence for multiple roles that could affect granule exocytosis-dependent target cell killing

One important mechanism cytotoxic T lymphocytes (CTLs) use to kill virus-infected, transplanted or tumour targets is exocytosis of granules that contain cytotoxic agents such as perforin and granzymes. Granule exocytosis-dependent target cell killing is a complex process, involving initial T-cell receptor (TCR)-dependent signalling that includes Ca2+ influx and activation of protein kinase C, shape changes that serve to bind the CTL to the target and, finally, exocytosis of lytic granules at the site of contact with the target cell. Although there is reason to propose that multiple steps in the lytic process could involve the actin cytoskeleton of CTLs, few studies have examined this issue, and those that have do not allow the specific step(s) involved to be determined. We have used the potent membrane-permeant actin cytoskeleton-modifying drugs jasplakinolide and latrunculin A to investigate the actin dependence of defined processes that are expected to be important for granule exocytosis-dependent killing. Our results, obtained using TALL-104 human leukaemic CTLs as a model system, are consistent with the idea that a functional actin cytoskeleton is required for TCR/CD3-dependent signalling, for activation of store-dependent Ca2+ influx and for CTL shape changes. When cells were stimulated with solid-phase anti-CD3 antibodies, treatment with either jasplakinolide or latrunculin A abolished granule exocytosis. However, when cells were stimulated in a manner that bypasses TCR/CD3-dependent signalling, granule exocytosis was not significantly altered, suggesting that the actin cytoskeleton does not function as a barrier to exocytosis.

Strategies using the immune system for therapy of brain tumors

Phase II immunotherapy and gene therapy studies should be pursued because of encouraging results in many phase I studies. Future testing in this field may consider modifications of some of the above-mentioned combined strategies. For instance, in the immunization and adoptive transfer studies performed by Holladay et al and by Plautz et al, the systemic adoptive transfer could be altered to intratumoral placements of effector cells. This permutation may be more efficacious because local adoptive immunotherapy approaches involve placement of effector cells where they are needed. Additionally, new avenues of gene therapy are being explored that may offer added beneficial effects for immunization, local or systemic adoptive immunotherapy, or combined chemotherapy and adoptive immunotherapy of tumors. With new genetic tools, such as microarray analyses, SEREX, and creation of cDNA libraries from tumor cells, significant progress in the treatment of neoplasms in the immunologically privileged brain should be forthcoming.

Role of calcium influx in cytotoxic T lymphocyte lytic granule exocytosis during target cell killing

One mechanism cytotoxic T lymphocytes use to kill targets is exocytosis of cytotoxic agents from lytic granules, a process that requires Ca(2+) influx. We investigated the role of Ca(2+) influx in granule exocytosis using TALL-104 human leukemic cytotoxic T cells triggered via a bispecific antibody containing an anti-CD3 F(ab') to kill Raji B lymphoma cells. Using a novel fluorescence method, we detected target-directed release of approximately 15% of lytic granules during killing. Consistent with previous work, we observed sustained CTL Ca(2+) gradients during killing, but gradients reflect the behavior of Fura-2 in granules. Rapid imaging experiments suggest that Ca(2+) channels are not polarized during killing, indicating that Ca(2+) influx does not direct granule reorientation. Furthermore, we find that Ca(2+) acts via a high-affinity interaction to promote granule exocytosis.

Ex vivo purging of stem cell autografts using cytotoxic cells

Autologous stem cell transplantation (SCT) is the treatment alternative offered to patients that cannot benefit from allogeneic transplantation due to lack of suitable donor or age limitations. However, the outcome of autologous SCT is largely hindered by the high relapse rate. Two major factors can account for relapse after autologous SCT: the persistence of residual malignant cells resistant to chemo/radiotherapy left either in the body or in the autograft. Therefore, the rationale for purging autografts of residual malignant cells comes from the limitations of conventional high-dose chemo/radiotherapy in achieving a complete eradication of residual tumor cells in the marrow. To date, different purging modalities have been exploited. Immunological methods of purging present the advantage of being non-cross-reactive with conventional chemotherapy. These immunologic methods include depletion using antibody targeting of the malignant cells, ex vivo activation/generation of the autologous cytotoxic cells, in particular that of natural killer/lymphokine-activated killer (NK/LAK) and cytokine-induced killer (CIK) cells, and ex vivo purging of autografts using cytotoxic cell lines. The generation of ex vivo-expanded and activated autologous cytotoxic cells (CTL or NK) has generated increasing interest for the treatment of different malignancies. Unfortunately, the isolation and expansion of these cells have proven to be technically difficult. As an alternative, the use of cytotoxic cell lines as immune effectors has been proposed. The two available human cytotoxic cell lines TALL104 and NK-92 are currently in clinical trials and a number of studies have suggested their effectiveness as an immunotherapeutic agent including for ex vivo purging of autografts.

Immunologic approaches to therapy for brain tumors

Malignant brain tumors are notoriously invasive. Although surgical debulking can relieve the patient of the main mass of tumor, adjuvant treatments are needed to target the glioma cells that infiltrate through normal parenchyma as single cells or pockets of tumor cells from which recurrent tumors arise. Successful adjuvant cellular therapy of brain tumors, or activation of endogenous immune cells, requires that either cell effectors make direct contact with tumor cells or come within close proximity to them and exert an indirect effect. This review examines current clinical trials aimed at direct lysis of glioma cells and trials making gliomas more visible to the endogenous immune system.

Immunologic methods of purging in autologous stem cell transplantation

Malignant cells in the stem cell product have been shown to contribute to disease recurrence in patients who relapse after autologous transplantation. Immunologic methods of purging tumor cells from stem cell products focus on either removal of specific target cells or positive selection of HPC. mAb are the key component of many purging strategies and are employed both in vitro and in vivo. Cytotoxic cellular therapies are an emerging method of tumor cell eradication.

Role of CD38 and Its Ligand in the Regulation of MHC-Nonrestricted Cytotoxic T Cells

Human CD38 is a type II transmembrane glycoprotein that regulates lymphocyte adhesion, proliferation, and cytokine production. The mAb Moon-1 recognizes a ligand for CD38 (CD38L) and specifically inhibits CD38-mediated cell adhesion. To analyze the role of CD38 and its ligand in MHC-nonrestricted T cell activation, we examined the effects of Moon-1 and the anti-CD38 mAb IB4 on the effector functions of the IL-2-dependent T cell line TALL-104 (CD3/TCR-αβ+, CD8+, CD56+) and of LAK cells (90% CD3+). TALL-104 cells were almost 100% reactive with both mAbs, whereas the reactivity of LAK cells for IB4 and Moon-1 ranged from 10 to 60% among different donors. From 78 to 94% of the cytotoxic CD8+/CD56+ LAK subset was CD38L+. Like mAb OKT3 (anti-CD3), and at variance with IB4, Moon-1 drastically enhanced the cytotoxicity of TALL-104 and CD8+ LAK cells against a resistant tumor target. Granule exocytosis did not appear to play a role in Moon-1-induced cytotoxicity. Moreover, neither IB4 nor Moon-1 induced [Ca2+]i mobilization in LAK and TALL-104 cells. Whereas stimulation of CD3 and CD38 resulted in a dramatic induction of cytokine (granulocyte-macrophage-CSF, IFN-γ, TNF-α, and TNF-β) release by both TALL-104 and LAK cells, ligation of CD38L was not followed by cytokine production in TALL-104 cells. Thus, cytotoxicity and cytokine release are independently regulated, at least in this system. These data demonstrate that CD38 and its ligand can regulate some T cell functions using signaling pathways distinct from those of CD3.

Introducing graft-versus-leukemia into autologous stem cell transplantation

Although autologous transplantation of stem cells is widely used to support high-dose chemotherapy and radiation for the treatment of hematologic malignancies, relapse is a severe impediment to its wide use, especially in patients receiving transplants for leukemia. This is related to the infusion of leukemic cells in the autograft and the lack of an allogenic graft-versus-leukemia (GVL) effect. This review discusses the current approaches that are under study to introduce a GVL effect into autologous transplantation.

Effects of lethal irradiation and cyclosporin A treatment on the growth and tumoricidal activity of a T cell clone potentially useful in cancer therapy

The TALL-104 cell line, originally derived from a patient with T cell leukemia, can be maintained indefinitely in culture in the presence of interleukin-2 (IL-2) and is endowed with a highly potent major-histocompatibility-complex (MHC)-non-restricted tumoricidal activity both in vitro and in animal models. The present study analyzes in detail the short- and long-term effects of irradiation and cyclosporin A (CsA) treatment on the growth and tumoricidal function of this T cell clone as compared to polyclonal lymphokine-activated killer (LAK) cell preparations from healthy donors. DNA and RNA syntheses by both TALL-104 and LAK cells were irreversibly arrested a few hours after irradiation with 40 Gy. However, 4-h 51Cr-release assays, performed on different days (day 1 to day 7) after irradiation, showed that the cytotoxic efficiency of TALL-104 cells against hematopoietic and solid tumor targets was only modestly reduced, whereas that of LAK cells was severely inhibited. Moreover, the cytotoxic responses to recombinant human IL-2 and IL-12, measured 18 h after irradiation and cytokine addition, were normal in the case of TALL-104 cells but were abolished in the case of LAK cells. Co-culture of IL-2- or IL-12-preactivated TALL-104 cells with a tumor target for 5 days in the absence of cytokines resulted in a lower efficiency of lysis, as compared to the non-irradiated effectors, especially if the initial stimulus was IL-12. These findings suggest the requirement of multiple cytokine stimulation for optimal expression of tumoricidal activity by lethally irradiated TALL-104 cells. CsA, while abrogating TALL-104 cell proliferation at the low dose of 0.5 microgram/ml, inhibited their cytotoxic function marginally only at high doses (100 micrograms/ml). By contrast, CsA reduced dose-dependently the cytotoxicity of LAK cells starting at very low doses (0.5 microgram/ml). CsA did not impair the ability of TALL-104 and LAK cells to produce interferon (IFN) gamma, tumor necrosis factor (TNF) alpha, and granulocyte/macrophage-colony-stimulatory factor (GM-CSF) in response to IL-2, IL-12, or tumor targets. Irradiation reduced drastically IFN gamma production by LAK, but not TALL-104 cells; release of TNF alpha and GM-CSF by either type of effector was inhibited by 10%-50%, depending on the stimulus. The high resistance and immunosuppressive drugs renders tis immortal T cell clone a potentially safe and effective reagent for new adoptive-transfer approaches to cancer in MHC-incompatible recipients.

Reversal of acute myelogenous leukemia in humanized SCID mice using a novel adoptive transfer approach

Advanced human malignancies cannot be permanently cured by adoptive transfer of autologous lymphokine-activated killer (LAK) cells. Moreover, administration of high doses of IL-2 to maintain LAK activity in vivo is associated with severe toxicity. In this study, we tested the anti-tumor efficacy of a uniquely potent MHC non-restricted human killer T cell clone (TALL-104) in humanized severe combined immunodeficient (SCID) mice bearing acute myelogenous leukemia (AML). We show that, in appropriate experimental conditions, TALL-104 cells could effectively reverse the aggressive growth of the myelomonocytic leukemia cell line U937 in SCID mouse tissues, leading to complete abrogation of AML. A single transfer of TALL-104 cells at the time of tumor challenge in combination with recombinant human (rh) IL-12 (1 microgram/d) prolonged significantly the life of the mice. However, eradication of leukemia, as monitored both clinically and by PCR, was achieved by repeated injection of the effectors at close intervals. Complete cure was obtained also upon transfer of lethally irradiated (non-proliferating) TALL-104 cells together with low doses of rh IL-2 (100 U/d). Most notably, of the mice that received multiple transfers of TALL-104 cells without cytokines in an advanced disease stage, 50% were clinically cured, and 50% survived significantly longer. The potential of TALL-104 cells as an effective and safe leukemia purging agent is discussed.

Inducible expression of granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-alpha, and interferon-gamma in two human cytotoxic leukemic T-cell lines

We investigated the ability of the TALL-103/2 and TALL-104 leukemic cell lines to produce lymphokines in response to activation signals, such as tumor cells and anti-CD3 (OKT3) or -CD2 (B67.1) monoclonal antibodies (mAb) or both. Both cell lines were found to produce high levels of interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and granulocyte-macrophage colony-stimulating factor (GM-CSF). The latter lymphokine is induced by lysable tumor cells and by immobilized OKT3 and B67.1 mAb only in the presence of interleukin (IL-2). IFN-gamma and TNF-alpha are induced upon CD3 but not CD2 stimulation, both in the presence and absence of IL-2. Interestingly, the B67.1 mAb amplifies the OKT3-induced responses by 2- to 10-fold, bringing the IFN-gamma and TNF-alpha levels of production up to 200 U/ml. Thus, simultaneous triggering of the CD2 and CD3 signaling pathways results in a very efficient lymphokine release. Of all the tumor cell lines tested as inducers, only K562 cells are able to stimulate the production of IFN-gamma and TNF-alpha in TALL-103/2 and TALL-104 cells, especially upon culture in IL-2. Lymphokine mRNA expression after stimulation with mAb or K562 cells peaks at 2 h in both cell lines. No messages are detectable in TALL-103/2 cells at 8 h, whereas in TALL-104 cells, IFN-gamma and GM-CSF transcripts are still present at 8 and 20 h, respectively. The inducible and highly regulatable expression of lymphokine release by these cell lines provides a unique model for studying mechanisms of lymphokine induction by different biological agents.