Fibrosis inhibits ablation lesion formation in muscle tissue

Introduction

Myocardial fibrosis is a trigger for both atrial and ventricular arrhythmia. Ventricular fibrosis correlates with ventricular tachycardia, ventricular fibrillation, and sudden death. Besides medical therapy, radiofrequency (RF) ablation is an important therapeutical option to treat ventricular arrhythmia. Our study gains insights into effectivity of RF ablation depending on the degree of fibrosis.

Methods

Using a wet lab, we created with radiofrequency (RF) ablation lesions in parts of restructured beef with a defined, homogenous content of 0, 10, 20 and 50% fiber. We calculated the volume of ablation zones (called lesion volume below). Both common ablation modes low-power long-duration (LPLD: 30 W, 30 s) and high-power short-duration (HPSD: 70 W, 10 s) were tested. Lesion volumes of fibrotic beef were compared to lesion volumes of fibrotic-free beef using an ordinary ANOVA. The effect and interaction of fibrosis and ablation mode to the lesion volume was tested by a two-way ANOVA.

Results

Higher degrees of fibrosis create smaller lesion volumes (M = mean volume ablation zone): M (0%) = 322 mm3 (SD 187 mm3), M (10%) = 226 mm3 (SD 94.8), M (20%) = 217 mm3 (SD 103 mm3) and M (50%) = 186 mm3 (SD 92.7 mm2). Lesion volumes in fibrotic tissue differ significantly from lesion volumes in fibrotic-free tissue (F(3,124) = 6.94, p<0.001). There is a significant difference in lesion volumes for all degrees of fibrosis compared to fibrosis-free tissue (MD = mean difference of ablation zone volumes between 0% fibrosis and 10, 20 and 50% fibrosis): MD (0, 10%) = 95.6 mm3 (95% confidence interval (20.8–170), p=0.008), MD (0, 20%) = 105 mm3 (95% confidence interval (30.4–180), p=0.003) and MD (0, 50%) = 135 mm3 (95% confidence interval (60.7–210), p<0.001). We also found a significant difference in lesion volumes related to the content of fiber in a comparison of all groups (F(3,120) = 7,49, p≪0.001). There is no significant difference in lesion volumes related to the used ablation mode (F(1,120) = 2.89, p=0.09). There is also no significant difference in lesion volumes related to the interaction between the content of fiber and the ablation mode (F(3,120) = 1.23, p=0.3).

Conclusion

Lesions created by RF ablation are influenced by fibrosis. A higher content of fibrosis is associated with smaller lesion volumes. Neither LPLD nor HPSD ablation mode shows an advantage in fibrotic tissue.

Funding Acknowledgement

Type of funding sources: None.

Effect of glutamine on doxorubicin-induced cardiotoxicity: an echocardiographic assessment

Abstract #6143

Background: Doxorubicin (DOX) is a widely used chemotherapeutic agent with a dose-dependent cardiotoxicity. Previous studies showed that dietary glutamine (GLN) reduced cardiac oxidative damages in rats treated with DOX through the increase of cardiac and blood glutathione, reduction of cardiac lipid peroxidation and reducing cardiac apoptosis. The present study aimed to examine further the effect of GLN on DOX-induced cardiac injury and to gain insight into the physiological aspects of this process by using high-resolution micro-ultrasound imaging and Doppler echocardiography.
 Materials and Methods: Female Fisher 344 rats (n=12) were randomized into 2 groups: (i) GLN-supplemented (n=6) and ii) controls (n=6). GLN-supplemented rats received 1g/kg/day GLN via gavage starting 1 week before DOX administration. DOX (12 mg/kg) was injected i.p. in all animals. Each animal was examined before DOX administration, 3 days, 7 days, and 10 days after DOX administration using ultrasound imaging system Vevo 770 (VisualSonics, Toronto, ON, Canada). RMVTM 716 "high frame" scan head, designed for real-time small animal imaging applications, was used. The short-axis imaging was taken in B-mode to view the left ventricle (LV) movement during diastole and systole. Anatomical M-mode was used to obtain LV measurements including LV end-diastolic and systolic inner diameters, LV posterior wall, LV ejection fraction (%EF) and LV fraction shortening (%FS). The LV filling was evaluated by pulsed-Doppler sampling of the mitral valve (MV) inflow. The peak E-wave velocity (E), peak A-wave velocity (A) and the MV E/A ratio were obtained. All data and images were saved and analyzed by Vevo 770 Analytic Software (VisualSonics, Toronto, ON, Canada).
 Results: Ten days after DOX treatment the control animals had: i) increased LV posterior wall end-diastolic thickness of an average from 1.7 mm before DOX administration to 1.8 mm and end-systolic from 2.9 mm to 3.7 mm; ii) reduction of the %EF by 10% and %FS by 14%; and iii) increased MVE by 30% with a resulting MVE/A ratio >2.0; all these suggestive of the development of restrictive cardiomyopathy (RCM). RCM, characterized by thickening and increased rigidity of the endocardium due to infiltration and fibrosis, restrictive ventricular filling with MVE/A >2.0 and in some cases reduction of the EF, has been reported in several clinical studies of patients treated with DOX. In GLN-supplemented rats of this study there was no statistically significant difference between posterior wall thickness before and after DOX administration, MVE/A ratio was maintained between 1.4 and 1.8; and EF was reduced by 2% only.
 Conclusions: The results from this study are in agreement with our previous data showing that GLN is able to reduce cardiac oxidative damages caused by DOX. This data further confirmed the safety of GLN supplementation and its cardioprotective effects during chemotherapeutic treatment with DOX.
 Acknowledgements: This work was supported by a grant from Susan G. Komen to VKT.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6143.

Reduced expression of plakoglobin correlates with adverse outcome in patients with neuroblastoma

Plakoglobin and its homologue beta-catenin are cytoplasmic proteins that mediate adhesive functions by interacting with cadherin receptors and signaling activities by interacting with transcription factors. It has been suggested that plakoglobin can suppress tumorigenicity whereas beta-catenin can act as an oncogene. We investigated the correlation between the expression pattern of N-cadherin, beta-catenin, and plakoglobin and tumor behavior in primary tumors of 20 neuroblastoma patients of all stages and in 11 human neuroblastoma cell lines. N-cadherin and beta-catenin were detected in 9 of 11 and 11 of 11 cell lines, respectively, whereas plakoglobin was undetectable or severely reduced in 6 of 11 cell lines. Tumor cells from 16 of 20 patients expressed N-cadherin and 20 of 20 patients expressed beta-catenin at levels similar to those of normal ganglion cells. Plakoglobin was undetectable in 9 of 20 tumors. Plakoglobin deficiency in the primary tumors was significantly associated with adverse clinical outcome. Five of the patients with plakoglobin-negative tumors died whereas four patients are alive without evident disease. In contrast, all patients with plakoglobin-positive tumors are alive; 2 of 11 are alive with the disease and 9 of 11 are alive without evident disease. These results suggest that down-regulation of plakoglobin may be of prognostic value for neuroblastoma patients as predictor of poor outcome.

Expression of wild-type p53 and Bcl-2 family genes oscillates with recurrent remission and relapse in an unusual case of low-grade lymphoma

Downregulation of apoptosis has been proposed as a mechanism of clonal expansion in low-grade B cell neoplasms. We have previously described an unusual case of CD5+ B cell lymphoma characterized by cycles of leukemic phase alternating with spontaneous remission. In the present study, we examined the involvement of apoptosis-related proteins in the progression of this cyclic lymphoma ex vivo. During the leukemic phases, the clonal cells were activated blasts expressing elevated levels of wild-type (wt) p53, Bcl-2, Bcl-x(L), and Bax, while Bak expression increased during the decline of lymphocytosis. Bax heterodimerized with Bcl-2 but not with Bcl-x(L). The anti-apoptotic Bcl-2/Bax heterodimers peaked during early leukemic phases and declined during regression. The elevation in Bcl-2, Bcl-x(L) and Bax expression during early leukemic phases seems to result from cell activation since a similar increase was induced by activating the remission phase leukemic cells in culture. The data suggest that wt p53, Bcl-x(L), and Bcl-2/Bax heterodimers support the accumulation of activated leukemic cells during the leukemic phases, while Bax and Bak may be involved in their decline during regression.

Amplification of immunological functions by subcutaneous injection of intermediate-high dose interleukin-2 for 2 years after autologous stem cell transplantation in children with stage IV neuroblastoma

BACKGROUND

Immunotherapy given post-autologous stem cell transplantation may eliminate residual tumor cells escaping the conditioning protocol.

METHODS

Five children suffering from stage IV neuroblastoma were treated by recombinant interleukin-2 (IL-2) post-autologous peripheral blood stem cell transplantation. The patients' peripheral mononuclear cells were monitored for CD3+ and CD56+ levels, their proliferative response and killing of various cell lines targets.

RESULTS

An increase in the level of total lymphocytes, mainly due to expansion of T cells, and enhanced proliferative response to phytohemaglutinin were observed. Elevated cytotoxicity against K562 and neuroblastoma target cells was detected in four patients and against K562 targets in one patient. Toxicity included mild thrombocytopenia, and fever in four patients and mild to moderate encephalopathy which necessitated withdrawing one patient from the protocol. Three of five patients studied are alive today, one of them whose IL-2 was stopped, is in relapse. Two patients have died.

CONCLUSIONS

Immunotherapy with s.c. intermediate-high dose IL-2 is feasible and results in expansion of T cells and in stimulation of killing activity against several targets including in some cases, neuroblastoma tumor cells.

Neoplastic cell activation and proliferative response to CD40-ligand characterize recurrent leukemic bouts in an unusual case of low grade lymphoma

Spontaneous fluctuations in activity of low-grade B cell lymphomas are common but not understood. An explanation may be offered by studying an atypical SLL/CLL case characterized by recurrent cycles of leukemic phase alternating with spontaneous remission (1). During remissions, residual IgMkappa+ leukemic cells exhibited resting phenotype, low proliferative response to CD4O-ligand and delayed apoptosis. In contrast, the acute phase counterparts were phenotypically activated, underwent rapid apoptosis in culture and proliferated extensively in response to membrane-anchored CD40-ligand. Transient bursts of serum TNFalpha and IL-10 preceded the acute phases, which were characterized by the co-existence of CD40-ligand+ T lymphocytes and lymphoma cells in the bone marrow. Based on ex-vivo and in-vitro data, we suggest that changes in the lymphoma milieu affect the neoplastic cell activation status, rate of proliferation in response to activated T cells and rate of apoptosis. These responses may underlie both the induction and spontaneous regression of the acute phases in this unique lymphoma. Our findings raise the possibility that part of this mechanism may have evolved during transformation of indolent common CLL to its more aggressive form.

Thrombin promotes platelet-mediated melanoma cell adhesion to endothelial cells under flow conditions: role of platelet glycoproteins P-selectin and GPIIb-IIIA

We investigated the role of platelets in human melanoma cell (line 397) interaction with vascular endothelial cells (ECs) under flow conditions. The ability of the tumour cells to adhere to the EC monolayer was significantly reduced by application of flow at a shear rate of 250 s(-1). A 2.2-fold increase in tumour cell adhesion to ECs under flow was observed upon addition of thrombin receptor agonist peptide (TRAP)-activated platelets but not resting platelets. A similar increase (2.5-fold) in tumour cell adhesion to ECs under flow was observed when the tumour cells were incubated with resting platelets on thrombin-treated ECs. However, thrombin treatment of the ECs alone had no effect on tumour cell adhesion in the absence of platelets. The enhancement of tumour cell adhesion to ECs by TRAP-activated platelets was virtually abolished by blockade of the platelet glycoproteins P-selectin and GPIIb-IIIa by monoclonal antibodies. Blockade of P-selectin also inhibited the direct adhesion of TRAP-activated platelets to ECs, but did not affect the interaction of the tumour cells with platelets immobilized on subendothelial extracellular matrix (ECM). Blockade of GPIIb-IIIa inhibited both platelet-EC and platelet-tumor cell interactions. Our results indicate that tumour cell adhesion to the endothelium under flow is enhanced by platelets under conditions that allow platelet adhesion to ECs. Inhibition studies suggest that activated platelet adhesion to ECs is mediated by P-selectin and GPIIb-IIIA, and tumour cell adhesion to EC-bound platelets--mainly by GPIIb-IIIa.

Platelets mediate tumor cell adhesion to the subendothelium under flow conditions: involvement of platelet GPIIb-IIIa and tumor cell alpha(v) integrins

The aim of our study was to explore the role of platelets and their specific integrin receptors in mediating the interaction of 4 human tumor cell lines (3 melanoma and 1 carcinoma) with the extracellular matrix (ECM) under static and arterial flow conditions. Under static conditions, all 4 cell lines adhered to the ECM. The adhesion capacity of all 4 cell lines was virtually abolished by application of flow during incubation with the ECM. Under static conditions, tumor cell adhesion was not affected by adding platelets to the cell suspension and was slightly reduced by pre-coating the ECM with platelets prior to the addition of tumor cells. In contrast, under flow conditions, platelets significantly increased tumor cell adhesion to the ECM, the enhancing effect being more pronounced when platelets were pre-incubated with the ECM prior to the addition of tumor cells than when incubated simultaneously with the cells. Platelet-mediated tumor cell adhesion under flow was markedly inhibited by blockade of the platelet GPIIb-IIIa or of the tumor cell alpha(v) integrins. Platelets of a Glanzmann thrombastenia (GT) patient were unable to support tumor cell adhesion to the ECM under flow. Our results suggest that the interaction of tumor cells with subendothelium-bound platelets under flow conditions is mediated by platelet GPIIb-IIIa and by tumor cell alpha(v) integrins independently of the nature of the beta subunit.

Cloning of the murine lymphocyte function-associated molecule-1 alpha-subunit and its expression in COS cells

The lymphocyte function-associated molecule 1 (LFA-1, CD11a/CD18) is an integrin that mediates adhesion of immune cells by interaction with two members of the Ig superfamily, ICAM-1 and ICAM-2. LFA-1 consists of an alpha subunit (Mr = 180,000) and a beta subunit (Mr = 95,000). We report here the isolation and expression of the murine alpha subunit cDNA (GenBank accession no. M60778). The deduced sequence comprises a 1061 amino acid extracellular domain, a 29 amino acid transmembrane region, and a 50 amino acid cytoplasmic domain. It has a 72% amino acid identity with its human counterpart and 34% identity with the murine Mac-1 alpha subunit. The murine LFA-1 alpha subunit could be expressed on the cell surface of a fibroblastoid cell line, COS, by cotransfection with either the human or murine beta subunit cDNA.

Cloning of the murine lymphocyte function-associated molecule-1 alpha-subunit and its expression in COS cells

The lymphocyte function-associated molecule 1 (LFA-1, CD11a/CD18) is an integrin that mediates adhesion of immune cells by interaction with two members of the Ig superfamily, ICAM-1 and ICAM-2. LFA-1 consists of an alpha subunit (Mr = 180,000) and a beta subunit (Mr = 95,000). We report here the isolation and expression of the murine alpha subunit cDNA (GenBank accession no. M60778). The deduced sequence comprises a 1061 amino acid extracellular domain, a 29 amino acid transmembrane region, and a 50 amino acid cytoplasmic domain. It has a 72% amino acid identity with its human counterpart and 34% identity with the murine Mac-1 alpha subunit. The murine LFA-1 alpha subunit could be expressed on the cell surface of a fibroblastoid cell line, COS, by cotransfection with either the human or murine beta subunit cDNA.

Lymphokine-activated killer (LAK) cells: interferon-gamma synergizes with interleukin-2 to induce LAK cytotoxicity in homogeneous leukemic preparations

Lymphokine-activated killer (LAK) cells are generated by the incubation of lymphocytes with high levels of interleukin-2 (IL-2). We report here that interferon-gamma (IFN-gamma) acts synergistically with low levels of IL-2 to promote LAK differentiation in peripheral blood lymphocytes as well as in homogeneous T acute lymphocytic leukemic cells exhibiting LAK precursor reactivity. No augmentation of LAK response was observed with IFN-alpha-2, IFN-beta-1, and IFN-beta-2/IL-6. The synergism between IL-2 and IFN-gamma was expressed in the ability of activated lymphocytes to lyse natural killer resistant cell line targets and surgically removed melanoma cells. The augmented LAK response due to IFN-gamma does not reflect up-regulation of the high-affinity IL-2 receptors consisting both of alpha and beta subunits, since expression of the alpha (Tac) subunit on the responding leukemic cells was not increased by IFN-gamma. The observed IFN-gamma/IL-2 synergism in the induction of monoclonal LAK precursors suggests that a single precursor cell responds to both IFN-gamma and IL-2 and that different mechanisms underlie the basal IL-2-mediated LAK response and its enhancement by IFN-gamma.

T cell activation: independent induction of killing activity and interleukin 2 secretion in cytolytic hybridomas

Memory-like cytotoxic T lymphocytes (CTL) hybridomas exhibiting inducible killing activity and IL2 production were used to analyze the anamnestic response of CTL. Four activating agents were examined; anti-Thy-1 monoclonal antibody G7, staphylococcal enterotoxin B, interferon (IFN)-alpha/beta and IFN-gamma. These agents seemed to affect CTL activities in three distinct ways. Anti-Thy-1 monoclonal antibody, like specific antigen, was found to be a potent inducer of specific killing and IL2 production, whereas staphylococcal enterotoxin B induced IL2 production, but not cytolytic activity. On the other hand, IFN-alpha/beta and IFN-gamma effectively stimulated cytotoxicity without inducing IL2 production. The independent triggering of specific killing and IL2 secretion in the monoclonal cytolytic hybridomas suggests that in CTL distinct signals stimulate killing activity and IL2 production. The results also suggest that IFN-alpha/beta and IFN-gamma trigger the cytolytic program through an alternative activation pathway which does not involve the T cell receptor.

Resistance of cytolytic lymphocytes to perforin-mediated killing. Induction of resistance correlates with increase in cytotoxicity

CTL and NK cells cultured in vitro are known to produce a cytolytic pore-forming protein (PFP, perforin) localized in their cytoplasmic granules. Using purified perforin, we showed here that both cloned CTL and primary killer cell populations, including allospecific CTL, NK/lymphokine-activated killer cells, and MHC-non-restricted CTL, were more resistant to perforin-mediated killing than other lymphocyte populations and cell types. Similar results were obtained with both murine and human cytolytic lymphocyte populations. Resistance of killer cells to perforin correlated in general with their cytolytic capability. Thus, cells that have acquired competence to kill after stimulation with Con A, IL-2, or leukocyte-conditioned medium, were also the more resistant cells. IL-2-independent CTL lines and hybridomas derived in our laboratories could be triggered to become cytotoxic and perforin resistant by short-term stimulation with various cytokines, indicating that the acquisition of resistance to perforin-mediated lysis was independent of cell proliferation. Activation of one IL-2-independent CTL line with IL-2 also resulted in enhanced production of perforin and in enhanced serine esterase activity. The acquisition of cell resistance to perforin by these IL-2-independent cell lines after activation with stimulatory reagents was independent of protein and RNA neosynthesis: emetine, cycloheximide, and actinomycin D, while effectively blocking the incorporation of [35S]methionine into cell proteins, did not affect the induced increase in perforin resistance.

Induction of c-ets and c-fos gene expression upon antigenic stimulation of a T cell hybridoma with inducible cytolytic capacity

Expression of cellular oncogenes was studied in a T cell hybridoma that undergoes cytolytic activation when stimulated by specific antigen or by anti-Thy-1 antibody. The activation occurs without induction of hybridoma proliferation, providing a model to examine oncogene expression during functional differentiation of lymphocytes. We found that c-fos and c-ets-1 mRNAs were transiently induced at high levels in the hybridoma 30 min and 4 h after stimulation, respectively. c-myc and c-ets-2 oncogenes were constitutively expressed in the hybridoma and their mRNA levels were unaffected during 4 h of stimulation, although c-myc expression was reduced in the later stage of stimulation. Inhibitors of T cell activation, cyclosporin A and anti-LFA-1 antibody, blocked the induction of c-fos and c-ets-1 mRNAs without reducing the levels of c-myc and c-ets-2. The results indicate that the functional activation of the CTL hybridoma is associated with induction of c-fos and c-ets-1 genes.

Interleukin 2 induces human acute lymphocytic leukemia cells to manifest lymphokine-activated-killer (LAK) cytotoxicity

Lymphokine-activated killer cells (LAK) were originally distinguished from natural killers (NK) and cytotoxic T lymphocytes. Recently, however, IL 2-activated NK cells were suggested as the major source of LAK reactivity in human peripheral blood (PBL). Because certain T cell acute lymphoblastic leukemia (T-ALL) cells are phenotypically similar to LAK precursors, we have asked whether these leukemic cells can be induced toward LAK-cytotoxicity and express NK reactivity before stimulation. Five out of seven T-ALL preparations were induced by IL 2 to kill target cells. The cytotoxicity of the leukemic-LAK cells resembled that of normal LAK effectors as they lysed efficiently the NK-resistant target Daudi, as well as fresh human sarcoma, carcinoma, and renal cancer cells but not normal PBL. The ALL-LAK precursors phenotype was T3-, T4-, T8-, and T11+, similar to most normal LAK precursors. In contrast to normal PBL that generated LAK effectors when their proliferation was inhibited, the irradiated, nonproliferating T-ALL leukemic cells did not respond to IL 2. Therefore, the T-ALL LAK cytotoxicity was attributed to the leukemic cells rather than to residual normal lymphocytes. The IL 2-responding T-ALL cells did not express autonomous NK type cytotoxicity, suggesting that they reflect LAK precursors of non-NK origin. The homogeneous leukemic preparations with inducible LAK cytotoxicity described herein provide a model system for studying normal LAK cells.

Interleukin 2 induces human acute lymphocytic leukemia cells to manifest lymphokine-activated-killer (LAK) cytotoxicity

Lymphokine-activated killer cells (LAK) were originally distinguished from natural killers (NK) and cytotoxic T lymphocytes. Recently, however, IL 2-activated NK cells were suggested as the major source of LAK reactivity in human peripheral blood (PBL). Because certain T cell acute lymphoblastic leukemia (T-ALL) cells are phenotypically similar to LAK precursors, we have asked whether these leukemic cells can be induced toward LAK-cytotoxicity and express NK reactivity before stimulation. Five out of seven T-ALL preparations were induced by IL 2 to kill target cells. The cytotoxicity of the leukemic-LAK cells resembled that of normal LAK effectors as they lysed efficiently the NK-resistant target Daudi, as well as fresh human sarcoma, carcinoma, and renal cancer cells but not normal PBL. The ALL-LAK precursors phenotype was T3-, T4-, T8-, and T11+, similar to most normal LAK precursors. In contrast to normal PBL that generated LAK effectors when their proliferation was inhibited, the irradiated, nonproliferating T-ALL leukemic cells did not respond to IL 2. Therefore, the T-ALL LAK cytotoxicity was attributed to the leukemic cells rather than to residual normal lymphocytes. The IL 2-responding T-ALL cells did not express autonomous NK type cytotoxicity, suggesting that they reflect LAK precursors of non-NK origin. The homogeneous leukemic preparations with inducible LAK cytotoxicity described herein provide a model system for studying normal LAK cells.

Antigen/mitogen induced cytolytic activity and IL-2 secretion in memory-like CTL-hybridomas

Memory-like monoclonal CTL hybridomas, derived from fusion of the AKR thymoma BW5147 with secondary CTL generated in vivo or in MLC cultures, have been used to study the mechanism whereby antigen/mitogen induces anamnestic CTL responses. Specifically, we have asked whether induction of cytolytic activity can be promoted by an antigenic/mitogenic signal without involvement of IL-2 receptors, IL-2, or other extrinsic factors. We have found that antigen/lectin alone can trigger the cytolytic potential of the hybridomas and induce IL-2 secretion. Pure IL-2 and conditioned medium were ineffective inducers of cytotoxicity. Moreover, IL-2 receptors were not detected on the hybrid cells before and after antigenic stimulation, demonstrating that expression of IL-2 receptors and induction of specific killing activity are not genetically linked. Non-activated and activated cells conjugated with target cells equally well, suggesting that induction of cytolytic activity involves a post target cell binding step. Close linkage between cytotoxicity and IL-2 secretion has been observed: induction of killing was consistently associated with IL-2 secretion and stimulation of both activities could be blocked by Cyclosporin A. IL-2 was secreted by the CTL hybrids as early as 3 h following stimulation. We propose that the immediate supply of IL-2 by such memory CTL enhances antigenic response of other, IL-2-dependent T cells.

Rearrangement and transcription of a T-cell receptor beta-chain gene in different T-cell subsets

The functionally defined sets of T lymphocytes--helper T cells, cytotoxic T cells, and suppressor T cells--were examined for the possible involvement of a recently identified T-cell receptor beta gene locus in receptor formation. Since gene rearrangements are required for functional gene expression, cloned T-cell lines from each of the groups were surveyed for the expression of unique gene rearrangements. In addition, cell lines that showed gene rearrangements were further tested for the expression of the mature 1.2- to 1.3-kilobase mRNA transcribed from a productive gene rearrangement. The results of such experiments show that helper and cytotoxic T cells may use a common beta chain of the receptor, whereas suppressor cells do so rarely, if at all.

Mechanism of action of Cyclosporin A: inhibition of lymphokine secretion studied with antigen-stimulated T cell hybridomas

We have employed bifunctional T cell hybridomas, which can be stimulated to secrete lymphokine(s) and lyse specific target cells, to analyze the effect of Cyclosporin A (CsA) on T cell helper and effector functions. We report here the effects of CsA on antigen- and lectin-induced lymphokine secretion. We have found that a pharmacologic level of CsA (10 ng/ml) blocks antigen- and lectin-driven interleukin 2 (IL 2) secretion without affecting cell proliferation. In addition, one monoclonal hybridoma that is induced by concanavalin A to secrete colony stimulating factors (CSF) as well as IL 2 is concomitantly blocked by CsA for production of IL 2 and CSF. Because the hybridomas grow constitutively and are devoid of functional IL 2 receptors, they permit analysis of the kinetics of the inhibitory response. We have shown that CsA blocks not only stimulation of lymphokine secretion but also ongoing IL 2 production, probably by interfering with the effective interaction of receptor and antigen. Thus, blocking of IL 2 secretion from preactivated cells by CsA occurs by 1 to 2 hr, the time required to stop IL 2 production by removal of Ag/Lectin stimulator. The results are consistent with a mechanism of action of CsA on T cells that involves a direct interference of CsA with binding of Ag to Ag-receptor and results in blocking of induction and active secretion of multiple lymphokines.

Mechanism of action of Cyclosporin A: inhibition of lymphokine secretion studied with antigen-stimulated T cell hybridomas

We have employed bifunctional T cell hybridomas, which can be stimulated to secrete lymphokine(s) and lyse specific target cells, to analyze the effect of Cyclosporin A (CsA) on T cell helper and effector functions. We report here the effects of CsA on antigen- and lectin-induced lymphokine secretion. We have found that a pharmacologic level of CsA (10 ng/ml) blocks antigen- and lectin-driven interleukin 2 (IL 2) secretion without affecting cell proliferation. In addition, one monoclonal hybridoma that is induced by concanavalin A to secrete colony stimulating factors (CSF) as well as IL 2 is concomitantly blocked by CsA for production of IL 2 and CSF. Because the hybridomas grow constitutively and are devoid of functional IL 2 receptors, they permit analysis of the kinetics of the inhibitory response. We have shown that CsA blocks not only stimulation of lymphokine secretion but also ongoing IL 2 production, probably by interfering with the effective interaction of receptor and antigen. Thus, blocking of IL 2 secretion from preactivated cells by CsA occurs by 1 to 2 hr, the time required to stop IL 2 production by removal of Ag/Lectin stimulator. The results are consistent with a mechanism of action of CsA on T cells that involves a direct interference of CsA with binding of Ag to Ag-receptor and results in blocking of induction and active secretion of multiple lymphokines.

Memory CTL-hybridoma: a model system to analyze the anamnestic response of cytolytic T lymphocytes

We have previously described monoclonal CTL-hybridomas growing continuously in culture in the absence of a known antigenic stimulus or growth-promoting factor(s), exhibiting specific anti-H-2Db killing activity in vitro after a distinct 2-hr lag period before the onset of lysis. Here we provide evidence indicating that the hybridoma Md 26.15 represents "memory" CTL, and we examine the mechanism whereby they respond to antigen/mitogen. The brief period (2 to 3 hr) required for stimulation suggests that expression of potentiated effector function(s) after stimulation requires no cell replication. The frequency of effector hybridoma cells capable of specific binding to target cells before and after stimulation is the same, as determined in a direct hybridoma-target cell conjugation test, although cytolytic activity is markedly enhanced. On the other hand, kinetic and cell dispersion assays indicate that the potentiation of cytolytic activity can be attributed to shortening of the lag period of killing as well as to a small enhancement in the recycling ability of cytolytic effectors. We suggest that shortening of the lag period involves activation of potential effectors, which is manifested at a post-binding stage of effector-target interaction. The CTL hybridoma described herein provides a unique model system for studying CTL reactivation.

Memory CTL-hybridoma: a model system to analyze the anamnestic response of cytolytic T lymphocytes

We have previously described monoclonal CTL-hybridomas growing continuously in culture in the absence of a known antigenic stimulus or growth-promoting factor(s), exhibiting specific anti-H-2Db killing activity in vitro after a distinct 2-hr lag period before the onset of lysis. Here we provide evidence indicating that the hybridoma Md 26.15 represents "memory" CTL, and we examine the mechanism whereby they respond to antigen/mitogen. The brief period (2 to 3 hr) required for stimulation suggests that expression of potentiated effector function(s) after stimulation requires no cell replication. The frequency of effector hybridoma cells capable of specific binding to target cells before and after stimulation is the same, as determined in a direct hybridoma-target cell conjugation test, although cytolytic activity is markedly enhanced. On the other hand, kinetic and cell dispersion assays indicate that the potentiation of cytolytic activity can be attributed to shortening of the lag period of killing as well as to a small enhancement in the recycling ability of cytolytic effectors. We suggest that shortening of the lag period involves activation of potential effectors, which is manifested at a post-binding stage of effector-target interaction. The CTL hybridoma described herein provides a unique model system for studying CTL reactivation.

Blocking by cyclosporine of antigen-induced maturation and lymphokine secretion by cytotoxic T lymphocyte hybridomas

We have investigated the effect of cyclosporin (Cys) on the maturation of cytotoxic T lymphocytes (CTL), and on the induction of interleukin-2 (IL-2) secretion using two bifunctional CTL hybridomas. Both hybridomas can be stimulated with allogeneic cells to secrete IL-2 and to specifically kill target cells. Cys, at 10-50 ng/ml, eliminates the induction of both functions (secretion and lysis). Although maturation of both specific and lectin-mediated killing by the hybrid cells exhibits high sensitivity to Cys, the actual killing of target cells by previously activated cells is less affected. Our results suggest that pharmacological levels of Cys directly interfere with the antigen-responsiveness of helper-independent cytotoxic T cells, as represented by these hybridomas, and prevent their maturation.

Lymphokine-activated killer cells: lysis of fresh syngeneic natural killer-resistant murine tumor cells by lymphocytes cultured in interleukin 2

Normal splenocytes that are cultured in the lymphokine, interleukin 2 (IL-2), for as short as 2 days develop lytic activity for fresh syngeneic natural killer-resistant tumor cells as well as natural killer-sensitive YAC cells in a 4-hr 51Cr release assay. Lymphokine-activated killer (LAK) cells do not lyse syngeneic fresh lymphocytes but do lyse syngeneic concanavalin A-induced lymphocyte blasts. Lysis is not due to the presence of lectin or xenogeneic serum and appears to be an intrinsic property of lymphocytes activated in IL-2. The activation appears universal in that lymphocytes from all strains of mice activated in this manner exhibited similar patterns of lysis for fresh tumor target cells. To characterize the cells responsible for this lysis, we analyzed the phenotypic expression of surface markers on these cells with depletion techniques using monoclonal antibody and complement. These studies indicate that the precursor of the LAK cell is Thy-1+ and nonadherent to plastic or nylon wool. Lysis of syngeneic tumor was inhibited when LAK cells were treated with an anti-Thy-1.2, or anti-Lyt-2.2 monoclonal antibody and complement but not with anti-Lyt-1.2 monoclonal antibody and complement, indicating that the observed lytic activity was due to a Thy-1+ Lyt-1-2+ cell. Furthermore, LAK cell-mediated lysis could be inhibited by the addition of anti-Lyt-2 or LFA-1 monoclonal antibody to cytotoxicity assays. Cold target inhibition analysis revealed that the syngeneic tumor cells were lysed by recognition of a determinant not present on normal lymphocytes or lymphocyte blasts. This lysis of fresh solid tumor cells by lymphoid cells grown in IL-2 may be of value in the study of tumor-host immunological interactions. The biological significance of tumor lysis by IL-2-activated cells requires further study.

Monoclonal cytotoxic T lymphocyte hybridomas capable of specific killing activity, antigenic responsiveness, and inducible interleukin secretion

We have recently described the production of cytotoxic T lymphocyte (CTL) hybridomas that grow continuously in culture, exhibiting constitutive, allospecific (anti-H-2b) killing activity. We now report on the response of these monoclonal CTL hybridomas to specific antigen (H-2Db) and to mitogenic lectins. Both specific antigen and T cell mitogens enhance hybridoma-mediated specific target cell killing. In addition, stimulated, but not unstimulated hybridoma cells secrete considerable amounts of IL 2 into the culture medium. Repeated cloning of the hybridomas provides strong evidence that both killing activity and IL 2 secretion can be attributed to one cell. Unfractionated Con A supernatants, containing IL 2 and other factors known to influence T cell responsiveness, or IL 2-containing media of stimulated hybridomas affect neither the growth nor the lytic activity of the hybridomas. Anti-LFA-1 monoclonal antibody, a potent inhibitor of CTL and CTL hybridoma-mediated target cell lysis, abolishes antigen- or mitogen-induced IL 2 secretion by the CTL hybridomas. Involvement of a single hybridoma receptor in antigen recognition (afferent and efferent) and in initiating IL 2 secretion is proposed. The CTL hybridomas displaying retarded killing activity before the antigenic or mitogenic stimulation appear to represent an intermediate stage in CTL differentiation, reminiscent of "memory" CTL.

Monoclonal cytotoxic T lymphocyte hybridomas capable of specific killing activity, antigenic responsiveness, and inducible interleukin secretion

We have recently described the production of cytotoxic T lymphocyte (CTL) hybridomas that grow continuously in culture, exhibiting constitutive, allospecific (anti-H-2b) killing activity. We now report on the response of these monoclonal CTL hybridomas to specific antigen (H-2Db) and to mitogenic lectins. Both specific antigen and T cell mitogens enhance hybridoma-mediated specific target cell killing. In addition, stimulated, but not unstimulated hybridoma cells secrete considerable amounts of IL 2 into the culture medium. Repeated cloning of the hybridomas provides strong evidence that both killing activity and IL 2 secretion can be attributed to one cell. Unfractionated Con A supernatants, containing IL 2 and other factors known to influence T cell responsiveness, or IL 2-containing media of stimulated hybridomas affect neither the growth nor the lytic activity of the hybridomas. Anti-LFA-1 monoclonal antibody, a potent inhibitor of CTL and CTL hybridoma-mediated target cell lysis, abolishes antigen- or mitogen-induced IL 2 secretion by the CTL hybridomas. Involvement of a single hybridoma receptor in antigen recognition (afferent and efferent) and in initiating IL 2 secretion is proposed. The CTL hybridomas displaying retarded killing activity before the antigenic or mitogenic stimulation appear to represent an intermediate stage in CTL differentiation, reminiscent of "memory" CTL.

Lymphoid cell surface interaction structures detected using cytolysis-inhibiting monoclonal antibodies

We screened monoclonal antibodies obtained by xenogeneic immunization for their capacity to inhibit T cell-mediated cytolysis. These antibodies fell into two classes according to the cell structures they recognized, of 30-35 K and 94-180 K apparent molecular weight, respectively. The main features of these structures and of their interaction with the corresponding antibodies were reviewed. The inhibition of cytolysis by these antibodies was shown to occur mainly at the effector cell level, at the recognition stage of cytolysis, and to depend on the nature of target cells, effector cells, and link between these cells. T cell functions other than cytolysis were also inhibited by some of these antibodies. We considered various possible mechanisms to account for the inhibition of cytolysis by these mAb. We favor an hypothesis based on inhibition by these mAb of lymphoid cell surface interaction structures. This hypothesis was discussed within the general framework of cell interaction structures in immunological and non-immunological experimental systems.

Cytotoxic T lymphocyte hybridomas that mediate specific tumor-cell lysis in vitro

Cytotoxic hybridomas were generated by polyethylene glycol-induced fusion of cytotoxic T lymphocytes (CTL) and BW5147 lymphoma cells. The CTL populations used for fusion were obtained from BALB/c (H-2d) mice primed with leukemia EL4 of C57BL/6 (H-2b) and restimulated either in vivo or in vitro. To circumvent possible CTL-mediated nonspecific lysis of BW5147 cells during fusion, the CTL were transiently inactivated by trypsin prior to fusion. Four cytolytically active hybridomas were obtained, cloned, and subcloned. Hybrid clones lysed all H-2b leukemic target cells tested but not lipopolysaccharide- or concavanalin A-stimulated C57BL/6 lymphoblasts or non-H2b target tumor cells. The mechanism of hybridoma-mediated killing of target cells in vitro appears to be similar to that of parental CTL, although some differences have been observed. The hybridomas appear to possess neither natural killing nor antibody-dependent cytolytic activity. Clones of hybrids propagated in culture for over 6 months without the addition of known external stimulus (i.e., independent of cell growth factor and antigen) exhibit specific lytic activity against H-2b tumor cells. Such autonomous hybridomas will provide a tool for studying the mechanism of CTL-mediated lysis and the nature of the CTL receptors.

Cell surface glycoproteins of cytotoxic T lymphocytes induced in vivo and in vitro

CTL-blasts, generated in vitro or obtained from educated spleens in vivo, have previously been shown to display high levels of a unique membrane glycoprotein T145 (ca. 145,000 daltons), inferred to be a common CTL marker and implicated in CTL cytotoxicity. As shown here, however, these suggestions do not hold for all cytotoxic T lymphocytes. We have shown that T145 is not expressed on highly active CTL-induced in vivo by a standard alloimmunization protocol. The finding that several CTL populations are T145 positive, whereas others are T145 negative, may be due to the existence of functional CTL in 2 stages of differentiation or may represent different CTL lineages. In addition, no correlation was found between cytolytic activity and expression of T145. The functional significance of T145 on CTL is discussed.

Cell surface glycoproteins of cytotoxic T lymphocytes induced in vivo and in vitro

CTL-blasts, generated in vitro or obtained from educated spleens in vivo, have previously been shown to display high levels of a unique membrane glycoprotein T145 (ca. 145,000 daltons), inferred to be a common CTL marker and implicated in CTL cytotoxicity. As shown here, however, these suggestions do not hold for all cytotoxic T lymphocytes. We have shown that T145 is not expressed on highly active CTL-induced in vivo by a standard alloimmunization protocol. The finding that several CTL populations are T145 positive, whereas others are T145 negative, may be due to the existence of functional CTL in 2 stages of differentiation or may represent different CTL lineages. In addition, no correlation was found between cytolytic activity and expression of T145. The functional significance of T145 on CTL is discussed.

Enucleated cytotoxic T lymphocytes bind specifically to target cells in vitro

We report the isolation of enucleated particles (cytoplasts) from mouse cytotoxic T lymphocytes (CTLs) which, like intact CTLs, can specifically bind to target cells (TCs) in vitro. CTL-enriched populations were enucleated by centrifugation on a Ficoll density gradient at 31 C in the presence of cytochalasin B. The resulting cytoplasts which consist of 99% of enucleated particles retained about 40% of the nucleated cells' protein but less than 1% of their DNA. The presence of cell surface membrane antigens Thy 1.2 and H-2 on the cytoplasts indicated that their surface membranes originated from the plasma membranes of the intact cells. Electron microscopy of cytoplasts revealed two types of particles, one (type a) contained cytoplasmic organelles such as mitochondria, Golgi apparatus, microfilaments, and microvilli, while the second (type b) contained little cytoplasm and no microfilaments or microvilli. The evidence presented suggests that only type a cytoplasts can bind specifically to TCs. The specific binding to TCs by type a and not type b cytoplasts shows that while the CTL nucleus or nucleus-associated structures affected by enucleation are not essential for specific CTL receptor activity, cytoskeletal structures and activities related to these structures must be preserved.

HeLa cell poly(A)- mRNA codes for a subset of poly(A)+ mRNA-directed proteins with an actin as a major product

Poly(A)+ and poly(A)- mRNA from HeLa cells were separated and translated in heterologous messenger-dependent protein synthesizing systems. Two-dimensional electrophoretic analysis revealed three classes of polypeptides. At the level of detectability in the electropherograms, a small number (about 10) of proteins were detected only among the poly(A)- mRNA products, a larger number (about 40) were produced by both poly(A)- and poly(A)+ mRNA, and a large number of polypeptides were found exclusively in the poly(A)+ mRNA products. The major product of both poly(A)+ and poly(A)- mRNA was shown to be the beta form of actin.Previous cross hybridization measurements suggested little homology between poly(A)+ and poly(A)- mRNA populations. In view of the apparent identity of many poly(A)- products with those of poly(A)+, the homology between poly(A)+ and poly(A)- mRNA sequences was examined in greater detail. cDNA complementary to only the most abundant poly(A)+ message sequences was prepared. About 10% of this cDNA hybridized to abundant sequences in the poly(A)- fraction. This corresponded to only 2% of the total mass of poly(A)+ mRNA and accounted for the failure to detect cross hybridization in previous experiments. Thus, a small number of poly(A)+ sequences appear to be present in relatively high concentration in poly(A)- mRNA as evidenced by both the translation products and the cross hybridization results.

A cytoskeletal structure with associated polyribosomes obtained from HeLa cells

A method is described by which HeLa cells can be fractionated to reveal a skeletal-like structure in the cytoplasm. This cytoskeleton has many of the cell's ultrastructural features, such as 100A filaments, microfilaments, centrioles, and microspikes, although most of the cellular protein, membranes, and microtubules have been extracted. Associated with the cytoskeleton are most of the polysomal, but not the monomeric, ribosomes. These polysomes are distributed throughout the cytoskeleton except in the region of the 100A filaments, which resembles the distribution in intact cells. Degradation of mRNA with low levels of ribonuclease releases most ribosomes from the cytoskeleton. Prior disaggregation of polyribosomes in vivo releases ribosomes but not mRNA. Cytochalasin B administered in vivo releases the mRNA from the cytoskeleton. These results suggest an attachment of polyribosomes to the cytoskeleton via mRNA.

Poliovirus-induced inhibition of polypeptide initiation in vitro on native polyribosomes

The inhibition of HeLa cell protein synthesis by poliovirus was studied by examining initiation in vitro on endogenous host polyribosomes. At an early stage, before major viral RNA replication and protein synthesis begins, the initiation of translation on cellular mRNA is strongly inhibited. Fractionation of extracts from infected cells shows that the lesion is associated mainly with the crude polyribosome fraction. The cellular mRNA appears unchanged and is as active as mRNA from control cells in stimulating incorporation. The native ribosomal subunits and KCl-washed polyribosomes from the infected cells are also active. Only the ribosomal wash fraction prepared from the inhibited polyribosomes had reduced activity. However, the reduction in the ribosomal wash activity measured in a reconstructed system is not as large as the inhibition seen with "native" polyribosomes. The results indicate that a viral induced inhibition is probably associated with the ribosomal wash fraction, but the reconstructed system is not equivalent to the "native" inhibited system.

The effect of tRNA derivatives bound with natural or synthetic mRNA on the interaction of Escherichia coli ribosomes with colicin E3

Ribosomal binding complexes directed by poly(U) or T4 mRNA were formed with aminoacyl-tRNA or its derivatives bound to predominantly the P or A binding site. The defined binding complexes were reacted with colicin E3 and the reaction was assessed by the ability of the complexes to proceed with polypeptide synthesis. The results indicated that only one of the four complexes tested was completely resistant to colicin E3-induced inactivation: that of Phe-tRNA bound in the presence of poly(U) to the A-site. The poly(U) directed complex of AcPhe-tRNA and the T4-mRNA-directed complex at the A-site appeared slightly resistant, while the T4 mRNA initiation complex was inactivated by colicin E3 in a manner similar to non-complexed ribosomes. Colicin E3 added to ribosomes after protein synthesis had been initiated affected the subsequent polymerization in a manner corresponding to the response of the binding complexes. Thus, poly(U)-translating ribosomes were less affected than ribosomes translating the viral mRNA. The vulnerability of natural-mRNA-directed binding complexes to inactivation by colicin E3 is in accord with the mode of inactivation by the colicin in vivo.