Cord blood T cells retain early differentiation phenotype suitable for immunotherapy after TCR gene transfer to confer EBV specificity

Adoptive T cell therapy can be effective for Epstein-Barr virus (EBV)-associated posttransplant lymphoproliferative disease and melanoma. Transducing high-affinity TCR genes into T lymphocytes is an emerging method to improve potency and specificity of tumor-specific T cells. However, both methods necessitate in vitro lymphocyte proliferation, generating highly differentiated effector cells that display reduced survival and antitumor efficacy postinfusion. TCR-transduction of naive lymphocytes isolated from peripheral blood is reported to provide superior in vivo survival and function. We utilized cord blood (CB) lymphocytes, which comprise mainly naive cells, for transducing EBV-specific TCR. Comparable TCR expression was achieved in adult and CB cells, but the latter expressed an earlier differentiation profile. Further antigen-driven stimulation skewed adult lymphocytes to a late differentiation phenotype associated with immune exhaustion. In contrast, CB T cells retained a less differentiated phenotype after antigen stimulation, remaining CD57-negative but were still capable of antigen-specific polyfunctional cytokine expression and cytotoxicity in response to EBV antigen. CB T cells also retained longer telomeres and in general possessed higher telomerase activity indicative of greater proliferative potential. CB lymphocytes therefore have qualities indicating prolonged survival and effector function favorable to immunotherapy, especially in settings where donor lymphocytes are unavailable such as in solid organ and CB transplantation.

MHC immunoevasins: protecting the pathogen reservoir in infection

Alteration of antigen recognition by T cells as result of insufficient major histocompatibility complex (MHC)-dependent antigen-presenting function has been observed in many cases of infections, particularly in in vitro systems. To hide themselves from an efficient immune response, pathogens may act on MHC-related functions at three levels: (i) by limiting the number of potential antigens that can be presented to naïve T cells; (ii) by synthesizing proteins which directly affect MHC cell-surface expression; and (iii) by altering the normal intracellular pathway of peptide loading on MHC. Here, we review examples of pathogens' action on each single step of MHC function and we suggest that the result of these often synergistic actions is both a limitation of the priming of naïve T cells and, more importantly, a protection of the pathogen's reservoir from the attack of primed T cells. The above mechanisms may also generate a skewing effect on immune effector mechanisms, which helps preserving the reservoir of infection from sterilization by the immune system.

Synovial fluid from patients with rheumatoid arthritis inhibits neutrophil apoptosis: role of adenosine and proinflammatory cytokines

OBJECTIVE

In synovial fluid (SF) from patients with rheumatoid arthritis (RA), neutrophils are exposed to proinflammatory mediators endowed with either anti-apoptotic or pro-apoptotic properties. We investigated neutrophil apoptosis in the presence of SF from 11 RA patients.

METHODS

SF was obtained from affected knees of 11 patients with RA. Human neutrophil apoptosis was evaluated by light microscopic examination and flow-cytometric analysis of annexin V binding. Immune complex-induced neutrophil activation was evaluated as superoxide anion production. Adenosine levels in SF were detected by chromatographic analysis and cytokine levels were studied by enzyme-linked immunosorbent assay.

RESULTS

Spontaneous and immune complex-triggered neutrophil apoptosis was reduced by SF from eight out of 11 patients. Immune complex-induced neutrophil activation was unaffected by SF. The cytokines tested had no role in promoting the anti-apoptotic activity of SF. On the contrary, the anti-apoptotic activity of SF was found to depend on the presence of adenosine. Adenosine levels detected in the various samples of SF correlated significantly with the anti-apoptotic activity of the fluids and with the number of apoptotic neutrophils detected in the articular exudate.

CONCLUSION

The microenvironment of rheumatoid SF is a proinflammatory milieu responsible for the in loco persistence of activated and long-surviving neutrophils. Adenosine plays a crucial role in this phenomenon, which is related to anti-apoptotic activity.

Bone marrow transplantation from unrelated donors: the impact of mismatches with substitutions at position 116 of the human leukocyte antigen class I heavy chain

The hypothesis was tested that amino acid substitutions in specific positions within human leukocyte antigen class I heavy chain would have different impacts on transplant-related mortality (TRM) in patients receiving transplanted bone marrow from unrelated donors. One hundred patients and their unrelated donors were typed by sequence-based typing for the human leukocyte antigen (HLA)-A, -B, and -C loci. All pairs were matched for DRB1, DRB3, DRB4, DRB5, DQA1, and DQB1 loci. Forty pairs were also matched at class I, and 60 pairs had one or more mismatches at class I loci. It was found that substitutions at positions 116 and 114 of class I heavy chain significantly increased the risk for TRM in univariate and bivariate Cox analyses. Conversely, no association between number of multiple mismatches or number of amino acid substitutions and TRM was seen when positions 116 and 114 were adjusted for. Variables predictive of TRM in multivariate Cox analysis were number of cells infused, diagnosis (chronic myeloid leukemia [CML] or non-CML), and amino acid substitution at position 116 or 152. The only variable predictive of severe acute graft-versus-host disease (GVHD) in multivariate Cox analysis was substitution at position 116. Actuarial risk for acute GVHD grade III-IV, TRM, and relapse in pairs with substitutions at position 116 (n = 37) compared to other pairs (n = 63) was, respectively, 36% versus 14% (P =.01), 59% versus 28% (P =.001), and 25% versus 31% (P =.4). In conclusion these data suggest that substitutions at position 116 of class I heavy chain increase the risk for acute GVHD and TRM in patients who receive transplanted bone marrow from unrelated donors.

Immune complex stimulation of neutrophil apoptosis: investigating the involvement of oxidative and nonoxidative pathways

Neutrophils are involved in the pathogenesis of various inflammatory diseases. One of the mechanisms by which neutrophilic inflammation is generated is immune complex (IC) deposition in tissue. As the clearance of apoptotic neutrophils from inflamed sites is considered a crucial determinant for the resolution of inflammation, we investigated the effects of IC-induced neutrophil activation on apoptosis and the mechanisms regulating neutrophil survival. Our results show that IC stimulated apoptosis efficiently. The percentage of apoptotic neutrophils was reduced by the anti-FcgammaRII mAb IV.3, but not by anti-FcgammaRIII mAb 3G8. The spontaneous apoptosis was completely inhibited by the antioxidant compound catalase, which in turn prevented only partially the apoptosis in presence of IC. The oxidative metabolism triggered by IC was inhibited only blocking both FcgammaRII and FcgammaRIII. Neutrophils from patients with chronic granulomatous disease, congenitally incapable of producing oxidants, showed low level of spontaneous apoptosis, but underwent a nearly 3-fold increment in the apoptosis rate when incubated with IC. In conclusion, neutrophil apoptosis appears to be a process governed by multiple pathways, some of which are strictly ROS-dependent, others acting in a nonoxidative manner. In particular, the herein shown FcgammaRII-dependent, ROS-independent, signal-inducing neutrophil apoptosis may uncover new pharmacological targets for the promotion of cell removal from sites of inflammation, thereby favoring the resolution of the inflammatory process.

Spontaneous apoptosis in neutrophils is associated with downregulation of HLA Class I and is prevented by ligation of Class I

In many types of cells, ligation of human leukocyte antigens (HLA) Class I molecules with specific mAbs results in the transduction of signals that trigger different cell functions. We have investigated the effects of Class I ligation in human neutrophils. After several hours in culture, neutrophils split spontaneously into two subpopulations, one with normal and the other with reduced levels of Class I. The latter subpopulation displayed high binding capacity for Annexin V, showed a hypodiploid peak, electrophoretic DNA fragmentation, and morphological features of apoptotic cells. The addition of drugs known to delay apoptosis (GM-CSF or cAMP) resulted in a reduction of Class I modulation. Furthermore, ligation of surface Class I with F(ab')2 fragments of the anti-Class I mAb W6/32 resulted in a delay in the progression of apoptosis. These data indicate that this surface Class I molecule is a marker of age-related apoptosis, and the ligation of these molecules results in the transduction of a signal that inhibits apoptosis. Thus, the downregulation of HLA Class I molecules in aging neutrophils prevents their halting the apoptotic process.

HLA-G, -E, -F preworkshop: tools and protocols for analysis of non-classical class I genes transcription and protein expression

Non-classical MHC class I HLA-E, -F, and -G molecules differ from classical class I histocompatibility antigens by specific patterns of transcription, protein expression, and immunological functions. Restriction of the expression pattern of these non-classical antigens may play a key role in modulation of immune responses during pregnancy and diseases but remains to be additionally defined. A specific component of the second International Conference on HLA-G and the 13th HLA-G Histocompatibility Workshop will be dedicated to the analysis of transcription and expression of non-classical class I genes in normal and pathological tissues. In a first step, referred to as the preworkshop, we here report the analysis and conclusions of a working group which was constituted to gather and validate optimal reagents and protocols allowing RT-PCR analysis of HLA-E, -F, -G transcript levels and flow cytometry and immunochemistry analysis of HLA-G expression in cells and tissues. As a result of this work, use of specific primers and probes detecting alternative transcripts of HLA-E, -F, and G have been validated in transfected cells expressing differential pattern of HLA class I antigens. Analysis of the specificity and affinity of collected antibodies has allowed definition of reagents to be proposed for immunochemistry and flow cytometry analysis of HLA-G expression in normal and pathological tissues during the workshop. This work has allowed constitution of an extended workshop group which is now initiating analysis of non-classical class I transcription and expression in various cells and tissues, a collective contribution that will additionally refine our view of the expression of these antigens in normal and pathological situations.

Natural killer cells lyse autologous herpes simplex virus infected targets using cytolytic mechanisms distributed clonotypically

Natural killer (NK) cells have the capability of lysing targets that have down-regulated the expression of HLA class I molecules. Herpes simplex virus (HSV) infection results in a profound reduction of HLA class I molecules on the surface of infected cells. For this reason, NK cell populations kill efficiently HSV-infected cells. The recent availability of a panel of monoclonal antibodies directed to NK receptors for HLA class I (CD158a, CD158b, anti-p70, anti-p140, and CD94) allowed an accurate dissection of the NK cell subpopulations. Using this approach, the relationship between the expression of NK cell receptors and the capability of lysing HSV-infected cell targets was analyzed at the clonal level. NK cell clones were derived from healthy donors, and cytolytic properties were assayed against HSV-infected autologous fibroblasts. NK cell clones, classified according to the expression of natural killer-cell receptors on their surface, displayed a great heterogeneity of cytolytic properties against HSV-infected cells. Nevertheless, a more accurate functional analysis demonstrated not only that HSV infection downregulated the expression of HLA-A and HLA-B and did not modify the expression of HLA-C, but also that NK cell clones expressing the "activating" form of the anti HLA-C NK cell receptor were more cytolytic than other clones. This finding suggests that two different and clonally distributed mechanisms of NK cell activation may be employed by NK cells to kill HSV-infected autologous target cells.

Melanomas and melanoma cell lines do not express HLA-G, and the expression cannot be induced by gammaIFN treatment

HLA-G is an effective ligand of natural killer (NK) inhibitory receptors, HLA-G transcripts have been detected in several human tumors, and cytokines like gamma interferon (IFN) enable HLA-G molecules to be expressed. These findings are particularly upsetting in case of melanomas: IFN treatment is frequently included in melanoma therapeutic protocols, and downregulation of classical class I molecules occurs in nearly half of these tumors. Therefore, a melanoma cell downregulating classical class I and de novo expressing HLA-G, either constitutively or upon IFN treatment, is probably a stealthy target for the immune system, having inhibited both the cytotoxic T lymphocyte (CTL) and the NK activity. To elucidate this point we have investigated the expression of HLA-G molecules in 45 melanoma cell lines before and after gammaIFN treatment. Analysis was performed by immunofluorescence and flow cytometry, using the anti-HLA-G MoAbs 87G and G233, by Western blot, using the anti-HLA-G MEM/G1 MoAb and PAG1 antiserum, and by RT-PCR analysis. In addition, 8 melanoma tissues from patients free from therapy and 6 nevi were studied by immunohistochemistry using the 87G MoAb. No evidence was gathered of HLA-G expression, neither constitutive nor, in cell lines, after gammaIFN treatment. We therefore conclude that HLA-G expression is an uncommon event in melanomas, and that a therapy including IFNs cannot harm the patient by inducing the de novo expression of HLA-G molecules at least in its G1 isoform.

Activation-related differences in HLA class I-bound peptides: presentation of an IL-1 receptor antagonist-derived peptide by activated, but not resting, CD4+ T lymphocytes

We have compared by reverse phase HPLC the set of peptides eluted from HLA class I molecules in resting and activated CD4+ Jurkat cells. Two peptides were identified that are presented de novo upon activation. After sequencing, one of these peptides turned out to derive from IL-1R antagonist (IL-1Ra). In keeping with this observation, we found that activated, but not resting, Jurkat cells express IL-1Ra. These data indicate that activation of a CD4+ T cell line may result in presentation of peptides derived from proteins expressed de novo after activation. Since IL-1Ra was not known to be expressed by cells of the T lineage, we also investigated its pattern of expression in normal T lymphocytes. Reverse transcriptase-PCR analyses allowed us to demonstrate that IL-1Ra is expressed upon activation by normal CD4+ lymphocytes from peripheral blood and by thymocytes, but not by CD8+ T cells. Interestingly, of the two forms of IL-1Ra that have been detected in different cell lineages, the intracellular one and the secreted one, only the former is expressed by activated CD4+ T cells.

Activation-related differences in HLA class I-bound peptides: presentation of an IL-1 receptor antagonist-derived peptide by activated, but not resting, CD4+ T lymphocytes

We have compared by reverse phase HPLC the set of peptides eluted from HLA class I molecules in resting and activated CD4+ Jurkat cells. Two peptides were identified that are presented de novo upon activation. After sequencing, one of these peptides turned out to derive from IL-1R antagonist (IL-1Ra). In keeping with this observation, we found that activated, but not resting, Jurkat cells express IL-1Ra. These data indicate that activation of a CD4+ T cell line may result in presentation of peptides derived from proteins expressed de novo after activation. Since IL-1Ra was not known to be expressed by cells of the T lineage, we also investigated its pattern of expression in normal T lymphocytes. Reverse transcriptase-PCR analyses allowed us to demonstrate that IL-1Ra is expressed upon activation by normal CD4+ lymphocytes from peripheral blood and by thymocytes, but not by CD8+ T cells. Interestingly, of the two forms of IL-1Ra that have been detected in different cell lineages, the intracellular one and the secreted one, only the former is expressed by activated CD4+ T cells.

Characteristics of the cytosol-synthesized proteins generating class-I-bound peptides

The proteins synthesized in the cytosol are several thousand, and the number of peptides potentially able to be bound by class I molecules they can generate is therefore huge. On the other hand, the actual number of peptide-class I complexes required for CTL activation is around 200. We focused on the peptides bound by B27 molecules and by the whole class I. By comparing our results with analogous data from other laboratories, we found that 31 peptides matched protein sequences in data bases; in four cases, two peptides are derived from the same protein. The finding of four pairs of identical samples in a sampling of 31 peptides from a pool of unknown magnitude suggests that this pool is quite small. We have estimated the size of this pool by combinatorial analysis and by computer simulation, and we have found a most probable distribution of about 100 to the number of self-proteins that can actually generate peptides bound by class I molecules.

Cellular mechanisms of exogenous peptide binding to HLA class II molecules in B cells

We have investigated the ability of APC Class II molecules to bind and release exogenous peptides, two phenomena that are still poorly understood. In order to investigate the half-life of the complex of an exogenous peptide with DR molecules we have evaluated the uptake and release of the radiolabeled peptide 17-29-Tyr of influenza virus matrix protein (MA 17-29-Y) by a B-EBV cell line at different times and under different conditions. We have found that the kinetics of both binding and release of the peptide are very fast in living cells; using glutaraldehyde-fixed cells, the kinetics of the two phenomena are slow, closely resembling those observed with the same peptide and purified, immobilized DR molecules. As confirmed by the study of a specific T-cell clone activation, the Class II-MA 17-29-Y complexes are short-living ones, with an average half-life of 55 min, and the DR molecules that bind exogenous peptides continuously undergo peptidic exchange. These data, taken together, suggest that the APC are endowed with cellular mechanisms that increase the efficiency of both the loading and the unloading of Class II HLA with exogenous peptides. These mechanisms do not appear to require ATP or to involve newly synthesized Class II molecules, intracellular acidic compartments, or the microtubule-microfilament system. On the other hand, an undamaged cell membrane appears to be crucial for an efficient binding.

Cellular Mechanisms of Artificial Peptides Binding to HLA

On the basis of the consideration that cell-free models cannot precisely mimic the complexity of the intracellular environment, we used a system to investigate the mechanisms that enable antigen-presenting cells (APC) to bind exogenous peptides through their human leukocyte antigen (HLA) molecules. We evaluated the uptake of the radiolabeled peptide 17-29-Tyr of influenza virus matrix protein by B-EBV cell lines, under various conditions. The results can be summarized as follows: a) the kinetics of peptide binding and release are very fast in living, fully competent cells; b) the peptide-HLA complexes are short-living and the DR molecules continuously undergo peptidic exchange; c) using glutaraldehyde-fixed cells, the kinetics of the two phenomena are slow, closely resembling those observed with the same peptide and purified, immobilized DR molecules.

The data suggest that in APC, cellular mechanisms are operative that increase the efficiency of both loading and unloading of Class II HLA with exogenous peptides. This is likely to be related to the recycling of Class II molecules to intracellular compartments, were binding takes place.

The observation that the HLA-peptide complex is a dynamic structure, suggests the possibility of replacing natural peptides with synthetic ones at this level, in order to regulate the immune response.

Cellular mechanisms of artificial peptides binding to HLA

On the basis of the consideration that cell-free models cannot precisely mimic the complexity of the intracellular environment, we used a system to investigate the mechanisms that enable antigen-presenting cells (APC) to bind exogenous peptides through their human leukocyte antigen (HLA) molecules. We evaluated the uptake of the radiolabeled peptide 17-29-Tyr of influenza virus matrix protein by B-EBV cell lines, under various conditions. The results can be summarized as follows: a) the kinetics of peptide binding and release are very fast in living, fully competent cells; b) the peptide-HLA complexes are short-living and the DR molecules continuously undergo peptidic exchange; c) using glutaraldehyde-fixed cells, the kinetics of the two phenomena are slow, closely resembling those observed with the same peptide and purified, immobilized DR molecules. The data suggest that in APC, cellular mechanisms are operative that increase the efficiency of both loading and unloading of Class II HLA with exogenous peptides. This is likely to be related to the recycling of Class II molecules to intracellular compartments, were binding takes place. The observation that the HLA-peptide complex is a dynamic structure, suggests the possibility of replacing natural peptides with synthetic ones at this level, in order to regulate the immune response.

Binding of labelled influenza matrix peptide to HLA DR in living B lymphoid cells

T cells recognize protein antigens as fragments (peptides) held in a defined binding site of class I or class II major histocompatibility (MHC) molecules. The formation of complexes between various immunologically active peptides and different MHC molecules has been demonstrated directly in binding studies between the peptides and solubilized, purified molecules of class II MHC. Studies with intact cells, living or fixed, have not directly demonstrated the binding of the peptides to MHC molecules on antigen-presenting cells, but the formation of such complexes has been shown indirectly through the capacity of antigen-presenting cells to stimulate specific T cells. Here we report evidence that supports directly the binding of radiolabelled influenza matrix peptide 17-29 to products of the human class II MHC locus HLA-DR, on living homozygous B-cell lines, and we show that the kinetics of such binding is much faster with living cells than with fixed cells. Furthermore, whereas the peptide reacts with HLA-DR molecules of all alleles, it binds preferentially to DR1, the restricting element in antigen presentation.

Monocyte-derived macrophages as helper cells in monocyte-mediated cytolysis

Human peripheral blood monocytes (M), incubated with opsonized zymosan particles (OPZ), lysed human erythrocyte (RBC) targets, as detected by a 51Cr release method. Conversely, cells derived in vitro from M (monocyte-derived macrophages, MDM) were ineffective. When added to the M-RBC system, MDM enhanced the lysis. The lysis by M and M plus MDM was prevented by catalase, azide and amino acids (alanine, taurine), consistent with the requirement for hypochlorous acid (HOCl). Moreover, MDM per se incapable of generating HOCl augmented the HOCl recovery from the M-RBC system. The results provide evidence for a previously unrecognized form of interaction between two distinct populations of mononuclear phagocytes.

Augmentation of neutrophil-mediated erythrocyte lysis by cells derived in vitro from human monocytes

Neutrophilic polymorphonuclear leukocytes (PMNs) were incubated with opsonized zymosan and lysed human erythrocytes (RBCs) as measured by a 51Cr release method. Conversely, myeloperoxidase (MPO)-negative hydrogen peroxide (H2O2)-generating cells, derived in vitro from human monocytes (monocyte-derived cells (MDCs), were ineffective per se but capable of augmenting the lysis by PMNs. The lysis by PMNs and PMNs plus MDCs was inhibited by catalase, azide, taurine, and alanine, consistent with the requirement for hypochlorous acid (HOCl). As detected under conditions similar to those used for lytic assays, MDCs failed to produce HOCl but augmented the HOCl recovery from the PMN-RBC system. Moreover, when the extent of the lysis was plotted as a function of the HOCl recovery, a positive linear relationship was found. Although the actual size of the H2O2 extracellular pool could not be measured because of the inexistence of a reliable assay to probe our cytolytic model without perturbing the equilibrium of the system, the results presented suggest that MDCs enhance the PMN-mediated lysis by improving the HOCl production, presumably by supplying extra amounts of H2O2 to be handled by PMN MPO. In fact, the events mediated by MDCs could be reproduced by using an appropriate H2O2-generating enzymatic system (glucose-glucose oxidase). The present study provides direct evidence for the possibility of cooperation between MPO-positive and MPO-negative phagocytes in exerting functions (HOCl production and, in turn, cytolysis) possibly relevant to the outcome of inflammatory processes.

Relationship between antibody-dependent tumour cell lysis and primary granule exocytosis by human neutrophils

Neutrophil-mediated antibody-dependent cellular cytotoxicity (ADCC) against Raji target cells and neutrophil degranulation during the ADCC process were evaluated in the presence and in the absence of different agents able to interfere with the neutrophil release of granule components (anion channel blockers, colchicine, isoproterenol, dimethylxanthine, cAMP). When used at concentrations incapable of preventing the target cell recognition by neutrophils, the majority of these agents inhibited both the ADCC and the release of myeloperoxidase (MPO, primary granule marker) and lysozyme (LZM, primary and secondary granule marker). The inhibition of the ADCC correlated strictly with the inhibition of the MPO release. Thus, the results are consistent with the hypothesis that neutrophil primary granules play a major role in the cytolytic process.

Antibody-dependent tumour cytolysis by human neutrophils: effect of synthetic serine esterase inhibitors and substrates

The requirement for serine esterase activity in antibody-dependent cellular cytotoxicity (ADCC) in human neutrophils against Raji target cells has been investigated. The lysis was prevented when the serine esterase inhibitors TPCK and TLCK (chloromethyl-ketone derivatives of tosylamino acids) were introduced into the system. Moreover, neutrophils pretreated with TPCK or TLCK and washed were inhibited as well, via a process unaffected by the presence of adequate amounts of enzymatic substrates. This suggests that the inhibition mediated by TPCK and TLCK is independent of serine esterase blockade, therefore implying the inactivation of some other step crucial to the lysis. The addition of synthetic chymotrypsin substrates (tyrosine and phenylalanine esters) impaired the Raji cell lysis in a dose-related manner without altering the constitution of neutrophil-target conjugates. Trypsin ester substrates were ineffective. These results are in agreement with the involvement of a serine esterase activity with chymotrypsin-like specificity, which should participate in the lysis at a post-binding step. We conclude that neutrophil-mediated ADCC, as developed in our model system, needs the intervention of a serine esterase or esterases, like other systems of cell-mediated cytotoxicity.

Erythrocyte lysis by monocytes: investigations on the mechanism and role of the target cell hydrogen peroxide catabolizing pathways

The erythrocyte (RBC) lysis by human monocytes incubated with opsonized zymosan particles (OPZ), was inhibited by catalase, chloride-free medium, azide and hypochlorous acid (HOCl) scavengers (taurine, alanine). These findings suggest the requirement for the HOCl-generating myeloperoxidase-hydrogen peroxide-chloride system (MPO-H2O2-Cl- system). The HOCl-dependent lysis was increased by inhibiting RBC catalase with aminotriazole (AT). Conversely, the inhibition of RBC glutathione cycle with 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU) had no detectable effect. Moreover, the recovery of H2O2 and HOCl from OPZ-triggered monocytes was reduced by the presence of RBCs through a process almost completely preventable by pulsing RBCs with AT but not with BCNU. Thus, it appears that RBC targets protect themselves by consuming, primarily via catalase, significant amounts of monocyte-derived H2O2 with a consequent impairment of the HOCl generation. The results suggest a potential role of target cells in modulating the cytolysin production by monocytes.

Interference of target cell catalase with an early step of the neutrophil cytolytic pathway

The hypochlorous acid (HOCL)-dependent lysis of human red blood cells (HRBC) targets by neutrophils, activated with opsonized zymosan particles (OPZ), was increased by inhibiting HRBC catalatic activity with aminotriazole (AT; HRBCAT). The inhibition of HRBC glutathione cycle activity with carmustine (BCNU; HRBCBCNU) had no effect. In addition, the recovery of hydrogen peroxide (H2O2) and HOCL from neutrophils, activated under conditions similar to those used for cytotoxicity assay, was reduced by the presence of HRBC and restored by replacing HRBC with HRBCAT, but not with HRBCBCNU. Linear relationships were found between the increments in the neutrophil-mediated lysis, observed by using HRBCAT instead of HRBC, and the increments in the H2O2 or HOCL recovery, detected by replacing HRBC with HRBCAT. Together these data, coupled with the results obtained by probing neutrophil cytolysis with chemical agents, suggest that the increased cytolytic efficiency displayed by neutrophils against HRBCAT, inhibited in their catalatic activity, is due to an enhanced availability of neutrophil-derived H2O2, with a consequent enhancement in the HOCL production (according to the following reaction: (formula; see text). Thus it appears that HRBC catalase restrains the neutrophil cytolytic activity, by interfering with an early step of the pathway through which neutrophils generate cytotoxins.

Inhibition of neutrophil cytolysin production by target cells

Neutrophils, triggered by heat-aggregated human IgG (Agg.IgG), were found to lyse chicken red blood cells (CRBC) as determined by a 51Cr release method. The lysis was inhibited by azide, catalase, chloride-free medium and amino acids, suggesting the requirement for myeloperoxidase (MPO), hydrogen peroxide (H2O2), chloride ions (Cl-), and hypochlorous acid (HOC1), respectively. These results indicate that neutrophils lyse CRBC through an HOCl-(ie, MPO-H2O2-Cl-) dependent process. Although HOCl can react with neutrophil-derived nitrogenous (N-) compounds to yield chloramines, the main and well-characterized chloramines did not play a direct role in the lysis of CRBC in our model system. Thus, it appears that lysis is due either to HOCl or to an unknown compound derived from and with characteristics similar to HOCl. When CRBC were replaced with HRBC targets, no lysis could be observed. Treatment of HRBC with carmustine, to inhibit the glutathione cycle, did not affect the cell resistance to lysis by neutrophils. Conversely, the inhibition of HRBC catalase activity with aminotriazole (AT) made the cells susceptible to neutrophil-mediated HOCl-dependent lysis: this suggests that HRBC escape lysis by neutrophils through an AT-inhibitable, ie catalase-dependent, process. Through an identical catalase-dependent process, HRBC were capable of efficiently preventing the H2O2 and HOCl recovery from Agg.IgG-triggered neutrophils, tested under experimental conditions similar to those used for cytolytic assays. Together, these data suggest that HRBC targets, endowed with high catalase activity, escape neutrophil-mediated lysis by consuming (by catalase) neutrophil-derived H2O2, so that HOCl cannot be produced in amounts sufficient to promote lysis. Parallel experiments, performed with AT-treated CRBC, showed that these cells, endowed with a relatively low catalase content, only partially limit neutrophil cytolytic efficiency by a process qualitatively similar to that observed with HRBC targets. The results provide evidence that target cells can restrain neutrophil cytolytic efficiency by interfering with the MPO-H2O2-Cl system through their catalase activity.

Role of hypochlorous acid and chloramines in the extracellular cytolysis by neutrophil polymorphonuclear leukocytes

The lysis of human red blood cells (HRBC) by neutrophil polymorphonuclear leukocytes (PMN), triggered with opsonized zymosan (OPZ) particles, was inhibited by azide, catalase, Cl- -free medium and amino acids indicating the involvement of myeloperoxidase (MPO), hydrogen peroxide (H2O2), Cl- ions and hypochlorous acid (HOCl) respectively. Thus, the cytolytic process depends on the following reaction: (Formula: see text). Because the oxidizing agent HOCl is also the precursor of the chloramines, a group of oxidants formed by the reaction between HOCl and PMN-derived ammonia (NH4+) or amines (R-NH2), the observed HRBC lysis can be theoretically due to HOCl and/or chloramines. Nevertheless, we found that PMN-mediated cytotoxicity occurs as an unidirectional process, being HRBC targets lysed and PMN unaffected. This finding indicates that the cytotoxin must be relatively more efficient against HRBC as compared with PMN. In fact, reagent HOCl (used at concentrations comparable to those generated by PMN) but not chloramines displayed such a type of property. Taken together, the data suggest that HRBC are killed by PMN-derived HOCl without the requirement for chloramines: this implies that NH4+ and R-NH2, released by PMN, act as down-modulators of the cytotoxic process, serving as HOCl trapping agents.

Expression of cytolytic functions in HL-60 leukaemic cells after induction of polymorphonuclear leukocyte differentiation

Mature polymorphonuclear leukocytes (PMN) are capable of mediating phorbol myristate acetate (PMA)- and antibody (A)-dependent cellular cytotoxicity (DCC) against ox red blood cells (ORBC) by using oxidative means. The purpose of the present study was to investigate the acquirement of these cytotoxic functions during PMN ontogeny, using the promyelocytic HL-60 cell line as a model for PMN differentiation. HL-60 cells were induced to differentiate along the PMN pathway by exposure to dimethyl sulfoxide (DMSO). Uninduced HL-60 cells were found to be completely devoid of PMA-DCC and ADCC activity. DMSO-induced cells progressively acquired the capacity to kill ORBC and to undergo the activation of oxidative metabolic burst when triggered by PMA. Despite approximately 40% of them also were capable of binding IgG-sensitized ORBC, no ADCC activity and respiratory burst activation was observed: this finding indicates that maturing HL-60 cells require a more complete maturation than that induced by DMSO to actually exert ADCC. Together the results suggest that: a. the acquirement of both PMA-DCC and ADCC potential is a post-promyelocytic event; b. the cytotoxicity activating stimuli, PMA and IgG-coated targets, follow different post-receptor transductional pathways to trigger the effector cell lytic systems: only the PMA receptor-linked pathway develops during DMSO-driven differentiation of HL-60 cells.

Erythrocyte lysis by PMA-triggered neutrophil polymorphonuclears: evidence for an hypochlorous acid-dependent process

Human red blood cells (HRBC) were efficiently lysed when incubated with neutrophil polymorphonuclears (PMN) in the presence of phorbol-myristate-acetate (PMA), as detected by a 4-hr 51Cr release assay. The lysis was virtually absent in the presence of catalase, azide or cyanide and in the absence of chloride ions. These findings indicate the involvement of the myeloperoxidase (MPO)-hydrogen peroxide (H2O2)-chloride (Cl-) system in the cytolytic process. As the MPO-H2O2-Cl- system is capable of generating the powerful oxidant hypochlorous acid (HOCl), cytotoxicity assays were performed in the presence of taurine, glycine, serine and valine to scavenge this potentially lytic agent. Each of these compounds efficiently inhibited the HRBC lysis by PMA-triggered PMN, as well as the lysis caused by HOCl in a cell-free system. Thus, the results suggest that HOCl, or an agent with similar reactivity, plays a key role in the PMA-dependent PMN-mediated cytotoxicity against HRBC targets.

Cellular cytotoxicity mediated by granule-depleted neutrophil cytoplasts

Neutrophil-derived nucleus-and granule-free cytoplasts, consisting of cytosol enclosed by an intact plasma membrane, were able to destroy 51Cr-labelled ox red blood cells (ORBC) in the presence of phorbol myristate acetate (PMA). The slope of the target cell lysis vs the log of the cytoplast number was similar to that observed with neutrophils as effector cells. Nevertheless, a number of cytoplasts 60-80 times higher than that of neutrophils was required to obtain a common level of cytotoxicity. The ability of cytoplasts and neutrophils to lyse ORBC was completely abolished by catalase and unaffected by superoxide dismutase and mannitol, suggesting the involvement of hydrogen peroxide in the target cell damage. Addition of myeloperoxidase (MPO) to cytoplasts increased lysis. The MPO lysis by cytoplasts, except when experiments were carried out in the presence of MPO. The results indicate that neutrophil cytosol and plasma membrane represent the basic requirement for the PMA-dependent cytolytic process, whereas MPO behaves as a device to amplify lysis.

Extracellular cytotoxicity by phagocytosing polymorphonuclear neutrophilic leukocytes: enhancement by a chemotactic stimulus

This study investigated the influence of a chemotactic stimulus on the extracellular cytotoxicity mediated by phagocytosing polymorphonuclear neutrophilic leukocytes (PMN). We used N-formyl-methionyl-leucyl-phenylalanine (FMLP) as chemotactic peptide, opsonized zymosan as phagocytosable particle, and ox red blood cells (ORBC) as extracellular bystander targets. Phagocytosing PMN were found to kill ORBC efficiently, as determined by the 51Cr-release assay. FMLP, at the concentration of 100 nM, significantly enhanced the target cell lysis. PMN from two patients with chronic granulomatous disease and normal PMN plus catalase or free radical scavengers (mannitol, benzoate, histidine) were completely devoid of cytolytic activity both in the presence and in the absence of FMLP. The results indicate that the target cell lysis by phagocytosing PMN as well as the chemotactic peptide-related amplification of the lysis itself depend on the expression of the PMN oxidative cytotoxic potential. A similar response to a chemotactic stimulus in vivo could provide a mechanism for regulating PMN-dependent cytotoxic and inflammatory processes.

Down-regulation of K cell activity by neutrophils

Human neutrophils, activated by phorbol-myristate acetate (PMA), (A-neutrophils), were found to suppress lymphocytic killer (K) cell-mediated antibody-dependent cellular cytotoxicity (ADCC). Resting (R) neutrophils, ie, PMA-untreated cells, were completely ineffective. Suppression was optimal when A-neutrophils were added at the beginning of the ADCC assay. Furthermore, A-neutrophils were found to cause an approximately 80% reduction in the number of Raji target cell-bound lymphocytes. These data indicate that A-neutrophils inhibit K cell activity by interfering with the target cell recognition. A-neutrophils were capable of reducing the percentage of Fc receptor (FcR)-bearing lymphocytes with a half-time of 7.2 minutes, through a process preventable by the serine-protease inhibitors tosyl-lysine-chloromethyl ketone (TLCK) and lima bean trypsin inhibitor (LBTI). Conversely, A-neutrophils caused a very slow decrease in the amount of Raji cell-bound antibodies, as detected by the complement-mediated lytic assay. Thus, only lymphocyte FcR structures seem to be highly susceptible to neutrophil-derived TLCK- and LBTI-inhibitable proteases. Furthermore, supernatants from A-neutrophils were found to inhibit K cell ADCC and lymphocyte binding to Raji target cells. In addition, LBTI prevented the A-neutrophil-dependent and the supernatant-dependent inhibition of both K cell ADCC activity and lymphocyte-target cell conjugate formation. Together these data suggest that A-neutrophils suppress K cell function through a protease-mediated impairment of the FcR binding capacity. The results provide evidence that human neutrophils are endowed with mechanisms to regulate K cell ADCC activity.

Neutrophil-mediated cellular cytotoxicity triggered by immobilized aggregated IgG: an in vitro model of cell injury during immune complex diseases

Normal human neutrophils were found to destroy ox red blood-cell targets when incubated on micropore filters coated with aggregated IgG, as determined by the 51Cr release method. An intact neutrophil oxidative metabolism was essential for the cytotoxic event, since cells from patients with chronic granulomatous disease failed to exert any cytolysis. The target-cell destruction was prevented by catalase, azide, and cyanide and was enhanced by superoxide dismutase, suggesting involvement of the myeloperoxidase-hydrogen peroxide system. Neutrophil-mediated cytotoxicity was markedly amplified by the chemotactic peptide N-formyl-methionyl-leucylphenylalanine, as a result of an increased activity of the myeloperoxidase-hydrogen peroxide cytolytic system itself. This system of cytotoxicity provides a direct evidence for the neutrophil capacity of destroying bystander target cells under conditions simulating the in vivo immunologically mediated tissue injury and offers an excellent model to study events occurring during immune complex diseases.

Naturally-occurring cellular cytotoxicity mediated by neutrophil polymorphonuclears: requirements for the target cell lysis

The purpose of the present study was to investigate the general conditions under which neutrophil polymorphonuclears (PMN) mediate antibody-independent cytolysis in the presence of normal human serum (NHS). Normal PMN were found to kill rabbit red blood cells (RRBC) only when cultured with 1% NHS. NHS was per se incapable of lysing RRBC. PMN from a patient with Chronic Granulomatous Disease did not destroy RRBC targets even in the presence of 1% NHS. In addition, cytotoxicity by normal PMN was significantly reduced by scavengers of oxygen metabolites. The results suggest that the target cell lysis by PMN in the presence of NHS requires a synergistic interaction between at least two mediators: serum factor(s) and oxygen metabolite(s).

Chemotactic peptide enhancement of PMA triggered monocyte cytotoxicity

The chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP), per se incapable of triggering cytotoxicity, was found to significantly enhance phorbol myristate acetate (PMA)-dependent monocyte-mediated cytolysis of human red blood cell (HRBC) targets. Target cell lysis by PMA triggered monocytes was related to the release of superoxide anion and hydrogen peroxide, since cells from patients with chronic granulomatous disease and cells from normal donors, in the presence of superoxide dismutase or catalase, failed to exert significant cytotoxicity. An increased release of these mediators was found to be responsible for the FMLP-dependent amplification of the cytolytic reaction. The results indicate that chemotactic factors are able to enhance the release of cytotoxic mediators by monocytes and raise the possibility that cellular processes during monocyte chemotaxis could modulate the subsequent cytolytic activity.

Antibody-dependent killing of tumor cells by polymorphonuclear leukocytes. Involvement of oxidative and nonoxidative mechanisms

Antibody-dependent cellular cytotoxicity (ADCC) against Raji cells was used as a model system to investigate the polymorphonuclear leukocyte (PMN) mechanisms involved in tumor cell lysis. PMN killed target cells by nonoxidative means, as indicated by the following observations: PMN from patients with chronic granulomatous disease (CGD), defective in their metabolic burst, lysed Raji cells normally; impairment of the oxidative metabolism of normal PMN by phenylbutazone did not affect ADCC. Rosenthal's inhibitor of phospholipase A2 completely prevented the lysis, suggesting the involvement of this enzyme in the target cell damage. The inhibition of the Raji cell glutathione redox cycle by carmustine [1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)] increased cell susceptibility to PMN-mediated ADCC. This increment of lysis was related to oxidative killing systems. In fact, CGD PMN had an ADCC against BCNU-treated Raji cells lower than that mediated by normal PMN, but comparable to that observed with untreated targets, and phenylbutazone reduced the lysis of BCNU-treated Raji cells by normal PMN to the level observed with the use of untreated targets. The remaining ADCC against BCNU-treated Raji cells mediated by CGD PMN and by normal PMN in the presence of phenylbutazone was suppressed by Rosenthal's inhibitor. Thus PMN killed sensitized BCNU-treated Raji cells by use of both oxidative and nonoxidative means. The results indicate that the interaction of sensitized Raji cells with PMN triggers simultaneously oxidative and non-oxidative potentially lytic systems and the mediator(s) of Raji cell lysis actually operating may depend on the metabolic state of the target cells themselves. Therefore, the lysis of sensitized tumor cells might not reflect the simple effect of PMN tumoricidal systems; rather it should be regarded as a result of an inability of the target cells to escape the various PMN cytolytic mechanisms.

Target cell lysis mediated by concanavalin A-triggered human neutrophils

Human neutrophils, triggered by Concanavalin A, were cytotoxic against chicken red blood cell targets as determined by the 51Cr release method. The cytolysis increased with the effector: target ratio, reaching optimal levels when 2-4 neutrophils were available for each chicken red blood cell. The target cell lysis required an optimal release of highly reactive oxygen by-products by neutrophils, since neutrophils from a patient with chronic granulomatous disease failed to exhibit any cytolytic activity. Superoxide dismutase, catalase and inhibitors of heme-containing peroxidases (azide and cyanide) significantly inhibited the neutrophil-mediated cytotoxicity. Together these results indicate that superoxide anion and the myeloperoxidase-hydrogen peroxide system are simultaneously involved in the target cell injury by Concanavalin A-triggered neutrophils.

Neutrophil-mediated cellular cytotoxicity induced by zymosan-activated serum

Human neutrophils, incubated in the presence of zymosan-activated serum ( ZAS ), were able to damage ox red blood cells ( ORBC ) as assessed by a 4-hr 51Cr-release assay. Cells from a patient with chronic granulomatous disease were incapable of mediating ZAS -induced cytolysis. Cytotoxicity by normal neutrophils was prevented by N-ethyl-maleimide as well as by catalase, but heat-inactivated catalase and superoxide dismutase were completely ineffective. Heme enzyme inhibitors, azide and cyanide, only partially reduced the target cell lysis. The results indicate the involvement of products of the oxidative metabolism, mainly hydrogen peroxide, as cytolytic mediators. These mediators released by neutrophils may contribute to the tissue injury occurring during inflammation.

Defective neutrophil mobilization to skin chambers in cancer patients

The in vivo migration of neutrophils was evaluated in patients affected by epithelial carcinoma using the quantitative skin-chamber technique. The results demonstrated a significant impairment of the patients' neutrophil migration, which was reduced to approximately 4% of that of the controls. Patients' sera were able to inhibit the chemotactic responsiveness of normal neutrophils in vitro. It is therefore suggested that the defective in vivo migration of neutrophils in cancer patients is related to the presence of humoral cell-directed inhibitory activity. This defect of neutrophil function might contribute to the host-defense impairment of carcinoma patients.

Extracellular cytolysis by leukaemic blast cells

Leukaemic blast cells from 20 patients with acute leukaemia were examined for their capacity to mediate cytotoxicity against ox red blood cells in the presence of phorbol myristate acetate (PMA), a system widely employed as an in vitro model of tissue damage by metabolically activated mature phagocytes. Blasts from certain patients with myelomonocytic and monocytic leukaemia behaved like efficient killer cells. Conversely, leukaemic myeloblasts and promyelocytes as well as leukaemic lymphoblasts were ineffective. Blast cells capable of inducing the target cell lysis were also capable of mounting an oxidative respiratory burst upon challenge with PMA, as detected by the superoxide anion release. N-ethyl-maleimide, superoxide dismutase and catalase completely inhibited the cytotoxicity by monocytoid blast cells, suggesting the involvement of oxygen reactive products in the lethal hit itself. The cytolytic potential of blasts committed to monocytic differentiation might be an additional factor contributing to the tissue damage in a subpopulation of leukaemic patients.

Phagocytosis-dependent neutrophil-mediated extracellular cytotoxicity against different target cells

Normal human neutrophils, incubated with 0.2 mg/ml opsonized zymosan particles, were found to lyse human (H), ox (O) and chicken (C) red blood cell (RBC) targets as determined by the 51Cr release assay. The susceptibility to the lysis of the different target cells was HRBC less than ORBC less than CRBC. An intact neutrophil metabolic burst was essential for the cytotoxic event, since neutrophils from a patient with chronic granulomatous disease failed to kill all three target cells. HRBC and ORBC destruction was prevented by catalase and unaffected by azide, suggesting the requirement of hydrogen peroxide alone in the lethal hit. CRBC destruction was abolished by catalase and azide, suggesting the involvement of the myeloperoxidase-hydrogen peroxide system. Thus, different neutrophil cytolytic systems may become operative and may vary in their efficiency depending on the type of target cells.

Neutropenia and impaired neutrophil function in glycogenosis type Ib

The impairment of different neutrophil functions has recently been reported in some patients with glycogenosis Ib and neutropenia. However, no satisfactory explanation for these findings has so far been supplied. In order to investigate this problem, we have studied neutrophil functions (random locomotion and chemotaxis, O-2 release, [1-14C]glucose oxidation and cellular cytotoxicity) in two further patients with glycogenosis Ib and neutropenia. The results show that neutrophil dysfunctions related to the involvement of both hexose monophosphate shunt and anaerobic glycolysis were variable. The heterogeneity of neutrophil functional impairment in glycogenosis Ib and their possible relationship with the basic metabolic defect of the disease are discussed.

PHA-induced neutrophil-mediated cytotoxicity

Neutrophils activated by phytohemagglutinin (PHA) were cytotoxic to chicken red blood cells (CRBC), as determined by the 51Cr release assay. High levels of cytotoxicity were obtained when one CRBC was available for each effector cell. Neutrophils from patients with Chronic Granulomatous Disease (CGD), incapable of generating potentially toxic oxygen radicals, had a reduced cytotoxicity activity, suggesting the requirement for an intact oxidative metabolism in the PHA-induced neutrophil-mediated cytotoxicity. However, CGD neutrophils maintained approximately 50% of this activity, compared with normal cells. These findings support the conclusion that both oxygen-dependent and oxygen-independent mechanisms are necessary to achieve an efficient cytotoxicity.

Mechanisms of tumour cell destruction by PMA-activated human neutrophils

Phorbol myristate acetate (PMA)-activated neutrophils were found to destroy B lymphoblast tumour cells (Raji) as determined by the 51Cr release assay. The target cell lysis was prevented by azide, suggesting the involvement of the myeloperoxidase enzyme. Catalase and cytochrome c caused a marked impairment of the neutrophil-mediated cytolysis, whereas superoxide dismutase significantly enhanced the target cell destruction. These data indicate that hydrogen peroxide plays a key role in the target cell injury; superoxide anion appears to be devoid of direct cytotoxic activity, despite its requirement as a precursor of hydrogen peroxide. The target cell destruction required the presence of the iodide ion as oxidizable co-factor for the myeloperoxidase-hydrogen peroxide system. The chloride ion alone was uneffective. Inhibition of target cell metabolic pathways, involved in the cellular defences against oxidative injury, by the anti-neoplastic agent 1,3-bis-(2-chloroethyl)-1-nitrosurea (BCNU) resulted in an increased neutrophil-mediated cytolysis. Under the experimental conditions employed, PMA-activated neutrophils incubated with BCNU-treated Raji cells became cytotoxic also in the presence of the chloride ion alone as myeloperoxidase co-factor. Our results suggest that Raji target cell destruction by PMA-activated neutrophils depends on the myeloperoxidase-hydrogen peroxide-halide system. The cytolytic event is influenced by target cells themselves, which should be regarded as an active component of the cytotoxic system, capable of interfering with the lytic mediators of the effector cells.