Variable expression of CD3-zeta and associated protein tyrosine kinases in lymphocytes from patients with myeloid malignancies

Therapy Resistance and Disease Progression in CML: Mechanistic Links and Therapeutic Strategies

PURPOSE OF REVIEW

Despite the adoption of tyrosine kinases inhibitors (TKIs) as molecular targeted therapy in chronic myeloid leukemia, some patients do not respond to treatment and even experience disease progression. This review aims to give a broad summary of advances in understanding of the mechanisms of therapy resistance, as well as management strategies that may overcome or prevent the emergence of drug resistance. Ultimately, the goal of therapy is the cure of CML, which will also require an increased understanding of the leukemia stem cell (LSC).

RECENT FINDINGS

Resistance to tyrosine kinase inhibitors stems from a range of possible causes. Mutations of the BCR-ABL1 fusion oncoprotein have been well-studied. Other causes range from cell-intrinsic factors, such as the inherent resistance of primitive stem cells to drug treatment, to mechanisms extrinsic to the leukemic compartment that help CML cells evade apoptosis. There exists heterogeneity in TKI response among different hematopoietic populations in CML. The abundances of these TKI-sensitive and TKI-insensitive populations differ from patient to patient and contribute to response heterogeneity. It is becoming clear that targeting the BCR-ABL1 kinase through TKIs is only one part of the equation, and TKI usage alone may not cure the majority of patients with CML. Considerable effort should be devoted to targeting the BCR-ABL1-independent mechanisms of resistance and persistence of CML LSCs.

Dissecting the role of the CXCL12/CXCR4 axis in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is the most common adult acute leukaemia with the lowest survival rate. It is characterised by a build-up of immature myeloid cells anchored in the protective niche of the bone marrow (BM) microenvironment. The CXCL12/CXCR4 axis is central to the pathogenesis of AML as it has fundamental control over AML cell adhesion into the protective BM niche, adaptation to the hypoxic environment, cellular migration and survival. High levels of CXCR4 expression are associated with poor relapse-free and overall survival. The CXCR4 ligand, CXCL12 (SDF-1), is expressed by multiple cells types in the BM, facilitating the adhesion and survival of the malignant clone. Blocking the CXCL12/CXCR4 axis is an attractive therapeutic strategy providing a 'multi-hit' therapy that both prevents essential survival signals and releases the AML cells from the BM into the circulation. Once out of the protective niche of the BM they would be more susceptible to destruction by conventional chemotherapeutic drugs. In this review, we disentangle the diverse roles of the CXCL12/CXCR4 axis in AML. We then describe multiple CXCR4 inhibitors, including small molecules, peptides, or monoclonal antibodies, which have been developed to date and their progress in pre-clinical and clinical trials. Finally, the review leads us to the conclusion that there is a need for further investigation into the development of a 'multi-hit' therapy that targets several signalling pathways related to AML cell adhesion and maintenance in the BM.

Role of the ERK pathway for oxidant-induced parthanatos in human lymphocytes

Reactive oxygen species (ROS) are formed by myeloid cells as a defense strategy against microorganisms. ROS however also trigger poly(ADP-ribose) polymerase 1- (PARP-1) dependent cell death (parthanatos) in adjacent lymphocytes, which has been forwarded as a mechanism of immune escape in several forms of cancer. The present study assessed the role of mitogen-activated protein kinases (MAPKs), in particular the extracellular signal-regulated kinase (ERK), in ROS-induced signal transduction leading to lymphocyte parthanatos. We report that inhibitors of ERK1/2 phosphorylation upheld natural killer (NK) cell-mediated cytotoxicity under conditions of oxidative stress and rescued NK cells and CD8⁺ T lymphocytes from cell death induced by ROS-producing monocytes. ERK1/2 phosphorylation inhibition also protected lymphocytes from cell death induced by exogenous hydrogen peroxide (H₂O₂) and from ROS generated by xanthine oxidase or glucose oxidase. Phosphorylation of ERK1/2 was observed in lymphocytes shortly after exposure to ROS. ROS-generating myeloid cells and exogenous H₂O₂ triggered PARP 1-dependent accumulation of poly ADP-ribose (PAR), which was prevented by ERK pathway inhibitors. ERK1/2 phosphorylation was induced by ROS independently of PARP-1. Our findings are suggestive of a role for ERK1/2 in ROS-induced lymphocyte parthanatos, and that the ERK axis may provide a therapeutic target for the protection of lymphocytes against oxidative stress.

Tumor-primed NK cells: waiting for the green light

The functional impairment of natural killer (NK) cells has been frequently reported in cancer studies. As one of the central components of host anti-tumor immunity, NK cells exert cellular cytotoxicity against tumor cells, and secrete a cytokine milieu to inhibit tumor progression and enable the recruitment of other immune cells to the tumor site. The unlocking of the full functional potential of NK cells requires successful progression through discrete activation stages that are tightly regulated by a complex array of signaling molecules. Target cell susceptibility to NK cell-mediated killing is dependent on the intensity and specific combination of ligand expression for NK cell receptors. Tumor cells utilize numerous strategies for evading NK cells, including the downregulation of important NK cell-activating ligands. Here, we review key studies on NK cell activation requirements, and argue, based on our findings from NK cell-tumor interactions, that the altered characteristics of tumor-associated NK cells are indicative of unmet signaling requirements for full NK cell activation, rather than NK cell dysfunction in cancer.

Lytic activity against primary AML cells is stimulated in vitro by an autologous whole cell vaccine expressing IL-2 and CD80

Despite being of the myeloid lineage, acute myeloid leukaemia (AML) blasts are of low immunogenicity, probably because they lack the costimulatory molecule CD80 and secrete immunosuppressive factors. We have previously shown that in vitro stimulation of autologous peripheral blood mononuclear cells (PBMCs) with primary AML cells modified to express CD80 and IL-2 promotes proliferation, secretion of Th1 cytokines and expansion of activated CD8(+) T cells. In this study, we show that allogeneic effector cells (from a healthy donor or AML patients) when stimulated with IL-2/CD80 modified AML blasts were able to induce the lysis of unmodified AML blasts. Effector cells stimulated with IL-2/CD80AML blasts had higher lytic activity than cells stimulated with AML cells expressing CD80 or IL-2 alone. Similarly, AML patient PBMCs primed with autologous IL-2/CD80 AML cells had a higher frequency of IFN-gamma secreting cells and show cytotoxicity against autologous, unmodified blasts. Crucially, the response appears to be leukaemia specific, since stimulated patient PBMCs show higher frequencies of IFN-gamma secreting effector cells in response to AML blasts than to remission bone marrow cells from the same patients. Although studied in a small number of heterogeneous patient samples, the data are encouraging and support the continuing development of vaccination for poor prognosis AML patients with autologous cells genetically modified to express IL-2/CD80.

Post-consolidation immunotherapy with histamine dihydrochloride and interleukin-2 in AML

The initial chemotherapy in acute myeloid leukaemia (AML) comprises a first phase of induction and a second phase of consolidation. In the majority of patients, the induction treatment leads to complete remission (CR), defined as microscopic disappearance of leukaemic disease along with the return of normal haematopoiesis. However, despite the introduction of more efficacious consolidation regimens, a worryingly large proportion of AML patients in CR will subsequently experience relapses with poor prospects of long-term survival. A relapse is assumed to be the result of expansion of residual leukaemic cells that have escaped the initial chemotherapy. The anti-leukaemic functions of T cells and natural killer (NK) cells has formed the background to the use of interleukin-2 (IL-2), a T- and NK cell-activating cytokine, with the aim to eliminate residual leukaemia and hence reduce the relapse rate in AML, but the clinical trials using IL-2 monotherapy have yielded disappointment. A recent phase III study has demonstrated that post-consolidation treatment with the combination of histamine dihydrochloride (HDC) and IL-2 significantly prevents relapse in AML patients. Here we account for the preclinical background to the use of HDC/IL-2 in AML along with a review of clinical results.

Natural killer cell-based immunotherapy in cancer: current insights and future prospects

As our understanding of the molecular mechanisms governing natural killer (NK) cell activity increases, their potential in cancer immunotherapy is growing increasingly prominent. This review analyses the currently available preclinical and clinical data regarding NK cell-based immunotherapeutic approaches in cancer starting from a historical background and an overview of molecular mechanisms taking part in NK cell responses. The status of NK cells in cancer patients, currently investigated clinical applications such as in vivo modulation of NK cell activity, ex vivo purification/expansion and adoptive transfer as well as future possibilities such as genetic modifications are discussed in detail.

T cell CD3 receptor zeta (TCRzeta)-chain expression in children with idiopathic nephrotic syndrome

Children with idiopathic nephrotic syndrome (INS) have an increased risk of developing life-threatening infections. Several studies have demonstrated functional abnormalities in the T lymphocytes of patients with nephrotic syndrome. Although T cells are activated in INS during relapse, as indicated by an increased expression of interleukin (IL)-2 receptor, these cells have a decreased ability to proliferate. The T-cell receptor (TCR) plays an important role in signal transduction and T cell activation, with the TCR-zeta (TCRzeta) chain being a key element in early signaling. We measured the expression of the TCRzeta chain in patients with INS (steroid resistant and steroid sensitive) during relapse and remission by flow cytometry and by PCR ELISA. The results showed a significant decrease in the expression of the TCRzeta chain at both the protein and mRNA level in INS patients during relapse as compared with normal controls (p < 0.05). In contrast, when patients with INS achieved remission, the expression of TCRzeta normalized and was similar to that expressed in normal controls. Therefore, a decreased expression of the TCRzeta chain may explain the abnormal function of T cells in patients with INS, and it may also contribute to the increased risk for infections seen in these patients.

Transduction with the antioxidant enzyme catalase protects human T cells against oxidative stress

Patients with diseases characterized by chronic inflammation, caused by infection or cancer, have T cells and NK cells with impaired function. The underlying molecular mechanisms are diverse, but one of the major mediators in this immune suppression is oxidative stress caused by activated monocytes, granulocytes, or myeloid-derived suppressor cells. Reactive oxygen species can seriously hamper the efficacy of active immunotherapy and adoptive transfer of T and NK cells into patients. In this study, we have evaluated whether enhanced expression of the antioxidant enzyme catalase in human T cells can protect them against reactive oxygen species. Human CD4(+) and CD8(+) T cells retrovirally transduced with the catalase gene had increased intracellular expression and activity of catalase. Catalase transduction made CD4(+) T cells less sensitive to H(2)O(2)-induced loss-of-function, measured by their cytokine production and ability to expand in vitro following anti-CD3 stimulation. It also enhanced the resistance to oxidative stress-induced cell death after coculture with activated granulocytes, exposure to the oxidized lipid 4-hydroxynonenal, or H(2)O(2). Expression of catalase by CMV-specific CD8(+) T cells saved cells from cell death and improved their capacity to recognize CMV peptide-loaded target cells when exposed to H(2)O(2). These findings indicate that catalase-transduced T cells potentially are more efficacious for the immunotherapy of patients with advanced cancer or chronic viral infections.

Graft-versus-leukemia effects of transplantation and donor lymphocytes

Allogeneic transplantation of hematopoietic cells is an effective treatment of leukemia, even in advanced stages. Allogeneic lymphocytes produce a strong graft-versus-leukemia (GVL) effect, but the beneficial effect is limited by graft-versus-host disease (GVHD). Depletion of T cells abrogates GVHD and GVL effects. Delayed transfusion of donor lymphocytes into chimeras after T cell-depleted stem cell transplantation produces a GVL effect without necessarily producing GVHD. Chimerism and tolerance provide a platform for immunotherapy using donor lymphocytes. The allogeneic GVL effects vary from one disease to another, the stage of the disease, donor histocompatibility, the degree of chimerism, and additional treatment. Immunosuppressive therapy before donor lymphocyte transfusions may augment the effect as well as concomitant cytokine treatment. Possible target antigens are histocompatibility antigens and tumor-associated antigens. Immune escape of tumor cells and changes in the reactivity of T cells are to be considered. Durable responses may be the result of the elimination of leukemia stem cells or the establishment of a durable immune control on their progeny. Recently, we have learned from adoptive immunotherapy of viral diseases and HLA-haploidentical stem cell transplantation that T-cell memory may be essential for the effective treatment of leukemia and other malignancies.

Alterations in the expression pattern of TCR zeta chain in T cells from patients with hematological diseases

The TCR zeta chain, a component of the T cell receptor (TCR)/CD3 complex, plays a significant role in the assembly of the receptor complex and in connecting antigen recognition to the intracellular signal transduction apparatus. Recently, studies have demonstrated altered expression and function of this signal transduction molecule in T cells from patients with hematological diseases. In this review, current knowledge concerning the biological feature and function of TCR zeta protein, splice variant and mutation of TCR zeta chain gene and alteration of expression pattern in hematological diseases and the related mechanism are summarized.

(-)-Epigallocatechin gallate regulates CD3-mediated T cell receptor signaling in leukemia through the inhibition of ZAP-70 kinase

The zeta chain-associated 70-kDa protein (ZAP-70) of tyrosine kinase plays a critical role in T cell receptor-mediated signal transduction and the immune response. A high level of ZAP-70 expression is observed in leukemia, which suggests ZAP-70 as a logical target for immunomodulatory therapies. (-)-Epigallocatechin gallate (EGCG) is one of the major green tea catechins that is suggested to have a role as a preventive agent in cancer, obesity, diabetes, and cardiovascular disease. Here we identified ZAP-70 as an important and novel molecular target of EGCG in leukemia cells. ZAP-70 and EGCG displayed high binding affinity (Kd = 0.6207 micromol/liter), and additional results revealed that EGCG effectively suppressed ZAP-70, linker for the activation of T cells, phospholipase Cgamma1, extracellular signaling-regulated kinase, and MAPK kinase activities in CD3-activated T cell leukemia. Furthermore, the activation of activator protein-1 and interleukin-2 induced by CD3 was dose-dependently inhibited by EGCG treatment. Notably, EGCG dose-dependently induced caspase-mediated apoptosis in P116.cl39 ZAP-70-expressing leukemia cells, whereas P116 ZAP-70-deficient cells were resistant to EGCG treatment. Molecular docking studies, supported by site-directed mutagenesis experiments, showed that EGCG could form a series of intermolecular hydrogen bonds and hydrophobic interactions within the ATP binding domain, which may contribute to the stability of the ZAP-70-EGCG complex. Overall, these results strongly indicated that ZAP-70 activity was inhibited specifically by EGCG, which contributed to suppressing the CD3-mediated T cell-induced pathways in leukemia cells.

Oxygen Radicals Induce Poly(ADP-Ribose) Polymerase-Dependent Cell Death in Cytotoxic Lymphocytes

Cytotoxic T cells and NK cells will acquire features of apoptosis when exposed to oxygen radicals, but the molecular mechanisms underlying this phenomenon are incompletely understood. We have investigated the role of two enzyme systems responsible for execution of cell death, caspases and the poly(ADP-ribose) polymerase (PARP). We report that although human cytotoxic lymphocytes were only marginally protected by caspase inhibitors, PARP inhibitors completely protected lymphocytes from radical-induced apoptosis and restored their cytotoxic function. The radical-induced, PARP-dependent cell death was accompanied by nuclear accumulation of apoptosis-inducing factor and a characteristic pattern of large-fragment DNA degradation. It is concluded that the PARP/apoptosis-inducing factor axis is critically involved in oxygen radical-induced apoptosis in cytotoxic lymphocytes.

NKp46 and NKG2D receptor expression in NK cells with CD56dim and CD56bright phenotype: regulation by histamine and reactive oxygen species

The cytotoxicity of natural killer (NK) cells is dependent on the interaction between target cell ligands and a series of stimulatory receptors on NK cells. Two of these triggering receptors, the NKp46 natural cytotoxicity receptor (NKp46) and the major histocompatibility complex (MHC) class I-interactive NKG2D receptor, are deficiently expressed by NK cells recovered from patients with acute myeloid leukaemia (AML), but little is known regarding the regulation of NKp46 and NKG2D expression. Here we report that mononuclear and polymorphonuclear phagocytes downregulate the cell surface density of NKp46 and NKG2D on NK cells with CD56(dim) phenotype in vitro by a mechanism that is dependent on the availability of phagocyte-derived reactive oxygen species (ROS). Histamine maintained NKp46 and NKG2D expression despite the presence of inhibitory phagocytes by targeting an H2 receptor on phagocytes. By contrast, NKp46 and NKG2D expression by the CD56(bright) subset of NK cells was resistant to inhibition by phagocytes. Our findings are suggestive of a novel mechanism of relevance to the regulation of NKp46/NKG2D receptor expression. Moreover, our findings suggest that the previously reported action of histamine on NK cell-mediated killing of leukaemic cells may be related to the preservation of activatory NK-cell receptors.

Mechanisms of tumor evasion

The results from in vitro immunological experiments, murine tumor models and patients with cancer clearly demonstrate that tumors have multiple mechanisms to evade the immune response. During the early stages of tumor development malignant cells can be poor stimulators, present poor targets or become resistant to the innate immune response, while at later stages, progressively growing tumors impair the adaptive immune response by blocking the maturation and function of antigen presenting cells and causing alterations in T cell signal transduction and function. Preliminary results also suggest a correlation between some of these changes and an increased metastatic potential of the tumor cells, a diminished response to immunotherapy, and poor prognosis. Carefully coordinated basic research studies and clinical immunotherapy trials will be required to fully determine the impact on the outcome of the disease and the response to treatment. However, understanding the mechanisms used by tumor cells to evade the immune system could result in new therapeutic approaches for preventing and/or reversing these immune alterations and have the potential of improving the current results of immunotherapy trials.

Analysis of the susceptibility of CD57 T cells to CD3-mediated apoptosis

After stimulation with anti-CD3 antibody in vitro, CD57(+) T cells showed a greater susceptibility to apoptosis than CD57(-)alphabetaT cell receptor (TCR)(+) T cells (regular alphabeta T cells). The apoptotic fraction of CD57(+) T cells showed an increased production of active caspase-3. An increase in both Fas expression and Fas-ligand (FasL) production was also observed in CD57(+) T cells, whereas the expression of survivin was suppressed in CD57(+) T cells compared to that of regular alphabeta T cells. CD57(+) T cells display a biased expansion of a few Vbeta T cell fractions in individuals, but such Vbeta T cells were not specifically susceptible to CD3-mediated apoptosis. The TCR expression level of CD57(+) T cells was much lower than that of regular T cells and anti-TCR antibody stimulation induced a smaller apoptotic proportion of CD57(+) T cells than did anti-CD3 antibody. Although the CD3epsilon expression levels were similar in both T cell subsets, the CD3zeta level of CD57(+) T cells was significantly higher than that of regular T cells. These results suggest that several apoptotic and anti-apoptotic molecules are involved in the CD3-induced apoptosis of CD57(+) T cells and raise the possibility that the imbalance in expression of the CD3epsilon and CD3zeta chains may also contribute to the susceptibility of CD57(+) T cells to undergo apoptosis.

Mechanisms of tumor evasion from the immune response

The results from in vitro immunological experiments, murine tumor models and patients with cancer clearly demonstrate that tumors have multiple mechanisms to evade the immune response. During the early stages of tumor development malignant cells can be poor stimulators, present poor targets or become resistant to the innate immune response, while at later stages, progressively growing tumors impair the adaptive immune response by blocking the maturation and function of APCs and causing alterations in T-cell signal transduction and function. Preliminary results also suggest a correlation between some of these changes and an increased metastatic potential of the tumor cells, a diminished response to immunotherapy, and poor prognosis. Carefully coordinated basic research studies and clinical immunotherapy trials will be required to fully determine the impact of these mechanisms of tumor evasion on the outcome of the disease and the response to treatment. However, understanding the mechanisms used by tumor cells to evade the immune system could result in new therapeutic approaches for preventing and/or reversing these immune alterations and could have the potential of improving the current results of immunotherapy trials.

Immunotherapy and immunoselection -- tumour escape as the final hurdle

Tumours are immunogenic and are commonly infiltrated by anti-cancer effector cells. Why, then, are they not completely rejected by the host? Unfortunately, tumours are Darwinian paragons, winning the battle against the forces of natural immune selection. Some of the latter can even act as double-edged swords, actually being subverted to become pro-tumorigenic. Prevention or reversal of tumour escape from the immune response therefore offers the possibility of reconstituting effective anti-tumour immunity and remains the major challenge for 21st century tumour immunology.

Graft-versus-leukemia reactions in allogeneic chimeras

There is a strong graft-versus-leukemia (GVL) effect of allogeneic stem cell transplantation (SCT) due to elimination of tumor cells by alloimmune effector lymphocytes. When leukemia relapses after allogeneic SCT, donor lymphocyte transfusions (DLTs) can induce sustained remissions in some patients. This review summarizes the current status on clinical use of DLT, the basis of GVL reactions, problems associated with this therapy, and new strategies to improve DLT. Several multicenter surveys demonstrated that the GVL effect of DLT is most effective in chronic myelogenous leukemia (CML), whereas it is less pronounced in acute leukemia and myeloma. Cytokine stimulation to induce differentiation of myeloid progenitor cells or to up-regulate costimulatory molecules on tumor cells may improve the efficacy of DLT. Infections and graft-versus-host disease (GVHD) are major complications of DLT. Control of GVHD may be improved using suicide gene-modified T cells for DLT, allowing T-cell elimination if severe GVHD develops. Hopefully, in the future, GVL effect can be separated from GVHD through adoptive transfer of selected T cells that recognize leukemia-specific antigens or minor histocompatibility antigens, which are expressed predominantly on hematopoietic cells, thereby precluding attack of normal tissues. In patients with leukemia and lymphomas with fast progression, tumor growth may outpace development of effector T cells. Here it may be preferable to select stem cell transplant donors with HLA-mismatches that allow alloreactive natural killer cells, which appear early after transplantation, to retain their cytolytic function. New approaches for adoptive immune therapy of leukemia, which promise a better prognosis for these patients, are being developed.

Signalling molecules and cytokine production in T cells of multiple myeloma-increased abnormalities with advancing stage

T-cell immune dysfunction in patients with malignant tumours has been attributed to the altered expression of components of the T-cell receptor (TCR)/CD3 complex and their associated intracellular protein tyrosine kinases. In this study, four-colour flow cytometry was applied to study the surface bound molecules TCRalphabeta, CD28, CD152 and CD154 involved in T-cell signalling and the signal transduction molecules CD3zeta, p56lck, p59fyn, ZAP-70 and phosphatidyl-inositol-3 kinase (PI3-k) as well as the intracellular cytokines interferon-gamma (IFN-gamma), interleukin (IL)-4 and IL-2 as a functional read-out of non-stimulated and superantigen (staphylococcus enterotoxin B)-stimulated blood T cells of multiple myeloma (MM) patients at different stages of the disease. Multiple abnormalities were demonstrated in the CD4 and CD8 populations, both under non-stimulated and superantigen-stimulated conditions. There was a marked reduction, particular in advanced stage MM, in the proportion of CD4 and CD8 cells expressing CD28, CD152, CD3zeta, p56lck, ZAP-70 and PI3-k. The level of intracellular T-cell cytokines (IFN-gamma, IL-2 and IL-4) was normal or increased in non-stimulated cells but activation-induced cytokine production was impaired. These results illustrated profound and multiple T-cell signalling defects, from the surface and down-stream, consistent with involvement of a master T-cell function, especially in advanced stage MM. These data should be taken into consideration when developing immune-based therapeutic approaches and when applying new emerging technologies that aim to restore T-cell functions.

No alteration in NK function or zeta chain expression in NK and T cells of cervical cancer patients

OBJECTIVE

To investigate in vitro natural killer (NK) cell activity and expression of signal-transducing zeta chains in patients with cervical cancer.

PATIENTS AND METHODS

Experiments were performed with frozen lymphocytes from patients at all disease stages and from healthy controls. Thawed NK were activated by overnight incubation in interferon-gamma (IFN-gamma); activity against two target cell lines was assessed by 4-h (51)Cr release assay. Targets chosen were K562, an erythroleukemic cell line, and a cervical carcinoma cell line designated 808. T and NK cell zeta chain expression was measured by flow cytometry.

RESULTS

Patients' NK were found to be as cytotoxic as those of normal controls against cell lines K562 and 808. Patient T and NK cells did not show significant down-regulation of the zeta chain.

CONCLUSIONS

We have found no evidence to suggest that loss of zeta chains is a mechanism for immunocompromise in patients with cervical carcinoma. IFN-recoverable patient NK activity is not reduced compared to matched controls. This may be clinically relevant since NK are active against cells exhibiting class I human leukocyte antigen (HLA) down-regulation and many cervical cancers show loss of HLA.

Quantification and cytokine production of circulating lymphoid and myeloid cells in acute myelogenous leukaemia

A simple assay was developed to assess the potential of patients with acute myelogenous leukaemia (AML) to respond to immunotherapy. Lymphocytes, monocytes and leukaemic blasts with their corresponding intracellular cytokine profiles were evaluated by four-colour flow cytometry. In 50 microl samples of whole blood, surface labelling for CD45, CD8 and CD3 was used for cell identification prior to intracellular staining for interleukin (IL)-4, IL-10, IL-12 and interferon (IFN)-gamma. Absolute numbers of CD8(+) and CD8(-) (putative CD4(+)) T-cells, NK cells (CD8(+)/CD3(-)) and monocytes were determined by reference to a fixed number of added fluorescent beads. The absolute numbers of CD8(-) and CD8(+) T-cells in the blood of patients with AML were similar to those of normal controls. More of the lymphocytes in the blood of leukaemic patients spontaneously produced cytokines compared with those of controls. Furthermore, primary AML blasts secreted predominantly IFN-gamma. After recovery from chemotherapy, lymphocyte counts tended to be lower than in normals and reduction of NK cells reached significance after the second chemotherapy (P=0.01). A prominent CD8(lo)/CD3(lo-int) lymphocyte subset appeared after recovery in some patients. This laboratory application of the study of cell subsets and intracellular cytokines in patients undergoing treatment may be helpful in monitoring immunological responses in AML.

Biology of natural killer cells in cancer and infection

NK cells are the important cells of the immune system derived from stem cells in the marrow. Their physiology is tightly regulated to control proliferation, cytotoxicity and cytokine production. In cancer, NK cells may be abnormal due to the cancer itself or possibly related to its therapy. The finding of class I recognizing inhibitory receptors may play a role in stem cell transplant rejection, immune surveillance and cancer immunotherapy. NK cells should no longer be thought of as direct cytotoxic killers alone, as they clearly play a critical role in cytokine production which may be important to control cancer and infection. Understanding NK cell function and homing may lead to novel therapeutic strategies for the treatment of human disease.

Defective expression and function of natural killer cell-triggering receptors in patients with acute myeloid leukemia

The cytolytic function of natural killer (NK) cells is induced by the engagement of a series of activating receptors and coreceptors some of which have recently been identified and collectively termed natural cytotoxicity receptors (NCRs). Here, we analyzed the cytolytic function of NK cells obtained from patients with acute myeloid leukemia (AML). In sharp contrast with healthy donors, in most (16 of 18) patients with AML the majority of NK cells displayed low NCR surface density (NCR(dull)). This phenotype correlated with a weak cytolytic activity against autologous leukemic cells that could not be reversed by the monoclonal antibody-mediated disruption of HLA class I/killer immunoglobulinlike receptor interaction. The remaining 2 patients were characterized by NK cells having an NCR(bright) phenotype. Surprisingly, although displaying NCR-mediated cytolytic activity, these NCR(bright) NK cells were unable to kill autologous leukemic blasts. Importantly, the leukemic blasts from these 2 patients were also resistant to lysis mediated by normal NCR(bright) allogeneic NK cells. Our study suggests that in most instances the inability of NK cells to kill autologous leukemic blasts is consequent to low NCR surface expression. In few cases, however, this failure appears to involve a mechanism of tumor escape based on down-regulation of ligands relevant for NCR-mediated target cell recognition.

Microenvironment produced by acute myeloid leukemia cells prevents T cell activation and proliferation by inhibition of NF-kappaB, c-Myc, and pRb pathways

Tumors produce a variety of immunosuppressive factors which can prevent the proliferation and maturation of a number of normal hemopoietic cell types. We have investigated whether primary acute myeloid leukemia (AML) cells have an effect on normal T cell function and signaling. Tumor cell supernatant (TSN) from AML cells inhibited T cell activation and Th1 cytokine production and also prevented activated T cells from entering the cell cycle. These effects occurred in the absence of AML cell-T cell contact. We have demonstrated that AML TSN contained none of the immunosuppressors described to date, namely gangliosides, nitric oxide, TGF-beta, IL-10, vascular endothelial growth factor, or PGs. Furthermore, IL-2 did not overcome the block, despite normal IL-2R expression. However, the effect was overcome by preincubation with inhibitors of protein secretion and abolished by trypsinization, indicating that the active substance includes one or more proteins. To determine the mechanism of inhibition, we have studied many of the major pathways involved in T cell activation and proliferation. We show that nuclear translocation of NFATc and NF-kappaB are markedly reduced in T cells activated in the presence of primary AML cells. In contrast, calcium mobilization and activation of other signal transduction pathways, namely extracellular signal-regulated kinase1/2, p38, and STAT5 were unaffected, but activation of c-Jun N-terminal kinase 1/2 was delayed. Phosphorylation of pRb by cyclin-dependent kinase 6/4-cyclin D and of p130 did not occur and c-Myc, cyclin D3, and p107 were not induced, consistent with cell cycle inhibition early during the transition from G(0) to G(1). Our data indicate that TSN generated by AML cells induces T cell immunosuppression and provides a mechanism by which the leukemic clone could evade T cell-mediated killing.

Reduced T-cell receptor CD3zeta-chain protein and sustained CD3epsilon expression at the site of mycobacterial infection

Control of mycobacterial infection by the cellular immune system relies both on antigen-presenting cells and on T lymphocytes. The quality of an effective cellular immune response is dependent on functional signal transduction residing in the cytoplasmic tails of the T-cell receptor CD3 components. In order to investigate potential effects of mycobacteria on T-cell receptor signalling, we examined the protein expression of T-cell signal transduction molecules (CD3zeta, ZAP-70, p59fyn, p56lck). In Western blots of peripheral blood mononuclear cells of Mycobacterium tuberculosis infected patients, only the CD3zeta-chain showed a marked reduction in protein expression. To investigate the situation in situ, immunoenzymatic and immunofluorescence stainings for CD3epsilon and CD3zeta expression were performed on sections of normal lymphoid tissue, M. leprae infected and sarcoid tissue. CD3epsilon and CD3zeta expression were similar with respect to intensity, localization and the number of cells stained in normal lymphoid tissue and in sarcoid granulomas. In contrast, the granulomas of M. leprae infected tissues showed a significantly reduced expression of CD3zeta compared to CD3epsilon. Using double immunofluorescence analysis, virtually no CD3zeta expression could be detected in comparison to the CD3epsilon expression in the lesions. Apparently, mycobacteria are capable of significantly reducing CD3zeta-chain expression, which may be restored by cytokines. IL-2-enhanced zeta-chain expression and T-cell effector functions, defined by interferon-gamma release, in M. tuberculosis-specific and human leucocyte antigen-DR restricted CD4+ T cells isolated from granuloma lesions from patients with pulmonary tuberculosis. Because CD3zeta is essential for CD3 signalling and for eliciting T-cell effector functions, reduced CD3zeta protein expression could result in altered signal transduction and inefficient T-cell effector functions. Alternatively, reduced CD3zeta-chain expression may protect T cells from repetitive TCR stimulation associated with anergy or apoptosis.

The biology of natural killer cells in cancer, infection, and pregnancy

OBJECTIVE

NK cells are important cells of the immune system. They are ultimately derived from pluripotent hematopoietic stem cells. NK cell cytotoxicity and other functions are tightly regulated by numerous activating and inhibitory receptors including newly discovered receptors that selectively recognize major histocompatibility complex class I alleles. Based on their defining function of spontaneous cytotoxicity without prior immunization, NK cells have been thought to play a critical role in immune surveillance and cancer therapy. However, new insights into NK cell biology have suggested major roles for NK cells in infection control and uterine function. The purpose of this review is to provide an update on NK cell function, ontogeny, and biology in order to better understand the role of NK cells in health and disease.

DATA SOURCES

In the Medline database, the major subject heading "Natural Killer Cells" was introduced in 1983, identifying 16,848 citations as of December 31, 2000. Since 1986, there have been approximately 1000 citations per year under this subject heading. In this database, 68% of manuscripts are limited to human NK cells; 40% of citations cross with the major sub-heading of cytotoxicity, 40% with cytokines, 36% with neoplasm, 5% with antibody-dependent cellular cytotoxicity, 2.8% with pregnancy, and 1.3% with infection. Of references from the year 2000-2001, 46 were selected to combine with contributions from earlier literature.

CONCLUSIONS

NK cells should no longer be thought of as direct cytotoxic killers alone as they clearly serve a critical role in cytokine production which may be important to control cancer, infection, and fetal implantation. Understanding mechanisms of NK cell functions may lead to novel therapeutic strategies for the treatment of human disease.

Targeting of a B7-1 (CD80) immunoglobulin G fusion protein to acute myeloid leukemia blasts increases their costimulatory activity for autologous remission T cells

Transfection of tumor cells with the gene encoding the costimulatory molecule B7-1 (CD80), the ligand for CD28 and cytotoxic T lymphocye antigen-4 on T cells, has been shown to result in potent T-cell-mediated antitumor immunity. As an alternative approach, this study analyzed the costimulatory capacity of a human B7-1 immunoglobulin G (IgG) fusion protein targeted to the cell membrane of human acute myeloid leukemia (AML) blasts. Flow cytometric analysis revealed a low constitutive expression of B7-1 on human AML blasts (on average, 3.0 +/- 4.3%; n = 50). In contrast, the expression of B7-2 (CD86) was highly heterogeneous and higher in AML blasts of French-American-British classification types M4 and M5 (P <.0001). The B7-1 IgG fusion protein used in this study efficiently costimulated the proliferation of resting and preactivated T cells when immobilized on plastic. After preincubation with B7-1 IgG, specific binding of the fusion protein to the high-affinity Fcgammareceptor I (CD64) on leukemic cells was demonstrated and was found to increase the proliferation of both allogeneic and autologous T cells in costimulation experiments. Furthermore, targeting of B7-1 IgG to the tumor membrane resulted in increased proliferation of autologous remission T cells and had the potential to generate an enhanced redirected cytotoxic T-cell response against autologous AML blasts. In summary, the targeting of B7-1 IgG fusion protein described in this study represents a strategy alternative to gene therapy to restore the expression of the costimulatory molecule B7-1 on human AML blasts, thereby enhancing their immunogenicity for autologous T cells. This new approach may have implications for T-cell-mediated immunotherapy in AML.

Alleviating oxidative stress in cancer immunotherapy: a role for histamine?

Interleukin-2 is a remarkable activator of lymphocytes with anti-neoplastic properties such as T-cells or natural killer cells, but tumor regression only rarely occurs in interleukin-2-treated cancer patients. In this review, we focus on interactions between monocytes/macrophages and T-cells/natural killer-cells, and in particular the role of such interactions for the outcome of cancer immunotherapy with interleukin-2. We propose that interleukin-2 therapy should be supplemented with compounds that alleviate toxicity inflicted by monocyte/macrophage-derived reactive oxygen metabolites within and around tumors. The hypothesis is founded on data demonstrating that (i) functions of intratumoral lymphocytes in many human malignant tumors are inhibited by reactive oxygen metabolites, generated by neighboring monocytes/macrophages, (ii) interleukin-2 only weakly activates T-cells or natural killer cells in an environment of oxidative stress, and (iii) inhibitors of the formation of reactive oxygen metabolites or scavengers of reactive oxygen metabolites synergize with interleukin-2 to activate these lymphocyte subsets. We also review the preclinical background to the use of histamine dihydrochloride, an inhibitor of reactive oxygen metabolite formation in monocytes/macrophages, as a supplement to cancer immunotherapy with interleukin-2.

Natural killer cell dysfunction and apoptosis induced by chronic myelogenous leukemia cells: role of reactive oxygen species and regulation by histamine

Natural killer (NK) cells are deficient in patients with chronic myelogenous leukemia (CML), but the mechanisms responsible for the dysfunction are not completely understood. This study reports that CML cells effectively inhibit the baseline and interleukin-2 (IL-2)-induced NK cell cytotoxicity against a CML cell-derived line (K562). A sizable fraction of NK cells subsequently acquired features characteristic of programmed cell death/apoptosis. The CML cell-mediated inhibition of NK cells required triggering of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-mediated formation of reactive oxygen species (ROS) and was prevented by catalase, a scavenger of ROS, and by histamine, acting via H2-receptor–mediated inhibition of ROS production in CML cells. In contrast, nonmalignant neutrophilic granulocytes inhibited NK cells via ROS production without the requirement of exogenous NADPH oxidase-triggering stimuli. We propose that paracrine production of ROS may contribute to the dysfunction of NK cells in CML and that histamine may serve as an autocrine inhibitor of ROS formation in leukemic granulocytes.

Natural killer cell dysfunction and apoptosis induced by chronic myelogenous leukemia cells: role of reactive oxygen species and regulation by histamine

Natural killer (NK) cells are deficient in patients with chronic myelogenous leukemia (CML), but the mechanisms responsible for the dysfunction are not completely understood. This study reports that CML cells effectively inhibit the baseline and interleukin-2 (IL-2)-induced NK cell cytotoxicity against a CML cell-derived line (K562). A sizable fraction of NK cells subsequently acquired features characteristic of programmed cell death/apoptosis. The CML cell-mediated inhibition of NK cells required triggering of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-mediated formation of reactive oxygen species (ROS) and was prevented by catalase, a scavenger of ROS, and by histamine, acting via H2-receptor–mediated inhibition of ROS production in CML cells. In contrast, nonmalignant neutrophilic granulocytes inhibited NK cells via ROS production without the requirement of exogenous NADPH oxidase-triggering stimuli. We propose that paracrine production of ROS may contribute to the dysfunction of NK cells in CML and that histamine may serve as an autocrine inhibitor of ROS formation in leukemic granulocytes.

Histamine: a novel approach to cancer immunotherapy

The functions of intratumoral lymphocytes in many human malignant tumors are inhibited by reactive oxygen species (ROS), generated by adjacent monocytes/macrophages (MO). In vitro data suggest that immunotherapeutic cytokines such as interleukin-2 (IL-2) or interferon-alpha (IFN-alpha) only weakly activate T cells or natural killer (NK) cells in a reconstituted environment of oxidative stress and that inhibitors of the formation of ROS or scavengers of ROS synergize with IL-2 and IFN-alpha to activate T cells and NK cells. In this review, we focus on the immunoenhancing properties of histamine, a biogenic amine. Histamine inhibits ROS formation in MO via H2-receptors; thereby, histamine protects NK cells from MO-mediated inhibition and synergizes with IL-2 and IFN-alpha to induce killing of NK cell-sensitive human tumor cells in vitro. Histamine also optimizes cytokine-induced activation of several subsets of T cells by affording protection against MO-inflicted oxidative inhibition. The putative clinical benefit of histamine as an adjunct to immunotherapy with IL-2 and/or IFN-alpha is currently evaluated in clinical trials in metastatic malignant melanoma and acute myelogenous leukemia.

All infiltrating T-lymphocytes in Hodgkin's disease express immunohistochemically detectable T-cell receptor zeta-chains in situ

AIM

We studied the expression of TCR zeta-chain on tumour-infiltrating lymphocytes in EBV-positive and EBV-negative cases of Hodgkin's disease (HD), to assess whether downregulation of TCR zeta-chain on tumour-infiltrating lymphocytes might be a mechanism for immune escape of the neoplastic cells.

METHODS AND RESULTS

By immunohistochemistry we investigated tissue of 27 cases of primary HD, both paraffin embedded and frozen, for the presence of T-cell receptor complex zeta-chain and other T-cell markers on the reactive cells. Strong membranous staining of TCR zeta-chain was present in all cases in frozen tissue. In contrast, in paraffin-embedded material substantial loss of TCR zeta-chain was detected in old (> 6 years) tissues. However, no differences in either the number of positive cells or their staining intensity were observed in EBV-positive and negative cases of HD as detected in frozen tissue. Storage of paraffin-embedded tissue leads to a rapid and substantial loss of TCR zeta-chain reactivity compared to frozen material of the same HD cases. Staining reactivity of other T-cell markers (CD3, CD4 and CD8) on paraffin-embedded material remained unaffected. Immunofluorescent double-staining confirmed colocalization and coexpression of TCR zeta-chain and CD3.

CONCLUSIONS

In frozen biopsies of primary HD TCR zeta-chain was expressed on all reactive CD3-positive cells, both in EBV-positive and EBV-negative cases. This suggests that zeta-chain downregulation is not a likely mechanism whereby neoplastic cells of HD can escape immune surveillance.

Sustaining the graft-versus-tumor effect through posttransplant immunization with granulocyte-macrophage colony-stimulating factor (GM-CSF)–producing tumor vaccines

For many cancers, autologous bone marrow transplantation (BMT) achieves a minimal residual disease state, yet relapse rates remain high. Using a syngeneic murine bone marrow transplant model, we demonstrate that vaccination with irradiated granulocyte-macrophage colony-stimulating factor (GM-CSF)–producing autologous tumor cells is effective in the post-BMT period and actually results in a greater tumor-free survival than vaccination in the nontransplant setting. Employing T cells specific for a model tumor-antigen, we find that transplantation of the tumor-bearing host results in a massive expansion and activation of tumor-specific T cells in the early posttransplant period, but this response rapidly declines in association with tumor progression. Immunization with irradiated GM-CSF tumor cells during the period of immune reconstitution results in the sustained amplification and activation of this response that closely correlates with freedom from relapse. These results demonstrate the feasibility of integrating GM-CSF vaccines in the postautologous BMT setting and suggest mechanisms that may contribute to the observed efficacy of immunization during the critical period of immune reconstitution.

Sustaining the graft-versus-tumor effect through posttransplant immunization with granulocyte-macrophage colony-stimulating factor (GM-CSF)–producing tumor vaccines

For many cancers, autologous bone marrow transplantation (BMT) achieves a minimal residual disease state, yet relapse rates remain high. Using a syngeneic murine bone marrow transplant model, we demonstrate that vaccination with irradiated granulocyte-macrophage colony-stimulating factor (GM-CSF)–producing autologous tumor cells is effective in the post-BMT period and actually results in a greater tumor-free survival than vaccination in the nontransplant setting. Employing T cells specific for a model tumor-antigen, we find that transplantation of the tumor-bearing host results in a massive expansion and activation of tumor-specific T cells in the early posttransplant period, but this response rapidly declines in association with tumor progression. Immunization with irradiated GM-CSF tumor cells during the period of immune reconstitution results in the sustained amplification and activation of this response that closely correlates with freedom from relapse. These results demonstrate the feasibility of integrating GM-CSF vaccines in the postautologous BMT setting and suggest mechanisms that may contribute to the observed efficacy of immunization during the critical period of immune reconstitution.

Adjuvant histamine in cancer immunotherapy

Interleukin-2 (IL-2) is an effective activator of lymphocytes with anti-neoplastic properties such as T-cells or natural killer cells, and this property of IL-2 has formed the basis for its widespread used as an immunotherapeutic agent in human neoplastic disease. In recent years, IL-2 therapy for solid neoplastic diseases and hematopoietic cancers has been supplemented with histamine dihydrochloride with the aim of counteracting immunosuppressive signals from monocytes/macrophages. Here we review the preclinical basis for the use of histamine as an adjunct to IL-2 in cancer immunotherapy.

Immunotherapy of AML: future directions

Immunotherapy in the form of allogeneic GvL has been curing AML patients for nearly 30 years but our understanding of the mechanisms has been poor. Our rapidly evolving understanding of the human immune system and the concomitant technical developments in ex vivo cell manipulation, the vision of funding bodies, the dedication of clinical and research staff, and above all the commitment of our patients, promise substantial progress in the treatment of this disease in the year 2000 and beyond.

New Developments in the Therapy of Acute Myelocytic Leukemia

Current conventional treatment for patients with acute myelogenous leukemia results in a high percentage of clinical responses in most patients. However, a high percentage of patients still remain refractory to primary therapy or relapse later. This review examines the search for new agents and new modes of therapy. In Section I, Dr. Estey discusses new agents directed at various targets, such as CD33, angiogenesis, inappropriately methylated (suppressor) genes, cell cycle checkpoints, proteosomes, multidrug resistance (MDR) gene, mitochondrial apoptotic pathway. He also reviews preliminary results of phase I trials with the nucleoside analog troxacitabine and liposomal anthracyclin and suggests new strategies for trials of new agents.

In Section II, Dr. Jones revisits differentiation therapy and presents results of preclinical and clinical studies that demonstrate that a variety of clinically applicable cell cycle inhibitors (interferon, phenylbutyrate, vitamin D, retinoids, bryostatin-1) preferentially augments growth factor-mediated induction of myeloid leukemia terminal differentiation, as well as blocks growth factors' effects on leukemia proliferation. The combination of cell cycle inhibition plus myeloid growth factors may offer a potential treatment for resistant myeloid leukemias.

In Section III, Drs. Levitsky and Borrello address the question of tumor vaccination in AML and shows that, although tumor rejection antigens in AML have not been formally identified to date, a growing number of attractive candidates are ripe for testing with defined antigen-specific vaccine strategies. Interestingly, the ability to drive leukemic blasts to differentiate into competent antigen presenting cells such as dendritic cells may be exploited in the creation of cellular vaccines. Ultimately, the successful development of active immunotherapy for AML will require integration with dose-intensive chemotherapy, necessitating a more complete understanding of host immune reconstitution.

In Section IV, Dr. Slavin reviews the concept of delivering non-myeloablative stem cell transplantation (NST) and delayed lymphocyte infusion (DLI) to increase tolerance in particular in high risk and older patients, and take advantage of the graft-versus-leukemia (GVL) effect.

All these approaches hold promise in reducing morbidity and mortality and differ from the older concepts aiming at delivering the highest possible doses of chemotherapy and/or total body irradiation to reach maximum leukemia cell kill, whatever the toxicity to the patient.

New Developments in the Therapy of Acute Myelocytic Leukemia

Current conventional treatment for patients with acute myelogenous leukemia results in a high percentage of clinical responses in most patients. However, a high percentage of patients still remain refractory to primary therapy or relapse later. This review examines the search for new agents and new modes of therapy. In Section I, Dr. Estey discusses new agents directed at various targets, such as CD33, angiogenesis, inappropriately methylated (suppressor) genes, cell cycle checkpoints, proteosomes, multidrug resistance (MDR) gene, mitochondrial apoptotic pathway. He also reviews preliminary results of phase I trials with the nucleoside analog troxacitabine and liposomal anthracyclin and suggests new strategies for trials of new agents.

In Section II, Dr. Jones revisits differentiation therapy and presents results of preclinical and clinical studies that demonstrate that a variety of clinically applicable cell cycle inhibitors (interferon, phenylbutyrate, vitamin D, retinoids, bryostatin-1) preferentially augments growth factor-mediated induction of myeloid leukemia terminal differentiation, as well as blocks growth factors' effects on leukemia proliferation. The combination of cell cycle inhibition plus myeloid growth factors may offer a potential treatment for resistant myeloid leukemias.

In Section III, Drs. Levitsky and Borrello address the question of tumor vaccination in AML and shows that, although tumor rejection antigens in AML have not been formally identified to date, a growing number of attractive candidates are ripe for testing with defined antigen-specific vaccine strategies. Interestingly, the ability to drive leukemic blasts to differentiate into competent antigen presenting cells such as dendritic cells may be exploited in the creation of cellular vaccines. Ultimately, the successful development of active immunotherapy for AML will require integration with dose-intensive chemotherapy, necessitating a more complete understanding of host immune reconstitution.

In Section IV, Dr. Slavin reviews the concept of delivering non-myeloablative stem cell transplantation (NST) and delayed lymphocyte infusion (DLI) to increase tolerance in particular in high risk and older patients, and take advantage of the graft-versus-leukemia (GVL) effect.

All these approaches hold promise in reducing morbidity and mortality and differ from the older concepts aiming at delivering the highest possible doses of chemotherapy and/or total body irradiation to reach maximum leukemia cell kill, whatever the toxicity to the patient.

Expression of signal-transducing zeta chain in peripheral blood T cells and natural killer cells in patients with Hodgkin's disease in different phases of the disease

A number of phenotypic and functional alterations have been described in T cells of cancer patients. These changes are believed to reflect an impaired T-cell mediated immunity, which in turn, may result in a decreased capacity to generate an effective antitumor response. Several mechanisms have been proposed to explain depressed immunity in cancer patients including tumor-derived suppressor factors, abnormal cytokine production, deletion or inactivation of tumor-reactive T-cells. To investigate the mechanism underlying the immunodeficiency in Hodgkin's disease (HD) we studied the expression of T cell receptor zeta chain, which plays a vital role in the cascade of events leading to T and NK cell activation. The expression of the zeta chain of the T cell receptor/CD3 complex was analyzed by dual colour immunofluorescence on peripheral blood T lymphocytes: CD3+, CD4+, CD8+ and NK-cells (CD56+) in patients in different phases of the disease. Zeta chain was significantly reduced on CD3, CD4, CD8, and CD56 positive cells from patients in active phase of the disease compared with normal controls (p=0.05). In patients tested in complete clinical remission the values were normal except for the subpopulation of CD8+ cells in which the expression of zeta chain remained significantly reduced compared with controls. Downregulation of CD3/zeta-chain in PBLs and NK cells in active phase of HD- and to a lesser extent in clinical remission may contribute to immunodeficiency associated with the disease.

Histamine protects T cells and natural killer cells against oxidative stress

Oxidative stress inflicted by monocytes/macrophages (MO) is recognized as an important immunosuppressive mechanism in human neoplastic disease. We report that two types of lymphocytes of relevance for protection against malignant cells, T cells and natural killer (NK) cells, became anergic to the T cell and NK cell activator interleukin-2 (IL-2) after exposure to MO-derived reactive oxygen metabolites and subsequently acquired features characteristic of apoptosis. The MO-induced anergy and apoptosis in T cells and NK cells were reversed by histamine, an inhibitor of reactive oxygen metabolite synthesis in MO. We propose that strategies to circumvent oxidative inhibition of lymphocytes may be of benefit in immunotherapy of neoplastic disease.