Régis Costello

Reciprocal Expression of the TNF Family Receptor Herpes Virus Entry Mediator and Its Ligand LIGHT on Activated T Cells: LIGHT Down-Regulates Its Own Receptor

The TNF receptor (TNFR) family plays a central role in the development of the immune response. Here we describe the reciprocal regulation of the recently identified TNFR superfamily member herpes virus entry mediator (HVEM) (TR2) and its ligand LIGHT (TL4) on T cells following activation and the mechanism of this process. T cell activation resulted in down-regulation of HVEM and up-regulation of LIGHT, which were both more pronounced in CD8+ than CD4+ T lymphocytes. The analysis of HVEM and LIGHT mRNA showed an increase in the steady state level of both mRNAs following stimulation. LIGHT, which was present in cytoplasm of resting T cells, was induced both in cytoplasm and at the cell surface. For HVEM, activation resulted in cellular redistribution, with its disappearance from cell surface. HVEM down-regulation did not rely on de novo protein synthesis, in contrast to the partial dependence of LIGHT induction. Matrix metalloproteinase inhibitors did not modify HVEM expression, but did enhance LIGHT accumulation at the cell surface. However, HVEM down-regulation was partially blocked by a neutralizing mAb to LIGHT or an HVEM-Fc fusion protein during activation. As a model, we propose that following stimulation, membrane or secreted LIGHT binds to HVEM and induces receptor down-regulation. Degradation or release of LIGHT by matrix metalloproteinases then contributes to the return to baseline levels for both LIGHT and HVEM. These results reveal a self-regulating ligand/receptor system that contributes to T cell activation through the interaction of T cells with each other and probably with other cells of the immune system.

The TNF Superfamily Members LIGHT and CD154 (CD40 Ligand) Costimulate Induction of Dendritic Cell Maturation and Elicit Specific CTL Activity

LIGHT is a recently identified member of the TNF superfamily that is up-regulated upon activation of T cells. Herpesvirus entry mediator, one of its receptors, is constitutively expressed on immature dendritic cells (DCs). In this report, we demonstrate that LIGHT induces partial DC maturation as demonstrated by Ag presentation and up-regulation of adhesion and costimulatory molecules. LIGHT-stimulated DCs show reduced macropinocytosis and enhanced allogeneic stimulatory capacity but fail to produce significant amounts of IL-12, IL-6, IL-1β, or TNF-α compared with unstimulated DCs. However, LIGHT cooperates with CD154 (CD40 ligand) in DC maturation, with particular potentiation of allogeneic T cell proliferation and cytokine secretion of IL-12, IL-6, and TNF-α. Moreover, LIGHT costimulation allows DCs to prime in vitro-enhanced specific CTL responses. Our results suggest that LIGHT plays an important role in DC-mediated immune responses by regulating CD154 signals and represents a potential tool for DC-based cancer immunotherapy.

Surface expression and function of p75/AIRM-1 or CD33 in acute myeloid leukemias: Engagement of CD33 induces apoptosis of leukemic cells

p75/AIRM-1 is a recently identified inhibitory receptor expressed by natural killer and myeloid cells displaying high homology with CD33. Crosslinking of p75/AIRM-1 or CD33 has been shown to sharply inhibit the in vitro proliferation of both normal myeloid cells and chronic myeloid leukemias. In this study, we analyzed acute myeloid leukemic cells for the expression of p75/AIRM-1. p75/AIRM-1 marked the M5 (11/12) and M4 (2/2) but not the M1, M2, and M3 subtypes according to the French–American–British classification. Cell samples from 12 acute myeloid leukemias were cultured in the presence of granulocyte/macrophage colony-stimulating factor. Addition to these cultures of anti-CD33 antibody resulted in ≈70% inhibition of cell proliferation as assessed by [3H]thymidine uptake or by the recovery of viable cells. Anti-p75/AIRM-1 antibody exerted a strong inhibitory effect only in two cases characterized by a high in vitro proliferation rate. After crosslinking of CD33 (but not of p75/AIRM-1), leukemic cells bound Annexin V and displayed changes in their light-scattering properties and nucleosomal DNA fragmentation, thus providing evidence for the occurrence of apoptotic cell death. Remarkably, when anti-CD33 antibody was used in combination with concentrations of etoposide insufficient to induce apoptosis when used alone, a synergistic effect could be detected in the induction of leukemic cell death. These studies provide the rationale for new therapeutic approaches in myeloid leukemias by using both chemotherapy and apoptosis-inducing mAbs.

What is the real role of CD40 in cancer immunotherapy

Abstract The CD40–CD40 ligand (CD40L) system is of pivotal importance in the immune response via interactions between T cells and antigen-presenting cells. Recent reports have demonstrated that CD40 triggering improves tumour immunogenicity. Nonetheless, as discussed here, the implications of the CD40–CD40L system in host–tumour interactions are pleiotropic and should be evaluated carefully before targeting CD40 for antitumour strategies.

Primary plasma cell leukaemia: a report of 18 cases

Primary plasma cell leukaemia (P-PCL) is a variant of multiple myeloma (MM) first diagnosed in the leukemic phase, with >2000/mm(3) circulating plasma cells (PCs) and plasmacytosis >20% of the white cell count. We investigated the clinical characteristics, therapy, immunophenotype and prognosis factors of 18 patients. Common features at diagnosis were asthenia (seven patients), renal insufficiency (ten patients), bone pain (seven patients), splenomegaly or hepatomegaly (five patients). Hypercalcemia was present at diagnosis in seven patients and was the most potent poor prognosis factor (P<0.05). Most patients (16 out of 18) were treated with an anthracyclin containing regiment; complete remission was attained in one patient and partial remission in 11 patients while six patients had no response. The median survival time from diagnosis was 7 months (2--12, 95% confidence interval), but response to treatment had favorable predictive value (P<0.05). The PCs were usually positive for mature B-cell markers (PCA-1, CD38). They expressed integrins which may increase their binding to endothelial cells and thus participate in PCL physiopathology by favoring plasmocyte extramedullary spread.

Regulation of CD80/B7‐1 and CD86/B7‐2 molecule expression in human primary acute myeloid leukemia and their role in allogenic immune recognition

Clinical data and animal models afford evidence for anti‐leukemia immunity in humans, but the interactions critical for blast cell recognition are unresolved. Expression of B7 molecules by antigen‐presenting cells (APC) provides co‐stimulatory signals to T lymphocytes via CD28 and CTLA‐4 which prevent the induction of alloantigen‐specific tolerance. Conversely, expression of CD40 ligand by stimulated T cells activates APC via CD40. In human hematological B cell malignancies (follicular lymphoma and chronic lymphocytic leukemia), the defect in alloantigen presentation of tumoral cells can be repaired by up‐regulation of B7 and other co‐stimulatory molecules via CD40. We studied the role of B7 molecules in alloimmune recognition and the various ways to improve the antitumoral response on peripheral blood leukemic cells from 20 patients with a diagnosis of primary acute myeloid leukemia (AML). We focused on myelo/monocytic M4/M5 French‐American‐British classification subtypes which are considered as the neoplastic counterpart of normal monocytes, a prototypic APC. In one‐way mixed lymphocyte reaction of CD4+ T cells against leukemic cells, differences in B7‐1, B7‐2 or CD40 expression by AML cells did not induce specific cytokine secretion; interleukin (IL)‐2 and interferon (IFN)‐γ were detected but not IL‐4, corresponding to a Th1 pattern. Blockade experiments showed that proliferation and IFN‐γ secretion only partially depended on B7 molecules, which in contrast had a pivotal role in IL‐2 synthesis. In contrast with murine models which suggest a pivotal role for CD80/B7‐1 in the immune response against AML, our data support a greater role for CD86/B7‐2, in line with the baseline expression of CD86/B7‐2 and lack of CD80/B7‐1 on most M4/M5 AML cells. AML cell stimulation via CD40: (1) significantly improved IL‐2 secretion but not proliferation of responding T lymphocytes, (2) increased CD54/ICAM‐1 expression in three quarters of cases, (3) failed in most cases to induce CD40‐specific CD80/B7‐1 up‐regulation and (4) had a weak effect on CD86/B7‐2 expression. These data contrast with the very efficient up‐regulation of both B7 co‐stimulatory molecule expression and tumoral cell alloimmune recognition following CD40 stimulation in B cell malignancy models. The role of the defective B7 molecule up‐regulation by the CD40 pathway in inefficient tumor immunogenicity of primary AML cells has to be further investigated, in particular using transfection experiments of CD80/B7‐1‐deficient AML cell lines. From our in vitro data we conclude that B7 molecules play an important role in the alloimmune surveillance of AML as suggested by the high B7 molecule dependency of IL‐2 secretion. Nonetheless, the contribution of B7 molecules to alloimmune T cell proliferation against primary AML cells in human and the way to improve it – regulation via CD40 in particular – differ from B cell malignancies and murine models, suggesting the requirement for specific strategies in the development of antitumor immunity.

LIGHT costimulates CD40 triggering and induces immunoglobulin secretion; a novel key partner in T cell‐dependent B cell terminal differentiation

The T cell‐dependent differentiation and function of B lymphocytes are tightly regulated by TNF ligands (L) and receptors interactions, such as CD40/CD40L, CD27/CD70 and CD134/CD314L. The LIGHT/HVEM system [homologous to lymphotoxin, inducible expression, competing for GpD of herpes virus, that binds to the herpes virus entry mediator (HVEM), and is expressed on activated T lymphocytes) focused our attention since HVEM has a large distribution that, in addition to T cells, DC or NK, includes tumor and normal B lymphocytes. HVEM was expressed on memory and naive B cells from peripheral blood or tonsils, but not on germinal center (GC) B cells. Costimulation by CD40L+LIGHT induced LIGHT expression at the B lymphocyte surface by a transcriptional mechanism since we detected de novo expression of LIGHT‐specific mRNA. LIGHT expression was further enhanced by triggering of surface IgM, a stimulus that mimics a normal step of B cell physiology, i.e. specific antigen encounter. Stimulation by LIGHT increased the B cell proliferation induced by CD40L, and induced IgG and IgM (but not IgA) secretion. We conclude that LIGHT costimulation, that mimics the B cell encounter with activated LIGHT‐expressing T lymphocytes, enhances both B cell proliferation and Ig production, and thus has a central importance for humoral immunity development.

The co-expression of 2B4 (CD244) and CD160 delineates a subpopulation of human CD8+ T cells with a potent CD160-mediated cytolytic effector function.

Within human CD8+ T lymphocytes, the CD27−CD45RAhigh or CD56+ phenotypes contribute to precisely define the cells with CTL effector function. Novel markers were demonstrated to correlate with CTL properties, such as the 2B4 (CD244) receptor, a member of the CD2 subset of the immunoglobulin superfamily or the glycosylphosphatidylinositol‐anchored CD160 receptor. We performed a study of these markers to further define the population of effectors with CTL functions. Here we show that cytotoxic subpopulations defined by surface markers CD160, CD56 and CD57 are mostly contained in the 2B4+CD8+ T cell population. Expression of CD160 identifies two populations in the 2B4+ population. The 2B4+CD160+ subset expresses a bona fide CTL phenotype. The co‐expression of 2B4 and CD160 defines T cells containing high amounts of perforin and granzyme B. During CTL ontogeny, an up‐regulation of 2B4 and CD160 is observed from a naive to a terminally differentiated phenotype. Finally, we demonstrated that CD160 triggering failed to induce cytotoxicity per se, but costimulated CD3‐redirected killing. We conclude that the co‐expression of 2B4 and CD160 defines a CD8+ T lymphocyte subpopulation with high CTL activity.

Hematological malignancies escape from NK cell innate immune surveillance: mechanisms and therapeutic implications.

Hematological malignancies treatment improved over the last years resulting in increased achievement of complete or partial remission, but unfortunately high relapse rates are still observed. Therefore, sustainment of long-term remission is crucial. Immune system has a key role in tumor surveillance. Natural killer (NK) cells, at the frontier of innate and adaptive immune system, have a central role in tumor cells surveillance as demonstrated in the setting of allogenic stem cell transplantation. Nevertheless, tumor cells develop various mechanisms to escape from NK cells innate immune pressure. Abnormal NK cytolytic functions have been described in nearly all hematological malignancies. We present here various mechanisms involved in the escape of hematological malignancies from NK cells surveillance: NK cells quantitative deficiency and NK cell qualitative deficiency by increased inhibition signaling or decreased activating stimuli. A challenge of immunotherapy is to restore an efficient antitumor response. A combination of classical therapy plus immune modulation strategies will soon become a standard of care for hematological malignancies.

Natural killer cells and malignant haemopathies: a model for the interaction of cancer with innate immunity

Despite recent progress in the therapeutic approach of malignant haemopathies, their prognoses remain frequently poor. Immunotherapy offers an alternative of great interest in this context but defect or abnormal expression of human leukocyte antigens (HLA), frequently observed in cancer cells, limits its efficiency. Natural killer (NK) cells, which are able to kill target cells in a HLA-independent way, represent a novel tool in the treatment of haematological malignancies. Abnormal NK cytolytic function is observed in all the haematological malignancies studied, such as acute leukaemia, myelodysplastic syndromes or chronic myeloid/lymphoid leukaemia. Several mechanisms are involved in the alterations of NK cytotoxicity: decreased expression of activating receptors, increased expression of inhibitory receptors or defective expression of NK ligands on target cells. Further studies are needed to identify how each type of haematological malignancy escapes from the innate immune response. Attempts to increase the expression of activating receptors, to counteract inhibitory receptors expression, or to increase NK cell cytotoxic capacities could overcome tumour escape from innate immunity. These therapies are based on monoclonal antibodies or culture of NK cells in presence of cytokines or dendritic cells. Moreover, many novel drugs used in haematological malignancies [tyrosine kinase inhibitors, IMIDs®, proteasome inhibitors, demethylating agents, histone deacetylase inhibitors (HDACis), histamine dihydrochloride] display interesting immunomodulatory properties that affect NK cells. These data suggest that combined modalities associating cytotoxic drugs with innate immunity modulators may represent a major breakthrough in tumour eradication.