Antonio Curti

The P2X7 Receptor: A Key Player in IL-1 Processing and Release

Human IL-1 family proteins are key mediators of the host response to infections, injury, and immunologic challenges. The mechanism by which IL-1 activates proinflammatory responses in target cells, and the plasma membrane receptors involved, is fairly well known. This has led to the development of innovative drugs that block IL-1 downstream to its synthesis and secretion. On the contrary, the mechanism of IL-1 and other IL-1 family members (e.g., IL-18) maturation and release is incompletely understood. Accruing evidence points to a plasma membrane receptor for extracellular ATP, the P2X7 receptor, as a key player in both processes. A deeper understanding of the mechanism by which the P2X7 receptor triggers IL-1 maturation and exteriorization may suggest novel avenues for the treatment of inflammatory diseases and provide a deeper insight in the fundamental mechanism of protease activation and cellular export of proteins lacking a leader sequence.

Successful transfer of alloreactive haploidentical KIR ligand-mismatched natural killer cells after infusion in elderly high risk acute myeloid leukemia patients

Thirteen patients with acute myeloid leukemia, 5 with active disease, 2 in molecular relapse, and 6 in morphologic complete remission (CR; median age, 62 years; range, 53-73 years) received highly purified CD56(+)CD3(-) natural killer (NK) cells from haploidentical killer immunoglobulin-like receptor-ligand mismatched donors after fludarabine/cyclophosphamide immunosuppressive chemotherapy, followed by IL-2. The median number of infused NK cells was 2.74 × 10(6)/Kg. T cells were < 10(5)/Kg. No NK cell-related toxicity, including GVHD, was observed. One of the 5 patients with active disease achieved transient CR, whereas 4 of 5 patients had no clinical benefit. Both patients in molecular relapse achieved CR that lasted for 9 and 4 months, respectively. Three of 6 patients in CR are disease free after 34, 32, and 18 months. After infusion, donor NK cells were found in the peripheral blood of all evaluable patients (peak value on day 10). They were also detected in BM in some cases. Donor-versus-recipient alloreactive NK cells were shown in vivo by the detection of donor-derived NK clones that killed recipients targets. Adoptively transferred NK cells were alloreactive against recipients cells, including leukemia. In conclusion, infusion of purified NK cells is feasible in elderly patients with high-risk acute myeloid leukemia. This trial was registered at www.clinicaltrial.gov as NCT00799799.

The role of indoleamine 2,3-dioxygenase in the induction of immune tolerance: focus on hematology

The regulation of the interaction between the immune system and antigens, which may lead to the induction of immune tolerance, is critical both under physiologic conditions and in different pathological settings. In the past few years, major strides have been made in our understanding of the molecular and cellular bases of this process. Novel pathways have been identified and several novel therapeutic agents are currently under clinical investigation for those diseases in which the normal balance between activation and suppression of the immune response is altered. The tryptophan catabolic enzyme, indoleamine 2,3-dioxygenase (IDO), is one of the key players involved in the inhibition of cell proliferation, including that of activated T cells. Recent works have demonstrated a crucial role for IDO in the induction of immune tolerance during infection, pregnancy, transplantation, autoimmunity, and neoplasias, including hematologic malignancies. In this review, the role of IDO in the induction of immunologic tolerance is addressed with a specific focus on its recently discovered effect on hematologic malignancies.

Granulocyte colony‐stimulating factor promotes the generation of regulatory DC through induction of IL‐10 and IFN‐α

We have recently demonstrated that G‐CSF promotes the generation of human T regulatory (TREG) type 1 cells. In this study, we investigated whether the immunomodulatory effects of G‐CSF might be mediated by DC. CD14+ monocytes were cultured with serum collected after clinical administration of G‐CSF (post‐G), which contained high amounts of IL‐10 and IFN‐α. Similar to incompletely matured DC, monocytes nurtured with post‐G serum acquired a DC‐like morphology, expressed high levels of costimulatory molecules and HLA‐DR, and exhibited diminished IL‐12p70 release and poor allostimulatory capacity. Importantly, post‐G DC‐like cells were insensitive to maturation stimuli. As shown by neutralization studies, IFN‐α and, even more pronounced, IL‐10 contained in post‐G serum inhibited IL‐12p70 release by post‐G DC‐like cells. Furthermore, phenotypic and functional features of post‐G DC‐like cells were replicated by culturing post‐G monocytes with exogenous IL‐10 and IFN‐α. Post‐G DC‐like cells promoted Ag‐specific hyporesponsiveness in naive allogeneic CD4+ T cells and orchestrated a TREG response that was dependent on secreted TGFβ1 and IL‐10. Finally, neutralization of IL‐10 and IFN‐α contained in post‐G serum translated into abrogation of the regulatory features of post‐G DC‐like cells. This novel mechanism of immune regulation effected by G‐CSF might be therapeutically exploited for tolerance induction in autoimmune disorders.

The addition of plerixafor is safe and allows adequate PBSC collection in multiple myeloma and lymphoma patients poor mobilizers after chemotherapy and G-CSF

We report 13 multiple myeloma (MM) or lymphoma patients who were failing PBSC mobilization after disease-specific chemotherapy and granulocyte-CSF (G-CSF), and received plerixafor to successfully collect PBSCs. Patients were considered poor mobilizers when the concentration of PB CD34+ cells was always lower than 10 cells/μL, during the recovery phase after chemotherapy and/or were predicted to have inadequate PBSC collection to proceed to autologous transplantation. Plerixafor (0.24 mg/kg) was administered subcutaneously for up to three consecutive days, while continuing G-CSF, 10–11 h before the planned leukapheresis. Plerixafor administration was safe and no significant adverse events were recorded. We observed a 4.7 median fold-increase in the number of circulating CD34+ cells after plerixafor as compared with baseline CD34+ cell concentration (from a median of 6.2 (range 1–12) to 21.5 (range 9–88) cells/μL). All patients collected >2 × 106 CD34+ cells/kg in 1–3 leukaphereses. In all, 5/13 patients have already undergone autograft with plerixafor-mobilized PBSCs, showing a rapid and durable hematological recovery. Our results suggest that the pre-emptive addition of plerixafor to G-CSF after chemotherapy is safe and may allow the rescue of lymphoma and MM patients, who need autologous transplantation but are failing PBSC mobilization.

Acute myeloid leukemia cells constitutively express the immunoregulatory enzyme indoleamine 2,3-dioxygenase

Acute myeloid leukemia cells constitutively express the immunoregulatory enzyme indoleamine 2,3-dioxygenase

Generation and functional characterization of human dendritic cells derived from CD34 ˛ cells mobilized into peripheral blood: comparison with bone marrow CD34 ˛ cells

Dendritic cells (DCs) are the most powerful professional antigen‐presenting cells (APC), specializing in capturing antigens and stimulating T‐cell‐dependent immunity. In this study we report the generation and characterization of functional DCs derived from both steady‐state bone marrow (BM) and circulating haemopoietic CD34+ cells from 14 individuals undergoing granulocyte colony‐stimulating factor (G‐CSF) treatment for peripheral blood stem cells (PBSC) mobilization and transplantation. Clonogenic assays in methylcellulose showed an increased frequency and proliferation of colony‐forming unit‐dendritic cells (CFU‐DC) in circulating CD34+ cells, compared to that of BM CD34+ precursors in response to GM‐CSF and TNF‐α with or without SCF and FLT‐3L. Moreover, peripheral blood (PB) CD34+ cells generated a significantly higher number of fully functional DCs, as determined by conventional mixed lymphocyte reactions (MLR), than their BM counterparts upon different culture conditions. DCs derived from mobilized stem cells were also capable of processing and presenting soluble antigens to autologous T cells for both primary and secondary immune response. Replacement of the early‐acting growth factors SCF and FLT‐3L with IL‐4 at day 7 of culture of PB CD34+ cells enhanced both the percentage of total CD1a+ cells and CD1a+CD14− cells and the yield of DCs after 14 d of incubation. In addition, the alloreactivity of IL‐4‐stimulated DCs was significantly higher than those generated in the absence of IL‐4. Furthermore, autologous serum collected during G‐CSF treatment was more efficient than fetal calf serum (FCS) or two different serum‐free media for large‐scale production of DCs. Thus, our comparative studies indicate that G‐CSF mobilizes CD34+ DC precursors into PB and circulating CD34+ cells represent the optimal source for the massive generation of DCs. The sequential use of early‐acting and intermediate‐late‐acting colony‐stimulating factors (CSFs) as well as the use of autologous serum greatly enhanced the growth of DCs. These data may provide new insights for manipulating immunocompetent cells for cancer therapy.

Stem Cell Factor and FLT3-Ligand Are Strictly Required to Sustain the Long-Term Expansion of Primitive CD34+DR− Dendritic Cell Precursors

We studied cytokine-driven differentiation of primitive human CD34+HLA-DR− cells to myeloid dendritic cells (DC). Hemopoietic cells were grown in long-term cultures in the presence of various combinations of early acting cytokines such as FLT3-ligand (FLT3-L) and stem cell factor (SCF) and the differentiating growth factors GM-CSF and TNF-α. Two weeks of incubation with GM-CSF and TNF-α generated fully functional DC. However, clonogenic assays demonstrated that CFU-DC did not survive beyond 1 wk in liquid culture regardless of whether FLT3-L and/or SCF were added. FLT3-L or SCF alone did not support DC maturation. However, the combination of the two early acting cytokines allowed a 100-fold expansion of CFU-DC for >1 month. Phenotypic analysis demonstrated the differentiation of CD34+DR− cells into CD34−CD33+DR+CD14+ cells, which were intermediate progenitors capable of differentiating into functionally active DC upon further incubation with GM-CSF and TNF-α. As expected, GM-CSF and TNF-α generated DC from committed CD34+DR+ cells. However, only SCF, with or without FLT3-L, induced the expansion of DC precursors for >4 wk, as documented by secondary clonogenic assays. This demonstrates that although GM-CSF and TNF-α do not require additional cytokines to generate DC from primitive human CD34+DR− progenitor cells, they do force terminal differentiation of DC precursors. Conversely, FLT3-L and SCF do not directly affect DC differentiation, but instead sustain the long-term expansion of CFU-DC, which can be induced to produce mature DC by GM-CSF and TNF-α.

Extracellular ATP Exerts Opposite Effects on Activated and Regulatory CD4+ T Cells via Purinergic P2 Receptor Activation

It has been reported that ATP inhibits or stimulates lymphoid cell proliferation depending on the cellular subset analyzed. In this study, we show that ATP exerts strikingly opposite effects on anti-CD3/CD28–activated and regulatory CD4+ T cells (Tregs), based on nucleotide concentration. We demonstrate that physiological concentrations of extracellular ATP (1–50 nM) do not affect activated CD4+ T cells and Tregs. Conversely, higher ATP concentrations have a bimodal effect on activated CD4+ T cells. Whereas 250 nM ATP stimulates proliferation, cytokine release, expression of adhesion molecules, and adhesion, 1 mM ATP induces apoptosis and inhibits activated CD4+ T cell functions. The expression analysis and pharmacological profile of purinergic P2 receptors for extracellular nucleotides suggest that activated CD4+ T cells are induced to apoptosis via the upregulation and engagement of P2X7R and P2X4R. On the contrary, 1 mM ATP enhances proliferation, adhesion, migration, via P2Y2R activation, and immunosuppressive ability of Tregs. Similar results were obtained when activated CD4+ T cells and Tregs were exposed to ATP released by necrotized leukemic cells. Taken together, our results show that different concentrations of extracellular ATP modulate CD4+ T cells according to their activated/regulatory status. Because extracellular ATP concentration highly increases in fast-growing tumors or hyperinflamed tissues, the manipulation of purinergic signaling might represent a new therapeutic target to shift the balance between activated CD4+ T cells and Tregs.

Phase I/II clinical trial of sequential subcutaneous and intravenous delivery of dendritic cell vaccination for refractory multiple myeloma using patient-specific tumour idiotype protein or idiotype (VDJ)-derived class I-restricted peptides

Fifteen multiple myeloma (MM) patients who had failed maintenance therapy after tandem autologous stem cell transplantation underwent anti‐idiotype (Id) vaccination with dendritic cells (DCs). CD14+‐derived DCs were loaded with the autologous Id as whole protein (=6) or Id‐derived class I‐restricted peptides (=9) and keyhole limpet hemocyanin (KLH). Vaccination consisted of three subcutaneous (sc) and two intravenous injections of increasing DC doses at 2 weeks interval. DC therapy was well tolerated. Most patients developed both humoral and T‐cell responses to KLH, suggesting immunocompetence. Eight of 15 patients developed an Id‐specific T‐cell proliferative response, 8/15 increased interferon‐γ‐secreting T cells and 4/15 showed an Id‐positive delayed‐type hypersensitivity test. Anti‐Id cytotoxic T‐lymphocyte precursors increased after DC vaccination in 2/2 evaluable patients. A more robust T‐cell response was observed after sc DC injections and increased Id‐specific T‐cell proliferation was found up to 1 year after vaccination. VDJ‐derived peptides were as effective as the whole protein in stimulating T‐cell responses. Clinically, 7/15 patients have stable disease after a median follow‐up of 26 months, one patient achieved durable partial remission after 40 months, and seven patients progressed. In conclusion, sc injections of cryopreserved Id‐pulsed DCs were safe and, in contrast with intravenous administrations, induced anti‐MM T‐cell responses.