Polarization of allogeneic T-cell responses by influenza virus-infected dendritic cells

The developing immune response in the lymph nodes of mice infected with influenza virus has both Th1- and Th2-type characteristics. Modulation of the interactions between antigen-presenting cells and T cells is one mechanism that may alter the quality of the immune response. We have previously shown that the ability of dendritic cells (DC) to stimulate the proliferation of alloreactive T cells is changed by influenza virus due to viral neuraminidase (NA) activity. Here we show that DC infected with influenza virus A/PR/8/34 (PR8) stimulate T cells to produce different types of cytokines in a dose-dependent manner. Optimal amounts of the Th1-type cytokines interleukin-2 (IL-2) and gamma interferon (IFN-gamma) were produced from T cells stimulated by DC infected with low doses of PR8, while the Th2-type cytokines IL-4 and IL-10 were produced only in response to DC infected with high doses of PR8. IL-2 and IFN-gamma levels corresponded with T-cell proliferation and were dependent on the activity of viral NA on the DC surface. In contrast, IL-4 secretion required the treatment of T cells with NA. Since viral particles were released only from DC that are infected with high doses of PR8, our results suggest that viral NA on newly formed virus particles desialylates T-cell surface molecules to facilitate a Th2-type response. These results suggest that the activity of NA may contribute to the mixed Th-type response observed during influenza virus infection.     

Adoptive transfer of T-cell precursors enhances T-cell reconstitution after allogeneic hematopoietic stem cell transplantation

Immunoincompetence after allogeneic hematopoietic stem cell transplantation (HSCT) affects in particular the T-cell lineage and is associated with an increased risk for infections, graft failure and malignant relapse. To generate large numbers of T-cell precursors for adoptive therapy, we cultured mouse hematopoietic stem cells (HSCs) in vitro on OP9 mouse stromal cells expressing the Notch-1 ligand Delta-like-1 (OP9-DL1). We infused these cells, together with T-cell-depleted mouse bone marrow or purified HSCs, into lethally irradiated allogeneic recipients and determined their effect on T-cell reconstitution after transplantation. Recipients of OP9-DL1-derived T-cell precursors showed increased thymic cellularity and substantially improved donor T-cell chimerism (versus recipients of bone marrow or HSCs only). OP9-DL1-derived T-cell precursors gave rise to host-tolerant CD4+ and CD8+ populations with normal T-cell antigen receptor repertoires, cytokine secretion and proliferative responses to antigen. Administration of OP9-DL1-derived T-cell precursors increased resistance to infection with Listeria monocytogenes and mediated significant graft-versus-tumor (GVT) activity but not graft-versus-host disease (GVHD). We conclude that the adoptive transfer of OP9-DL1-derived T-cell precursors markedly enhances T-cell reconstitution after transplantation, resulting in GVT activity without GVHD.     

Cytolytic pathways in haematopoietic stem-cell transplantation

The remarkable activity of donor T cells against malignant cells in the context of an allogeneic haematopoietic stem-cell transplantation (HSCT) is arguably, at present, the most potent clinical immunotherapy for cancer. However, alloreactive donor T cells are also important effector cells in the development of graft-versus-host disease (GVHD), which is a potentially lethal complication for recipients of an allogeneic HSCT. Therefore, the separation of the GVHD and graft-versus-tumour (GVT) activity of donor T cells has become a topic of great interest for many investigators. Recent studies have shown that donor T cells make differential use of their cytolytic pathways in mediating GVHD and GVT effects. Therefore, the selective blockade or enhancement of cytolytic pathways provides an intriguing therapeutic opportunity to separate the desired GVT effect from the potentially devastating GVHD.     

Effect of L-ornithine on proliferative and cytotoxic T-cell responses in allogeneic and syngeneic mixed leukocyte cultures

The effect of L-ornithine on cytotoxic and proliferative responses in mixed leukocyte cultures has been analyzed. The activation of cytotoxic T lymphocytes (CTL) was strongly inhibited when 9 X 10(-3) M L-ornithine was added at the initiation of the cultures. The CTL precursor cells were not completely and irreversibly inactivated, however, since the cells generated normal cytotoxic activity if resuspended after 6 days in fresh culture medium together with a fresh set of stimulator cells. Experiments in microcultures with nylon-wool-nonadherent T-cell-enriched spleen cells as responder cells and "plastic adherent cells" as stimulator cells revealed that the cytotoxic responses were almost completely suppressed if ornithine was added within the first 20 hr but were only partially suppressed if ornithine was added after 48 hr. Also, ornithine had only a mild suppressive effect on proliferative responses in allogeneic and syngeneic mixed leukocyte cultures. The strong suppressive effect of the cytotoxic response was therefore not explained by a general toxic effect of L-ornithine on the responding cells in the culture. The addition of interleukin 2 (IL-2)-containing EL-4 supernatants did not prevent but rather enhanced the suppressive effect of L-ornithine. This indicated that the inhibitory effect was not (exclusively) expressed at the level of the IL-2-producing helper T cells. Since activated macrophages have been reported to secrete arginase, it appears that L-ornithine may be part of a regulatory circuit that selectively regulates the development of cytotoxic effector T cells.     

Immune reconstitution following hematopoietic stem-cell transplantation

BACKGROUND: Reconstitution of the immune system following allogeneic stem-cell transplantation is a complex process that requires successful engraftment of the hematopoietic stem cell, as well as adequate thymic function. As the majority of patients have reduced thymic function due to age, hormonal changes, as well as the damage caused by conditioning and GvHD, immune recovery is often delayed and incomplete. Following graft infusion there is rapid proliferation of natural killer (NK) cells that appear to proceed directly from the hematopoietic stem cell. B-cell function is dependent on specific maturation development in the BM micro-environment, as well as CD4 help. The CD8 population expands rapidly due to proliferation of many memory cells that react against Class I Ags, as well as viral molecules. Expansion of T-helper cells originates mainly from the memory pool that is present in the bone marrow graft. Naive cells require competent thymus hence the CD4 cell counts may be subnormal with clinical immunodeficiency. Controversy remains as to the capacity of the thymus to recover and thus extra thymic proliferation of T cells have been postulated. However these cells appear to have a limited capacity to expand and a fixed repertoire. DISCUSSION: Donor lymphocyte infusions may contribute a competent CD4 population that can cause GvHD, but have limitations in the capacity to respond to new antigens. Future research needs to be concentrated on improving the capacity of the thymus to reconstitute a functional naive population.     

Inhibition of allogeneic T-cell responses by dendritic cells expressing transduced indoleamine 2,3-dioxygenase

BACKGROUND: Indoleamine 2,3-dioxygenase (IDO) is an enzyme involved in the catabolism of tryptophan and has been shown to prevent rejection of the fetus during pregnancy by inhibiting alloreactive T cells. METHODS: In this study we investigated dendritic cells (DCs) that are transfected with IDO cDNA in the inhibition of T-cell proliferation after antigen-specific interaction. XS106 DCs, derived from A/J mice (H-2k), were transduced with IDO with a gene-delivery system using a recombinant adenoviral vector. RESULTS: Western blotting and immune staining revealed IDO expression in XS106 DCs transduced with IDO (XS106-IDO DCs), and its catabolic effect was confirmed by an increase in kynurenine concentration. Fluorescence-activated cell sorting revealed that XS106-IDO DCs were not changeable for Ia, CD80, and CD86 expression. After XS106-IDO DCs were co-cultured with C57BL/6 allogeneic splenic T cells, the proliferation of the T cell was significantly inhibited. The co-cultured T cells with XS106-IDO DCs exhibited cell-cycle arrest. Furthermore, injection of XS160-IDO DCs into the footpads of C57BL/6 (H-2b) mice demonstrated a reduced T-cell response against allo-antigen. CONCLUSIONS: These results suggest that overexpression of IDO in the DCs effectively inhibited T-cell proliferation, and may expand a new immunomodulatory strategy for the prevention of allo-rejection of organ transplantation.     

Immune ablation and stem-cell therapy in autoimmune disease. Experimental basis for autologous stem-cell transplantation

Treatment of rats suffering from florid chronic progressive systemic arthritis or from chronic remitting/relapsing encephalomyelitis with autologous bone marrow transplantation (BMT) is highly effective. This finding was unexpected as the genotype of the bone marrow largely determines the susceptibility of both spontaneous and induced autoimmune diseases in rodents. The success of autologous stem-cell transplantation depends on the completeness of eradication of the effectors of autoimmune disease, in other words activated and memory T lymphocytes. The reviewed experimental data, when translated to the clinic, indicate that the patients should be subjected to a conditioning regimen that induces maximal lymphoablation and that the autologous transplant has to be T-cell depleted.     

Immune ablation and stem-cell therapy in autoimmune disease: Experimental basis for autologous stem-cell transplantation

Treatment of rats suffering from florid chronic progressive systemic arthritis or from chronic remitting/relapsing encephalomyelitis with autologous bone marrow transplantation (BMT) is highly effective. This finding was unexpected as the genotype of the bone marrow largely determines the susceptibility of both spontaneous and induced autoimmune diseases in rodents. The success of autologous stem-cell transplantation depends on the completeness of eradication of the effectors of autoimmune disease, in other words activated and memory T lymphocytes. The reviewed experimental data, when translated to the clinic, indicate that the patients should be subjected to a conditioning regimen that induces maximal lymphoablation and that the autologous transplant has to be T-cell depleted.     

Monitoring of human cytomegalovirus and virus-specific T-cell response in young patients receiving allogeneic hematopoietic stem cell transplantation

In allogeneic hematopoietic stem-cell transplantation (HSCT) recipients, outcome of human cytomegalovirus (HCMV) infection results from balance between viral load/replication and pathogen-specific T-cell response. Using a cut-off of 30,000 HCMV DNA copies/ml blood for pre-emptive therapy and cut-offs of 1 and 3 virus-specific CD4(+) and CD8(+) T cells/μl blood for T-cell protection, we conducted in 131 young patients a prospective 3-year study aimed at verifying whether achievement of such immunological cut-offs protects from HCMV disease. In the first three months after transplantation, 55/89 (62%) HCMV-seropositive patients had infection and 36/55 (65%) were treated pre-emptively, whereas only 7/42 (17%) HCMV-seronegative patients developed infection and 3/7 (43%) were treated. After 12 months, 76 HCMV-seropositive and 9 HCMV-seronegative patients (cumulative incidence: 90% and 21%, respectively) displayed protective HCMV-specific immunity. Eighty of these 85 (95%) patients showed spontaneous control of HCMV infection without additional treatment. Five patients after reaching protective T-cell levels needed pre-emptive therapy, because they developed graft-versus-host disease (GvHD). HSCT recipients reconstituting protective levels of HCMV-specific T-cells in the absence of GvHD are no longer at risk for HCMV disease, at least within 3 years after transplantation. The decision to treat HCMV infection in young HSCT recipients may be taken by combining virological and immunological findings.     

Concanavalin A-induced suppressor cell activity for T-cell proliferative responses: Autologous and allogeneic suppression in aging humans

Peripheral blood mononuclear cells from 48 healthy subjects of ages varying from 20 to 94 years were evaluated for the ability to generate suppressor cell activity following in vitro incubation with concanavalin A. The suppression of proliferative responses by autologous and young, allogeneic lymphocytes to phytohemagglutinin was assessed using suppressor/ responder cell ratios ($\text{S}\text{R}$) of 2:1 and 1:1 and by using a summation index. Inducible suppressor cell activity for autologous responder cells was comparable between 24 aged (76.0 ± 10.9 years) and 20 young (26.8 ± 4.6 years) subjects. However, aged subjects exhibited a significant decrease in suppressor cell activity ($\text{S}\text{R}\text{= 1}$) when allogeneic responder cells were utilized. Our results indicate that autologous inducible suppressor cell activity is preserved in the aged population, whereas allogeneic activity is impaired.     

Immune ablation and stem-cell therapy in autoimmune disease. Immunological reconstitution after high-dose immunosuppression and haematopoietic stem-cell transplantation

Studies on immunological reconstitution after immune ablation and stem-cell therapy may yield important clues to our understanding of the pathogenesis of human autoimmune disease, due to the profound effects of function and organization of the immune system. Such studies are also indispensable when linking clinical sequelae such as opportunistic infections to the state of immune deficiency that ensues after the treatment. Much has been learnt on these issues from comparable studies in haemato-oncological diseases, although it remains to be proven that the data obtained from these studies can be extrapolated to rheumatological autoimmune diseases. Preliminary results from pilot studies in various rheumatological conditions not only pointed to clinical efficacy of the new treatment modality but also unveiled marked effects on T-cell receptor repertoires of circulating T lymphocytes, on titres of autoantibodies and T- and B-cell subsets.