Biomedical subjects

R Bacchetta

Publications and source records attributed to R Bacchetta.

26 records · Page 2Linked to original sources

PubMed1992

Interleukin 10 inhibits allogeneic proliferative and cytotoxic T cell responses generated in primary mixed lymphocyte cultures.

The effects of IL-10 on the generation of alloreactivity in primary mixed lymphocyte cultures (MLCs) were investigated. IL-10 inhibited in a dose-dependent fashion the alloantigen-induced proliferative responses. The suppressive effect was maximal when IL-10 was added at the beginning of the cultures, suggesting that it acts on the early stages of T cell activation. The proliferative responses were enhanced in the presence of a neutralizing anti-IL-10 mAb, indicating that endogenously produced IL-10 suppresses proliferation in primary MLC. The inhibitory effects of IL-10 were observed irrespective of whether irradiated allogeneic peripheral blood mononuclear cells, purified monocytes or freshly isolated B cells were used as stimulator cells. The proliferation of both the CD4+ and CD8+ T cell subsets was inhibited to a similar extent. The reduced proliferative responses were only minimally restored by high concentrations of exogenous IL-2, indicating that the effects of IL-10 are not exclusively due to inhibition of IL-2 synthesis. Furthermore, the production of IL-2, interferon (IFN)-gamma, IL-6, granulocyte macrophage colony stimulating factor, and tumor necrosis factor-alpha in primary MLCs was diminished by IL-10 and enhanced in the presence of anti-IL-10 mAb. The strongest effects were observed on the production of IFN-gamma. Although IL-10 reduces the proliferative responses, the ratios of CD3+CD4+ and CD3+CD8+ T cells remained the same in IL-10 treated and control cultures, yet the percentages of activated CD3+ T cells, as judged by CD25 and HLA-DR expression, were consistently reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoimmunity↗

PubMed1992

T cell repertoire and tolerance after fetal stem cell transplantation.

We studied the T cell repertoire and the mechanism of tolerance in two patients with severe combined immunodeficiency transplanted with HLA mismatched fetal liver stem cells. They are 17 and 5 years old now, healthy, and show normal immunoresponses to recall antigens. Their T cells are of donor origin, whereas monocytes and B cells remained of the host. The NK cells have different sources since in one patient they derive from the donor and in the other one from the host. Despite the HLA mismatch between donor and host cells, no acute or chronic graft-versus-host disease was observed. In vitro experiments with PBMC showed specific nonresponsiveness for the HLA antigens expressed by the host cells. However, an extensive clonal analysis showed that CD4+ and CD8+ host-reactive T cell clones recognizing class II and class I HLA molecules of the host, respectively, were present in the peripheral blood of both patients. Limiting dilution experiments indicated that the frequency of CD8+ host-reactive cells was in the same range as that observed for alloreactive T cells. In contrast, no donor reactive CD8+ T cells could be isolated. Host-reactive CD4+ and CD8+ T cell clones were normal in their capacity to produce IL-2, IFN-gamma, GM-CSF and IL-5, but they failed completely to synthesize IL-4. In addition, CD4+ T cell clones from patient RV secreted very high levels of IL-10. Interestingly, exogenous IL-10 was able to inhibit the proliferative responses of the CD4+ host-reactive T cell clones. Our data demonstrate that host-reactive cells are not deleted from the donor T cell repertoire following allogenic fetal liver stem cell transplantation. Therefore, in vivo tolerance between the host and the donor is maintained by a peripheral autoregulatory mechanism in which cytokines may play a role.

Adolescent↗

PubMed1991

Natural killer cell clones can efficiently process and present protein antigens.

NK cell clones obtained from three different donors were tested for their ability to present soluble proteins to Ag-specific T cell clones. All NK clones were CD2+CD3-CD56+, whereas the expression of CD16 varied from clone to clone. The NK cell clones were able to process and present tetanus toxoid (TT) to TT-specific T cell clones in a class II HLA restricted manner. The capacity of NK cell clones to function as APC was also observed using the house dust mite allergen Der p I and the Der p I-derived peptide Val89-Cys117. As with EBV-transformed B cell line, NK cell clones could present the peptide 3-13 derived from the 65-kDa heat shock protein of Mycobacterium leprae, but they were unable to present the whole M. leprae Ag. Freshly isolated NK cells, IL-2-activated NK cells, and NK cell lines expanded in vitro could also process and present TT. The ability of the different NK populations to act as accessory cells correlated with their levels of class II HLA expression. These data demonstrate that NK cell clones can efficiently function as APC, however they may be restricted in the types of Ag that they can process.

Allergens↗

PubMed1991

A SCID patient reconstituted with HLA-incompatible fetal stem cells as a model for studying transplantation tolerance.

We studied a severe combined immunodeficiency (SCID) patient who received transplantations with completely HLA-mismatched fetal liver and thymus from two different donors. The patient is now 14 years old, healthy and shows normal immunoresponses to recall antigens. His T cells are of donor origin, whereas the monocytes, B cells, and natural killer (NK) cells are of the recipient. The successful immunological reconstitution raised questions as to how T and B cells could collaborate across an HLA barrier and how tolerance was achieved. We have shown that tetanus toxin-specific T cell clones isolated from this patient recognized this antigen in the context of host and not of donor HLA-DR, indicating that those cells were educated in the host environment, presumably the thymus. Despite this, an unexpectedly high frequency of host-reactive clones was found that could recognize MHC antigens of the host. It was particularly striking that CD8+ CTL clones were obtained that recognized class I MHC antigens on the host cells. Nevertheless, the patient did not show any sign of acute or chronic graft-versus-host disease (GVHD). These data indicated that no or only incomplete clonal deletion had taken place in this patient and suggest the presence of a peripheral suppressor mechanism. Thus far, we have no indication for the existence of suppressor T cells. Inasmuch as it was found that host-reactive T cells fail to produce IL-4, which is exceptional for CD4+ T cells, we are exploring the possibility that abnormal cytokine production patterns of host-reactive T cells are associated with suppression of these cells in vivo.

B-Lymphocytes↗

PubMed1990

Host-reactive CD4+ and CD8+ T cell clones isolated from a human chimera produce IL-5, IL-2, IFN-gamma and granulocyte/macrophage-colony-stimulating factor but not IL-4.

In the present study, we investigated the lymphokine production patterns in a series of CD4+ and CD8+ host-reactive T cell clones isolated from PBL of a SCID patient, who was immunologically reconstituted by two allogeneic fetal liver and thymus transplantations 13 years ago. We demonstrate that these donor-derived T cell clones, specifically reacting with the MHC Ag expressed on the recipient cells, do not produce IL-4 and do not express IL-4 mRNA upon Ag or polyclonal stimulations. In contrast, CD4+ tetanus toxin-specific T cell clones isolated from the same patient and having the same HLA phenotype produced normal amounts of IL-4 upon activation. These data suggest that the failure to produce IL-4 is a specific characteristic of these host-reactive clones and is not due to a genetic defect of the transplanted cells. Furthermore, different modes of activation resulted in simultaneous production of IL-5, IL-2, IFN-gamma, granulocyte/macrophage-CSF, and transcription of the TNF-beta gene by the host-reactive clones, indicating that the lack of IL-4 production is not related to the mode of activation. The finding that some of these clones produce significant levels of IL-5 but no IL-4 indicates that the IL-4 and IL-5 genes are not always coexpressed in activated human T cells.

Antigens, CD↗

PubMed1988

Antigen recognition by MHC-incompatible cells of a human mismatched chimera.

Tetanus toxin (TT)-specific T cell clones of donor origin were obtained from a patient with severe combined immunodeficiency (SCID) successfully reconstituted by transplantation of allogeneic fetal liver and thymus cells from two different donors performed 10 yr ago. A series of these clones recognized TT in the context of "allo" class II HLA determinants expressed by recipient APC. The restriction element of two T cell clones with the HLA phenotype of the first donor (HLA-DR1,8) and one T cell clone with the HLA phenotype of the second transplant (HLA-DR3,9) was HLA-DR4 of the recipient, whereas other T cell clones derived from the second transplant recognized TT in the context of HLA-DR5 of the recipient's APC. These latter T cell clones were not able to proliferate in response to TT when autologous APC were used. These data demonstrate that recipient and donor cells having different HLA phenotypes could cooperate across the allogeneic barrier and that MHC restriction of antigen (Ag) recognition is independent from the MHC genotype of the T cells but is influenced by the environment in which the T cells mature. We also isolated T cell clones that were able to recognize processed TT presented by all allogeneic EBV cell lines tested, indicating that the Ag specificity of these clones was not restricted by a particular class II MHC molecule. The Ag-specific proliferative response of one of these clones could be blocked by anti-class II MHC mAbs. These results demonstrate that in addition to Ag recognition in the context of specific class II MHC Ags, other types of Ag-specific responses may occur in this human chimera. It is not clear whether this "allo" plus Ag recognition is the result of education of transplanted fetal cells in the host thymus. Taking into consideration our previous findings indicating that alloreactive T cell clones specific for the recipient cells could be isolated in vitro from the PBL of the same patient, our data suggest that the mechanism for deletion of self-reactive clones and the generation of MHC-restricted responses are different.

Antibodies, Monoclonal↗

PubMed1988

Interleukin-2 production and interleukin-2 receptor expression in children with newly diagnosed diabetes.

In the present study, we investigated the interleukin-2 (IL-2) production and the proliferative responses by peripheral blood mononuclear cells (PBMNC) of 23 children suffering from insulin-dependent diabetes mellitus (IDDM). In addition, the presence of circulating activated T lymphocytes expressing the interleukin-2 receptor (IL-2 R) and HLA-DR antigens was evaluated. The patients were tested at hospital admittance, before starting insulin treatment. Decreased IL-2 production by phytohemagglutinin (PHA)-activated PBMNC of IDDM patients was observed when compared to normal donors. In contrast, the proliferative responses of PBMNC to PHA and Con A were in the normal range. The expression of IL-2 R on patient's lymphocytes was not different from that observed in normal donors, whereas the relative and absolute number of HLA-DR+ T cells was increased. These results confirm the presence in IDDM patients of an imbalanced cellular immune response and demonstrate that the IL-2 deficiency is already present at the diagnosis and is not correlated with insulin administration.

Adolescent↗

PubMedDate not supplied

Induction of transplantation tolerance in humans using fetal cell transplants.

When engrafted with donor stem cells and lymphoid cells, patients develop transplantation tolerance to donor antigens. We analyzed the mechanism of tolerance induction in immunoincompetent recipients whose immunity has been reconstituted by transplantation of mismatched stem cells. Seven infants or human fetuses received fetal liver transplants as a treatment for severe combined immunodeficiency disease. After reconstitution of immunity by lymphocytes developed from donor stem cells, T-cell clones were produced and analyzed. Because donors and recipients were HLA mismatched, it was easy to demonstrate the donor origin of the T-cell clones. These clones were shown to have developed tolerance to histocompatibility antigens of the stem cell donor via a process of clonal deletion (probably as a result of contact with donor-derived macrophages and dendritic cells). They were also tolerant to histocompatibility antigens of the host but through a different mechanism: many clones recognized these antigens but had no detrimental effect on the target cells exhibiting host antigens, either in vitro or in vivo. Clonal anergy was therefore the cause of this tolerance to host determinants, resulting in a lack of graft-versus-host disease and of autoimmunity. The contact between developing T cells of donor origin and host epithelial cells within the host thymus may explain this colonal anergy. It should be noted that all patients had high serum levels of interleukin-10, which might have contributed to the persistent engraftment and tolerance.

Fetal Tissue Transplantation↗