Peptide-presenting Cells Research Articles

T-cell selection in the thymus: a spatial and temporal perspective.

The ability of T cells to respond to a wide array of foreign antigens while avoiding reactivity to self is largely determined by cellular selection of developing T cells in the thymus. While a great deal is known about the cell types and molecules involved in T-cell selection in the thymus, our understanding of the spatial and temporal aspects of this process remain relatively poorly understood. Thymocytes are highly motile within the thymus and travel between specialized microenvironments at different phases of their development while interacting with distinct sets of self-peptides and peptide presenting cells. A knowledge of when, where, and how thymocytes encounter self-peptide MHC ligands at different stages of thymic development is key to understanding T-cell selection. In the past several years, our laboratory has investigated this topic using two-photon time-lapse microscopy to directly visualize thymocyte migration and signaling events, together with a living thymic slice preparation to provide a synchronized experimental model of T-cell selection insitu. Here, we discuss recent advances in our understanding of the temporal and spatial aspects of T-cell selection, highlighting our own work, and placing them in the context of work from other groups.

Tuning formulation of multipeptide vaccination for melanoma patients at high risk of relapse

18014 Background: Vaccination with MAGE peptides is followed by tumor regression in 10–20% of metastatic melanoma patients with detectable disease, mostly those with only SC or lymph node metastases. Anti-vaccine cytolytic T lymphocyte (CTL) responses have been observed in about 50% of the regressor patients, suggesting that these vaccines were poorly immunogenic. Recent reports have documented convincing CTL responses in patients vaccinated with peptides administered in a water-in-oil emulsion with Montanide, a clinical grade incomplete Freund’s adjuvant. After SC injection, this vaccine stimulates a local inflammation which could help to the recruitment of peptide presenting cells. Considering the absence of an effective treatment to prevent relapses of cutaneous melanoma, we applied this vaccination modality in an adjuvant setting. Methods and Results: We vaccinated 14 HLA-A2 melanoma patients with no evidence of disease but at high risk of relapse, with 4 antigenic peptides (MAGE-3.A2, NA17.A2, Tyrosinase.A2 and gp100.A2) emulsified in Montanide ISA51. Seven patients received 5 vaccinations, every 3 weeks, consisting of 4 injections of 900 μg of one peptide and 1 ml Montanide. Seven other patients received the same vaccines but with 300 μg of each peptide. Toxicity was limited to grade II, at the injection sites. Two thirds of the patients mounted a CTL response to peptide gp100.A2, and 50% to peptide NA17.A2. The lower doses of peptides were as immunogenic as the higher. Conclusions: These encouraging results indicate that this simple vaccination modality is not toxic and clearly immunogenic. We wish to formally assess the role of the immunological adjuvant Montanide in these CTL responses by vaccinating a third group of patients with the same 4 antigenic peptides without Montanide. We will also vaccinate with a mix of the 4 peptides and Montanide all injected at one site, as this will reduce the number of injections and could facilitate immunological helper effects of each peptide on the others. Finally, depending on the immunological results obtained with these two additional cohorts of patients, the best modality will be used in a larger study to evaluate clinical efficacy. No significant financial relationships to disclose.

Influence of HLA-DR on the phenotype of CD4+ T lymphocytes specific for an epitope of the 16-kDa alpha-crystallin antigen of Mycobacterium tuberculosis.

T helper phenotype may be influenced by cytokine milieu, the differential expression of co-stimulatory molecules, antigen dose, and by differences in affinity at the TCR-peptide-MHC interface. We investigated the latter hypothesis by examining the response of six HLA-DR-restricted CD4+ T cell lines specific for the immunodominant and permissively recognized p91-110 epitope of the 16-kDa alpha-crystallin protein of Mycobacterium tuberculosis. Each line was generated from a sensitized HLA-DR-heterozygous donor and all proliferated when peptide was presented by autologous irradiated peripheral blood mononuclear cells. However, when HLA-DR-matched homozygous Epstein-Barr-virus-transformed B cell lines (L-BCL) were used as peptide-presenting cells there was heterogeneity in the response. The most pronounced proliferative response, and the highest IFN-gamma secretion and cytolytic activity was stimulated by L-BCL expressing molecules (DRB1*0101, *1501 and *0401) with high affinity (IC50 < 10 microM) for the 16p91-110 peptide. By comparison, IL-4 secretion or a lower proliferative response could occur when peptide was presented by alleles of high, or of intermediate (10 microM < IC50 < 100 microM), affinity. These data support the hypothesis that the host MHC can influence CD4+ phenotype and have implications for subunit vaccination against tuberculosis.

Noncytotoxic Human CD4+ T-Cell Clones Presenting and Simultaneously Responding to an Antigen Die of Apoptosis

Activated T-cells expressing MHC class II surface antigens are able to present antigen and thus function as peptide-presenting cells (T-APCs). In this study we investigated whether antigen presentation by T-cells induced programmed cell death. As a model we used tetanus p30 peptide (as 947-967)-specific, noncytotoxic CD4+ T-cell clones (C11 and C31). For experimental purposes these T-cell clones were stimulated (a) with p30 peptide-pulsed and fixed EBV-transformed antigen-presenting cells (B-APCs), (b) with p30-pulsed and fixed activated T-cells as APCs (as T-APCs we used either the T-cell clones themselves or an autologous T-cell clone (CT3) with p30 unrelated specificity), or (c) with soluble p30 peptide. The efficiency of antigen presentation was monitored by measuring proliferation as [3H]thymidine uptake. Apoptosis was measured by quantifying fragmented, cytoplasm DNA with the fluorescent dye 4,6-diamidino-2-phenylindole or by visualizing fragmented DNA by gel electrophoresis. Stimulation with p30-pulsed and fixed B-APCs or T-APCs induced proliferation but no apoptosis of the responding T-cells. However, stimulation of cloned T-cells with soluble peptide induced up-regulation of the FAS surface molecules and apoptosis, which was dependent on the peptide doses. Because cloned T-cells express HLA class 11 molecules, they can theoretically exert both functions at once: antigen presentation and antigen response when they are stimulated with soluble peptide. Because death by apoptosis is only seen under such circumstances, we suggest that T-cells simultaneously presenting and responding to an antigen die of apoptosis and thus contribute to the down-regulation of the immune response. Such phenomena might occur in HIV infection when activated CD41 T-cells take up gp120 via their CD4 molecules, present it on their HLA class II surface antigens, and are simultaneously stimulated via their TCR.