Induction of T cell anergy by liposomes with incorporated major histocompatibility complex (MHC) II/peptide complexes.

PURPOSE: The aim of this study was to use small unilamellar liposomes with incorporated MHC II/peptide complexes as a carrier system for multivalent antigen presentation to CD4 + T cells. METHODS: Purified peptide pre-loaded MHC II molecules were incorporated into small unilamellar liposomes and tested for their ability to activate A2b T cells. The outcome of T cell activation by such liposomes in the absence of accessory cells was tested via flow cytometry and a T cell anergy assay. RESULTS: Provided the presence of external co-stimulation, MHC II/ peptide liposomes were able to induce proliferation of the A2b T cell clone. More importantly incubation of these T cells with MHC II/ peptide liposomes in the absence of co-stimulation did not induce proliferation, however, a MHC/peptide ligand-density dependent down-regulation of the TCR was observed. Interestingly, when T cells after incubation with the MHC II/peptide liposomes were restimulated with their specific antigen in the presence of professional APC, these cells were anergic. CONCLUSIONS: We propose MHC II/peptide liposomes as a novel means to induce T cell anergy. The possibility to prepare 'tailor-made' liposomal formulations may provide liposomes with an important advantage for applications in immunotherapy.

Modulation of Th2 responses by peptide analogues in a murine model of allergic asthma: amelioration or deterioration of the disease process depends on the Th1 or Th2 skewing characteristics of the therapeutic peptide.

Allergen-specific CD4+ Th2 cells play an important role in the immunological processes of allergic asthma. Previously we have shown that, by using the immunodominant epitope OVA323-339, peptide immunotherapy in a murine model of OVA induced allergic asthma, stimulated OVA-specific Th2 cells, and deteriorated airway hyperresponsiveness and eosinophilia. In the present study, we defined four modulatory peptide analogues of OVA323-339 with comparable MHC class II binding affinity. These peptide analogues were used for immunotherapy by s.c. injection in OVA-sensitized mice before OVA challenge. Compared with vehicle-treated mice, treatment with the Th2-skewing wild-type peptide and a Th2-skewing partial agonistic peptide (335N-A) dramatically increased airway eosinophilia upon OVA challenge. In contrast, treatment with a Th1-skewing peptide analogue (336E-A) resulted in a significant decrease in airway eosinophilia and OVA-specific IL-4 and IL-5 production. Our data show for the first time that a Th1-skewing peptide analogue of a dominant allergen epitope can modulate allergen-specific Th2 effector cells in an allergic response in vivo. Furthermore, these data suggest that the use of Th1-skewing peptides instead of wild-type peptide may improve peptide immunotherapy and may contribute to the development of a successful and safe immunotherapy for allergic patients.

Liposomes in autoimmune diseases: selected applications in immunotherapy and inflammation detection.

In this contribution three examples are discussed of ongoing research where liposomes are used as carrier systems for immunotherapy and inflammation detection in autoimmune diseases. Liposomes can be used as carrier systems of antigenic peptides to peripheral blood mononuclear cells. The second example deals with their use as carrier systems for MHC-peptide complexes for multivalent Ag-presentation to autoreactive T lymphocytes to specifically modulate the activity of these T lymphocytes. The third example relates to our work on long circulating liposomes which are currently being tested in man for their potential to image inflammation sites.

Liposomes with incorporated MHC class II/peptide complexes as antigen presenting vesicles for specific T cell activation.

PURPOSE: The purpose of this study was to design a well-characterized liposomal carrier system for multivalent antigen presentation in order to activate T cells. METHODS: MHC class II molecules were loaded with peptide and subsequently reconstituted into liposomes. A FACS assay was developed to monitor peptide loading and MHC class II incorporation in the liposomes. For in vitro testing of the resulting MHC class II/peptide liposomes, a T cell hybridoma assay was employed. RESULTS: The FACS assay provided a qualitative means to visualize the amount of incorporated MHC class II and peptide molecules that were oriented in the appropriate way for antigen presentation to the T cells. Interestingly, when MHC class II molecules were loaded with the appropriate peptide prior to liposome incorporation, such liposomes were fully capable of inducing IL-2 production of a T cell hybridoma. CONCLUSIONS: This is the first article showing that MHC class II/peptide liposomes can serve as 'artificial antigen presenting cells' for activation of a CD4+ T cell hybridoma. As compared to soluble MHC class II/peptide complexes, the multivalency of liposomal complexes may be an important advantage when studying possible applications in immunotherapy.

Anergic T cells actively suppress T cell responses via the antigen-presenting cell.

We here show that anergic T cells are active mediators of T cell suppression. In co-culture experiments, we found that anergic T cells, derived from established rat T cell clones and rendered anergic via T cell presentation of the specific antigen (Ag), were active inhibitors of T cell responses. Anergic T cells inhibited not only the responses of T cells with the same Ag specificity as the anergic T cells, but were also capable of efficiently inhibiting polyclonal T cell responses directed to other epitopes. This suppression required close cell-cell contact between antigen-presenting cells (APC), anergic T cells and responder T cells, and only occurred when the epitope recognized by the anergic T cell was present. The suppression was not caused by passive competition for ligands on the APC surface, IL-2 consumption, or cytolysis, and was not mediated by soluble factors derived from anergic T cells that were stimulated with their specific Ag. When responder T cells were added 24 h after co-culturing anergic cells in the presence of Ag and APC, T cell responses were still suppressed, indicating that the suppressive effect was persistently present. However, anergic T cells were not able to suppress responder T cells that had already received a full activation signal. We propose that suppression by anergic T cells is mediated via the APC, either through modulation of the T cell-activating capacity of the APC (APC/T cell interaction), or by inhibition of T cells recognizing their ligand in close proximity on the same APC (T/T cell interaction).