T cell epitopes of HCgp-39 that were defined in HLA-DR4 transgenic mice stimulated T cells from human subjects carrying RA-associated HLA-DR4 alleles. HLA-DR4 molecules may influence the disease process in RA both by presentation of selected peptide epitopes and by promoting the production of proinflammatory cytokines in synovial joints.
We sought to identify an altered peptide ligand (APL) based on the endogenously expressed synovial auto-epitope of human cartilage glycoprotein-39 (HC gp-39) for modulation of cognate, HLA-DR4-restricted T cells. For this purpose we employed a panel of well-characterized T cell hybridomas generated from HC gp-39-immunized HLA-DR4 transgenic mice. The hybridomas all respond to the HC gp-39(263-275) epitope when bound to HLA-DR4(B1*0401) but differ in their fine specificities. First, the major histocompatibility complex (MHC) and T-cell receptor (TCR) contact residues were identified by analysis of single site substituted analogue peptides for HLA-DR4 binding and cognate T cell recognition using both T hybridomas and polyclonal T cells from peptide-immunized HLA-DR4 transgenic mice. Analysis of single site substituted APL by cognate T cells led to identification of Phe265 as the dominant MHC anchor. The amino acids Ala268, Ser269, Glu271 and Thr272 constituted the major TCR contact residues, as substitution at these positions did not affect HLA-DR4(B1*0401) binding but abrogated T cell responses. A structural model for visualisation of TCR recognition was derived. Second, a set of non-classical APLs, modified at the MHC key anchor position but with unaltered TCR contacts, was developed. When these APLs were analysed, a partial TCR agonist was identified and found to modulate the HC gp-39(263-275)-specific, pro-inflammatory response in HLA-DR4 transgenic mice. We identified a non-classical APL by modification of the p1 MHC anchor in a synovial auto-epitope. This APL may qualify for rheumatoid arthritis immunotherapy.
Tumor immunity developing as a response to an autologous colon-tumor/bacillus Calmette-Guérin (BCG) vaccine appears to be associated with induction of CD4+ helper T cells, implied by the observation that vaccine efficacy is associated with major histocompatibility complex class-II molecule expression on the vaccine tumor cells. Therefore, in an attempt to identify colon-tumor-associated antigens responsible for conferring immunity, we examined and compared the proliferative responses of peripheral-blood lymphocytes (PBL) from patients immunized with the autologous tumor/BCG vaccine to T-cell lines cloned expanded from colon-tumor-infiltrating lymphocytes to 5 antigens isolated on the basis of their reactivity by colon-tumor-reactive human monoclonal antibodies. Enzymatically dissociated colon tumors provided a source for establishment of cloned T-cell lines, tumor cell lines propagated in vitro or in vivo as nude-mouse xenografts and EBV-transformed B-cell lines used as antigen-presenting cells. Of 104 different T-cell lines tested, only 3 proliferated in response to CTAA 28A32-46K, and I to the CTAA28A32-32K antigen. In contrast, PBL from 64% of patients immunized with the autologous colon-tumor/BCG vaccine responded to the CTAA 28A32-32K antigen. This antigen is related to a family of calcium- and phospholipid-binding placental proteins termed annexins. Since proliferative responses developed to this antigen after vaccination in 64% of individuals, this antigen may be an important common colon-tumor-associated rejection antigen.
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