Eur. J. Immunol. 1993. 23: 2967-2971 Tcell receptor antagonists and HLA-DQ blockers 2967 Horacio M. Serra, Claire Crimi, Alessandro Sette and Esteban Celis Cytel, San Diego zyxwvutsrq Fine restriction analysis and inhibition of antigen recognition in HLA-DQ-restricted T cells by major histocompatibility complex blockers and T cell receptor antagonists The role of polymorphic residues of the zyxw f3 chain of human histocompatibility leukocyte antigen-DQwYw6 in antigen presentation to a hepatitis B surface antigen-specific T cell clone was studied. The results obtained demonstrate that the residue situated at position 57 of the f3 chain (a valine) is critical for presentation of antigen by antigen-presenting cells to the DQ-restricted T cell clone. Experiments were also done to study the feasibility of peptide blocking of antigen recognition by DQ-restricted T cells. The results indicate that peptides known to associate with DQ molecules are capable of blocking the presentation of antigen to the DQ-restricted T cell clone, presumably by competing with antigen for binding to major histocompatibility complex (MHC) molecules. Moreover, truncations of the stimulatory antigenic peptide resulted in the production of T cell receptor antagonists, which inhibited the response of the T cells to antigen at 10-100-fold lower concentrations than conventional MHC blockers. The role of DQ-restricted T cell responses and peptide blocking approaches in autoimmunity are discussed. 1 Introduction T cells recognize antigenic peptides complexed with MHC molecules expressed on the APC surface [l, 21. Helperhn- ducer Tcells, which express the CD4 cell surface marker, respond to peptides that bind to the HLA-DR, -DP or -DQ MHC molecules. Most of the reported CD4+ Tcells are restricted by DR molecules. Far fewer are restricted by DP and DQ [3,4]. The reason for this scarcity of HLA- DQ-restricted Tcells is not known. Low expression of DQ in comparison to DR by APC, and possible suppressive factors released by DQ-restricted Tcells in culture [5, 61 could be important factors. CD4+ T cells are crucial for beneficial immune responses that result in the amplification of protective immunity. However, in some instances CD4+ Tcells may also play a role in triggering and perpetuating unwanted responses such as allergic and autoimmune reactions. Moreover, the incidence of particular autoimmune diseases is strongly associated with certain MHC class I1 alleles [7]. In the case of insulin-dependent (Type I) diabetes, the frequency of the disease is closely associated to some DQ allelic forms, and thus putative autoantigenic peptides are suspected to bind to some HLA-DQ molecules. Because of'the low availability of stable antigen-specific T cell clones that recognize antigen in the context of HLA-DQ molecules, and of the lack of reliable DQ-specific in zyxwvutsr vim binding assays, little is known with respect to the association of peptides to DQ molecules. The role of polymorphic [I 119771 Correspondence: Esteban Celis, Cytel, 3525 John Hopkins Court, San Diego, CA 92121, USA (Fax: 61 95 52 8801) Abbreviation: HBS: Hepatitis B surface antigen Key words: Tcell receptor antagonists zyxwvutsr I Major histocompatibility complex blockers zyxwvutsrq / Hepatitis B virus I Hepatitis B surface antigen residues of the a and p chains of HLA-DQ in peptide binding, and presentation to Tcells, is also as yet unde- fined. A putative therapeutical approach in autoimmunity is based on compounds capable of blocking antigen presen- tation to autoreactiveT cells. Examples of such compounds are peptides binding to h4HC class I1 molecules, and thereby competing for the binding site with the autoanti- genic peptide [8, 91. Another possible therapy applicable to autoimmune disorders is the use of Tcell receptor (TcR) antagonist peptides. This approach is based on the recent report that peptides which bear a sequence similarity with the antigenic peptide are capable of inhibiting DR- restricted Tcell responses at much lower (10-100 fold) concentrations than typical MHC blocking peptides [ 10, 111. TcR antagonist peptides were typically produced by conservative amino acid substitutions of TcR contact residues [lo, 111.To date both of these approaches (MHC blocking and TcR antagonist peptides) have only been demonstrated in the human system using HLA-DR- restricted Tcells. The work presented herein was undertaken to study the role of HLA-DQ, in particular its polymorphic residues, in the presentation of antigenic peptide to a DQwl-restricted CD4+ Tcell clone, which is specific for the preSl region of hepatitis B surface antigen (HBS). In addition, we explored the feasibility of peptide blocking of DQ-restricted T cells and the production of antagonist peptides for these T cells. 2 Materials and methods zyx 2.1 Antigens and peptides Synthetic peptides were prepared on an Applied Biosys- tems machine (Foster City, CA) as described [l, 101. The peptides used in the present study together with known MHC restricting elements appear in Table 1. 0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1993 OO14-2980/93/1111-2967$10.OO + ,2510