The CD4⁺ T‐cell epitope‐binding register is a critical parameter when generating functional HLA‐DR tetramers with promiscuous peptides

Abstract

Detection of CD4 1 T cells specific for tumor-associated antigens is critical to investigate the spontaneous tumor immunosurveillance and to monitor immunotherapy protocols in patients. We investigated the ability of HLA-DR*1101 multimers to detect CD4 1 T cells specific for three highly promiscuous MAGE-A3 derived peptides: (p39), MAGE-A3 281-295 (p57) and MAGE-A3 286-300 (p58). Tetramers stained specific CD4 1 T cells only when loaded with p39, although all peptides activated the specific T cells when presented by plasticbound HLA-DR*1101 monomers. This suggested that tetramer staining ability was determined by the mode rather than the affinity of peptide binding to HLA-DR*1101. We hypothesized that peptides should bear a single P1 anchor residue to bind all arms of the multimer in a homogeneous register to generate peptide-HLA-DR conformers with maximal avidity. Bioinformatics analysis indicated that p39 contained one putative P1 anchor residue, whereas the other two peptides contained multiple ones. Designing p57 and p58 analogues containing a single anchor residue generated HLA-DR*1101 tetramers that stained specific CD4 1 T cells. Producing HLA-DR*1101 monomers linked with the optimized MAGE-A3 analogues, but not with the original epitopes, further improved tetramer efficiency. Optimization of CD4 1 T-cell epitope-binding registers is thus critical to generate functional HLA-DR tetramers.Key words: Anchor residues . HLA-DR Ã 1101 . MAGE-A3 . MHC tetramers . Tumor antigens Supporting Information available online IntroductionAnimal studies have clearly shown the critical role for CD4 1 T cells in anti-tumor immune response; nevertheless, little is known as yet about spontaneous tumor-specific CD4 1 T-cell responses in patients [1,2]. This knowledge would be instrumental to the definition of the mechanisms underlying tumor immunosurveillance and, possibly, tumor escape, as well as for the correct design of optimal vaccination strategies.CD4 1 T-cell responses specific for tumor associated antigens (TAA) can be investigated at the single cell level by using soluble [3][4][5][6]. The identification of primary antigen-specific CD4 1 T cells by peptide-pulsed MHC class II tetramers seems, however, less straightforward than that of CD8 1 T cells by peptide-loaded MHC class I tetramers [7,8]. Several biological and structural characteristics of the CD4 1 T-cell response that differ from those displayed by the CD8 1 one seem to affect the capacity of MHC class II tetramers to optimally stain specific CD4 1 T cells ex vivo: (i) the lower frequency of peptide-specific CD4 1 T cells, (ii) their apparent lower affinity for the peptide-MHC class II complexes [9][10][11][12][13], and (iii) the requirement for an activation-induced TCR reorganization to bind with sufficient avidity cognate peptide-MHC class II tetramers [12,14,15].Furthermore, the open structure of the MHC class II molecules allows peptides as long as 20 aa to extend out of the binding groove at both ends [16][17][18]. It is thus possible that a peptide,...

A Population Response Analysis Approach To Assign Class II HLA-Epitope Restrictions

“…Many HLA allelic variants are functionally similar (24-26). As a result, a given epitope may be restricted by multiple HLA molecules encoded by a particular locus (especially if they are close variants), or even molecules from different loci (promiscuous restriction).…”

Vaccination with LAG-3Ig (IMP321) and Peptides Induces Specific CD4 and CD8 T-Cell Responses in Metastatic Melanoma Patients—Report of a Phase I/IIa Clinical Trial

“…This may possibly be associated with lower TCR affinity, and/or different fine specificity. Indeed, it has been shown that a given peptide can make different configurations on a particular MHC class II protein, resulting in different epitopes recognized by different TCR (fine) specificities (43)(44)(45). In this regard, our observations are based solely on a single patient.…”

CD4+T‐cell immunity to theBurkholderia pseudomalleiABC transporter LolC in melioidosis

“…There has been considerable interest and progress with respect to initiatives to define and fine‐map peptide epitope/HLA class II interactions in clinical settings 26. We next set out to determine whether the epitopes predicted through HLA transgenic models and predictive algorithms had relevance to T‐cell responses of humans exposed to Bp.…”