ePoster Presentation 49th Annual Scientific Meeting of the Australian and New Zealand Society for Immunology 2021

Despite no evidence of a T1D-specific clonotype, the ‘X-ID peptide’ stimulates human T1D specific CD4+ T-cell responses (#227)

Pushpak Bhattacharjee 1 , Eleonora Tresoldi 1 , Miha Pakusch 1 , Stuart Mannering 1
  1. SVI, Fitzroy, VIC, Australia

In 2019, Ahmed et al. reported that a rare population of lymphocytes expresses both B and T cell surface markers that they called Dual Expressors (DEs). They proposed that DEs were more prevalent in the peripheral blood mononuclear cells (PBMC) of people with type 1 diabetes (T1D) than people without T1D.  DE cells were reported to express a very restricted immunoglobulin repertoire and the dominant clonotype was called the ‘X-clonotype’. The CDR3 of the X-clonotype encodes an autoantigen, ‘X-ID peptide’ which stimulated T1D-specific CD4+ T-cell. X-ID specific CD4+ T cells were reported to cross react with insulin B9-23. We sought to confirm Ahmed et al’s observations. In contrast to Ahmed et al, we did not find any association between T1D and the frequency of DEs, also later confirmed by Japp et al., 2021. However, we found that > 52% (10 of 19) of our PBMC samples from T1D subjects responded to X-ID peptide, while only 15 % (1 in 7) HLA matched non-T1D samples responded to this peptide. Intriguingly, responses to full-length C-peptide (PI33-63) correlated strongly (R2=0.97 T1D, R2=0.98 non-T1D) with responses to X-ID peptide. To confirm the specificity of X-ID peptide reactive CD4+ T cells we used the CFSE-based proliferation assay to identify X-ID responsive CD4+ T cells from the PBMC of people with T1D. Responding cells were sorted and their TCRs sequenced using 10X single- cell sequencing. The X-ID specific responses were confirmed for these TCRs. None of the X-ID specific TCRs responded to full-length C-peptide. Although we could not confirm Ahmed et al’s findings relating to DE cells we did confirm their observations relating to T cell responses to X-ID peptide. The origin of the X-ID antigen, and the role responses to X-ID peptide plays in human T1D is remains to be fully elucidated.

  1. Japp et al., 2021. TCR+/BCR+ dual-expressing cells and their associated public BCR clonotype are not enriched in type 1 diabetes. Cell, 184(3):827-839.e14. doi: 10.1016/j.cell.2020.11.035.
  2. Ahmed et al., 2019. A Public BCR Present in a Unique Dual-Receptor-Expressing Lymphocyte from Type 1 Diabetes Patients Encodes a Potent T Cell Autoantigen. Cell, 177(6):1583-1599.e16. doi: 10.1016/j.cell.2019.05.007.