HLA-C04:09N is expressed at the cell surface and triggers peptide-specific T-cell activation

• Published in: Haematologica (Roma) 2024-04, Vol.109 (4), p.1121-1127
• Main Authors: Welters, Carlotta, Welters, Marthe-Lina, Stadler, Serena, Bullinger, Lars, Strobel, Julian, Hackstein, Holger, Dhamodaran, Arunraj, Blankenstein, Thomas, Hansmann, Leo
• Format: Article
• Language: English
• Subjects: Cell Therapy & Immunotherapy; HLA-C Antigens - genetics; Humans; Leukocytes, Mononuclear; Peptides; Receptors, Antigen, T-Cell; T-Lymphocytes, Cytotoxic
• ISSN: 0390-6078; 1592-8721; 1592-8721
• DOI: 10.3324/haematol.2023.283812

The null allele HLA-C*04:09N differs from HLA-C*04:01 in a frameshift mutation within its cytoplasmic domain, resulting in translation of 32 additional amino acids that are assumed to prevent cell surface expression. However, we recently identified a multiple myeloma-reactive T-cell receptor (TCR) that appeared to recognize antigen presented on HLA-C*04:09N and encouraged us to ask whether HLA-C*04:09N, albeit not easily detectable at the cell surface, can present antigen sufficient for T-cell activation. We generated two HLA-class I-deficient cell lines, re-expressed HLAC* 04:09N, detected HLA expression by flow cytometry, and tested for T-cell activation using a cytomegalovirus peptide- specific HLA-C*04:01-restricted TCR. In both cell lines, HLA-C*04:09N expression was detectable at the cell surface and could be enhanced by IFN-γ exposure. Recombinant HLA-C*04:09N expression was sufficient for T-cell activation in vitro, which could be blocked by an HLA-class I-specific antibody, suggesting HLA-TCR interaction at the cell surface. Peripheral blood mononuclear cells isolated from an individual who physiologically expressed HLA-C*04:09N triggered peptide-specific T-cell activation, confirming our results with cells with natural HLA expression levels. In conclusion, we present peptide-specific HLA-C*04:09N-restricted T-cell activation and suggest consideration of this allele in the appropriate clinical context, such as allogeneic stem cell transplantation, or in the setting of cellular therapy.