101. Apparent Lack of
- Author
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Paul G, Kemps, Timo C, Zondag, Eline C, Steenwijk, Quirine, Andriessen, Jelske, Borst, Sandra, Vloemans, Dave L, Roelen, Lenard M, Voortman, Robert M, Verdijk, Carel J M, van Noesel, Arjen H G, Cleven, Cynthia, Hawkins, Veronica, Lang, Arnoud H, de Ru, George M C, Janssen, Geert W, Haasnoot, Kees L M C, Franken, Ronald, van Eijk, Nienke, Solleveld-Westerink, Tom, van Wezel, R Maarten, Egeler, Auke, Beishuizen, Jan A M, van Laar, Oussama, Abla, Cor, van den Bos, Peter A, van Veelen, and Astrid G S, van Halteren
- Subjects
Adult ,Male ,Proto-Oncogene Proteins B-raf ,neopeptide ,HLA-A Antigens ,Immunology ,T cell ,CD8-Positive T-Lymphocytes ,Langerhans Cell Histiocytosis ,neoantigen ,BRAF ,Human Leukocyte Antigen ,Histiocytosis, Langerhans-Cell ,Antigens, Neoplasm ,Cell Line, Tumor ,Neoplasms ,Mutation ,Humans ,Female ,Child ,Original Research - Abstract
Langerhans Cell Histiocytosis (LCH) is a neoplastic disorder of hematopoietic origin characterized by inflammatory lesions containing clonal histiocytes (LCH-cells) intermixed with various immune cells, including T cells. In 50–60% of LCH-patients, the somatic BRAFV600E driver mutation, which is common in many cancers, is detected in these LCH-cells in an otherwise quiet genomic landscape. Non-synonymous mutations like BRAFV600E can be a source of neoantigens capable of eliciting effective antitumor CD8+ T cell responses. This requires neopeptides to be stably presented by Human Leukocyte Antigen (HLA) class I molecules and sufficient numbers of CD8+ T cells at tumor sites. Here, we demonstrate substantial heterogeneity in CD8+ T cell density in n = 101 LCH-lesions, with BRAFV600E mutated lesions displaying significantly lower CD8+ T cell:CD1a+ LCH-cell ratios (p = 0.01) than BRAF wildtype lesions. Because LCH-lesional CD8+ T cell density had no significant impact on event-free survival, we investigated whether the intracellularly expressed BRAFV600E protein is degraded into neopeptides that are naturally processed and presented by cell surface HLA class I molecules. Epitope prediction tools revealed a single HLA class I binding BRAFV600E derived neopeptide (KIGDFGLATEK), which indeed displayed strong to intermediate binding capacity to HLA-A*03:01 and HLA-A*11:01 in an in vitro peptide-HLA binding assay. Mass spectrometry-based targeted peptidomics was used to investigate the presence of this neopeptide in HLA class I presented peptides isolated from several BRAFV600E expressing cell lines with various HLA genotypes. While the HLA-A*02:01 binding BRAF wildtype peptide KIGDFGLATV was traced in peptides isolated from all five cell lines expressing this HLA subtype, KIGDFGLATEK was not detected in the HLA class I peptidomes of two distinct BRAFV600E transduced cell lines with confirmed expression of HLA-A*03:01 or HLA-A*11:01. These data indicate that the in silico predicted HLA class I binding and proteasome-generated neopeptides derived from the BRAFV600E protein are not presented by HLA class I molecules. Given that the BRAFV600E mutation is highly prevalent in chemotherapy refractory LCH-patients who may qualify for immunotherapy, this study therefore questions the efficacy of immune checkpoint inhibitor therapy in LCH.
- Published
- 2019