Apparent lack of BRAF(V600E) derived HLA class I presented neoantigens hampers neoplastic cell targeting by CD8(+) T cells in langerhans cell histiocytosis

Kemps, P.G.; Zondag, T.C.; Steenwijk, E.C.; Andriessen, Q.; Borst, J.; Vloemans, S.; ... ; Halteren, A.G.S. van (2020)

Article / Letter to editor

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 BRAF(V600E) driver mutation, which is common in many cancers, is detected in these LCH-cells in an otherwise quiet genomic landscape. Non-synonymous mutations like BRAF(V600E) 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 BRAF(V600E) 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 BRAF(V600E) 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 BRAF(V600E) 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 BRAF(V600E) 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 BRAF(V600E) 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 BRAF(V600E) protein are not presented by HLA class I molecules. Given that the BRAF(V600E) 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.

• Langerhans Cell Histiocytosis
• BRAF
• neoantigen
• neopeptide
• Human Leukocyte Antigen
• T cell

• All authors: Kemps, P.G.; Zondag, T.C.; Steenwijk, E.C.; Andriessen, Q.; Borst, J.; Vloemans, S.; Roelen, D.L.; Voortman, L.M.; Verdijk, R.M.; Noesel, C.J.M. van; Cleven, A.H.G.; Hawkins, C.; Lang, V.; Ru, A.H. de; Janssen, G.M.C.; Haasnoot, G.W.; Franken, K.L.M.C.; Eijk, R. van; Solleveld-Westerink, N.; Wezel, T. van; Egeler, R.M.; Beishuizen, A.; Laar, J.A.M. van; Abla, O.; Bos, C. van den; Veelen, P.A. van; Halteren, A.G.S. van
• Date: 2020-01-10
• Journal: Frontiers in Immunology
• Volume: 10
• DOI: doi:10.3389/fimmu.2019.03045
• Link: https://www.frontiersin.org/articles/10.3389/fimmu.2019.03045/full