Identification of T-Cell Receptors Specific to Antigens Presented By HLA-B4002 and B5401 in Acquired Aplastic Anemia
Authors: Hosokawa Kohei , Kobayashi Eiji , Akatsuka Yoshiki , Espinoza Luis , Nakagawa Noriharu , Mikoto Tanabe , Tsuji Noriaki , Yoroidaka Takeshi , Mizumaki Hiroki , Nguyen Thi Mai Anh , Katagiri Takamasa , Shitaoka Kiyomi , Hamana Hiroshi , Kishi Hiroyuki , Nakao Shinji 
Published: November 2019

[Background] Leukocytes that lack HLA class I alleles derived from hematopoietic stem progenitor cells (HSPCs) that undergo copy number neutral loss of heterozygosity of the short arm of chromosome 6 (6pLOH) or HLA allelic mutations are often detected in acquired aplastic anemia (AA) patients. The presence of HLA class I allele-lacking leukocytes provides compelling evidence that cytotoxic T lymphocytes (CTLs) are involved in the development of AA. Our recent study showed that, among several HLA-class I alleles that are likely to be lost as a result of 6pLOH, HLA-B*40:02 is the most frequently lost allele in AA. Therefore, HLA-B*4002 is thought to play a critical role in the autoantigen presentation by HSPCs to CTLs. We previously identified the T-cell receptor (TCR) sequences from bone marrow (BM) CD8+ T cells in two CsA-dependent AA patients possessing B4002-lacking leukocytes (Case 1, Espinoza et al, Blood Adv, 2018) and B5401-lacking leukocytes (Case 2, Elbadry et al, Haematologica, 2019) by single-cell T-cell receptor (TCR) sequencing. Identifying the TCRs specific to antigens presented by these HLA class I alleles should allow us to screen autoantigens in AA. [Method] We established B4002+ or B5401+ K562 cell lines expressing CD80 and CD137L for the screening of antigen-specific T cell responses. To identify ligands of the TCR, we transfected peripheral blood (PB) T cells with a retrovirus vector containing different TCR cDNA derived from BM T cells and examined their responses to B4002+CD80+CD137L+ or B5401+CD80+CD137L+ K562 cells. Specific responses of each TCR transfectant to K562 cells or iPSC-derived CD34+ cells were determined using an enzyme-linked immunosorbent assay for detecting IFN-γ. Deep TCR sequencing of a current PB sample taken from the same patients was performed to determine whether or not T cells with specific TCRs persisted after successful immunosuppressive therapy (IST). [Results] In Case 1, two TCR transfectants (TCR-K1 and TCR-K2 which were the third- and second-most frequent TCRs in the BM T cells, respectively) secreted greater IFN-γ levels (1730 pg/mL and 2157 pg/mL, respectively) in response to B4002+CD80+CD137L+ K562 cells than those secreted by the other six transfectants (710 to 1184 pg/mL, respectively). TCR-K1 and TCR-K2 did not respond to an A2402+ counterpart (Figure). Notably, deep TCR sequencing of a current PB sample taken from Case 1 nine years after BM sampling revealed the persistence of the TCR-K1 sequence, suggesting that TCR-K1 may be responsible for CsA dependency of this patient. Deep TCR sequencing of other three AA patients with B4002-lacking leukocytes revealed decreased diversity of the T cell repertoire in CD8+ T cells but failed to reveal the same TCR motifs as Case 1. In Case 2, two TCR transfectants (TCR-K3 and TCR-K4) showed a specific response to B5401+CD80+CD137L+ K562 cells. Furthermore, these 2 TCR transfectants secreted higher amounts of IFN-γ (1.7 and 2.0 folds for TCR-K3 and TCR-K4, respectively) in response to wild-type iPSC-derived CD34+ cells than to B5401(-) CD34+ cells. [Conclusions] Our results suggest that these TCR transfectants recognized some intrinsic antigens derived from K562 cells in a B4002 or B5401-restricted manner. These TCR transfectants are the ideal tools for screening libraries of cDNA expressed by B4002+ COS/293T cells to identify autoantigens in AA.
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Disclosures
Yoroidaka: Ono Pharmaceutical: Honoraria. Nakao:Takeda Pharmaceutical Company Limited: Honoraria; Bristol-Myers Squibb: Honoraria; Alaxion Pharmaceuticals: Honoraria; Ohtsuka Pharmaceutical: Honoraria; Daiichi-Sankyo Company, Limited: Honoraria; Janssen Pharmaceutical K.K.: Honoraria; SynBio Pharmaceuticals: Consultancy; Chugai Pharmaceutical Co.,Ltd: Honoraria; Ono Pharmaceutical: Honoraria; Celgene: Honoraria; Kyowa Kirin: Honoraria; Novartis Pharma K.K: Honoraria.