ALK as a novel lymphoma-associated tumor antigen: identification of 2 HLA-A2.1-restricted CD8+ T-cell epitopes

Oncogenic anaplastic lymphoma kinase (ALK) fusion proteins (NPM/ALK and associated variants) are expressed in about 60% of anaplastic large cell lymphomas (ALCLs) but are absent in normal tissues. In this study, we investigated whether ALK, which is expressed at high levels in lymphoma cells, could be a target for antigen-specific cell-mediated immunotherapy. A panel of ALK-derived peptides was tested for their binding affinity to HLA-A*0201 molecules. Binding peptides were assessed for their capacity to elicit a specific immune response mediated by cytotoxic T lymphocytes (CTLs) both in vivo, in HLA-A*0201 transgenic mice, and in vitro in the peripheral blood lymphocytes (PBLs) from healthy donors. Two HLA-A*0201-restricted CTL epitopes, p280-89 (SLAMLDLLHV) and p375-86 (GVLLWEIFSL), both located in the ALK kinase domain were identified. The p280-89- and p375-86-induced peptide-specific CTL lines were able to specifically release interferon-gamma (IFN-gamma) on stimulation with ALK peptide-pulsed autologous Epstein-Barr virus-transformed B cells (LCLs) or T2 cells. Anti-ALK CTLs lysed HLA-matched ALCL and neuroblastoma cell lines endogenously expressing ALK proteins. CTL activity was inhibited by anti-HLA-A2 monoclonal antibody CR11.351, consistent with a class I-restricted mechanism of cytotoxicity. These results show the existence of functional anti-ALK CTL precursors within the peripheral T-cell repertoire of healthy donors, clearly indicating ALK as a tumor antigen and ALK-derived peptides, p280-89 and p375-86, as suitable epitopes for the development of vaccination strategies.