MAGE-specific CD8 T cells are not exhausted in HCC patients

Hepatocellular carcinoma (HCC) is the second-leading cause of cancer-related deaths worldwide with limited therapeutic options especially for late stage patients. Since CD8 T-cell responses targeting tumor associated antigens (TAA) beneficially influence patients' survival, immunotherapy based on TAA-specific CD8 T cells is considered to be a promising approach. However, determinants of TAA-specific T-cell responses are largely unknown. Melanoma-associated antigen (MAGE) is a TAA that is expressed in HCC and CD8 T cells targeting MAGE are detectable in HCC patients. Hence, we characterized MAGE-specific CD8 T cells in detail to define determinants of MAGE-specific CD8 T-cell responses and to assess the immunotherapeutic potential in HCC patients. In particular, we analyzed the phenotype of circulating MAGE-specific CD8 T cells derived from the peripheral blood of HCC patients (n = 32), patients with liver cirrhosis (n = 16), healthy donors (HD) (n = 16) and melanoma patients (n = 13) by multicolour flow cytometry after peptide/MHC class I-tetramer-based magnetic bead enrichment For this, peptide/HLA-A*02-tetramers loaded with MAGE-A3_271-279 or peptide/HLA-A*03-tetramers loaded with MAGE-A1_96-104 were used. In addition, corresponding antigen levels of MAGE-A3_271-279 and MAGE-A1_96-104 in serum were analyzed by ELISA.

Our data revealed that the frequency of circulating MAGE-specific CD8 T cells was significantly reduced in HCC patients compared to HD. Of note, similar to HCC patients, frequencies of MAGE-specific CD8 T cells were also diminished in patients with liver cirrhosis compared to HD. MAGE-specific CD8 T cells exhibited a naïve-like phenotype in patients suffering from liver cirrhosis and HCC. The few antigen-experienced MAGE-specific CD8 T cells that could be detected in HCC patients expressed high levels of CD127 and TCF1 reflecting high potential of homeostatic proliferation and only a minor fraction exhibited PD-1 expression. Importantly, in addition to the minor PD-1 expression, antigen-experienced MAGE-specific CD8 T cells lacked the Eomeshi Tbetdim signature of exhausted T cells. Of note, while MAGE-A3 was not detectable with the applied method, serum levels of MAGE-A1 were significantly higher in HCC patients compared to HD but were comparable to patients with liver cirrhosis.

In sum, our data suggest that T cell exhaustion is not a major mechanism of T cell failure in HCC. Thus, immunotherapeutic strategies targeting exhausted T cells are probably not efficient to induce MAGE-specific CD8 T cells in HCC patients and rather a prime/boost strategy is required in MAGE positive HCC patients.