High Frequency of Functionally Active Melan-A–Specific T Cells in a Patient with Progressive Immunoproteasome-Deficient Melanoma

Abstract

Tumor-reactive T cells play an important role in cancer immunosurveillance. Applying the multimer technology, we report here an unexpected high frequency of Melan-A-specific CTLs in a melanoma patient with progressive lymph node metastases, consisting of 18 and 12.8% of total peripheral blood and tumor-infiltrating CD8 ؉ T cells, respectively. Melan-A-specific CTLs revealed a high cytolytic activity against allogeneic Melan-A-expressing target cells but failed to kill the autologous tumor cells. Loading of the tumor cells with Melan-A peptide reversed the resistance to killing, suggesting impaired function of the MHC class I antigen processing and presentation pathway. Mutations of the coding region of the HLA-A2 binding Melan-A 26 -35 peptide or down-regulation of the MHC class I heavy chain, the antigenic peptide TAP, and tapasin could be excluded. However, PCR and immunohistochemical analysis revealed a deficiency of the immunoproteasomes low molecular weight protein 2 and low molecular weight protein 7 in the primary tumor cells, which affects the quantity and quality of generated T-cell epitopes and might explain the resistance to killing. This is supported by our data, demonstrating that the resistance to killing can be partially reversed by pre-exposure of the tumor cells to IFN-␥, which is known to induce the immunoproteasomes. Overall, this is the first report of an extremely high frequency of tumor-specific CTLs that exhibit competent T-cell-effector functions but fail to lyse the autologous tumor cells. Immunotherapeutic approaches should not only focus on the induction of a robust antitumor immune response, but should also have to target tumor immune escape mechanisms.

Reduced tumor‐antigen density leads to PD‐1/PD‐L1‐mediated impairment of partially exhausted CD8+ T cells

“…In fact, clinical progressive disease has been observed not only following MHC down-regulation, but also upon impairments in the antigen processing [36,37]. Therefore, our data indicate that patients may benefit from PD-1/PD-L1 blockade even if the PD-L1 expression on their tumor is found to be low. )…”

Blockade of PD‐L1 (B7‐H1) augments human tumor‐specific T cell responses in vitro

“…53 Furthermore, we were able to show that TIL express PD-1 at higher levels compared to PBL, which may explain the observations of clinical tumor progression despite the presence of tumor-specific T cells infiltrating the tumors. 46 PD-L1 represents a recently identified coinhibitory molecule belonging to the B7 family molecules. 24 In the majority of studies, ligation of the cognate receptor PD-1 leads to negative regulation of T cell responses in vitro.…”

“…45 TIL and PBL were cultured in RPMI, supplemented with 2 mM L-glutamine (Biochrom, Berlin, Germany), 40 U/ml penicillin 1 40 lg/ml streptomycin (Gibco), 1 mM sodium-pyruvate (PAN), 13 nonessential amino acids (PAN), 13 MEM vitamines (PAN, Aidenbach, Germany), 50 lM 2-Mercato-Ethanol (ME) and 10% pooled AB human serum (PAN). The human melanoma cell lines Me275, Mel493, Mel108, MelImSi, Na8 and MeR190 have been described before, 8,46 and were cultured in supplemented RPMI plus 10% FCS. Cocultures of tumor cell lines and lymphocytes were performed in cell culture medium containing human serum.…”

BCR-ABL fusion regions as a source of multiple leukemia-specific CD8+ T-cell epitopes

“…60,61 Thus for immunotherapy it is essential to know which proteasome type is expressed in the leukemic cells. 62 Western blotting with subunit-specific antibodies revealed that purified 20S proteasomes isolated from blast crisis CML cells consisted exclusively of the immunotype (Figure 1).…”