Myeloid-derived suppressor cells (MDSC) potently repress antitumor immunity. The amount of MDSC in the blood of melanoma patients declines in response to vemurafenib, an inhibitor of oncogenic BRAF ...signaling that abrogates the ability of malignant cells to induce MDSC. This suggests that vemurafenib may be used in combination with various immunotherapeutic agents for the induction of long-lasting tumor regression.
The cytotoxic activity of T cells selects the outgrowth of tumor cells that escape from immune surveillance by different strategies. The different mechanisms that interfere with immune recognition ...and limit vaccination efficiency are still poorly understood. We analysed six cell lines established from different metastases of melanoma patient UKRV-Mel-20 for specific characteristics known to have an impact on the tumor-T cell interaction: (1) alterations in the HLA class I phenotype, (2) expression of Fas/CD95, and (3) expression of specific cytokines and chemokines. One of the cell lines, UKRV-Mel-20f, exhibited an HLA class I haplotype loss and just this cell line was also characterised by the expression of Fas/CD95 and of relatively high levels of proinflammatory chemokines suggesting that the cytotoxic activity of tumor-infiltrating T cells might have selected the outgrowth of this tumor cell variant. All other cell lines analysed showed no alterations in HLA class I expression, but, in contrast to UKRV-Mel-20f, expressed much lower levels of Fas/CD95 and of proinflammatory chemokines and some of them produced high levels of immunosuppressive TGF-beta1. These results suggest that in patient UKRV-Mel-20, tumor cells interfere with T cell recognition by different strategies which might partially explain why this patient did not have a clinical response to an autologous tumor cell vaccine.
As tumor antigen-specific CD4+ T cells can mediate strong therapeutic anti-tumor responses in melanoma patients we set out to establish a comprehensive screening strategy for the identification of ...tumor-specific CD4+ T cell epitopes suitable for detection, isolation and expansion of tumor-reactive T cells from patients.
To scan the human melanoma differentiation antigens TRP-1 and TRP-2 for HLA-DRB1*0301-restricted CD4+ T cell epitopes we applied the following methodology: Splenocytes of HLA-DRB1*0301-transgenic mice immunized with recombinant adenovirus encoding TRP-1 (Ad5.TRP-1) or TRP-2 (Ad5.TRP-2) were tested for their T cell reactivity against combinatorial TRP-1- and TRP-2-specific peptide libraries. CD4+ T cell epitopes thus identified were validated in the human system by stimulation of peripheral blood mononuclear cells (PBMC) from healthy donors and melanoma patients. Using this strategy we observed that recombinant Ad5 induced strong CD4+ T cell responses against the heterologous tumor antigens. In Ad5.TRP-2-immunized mice CD4+ T cell reactivity was detected against the known HLA-DRB1*0301-restricted TRP-2(60-74) epitope and against the new epitope TRP-2(149-163). Importantly, human T cells specifically recognizing target cells loaded with the TRP-2(149-163)-containing library peptide or infected with Ad5.TRP-2 were obtained from healthy individuals, and short term in vitro stimulation of PBMC revealed the presence of epitope-reactive CD4+ T cells in melanoma patients. Similarly, immunization of mice with Ad5.TRP-1 induced CD4+ T cell responses against TRP-1-derived peptides that turned out to be recognized also by human T cells, resulting in the identification of TRP-1(284-298) as a new HLA-DRB1*0301-restricted CD4+ T cell epitope.
Our screening approach identified new HLA-DRB1*0301-restricted CD4+ T cell epitopes derived from melanoma antigens. This strategy is generally applicable to target antigens of other tumor entities and to different HLA class II molecules even without prior characterization of their peptide binding motives.
Resistance to immunotherapy is due in some instances to the acquired stealth mechanisms of tumor cells that lose expression of MHC class I antigen-presenting molecules or downregulate their class I ...antigen-presentation pathways. Most dramatically, biallelic β2-microglobulin (B2M) loss leads to complete loss of MHC class I expression and to invisibility to CD8
+
T cells. MHC class I expression and antigen presentation are potently upregulated by interferon-γ (IFNγ) in a manner that depends on IFNγ receptor (IFNGR) signaling via JAK1 and JAK2. Mutations in these molecules lead to IFNγ unresponsiveness and mediate loss of recognition and killing by cytotoxic T lymphocytes. Loss of MHC class I augments sensitivity of tumor cells to be killed by natural killer (NK) lymphocytes, and this mechanism could be exploited to revert resistance, for instance, with interleukin-2 (IL-2)-based agents. Moreover, in some experimental models,potent local type I interferon responses, such as those following intratumoral injection of Toll-like receptor 9 (TLR9) or TLR3 agonists, revert resistance due to mutations of JAKs.
Immune-checkpoint blockade (ICB) has demonstrated efficacy in many tumor types, but predictors of responsiveness to anti-PD1 ICB are incompletely characterized. In this study, we analyzed a ...clinically annotated cohort of patients with melanoma (n = 144) treated with anti-PD1 ICB, with whole-exome and whole-transcriptome sequencing of pre-treatment tumors. We found that tumor mutational burden as a predictor of response was confounded by melanoma subtype, whereas multiple novel genomic and transcriptomic features predicted selective response, including features associated with MHC-I and MHC-II antigen presentation. Furthermore, previous anti-CTLA4 ICB exposure was associated with different predictors of response compared to tumors that were naive to ICB, suggesting selective immune effects of previous exposure to anti-CTLA4 ICB. Finally, we developed parsimonious models integrating clinical, genomic and transcriptomic features to predict intrinsic resistance to anti-PD1 ICB in individual tumors, with validation in smaller independent cohorts limited by the availability of comprehensive data. Broadly, we present a framework to discover predictive features and build models of ICB therapeutic response.
Classical MHC molecules present processed peptides from endogenous protein antigens on the cell surface, which allows CD8 super(+) cytotoxic T lymphocytes (CTLs) to recognize and respond to the ...abnormal antigen repertoire of hazardous cells, including tumor cells. The light chain, beta 2-microglobulin ( beta 2m), is an essential constant component of all trimeric MHC class I molecules. There is convincing evidence that beta 2m deficiency generates immune escape phenotypes in different tumor entities, with an exceptionally high frequency in colorectal carcinoma (CRC) and melanoma. Damage of a single beta 2m gene by LOH on chromosome 15 may be sufficient to generate a tumor cell precommitted to escape. In addition, this genetic lesion is followed in some tumors by a mutation of the second gene (point mutation or insertion/deletion), which produces a tumor cell unable to express any HLA class I molecule. The pattern of mutations found in microsatellite unstable colorectal carcinoma (MSI-H CRC) and melanoma showed a striking similarity, namely the predominance of frameshift mutations in repetitive CT elements. This review emphasizes common but also distinct molecular mechanisms of beta 2m loss in both tumor types. It also summarizes recent studies that point to an acquired beta 2m deficiency in response to cancer immunotherapy, a barrier to successful vaccination or adoptive cellular therapy.
T-cell-based immunotherapy of melanoma becomes ineffective when β2m-deficient tumor cells of a human leukocyte antigen (HLA) class I-negative phenotype grow out. We demonstrated that an ...early-acquired chromosomal deletion and subsequent inactivating gene mutation lead to β2m deficiency, suggesting that melanoma cells can genetically evolve to avoid being recognized by CD8
+
T cells.
Large genome‐scale studies are deposited in various public sequence repositories. However, their access and analysis can be non‐trivial to infrequent users. Here, we present a new database connecting ...whole transcriptomes with clinical data for straight‐forward access and analysis of patient‐specific samples. Users can perform association tests of survival and gene expression across different cohorts, identify cell‐type expressions, or correlate the presence of immune cells. In summary, we present a new data hub for bench scientists to perform replication and discovery studies.
Abstract Despite the recent success of MAPK and immune checkpoint inhibitors in advanced melanoma, intrinsic and acquired resistance mechanisms determine the efficacy of these therapeutic approaches. ...Therapy resistance in melanoma is not solely driven by genetic evolution, but also by epigenetically driven adaptive plasticity. Melanoma cells are shifting between different transcriptional programs, cell cycle states and differentiation phenotypes reflecting a highly dynamic potential to adapt to various exogenous stressors including immune attack or cancer therapies. This review will focus on the dynamic interconversion and overlap between different melanoma cell phenotypes in the context of therapy resistance and a dynamically changing multicellular microenvironment.
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