Longitudinal analysis of MART-1/HLA-A2-reactive T cells over the course of melanoma progression

How to overcome resistance to immune checkpoint inhibitors in colorectal cancer: From mechanisms to translation

Immunotherapy, especially with immune checkpoint inhibitors (ICIs), has shown advantages in cancer treatment and is a new hope for patients who have failed multiline therapy. However, in colorectal cancer (CRC), the benefit is limited to a small subset of patients with microsatellite instability-high (MSI-H) or mismatch repair-deficient (dMMR) metastatic CRC (mCRC). In addition, 45% to 60% of dMMR/MSI-H mCRC patients showed primary or acquired resistance to ICIs. This means that these patients may have potential unknown pathways mediating immune escape. Almost all mismatch repair-proficient (pMMR) or microsatellite-stable (MSS) mCRC patients do not benefit from ICIs. In this review, we discuss the mechanisms of action of ICIs and their current status in CRC. We then discuss the mechanisms of primary and acquired resistance to ICIs in CRC. Finally, we discuss promising therapeutic strategies to overcome resistance to ICIs in the clinic.

Drug Resistance in Colorectal Cancer: From Mechanism to Clinic

Colorectal cancer (CRC) is one of the leading causes of death worldwide. The 5-year survival rate is 90% for patients with early CRC, 70% for patients with locally advanced CRC, and 15% for patients with metastatic CRC (mCRC). In fact, most CRC patients are at an advanced stage at the time of diagnosis. Although chemotherapy, molecularly targeted therapy and immunotherapy have significantly improved patient survival, some patients are initially insensitive to these drugs or initially sensitive but quickly become insensitive, and the emergence of such primary and secondary drug resistance is a significant clinical challenge. The most direct cause of resistance is the aberrant anti-tumor drug metabolism, transportation or target. With more in-depth research, it is found that cell death pathways, carcinogenic signals, compensation feedback loop signal pathways and tumor immune microenvironment also play essential roles in the drug resistance mechanism. Here, we assess the current major mechanisms of CRC resistance and describe potential therapeutic interventions.

MAP Kinase Inhibition Promotes T Cell and Anti-tumor Activity in Combination with PD-L1 Checkpoint Blockade

Targeted inhibition of mitogen-activated protein kinase (MAPK) kinase (MEK) can induce regression of tumors bearing activating mutations in the Ras pathway but rarely leads to tumor eradication. Although combining MEK inhibition with T-cell-directed immunotherapy might lead to more durable efficacy, T cell responses are themselves at least partially dependent on MEK activity. We show here that MEK inhibition did profoundly block naive CD8(+) T cell priming in tumor-bearing mice, but actually increased the number of effector-phenotype antigen-specific CD8(+) T cells within the tumor. MEK inhibition protected tumor-infiltrating CD8(+) T cells from death driven by chronic TCR stimulation while sparing cytotoxic activity. Combining MEK inhibition with anti-programmed death-ligand 1 (PD-L1) resulted in synergistic and durable tumor regression even where either agent alone was only modestly effective. Thus, despite the central importance of the MAP kinase pathway in some aspects of T cell function, MEK-targeted agents can be compatible with T-cell-dependent immunotherapy.

Serum levels of vascular endothelial growth factor are increased and correlate with malnutrition, immunosuppression involving MDSCs and systemic inflammation in patients with cancer of the digestive system

Vascular endothelial growth factor (VEGF) reportedly has an important role in the progression of malignant neoplasms and has been reported to induce myeloid-derived suppressor cells (MDSCs) that appear in cancer and inflammation. In the present study, serum concentrations of VEGF were measured in patients with digestive system cancer and the correlations with nutritional damage, immune suppression and systemic inflammation were analyzed. A significant increase in VEGF serum levels was observed in patients with esophageal, gastric and colorectal cancers compared with healthy volunteers. Levels of VEGF were inversely correlated with the serum concentrations of albumin, prealbumin and retinol-binding protein. The serum concentrations of VEGF were inversely correlated with the production of interleukin (IL)-12 and correlated with MDSC counts. VEGF levels were also correlated with neutrophil and neutrophil/lymphocyte counts and inversely correlated with lymphocyte count. Serum VEGF levels were divided at a cutoff of 500 pg/ml, with levels of prealbumin and retinol-binding protein significantly decreased in patients with higher VEGF levels. The stimulation index and IL-12 production were significantly decreased in the group with higher VEGF levels and MDSC counts tended to be higher in this group. These results demonstrated that increased production of VEGF was correlated with systemic inflammation, nutritional impairment and the inhibition of cell-mediated immunity involving MDSCs.

Elevated serum levels of vascular endothelial growth factor is effective as a marker for malnutrition and inflammation in patients with ovarian cancer

Vascular endothelial growth factor (VEGF) reportedly plays an important role in the progression of malignant neoplasms. In the present study, measured serum concentrations of VEGF were measured in patients with ovarian cancer and correlations with nutritional damage and chronic inflammation were analyzed. A significant increase in serum levels in patients compared to healthy volunteers was observed. Levels of VEGF were inversely correlated with serum concentrations of prealbumin, transferrin and retinol-binding protein. VEGF levels were also correlated with serum levels of c-reactive protein (CRP), an effective marker of inflammation. CRP levels were significantly elevated in patients with stage III and IV disease and inversely correlated with serum concentrations of total protein, prealbumin, transferrin and retinol-binding protein. These results demonstrated that an increased production of VEGF correlated with nutritional impairment and inflammation.

High avidity cytotoxic T lymphocytes can be selected into the memory pool but they are exquisitely sensitive to functional impairment

High avidity cytotoxic T lymphocytes (CTL) are important in viral clearance and anti-tumor immunity, however, mechanisms for their optimal generation and maintenance in vivo remain unclear. Immunizing mice with an antibody-DNA vaccine encoding a single CTL epitope, induces a 100 fold higher avidity response than peptide vaccination with the identical epitope. The high avidity response is retained into memory and can be efficiently reactivated with an antibody-DNA boost. In contrast, reactivation of high avidity CTL with peptide, stimulated responses with a significant drop in avidity, suggesting loss or conversion of the high avidity CTL to lower avidity. Similarly, high avidity T cells maintained ex vivo were exquisitely sensitive to signaling with low doses of peptide (1 ng/ml) giving optimal TCR stimulation and resulting in retained avidity, proliferation and ability to kill specific targets. In contrast, high avidity T cells maintained ex vivo with supraoptimal TCR stimulation (10 µg/ml peptide) resulted in reduced avidity and failure to kill tumor cells. They also failed to proliferate, showed a significant increase in apoptosis and expressed high levels of the exhaustion marker programmed death-1 (PD-1) and low levels of the lymphocyte-activation gene 3 (LAG-3). This suggests high avidity T cells are recruited to the memory pool but can be lost by supraoptimal stimulation in vitro and in vivo. This is characterized by loss of function and an increase in cell death. The remaining CTL, exhibit low functional avidity that is reflected in reduced anti-tumor activity. This could contribute to failure of the immune system to control the growth of tumors and has implications for vaccination strategies and adoptive transfer of T cells.

Evidence of systemic Th2-driven chronic inflammation in patients with metastatic melanoma

PURPOSE

Immunotherapeutic modalities are commonly used for treatment of patients with melanoma. The therapeutic success in preclinical models has not yielded the expected clinical results. To understand this discrepancy, we attempted to define immune homeostasis of 209 patients with melanoma across stages of disease relative to normal controls.

EXPERIMENTAL DESIGN

Peripheral blood mononuclear cells (PBMC) and plasma were collected from patients and healthy donors. PBMC were analyzed for frequencies of natural killer, dendritic, and T cells and their functional status. Matched plasma samples were analyzed for the concentrations of 27 cytokines, chemokines, and growth factors. RNA was isolated from 24 metastatic melanoma tumor biopsies and profiled by microarray analysis.

RESULTS

The frequency of natural killer, T, and dendritic cells in patients does not significantly change across stages of melanoma. However, plasma concentrations of Th2 cytokines [interleukin (IL)-4, IL-5, IL-10, and IL-13] in tumor-bearing patients were significantly higher than those with resected melanoma. Expression array analysis of metastatic melanoma revealed that the malignant melanocytes were not the source of the Th2 cytokines but did highly up-regulate vascular endothelial growth factor (VEGF) transcripts, consistent with plasma VEGF concentrations. In vitro VEGF exposure of normal PBMC lead to repolarization from Th1 to Th2 emulating the state of metastatic melanoma.

CONCLUSIONS

Patients with metastatic melanoma exist in a state of Th2-mediated "chronic inflammation" as a result of at least VEGF overproduction by malignant tumors. These data support prior observations regarding the effect of VEGF on immune cell function and suggests consideration of VEGF inhibitors in future cancer immunotherapy clinical studies in metastatic melanoma.

Molecular upstaging of sentinel lymph nodes in melanoma: where are we now?

The presence of lymph node metastasis is the best predictor of disease progression and overall survival in patients who have melanoma. Lymphatic mapping and selective lymphadenectomy allows directed pathologic analysis of the node or nodes most likely to have metastatic disease. To diagnose metastatic disease in SLNs reliably requires a coordinated effort by nuclear medicine physicians, surgeons, and pathologists. Errors may occur if quality assurance is not emphasized at any point during the process. This, along with the presence of occult metastatic disease, may lead to disease recurrence and progression, even when SLN histologically are free of disease. Molecular up-staging of occult malignant disease has the potential to provide important information to facilitate the diagnosis, surveillance, and treatment of cancer. The detection of occult tumor cells in SLNs and blood provides a powerful tool for assessing early regional and systemic disease spread in patients who have AJCC stage II and III-not only melanoma but also other solid tumors. The use of varying panels of markers from different laboratories has hampered the interpretation of data and made it difficult to unravel the merits of molecular up staging. Molecular approaches have made a major impact on the field of infectious disease and should one day be of equal usefulness in the diagnosis of cancer.

Tumor stroma-associated antigens for anti-cancer immunotherapy

Immunotherapy has been widely investigated for its potential use in cancer therapy and it becomes more and more apparent that the selection of target antigens is essential for its efficacy. Indeed, limited clinical efficacy is partly due to immune evasion mechanisms of neoplastic cells, e.g. downregulation of expression or presentation of the respective antigens. Consequently, antigens contributing to tumor cell survival seem to be more suitable therapeutic targets. However, even such antigens may be subject to immune evasion due to impaired processing and cell surface expression. Since development and progression of tumors is not only dependent on cancer cells themselves but also on the active contribution of the stromal cells, e.g. by secreting growth supporting factors, enzymes degrading the extracellular matrix or angiogenic factors, the tumor stroma may also serve as a target for immune intervention. To this end several antigens have been identified which are induced or upregulated on the tumor stroma. Tumor stroma-associated antigens are characterized by an otherwise restricted expression pattern, particularly with respect to differentiated tissues, and they have been successfully targeted by passive and active immunotherapy in preclinical models. Moreover, some of these strategies have already been translated into clinical trials.

T-cell clonotypes in cancer

Cells of the immune system spontaneously recognize autologous tumor cells and T cells are believed to be the main effector cells for the immune surveillance of cancer. Recent advances in our understanding of basic and tumor immunology together with methodological developments implies that tumor specific T cells can now be studied functionally, phenotypically as well as molecularly. T cells recognize peptide antigens in the context of MHC molecules through the clonally distributed T-cell receptor (TCR), thus, the clonal distribution of the TCR offers the means to detect and track specific T cells based upon detection of the unique TCR. In this review, we present and discuss available data on TCR utilization of tumor specific T cells in murine models as well as spontaneous and treatment induced anti-tumor T-cell responses in humans.