Immunosuppressive Cancer Microenvironment Research Articles

Development of a DNA aptamer targeting IDO1 with anti-tumor effects

Immune checkpoint blockade has become an effective approach to reverse theimmune tolerance of tumor cells. Indoleamine 2,3-dioxygenase 1 (IDO1) is frequently upregulated in many types of cancers and contributes to the establishment of an immunosuppressive cancer microenvironment, which has been thought to be a potential target for cancer therapy. However, the development of IDO1 inhibitors for clinical application is still limited. Here, we isolated a DNA aptamer with a strong affinity and inhibitory activity against IDO1, designated as IDO-APT. By conjugating with nanoparticles, in situ injection of IDO-APT to CT26 tumor-bearing mice significantly suppresses the activity of regulatory Tcells and promotes the function of CD8+ Tcells, leading to tumor suppression and prolonged survival. Therefore, this functional IDO1-specific aptamer with potent anti-tumor effects may serve as a potential therapeutic strategy in cancer immunotherapy. Our data provide an alternative way to target IDO1 in addition to small molecule inhibitors.

Dickkopf-1: A Promising Target for Cancer Immunotherapy.

Clinical studies in a range of cancers have detected elevated levels of the Wnt antagonist Dickkopf-1 (DKK1) in the serum or tumors of patients, and this was frequently associated with a poor prognosis. Our analysis of DKK1 gene profile using data from TCGA also proves the high expression of DKK1 in 14 types of cancers. Numerous preclinical studies have demonstrated the cancer-promoting effects of DKK1 in both in vitro cell models and in vivo animal models. Furthermore, DKK1 showed the ability to modulate immune cell activities as well as the immunosuppressive cancer microenvironment. Expression level of DKK1 is positively correlated with infiltrating levels of myeloid-derived suppressor cells (MDSCs) in 20 types of cancers, while negatively associated with CD8+ T cells in 4 of these 20 cancer types. Emerging experimental evidence indicates that DKK1 has been involved in T cell differentiation and induction of cancer evasion of immune surveillance by accumulating MDSCs. Consequently, DKK1 has become a promising target for cancer immunotherapy, and the mechanisms of DKK1 affecting cancers and immune cells have received great attention. This review introduces the rapidly growing body of literature revealing the cancer-promoting and immune regulatory activities of DKK1. In addition, this review also predicts that by understanding the interaction between different domains of DKK1 through computational modeling and functional studies, the underlying functional mechanism of DKK1 could be further elucidated, thus facilitating the development of anti-DKK1 drugs with more promising efficacy in cancer immunotherapy.

Complement inhibitor factor H expressed by breast cancer cells differentiates CD14+ human monocytes into immunosuppressive macrophages

ABSTRACT Macrophages are a major immune cell type in the tumor microenvironment, where they display a tumor-supporting phenotype. Factor H (FH) is a complement inhibitor that also plays a role in several cellular functions. To date, the phenotype of monocytes stimulated with FH has been unexplored. We discovered that FH is a survival factor for CD14+ primary human monocytes, promoting their differentiation into macrophages in serum-free medium. This activity was localized to the C-terminal domains of FH and it was inhibited in plasma, indicating that the phenomenon may be most relevant in tissues. FH-induced macrophages display characteristics of immunosuppressive cells including expression of CD163 and CD206, release of the anti-inflammatory cytokine IL-10 and changes in metabolism. Furthermore, FH-induced macrophages express low levels of HLA-DR but high levels of co-inhibitory molecule programmed death-ligand 1 (PD-L1), and accordingly, a reduced capacity for T-cell activation. Finally, we show that FH is expressed by human breast cancer cells and that this correlates with the presence of immunosuppressive macrophages, breast cancer recurrence and severity of the disease. We propose that the expression of FH by tumor cells and the promotion of an immunosuppressive cancer microenvironment by this protein should be taken into account when considering the effectiveness of immunotherapies against breast cancer.

Hypoxia induces immunogenic cell death of cancer cells by enhancing the exposure of cell surface calreticulin in an endoplasmic reticulum stress-dependent manner.

Hypoxia is associated with resistance to anticancer therapies. Additionally, it is involved in the immune evasion of cancer cells by inducing an immunosuppressive microenvironment. However, the role of hypoxia in modulating the immunogenicity of cancer cells remains unknown. Hypoxia is known to induce endoplasmic reticulum (ER) stress, which serves a key role in inducing the cell surface exposure of calreticulin, a marker of immunogenic cell death. The present study investigated whether hypoxia influenced the immunogenicity of cancer cells using FACS, western blot analysis and syngenic mouse tumor model. The results revealed that hypoxia induced the cell surface exposure of calreticulin in human and mouse breast cancer cell lines depending on ER stress. Enhanced cell surface exposure of calreticulin induced by hypoxia resulted in an increase in anticancer immunity in a mouse model, which suggested that hypoxia induced immunogenic cell death. Notably, hypoxia did not significantly modulate the cell surface exposure of CD47, an antagonist of calreticulin function in cancer immunogenicity. These results suggest that hypoxia may enhance the immunogenicity of cancer cells themselves, in addition to its role in inducing an immunosuppressive cancer microenvironment.

Highlights of This Issue

The FGFR pathway is thought to drive oncogenic progression of many tumor types. Bahleda and colleagues report on the results of a first-in-human phase I trial of erdafitinib (JNJ-42756493), a potent, oral pan-FGFR tyrosine kinase inhibitor, conducted on patients with advanced-stage disease with known genetic activation of the FGFR pathway. This agent was well-tolerated and showed promising efficacy, especially in urothelial carcinoma and cholangiocarcinoma patients with FGFR alterations. These results have the potential to influence future treatment of patients with FGFR positive tumors.Myelofibrosis is morphologically characterized by the presence of atypical megakaryocytes and bone marrow fibrosis. To determine whether elimination of these abnormal megakaryocytes has therapeutic benefit for myelofibrosis patients, Gangat and colleagues conducted a phase 1 study of alisertib, an aurora kinase A inhibitor and megakaryocyte differentiation agent. Alisertib was well-tolerated and provided a modest clinical benefit for spleen size and symptom burden. Moreover, alisertib normalized megakaryocyte morphology and reduced fibrosis in a substantial number of patients. This study underscores the role of megakaryocytes in myelofibrosis and highlights the feasibility of targeting this lineage in this disease.Cancer vaccines have long been considered a promising tool for cancer therapy. However, many potential vaccines have been ineffective in clinical trials, in part due to the immunosuppressive cancer microenvironment. In a phase I trial, Gatti-Mays and colleagues examined BN-CV301, a modified cancer vaccine expressing MUC1 and CEA tumor antigens, as well as costimulatory molecules. Treatment-related adverse events were relatively minor. Patients with mutant KRAS responded particularly well to this regimen – five out of six patients showed either a partial response or stable disease after BN-CV301 vaccination. This improved vaccine shows promise for further clinical evaluation.Pancreatic ductal adenocarcinoma is a highly lethal cancer due, in part, to a high rate of recurrence. Groot and colleagues developed and validated an assay to detect KRAS hotspot mutations in circulating tumor DNA (ctDNA) in a CLIA laboratory setting. Detection of mutant KRAS in ctDNA at the time of surgery was associated with a greater risk of recurrence, while rising mutant KRAS levels in ctDNA provided an early prediction of recurrence. In several instances, the detection of mutant KRAS in ctDNA outperformed the measurement of CA 19-9 in serum. This liquid biopsy test for mutant KRAS shows great promise for monitoring disease in pancreatic cancer patients, potentially leading to earlier intervention.

Abstract IA02: Selection of cancer antigens and conditions for success of immunotherapy of cancer involving vaccination

Abstract Cancer antigens of choice include mutant DNA sequences encoding neo-antigens, selected cancer testis antigens, and differentiation antigens, in addition to viral antigens. Neo-antigens and viral antigens are the most attractive, because the T cell repertoire against these antigens has not been blunted by central thymic tolerance. Optimal vaccine platforms include DNA and RNA vaccines as well as synthetic long peptides and selected prime-boost protocols involving recombinant viruses encoding cancer antigens. The most effective cancer vaccines deliver concentrated antigen to both HLA class I and II molecules of DCs, promoting both CD4 and CD8 T cell responses. Suboptimal antigen selection, suboptimal vaccine design, and an immunosuppressive cancer microenvironment are the root causes of the lack of clinical efficacy of cancer vaccines in many clinical trials. Drugs or physical treatments can mitigate the immunosuppressive cancer microenvironment and include chemotherapeutics, radiation, inhibitors of T cell checkpoints, indoleamine 2,3-dioxygenase (IDO) inhibitors, agonists of selected TNF receptor family members, and inhibitors of undesirable cytokines. The specificity of therapeutic vaccination combined with such immunomodulation offers an attractive avenue for the development of future cancer therapies. Clinical benefit of certain therapeutic cancer vaccines has been established, usually by noting prolonged progression free or overall survival. Reviews of the properties and prospects of cancer vaccines have been listed below (1-3). The addition of one or more immunomodulation strategies may further enhance the potential of therapeutic cancer vaccines, including of those that have been only marginally active due to the immunosuppressive cancer microenvironment. We have established clinical benefit of a cancer vaccine as monotherapy in patients with premalignant disease induced by high risk human papilloma virus. Regression of lesions was associated with a better vaccine-induced immune response against the target antigens of the vaccine. However in patients with cervical cancer the vaccine monotherapy failed to install clinically effective immunity. Recently we showed in a pilot trial that vaccine-induced immunity could be markedly enhanced by combination with standard of care chemotherapy for late stage recurrent or metastatic cervical cancer. Increased levels of myeloid-derived suppressor cells were shown to be depleted by the carboplatin and paclitaxel chemotherapy to the low levels of healthy donors, while T cell numbers in PBMC remained intact. Timed vaccination with a single dose of vaccine at the MDSC nadir during chemotherapy led to a robust vaccine-induced T cell response (4). In a subsequent chemo-immunotherapy trial with three vaccine doses, spaced by three weeks, and in cohorts of patients at four different vaccine doses, the initiation and maintenance of robust tumor-specific T cell responses was confirmed and a broad dose response relationship of tumor-specific T cell responses was noted. Preliminary data on clinical outcomes relative to HPV-specific immune responses will be discussed. In summary, therapeutic benefit of cancer vaccines can be maximized in patients with established cancers by improving vaccine design and by using vaccines in combination with standard chemotherapies. In addition cancer vaccines can establish and/or maintain tumor-specific T cells in combination with checkpoint blockade or other immunomodulatory therapies. Finally, cancer vaccines can also help to sustain and expand adoptively transferred tumor-specific T cells.

Immune checkpoint‑targeted cancer immunotherapies

Tumor cells may express on their surface various characteristic antigens that can induce antitumor immunity. However, cancer in human body may induce an immunosuppressive microenvironment that limits immune response to its antigens. For many years scientists have tried to develop an immunotherapy which would induce a potent antitumor immune response and lead to an elimination of the disease. One of the most promising immunotherapies is blockade of immune checkpoints, i.e. a group of costimulatory molecules negatively regulating the immune system. Their blockade would overcome immune tolerance in the tumor microenvironment and amplify antitumor immunity. What's more, immune checkpoint blockade may turn out even more profitable, as some of immune checkpoints and their ligands are expressed on tumor surface and on tumor infiltrating lymphocytes, contributing to the immunosuppressive cancer microenvironment. Phase III clinical trials have confirmed efficacy of an anti‑CTLA‑4 antibody ipilimumab, thereby leading to its acceptance for the treatment of advanced melanoma. Thanks to promising results of the phase I clinical trials, a breakthrough therapy designation and an early approval for the treatment have been granted to anti‑PD‑1 antibodies ‑ nivolumab (for the treatment of advanced melanoma and advanced non‑small cell lung cancer) and pembrolizumab (for the treatment of advanced melanoma) and, in the treatment of advanced bladder cancer, an anti‑PD‑L1 antibody ‑ MPDL3280A as well. Other immune checkpoints, such as LAG‑3, TIM‑3, BTLA, B7‑H3 and B7‑H4, are also under early evaluation.

Therapeutic cancer vaccines.

The clinical benefit of therapeutic cancer vaccines has been established. Whereas regression of lesions was shown for premalignant lesions caused by HPV, clinical benefit in cancer patients was mostly noted as prolonged survival. Suboptimal vaccine design and an immunosuppressive cancer microenvironment are the root causes of the lack of cancer eradication. Effective cancer vaccines deliver concentrated antigen to both HLA class I and II molecules of DCs, promoting both CD4 and CD8 T cell responses. Optimal vaccine platforms include DNA and RNA vaccines and synthetic long peptides. Antigens of choice include mutant sequences, selected cancer testis antigens, and viral antigens. Drugs or physical treatments can mitigate the immunosuppressive cancer microenvironment and include chemotherapeutics, radiation, indoleamine 2,3-dioxygenase (IDO) inhibitors, inhibitors of T cell checkpoints, agonists of selected TNF receptor family members, and inhibitors of undesirable cytokines. The specificity of therapeutic vaccination combined with such immunomodulation offers an attractive avenue for the development of future cancer therapies.