Mechanisms of immune dysfunction in renal cell carcinoma

Mitochondria dysfunction in CD8+ T cells as an important contributing factor for cancer development and a potential target for cancer treatment: a review

CD8+ T cells play a central role in anti-tumor immunity. Naïve CD8+ T cells are active upon tumor antigen stimulation, and then differentiate into functional cells and migrate towards the tumor sites. Activated CD8+ T cells can directly destroy tumor cells by releasing perforin and granzymes and inducing apoptosis mediated by the death ligand/death receptor. They also secrete cytokines to regulate the immune system against tumor cells. Mitochondria are the central hub of metabolism and signaling, required for polarization, and migration of CD8+ T cells. Many studies have demonstrated that mitochondrial dysfunction impairs the anti-tumor activity of CD8+ T cells through various pathways. Mitochondrial energy metabolism maladjustment will cause a cellular energy crisis in CD8+ T cells. Abnormally high levels of mitochondrial reactive oxygen species will damage the integrity and architecture of biofilms of CD8+ T cells. Disordered mitochondrial dynamics will affect the mitochondrial number and localization within cells, further affecting the function of CD8+ T cells. Increased mitochondria-mediated intrinsic apoptosis will decrease the lifespan and quantity of CD8+ T cells. Excessively low mitochondrial membrane potential will cause the release of cytochrome c and apoptosis of CD8+ T cells, while excessively high will exacerbate oxidative stress. Dysregulation of mitochondrial Ca2+ signaling will affect various physiological pathways in CD8+ T cells. To some extent, mitochondrial abnormality in CD8+ T cells contributes to cancer development. So far, targeting mitochondrial energy metabolism, mitochondrial dynamics, mitochondria-mediated cell apoptosis, and other mitochondrial physiological processes to rebuild the anti-tumor function of CD8+ T cells has proved effective in some cancer models. Thus, mitochondria in CD8+ T cells may be a potential and powerful target for cancer treatment in the future.

Exploring the synergistic effects of cabozantinib and a programmed cell death protein 1 inhibitor in metastatic renal cell carcinoma with machine learning

Clinical evidence supports the combination of cabozantinib with an immune checkpoint inhibitor for the treatment of metastatic clear cell renal cell carcinoma (mccRCC) and suggests a synergistic antitumour activity of this combination. Nevertheless, the biological basis of this synergy is not fully characterized. We studied the mechanisms underpinning the potential synergism of cabozantinib combined with a PD1 inhibitor in mccRCC and delved into cabozantinib monotherapy properties supporting its role to partner these combinations. To model physiological drug action, we used a machine learning-based technology known as Therapeutic Performance Mapping Systems, applying two approaches: Artificial Neural Networks and Sampling Methods. We found that the combined therapy was predicted to exert a wide therapeutic action in the tumour and the microenvironment. Cabozantinib may enhance the effects of PD1 inhibitors on immunosurveillance by modulating the innate and adaptive immune system, through the inhibition of VEGF-VEGFR and Gas6-AXL/TYRO3/MER (TAM) axes, while the PD1 inhibitors may boost the antiangiogenic and pro-apoptotic effects of cabozantinib by modulating angiogenesis and T-cell cytotoxicity. Cabozantinib alone was predicted to restore cellular adhesion and hamper tumour proliferation and invasion. These data provide a biological rationale and further support for cabozantinib plus PD1 inhibitor combination and may guide future nonclinical and clinical research.

Enhanced 15-lipoxygenase activity and elevated eicosanoid production in kidney tumor microenvironment contribute to the inflammation and immune suppression

Macrophage infiltration is a hallmark in the majority of solid tumors. Our studies demonstrated that macrophages that infiltrate human renal cells carcinoma (RCC) display markedly enhanced expression and activity of 15-lipoxygenase-2 (15-LOX2). Obtained data suggest that enhanced lipoxygenase activity in tumor-associated macrophages stimulates cancer inflammation and causes immune dysfunction.

Advances in immune-based therapies of renal cell carcinoma

Renal cell carcinoma (RCC) is the most prevalent malignancy within the kidney, and over 40% of patients with RCC will die from their disease. Approximately a third of patients present with metastatic disease and a third of patients undergoing nephrectomy for clinically localized RCC will develop metastases. Metastatic RCC poses a therapeutic challenge due to its resistance to conventional modes of therapy such as chemotherapy and radiation therapy. While it is clear that strides have been made against metastatic RCC, the overall objective response rates of interleukin-2- and interferon-alpha-based immunotherapy remain at approximately 20%. Despite advances in biologic- and immune-based therapies, long-term survival for patients with metastatic RCC remains modest. Furthermore, the toxicity profile of these cytokine regimens is significant. Advances in the understanding of the nature of tumor antigens and their optimal presentation, and in the regulatory mechanisms that govern the immune system, have provided multiple novel immunotherapy intervention strategies with increased specificity and potentially fewer side effects. Such strategies are currently being tested in clinical trials.

Tumor-associated macrophages mediate immunosuppression in the renal cancer microenvironment by activating the 15-lipoxygenase-2 pathway

Renal cell carcinoma (RCC), the most common human kidney cancer, is frequently infiltrated with tumor-associated macrophages (TAM) that can promote malignant progression. Here, we show that TAMs isolated from human RCC produce substantial amounts of the proinflammatory chemokine CCL2 and immunosuppressive cytokine IL-10, in addition to enhanced eicosanoid production via an activated 15-lipoxygenase-2 (15-LOX2) pathway. TAMs isolated from RCC tumors had a high 15-LOX2 expression and secreted substantial amounts of 15(S)-hydroxyeicosatetraenoic acid, its major bioactive lipid product. Inhibition of lipoxygenase activity significantly reduced production of CCL2 and IL-10 by RCC TAMs. In addition, TAMs isolated from RCC were capable of inducing in T lymphocytes, the pivotal T regulatory cell transcription factor forkhead box P3 (FOXP3), and the inhibitory cytotoxic T-lymphocyte antigen 4 (CTLA-4) coreceptor. However, this TAM-mediated induction of FOXP3 and CTLA-4 in T cells was independent of lipoxygenase and could not be reversed by inhibiting lipoxygenase activity. Collectively, our results show that TAMs, often present in RCCs, display enhanced 15-LOX2 activity that contributes to RCC-related inflammation, immunosuppression, and malignant progression. Furthermore, we show that TAMs mediate the development of immune tolerance through both 15-LOX2-dependent and 15-LOX2-independent pathways. We propose that manipulating LOX-dependent arachidonic acid metabolism in the tumor microenvironment could offer new strategies to block cancer-related inflammation and immune escape in patients with RCC.

Reversal of myeloid cell-mediated immunosuppression in patients with metastatic renal cell carcinoma

PURPOSE

Tumor-induced immunosuppression remains a significant obstacle that limits the efficacy of biological therapy for renal cell carcinoma. Here we evaluate the role of CD33 myeloid-derived suppressor cells (MDSC) in the regulation of T-cell responses in renal cell carcinoma patients. We also examine effect of all-trans-retinoic acid (ATRA) on MDSC-mediated immune suppression.

EXPERIMENTAL DESIGN

CD33-positive myeloid cells were isolated from the peripheral blood of renal cell carcinoma patients with magnetic beads and tested in vitro for their ability to inhibit T-cell responses. T-cell function was evaluated using ELISPOT and CTL assays.

RESULTS

MDSC isolated from renal cell carcinoma patients, but not from healthy donors, were capable of suppressing antigen-specific T-cell responses in vitro through the secretion of reactive oxygen species and nitric oxide upon interaction with CTL. MDSC-mediated immune suppression and IFN-gamma down-regulation was reversible in vitro by exposing cells to the reactive oxygen species inhibitors. Moreover, ATRA was capable of abrogating MDSC-mediated immunosuppression and improving T-cell function by direct differentiation into antigen-presenting cell precursors.

CONCLUSIONS

These results may have significant implications regarding the future design of active immunotherapy protocols that may include differentiation agents as part of a multimodal approach to renal cell carcinoma immunotherapy.

Oxidative stress regulates expression of VEGFR1 in myeloid cells: link to tumor-induced immune suppression in renal cell carcinoma

Metastatic renal cell carcinoma (RCC) associates with overproduction of vascular endothelial growth factor (VEGF) due to the mutation/inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene. Herein we demonstrate that implantation of human RCC tumor cells into athymic nude mice promotes the appearance of VEGF receptor 1 (VEGFR1)/CD11b double-positive myeloid cells in peripheral blood. Avastin-mediated VEGF neutralization was capable of significantly reducing the numbers of circulating VEGFR1+ myeloid cells. Conversely, up-regulation of VEGFR1 by myeloid cells could also be achieved in vitro by coculturing bone marrow cells with RCC-conditioned medium or by short-term exposure of naive myeloid cells to oxidative stress. Treatment of myeloid cells with H2O2, lipid peroxidation product 4-hydroxy-2(E)-nonenal, or an inhibitor of thioredoxin reductase all resulted in increased expression of VEGFR1. Furthermore, after exposure to oxidative stress, myeloid cells acquire immunosuppressive features and become capable of inhibiting T cell proliferation. Data suggest that tumor-induced oxidative stress may promote both VEGFR1 up-regulation and immunosuppressive function in bone marrow-derived myeloid cells. Analysis of tumor tissue and peripheral blood from patients with metastatic RCC revealed that VEGFR1+ cells can be also found in cancer patients. Restoration of immunocompetence in metastatic RCC patients by pharmacological elimination of VEGFR1+ cells may have a significant impact on the therapeutic efficacy of cancer vaccines or other immune-based therapies.

Recent developments in renal cell cancer immunotherapy

Various immunotherapeutic approaches for the treatment of renal cell carcinoma (RCC) have been developed for > 90 years. Existing immunotherapeutic strategies against RCC include: systemic administration of cytokines; therapeutic vaccines based on tumor cells or dendritic cells; monoclonal antibodies; and adoptive immunotherapy (T cell transfer or allogeneic hematopoietic cell transplantation). However, the overall efficacy of immunotherapy for advanced RCC remains moderate. With the advent of molecularly targeted biological therapies that turned out to be significantly effective in the treatment of metastatic RCC, to many oncologists immunotherapy may seem to be moving into the periphery of RCC treatment strategies. However, for the last 2 years there has been significant progress made in immunotherapeutic approaches for the treatment of RCC. Immunotherapy still remains the only systemic therapeutic strategy that is believed to potentially cure RCC patients. The development of active and passive specific immunotherapeutic approaches, along with the possibility to 'switch off' particular immunosuppressive mechanisms (e.g., elimination of regulatory T cells, blockage of cytotoxic T lymphocyte antigen-4 signaling), have paved the way for future trials of new immunotherapies of RCC. However, the new studies will have to enroll optimally selected patients (nephrectomized, with non-massive metastases and good performance status) and will use tumor response criteria that are specifically optimized for clinical trials of immunotherapy.

Adjuvant treatment for renal cell carcinoma

Despite significant advances in the diagnosis, staging and treatment of patients with renal cell carcinoma, recurrence rates following surgical resection of locally aggressive tumours remain high. In an effort to delay disease progression and improve survival, the concept of adjuvant therapy has been proposed. Optimal adjuvant therapy for surgically resected renal cell carcinoma remains to be defined and the evaluation of adjuvant therapies will require properly controlled and adequately powered randomised trials. Promising preliminary results have been seen with active immunotherapies and agents that target critical signalling pathways, and there are several Phase III trials of these novel treatment options that are underway. In addition, classification of patients into high- and low-risk subgroups on the basis of a prognosis profile will serve as a useful means to guide clinicians in improving the selection of patients who are likely to derive benefit from adjuvant therapy. This will lead to a future area of investigation, which will be the identification of patients within the target population that should respond to a given treatment. This review will discuss the role and current status of adjuvant therapies for renal cell carcinoma.

Emerging drugs for renal cell carcinoma

Renal cell carcinoma (RCC) still represents a therapeutic challenge when patients have advanced or metastatic disease. Treatment using IL-2 and IFN-alpha continues to be the standard of care in patients who are able to tolerate such regimens. Targeted therapy may become the first-line treatment for patients resistant or intolerant to cytokines as new emerging drugs continue to be investigated. Understanding the genetic abnormalities related to the development of RCC (e.g., VHL gene abnormalities) and identifying molecular targets (e.g., epidermal growth factor, vascular endothelial growth factor and carbonic anhydrase IX) are playing a major role in the emergence of these novel agents for the treatment of this malignancy. Overall, these drugs are better tolerated and more acceptable to use by patients than the traditional cytokine-based regimens. The use of oral drugs to treat various malignancies including RCC seems to be the new paradigm of the future. Further understanding of their mechanisms of action and confirmation of their benefits on the clinical outcome is needed.