Devin B. Lowe

Immune Checkpoint Inhibitors: New Insights and Current Place in Cancer Therapy

The treatment of cancer has largely relied on killing tumor cells with nonspecific cytotoxic therapies and radiotherapy. This approach, however, has limitations including severe systemic toxicities, bystander effects on normal cells, recurrence of drug‐resistant tumor cells, and the inability to target micrometastases or subclinical disease. An increased understanding of the critical role of the immune system in cancer development and progression has led to new treatment strategies using various immunotherapies. It is now recognized that established tumors have numerous mechanisms of suppressing the antitumor immune response including production of inhibitory cytokines, recruitment of immunosuppressive immune cells, and upregulation of coinhibitory receptors known as immune checkpoints. This review focuses on the immune checkpoint inhibitors, a novel class of immunotherapy first approved in 2011. Our objective is to highlight similarities and differences among the three immune checkpoint inhibitors approved by the U.S. Food and Drug Administration—ipilimumab, pembrolizumab, and nivolumab—to facilitate therapeutic decision making. We conducted a review of the published literature and conference proceedings and present a critical appraisal of the clinical evidence supporting their use in the treatment of metastatic melanoma and advanced squamous non–small cell lung cancer (NSCLC). We also compare and contrast their current place in cancer therapy and patterns of immune‐related toxicities, and discuss the role of dual immune checkpoint inhibition and strategies for the management of immune‐related adverse events. The immune checkpoint inhibitors have demonstrated a dramatic improvement in overall survival in patients with advanced melanoma and squamous NSCLC, along with acceptable toxicity profiles. These agents have a clear role in the first‐line treatment of advanced melanoma and in the second‐line treatment of advanced squamous NSCLC.

Combined vaccine+axitinib therapy yields superior antitumor efficacy in a murine melanoma model.

Axitinib, a tyrosine kinase inhibitor of vascular endothelial growth factor receptors, has demonstrated modest efficacy when applied as a single agent in the setting of advanced-stage melanoma. On the basis of the reported ability of axitinib to ‘normalize’ the tumor vasculature, we hypothesize that combination therapy using axitinib plus specific peptide-based vaccination would promote superior activation and recruitment of protective T cells into the melanoma microenvironment, leading to enhanced treatment benefit. Using a subcutaneous M05 (B16.OVA) melanoma model, we observed that a treatment regimen consisting of a 7-day course of axitinib (0.5 mg/day provided orally) combined with a subcutaneous vaccine [ovalbumin (OVA) peptide-pulsed syngenic dendritic cells adenovirally engineered to produce IL-12p70] yielded superior protection against melanoma growth and extended overall survival when compared with animals receiving either single modality therapy. Treatment benefits were associated with: (a) a reduction in suppressor cell (myeloid-derived suppressor cells and Treg) populations in the tumor, (b) activation of tumor vascular endothelial cells, and (c) activation and recruitment of type-1, vaccine-induced CD8+ T cells into tumors. These results support the therapeutic superiority of combined vaccine+axitinib immunotherapy and the translation of such approaches into the clinic for the treatment of patients with advanced-stage melanoma.

DNA vaccines: successes and limitations in cancer and infectious disease.

Vaccination with plasmid DNA is an active area of investigation that is being applied to diseases including cancer and microbial pathogens associated with infectious diseases. Since its discovery, great progress has been made with the administration of DNA vaccines to initiate specific and effective immune responses against targeted illnesses. However, many obstacles still face its use in prophylactic and therapeutic vaccination scenarios. The nature of these difficulties alongside the successes and future of plasmid DNA will be discussed. J. Cell. Biochem. 98: 235–242, 2006.

Towards progress on DNA vaccines for cancer

Abstract.Cancer immunotherapy faces many obstacles that include eliciting immune reactions to self antigens as well as overcoming tumor-derived immunosuppressive networks and evasion tactics. Within the vaccine arsenal for inhibiting cancer proliferation, plasmid DNA represents a novel immunization strategy that is capable of eliciting both humoral and cellular arms of the immune response in addition to being safely administered and easily engineered and manufactured. Unfortunately, while DNA vaccines have performed well in preventing and treating malignancies in animal models, their overall application in human clinical trials has not impacted cancer regression to date. Since the establishment of these early trials, progress has been made in terms of increasing DNA vaccine immunogenicity and subverting the suppressive properties of tumor cells. Therefore, the success of future plasmid DNA use in cancer patients will depend on combinatorial strategies that enhance and direct the DNA vaccine immune response while also targeting tumor evasion mechanisms.

Intratumoral IL-12 Gene Therapy Results in the Crosspriming of Tc1 Cells Reactive Against Tumor-associated Stromal Antigens

HLA-A2 transgenic mice bearing established HLA-A2(neg) B16 melanomas were effectively treated by intratumoral (i.t.) injection of syngeneic dendritic cells (DCs) transduced to express high levels of interleukin (IL)-12, resulting in CD8(+) T cell-dependent antitumor protection. In this model, HLA-A2-restricted CD8(+) T cells do not directly recognize tumor cells and therapeutic benefit was associated with the crosspriming of HLA-A2-restricted type-1 CD8(+) T cells reactive against antigens expressed by stromal cells [i.e., pericytes and vascular endothelial cells (VEC)]. IL-12 gene therapy-induced CD8(+) T cells directly recognized HLA-A2(+) pericytes and VEC flow-sorted from B16 tumor lesions based on interferon (IFN)-γ secretion and translocation of the lytic granule-associated molecule CD107 to the T cell surface after coculture with these target cells. In contrast, these CD8(+) T effector cells failed to recognize pericytes/VEC isolated from the kidneys of tumor-bearing HHD mice. The tumor-associated stromal antigen (TASA)-derived peptides studied are evolutionarily conserved and could be recognized by CD8(+) T cells harvested from the blood of HLA-A2(+) normal donors or melanoma patients after in vitro stimulation. These TASA and their derivative peptides may prove useful in vaccine formulations against solid cancers, as well as, in the immune monitoring of HLA-A2(+) cancer patients receiving therapeutic interventions, such as IL-12 gene therapy.

Chronic inflammation and immunologic-based constraints in malignant disease

Acute inflammatory reactions benefit the host by supporting the effective clearance of pathogens and fostering wound healing, in addition to other self-preservative processes. However, when the inflammatory program is not resolved, becoming chronic in nature, it creates an environment conducive to cancer development and progression. Therefore, minimizing exposure to risk factors that contribute to chronic inflammation and reconditioning the host towards a state of (at least locoregional) acute inflammation would meaningfully impact cancer incidence and its treatment, respectively. Regarding cancer therapy, combinational treatments that both disrupt chronic inflammation and install specific adaptive type I immunity are predicted to enhance quality of life and extend the overall survival of patients.

Vaccines Targeting Tumor Blood Vessel Antigens Promote CD8+ T Cell-Dependent Tumor Eradication or Dormancy in HLA-A2 Transgenic Mice

We have recently shown that effective cytokine gene therapy of solid tumors in HLA-A2 transgenic (HHD) mice lacking murine MHC class I molecule expression results in the generation of HLA-A2–restricted CD8+ T effector cells selectively recognizing tumor blood vessel-associated pericytes and/or vascular endothelial cells. Using an HHD model in which HLA-A2neg tumor (MC38 colon carcinoma or B16 melanoma) cells are not recognized by the CD8+ T cell repertoire, we now show that vaccines on the basis of tumor-associated blood vessel Ags (TBVA) elicit protective Tc1-dependent immunity capable of mediating tumor regression or extending overall survival. Vaccine efficacy was not observed if (HLA-A2neg) wild-type C57BL/6 mice were instead used as recipient animals. In the HHD model, effective vaccination resulted in profound infiltration of tumor lesions by CD8+ (but not CD4+) T cells, in a coordinate reduction of CD31+ blood vessels in the tumor microenvironment, and in the “spreading” of CD8+ T cell responses to alternate TBVA that were not intrinsic to the vaccine. Protective Tc1-mediated immunity was durable and directly recognized pericytes and/or vascular endothelial cells flow-sorted from tumor tissue but not from tumor-uninvolved normal kidneys harvested from these same animals. Strikingly, the depletion of CD8+, but not CD4+, T cells at late time points after effective therapy frequently resulted in the recurrence of disease at the site of the regressed primary lesion. This suggests that the vaccine-induced anti-TBVA T cell repertoire can mediate the clinically preferred outcomes of either effectively eradicating tumors or policing a state of (occult) tumor dormancy.

Vaccines and Immunotherapeutics for the Treatment of Malignant Disease

The employment of the immune system to treat malignant disease represents an active area of biomedical research. The specificity of the immune response and potential for establishing long-term tumor immunity compels researchers to continue investigations into immunotherapeutic approaches for cancer. A number of immunotherapeutic strategies have arisen for the treatment of malignant disease, including various vaccination schemes, cytokine therapy, adoptive cellular therapy, and monoclonal antibody therapy. This paper describes each of these strategies and discusses some of the associated successes and limitations. Emphasis is placed on the integration of techniques to promote optimal scenarios for eliminating cancer.

Dasatinib promotes the expansion of a therapeutically superior T-cell repertoire in response to dendritic cell vaccination against melanoma

Dasatinib (DAS) is a potent inhibitor of the BCR-ABL, SRC, c-KIT, PDGFR, and ephrin tyrosine kinases that has demonstrated only modest clinical efficacy in melanoma patients. Given reports suggesting that DAS enhances T cell infiltration into the tumor microenvironment, we analyzed whether therapy employing the combination of DAS plus dendritic cell (DC) vaccination would promote superior immunotherapeutic benefit against melanoma. Using a M05 (B16.OVA) melanoma mouse model, we observed that a 7-day course of orally-administered DAS (0.1 mg/day) combined with a DC-based vaccine (VAC) against the OVA257–264 peptide epitope more potently inhibited tumor growth and extended overall survival as compared with treatment with either single modality. The superior efficacy of the combinatorial treatment regimen included a reduction in hypoxic-signaling associated with reduced levels of immunosuppressive CD11b+Gr1+ myeloid-derived suppressor cells (MDSC) and CD4+Foxp3+ regulatory T (Treg) populations in the melanoma microenvironment. Furthermore, DAS + VAC combined therapy upregulated expression of Type-1 T cell recruiting CXCR3 ligand chemokines in the tumor stroma correlating with activation and recruitment of Type-1, vaccine-induced CXCR3+CD8+ tumor-infiltrating lymphocytes (TILs) and CD11c+ DC into the tumor microenvironment. The culmination of this bimodal approach was a profound “spreading” in the repertoire of tumor-associated antigens recognized by CD8+ TILs, in support of the therapeutic superiority of combined DAS + VAC immunotherapy in the melanoma setting.

Fcγ Receptors Play a Dominant Role in Protective Tumor Immunity against a Virus-Encoded Tumor-Specific Antigen in a Murine Model of Experimental Pulmonary Metastases

ABSTRACT Simian virus 40 (SV40) large tumor antigen (Tag) represents a virus-encoded tumor-specific antigen expressed in many types of human cancers and a potential immunologic target for antitumor responses. Fc receptors are important mediators in the regulation and execution of host effector mechanisms against conditions including infectious diseases, autoimmunity, and cancer. By examining tumor protection in SV40 Tag-immunized wild-type BALB/c mice using an experimental pulmonary metastasis model, we attempted to address whether engagement of the immunoglobulin G Fc receptors (FcγRs) on effector cells is necessary to mediate antitumor responses. All immunized BALB/c FcγR−/− knockout mice developed anti-SV40 Tag antibody responses prior to experimental challenge with a tumorigenic cell line expressing SV40 Tag. However, all mice deficient in the activating FcγRI (CD64) and FcγRIII (CD16) were unable to mount protective immunologic responses against tumor challenge and developed tumor lung foci. In contrast, mice lacking the inhibitory receptor FcγRII (CD32) demonstrated resistance to tumorigenesis. These results underscore the importance of effector cell populations expressing FcγRI/III within this murine tumor model system, and along with the production of a specific humoral immune response, antibody-dependent cell-mediated cytotoxicity (ADCC) may be a functioning mechanism of tumor clearance. Additionally, these data demonstrate the potential utility of ADCC as a viable approach for targeting vaccination strategies that promote FcγRI/III scavenging pathways against cancer.