Chronic chemoimmunotherapy achieves cure of spontaneous murine mammary tumors via persistent blockade of posttherapy counter-regulation

Engineering Strategies for Immunomodulatory Cytokine Therapies - Challenges and Clinical Progress

Cytokines are immunoregulatory proteins involved in many pathological states with promising potential as therapeutic agents. A diverse array of cytokines have been studied in preclinical disease models since the 1950s, some of which became successful biopharmaceutical products with the advancement of recombinant protein technology in the 1980s. However, following these early approvals, clinical translation of these natural immune signaling molecules has been limited due to their pleiotropic action in many cell types, and the fact that they have evolved to act primarily locally in tissues. These characteristics, combined with poor pharmacokinetics, have hindered the delivery of cytokines via systemic administration routes due to dose-limiting toxicities. However, given their clinical potential and recent clinical successes in cancer immunotherapy, cytokines continue to be extensively pursued in preclinical and clinical studies, and a range of molecular and formulation engineering strategies are being applied to reduce treatment toxicity while maintaining or enhancing therapeutic efficacy. This review provides a brief background on the characteristics of cytokines and their history as clinical therapeutics, followed by a deeper discussion on the engineering strategies developed for cytokine therapies with a focus on the translational relevance of these approaches.

Chemoimmunotherapy as long-term maintenance therapy for cancer

Homeostatic immune regulatory mechanisms can mediate premature termination of therapy-induced antitumor T-effector cell responses. Administration of cyclophosphamide (CY) prior to intratumoral IL-12 and GM-CSF delivery blocked post-treatment T-suppressor cell rebound via elimination of the pre-existing T-suppressor cell pool, allowed repeated activation of antitumor cytotoxic T-cells and resulted in the cure of advanced spontaneous tumors.

Localized Interleukin-12 for Cancer Immunotherapy

Interleukin-12 (IL-12) is a potent, pro-inflammatory type 1 cytokine that has long been studied as a potential immunotherapy for cancer. Unfortunately, IL-12's remarkable antitumor efficacy in preclinical models has yet to be replicated in humans. Early clinical trials in the mid-1990's showed that systemic delivery of IL-12 incurred dose-limiting toxicities. Nevertheless, IL-12's pleiotropic activity, i.e., its ability to engage multiple effector mechanisms and reverse tumor-induced immunosuppression, continues to entice cancer researchers. The development of strategies which maximize IL-12 delivery to the tumor microenvironment while minimizing systemic exposure are of increasing interest. Diverse IL-12 delivery systems, from immunocytokine fusions to polymeric nanoparticles, have demonstrated robust antitumor immunity with reduced adverse events in preclinical studies. Several localized IL-12 delivery approaches have recently reached the clinical stage with several more at the precipice of translation. Taken together, localized delivery systems are supporting an IL-12 renaissance which may finally allow this potent cytokine to fulfill its considerable clinical potential. This review begins with a brief historical account of cytokine monotherapies and describes how IL-12 went from promising new cure to ostracized black sheep following multiple on-study deaths. The bulk of this comprehensive review focuses on developments in diverse localized delivery strategies for IL-12-based cancer immunotherapies. Advantages and limitations of different delivery technologies are highlighted. Finally, perspectives on how IL-12-based immunotherapies may be utilized for widespread clinical application in the very near future are offered.

Local expression of interleukin-2 by B16 melanoma cells results in decreased tumour growth and long-term tumour dormancy

The tumour microenvironment is complex containing not only neoplastic cells but also a variety of host cells. The heterogeneous infiltrating immune cells include subsets of cells with opposing functions, whose activities are mediated either directly or through the cytokines they produce. Systemic delivery of cytokines such as interleukin-2 ( IL-2) has been used clinically to enhance anti-tumour responses, but these molecules are generally thought to have evolved to act locally in a paracrine fashion. In this study we examined the effect of local production of IL-2 on the growth and the immune response to B16 melanoma cells. We found that the local production of IL-2 enhances the number of interferon-γ-expressing CD8 T and natural killer cells in the tumour, as well as inducing expression of vascular cell adhesion molecule 1 on tumour vessels. These responses were largely absent in interferon-γ knockout mice. The expression of IL-2 in the tumour microenvironment decreases tumour growth despite also enhancing Foxp3(+)  CD4(+) regulatory T cells and anti-inflammatory cytokines such as IL-10. Higher levels of IL-2 in the tumour microenvironment eliminated the progressive growth of the B16 cells in vivo, and this inhibition was dependent on the presence of either T cells or, to a lesser extent, natural killer cells. Surprisingly however, the B16 tumours were not completely eliminated but instead were controlled for an extended period of time, suggesting that a form of tumour dormancy was established.

Towards curative cancer immunotherapy: overcoming posttherapy tumor escape

The past decade has witnessed the evolvement of cancer immunotherapy as an increasingly effective therapeutic modality, evidenced by the approval of two immune-based products by the FDA, that is, the cancer vaccine Provenge (sipuleucel-T) for prostate cancer and the antagonist antibody against cytotoxic T-lymphocyte antigen-4 (CTLA-4) ipilimumab for advanced melanoma. In addition, the clinical evaluations of a variety of promising immunotherapy drugs are well under way. Benefiting from more efficacious immunotherapeutic agents and treatment strategies, a number of recent clinical studies have achieved unprecedented therapeutic outcomes in some patients with certain types of cancers. Despite these advances, however, the efficacy of most cancer immunotherapies currently under clinical development has been modest. A recurring scenario is that therapeutic maneuvers initially led to measurable antitumor immune responses in cancer patients but ultimately failed to improve patient outcomes. It is increasingly recognized that tumor cells can antagonize therapy-induced immune attacks through a variety of counterregulation mechanisms, which represent a fundamental barrier to the success of cancer immunotherapy. Herein we summarize the findings from some recent preclinical and clinical studies, focusing on how tumor cells advance their survival and expansion by hijacking therapy-induced immune effector mechanisms that would otherwise mediate their destruction.

Immunotherapy: a useful strategy to help combat multidrug resistance

Multidrug resistance (MDR) renders cancer cells relatively invulnerable to treatment with many standard cytotoxic anti-cancer agents. Cancer immunotherapy could be an important adjunct for other strategies to treat MDR positive cancers, as resistance to immunotherapy generally is unrelated to mechanisms of resistance to cytotoxic agents. Immunotherapy to combat MDR positive tumors could use any of the following strategies: direct immune attack against MDR positive cells, using MDR as an immune target to deliver cytotoxic agents, capitalization on other immune properties of MDR positive cells, or conditional immunotoxins expressed under MDR control. Additional insights into the immunogenic potential of some cytotoxic agents can also be brought to bear on these strategies. This review will highlight key concepts in cancer immunotherapy and illustrate immune principles and strategies that have been or could be used to help destroy MDR positive tumor cells, either alone or in rational combinations.