The adaptation model of immunity

The adaptation model of immunity: A new insight into aetiology and treatment of multiple sclerosis

Current research and drug development for multiple sclerosis (MS) is fully influenced by the self-nonself (SNS) model of immunity, suggesting that breakage of immunological tolerance towards self-antigens expressed in the central nervous system (CNS) is responsible for pathogenesis of MS; thus, immune suppressive drugs are recommended for the management of the disease. However, this model provides incomplete understanding of the causes and pathways involved in the onset and progression of MS and limits our ability to effectively treat this neurological disease. Some pre-clinical and clinical reports have been misunderstood; some others have been underappreciated because of the lack of a theoretical model that can explain them. Also, current immunotherapies are guided according to the models that are not designed to explain the functional outcomes of an immune response. The adaptation model of immunity is proposed to offer a new understanding of the existing data and galvanize a new direction for the treatment of MS. According to this model, the immune system continuously communicates with the CNS through the adaptation receptors (AdRs) and adaptation ligands (AdLs) or co-receptors, signal IV, to support cell growth and neuroplasticity. Alterations in the expression of the neuronal AdRs results in MS by shifting the cerebral inflammatory immune responses from remyelination to demyelination. Therefore, novel therapeutics for MS should be focused on the discovery and targeting of the AdR/AdL axis in the CNS rather than carrying on with immune suppressive interventions.

The adaptation model of immunity: Is the goal of central tolerance to eliminate defective T cells or self-reactive T cells?

The self-non-self model and the danger model are designed to understand how an immune response is induced. These models are not meant to predict if an immune response may succeed or fail in destroying/controlling its target. However, these immunological models rely on either self-antigens or self-dendritic cells for understanding of central tolerance, which have been discussed by Fuchs and Matzinger in response to Al-Yassin. In an attempt to address some questions that these models are facing when it comes to understanding central tolerance, I propose that the goal of negative selection in the thymus is to eliminate defective T cells but not self-reactive T cells. Therefore, any escape from negative selection could increase lymphopenia because of the depletion of defective naïve T cells outside the thymus, as seen in the elderly.

Multifaceted functions of chronic inflammation in regulating tumor dormancy and relapse

Inflammation is a double-edged sword exhibiting multifaceted functions. On one hand, it either induces tumor cell apoptosis, or establishes tumor dormancy by inhibiting tumor cell proliferation; on the other hand, it either facilitates the tumorigenesis process or reawakens dormant tumor cells, resulting in disease recurrences. Each outcome would depend on the balance between type I and type II inflammation as well as the duration of inflammation being acute or chronic. In this essay, we provide a critical review of the empirical evidence suggesting that chronic inflammation, dominated by type I inflammatory cells and cytokines as a result of trauma and microbiome dysbiosis, could facilitate the carcinogenesis process in normal cells and retain nascent transformed cells in a dormant state. On the other hand, an elevated type II inflammation along with inefficient resolution of type I inflammation following trauma or major surgeries could delay the wound healing process and promote the growth and reawakening of dormant tumor cells, resulting in disease recurrences. Finally, cytokines exhibiting type I and II inflammatory functions, simultaneously, tend to promote tumor recurrence when become chronic. Therefore, the risk of reawakening dormant tumor cells should be considered in cancer survivors who experience major surgeries and trauma, or suffer from chronic inflammatory diseases.

IFN-γ orchestrates tumor elimination, tumor dormancy, tumor escape, and progression

Tumor immunoediting consisting of three phases of elimination, equilibrium or dormancy, and escape has been supported by preclinical and clinical data. A comprehensive understanding of the molecular mechanisms by which antitumor immune responses regulate these three phases are important for developing highly tailored immunotherapeutics that can control cancer. To this end, IFN-γ produced by Th1 cells, cytotoxic T cells, NK cells, and NKT cells is a pleiotropic cytokine that is involved in all three phases of tumor immunoediting, as well as during inflammation-mediated tumorigenesis processes. This essay presents a review of literature and suggests that overcoming tumor escape is feasible by driving tumor cells into a state of quiescent but not indolent dormancy in order for IFN-γ-producing tumor-specific T cells to prevent tumor relapse.

A Theoretical Basis for the Efficacy of Cancer Immunotherapy and Immunogenic Tumor Dormancy: The Adaptation Model of Immunity

In the past decades, a variety of strategies have been explored to cure cancer by means of immunotherapy, which is less toxic compared with chemotherapy or radiation therapy, and could establish memory for long-lasting protection against tumor recurrence. These endeavors have been successful in offering therapeutic antibodies, vaccines, or cellular immunotherapies, which resulted in prolonging survival of some cancer patients; however, complete cures have not been consistently achieved. The conception, design, and implementation of these promising immunotherapeutic strategies have been influenced by two schools of thought in immunology, which include the "self-nonself" (SNS) model and the "danger" model. Further progress in cancer immunotherapy to achieve consistent cancer cures requires an evolution in our understanding of how the immune system works. The purpose of this review is to revisit premises and limitations of the SNS and danger models based on the outcomes of cancer immunotherapies by suggesting that both models are two sides of the same coin describing how the immune response is induced against cancer. However, neither explains how the immune response succeeds or fails in eliminating the tumor. To this end, the adaptation model has been proposed to explain efficacy of the immune response for achieving cancer cure.

Modes of Antigen Presentation by Lymph Node Stromal Cells and Their Immunological Implications

Antigen presentation is no longer the exclusive domain of cells of hematopoietic origin. Recent works have demonstrated that lymph node stromal cell (LNSC) populations, such as fibroblastic reticular cells, lymphatic and blood endothelial cells, not only provide a scaffold for lymphocyte interactions but also exhibit active immunomodulatory roles that are critical to mounting and resolving effective immune responses. Importantly, LNSCs possess the ability to present antigens and establish antigen-specific interactions with T cells. One example is the expression of peripheral tissue antigens, which are presented on major histocompatibility complex (MHC)-I molecules with tolerogenic consequences on T cells. Additionally, exogenous antigens, including self and tumor antigens, can be processed and presented on MHC-I complexes, which result in dysfunctional activation of antigen-specific CD8⁺ T cells. While MHC-I is widely expressed on cells of both hematopoietic and non-hematopoietic origins, antigen presentation via MHC-II is more precisely regulated. Nevertheless, LNSCs are capable of endogenously expressing, or alternatively, acquiring MHC-II molecules. Transfer of antigen between LNSC and dendritic cells in both directions has been recently suggested to promote tolerogenic roles of LNSCs on the CD4⁺ T cell compartment. Thus, antigen presentation by LNSCs is thought to be a mechanism that promotes the maintenance of peripheral tolerance as well as generates a pool of diverse antigen-experienced T cells for protective immunity. This review aims to integrate the current and emerging literature to highlight the importance of LNSCs in immune responses, and emphasize their role in antigen trafficking, retention, and presentation.

Gain of HIF-1α under normoxia in cancer mediates immune adaptation through the AKT/ERK and VEGFA axes

PURPOSE

Adaptation to host immune surveillance is now recognized as a hallmark of cancer onset and progression, and represents an early, indispensable event in cancer evolution. This process of evolution is first instigated by an immune selection pressure imposed by natural host surveillance mechanisms and may then be propagated by vaccination or other types of immunotherapy.

EXPERIMENTAL DESIGN

We developed a system to simulate cancer evolution in a live host and to dissect the mechanisms responsible for adaptation to immune selection. Here, we show that the oxygen-sensitive α subunit of hypoxia-inducible factor 1 (HIF-1α) plays a central role in cancer immune adaptation under conditions of normal oxygen tension.

RESULTS

We found that tumor cells gain HIF-1α in the course of immune selection under normoxia and that HIF-1α renders tumor cells resistant to lysis by tumor-specific cytotoxic T lymphocytes (CTL) in culture and in mice. The effects of HIF-1α on immune adaptation were mediated through VEGFA-dependent activation of the AKT and ERK signaling pathways, which induced an antiapoptotic gene expression network in tumor cells.

CONCLUSIONS

Our study therefore establishes a link between immune selection, overexpression of HIF-1α, and cancer immune adaptation under normoxia, providing new opportunities for molecular intervention in patients with cancer.