Time, space and contextual models of the immunity tolerance decision: bridging the geographical divide of Zinkernagel and Hengartner's 'Credo 2004'

Exploiting autoimmunity unleashed by low-dose immune checkpoint blockade to treat advanced cancer

As a result of the cancer immunotherapy revolution, more than 2000 immuno-oncology agents are currently being tested or are in use to improve responses. Not unexpectedly, the 2018 Nobel Prize in Physiology or Medicine was awarded to James P. Allison and Tasuku Honjo for their development of cancer therapy by the blockade of co-inhibitory signals. Unfortunately, manipulation of the co-inhibitory receptors has also resulted in a safety issue: widespread iatrogenic immune-related adverse events (irAEs). Autoimmunity is emerging as the nemesis of immunotherapy. Originally, it was assumed that CTLA-4 blockade selectively targets T cells relevant to the antitumour immune response. However, an uncontrolled pan T cell activation was induced compromising tolerance to healthy self-tissues. The irAEs are very similar to that of a chronic graft-versus-host-disease (GVHD) reaction following allogeneic bone marrow transplantation (BMT). We hypothesized that ipilimumab induced a graft-versus-malignancy (GVM) effect, which eradicated metastatic melanoma in a minority of patients, but also involved an auto-GVHD reaction that resulted in widespread autoimmunity in the majority. Therefore, we argued for a profound theoretical point against the consensus of experts. The task is not to desperately put the genie back in the bottle by immune-suppressive treatments, but instead to harness the autoimmune forces. In this way, the same goal could be achieved by an antibody as by the adoptive transfer of alloreactive donor lymphocytes, but without severe GVHD. The proof-of-principle of a low-dose-combination immune checkpoint therapy, consisting only of approved drugs and treatments, was demonstrated in 111 stage IV cancer patients.

Thoughts engendered by Bretscher's Two-step, Two-signal model for a peripheral self-non-self discrimination and the origin of primer effector T helpers

There are three questions under re-examination here that have been inspired by Bretscher's 'Two-step, Two-signal' model. First, what is the nature of the steps required in order for antigen-responsive cells to become effectors? Second, how does the immune system get started? Third and the most troublesome, what is the mechanism that relates the delivery of the two signals? To answer the first question, Bretscher proposes a pathway that I will place in another context by comparing it with what had been envisaged under the Associative Recognition of Antigen (ARA) model. The second question, how does the immune system gets started, is crucial to our understanding of the self-non-self discrimination. This problem boils down to, what is the origin of the first effector T helper (eTh) cells required to activate all antigen-responsive cells including the T helpers themselves (the primer problem)? To deal with this question, I proposed an antigen-independent pathway to primer eTh. Bretscher presents us with an antigen-dependent pathway to primer eTh. As competing models are precious in clarifying thinking and in guiding experimentation, I felt it important to reanalyse the two models and look for ways to decide between them. The third question deals with the requirement for and the mechanism of associative (linked) recognition of antigen (ARA). The concept of ARA is so compelling at both the experimental and theoretical levels that to save it, a new perspective will be introduced.

To drive or be driven: the path of a mouse model of recurrent pregnancy loss

This review is an example of the use of an animal model to try to understand the immune biology of pregnancy. A well-known model of recurrent spontaneous pregnancy loss is put in clinical, historical, and theoretical context, with emphasis on T cell biology.

Co-inhibitory molecules: Controlling the effectors or controlling the controllers?

Nearly forty years ago the concept was proposed that lymphocytes are negatively regulated by what are now called co-inhibitory signals. Nevertheless, it is only the more recent identification of numerous co-inhibitors and their critical functions that has brought co-inhibition to the forefront of immunologic research. Although co-inhibitory signals have been considered to directly regulate conventional T cells, more recent data has indicated a convergence between co-inhibitory signals and the other major negative control mechanism in the periphery that is mediated by regulatory T cells. Furthermore, it is now clear that lymphocytes are not the sole domain of co-inhibitory signals, as cells of the innate immune system, themselves controllers of immunity, are regulated by co-inhibitors they express. Thus, in order to better understand negative regulation in the periphery and apply this knowledge to the treatment of disease, a major focus for the future should be the definition of the conditions where co-inhibition controls effector cells intrinsically versus extrinsically (via regulatory or innate cells).

On the sorting of the repertoire: an analysis of Cohn's challenge to integrity (Dembic), Round 2

In analyzing the integrity model and other context-based models, Melvin Cohn excluded the possibility that regulatory T cells or germline selected mechanisms can contribute to defining the specificity of immune responses. Here I discuss in greater detail how both the experimental data and a quantitative view of the evolution of immune control mechanisms challenge Cohn's arguments.

On the critique by Colin Anderson of 'A reply to Dembic: on an end to the beginning of mis-understanding the immune response'

My proposal of a set of postulates that can be used to guide computer modeling has understandably met with significant criticism at two levels, semantic and conceptual. The major source of contention is my assumption that the sorting of the paratopic repertoire is both necessary and sufficient to explain the evolutionarily selected mechanism for the self-nonself discrimination. While 'necessary' is agreed upon, 'sufficient' is debatable as this commentary illustrates. My essay is in defense of 'sufficiency'.

Placing regulatory T cells into global theories of immunity: an analysis of Cohn's challenge to integrity (Dembic)

In broadening the integrity model, Zlatko Dembic provided one of the few plausible explanations for the existence of regulatory T cells that has been postulated to date and at the same time highlighted deficiencies of the associative antigen recognition model. In defending the virtues of associative antigen recognition, Melvin Cohn has challenged the integrity model and the concept that regulatory T cells have a role in defining the specificity of immune responses. The critique of Cohn's analysis I present here suggests that a greater consideration of quantitative evolutionary constraints removes most of the challenges to integrity.

On the opposing views of the self-nonself discrimination by the immune system

Today's generally accepted view of the self-nonself discrimination was voiced by Miller(1) in 2004 in a thought-provoking essay. In spite of its popularity, this position has its limitations, which are analyzed here with a view toward establishing an interactive discussion that hopefully will culminate in agreed upon decisive experiments. The inadequacies of Miller's view of the self-nonself discrimination and their resolution under the associative recognition of antigen model are analyzed.

A proliferation of pathogens through the 20th century

A substantial proportion of immunologists, microbiologists and health professionals--and, indeed, many dictionaries--currently regard the term pathogen as a synonym for a pathogenic organism (most often a micro-organism). I will argue that this is a distortion of its original meaning--'a specific causative agent of disease'. An analysis of the historical use of the term pathogen together with a comparison of the meanings of pathogen, pathogenic and pathogenesis suggest that this was an insidious change. It began as a convenient abbreviation, escalated into a misappropriation and is now lodged in bio-medicine's popular lexicon. In science, we should resist the pressures brought about by the mass action of common usage--unless there is a good, logical reason to accept this change. I propose that this common usage results in a distortion and leads to conceptual confusion, particularly when we try to understand the interaction between hosts and invasive organisms. This drift, in which pathogen becomes exclusively a living organism, is corrupting. There is a strong case for correcting and reversing it.

Biomarker profiles in serum and saliva of experimental Sjögren's syndrome: associations with specific autoimmune manifestations

INTRODUCTION

Sjögren's syndrome (SS) is a systemic autoimmune disease that mainly targets the exocrine glands. The aim of this study was to investigate the involvement of 87 proteins measured in serum and 75 proteins analyzed in saliva in spontaneous experimental SS. In addition, we intended to compute a model of the immunological situation representing the overt disease stage of SS.

METHODS

Nondiabetic, nonobese diabetic (NOD) mice aged 21 weeks were evaluated for salivary gland function, salivary gland inflammation and extraglandular disease manifestations. The analytes, comprising chemokines, cytokines, growth factors, autoantibodies and other biomarkers, were quantified using multi-analyte profile technology and fluorescence-activated cell sorting. Age-matched and sex-matched Balb/c mice served as a reference.

RESULTS

We found NOD mice to exhibit impaired salivary flow, glandular inflammation and increased secretory SSB (anti-La) levels. Thirty-eight biomarkers in serum and 34 in saliva obtained from NOD mice were significantly different from those in Balb/c mice. Eighteen biomarkers in serum and three chemokines measured in saliva could predict strain membership with 80% to 100% accuracy. Factor analyses identified principal components mostly correlating with one clinical aspect of SS and having distinct associations with components extracted from other families of proteins.

CONCLUSION

Autoimmune manifestations of SS are greatly independent and associated with various immunological processes. However, CD40, CD40 ligand, IL-18, granulocyte chemotactic protein-2 and anti-muscarinic M3 receptor IgG3 may connect the different aspects of SS. Processes related to the adaptive immune system appear to promote SS with a strong involvement of T-helper-2 related proteins in hyposalivation. This approach further established saliva as an attractive biofluid for biomarker analyses in SS and provides a basis for the comparison and selection of potential drug targets and diagnostic markers.

Tissue Homeostasis and Immunity – More on Models

This article continues the ongoing debate around models of the immune system. Earlier contributors have paid much attention to the various processes that lead to adaptive immune system aggression or tolerance. They have often based their discussions around facts that have been established by experimental investigation. However, both the observation and interpretation of these facts have been influenced by the function--or system goal--that is believed to have generated them. The perception of this function (of all or part of the immune system) is influenced by long established theories in immunology (e.g. horror autotoxicus, clonal deletion in utero, pathogen elimination, clonal selection, auto-immunity and so on) which, for many, have become enshrined as facts. One function that has had less consideration and has not been extensively investigated is the maintenance of tissue homeostasis. When the immune system is viewed from this perspective, the facts invite alternative interpretations. Whilst this perspective may not necessarily be the only valid one, let alone a correct one, viewing things this way--at least briefly--might help to expose hidden assumptions. It also emphasizes that the immune system is a system and, as such, it can by analysed through the principles of general systems theory.

On ‘Credo 2004’ as Viewed Under the ‘Development-Context’ Model of Colin Anderson

In analysing the Zinkernagel and Hengartner's 'Credo 2004,' Anderson introduces his 'development-context model' for the immunity-tolerance discrimination. He compares this model with the 'geographical model of Credo 2004' and our 'time-based two-signal model'. The discussion here deals with the advantages and limitations of the Anderson model considered largely at the level of principle. A meaningful discussion requires that we agree on the principle which separates the pathway of the effector output into two decision steps, the sorting of the repertoire and the regulation of effector class. The mechanism for the sorting of the repertoire is what might be referred to as the Self-Nonself discrimination. The black box approach, antigen-in, effector response-out, is what is referred to as the immunity-tolerance discrimination which includes the sorting of the repertoire. If this point of principle is accepted then we are left with a 'time-based two signal default model'.