Design, synthesis, and assessment of specific iNKT cell agonists for clinical applications

The proposed research will address fundamental questions about the influence of the structural activity relationship of CD1d-restricted iNKT cells and how we may take advantage of both their immunostimulatory and immunoregulatory properties to help treat a number of clinical conditions. By using an informed design approach to generating new iNKT cell agonists, we hope to develop a more rational strategy to exploit the diverse immunomodulatory properties of this family of compounds as potential immunotherapeutic drugs. iNKT?ncell?nligands such as alpha-GalCer associated analogues, and other novel synthetic agonists, have potential use in three therapeutic areas. First, the Th1 cytokine-inducing properties of alpha-GalCer-based agents could provide protection against a variety of pathogens as a short-term immunostimulatory boost. Second, the non-specific immune activation properties of these compounds may be exploited as vaccine immunoadjuvants to boost cytotoxic responses to various neoplasias and infectious diseases, and third, the Th2 cytokine-inducing properties of iNKT cell agonists may prove effective at controlling auto-aggressive immune responses. The key challenge remains how to activate and manipulate the different functions of iNKT cells selectively, through the use of specific agonists, which can then be translated into clinical applications. As the complex structures of current iNKT agonists based on alpha-GalCer are not particularly suitable for clinical development, there is an urgent need to develop new simpler compounds that are capable of inducing targeted human iNKT cell responses. This will be achieved by a process of informed, structural design. In addition we intend to maximise our chances of success by making structural modifications to the parent iNKT cell agonist, alpha-GalCer, to create new analogues, based on our previously acquired knowledge of the structural activity relationships (SAR!
s) that influence/govern their biological outcome. We will also use more sophisticated human in vitro screening assays to improve clinical translation of new agonists. In this application, our philosophy is to deliver a multidisciplinary, state-of-the-art programme of studies in order to address these goals. The proposed methodologies are novel and include: chemical synthesis, in silico design, human in vitro screening assays and novel in vivo verification models.

Invariant natural killer T cells (iNKT cells) are one of the key sentinel cells of the innate immune system. Their activation by foreign lipid antigens, dictates and directs a subsequent adaptive immune response to this stimulus, and in this way, microbial activation of iNKT cells can result in dendritic and B cell maturation, promoting specific cellular and antibody responses against invading pathogens. iNKT cells are also important mediators of cancer immunosurveillance, acting via direct recognition and lysis of malignant cells or through subsequent Th1 cytokine release, which promotes NK cell anti-tumour activity. These properties indicate their potential clinical application in developing both anti-microbial and anti-tumour vaccination/treatment strategies. In contrast to these immune-system-activating properties, iNKT cells also play a major role in suppressing autoimmune responses via induction of inhibitory Th2 cytokines and/or promotion of regulatory T cells to self-lipid antigens. In this mode of operation, they have the potential to suppress autoimmune diseases, such as NOD, EAE, and SLE. Whilst iNKT cells exhibit wide-ranging responses to activation, the key challenge remains how to activate and manipulate the different potential functions of iNKT cells selectively, through the use of specific agonists, which can then be translated into clinical applications. We believe this is now possible through a greater understanding of the structure-activity relationships (SARs) that govern iNKT-TCR-CD1d interactions, which can direct the design of new agonists towards predictable biological outcomes. By studying the SARs of previously identified glycolipid agonists, we have already identified a number of parameters including: i) binding affinity, ii) direct presentation or requirement for internalisation and processing, and iii) co-stimulatory molecule recruitment and activation, that dictate the type of immune response that results upon iNKT cell activation. We now propose to generate new iNKT cell agonists with simplified architectures and tailored immunological responses, which can be applied for therapeutic use. Assessment of their clinical potential will also be enhanced by the incorporation of various novel human in vitro assays into our bioactivity screening programme.