The Nanoscale Phenotype of Immune Responses in Health and Disease

Familiarity with the body's response to a cut or an infection - redness, tenderness and inflammation - belies the wonders taking place, where swarms of different cells move in to fight off germs, as well as repair the damage and deal with the debris. Far from conscious control, this reflex is essential for our survival. A simple view of this is that the immune system attacks germs which invade the body opportunistically. But over the last few decades, a painstaking, game-changing scientific adventure unfolded in which the world of immunity has opened up for what it really is: not simply a few types of immune cells which attack germs, but a multi-layered, dynamic lattice of interlocking sub-systems, one of the most complex and important frontiers of scientific enquiry we know of.
Advances in technology are helping us understand the immune system as never before, and to develop medicines which boost the system to fight cancer better, to dampen it to combat the symptoms of auto-immune disease, and to help develop better vaccines. Activating and inhibitory receptors on the surface of immune cells are critical determinants of immune activity. The level of each receptor and its ligand, and how well they bind, are primary determinants of disease outcomes. However, advances in microscopy are now revealing a host of other factors which control immune responses. This includes protrusions from immune cells which contact other cells, a complex nanoscale organisation of activating and inhibitory receptors, clusters of proteins secreted by immune cells to kill diseased cells, and novel mechanisms by which immune cells can detach from one target cell to attack again. Understanding immunity on a nanoscale is a major new frontier and will lead to completely new ideas for medicine.
My own research laboratory has decades of experience studying human immune cells called Natural Killer (NK) cells. These immune cells are able to directly kill cancer cells, and are a hot topic in developing new cancer therapies. NK cells are also important in viral defence, microbial pathogens, autoimmune diseases, reproductive complications and transplantation. Their activation is regulated by many activating and inhibitory receptors at their surface. However, the central tenet of this proposal is that their activity is also influenced by nanoscale processes, beyond simple ligation of receptors. For example, the presence of a receptor may remain similar in health and disease, but its nanoscale organisation can be altered to affect its activity. Also, it is entirely unexplored whether or not disease impacts NK cell protrusion density or the capacity of NK cells for serial killing, and so on. Indeed, nanoscale processes which regulate NK cells (and other immune cells) may be a major factor missing in our understanding of health and disease.
Here, we will compare NK cells from healthy donors and cancer patients, assessing every stage of their interaction with a cancer cell on a nanoscale - from an initial cell-cell contact to the assembly of a synapse, release of effector particles, subsequent detachment and serial engagement. Activating and inhibitory receptors will be mapped to understand signal integration and immune response thresholds, the structure and function of immune cell secretions will be analysed, and determinants of cell detachment and serial killing will be determined, and then compared in health and disease. Single cell secretions, visualised by super-resolution microscopy, will lead to a new approach to characterising immune responses. We will also compare types of NK cell. For example, it is entirely unexplored if memory-like NK cells exhibit faster interaction dynamics and greater serial killing. A large consortium of collaborators will facilitate this complex interdisciplinary endeavour, from using new instrumentation, developing image analysis and access to clinical samples. Strong links to industry will translate these new ideas to medicines.

Cell-contact dependent immune responses are vital to our health. We now know that an immune cell interaction with a target cell involves several stages: initial contact, assembly of an immune synapse, release of effector proteins, subsequent detachment and finally, engagement with another target. However at each stage, there is a paucity of understanding what happens on a nanoscale. Evidence is accumulating that initial contacts occurs via cell protrusions, such that their density and dynamics may control immune cell sensitivity. Also, the nanoscale organisation of activating and inhibitory receptors has a huge impact on activation thresholds as, for example, discrete receptor clusters can segregate or coalesce to impact membrane proximal signal integration. Then upon activation, proteins secreted to kill infected or cancerous cells are organised in nanoscale supramolecular attack particles which are little understood. More broadly, secretions, including exosomes, are heterogeneous and our understanding of their functions and variability is still in its infancy. Mechanisms for immune cell detachment are also not clear, but involve nanoscale processes for removing receptor interactions. Thus, focussing on human Natural Killer (NK) cells as cells vital for defence against infections and cancer, and with NK cell-based therapies currently a hot topic, we will study each of these processes using super-resolution microscopy in combination with molecular and cell biology techniques. We will compare different subsets of NK cells isolated from blood, lung tissue, bone marrow, tumours and leukaemia. We will also compare NK cell behaviour in 3D matrix, within model tumour spheroids, and when cells are kept under hypoxic conditions. This will lead to understanding NK cell responses on a nanoscale and how this impacts health and disease, in turn leading to novel ideas for medicine. Translational outcomes will be pursued with GSK, Bristol Myers Squibb and Continuum Life Sciences.