Construction of an in vitro lymphoid organoid: studying innate-adaptive immune cell interaction in a 3D culture system

The immune system is made up of two components, innate and adaptive. Innate immune cells, mainly dendritic cells, fight pathogens using defences that are quickly mobilised and triggered by cell surface molecules (receptors) that recognise a broad spectrum of pathogens. Adaptive immune cells, such as T cells, on the other hand provide a more specific and long-term protection against pathogens. Although the classification of immunity into innate and adaptive has served to simplify and facilitate the description of many immunological events, it is becoming increasingly evident that the interaction between innate and adaptive immune cells is crucial for mounting appropriate immune responses. This, therefore, necessitated the establishment of suitable culture systems and animal models for studying such interactions, and the use of these systems has so far been useful in understanding the interrelationships between dendritic cells and T cells. However, in trying to better recreate what happens in the human lymph nodes (the small organs where dendritic cells and T cells meet), we are proposing to construct a three-dimensional culture system that resembles a lymphoid organoid. This will hopefully be a more physiological system and one that will allow the development of further applications for studying cell-cell interactions. If successful, this system will eventually reduce the number of some animal experimentations. The development of such a system is timely given that the 7th amendment to the EU Cosmetics Directive will impose a marketing ban on new ingredients tested on animals from 2009 onwards. Our initiative is supported by Unilever, a company which has considerable experience and vested interest in the development of model systems for predicting the allergenic potential of new healthcare products.

Dendritic cells (DCs) are key regulators of the immune system. For instance, they are capable of stimulating lymphocytes to generate antigen-specific cell-mediated and humoral immune responses against pathogens and tumour cells and instruct T cells to tolerate self-antigens. Interaction between DCs and T cells takes place in lymph nodes (LN) which are aggregates of structured lympho-reticular tissue. The particular structure of LN and the presence of extra-cellular matrix (ECM) facilitate/guide cell migration, cell proliferation, cell differentiation, intracellular signalling and cell-cell interaction, which collectively determine the outcome of immune responses. However, in the vast majority of current in vitro models of DC-T cell interaction, these cells are studied in 2D (i.e. in tissue culture plates) and more importantly in the absence of ECM, conditions which do not restore the 3D architecture and many other properties of LN. Therefore, there is a real need to develop novel in vitro cell culture systems to better simulate the microenvironment in which these cells co-exist. Thus, the aim of this proposal is to engineer a lymphoid organoid comprising DCs co-cultured with naïve T cells in the presence of ECM, and within a perfusable 3D multi-cell environment, that is amenable to interactive control and monitoring of emergence, maturation and interaction of cells.