Artificial thymus tissue enables maturation of immune cells

The thymus plays a key role in the body's immune response. It is here where the T lymphocytes or T cells, a major type of immune defence cells, mature. Different types of T cells, designated to perform specific tasks, arise from progenitor cells that migrate to the thymus from the bone marrow.

Researchers at the Max Planck Institute of Immunology and Epigenetics in Freiburg have generated artificial thymus tissue in a mouse embryo to enable the maturation of immune cells. In this process, they discovered which signalling molecules control the maturation of T cells.

Their results represent the first step towards the production of artificial thymus glands that could be used to replace or augment the damaged organ.

As part of the immune response, the T cells are responsible for tracking down and destroying intruders and degenerated cells in the body. Their progenitors are formed in the bone marrow. Attracted by chemical signals, they migrate from there to the thymus.

This small organ, which is located above the heart, is divided into niches that provide the cells with environmental conditions necessary for their different development phases. The cells mature there into different types of T cells, which are eventually released into the body.

Signalling substances that are active in the various niches of the thymus play a crucial role in the maturation of the progenitor cells. A combination of four proteins - the two chemokines Ccl25 and Cxcl12, and the cytokine Scf and the Notch ligand DLL4 - determines whether progenitor cells are attracted to a particular niche in the thymus and how they develop there. It was not previously known which combination of factors is responsible for the development of a particular cell type.