FLT3Ligand

FLT3 ligand, also known as FLT3LG or FLT3L, is a cytokine that activates the FLT3 receptor (CD135) on hematopoietic progenitor cells. It is produced as a transmembrane precursor that can be proteolytically cleaved to release a soluble form, and both forms are biologically active.

Binding to FLT3 triggers signaling cascades including JAK/STAT, PI3K/AKT, and MAPK pathways, promoting progenitor survival, proliferation, and differentiation. Through these signals, FLT3L supports early stages of hematopoiesis and shapes the composition of the immune system.

In hematopoiesis, FLT3L is especially important for the development of dendritic cells, B cells, and natural killer cells from multipotent progenitors. In mice, absence of FLT3L leads to reduced dendritic cell numbers; administration of FLT3L expands conventional and plasmacytoid dendritic cells in vivo, illustrating its pivotal role in DC ontogeny.

Expression of FLT3L is found in several cell types, including stromal cells and certain immune and epithelial cells, and its levels can increase during infection or inflammation to support renewed immune cell production.

Clinical and research relevance include the use of recombinant FLT3L to generate dendritic cells from CD34+ progenitors in vitro and its exploration as an in vivo adjuvant to boost dendritic cell numbers for cancer vaccines and other immunotherapies. FLT3L is also involved in studies of immune reconstitution following hematopoietic stem cell transplantation and in contexts where modulation of dendritic cell populations is advantageous.