Leukocyte-specific transcript 1 protein is a protein that in humans is encoded by the LST1 gene.

Function: Possible role in modulating immune responses. Induces morphological changes including production of filopodia and microspikes when overexpressed in a variety of cell types and may be involved in dendritic cell maturation. Isoform 1 and isoform 2 have an inhibitory effect on lymphocyte proliferation.