Disclosed are human haemopoietic maturation factor polypeptides and DNA (RNA) encoding such haemopoietic maturation factor polypeptides. Also provided are procedures for producing such polypeptides by recombinant techniques and for using such polypeptides for treating leukemia, auto-immune diseases and blood related disorders. Antagonists against such polypeptides and their use as a therapeutic to prevent expansion of T-cell populations are also disclosed. Diagnostic assays are also disclosed to detect both the presence of mutations in the haemopoietic maturation factor nucleic acid sequences and altered levels of the protein.