Disclosed is human haemopoietic maturation factor polypeptides and DNA (RNA) encoding such haemopoietic maturation factor polypeptides. Also provided is a procedure for producing such polypeptides by recombinant techniques and the use of 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 is also disclosed. Diagnostic assays are also disclosed which detect the presence of mutations in the haemopoietic maturation factor nucleic acid sequences and altered levels of the protein.