The invention provides novel polynucleotides and polypeptides encoded by such polynucleotides and mutants or variants thereof that correspond to a novel human stem cell growth factor-like protein. These polynucleotides comprise nucleic acid sequences isolated from cDNA libraries from human testis cells (Hyseq clone identification numbers 2880984 and 2881695), from human fetal skin (Hyseq clone identification number 15375176), adult spleen (Hyseq clone identification number 14856094), and human endothelial cells (Hyseq clone identification numbers 13804756, 13687487, 13804756). Other aspects of the invention include vectors containing processes for producing novel human stem cell growth factor-like polypeptides, and antibodies specific for such polypeptides.