The invention concerns a human sialyl:transferase (hST30-1)11.99 and polynucleotide encoding it. The invention also concerns the process of producing the polypeptide by recombinant DNA technique. The methods for treating many diseases e.g. immunological disorder diseases, inflammation, tumor etc. utilizing the polypeptide are disclosed. The invention discloses the antagonist against the polypeptide and therapeutics thereof. The invention also discloses the uses of the polynucleotide, which encodes a human sialyl:transferase (hST30-1)11.99.