Responsible for synthesis of murine T-lymphocyte CT antigen. Can transfer N-acetylgalactosamine moiety from UDP-GalNAc to the low molecular weight acceptor 3'-sialyl-N-acetyllactosamine, to form a non-reducing terminal tetrasaccharide Sda blood group structure. Protein modification; protein glycosylation. Belongs to the glycosyltransferase 2 family.