We describe a method of expressing a recombinant protein comprising mannose-terminated N-glycans from a host cell, the method comprising: (a) introducing a nucleic acid encoding a recombinant protein into a Chinese Hamster Ovary (CHO) cell comprising a mutation in the GnT 1 gene (GenBank Accession Number AF343963) leading to loss of GnT 1 function; and (c) expressing the recombinant protein from the host cell, in which the expressed recombinant protein comprises a mannose-terminated glycan structure, and in which the method does not include a step of introducing functional GnT-I into the host cell. The method may be used for producing recombinant glucocerebrosidase with a mannose-terminated glycan structure, suitable for treatment or prevention of Gaucher's Disease.