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Actually, and unfortunately, 40mg/L is not terribly uncommon for most transient CHO systems. Reports of 1g/L in CHO tend to be for stable cell lines, not traditional transient systems. The short answer to your question is to try the ExpiCHO expression system. Many proteins have been expressed at >1g/L in the ExpiCHO system, with titers as high as 3g/L. ExpiCHO is a fully optimized CHO-based transient expression system that expresses at levels previously seen only in stable CHO cultures.