Fetal bovine serum (FBS) is a common supplement for In Vitro Cell Culture and bioprocessing. The composition of FBS is unknown and varies between batches, as well may contain animal viruses or prions. Because of these safety risks the elimination of all animal material is essential and offers optimal defined quality and safety for cellular based therapies and bioprocessing (Asher, Dev. in Biol. Standard., 1999).

Albumin is used in cell culture and in bio-manufacturing of therapeutic monoclonal antibodies and recombinant proteins. It is an important component of many serum-free cell culture systems such as those that utilize hybridoma or Chinese Hamster Ovary (CHO) cells. A new product, recombinant human serum albumin, is available under the commercial name Cellastim™ (InVitria). The use of Cellastim™ in the culturing of cell lines and in bioprocessing would allow for animal-free culture conditions.

Recombinant Human Serum Albumin: Cellastim™

Cellastim™ (InVitria) is a cell culture grade recombinant human serum albumin that is produced from an animal-free plant based expression system, ExpressTec (Nandi et al., Transgen. Res., 2005). The ExpressTec system achieves protein expression using the self-pollinating crops of rice and grain. The advantages of ExpressTec include high and stable expression of recombinant proteins, tissue specific expression in grain endosperm, rapid scalability to metric-ton quantities, prevention of Gene flow with self pollinating crops, low capital investment and production costs, and efficient processing and recovery (Huang, BioProcess, 2004).

Cellastim™ has similar biophysical characteristics and identical amino acid sequence as plasma derived human serum albumin. Cellastim™ is animal-free and immunoglobulin free. Studies have shown that Cellastim™ enhances cell growth in hybridoma cells and antibody productivity in CHO cells better than or equivalent to plasma derived human serum albumin (InVitria Cellastim™ product brochure, www.InVitria.com).

Adapting Cells to Serum-Free Environment

Conversion of cells to a serum-free media is optimal for cell culture under animal-free conditions. This process takes 2-6 weeks to ensure the high cellular survival. Two methods have been sited for this process, sequential adaptation and adaptation with condition medium (www.invitrogen.com). The first method, sequential adaptation, calls for serum-free media supplementation at 25% for the first Passage, 50% for the second passage, 75% for the third passage and 100% for the forth passage. The second process involves the adaptation with condition media. For the first passage 100% of serum supplemented media is used. For the second passage 50% of the media from passage 1 and 50% serum-free supplement is used, this process is repeated for passages 3 and 4. For the fifth passage the media is supplemented with 100% serum-free media. If cell doubling time and viability decreases prior to 100% serum-free conversion, cells should be passaged at the previous concentration for 2-3 passages to allow for cellular adjustment to the serum-free conditions. The use of a higher density cellular cultures is recommended for adaptation to serum-free conditions.

Conclusions

The conversion from serum supplemented media to serum-free media for cell culture and bioprocessing is essential for the elimination of animal components in the culturing media. The recombinant human serum albumin, Cellastim™, has been shown to enhance cell growth and productivity in cell lines under animal-free conditions and offers optimal defined quality and safety for cellular based therapies and bioprocessing (InVitria Cellastim™ product brochure, www.InVitria.com).