Fetal bovine serum (FBS) has low levels of complement[1] and IgG relative to calf or adult bovine serum. Despite this, the IgG content of FBS may range from 50 to 300 μg/mL.[2] These levels may be problematic for certain recombinant protein or monoclonal antibody purification processes. This is because purification of such biologicals typically involves capture steps such as affinity chromatography on Protein G or M sepharose resins, which would be expected to co-purify any bovine IgG introduced via FBS-supplemented culture medium.[3] Assurance of the expressed protein or monoclonal antibody purity following downstream purification is therefore greatly enhanced if the upstream cell culture involves serum-free medium or medium supplemented with IgG-depleted or Low IgG FBS (www.rmbio.com/igg-fbs-low-igg-low-endotoxin). There may also be other cell culture applications in which the presence of bovine IgG would be considered problematic. For such manufacturing and research applications, there have historically been a few options: 1) screening of donor sera for especially low IgG content; 2) reduction of the FBS content (as a percentage) in the culture medium; and 3) use of FBS that has been treated to specifically deplete its IgG content. The use of depleted FBS confers great advantages over the other two options, due to increased control over IgG levels and ability to maintain the concentrations of non-IgG serum constituents required for optimal cell growth and productivity.

IgG-depleted FBS is prepared by subjecting commercial-grade FBS to capture chromatography in analogy to the purification of manufactured monoclonal antibodies mentioned above. Proprietary methods are employed to maximize lot sizes for depleted serum and to reduce the depletion of non-IgG components of the serum being treated.

Many suppliers of serum offer IgG-depleted (a.k.a. IgG-stripped) FBS. Are there any differences in these? What should you be aware of when sourcing depleted FBS?

Characteristics to look for in commercially-offered IgG-stripped serum include 1) the specificity of the stripping process; 2) evidence of performance testing of the stripped serum by the serum supplier to assure that it retains desired attributes; 3) lot size and availability; and 4) continuity of supply. Specificity means: which protein components of serum are being removed along with the undesired IgG? Performance testing conducted by the supplier usually entails testing the stripped serum as an additive to cell culture medium for its ability to support cell growth, productivity (protein expression), and cytotoxicity, relative to the non-depleted control serum. Lot size is an important consideration, as some lot-to-lot variability in FBS performance is always a possibility. By purchasing as large a lot of Low IgG serum as possible, one can reduce the potential impact of such inter-lot variability on manufacturing/experimental results. In addition, procurement of larger lots will reduce the cost of release testing that may need to be performed on a lot-by-lot basis for this animal-derived material. Continuity of supply means that the IgG-depleted serum always will be in stock in large quantities such that the supply of the reagent is not subject to shortages.

As with other post-manufacturing serum treatments discussed in previous blogs, it is recommended that you evaluate a few lots of Low IgG serum in your specific cell culture application prior to purchasing a large quantity of this reagent.

 

  
     
  [1] Linscott WD Triglia RP. The bovine complement system. Adv Exp Med Biol 137: 413-430, 1981.   [2] Son KK, Tkach D, Rosenblatt J. Delipidated serum abolishes the inhibitory effect of serum on in vitro liposome-mediated transfection. Biochem Biophys Acta 1511: 201-205, 2001.    [3] Jacobs JM et al. QSYP Peptide sequence is selected from phage display libraries by bovine IgG contaminants in monoclonal antibody preparations. BioTechniques 34: 132-141, 2003.