We read with interest the article by Sotiropoulou and colleagues on defining optimal culture conditions for clinical-scale production of human mesenchymal stem cells . Our attention was basically drawn to the fact that although the authors went to the length of assessing eight different culture media, all media were supplemented with fetal calf serum. No groups incorporating serum-free synthetic medium or even human serum (autologous or commercially available) were included in the study design. In a preclinical setting, all animal- and/or human-derived products should ideally be excluded and synthetic recombinant alternatives used instead. Despite the very early recognition and adaptation of this concept in clinical work , only recently has wider application been allowed in emerging areas of stem cell research [3, 4]. Mesenchymal stem cell research has not been unscathed by this principle; rat mesenchymal stem cells have been shown to retain their proliferation and differentiation potential when cultured in serum-free medium . Under similar predefined conditions, mesenchymal stem cells were able to undergo directional differentiation toward the neuronal lineage .
Multiple reasons make such an approach favorable. Because serum is chemically ill-defined, a reduction of variability in qualitative and quantitative cell culture medium composition secondary to interbatch differences should be expected. This alone will eventually lead to a more robust level of quality control. The risk of prion, viral, or zoonose contamination will also be decreased in parallel with the demand on animals for product supply in accordance with the 3R principle of reduction. Serum contains a variety of proteins that may attach to cells in culture and act as antigenic substrates for immunological reactions once transplanted. This has been shown by Selvaggi et al. when patients infused with lymphocytes cultured in medium supplemented with fetal calf serum developed arthus-like reactions . The detection of newly formed antibodies to fetal calf serum is an indication that immune complex formation followed the cell infusions. In a more relevant clinical study, it has been hypothesized that the contact of skeletal myoblasts with fetal calf serum in culture was the cause of unexplained arrhythmias that led to significant malignant ventricular arrhythmias and sudden deaths in patients .
Until a chemically defined serum-free medium is widely available, autologous serum supplementation should not be overlooked. This modality is particularly useful in the clinical setting on a single-patient basis and aids overcoming the above and many ethical considerations. Autologous serum not only has been shown to be indistinguishable from fetal calf serum with regard to both isolation and expansion of human mesenchymal stem cells, but also proved to be superior with respect to osteogenic differentiation . In another study, autologous human serum provided sufficient ex vivo expansion of human bone marrow-derived mesenchymal stem cells while maintaining higher cell motility compared with fetal calf serum . In addition, switching to autologous human serum terminated the side effects associated with immune reactions in the aforementioned studies [7, 8].
It is imperative that as adult bone marrow-derived stem cell research enters the realm of clinical research, guidelines be implemented. There should be no rush to enter the clinical stage if the underlying basic research is not solid; this alone will lead to high-quality translational research. Cell culture medium composition should distance itself from animal products. Although autologous serum is a reliable and safe solution for small clinical studies, it will not be appropriate for future “off-the-shelf” availability of stem cell therapy.