Human mesenchymal stem or stromal cells (hMSCs) are an integral part
of cell-based therapeutics, with over 400 clinical trials recently completed or
in progress using hMSCs. As more research teams transition their stem
cell-based regenerative technologies to the clinic, the use of serum in the
cell production process has been, and will continue to be, a necessary evil
that must be managed. Luckily,
pharmaceutical regulatory agencies, driven by the biologics industry over the
last 30 years, have established guidances and guidelines that have helped to
demystify and clarify some critical aspects of dealing with animal components. As
it is important to have an understanding of how to manage serum during the
clinical translation of hMSCs, we have focused this blog post on this specific
topic
There
are many researchers in the MSC community who firmly believe that the FDA simply does not allow hMSCs
into clinical trials if the cells have been cultured in media supplemented with
animal serum. This is currently not the case, and in fact, Mendicino et al.
from the Center for Biologics
Evaluation and Research at the FDA reviewed all MSC regulatory filings and found
that over 80% of all regulatory submissions described the use of fetal bovine
serum (FBS) during the hMSC manufacturing process [1]. Several other analyses
of hMSC-based clinical trials in recent years have similarly shown that at
least 65-75% of trials utilize FBS [2,3,4]. Regardless, a push to remove serum
from the manufacturing process still continues due to regulatory, production
and supply chain concerns. Each of these
areas is detailed below.
(Note: when we refer to "clinical-grade" products below, this is not an official regulatory classification, it is meant to generally refer to materials that are destined for use in clinical testing of cell therapies.)
Regulatory
Compliance
The
main regulatory concerns associated with the use of xenogeneic serum include
the risk of contamination with non-human pathogens and inducing an unwanted
immune response. To account for such serious consequences, the FDA has put
several requirements in place for the production process of both clinical-grade
FBS and hMSCs:
- FBS: Clinical-grade FBS must be derived from cattle herds grown in countries that are USDA approved for import, with well-monitored animal health status [2]. The FBS should be processed under current good manufacturing practice (cGMP) standards that set minimum requirements for the facilities, materials and protocols used [2]. Every batch or lot of FBS must be traceable back to its country, slaughterhouse and herd of origin. Finally, all lots must be tested for adventitious agents (viral contamination), sterility (bacterial and fungal elements), endotoxin levels, mycoplasma content and other constituents [2,5]. While regulatory agencies address safety, it is up to the cell manufacturer to establish metrics around performance, as FBS has traditionally been both a major cost driver and a source of process variablity.
- Clinical-grade hMSCs: Clinical-grade hMSCs must be manufactured under cGMP standards, and this topic is covered extensively in the literature. As it pertains to serum use, each lot of serum used during the cell production process must be documented [5], and the final cell product must meet specific standards of identity, potency, purity and safety. Purity standards include freedom from unwanted contaminants (such as other cell types, endotoxins, residual proteins and animal serum) [6]. The FDA Code of Regulations for Biologics provides a guideline for vaccines that animal serum levels must be under 1 ppm in the final product formulation when serum is used in any part of the process [US FDA. 21 CFR 610.15 ]. While there is no direct guidance for cellular therapies, the 1ppm residual level has been used as a target in some cell therapy manufacturing processes [6] and is a good place to start when developing process specifications.
These
checks and balances have allowed clinical trials using FBS-cultured hMSCs to be
conducted safely. A meta-analysis by Lalu
et al.
showed that there was no evidence of infection or toxicity in any subjects
involved in clinical trials using FBS-cultured hMSCs [7]. Several other
clinical trials have described the use of FBS in cellular therapeutics and
biologics without any adverse side effects [8-12]. That said, it is best
practice to develop sufficient cell washing protocols after cell harvest, and
before formulation, to remove process impurities and get serum protein levels
down to acceptable levels [13].
For FDA resources on this topic, see:
