Many useful biologics have not translated into the clinic because of short half-lives, large doses, or multiple injections that make them cost-prohibitive. Engineered mesenchymal stem cells (MSCs) can overcome that hurdle for many proteins by functioning as bioreactors that continuously produce and release the therapeutic molecule into circulation.
Butyrylcholinesterase, a rare human enzyme that can neutralize organophosphate nerve toxins such as cocaine pesticides and sarin, is one example. “There are no treatments available to neutralize organophosphate poisoning, and current approaches to purify human butyrylcholinesterase are cost-prohibitive at scale,” Lorena R. Braid, PhD, president and CSO of Aurora BioSolutions, says in a RoosterBio webinar, “The Role hMSCs Play in Bioengineering Solutions for Military Medicine.”
Efforts to synthesize it have been ineffective. The problem, she explains, is that “Recombinant butyrylcholinesterase is insufficiently glycosylated, so largely fails to form tetramers, and has an extremely short half-life.”
Initially, umbilical cord MSCs appeared promising. Most produced high-activity tetramer complexes. “Fortuitously, they consistently produced a C5 variant of butyrylcholinesterase that confers 30% to 200% more activity than the tetramer,” Braid says. Umbilical cord MSCs, therefore, can produce a higher-potency butyrylcholinesterase product than the benchmark serum form.
The challenge is that MSCs appear to have an intrinsic capacity to monitor butyrylcholinesterase in the microenvironment and regulate output at a post-transcriptional level. “Without significant engineering to disrupt the butyrylcholinesterase feedback mechanism in the MSCs, we cannot guarantee butyrylcholinesterase output,” she says. “That would create a potentially insurmountable hurdle for regulatory approval.
Her team realized, however, that bacterial cholinesterase-engineered MSCs could offer a parallel biomanufacturing platform. “This modality (allows us) to manipulate the cells as much as necessary to maximize butyrylcholinesterase yields. We are working on bioprocess development to produce butyrylcholinesterase from MSCs at scale,” she says.
One of the key aspects of this stage of the work involves developing predictive metrics to identify high-yield MSC populations for in vivo and conventional biomanufacturing modalities.
To improve yields, Braid is using a new gene engineering media (by RoosterBio) to reduce the volume of viral particles needed for transduction, and developing a pre-conditioning protocol to further enhance transduction. That combination helps the team engineer “nearly 100% of the cells with low virus-to-cell ratios. We also are testing a range of bioreactors and media formulations to facilitate economical scaleup of our biomanufacturing platform.”
Aurora BioSolutions continues to develop ways to enable economical, high throughput protein purification and is expanding its repertoire of MSC-produced biologics. “We have introduced other endogenous human proteins with therapeutic potential into our MSC- based bioreactor modalities that have also proven difficult to manufacture in conventional production platforms,” Braid says.