After several years of intense systematic research, and toiling with a differentiation protocol, Dr. Doug Melton, and his lab at Harvard University, finally decoded the sequence of genes that needs to be activated to yield mature, insulin-producing beta cells in vitro.
While a few investigators have managed to get in the vicinity and generate precursors to beta cells, the final steps necessary for full maturation remained unknown. When compared to islets derived from humans, Melton’s beta cells respond in an identical fashion to glucose challenges (exposure to glucose), a true test of their constitution. The work was deservedly published in Cell, in October 2014, and was reason for Melton to venture up to Toronto recently to deliver a talk at the Charles H. Best Lectureship and Award at the University of Toronto.
With a great deal of foresight, Melton decided that if he was going to produce beta cells, his process must be in suspension conditions. So, he chose human induced pluripotent stem cells (HiPSCs) to start, and a spinner flask (see a video on YouTube here) that could hold enough media to grow a therapeutically relevant dose for transplant in humans (300mL), or about one billion cells.
The beauty of the process is its simplicity: there is no need for embryoid bodies; no transfer of cells between culture wares of different sizes; and, no fancy substrates. Just add the media to the flask, seed the iPS cells, start the spinner, and, with the perfectly timed addition of just the right amount of a number of different growth factors, you create beta cells. (OK, there are some complexities. But, the take home message is that the process itself is easily translatable to a bioreactor setting, where hundreds of doses can be produced in one batch). The cells, which begin as small clusters, slowly grow into aggregates that are similar in size to the islets found in a human pancreas. At US$6,000 per flask for media and reagents, and 40 days from start to finish, there is room for optimization. However, a baseline cost-of-goods under $10,000 is a great start.
During his talk, Melton reflected on the work completed so far and the challenges that remain. In his view we’ve “broken the back of the problem,” but there is much refinement needed. Only 30% of the cells created using his protocol produce insulin, while a few percent more are glucagon producing; the bulk of the remaining cells are largely uncharacterized. He plans to use gene profiling to identify all cell types created in the process.
Perhaps the most critical challenge is the engineering of a retrievable, biocompatible device (e.g. does not become isolated by the host’s body) to house the cells. Without a safe haven, any transplanted beta cells would quickly perish as the host’s immune system is alerted to their non-self nature, resulting in rapid destruction of the graft. Such a device will also be critical to adoption, as life-long immunosuppression would eliminate any hope of a cost-effective therapy.
Melton made a call to arms, stating he would collaborate with any bioengineer that brought him a potentially viable solution to the immuno-isolation of beta cells following transplant into humans. There are companies that have been working on medical devices for the delivery of beta cells, but none yet that offer full protection from the immune system. Encapsulation into microscopic beads, with chemically altered surfaces, is an approach Melton is currently investigating, along with Dr. Dan Anderson of MIT.
Moving forward, Melton will also address other needs, like drugs to boost insulin production. His lab has already established 50 iPS cell lines from type 1 and type 2 diabetes patients with varying traits (e.g. obese vs. skinny). These will be used for screening small molecule compounds to identify leads for drug development. Melton notes that no one has ever discovered a drug for type 2 diabetes screening the correct cell type. The advent of functioning beta cells in vitro opens up avenues for pharmaceutical development that will no doubt have an impact on diabetes management in the future.