Using CRISPR gene editing to develop human-compatible transplant organs from pigs
CEO: Paul Sekhri
Based: Cambridge, Massachusetts
The scoop: The world is short of transplantable organs, as the number of people in need of a transplant far exceeds that of available donors. Currently, more than 112,000 people are waiting for a lifesaving organ transplant in the U.S., according to the HHS’ Organ Procurement and Transplantation Network.
That far outpaces the fewer than 40,000 transplants performed in 2019, which was hailed as an all-time high, according to the United Network for Organ Sharing. On average, 17 patients died every day waiting for a transplant in 2018, the nonprofit organization estimates.
Enter eGenesis, a company aiming to alleviate the shortage by genetically editing organs from pigs to make them human-compatible.
What makes eGenesis fierce: On the genetic level, porcine tissues are very close to a human's. But that doesn’t mean pig organs are readily available for human use.
For one thing, concerns about the transmission of dangerous porcine endogenous retroviruses (PERVs) to humans have hindered the adoption of cross-species organ replacement, a process known as xenotransplantation.
eGenesis believes that CRISPR-Cas9—a virus-fighting mechanism naturally leveraged by bacteria—can simultaneously edit out multiple copies of viral elements from pig genomes so that the animals’ organs can be safely transferred to humans.
That’s more difficult than it sounds. Too many cuts might disrupt the genome in ways that make the cells nonfunctional, and CRISPR has its own off-target effects.
In 2015, Luhan Yang and her mentor at Harvard University, George Church, co-founded eGenesis. That same year, they published their work in Science. The team identified 62 genes essential for viral replication and infection and showed that their specially designed CRISPR-Cas9 successfully inactivated all those copies in pig kidney cells grown in lab dishes, which led to a 1,000-fold reduction of transmission to human cells.
But can the success in cell lines yield similar results in living animals, or in this case, give birth to fully inactivated pigs? In a 2017 Science cover study, the eGenesis team, alongside other Chinese researchers, zeroed in on 25 copies of functional PERVs. Despite multiple failures, not-so-perfect embryo differentiation rates and miscarriages in sows, the first PERV-free piglet was born. They named it Laika, after the dog that was the first animal to orbit the Earth.
That same year, eGenesis got its series A financing to the tune of $38 million, co-led by Biomatics Capital and ARCH Venture Partners.
Just as is the case in human-to-human organ donation, before xenotransplantation can be achieved, another critical hurdle needs to be tackled: immunological compatibility. That means the human immune system must tolerate an organ from a different species without launching an attack.
In 2019, Yang’s Chinese firm Qihan Bio and eGenesis used CRISPR9 to create what could be a prototype pig for human transplant. According to results published in bioRxiv, in pig ear cells, the team combined PERV knockout with other genetic changes. They knocked out three pig genes that play important roles in triggering immune responses and added nine human genes to improve the compatibility between the pig and human immunological and blood coagulation systems.
After embryo development with the edited cells, the extensively engineered pigs, dubbed PERVKO·3KO·9TG, appeared to have normal blood cells counts, coagulation functions and vital organ functions for liver, heart and kidney, all on top of PERV elimination, the team reported.
Further analysis showed that the pig cells were 90% less capable of binding to human antibodies compared with those from wild-type pigs. When co-cultured with human blood in lab dishes, the edited cells also experienced minimal toxicity.
“Successful creation of PERVKO·3KO·9TG pigs represents a significant step forward towards safe and effective porcine xenotransplantation, which also represents a synthetic biology accomplishment of engineering novel functions in a living organism,” the researchers wrote in the study.
Shortly before the new results went public, eGenesis pulled in a handsome $100 million in series B, led by the venture arm of Fresenius Medical Care, one of the world’s largest providers of kidney disease services. Bayer’s investment unit Leaps by Bayer also chipped in.
Now, the collaboration between eGenesis and Qihan is testing the safety and efficacy of the new organs in nonhuman primates before moving into the clinic.