Luhan Yang


Hi everyone. I am a postdoc from Church lab. Also a cofounder of Egenesis startup. Today I am going to talk about using genome engineering to make xenotransplantation a safe clinical reality for patients.

So here we are looking at the number of patients searching from unmet organ diseases. Over 2 million patients are suffering from organ failure. Only about 123,000 of them are put on the organ donor waiting list. Only 1/10th of them can get transplantation each year. There's a huge build-up and human life is at stake. In Asia, there is no donation culture. So hypothetically there are some ways to solve this problem: (1) make more donations, (2) use stem cells to produce organs, and then (3) utilize animal as a bioreactor and make the animal organs human-compatible. We start by engineering the somatic cell, and then we clone a transgenic pig and deliver an organ to a patient.

People have been persuing xenotransplanation for decades. Farmers invested in pigs for this in the 90s and it didn't work; there's huge rejection issues between human body and pig organs. People underestimate how many antigens they have to remove, and there was no tool for that. Also, pig cells cultured with a human cell will cause the pig virus to jump to human cell. This is where we think crispr can come into play. Our lab was one of the first to demonstrate that we can use crispr to engineer mammalian genome. We think the beauty of crispr is multiplexability. We can conduct engineering to remove the antigen and confirm that the pig organ has human compatibility.

Additionally, we can use this tool to eradicate the virus from the pig genome. This was a study published last year where we used a synthesizing technique that there are 62 copies of endodogenous retrovirus in pig (PERV). We can target the catalytic domain of the reverse transcriptase. We can knock these 62 copies of the virus out. If we culture these pig cells together with human cells, without modification, they are still prevalent-- but if we use our engineered cells, there was minimal infectivity similar to negative control. So our work increased this by almost 2 orders of magnitude. We also demonstrated we can solve the biggest problem in xenotransplantation.

Our second challenge was engineering pigs to have immunological features. There has been some progress in transgenic pigs where they each carry a modification. All the pigs are viable but it takes years for them to generate those pigs, and some of the modifications couldn't be implemented due to lack of tools. Over the past few months we have generated pig 2.0 cells. Also T cell changes.

Meanwhile, we are field testing somatic cell nuclear transfer (SCNT) so we can take the engineered cells and put them into pig abdomen and get pig blastocytes within one week. This helps us let us know what the impact is of our genetic modification on pig.

We are in the process of generating our pig 2.0. Every cell and tissue in our pig will have identical genome type. This is going to be a bioreactor for producing different tissue for liver transplants, pancreatic transplant, corneal transplant and heart tissue transplant. The advancement of gene editing will really innovate the field of xenotransplantation.

If we can solve the immunology issues, we can engineer these organs to be virus and cancer resistant. Or we can also produce essential amino acids inside these organs. Xenotransplantation is opening a backdoor for us to exercise a tool to push the envelope of gene editing in terms of impact on human.

Lastly I would like to thank George for being a visionary and my team specifically Marc for his efforts.

Q: In the paper where you describe inactivation of .. at the same time. Do they include all the families? C and the D and the A? Do they hit all of them? In the cell type, is that clonable? Is that cancer line clonable?

A: Yes. First, whether .. and second whether our cell line is clonable. Yes, there are A, B, and A-C if we keep all of them. There's some pseudogene where we only target those active, not touch other parts, to prevent genomic instability. And secondly, the cell is not clonable, but we're repeating the process in a clonable cell line to produce a transgenic pig with such a feature.

Q: Hi, Liam Holt from NYU. I am wondering about immune rejection. You mentioned changing the epigenetic surface of the cell. But also peptides from the interior of the cell. Can you break that pathway so that you don't get arbitrary pig peptides?

A: So you can rmeove the antigens from pig cell surface, the cell might still present peptides. This will trigger rejection. To fix such an issue, we're knocking out the antigens, and we're inserting the immune inhibitor CTAOIG, which can supress T-cell reaction.