Dennis Lo – TRANSCRIPT
When I first learned about the molecule of DNA I became fascinated by how such a seemingly simple molecule could uncode the genetic program of life. However this program, like many other programs could be corrupted and could cause life threatening disease like cancer and genetic diseases. And to diagnose these diseases, a doctor would frequently have to gain access to the cells with such mutations. But those cells could reside deep within one’s body.
Now, for example, to diagnose a cancer a doctor might have to do invasive biopsy of an internal organ. But every time he does this, there is a chance of bleeding. As another example to test for a baby before he was born a doctor would have to do pre-natal testing.
But typically, that method is performed by sampling the fluids from baby from deep within the uterus. And every time we do this, there is a chance that the baby might miscarry. And over the last few years there is a lot of effort to try to develop non-invasive methods which do not have such a risk. In particular researchers are interested in sampling the fluids that circulate in our body, like blood. And this field is generally referred to as liquid biopsy.
I first became interested in this field when I was a medical student studying obstetrics in Oxford. As a young student I wondered why did grown up doctors do dangerous things, such as sticking needles in the abdomen of pregnant women. And I was thinking that maybe we can do something better and safer. Why not just sample the mother’s blood and try to detect any fetal cells which might have entered into a mother’s circulation?
I even managed to persuade a professor in Oxford to let me work in his laboratory for a few months. I had no idea actually how long medical research could take. I actually initially naively thought that I could crack this in a few months’ time. But before I knew it, I spent eight years working on this project without a lot of success. I was lucky I wasn’t fired.
And then in the autumn of 1996 I came across two papers in a journal which said that cancer cells somehow release DNA into the blood plasma of cancer patients. Now plasma is this yellow fluid in which our blood cells swim in. And then I suddenly had a strange idea. I thought that a baby growing inside pregnant mother is actually a little bit like a cancer growing in a patient. And I thought that the placentural baby, which implanted in the uterus is a little bit invasive.
So I thought that if a smallish cancer can release enough DNA for us to see in the plasma, then surely a baby who to us at the end of the pregnancy could be like eight pounds, will surely deliver enough DNA for us to see. But the problem is that at that time I had just returned from Oxford to Hong Kong to start a new career. And I was born in Hong Kong so I had particular affiliation and attachment back there.
So at that time I really didn’t have a lot of resources, so I could only do something which was very readily available and cheap. And then I suddenly recalled when I was back in Oxford, being fed up as a medical student of the college food, I would actually sometimes cook instant noodles, back in my room. I actually got quite good at it. So what I did, is to boil some water to prepare soup base and then put the noodles in and a few minutes later you have a lovely dinner. And I was thinking what could be simpler than if I just boil some plasma and then maybe test a little bit of that boiled soup.
Now surprisingly, even with this crude preparation I was able to detect the male chromosome, that a male baby has released into his mother. And I saw no signal if a mother is carrying a baby girl. So this was the first demonstration of the presence of fetal DNA in maternal plasma. It hasn’t been shown before because previously, when people tried to look for fetal cells in the mother’s blood, plasma is the very first thing they throw away. And then even though the baby is so small compared with the mother, I was very surprised to find that actually the fetal DNA maternal plasma reached a mean of some 15%. And you can detect it as early as seven weeks of pregnancy which is very early.
And then I spent the next few years trying to develop new diagnostic method based on this technology. And the first thing I did – was because the first marker I found was on the male chromosome – so this technology can be used for sexing the baby, which is medically important, because some genetic diseases preferentially affect boys. They are the so called sex linked disease in which the disease gene is present on chromosome x and males have only one copy of this chromosome so we don’t have any back-up.
And one example of a genetic disease which is sex linked is hemophilia, which is a genetic disorder causing clotting problem of the blood. As another example I used this technology to detect the blood group type of the baby. And this could be important because sometimes the mother and baby’s blood group type do not match and a mother could produce antibody which could cause the placenta to attack the red blood cells of the baby.
Now those two applications – sexing and blood group typing – are very accurate. They are over 99% accurate and as a result, it’s now used in many parts of the world. So we next became more ambitious, we decided to actually tackle Down syndrome, which is perhaps the number one reason why many pregnant women go for pre-natal testing. And Down syndrome is caused by the baby having an abnormal number of chromosomes. And normally you detect Down syndrome by counting the number of chromosomes that a cell has within a cell membrane.
But the problem is, I am actually working on cell-free DNA floating around in the plasma. And so I don’t have the luxury of having the chromosomes nicely packaged within cells. So it actually took us ten years of trying different methods before we had to arrive to a method which is very robust and reliable. And this method involved sequencing millions of strands of DNA molecules in the plasma and had to work out the ratios of different chromosomes. And take into account of the fact that a fetal DNA only represents a minor percent of all the DNA in the mother’s plasma.
But the resulting method that we developed was surprisingly accurate – has an accuracy as 99.7% and because it was so accurate that within ten months after we published the first round trial of this technology in 2011, the test was introduced clinically in the U.S. and to date the technology is used by millions of pregnant women in over 90 countries around the world.
Now in China alone, every year 2 million of those tests are performed. And so we were encouraged about this development. So I was wondering how can we push this technology to its limit and what is the limit? The limit would be: can we use it to sequence the entire fetal genome?
Now that is a tough nut to crack because a human genome consists of 6 billion base pairs of genetic code. And initially I had no idea how we can do this. Until, one day, I went to see a Harry Potter movie with my wife, in a cinema like this, and it was in 3D. So I put on my 3D glasses and was waiting for the movie to start and then suddenly I saw the Harry Potter title flying towards me in 3D. And then suddenly my eyes were caught on to the H on the left hand side. And actually it looked to me at that time, that the H had two vertical strokes. Actually it looks like a pair of chromosomes.
So immediately I told my wife, who was sitting next to me, “I think I have an idea.” And then I spent the next two hours thinking about that idea. Actually, I never probably hoped a film would finish so quickly than that one. So within the movie finishing I just rushed home and wrote an email to my team, saying, “This is the idea, lets work on it.” And within a few months we managed to deduce the entire fetal genome from the mother’s blood, using this method.
But the problem is that the technology is very expensive. It’s cost us 200,000 US dollars for this one case. It is probably the most expensive case ever studied in Hong Kong medical history. But we were confident that with time the technology would get cheaper. Well it does. I think its going to have a major impact to pre-natal testing, because it can potentially allow us to diagnose basically any genetic disease using this method.
Now, so you can see that the development of non-invasive pre-natal testing has created a paradigm shift in pre-natal medicine. But is has also brought with it certain ethical, social and legal issues. Now for example, one of the early technologies I imagined is for sexing the baby, which of course was developed primarily for medical reasons. But, however, people can also use it for non-medical reasons. And actually indeed, in mainland China, pre-natal sexing for non-medical reasons is actually illegal.
But unfortunately in Hong Kong we do not have such laws. So now a number of companies have actually sprung up in Hong Kong to do exactly that. And every year now thousands of pregnant women in mainland China actually send the sample across to those companies. So actually a thing that the Hong Kong government would need to actually institute regulations to control this.
Now, as another example I told you about fetal whole genome sequencing. So this sort of technology will allow us to detect many different genetic variations that a a baby has got. But the problem is that our understanding of the function of human genome is incomplete. So when we see a change, we cannot always be sure whether there is a benign variation or whether there is a pathogenic mutation, which could be life threatening. So before that technology can be introduced clinically, we need to greatly enhance our genetic counseling infrastructure. So this perhaps highlights a point that while working on new technologies is exciting, we should not get ahead of ourselves, to use them prematurely before they and ourselves are ready.
Now, so the development of non-invasive pre-natal medicine has created a revolution in medical testing. So the medical community now thinks, maybe this technology will impact other areas of medicine, like cancer testing. Now, if regarded the release of DNA from a baby into his mother’s blood. And the release of DNA from a tumor into the patient’s blood as two parallel phenomena. So nineteen years ago, when we started working in this area, we decided that we are going to work on both of those in parallel, because we hoped that breakthroughs and advances in one of those areas would impact on the other side.
Now in the area of cancer we decide to focus on a cancer called Nasopharyngeal Cancer which is a cancer which is situated at the back of the nose. Now this is a cancer which is very common in South China. Let’s say in Hong Kong, a Chinese man like myself would have a life-time risk of this cancer of one in thirty-nine. I have actually lost one of my best friends from school to this disease. He passed away when he was just 37 years old. I have always wondered, “Could he be saved if we had detected the cancer earlier?”
Now, almost all cases of this cancer in China are associated with a virus infection. And the tumor cells will release this viral DNA into the blood stream of the patient and by measuring the concentration of this viral DNA, we can tell how severe the cancer is. The later stage disease will have a high concentration. You can also tell if a patient has responded to treatment or whether the cancer has come back after treatment. A very similar data now generated for other cancer types.
So it seems that the liquid biopsy of cancers is really a general approach in which we can detect and monitor cancer. So to find the proof if we can use this plasma DNA screening to detect cancer earlier, three years ago we launched an ambitious project to study 20,000 healthy men in Hong Kong, and to screen them for nasopharyngeal cancer using this technology. And now we are towards the final stage of this project. And the preliminary analysis of data shows that by screening we can actually detect three times as many early stage disease than otherwise without screening. So we believe that if we can roll out this technology nation-wide in China, the mortality of this cancer can potentially be halved.
So the challenge now is try to generalize the observation from this study to other cancer types. So we are working hard now in particular to see if we can apply the technology that we have originally developed for fetal whole genome sequencing, to the cancer side. Now if we can robustly and reliably and cheaply detect and tie cancer genome from plasma then this will potentially form the blueprint of a next generation of cancer test. But however we still have many issues to address.
Now for example let’s say that you can find in the blood of an individual the tell-tale signs of cancer. You still have to decide where is this cancer within the body? Now recently we have some new ideas about how we can do this, because we know that while billions of cells within our body will contain the same genome but actually that genome is modified in different ways, depending on where that DNA is coming from, from which tissue. And this phenomenon is called epi-genetic modification. It’s just like different apartments within an apartment building can have different decoration and different furniture.
So our DNA is modified in different ways, depending on where that genome is residing within our body. And we can now use this technology to trace any abnormality in the blood. I’d like to give you one example. Now recently a pregnant woman sent her blood sample to our laboratory for pre-natal testing. She wanted to know whether her baby is healthy or not. So we performed sequencing on her blood and actually found multiple abnormalities. So many laboratories would probably have interpreted that as meaning the baby is abnormal.
But however we performed this new technology of epi-genetic profiling and we found that strangely these aberrations are not coming from the fetus but instead they have the signature of lymphocytes which is a type of immune cells.
So as it turned out, this lady actually had a cancer of the lymphocytes and she was promptly treated. So basically you see this technology will allow us to trace the origin of any aberration we see in plasma. We call this plasma DNA tissue mapping. It’s in a way like a type of MRI scan which will also give you genomic information. So now we know actually when cells die in the body, like because of disease or other pathology, they will release DNA into circulation.
So by using this plasma DNA tissue mapping it will basically allow us to monitor cell death from different parts of the body, like from the brain if you had a stroke, from the heart if you’ve had a heart attack or from a transplanted organ, if we had an organ rejection. But excitingly this is only the beginning. Because now we know that cell-free DNA is not only found in the plasma, but is actually found in many other body fluids within our body, like from the urine, like from the saliva, or even in the fluid that bathes our brain. So we are barely scratching the surface of this technology.
So you see with cell-free DNA we have started a revolution in medical genomics which has opened a new window into our personal health. Thank you.