Session 7: Autoimmunity and Allergy
Transcript of Part 3: Discovery and Development of Natalizumab for the Treatment of Multiple Sclerosis
00:00:07.02 Hi. 00:00:07.22 I'm Ted Yednock and I'm an immunologist trained at the University of California in San Francisco. 00:00:11.17 And for a number of years, I worked for a company called Elan pharmaceuticals. 00:00:15.09 At Elan, and we developed a drug called Tysabri for the treatment of multiple sclerosis. 00:00:20.09 So, I'm going to talk about the identification and development of Tysabri in two lectures. 00:00:26.04 Today, I'm going to talk about the scientific underpinnings of Tysabri and how we think 00:00:31.02 it works by inhibiting immune cell infiltration of the central nervous system, 00:00:35.15 preventing the damage associated with the autoimmunity in MS. 00:00:40.11 I'll also talk about the preclinical work and the clinical studies that we did in order 00:00:44.10 to demonstrate that the drug was safe and efficacious. 00:00:48.03 In the second lecture, I'll talk about how we believe the selective mechanism of this drug 00:00:52.20 allowed for the emergence of a very rare but serious brain infection called 00:00:57.27 progressive multifocal leukoencephalopathy, or PML. 00:01:01.19 And I'll also talk about the complexity that that caused for patients, and physicians, 00:01:06.25 and the FDA, as well as the companies, in trying to understand how PML was associated 00:01:12.07 with Tysabri. 00:01:13.22 So, at first, I... 00:01:15.05 I will say a few words about multiple sclerosis. 00:01:22.00 So, MS is an autoimmune disease, of the CNS, as I mentioned. 00:01:26.02 It's involved in the destruction of myelin. 00:01:27.25 So, there's a very strong T and B cell response against myelin. 00:01:31.27 And once myelin is lost, you have impaired nerve conduction and neuronal loss. 00:01:36.11 Now, MS is... can happen anywhere in the central nervous system, so it can affect any part 00:01:40.26 of your body. 00:01:41.27 A patient may feel tingling in an arm or hand, or they may have loss of vision, or issues 00:01:49.15 with control of bladder function, or... or not be able to walk. 00:01:54.06 It affects about 300,000 patients in the United States. 00:01:57.06 It's more common in women than men. 00:01:59.12 And, as I've alluded to, it's a devastating disease and it affects people in the 00:02:02.25 prime of life, between the ages of 20 and 40. 00:02:06.04 But it can be seen at any age. 00:02:08.23 Now, usually, MS is a relapsing... it begins as a relapsing-remitting disease. 00:02:14.05 So, the attacks can come along very quickly, you know, vision loss can happen very quickly, 00:02:19.17 and then, over a period of days to months, there will be a degree of recovery to varying levels. 00:02:25.08 But after 15 or 20 years, the disease often becomes progressive. 00:02:30.18 And this happens in about 65% of patients. 00:02:33.23 And now, it's more of a chronic neurodegenerative disease, without the acute inflammatory attacks. 00:02:40.12 So, MRI is actually a very useful diagnostic and monitoring tool for multiple sclerosis. 00:02:46.14 So, this is an MRI image. 00:02:48.14 And what... what is often done in MS is that patients are given a contrasting agent called 00:02:53.22 gadolinium. 00:02:54.22 It's injected intravenously, and normally it's excluded from the brain. 00:02:58.27 However, in MS, when there's an active lesion, the blood-brain barrier is leaky and so gadolinium 00:03:04.03 will enter the brain and show up very prominently in an MRI. 00:03:08.03 Now, if you were to look at this lesion through a microscope, you would see this. 00:03:13.17 This is a... a blood vessel in multiple sclerosis. 00:03:17.09 And what's happened here is there are immune cells traveling throughout the body in the bloodstream 00:03:22.27 and... now, normally, they just go right through the brain. 00:03:25.10 But in the case of MS, there's something happening to the blood vessel wall, and the immune cells 00:03:30.12 will adhere to the vessel wall, migrate in, and accumulate in these large clusters around 00:03:36.15 the blood vessel. 00:03:37.15 And this basically is ground zero for demyelination and neuronal damage. 00:03:41.18 So, in 1990, we had a very simple hypothesis, and that was that if we could inhibit immune 00:03:48.00 cell attachment to the blood vessel wall we could prevent their migration into the brain 00:03:51.19 and all the damage associated with that. 00:03:53.26 And so... when I say adhesion molecule, picture Velcro. 00:03:57.22 So, we're trying to identify the little hooks on the... on the immune cell that allow it 00:04:01.22 to attach to the blood vessel wall, specifically at times of inflammation. 00:04:05.28 Now, since this is a brain disease, it's really important to be able to do these kind of studies 00:04:11.09 using an... an animal model. 00:04:12.23 So, the best animal model for multiple sclerosis is experimental autoimmune encephalomyelitis, 00:04:18.24 or EAE. 00:04:20.20 Now, in EAE... this is a... a... a model in the guinea pig, but we also use models in 00:04:25.19 mice and rats. 00:04:26.26 So, in this model, this is a brain... a slice through the brain of a guinea pig with EAE. 00:04:32.03 You can see a large blood vessel. 00:04:34.05 And in the blood vessel there are infiltrating immune cells, which are the blue cells, here. 00:04:39.23 And the section is stained with a red dye for myelin. 00:04:42.18 So, you can see that around the blood vessel there's a huge loss of myelin. 00:04:47.22 And then, also, the... the little green dots are axons, or nerve fibers, that are... are... 00:04:54.02 you're looking at them in cross-section. 00:04:56.07 And normally, over here, you can see that the nerve fibers are surrounded by red myelin, 00:05:01.12 so they're quite well insulated from each other. 00:05:03.27 But when the myelin is lost, the nerve cells or the nerve fibers are pushed around and clustered, 00:05:07.24 and the spacing between is occupied by immune cells and by edema. 00:05:11.15 And so you can see, with this kind of damage, how nerve conduction would be impaired. 00:05:18.18 This is the way the model progresses in animals. 00:05:21.03 So, in the guinea pig, we immunize the animals with spinal cord homogenate. 00:05:26.17 This causes a very strong response, again, of B cells and T cells to myelin. 00:05:31.19 And so that... by day 9 or 10, the immune cells will begin to infiltrate the 00:05:35.14 central nervous system, and you'll begin to see a degree of hind limb paralysis in the... in 00:05:40.01 the acute phase. 00:05:41.01 And then the animals begin to get a little bit better. 00:05:43.21 But then, by day 15 or so, the disease begins to, well, progress, and enters the chronic phase. 00:05:50.18 And the... the difference here is this is when demyelination begins. 00:05:53.20 So, once demyelination begins, the nerve fibers are pushed around, the immune cells are even 00:05:58.15 more activated, and the disease progresses with just more and more demyelination. 00:06:03.27 When we were first doing these experiments, we were a very small lab in a... 00:06:07.05 in a small company and we really didn't have a good model of EAE. 00:06:11.19 In fact, we weren't working in this area at all. 00:06:14.17 We... we were trying to develop therapeutics for Alzheimer's disease. 00:06:18.14 And we were trying to develop an animal model of Alzheimer's. 00:06:21.06 It would have been the world's first model, which... which we eventually did, but 00:06:25.15 our initial attempts weren't so good. 00:06:27.07 And in fact, we really were inducing a model in which there was a chronic inflammation. 00:06:33.21 And it's that kind of inflammation that initially got us interested in this area to begin with. 00:06:37.26 So, we took inflamed brains from these animals in this strange model of Alzheimer's disease, 00:06:43.24 and did a very simple experiment. 00:06:45.27 We took these sections and overlaid them or exposed them to a suspension of human lymphocytes. 00:06:51.20 And we found that the lymphocytes would adhere selectively to these inflamed vessels. 00:06:55.26 So, you can see these very dark blue, large circles are the human lymphocytes, and they're 00:07:02.06 adhering right in the center of these blood vessels, right where you would expect to see 00:07:06.06 blood cells in the circulation. 00:07:08.13 They don't bind elsewhere in the section and they didn't bind to non-inflamed vessels. 00:07:12.16 So, the fact that we were getting physical adhesion of these cells to inflamed vessels 00:07:18.21 suggests that this is probably a physiologically relevant... relevant interaction. 00:07:22.26 Because these ligands -- whatever these adhesive ligands... whatever they are -- were being 00:07:26.07 induced in the context of a whole brain. 00:07:29.04 We also isolated endothelial cells from rat brains and put them into culture, 00:07:34.25 stimulated them with TNF, and we found, there, 00:07:37.17 that lymphocytes would adhere here as well. 00:07:39.17 So, that was great. 00:07:41.00 We now had two different assays by which we could look at lymphocyte interaction with 00:07:44.21 inflamed endothelium, so we could screen for inhibitors of that interaction. 00:07:49.12 What we did is made thousands of antibodies against the lymphocyte surface, at random, 00:07:54.22 and screened for antibodies that would inhibit this. 00:07:56.25 So, in this assay, we could screen thousands of antibodies. 00:08:00.15 And in this one, we could screen umm... perhaps in dozens. 00:08:03.07 It was a much more cumbersome assay. 00:08:06.00 But, nonetheless, both assays gave us exactly the same answer. 00:08:09.22 And that is that alpha 4 beta 1 integrin is very important for lymphocytes and monocytes 00:08:15.28 to adhere to the... to the inflamed brain vessel. 00:08:18.16 So, in the presence of anti-alpha 4 or anti-beta 1, you can see that there was no longer any 00:08:24.00 human lymphocyte attachment to the vessels in this section. 00:08:29.09 So, this is what we thought was going on. 00:08:33.10 Lymphocytes and monocytes expressed alpha 4 beta 1 integrin and they were binding to 00:08:37.01 some ligand expressed by inflamed brain endothelial cells. 00:08:41.19 So, we also knew in 1990... and, in fact, I was... 00:08:45.01 I was kind of disappointed with this observation. 00:08:48.19 Because we knew that alpha 4 integrin was expressed by many cells in the circulation 00:08:53.13 -- lymphocytes, monocytes, eosinophils, basophils. 00:08:56.22 Unfortunately, it was low or negative on neutrophils, red blood cells, and platelets. 00:09:02.06 However, we had been hoping to find sort of a brain-specific adhesion molecule that was 00:09:06.15 expressed by a small subset of... of pathology-causing immune cells. 00:09:10.27 But, in fact, it was expressed very broadly. 00:09:13.20 Nonetheless, as you'll see, I believe that alpha 4 beta 1 integrin turned out to be 00:09:17.23 a pretty selective adhesion molecule for the CNS. 00:09:22.00 The molecule, alpha 4, had been cloned the year before by Yoshi Takada and Martin Hemler's group. 00:09:27.06 And a number of groups were also identifying the ligands for alpha 4. 00:09:32.13 For example, Elizabeth Wayner had found that an alternatively spliced form of fibronectin 00:09:36.20 was a ligand for alpha 4, and also Roy Lobb at Biogen had identified VCAM-1, 00:09:43.14 expressed by human umbilical vein endothelial cells in culture. 00:09:47.18 So... but no one really knew how alpha 4 beta 1 worked in vivo and how it contributed to 00:09:52.16 disease pathology. 00:09:54.00 And that's when we go back to umm... the need for a good animal model of EAE. 00:09:58.15 So, the model that we had with our Alzheimer's-inflamed brain wasn't really going to be good enough 00:10:03.21 for that. 00:10:04.21 So, we went down the street and visited Larry Steinman at Stanford. 00:10:09.19 And Larry Steinman is a world expert in multiple sclerosis and in EAE. 00:10:14.10 And we took... we went to him and showed him our results with alpha 4 beta 1 integrin, 00:10:18.17 and we had antibodies against alpha 4, and we asked him if he could help us test it in 00:10:23.05 a... in a really good model of EAE. 00:10:25.09 And that's exactly what he did. 00:10:27.03 Ni... 00:10:28.03 Nathan Karin, who was a postdoc in his lab at the time, was working with a rat model 00:10:32.21 of EAE. 00:10:33.21 So, the first thing we did was confirm that using brain... sections of inflamed brain 00:10:38.11 from animals with... rats with EAE, that we had the same sort of lymphocyte adhesion, 00:10:43.04 and that it was completely dependent upon alpha 4 integrin. 00:10:46.14 Nathan then tested one of our antibodies against alpha 4 and found that it was very protective 00:10:52.00 in preventing disease in these... in this animal model. 00:10:54.21 So, that was great. 00:10:56.09 Based on that, we... we started bringing in a number of different EAE models into our... 00:11:01.07 our little lab. 00:11:02.26 This was one, again, in the guinea pig. 00:11:04.25 And here we wanted to characterize more thoroughly what... how alpha 4 integrin works, how quickly 00:11:10.12 it works, and the impact that it can have on the disease. 00:11:13.15 So, in this study, we labeled lymphocytes with indium-111, which is a very high gamma emitter. 00:11:20.19 And we found that if you inject the cells back into the bloodstream they will migrate 00:11:25.18 to the brain. 00:11:26.18 So, you can just take out the brain and do a gamma count and see how many cells there. 00:11:30.07 But, in the presence of anti-alpha 4, inhibition was 80 or 90%. 00:11:35.11 So, in this short-term migration assay, lasting about 18 hours, alpha 4 integrin was clearly 00:11:41.09 affecting the ability of cells to migrate into the brain. 00:11:45.17 And then we treated guinea pigs with the antibody, just at the onset of disease. 00:11:51.06 This was like day 10 or 11, just when paralysis was beginning but before demyelination had happened. 00:11:57.28 And what we found is that by day 20 we had a very strong impact in preventing demyelination. 00:12:02.28 So, in the control-treated animal, you can see that they're... we have stained these 00:12:07.19 sections of spinal cord with a blue dye for myelin, and there's an extensive loss of myelin 00:12:14.01 by day 20 in the control animals. 00:12:16.01 However, in the presence of anti-alpha 4, the myelin is almost completely intact. 00:12:20.05 So, there was very strong protection against the loss of myelin. 00:12:26.22 We next... we next treated animals at day 20. 00:12:30.15 So, this is after demyelination has already occurred. 00:12:34.02 And we treated them for a long time -- 56 days -- because you wanted to see if it would 00:12:38.06 impact the disease and if that impact would last. 00:12:42.04 And what we saw was this: a very strong reversal of the paralysis and... that lasted for 00:12:47.17 the entire time of the treatment. 00:12:50.19 Okay, so we did this experiment a number of times, looking at different time points to 00:12:54.19 see what impact that we would have on myelin. 00:12:58.07 So, in this study, we treated the animals after demyelination had already occurred, 00:13:05.03 and then we inhibited alpha 4 integrin for various periods of time. 00:13:09.17 We found that after 20 or 40 days of treatment that we actually would allow myelin to repair. 00:13:15.26 So, the way we knew this was that under control conditions myelin is either present or it's not. 00:13:22.21 So, over here, you can see that... here is myelin, this is an area where the myelin 00:13:27.08 has been eliminated, and the... the line between the two is very, very stark. 00:13:31.25 So, it's either there or it's not. 00:13:34.17 However, in animals that had been treated with an inhibitor of alpha 4 integrin, 00:13:37.23 we saw this very pale blue pallor, which we confirmed by electron microscopy to be regeneration 00:13:44.16 of myelin. 00:13:45.16 So, we believe that what was happening is that by inhibiting immune cell infiltration 00:13:49.14 into the CNS we were dampening down this inflammatory response and basically creating an environment 00:13:55.22 that was permissive for remyelination. 00:13:57.22 So, these are the studies that led to the development of Tysabri, which is a... we took 00:14:05.20 our best antibody against alpha 4 integrin and humanized it by CDR grafting. 00:14:10.16 And this was done in collaboration with the MRCC in London. 00:14:14.19 And fortunately, the antibody retained the full potency of its murine parent. 00:14:22.00 Just to give a perspective on scale, this is a model of an antibody next to a model 00:14:26.26 of an integrin. 00:14:28.10 Umm... the... the antibody actually binds to the head group, up here, which is the 00:14:33.02 business end of the integrin. 00:14:34.02 This is where it binds to ligands. 00:14:35.22 Now, recently, the crystal structure of natalizumab bound to the head groups of alpha 4 integrin 00:14:42.04 has actually been solved, by Yamel Yu in Timothy Spring... in Tim Springer's group. 00:14:48.11 So, this is looking at the crystal structure, just at the head groups of the integrin umm... 00:14:54.23 and the blue is beta 1 and the green is alpha 4. 00:14:58.18 And the ligand binding site -- this is for VCAM-1 -- is right in between the two. 00:15:03.03 So, there are critical contact residues on both sides of the line. 00:15:06.12 Now, natalizumab, he found, bounds right next to this. 00:15:10.11 So, the binding actually doesn't overlap. 00:15:12.26 And, in fact, if you take the business end of VCAM, the first domain, it will bind just 00:15:18.16 fine in the presence of... of Tysabri. 00:15:21.20 However, the second domain of VCAM causes steric hindrance, so that, when natalizumab... 00:15:29.10 when natalizumab is bound in the presence of the full-length ligand, its binding energy 00:15:34.10 is greatly decreased because of the steric hindrance. 00:15:37.06 What they also noticed in the lab was three critical contact residues within the natalizumab 00:15:43.14 binding site that help to explain observations that we had made a number of years earlier. 00:15:48.12 So, when you're developing a drug, it's important to have animal species for efficacy testing, 00:15:53.05 but you also need to have two different animal species for toxicology. 00:15:56.27 You need to be able to show that it's safe in at least two species. 00:16:00.28 So, we were disappointed because our... our best model for EAE at the time was in the rat. 00:16:06.22 However, the rat has a mutation in one of these critical residues, and we found that 00:16:10.16 the antibody didn't react. 00:16:12.28 There also was an EAE model in the marmoset monkey, which was a model that was set up 00:16:18.05 at UCSF. 00:16:19.05 And, again, we found that our antibody did not react with the monkey, which... we were 00:16:22.11 really surprised, because it's very closely related to the human. 00:16:26.12 But now it makes sense with... with the finding that there's a mutation in one of these critical 00:16:31.02 amino acids. 00:16:32.12 So, we did find, however, that the... the antibody reacted with cynomolgus monkey and 00:16:38.20 with guinea pig. 00:16:39.20 And, as you can see, that the sequence of these... of the three critical contact residues 00:16:44.03 in these species are identical to those in human. 00:16:46.27 And these are the species that we had chosen for our toxicology. 00:16:52.21 So, in order to develop a drug, you need to do a lot of toxicology studies. 00:16:58.21 This is just a subset of the things that we did. 00:17:00.21 And I'm not going to go through all these, other than to mention a couple findings. 00:17:05.18 First of all, in the first study up here, it was a six-month study in cynomolgus monkey 00:17:10.15 involving very high doses of... of natalizumab. 00:17:13.08 Umm... natalizumab, by the way, is the generic name for Tysabri. 00:17:17.12 So, we did 60 milligrams per kilogram dosing every week. 00:17:22.12 And, in patients, we find that 3 milligrams per kilogram dosed every month 00:17:27.06 is what it takes for efficacy. 00:17:29.15 So, in fact, in the monkeys, we were achieving blood levels more than a thousand-fold that 00:17:33.28 you would find in humans. 00:17:35.10 So, at the end of 6 months, we looked to see what impact it would have, particularly on 00:17:40.02 the immune system. 00:17:41.03 Remember, alpha 4 integrin is expressed by almost all circulating mononuclear cells. 00:17:46.00 And so we were quite interested to see what would happen in the immune system. 00:17:50.17 And much to our relief, we found that hematopoiesis... bone marrow was... was very much intact, so 00:17:57.10 lymphocytes and red blood cells were being made normally. 00:18:00.05 And this was important because alpha 4 integrin had been shown to be involved in hematopoiesis. 00:18:04.11 We also did immunotoxics... immunotox... immunotoxicity profiling and found that if you vaccinated 00:18:13.20 animals in the presence of Tysabri the... they responded just... just fine to the vaccine. 00:18:18.24 There was a slight delay in the initial antibody response, but the animals quickly caught up. 00:18:25.01 And other than that, in these studies we also looked at the impact of natalizumab on implantation, 00:18:31.03 in development, and... as well as on development of the fetus during the full pregnancy, 00:18:37.16 and found very little impact there. 00:18:39.25 So, to summarize our... our preclinical and our toxicology studies, functional screens 00:18:47.09 are... are really important when trying to understand a disease process. 00:18:50.10 And this may be an obvious thing to say, but I'm just so impressed with the simplicity 00:18:54.26 of the tissue assay that we had performed, looking at the endogenous induction of ligands 00:19:01.13 involved in this inflammatory process. 00:19:03.19 In fact, this tissue assay is something that was established by Stamper and Woodruff in the 70s, 00:19:08.22 and had... has been used successfully for identifying a number of immune adhesion receptors. 00:19:14.20 Our other findings were that anti-alpha 4 was effective in multiple models of CNS inflammation, 00:19:19.19 whether it was a very funny Alzheimer's model or EAE. 00:19:22.18 And, in fact, in different labs around the world, it's been shown to be effective in 00:19:27.10 rat, mouse, guinea pig, and primate EAE, as well as 00:19:31.03 two different models of CNS viral inflammation. 00:19:34.14 So, these are models in which there's a CNS infection by a virus, the immune system goes 00:19:39.26 in to fight the virus and causes damage, and we found that anti-alpha 4 was actually protective there. 00:19:46.04 It protected against the damage and the... the body was still able to effectively fight 00:19:51.00 the virus. 00:19:52.00 So, again, it was suggest... suggesting that... that natalizu... natalizumab would be safe. 00:19:57.20 There was a lot of criticism of EAE models, because it doesn't exactly mimic the processes 00:20:04.07 of multiple sclerosis. 00:20:05.26 But in a case like this, where we're focusing on the immune infiltration aspect, I think 00:20:10.25 it's actually a very good model. 00:20:12.20 Because immune cells need to enter the brain to effectively induce EAE, and they also need 00:20:17.05 to go into the brain to cause MS. 00:20:19.24 So, by studying mechanisms involved in this infiltration process, I think that EAE reflects 00:20:25.22 what's happening in humans. 00:20:28.08 And then, finally, natalizumab appears to be safe and well tolerated in preclinical safety studies. 00:20:33.17 Again, this was important because... because of alpha 4 integrin's broad distribution. 00:20:38.00 It just speaks to the fact that toxicology is an empirical science. 00:20:42.12 You really don't know until you test it. 00:20:45.15 And then, even then, it's important to remember that you always need to be vigilant. 00:20:50.19 So, these are the studies that led to the clinical program for natalizumab. 00:20:55.19 In the first case, we looked at a Phase I study in healthy volunteers and found that 00:21:00.14 the antibody was well tolerated with low immunogenicity. 00:21:03.07 And this is just with a single dose. 00:21:05.11 And we also were able to determine that it has a 12 day half-life, which is sufficient 00:21:10.02 for once a month dosing at 3 milligrams per kilogram. 00:21:13.26 So, reasonable dosing. 00:21:16.15 As we saw in the animal models, there was a two-fold increase in the number of circulating lymphocytes. 00:21:22.14 This is reflec... this is consistent with the drug's mechanism of action. 00:21:26.11 It's making it a bit more difficult for cells to get out of the blood stream into tissues. 00:21:30.02 And so you quickly establish a new equilibrium, which involves more lymphocytes in the blood. 00:21:36.13 But this two-fold increase really represents just the higher end of normal range. 00:21:41.24 Based on those studies, it went into a Phase II study. 00:21:44.02 And... and initially we... our idea was to treat acute flares in MS. 00:21:49.26 So, a patient would have a flare, they would come in to the doctor, get a dose of natalizumab, 00:21:54.21 and hopefully we would quickly dampen down that flare and prevent the damage associated 00:21:59.02 with it. 00:22:00.02 In fact, what we found... and this is with two doses covering two months... we found 00:22:05.18 that there was no impact at all on the time of resolution or the outcome of that relapse. 00:22:12.02 So apparently, by the time a patient is feeling the onset of a relapse, the immune cells are 00:22:17.05 already in the brain, and by inhibiting more it really does not have an impact. 00:22:22.00 However, what we did notice in the study was that by the end of the second month the new 00:22:28.12 lesion development in MRI... by MRI had basically stopped. 00:22:31.28 So, this is looking at the cumulative number of new gadolinium-enhancing lesions by MRI. 00:22:38.11 And you can see that in the placebo group, in red, that there's a pretty consistent accumulation 00:22:43.02 of new lesions. 00:22:44.05 But, by the fourth week on natalizumab, these lines are beginning to diverge. 00:22:49.02 And so that... by the eighth week, the second month, when the drug is still on board, 00:22:53.11 you can see that new lesion activity had... had almost stopped. 00:22:57.05 At the next time point, when the drug was gone, MRI activity began to return. 00:23:01.14 So, this result led us to the idea that, since the drug appeared to be safe, perhaps we could 00:23:06.08 take it into MS for chronic treatment -- prevent the development of new lesions and hopefully 00:23:11.07 have an impact on the progression of disease. 00:23:14.12 So, this led to the our Phase IIb study, and this was a six-month study involving 00:23:21.18 monthly dosing as well as MRIs, which are indicated by the Ms, and then we follow the patients 00:23:27.27 for six months after that. 00:23:29.24 210 patients, looking at placebo and two different doses of drug. 00:23:34.11 And the primary endpoint would be looking... was looking at lesion burden, as well as relapse rate. 00:23:40.23 This is what we found. 00:23:41.27 So, in the months before treatment began, and at the time of treatment, all three groups 00:23:46.17 had sim... very similar levels of MRI activity. 00:23:51.00 And then, looking at the placebo group, they maintain this level of activity pretty consistently 00:23:55.11 over the six-month period. 00:23:57.03 However, in the groups that were treated with natalizumab, 00:24:00.06 and this is both for the 3 and the 6 milligram group, 00:24:03.12 you can see that MRI activity almost completely stopped. 00:24:06.19 So, again, by the second month, activity was very, very low. 00:24:10.08 Now, I have to say I... 00:24:11.15 I was sitting in the audience of the company when we first saw these results and it... 00:24:19.07 it really took my breath away. 00:24:20.15 This is... this was a day that I will remember in my career. 00:24:23.07 And I think that it... it really changed the way I look at things from then on out, 00:24:28.07 because as a scientist working in the bench it's really hard to believe that you can have an impact 00:24:32.20 on human disease. 00:24:33.22 And so this...this really made me believe that and, as I said, has had a long-lasting impact. 00:24:41.08 The drug also affected the number of relapses. 00:24:43.28 So, there was about a 50% reduction in the number of relapses, as well as a number of 00:24:48.02 patients who had a relapse. 00:24:50.00 And also decreased the need for steroid rescue. 00:24:52.25 So, these patients, if they had a flare, could... had the option of having steroid and on natalizumab 00:24:59.11 they did not feel the need to do that. 00:25:02.25 This is looking at the same data, the MRI data. 00:25:07.06 So, the blue line is 6 milligrams per kilogram, the red line is 3 milligrams per kilogram. 00:25:13.23 And so... you can see that... you can see that the drug is... for 3 milligrams per kilogram, 00:25:20.26 when it begins to go away, MRI activity returns. 00:25:24.25 And with 6 milligrams per kilogram, it takes a little bit longer for... for activity to resume. 00:25:29.07 You can overlay lymphocyte counts on top of this. 00:25:33.06 So, this is looking at the number of lymphocytes in the bloodstream. 00:25:36.22 And at a very beginning, you can see that there's this... this increase to lymphocyte 00:25:39.22 counts that's maintained very stably throughout the treatment period. 00:25:43.01 But then, in the 3 milligram per kilogram due... dose group, you can see that as the 00:25:47.12 drug goes away the lymphocyte counts drop, and the MRI activity goes up. 00:25:52.07 And with the 6 milligram per kilogram group, you can see this is... this is basically shifted 00:25:56.11 by a month. 00:25:57.11 So, the cell counts drop and the MRI activity comes up a little bit later. 00:26:01.07 So, this is very consistent. 00:26:02.16 This finding is very consistent with the mechanism of action that we're thinking. 00:26:06.07 As blood cells leave the... as immune cells leave the bloodstream, the MRI activity would 00:26:12.14 resume. 00:26:13.14 Alright, so our... for our Phase III studies in relapsing-remitting multiple sclerosis, 00:26:19.08 in order to get approval for a drug you actually have to have two separate Phase III studies. 00:26:24.03 And so both of these were about a thousand patients. 00:26:26.15 Umm... the first one involved monotherapy, so it was just Tysabri versus placebo. 00:26:31.11 The second one was on... with patients who were already on interferon beta, which was 00:26:36.05 the standard of care for MS patients. 00:26:38.28 And in this case, these patients were having disease breakthrough even on interferon. 00:26:42.27 So, the trial was natalizumab... natalizumab plus interferon versus interferon by itself. 00:26:49.05 So, this was a randomized double-blind study, as were the Phase II, and involved patients 00:26:55.08 who had to have at least one relapse in the prior year to the study. 00:26:58.14 It was a two-year treatment with an early assessment at one year. 00:27:04.24 And the findings were very consistent with what we saw in Phase II. 00:27:07.13 The number of gadolinium-enhancing lesions, both in first year... in the first year, 00:27:12.28 as well as the second year, were inhibited by 92%. 00:27:15.17 So, very strong inhibition of... of this apparently acute inflammatory reaction. 00:27:21.15 And this translated to a 68% reduction in relapse rate, again, both in the first year 00:27:26.26 and the second year, as well as in the third year. 00:27:30.02 This is an open label extension study at this point, so there isn't a placebo control because 00:27:34.02 everyone's on drug. 00:27:35.13 But, in all three years, the disease activity or the relapse activity was reduced to the 00:27:40.22 same basal level. 00:27:45.21 And this is an interesting finding. 00:27:47.05 This is a subset analysis looking at how different levels of activity would impact the efficacy 00:27:54.03 of the drug. 00:27:55.03 So, this is comparing patients who had had one relapse at the onset of when they were 00:27:59.14 coming into the trial in the previous year versus three relapses in the previous year. 00:28:04.22 And so you can see that patients who had high levels of disease activity, relapse activity 00:28:09.11 was inhibited down to the same level as everyone else. 00:28:12.07 So, it appears as though natalizumab has a very strong effect on patients with 00:28:16.23 highly active disease, inhibiting the... the relapse rate down to the same level. 00:28:24.14 And then, finally, this is the critical primary endpoint, at the second year of analysis. 00:28:29.04 And this was, how does it affect the overall progression of the disease in patients, 00:28:33.04 as measured by the standard EDSS scale? 00:28:36.24 And you can see that there's about a 54% reduction when looking at a sustained response over 00:28:41.28 six months. 00:28:42.28 Again, another subset analysis, looking at patients with highly active disease. 00:28:48.05 Again, there's an even stronger reduction, a 64% reduction, in the progression of EDS scores 00:28:54.22 in patients with... with more than two relapses and gadolinium lesions before they 00:28:59.15 came into the study. 00:29:02.28 And then, finally, this was not a point... this was not a formal endpoint in the study, 00:29:07.07 but nonetheless was a measure that was done. 00:29:09.23 And this is the MSFC scale. 00:29:12.22 And here you can see that the placebo patients... well, actually, what's interesting about this 00:29:16.08 scale is that it involves ability to walk, ability to have dexterity in the hands, 00:29:22.09 as well as cognitive function, a measure of cognitive function. 00:29:26.21 You can see that the placebo group maintained fairly stably over the two-year period, whereas 00:29:31.21 patients on natalizumab actually showed a level of improvement. 00:29:36.18 Importantly, these findings have been consistent across a number of studies. 00:29:42.04 These are actually looking at registrations and observational studies done by MS investigators 00:29:47.09 across the world, and very similar levels of efficacy with respect to relapse rate. 00:29:52.15 So, in summary, two years of treatment with natalizumab decreases disease activity, reduces 00:29:58.24 the risk of relapse by 68%, and reduces the risk of sustained disability progression by 00:30:05.04 42-54%. 00:30:06.04 To summarize the drug's safety in these clinical trials, these two-year clinical trials, 00:30:13.06 common adverse events were headache, fatigue, and arthralgias, 00:30:15.25 which are commonly seen in clinical trials. 00:30:18.22 There also were a few more infusion site reactions in natalizumab versus placebo. 00:30:24.21 Natalizumab actually causes a persistent anti... anti-natalizumab response in about 6% of patients. 00:30:32.04 And so, in these patients, actually, the drug loses this efficacy because the antibody response 00:30:36.26 causes it to be cleared very, very quickly, which is consistent with the infusion site reactions. 00:30:43.19 Importantly, there was a similar incidence of infections and malignancies between the 00:30:48.13 two groups. 00:30:49.13 In fact, if you look at this more closely, this is looking at the risk of all infections, 00:30:54.17 and this is for both studies combined. 00:30:57.05 So, both the monotherapy as well as the interferon therapy trial. 00:31:03.10 And you can see that there is no measurable difference in the rate of overall infection 00:31:08.16 between natali... natalizumab and placebo. 00:31:14.05 So, this is just the timeline of development, looking back in the beginning at 1990, 00:31:20.27 when the target was... of alpha 4 integrin was first identified for multiple sclerosis. 00:31:25.13 The antibody was humanized. 00:31:27.28 About five years later we started the clinical trials. 00:31:31.14 Biogen came in with Elan in about the year 2000. 00:31:36.01 And when developing a drug like this for multiple sclerosis, it's very expensive, because the 00:31:41.01 trials are large, there's a lot of MRI measurements, and so it's really important to have a partner. 00:31:45.18 And, in fact, Biogen was a great partner, because they already had a highly effective 00:31:51.03 drug for multiple sclerosis in the clinic and they knew a lot about... about the disease. 00:31:55.25 Shortly after the partnership was when we had the readout of the Phase II data, 00:32:00.16 you know, the day that... that changed my career. 00:32:03.01 So, I think that Biogen was very happy about that as well. 00:32:06.24 The phase III study was then shortly initiated. 00:32:09.20 The drug was approved in... in November of 2004. 00:32:13.14 The Phase... the second year of the Phase III study completed and read out shortly thereafter. 00:32:19.01 So, all said, 15 years from conception, 10 years of clinical experience involving 4,000 patients. 00:32:28.02 Now, in the second part of my talk, I'm going to discuss what happens next. 00:32:32.13 And this was just three months after the drug was approved. 00:32:35.15 This was in February of 2005. 00:32:37.23 The entire world for Tysabri changed. 00:32:41.03 So, in February of that year, we found our first two cases of PML. 00:32:45.21 And PML is a viral infection in the central nervous system that usually results in death 00:32:50.04 or severe disability. 00:32:51.04 So, it's a very serious infection. 00:32:55.01 Two patients in the MS trial had developed PML. 00:32:58.22 And amazingly, they had developed PML almost within a week of each other. 00:33:02.12 So, after ten years of clinical experience, two patients developed PML within a week. 00:33:06.23 And so this was alarming to everyone, because it... it suggested, well, maybe this is 00:33:11.04 just the tip of the iceberg, and half the patients could have PML. 00:33:14.13 So, dosing of the drug was suspended. 00:33:17.21 And we undertook a comprehensive safety evaluation at that point. 00:33:21.11 This was extremely complicated, because there were 3,000 patients involved or already 00:33:26.05 are still... are still in clinical trials, as well a number of patients who were just beginning 00:33:30.24 to take the drug from its approval. 00:33:34.04 So, what I'll talk about in my second part, in the second lecture, is how the medical 00:33:39.15 and regulatory communities working together with the companies established a path to allow 00:33:44.04 natalizumab to return, as well as the work that we've done since then to better understand 00:33:48.17 the safety of natalizumab and how PML can be monitored. 00:33:51.25 So, at this point, I just want to end by thanking all of the collaborators in the... both the 00:33:58.17 preclinical and clinical studies. 00:34:00.05 I... 00:34:01.05 I will at the end of my second lecture actually give a more detailed list of some of those contributors. 00:34:06.10 But needless to say, there were a ton of very talented people involved in the development 00:34:11.10 of this drug. 00:34:12.11 And also I want to thank the many patients who participated in the clinical trials. 00:34:17.22 Without their participation, it would be impossible to dev... to develop therapies for... for disease.