Genocea’s Herpes Vaccine Heads For Critical Proving Ground
No one has made an effective vaccine for herpes simplex virus 2 (HSV-2), better known as genital herpes. That’s because no one has been able to harness the immune system to attack the virus while it’s hiding out, dormant, inside cells. While there’s a long road ahead, Genocea Biosciences says it has a shot to be the first—assuming the early immunologic signs it is seeing in a clinical trial end up translating into fewer symptoms of the chronic sexually transmitted disease.
Cambridge, MA-based Genocea is announcing some interim data from its first human clinical trial for its experimental vaccine, GEN-003, for HSV-2 today at the Interscience Conference on Antimicrobial Agents and Chemotherapy in Denver.
The results of the 143-patient study are positive, so far: Its vaccine appears to be well tolerated by patients, to trigger an immune system response, and slow down the rate at which the virus replicates in the body. But they’re also very preliminary: Genocea now has to play the waiting game and track these patients for a year to see if its scientific hypothesis actually translates to fewer of the outbreaks of genital blisters and sores that patients suffer from. If the results hold up over time, Genocea will gear up for its biggest test to date—a mid-stage clinical that will likely sink or swim based on GEN-003’s ability to confirm it can curb those symptoms.
GEN-003 is the first, most advanced product of Genocea’s quick-hit vaccine production platform. That technology, which came out of the labs of Harvard University professor Darren Higgins, is supposed to differentiate Genocea from other vaccine makers in two ways: significantly cutting down on the time it takes to discover the right antigens for a vaccine, which is important because antigens are the substances that people can form antibodies against. Genocea also envisions making vaccines that triggers a response from both B cells (the ones that form antibodies) and T cells. All of the approved vaccines to date work in a more limited way, by only coaxing B cells to fight viruses.
This, according to CEO Chip Clark, is the reason that no one to date has been able to make a vaccine that can treat—let alone prevent—HSV-2. While this virus spends some of its life cycle floating in the blood, where B cells can reach it, it spends more of its time hiding from those antibodies inside nerve tissue at the base of the spine, where it can grow and replicate. T cells, however, have the ability to recognize this infected tissue, if trained to do so, and kill the virus.
This is the type of thing Genocea hopes GEN-003 will be able to do. The experimental vaccine is a combination of both a B cell and T cell antigen, and an immune-boosting compound (adjuvant) called Matrix-M that Genocea licensed from Sweden-based Isconova AB. The idea is by triggering a T cell response, GEN-003 would hit HSV-2 while it’s seemingly dormant and tuckered away in cells—the time between HSV-2 patients’ outbreaks. By doing so, the vaccine, in theory, would slow down what is known as “viral shedding.” This is when HSV-2, after replicating in cells in the spinal column, migrates to the genitals.
Genocea’s first effort to test this theory enrolled 143 volunteers with a history of moderate-to-severe, recurrent HSV-2 infections—or, those who have between 3 and 9 outbreaks of genital lesions per year, according to Clark. Those patients, recruited at seven clinics in the U.S., were broken into groups and randomly given small (10 micrograms), medium (30 micrograms), or large (100 micrograms) dosed injections of GEN-003, or a placebo. Each patient in each vaccinated group was given three total injections—one every three weeks. Genocea then used samples that patients collected themselves twice a day to track both B cell and T cell response, and the rate of viral shedding.
“To be clear, you don’t have symptoms unless you have viral shedding. We powered the study for viral shedding because there are way more [of these] events, than outbreak events,” Clark says.
In those purely scientific measures, the study is on track. Genocea reported that patients who got the vaccine saw that viral shedding reduced by up to 51 percent at the highest dose, compared to no decline whatsoever among the placebo group. That number, which Genocea says was statistically significant, or unlikely to be due to chance, correlated with an increased response from T cells and B cells. Clark says Genocea will now track those patients over the course of a year, and see how durable the vaccine’s response is.
While these results are the first indication Genocea has that it may be on to something, regulators are going to want to see this translate into a clinical benefit. So Genocea’s first real big test will come next year, when it starts a second trial that will likely be judged both by viral shedding rates and a reduction in symptoms.
Clark says that while the current study doesn’t sink or swim on symptom reduction, Genocea is still tracking it. So far, Clark cites one encouraging data trend. In an “exploratory” analysis the company did after 119 days of follow-up, one of the groups that got GEN-003 is showing a “strong trend” in the delay between an injection and the next occurrence of symptoms, according to Clark. On average, he says, the placebo patients saw their first recurrence occur 45 days after starting a regimen. By comparison, more than half of the patients in one of the groups getting GEN-003 (Clark declined to identify which) haven’t yet experienced an outbreak, he says.
“It’s too early to tell that that’s significant—if it were significant it would be a very meaningful difference, of course, but that’s still to be seen,” he says.
Genocea will have all the data from this study in the second quarter of 2014, and then likely test the same type of patient population with the two highest doses it is currently administering to patients in its second trial.
While GEN-003’s first day of clinical reckoning is a ways away, the potential payoff, should it prove to provide a real benefit, is big. Clark says between the U.S., U.K., France, Germany, Italy, Canada, and Japan, there are about 12 million people who are both affected with HSV-2 and showing symptoms. If Genocea were to price GEN-003 against the typical vaccine, it would amount to between $100 to $300 per patient, per year, creating a market opportunity worth more than $3 billion at the high end of the range, he says.
Today, people with HSV-2 typically take oral antiviral drugs like valaciclivir (Valtrex) either only when they have outbreaks, or daily. Genocea envisions HSV 2 patients combining those antivirals with periodic shots of GEN-003—how often isn’t known as of yet given Genocea doesn’t know how long the immune response lasts.
“They work by complementary mechanisms of action and so the protection should be increased in combination,” Clark says. “We haven’t proven that yet, of course, but that’s a reasonable theory that we would expect to test at some point.”