March 31, 2014
Gene therapy is one of several avenues being explored by researchers hunting for a way to beat HIV once and for all. But to many of us, even within the health care community, the science being conducted in this area is a black box: We periodically read about study results, be they encouraging or discouraging, without understanding much of the effort behind them.
Let's see if we can peel back the lid on this black box a little bit.
At CROI 2014, a major HIV research conference that recently took place in Boston, I met David Harrich, Ph.D., an associate professor at the QIMR Berghofer Medical Research Institute in Queensland, Australia. He was at CROI to present a poster on a potential form of HIV gene therapy that has been in development for the better part of two decades. It goes by the name of Nullbasic.
Before we get deeply into the study, take me back to the beginnings of Nullbasic. How was it discovered? How did you all realize what it was capable of?
This project began about 1987. I was a research assistant working for Professor Richard Gaynor at UCLA [the University of California-Los Angeles]. He had the idea that you could make some mutations in a virus protein, and that [it would have] a dominant effect, or be able to inhibit, the wild-type protein. An idea of fighting fire with fire, as some people like to describe it.
It works. But when we started those studies, we didn't have all the tools. We didn't exactly know all the things that we know today.
By "works," I assume you're referring to within lab cultures, right?
Yeah. In an in vitro laboratory setting, we could show some inhibition. But that got put onto a back burner.
I kept working on it over the years. About 10 years later, I made some discoveries that a protein had additional activities to help the virus grow. And I thought, "Can we do the same trick? Can we mutate the protein and inhibit the virus?"
It turned out to be the same mutant that my mentor discovered, only we changed the protein in other ways, made it more stable so that there was more of the protein around. In a nutshell: We took these Tat mutants, and we call this Nullbasic -- "null" in that it doesn't have a basic domain; they're the mutations in this part of the protein that is called the "basic" region. It lacks the basic domain.
Lo and behold, when we put this protein into human T cells, we find that HIV will no longer grow.
What's the significance of the Tat mutant?
The significance is that normally, this Tat protein is critical for the virus to replicate. What Tat has to do is interact with other cellular or viral proteins. It's sort of like a helper: It goes around in the cells, says, "OK. We need this to grow." It grabs it and uses these cellular proteins.
What this mutant [Nullbasic] does is, it's able to grab onto these cellular proteins that HIV requires, but it can't complete the job. In other words, it squanders all the things that HIV would normally require and therefore HIV stops growing. In addition, this protein actually targets one of the virus's own proteins; this is called reverse transcriptase. It targets reverse transcriptase and it stops that enzyme from doing its job.
You guys are looking into developing this as a potential gene therapy.
Why not an antiretroviral?
Well, we think investigation of some of these roles that it has, some of these mechanisms that it uses to inhibit HIV, could lead to new drug discovery. And we are pursuing that. But as an antiviral, this is a very dominant phenotype. In our hands, it seems to work each time.
By each time, you mean ... ?
I mean, it doesn't matter. Each experiment we try: We introduce this protein to human T cells; the virus no longer grows in those cells. We cannot detect virus replication, virus production. Normally, HIV gets into a cell and it produces virus. When HIV gets into one of these changed cells, protected cells, we can actually not detect virus being made.
No RNA shows up?
We see no virus particles. There's probably some virus RNA in the cells. We're still looking at that. We haven't finished those studies. But we know the virus particles are no longer produced.
How do you tie this in to the generalized research that's going on right now when it comes to gene therapy?
I think this is at a much earlier stage than some of the things that you've heard at CROI, which are further developed. It fits along the same lines; it fits into the avenue that treating a patient with Nullbasic gene could lead to a functional cure for AIDS. In other words, a person would still be infected by HIV, but they would have a repertoire of T cells that were no longer susceptible to infection, or would die from HIV infection.
This is the thing that fascinates me: the last sentence of your conclusion. You're saying here, "Our data suggest that Nullbasic can protect cells from infection as well as suppress the reactivation of latent HIV," which is the opposite of what several paths of the research toward a cure are trying to do -- which is activate and then destroy the latent HIV.
Absolutely. This is the flip side of the coin. And it's not the only one: There's another group in Australia, led by Tony Kelleher, that has another method of gene therapy that can essentially achieve the same thing, by silencing HIV directly in infected cells.
These are strategies that if -- once you have these cells -- should they see HIV, and HIV gets into the cells and integrates, it simply won't be able to produce any more virus.
Could this therapy get into reservoirs that already exist? I'm thinking about this in the context of a person who is already infected with HIV, who is maybe chronically infected. So HIV is already hiding out somewhere.
The difficulty is targeting this kind of a therapy to those cells. It's difficult to go in with a laser beam and, say, only into latent reservoir cells, and shunt the virus to there. I don't know that we have that technology, to go in with that fine-toothed comb.
The gene therapy being explored by other researchers in early human trials: That's all systemic, right?
It's all systemic. And the idea: Most of the gene therapy that is being proposed is to produce HIV-resistant cells. This is along the same line.
You've heard about CCR5-delta 32 mutations, and the gene editing to make CCR5-negative cells? [Nullbasic] does it in a different way. Instead of making them not infectable by HIV, these cells could become infected -- but then the HIV could do nothing. It would get into these cells and take up knitting. That's about it.
This is supposed to be the "towards-a-cure" section [of the poster exhibition hall]. Did you know that?
I did not. Based on the title hanging from the ceiling, "HIV Persistence," it suggests it's not precisely toward a cure.
If you look at where we're at, from here down to the end [of this row], these posters are about "towards-a-cure." Many of them are about reducing the reservoirs, and how hopefully you can then eliminate them. I'm the only one that's [on] the other side [of the issue].
If HIV gets in and can't do anything, can't make any virus, who cares? The whole idea is to stop making virus. That's the idea. And you either do that by eliminating the reservoirs so you can stop making virus, or you just create cells that are resistant to virus. [Nullbasic-treated] cells will not make virus.
I realize this is all based on lab study -- everything in this section. But is this not a potential path to a vaccine?
Well, it's a type of intracellular vaccine. You've heard of innate immunity? You hear all these restriction factors: APOBEC; TRIM5alpha; tetherin; SAMHD1. This is an artificial restriction factor. This is inside a cell. A cell makes those factors; it makes those proteins. The whole idea of those proteins is to stop virus infection.
[With Nullbasic,] we've now made an HIV protein that's a restriction factor. It stops the cells from making virus.
APOBEC mucks with reverse transcription. This mucks with reverse transcription. This is [also] the only factor I know of that also has effects on gene expression: It downregulates gene expression, and it downregulates the production of RNAs that make the envelope and the capsid protein. So cells don't make new particles.
So it hits from multiple angles, making it more likely to work successfully?
It is like three drugs. In other words, cART, combined antiretroviral therapy, uses drugs that target more than one enzyme, or more than one molecule: a receptor on the cell surface, or reverse transcriptase, or integrase. This targets three viral targets: reverse transcriptase, Rev and Tat.
Consequently, we've not been able to grow a virus that's resistant.
To what extent do you feel it's even theoretically possible that HIV could mutate around this?
Well, we've tried, and we haven't generated one. We've tried for months and months, co-culturing and growing, taking these cells that we knew were HIV infected and hitting them with drugs to induce some virus, then taking those and doing it over and over again.
Have you tried with different strains of virus?
That's on the card; we have all the clades now. This, of course, is only done with laboratory virus. But those experiments are with a Ph.D. student in Australia.
I assume that, in a case like this, tropism isn't going to have too much of an effect?
No. We have tried it with CXCR4. We've tried it with T-tropic and M-tropic viruses. Those are the two that people like to talk about -- which is kind of a misnomer; you know: It's R5 or X4 viruses. We've tried it with both; it works on both.
The mechanism of inhibition isn't based on the receptor; it's based on the viral enzymes. There could be some differences in reverse transcriptase, or differences in Tat, or even differences in Rev -- and in amino acid level -- that can be slightly different, in which this may not work as well. We'll just have to wait and see.
Where will this research head next?
We're going to humanize mice, is the next step. With these mice, we can do experiments out to six months to a year, if we're lucky, to see whether or not we can keep HIV from growing.
The problem with this protein [on which Nullbasic is based] is it has a bad reputation.
How do you mean?
The wild-type protein is associated with cytotoxicity. We've looked for cytotoxic effects of this protein as best we can, with the assays that we have available. We haven't seen any. So we think that particular mutations [found in Nullbasic] have downregulated, or negated, these cytotoxic effects that are associated with wild-type Tat.
Will you be more able to tease out any possible risk with these mice studies?
That's why we do these short-term mouse studies: The whole idea is that, in primary cells, we can only do an experiment for two or three weeks in a test tube. That's it; the cells die. Using those same cells, you can go into a mouse and go about eight or 10 weeks, if you're lucky. We've taken it out five weeks [in our poster], because I wanted data for the conference. And the cells are fine.
As for the humanized mouse: Now we're not going into the CD4 cells; we're going to go with CD34 cells -- a completely different cell type. We've done an experiment with CD34s. We've introduced the protein into them. We've induced them to grow in vitro, and they look fine. We don't see any cell death. We don't see any changes in their cell proliferation, the way they divide. We don't see anything yet.
What we have to do now is transduce CD34s and put them into a mouse, see if they engraft, and see if those cells develop immune cells. Can it change the way the immune cells grow, or the way they develop? Does this have any effects on developmental biology? There's a lot of very fundamental questions that have to be addressed.
How hopeful are you overall that this type of approach can result in something that ultimately -- I'm not saying, one year, five years or even 10 -- but that ultimately can find its way into humans and be a viable treatment option?
Some people say this will never work. I get that all the time.
I'm guessing you would not have been researching this for the past 18 years if you felt it couldn't work.
It's got a chance, right?
I keep doing experiments to see if this will fail. I don't do experiments to see if it works; I do experiments to see if this protein fails. As soon as I see that it's toxic or has detrimental effects, why bother? Then I'll stop. That was the whole point of that last panel [in my poster]: What happens in a mouse? Do these cells live? Are they healthy? Do they look OK?
The answer so far has been OK. When we'll go into CD34s, if we try it a few times and we find out those cells die, the project's over. So far it's crossed every hurdle. If I get to CD34s and it works, then I'm going to be more hopeful.
Every time you jump one of these hurdles, you become a little more hopeful; but also maintain your skepticism. You can't get sucked into your own science. The job of a scientist is to see if something holds true.
The hypothesis is that Nullbasic can protect human cells from HIV and cause no detrimental effects. We're testing that hypothesis. As soon as we show that the answer to that is, "It's not true," then the project will stop. I'm hopeful.
I'd wish you luck, but the answer's already out there; we just don't know what it is yet.
The answer is out there. I know. We just need people and money to do the work.
This transcript has been edited for clarity.
Myles Helfand is the editorial director of TheBody.com and TheBodyPRO.com.
Follow Myles on Twitter: @MylesatTheBody.