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Engineered Virus Targets HIV-Infected Cells
Interview with Garry Nolan, Ph.D.by John S. James
Two research teams, one at Yale and the other at the Federal Research Center for virus Diseases of Animals in Tubingen, Germany, have produced viruses which can enter and, in certain cases destroy, only HIV-infected cells. Although human use of such viruses will need more research and extensive ethical review, the same mechanism could be used almost immediately to target liposomes, which are already in widespread use for drug delivery -- potentially improving existing AIDS drugs by delivering them directly into infected cells, not to the body as a whole. The new research was published September 5 in the journal Cell; articles appeared in The New York Times and other newspapers on September 6.
How was a virus engineered to enter only HIV-infected cells? The targeting works by exactly the same mechanism that HIV itself uses to enter human CD4 cells -- only in reverse. HIV enters human cells when a viral protein, gp120, which is on the surface of the HIV particle, interacts with the CD4 receptor (a protein which is normally on the surface of human T-cells, and certain other human immune-system cells); this interaction causes the virus to merge with the cell, infecting that cell. [It is now known that the CD4 receptor is not enough to allow HIV to enter a human cell; there must also be another protein called a co-receptor. Several co- receptors have been discovered, including CCR5, and CXCR4 (also called fusin); others may be found in the future. Differences in co-receptors cause some strains of HIV to infect T-cells, while others infect macrophages, or other human immune cells.]
The team at Yale created an anti-HIV virus by starting with the vesicular stomatitus virus (VSV), which causes a disease in animals. This virus was genetically engineered to remove the protein which normally allows it to enter certain animal cells. Instead, the virus was given the genetic machinery to produce the human CD4 receptor, and also one of the human co- receptors which is used by HIV.
This virus cannot enter any normal cell. But if a T-cell or other human cell has been infected by HIV, the HIV protein gp120 will eventually appear on that cell's surface. Then the genetically engineered virus can fuse with and infect that cell, because of the interaction between gp120 (on the cell this time, not on the virus) with the human receptor proteins (which have been placed onto the engineered virus).
The other research team in Tubingen started with the rabies virus, and made it able to enter HIV-infected cells. This virus did not kill the cells efficiently, although it could be engineered to do so.
So far all these experiments have been done in laboratory cell cultures. Clearly there are major ethical questions to address before the virus could be tried in humans. But as Dr. Nolan points out, the same techniques could also be used to target liposomes, which are already widely studied as drug-delivery vehicles -- making existing drugs such as protease inhibitors more effective, by delivering them only to the infected cells.
On September 14 AIDS Treatment News spoke to Garry P. Nolan, Ph.D., Assistant Professor in the Department of Molecular Pharmacology at Stanford University, who wrote the review of this work which appeared with the research reports in Cell.
AIDS Treatment News: The virus produced by the Yale group was able not only to kill the infected cells it first entered, but to reproduce and kill more HIV-infected cells?
Dr. Nolan: Yes it could replicate. Then it would seek out the other infected cells. Apparently this virus lived long enough in these experiments that even low levels of HIV production could be targeted. We know this because HIV replication appeared to start up again every couple of weeks or so in the cell culture, then be suppressed by the engineered virus. The HIV probably remained in rare cells in a latent form, periodically becoming active and then being suppressed again.
The concern now is that one must be very careful of any replicating system. The researchers are going ahead with monkey studies, I understand, not with people. One possible problem is that this kind of virus might be infectious not only to the person you provide it to, but also to any sexual partners that HIV-infected person might have contact with, who also have HIV. Anybody who is HIV-positive could become an outlet for this virus, which is why I believe we need research on how one could control the virus, and tone it down. The medical and ethical review will take some time.
What could be done now is to use liposomes, instead of viruses. You could put CD4 and CXCR4 onto the surface of liposomes, to target them only to HIV-infected cells. Rather than delivering a virus, this technique would deliver packets of drugs, using the receptors to target them much more effectively than conventional liposomes. This approach might greatly improve the effectiveness of drugs like protease inhibitors, while reducing their toxicity.
It is unlikely that the liposome technology would be very useful for drugs that attack the virus early in its life cycle. Reverse transcriptase inhibitors such as AZT, for example, must be in the cell before the virus is integrated into the human genome. At that time the cell will not have enough gp120 on its surface to make it a target for the engineered viruses.
ATN: Why did these studies use CXCR4 (fusin), instead of other co-receptors?
Dr. Nolan: You are not just limited to CXCR4. You could have used one of the other HIV co-receptors as well. It might be possible to design liposomes that include all the co- receptors, to target them against all of the different kinds of cells that HIV infects. And one could do the same thing with viruses.
Avoiding Viral Resistance
The advantage of using receptors in this way, to target viruses or liposomes to particular cells, is that HIV does not have a way around it. If HIV mutates so that the engineered virus cannot bind with it, then that HIV could no longer enter human cells [because it needs the interaction between gp120 and the human receptors to do so]. This is one of the first times we can design something that the virus probably cannot escape.
HIV can mutate quickly against a drug which attacks it directly. But if you design a treatment which prevents the virus from using the cellular protein which it must use, then the virus may be blocked. This strategy has not received enough attention in HIV drug development. Existing drugs target the virus, rather than its interaction with what the virus takes advantage of in the body.
ATN: What has to happen first to develop such a liposome for treatment?
Dr. Nolan: Companies need learn how to scale up the production of these proteins. CD4 will be relatively easy. But the co-receptor will probably pose some difficulty, because it is an integral membrane protein. Someone will have to learn how to purify these co-receptors, and then incorporate them into liposomes.
ATN: Wouldn't it be faster with the viruses, since one already exists in the laboratory, and can reproduce itself?
Dr. Nolan: There are major issues. You do not want to scare everybody that you will be releasing new viruses. Certainly people are going to be thinking about the safety issues. What happens if you give a replication-competent pathogen to an immunocompromised patient? Somebody is going to have to volunteer. Don't be surprised if it does not go quite the way you want it to.
ATN: One science-fiction thought is that if this approach did work, it might be possible to treat the worldwide epidemic by treating one person. Of course that would be a long time from now.
Dr. Nolan: People will test the virus idea with animals fairly soon.
But meanwhile, what can be done now is to look at the liposome technology for delivering drugs, and ask what drugs could be encapsulated. There is lots of technology already about liposomes, since they are being researched heavily for standard medical treatment. The trouble has always been that liposomes are not specific enough, and also that they do not have the ability to fuse with cells. But adding the CD4 and a co-receptor basically provides a self-loaded trigger. It pulls the trigger for the virus, when it binds next to the cell. Then the liposome will fuse with the cell and deliver the drug.
What would we want to deliver? The obvious approach is a drug to kill the infected cell. But it might also be possible to deliver something which specifically seeks out the virus in the DNA, and does not kill the cell but shuts the virus down. People are talking about what is called "triplex DNA"; it is a way of basically delivering a clamp to a target cell, to the cell's DNA. It clamps down on a piece of the viral DNA within the cell's genome, and never lets go, basically locking the DNA in an 'off' position. So the virus could still be there, but it would be permanently inactive.
Besides triplex DNA, some other technologies are being developed -- for example, for creating small molecules that will bind to specific DNA sequences. Using receptor proteins (to target either viruses or liposomes) may help solve the difficult problems of delivering these potential treatments into the appropriate cells.
Efavirenz (SUSTIVA) Expanded Access Begins October 1by John S. James
On September 15 DuPont Merck announced an expanded access program to provide efavirenz (SUSTIVATM, formerly DMP 266) to "patients failing on, or intolerant to, their current regimen, and who in the judgment of their physician have no other appropriate treatment options available" (this and later quotes are from a physician's brochure describing the program). Because of limited drug supply for the next three months, the program is currently open only to those who have had a CD4 count less than or equal to 50, within the last 90 days.
Efavirenz "must be used with at least one or more antiviral drugs to which the patient has had no prior exposure. At least one other drug must be changed in a failing regimen if SUSTIVA is added. Optimally, when possible, the failing regimen should be changed entirely. If a patient is intolerant to an existing antiviral drug and the viral load is undetectable, SUSTIVA may be substituted for the agent that is not tolerated." For this program, patients must be at least 13, not be "hospitalized for any reason and/or being treated for an acute, serious life-threatening condition such as Pneumocystis carinii pneumonia or sepsis, or requiring IV antibiotics or chemotherapeutic agents." Other exclusions include concomitant use of terfenadine, astemizole, or cisapride, use of NNRTIs within 14 days of beginning this program, certain abnormal lab values, and pregnant or breastfeeding women.
Importantly, patients in this program may also be receiving experimental medications through other expanded-access programs. In fact, DuPont Merck, Glaxo Wellcome, and Gilead are working together to facilitate joint enrollment (for efavirenz, 1592, and adefovir) for appropriate patients, so that patients who are unable to use the approved treatments can start more than one new drug at the same time.
While the drug will be provided for free, patients or their insurance must pay for the CD4 and blood-chemistry tests required to qualify for the efavirenz program, and for any other expenses.
For more information, patients or physicians can call the SUSTIVA Expanded Access Program, 1-800-998-6854, 8 a.m. to 6 p.m. Eastern time, Monday through Friday.
Note: The generic name is pronounced EF-AH'-VIR-ENZ, and the trade name is pronounced SUS-TEE'-VAH.
Efavirenz (SUSTIVA, Formerly DMP-266) 48-Week Data Announced
Efavirenz (brand name SUSTIVATM, formerly known as DMP-266) in combination with indinavir (Crixivan®) resulted in an average viral load reduction of 2.38 logs out of a possible 2.49 logs (see "Note on Viral Load," below), after 48 weeks of treatment, in a phase II trial in which 59 patients received this combination. The average CD4 cell count increase was 240. A comparison group, which received indinavir alone for the first 12 weeks and then the combination, at 48 weeks had a 1.89 log average reduction out of a possible 2.42 logs, with an average CD4 increase of 150. The proportion of volunteers whose viral load was reduced to below the limit of quantification (400 copies, in this trial) was 88% in the combination arm, vs. 68% in the arm which started with indinavir alone and later switched to the combination. These results were released September 16 at the Infectious Disease Society of America 35th Annual Meeting in San Francisco (IDSA '97).
Efavirenz, being developed by DuPont Merck, in Wilmington, Delaware, is a non-nucleoside reverse transcriptase inhibitor which is effective against many HIV variants which are resistant to other NNRTIs. Resistance to efavirenz does develop slowly in laboratory tests, however, so this drug should only be used in antiretroviral combinations, never alone. A practical advantage of efavirenz over most other antiretroviral treatments is that it needs to be taken only once a day.
Additional data from another study -- not yet unblinded even for the researchers -- will be presented at the Sixth European Conference on Clinical Aspects and Treatment of HIV Infection, October 11-15 in Hamburg, Germany.
An expanded access program for patients who have failed other antiretroviral treatments was announced on September 15 (see "Efavirenz (SUSTIVA) Expanded Access Begins October 1," below).
Note on Viral Load
DuPont Merck is reporting its viral load results in a more accurate way than has been customary until now. The AIDS community should have a better understanding of the meaning of low viral load numbers, and should distinguish between "undetectable" and "below the limit of quantification."
The only viral load test approved by the FDA, the Roche Amplicor test, has a limit of quantification of 400 copies. If the viral load is less than that, the test does produce a number; however, that number is not considered reliable. If the viral load is extremely low, the test will find no virus at all and deliver a result of zero. Only zero -- not just any number under 400 -- really means that the viral load is "undetectable"; under 400 but not zero should more correctly be called "below the limit of quantification." There probably is a real difference, with a truly undetectable result meaning that there is less virus present, and probably a better prognosis for the patient, than a test result which did detect virus, but not enough to produce a reliable numerical estimate.
In reporting the results of clinical trials, any number under 400 (including zero) must be taken as 400 for computing the average change in viral load while on a treatment -- since otherwise, inaccurate figures would be used in the averaging. This conservative approach does create a problem, however. For example, if a volunteer has a baseline viral load of 40,000 copies, the maximum possible recorded drop would be two logs (100 fold, from 40,000 copies to 400) -- even if the treatment was able to reduce the viral load by more than two logs. The drug effect will often be underestimated, just because the viral load did not start high enough to show the full antiretroviral suppression.
This is why DuPont Merck is reporting an additional number with its results -- for example, "patients achieved a 2.38 log average reduction in HIV-RNA levels out of a possible 2.49 log" for the combination arm of the trial reported above. The 2.49 log reduction is what would have been achieved if the treatment had worked perfectly and eliminated all of the virus. When the actual average reduction is close to the maximum possible one which could have been seen in the trial (as in this case), that usually means that many of the volunteers went below the level of quantification, and that the treatment actually produced a greater viral decline than this particular trial could measure.
T-20: Entirely New Antiretroviral
by John S. James
A drug which works against HIV by an entirely new mechanism of action has shown clear antiviral activity in a small proof-of-concept human trial.
T-20, developed from virology knowledge gained through influenza research, is a 36-amino-acid peptide designed to block a critical step in the process by which HIV binds to and enters cells. The data showing antiretroviral activity in humans was first presented September 16 at the Infectious Disease Society of America 35th Annual Meeting in San Francisco (IDSA '97) .
Volunteers received the drug in four different doses, 3 mg, 10 mg, 30 mg, and 100 mg, every 12 hours, for 14 days. The highest dose group had a viral load decrease of at least 1.5 logs. (But all four patients who received this dose had their viral load go below the 500-copy limit of the test, so the actual decrease was probably greater.) A dose response was found, with the next lower dose (30 mg) having only a 0.48 log viral load decrease. The high-dose group had a CD4 count increase of 52 -- but the real improvement may be larger, since this change was measured after only 14 days, not enough time for the counts to fully recover. All four volunteers at the high dose had increased appetite and felt better.
No side effects are known.
T-20 has one important disadvantage: it must be injected, either twice a day or continuously (which would probably be better, judging from the 2.7-hour half life of the drug in the body). Today patients can use a small electronic pump, like wearing a pager, which provides continuous or other programmed drug injections.
What is still not known is whether T-20 will be tolerable and effective in long-term use.
The researchers below are at the University of Alabama at Birmingham, and at Trimeris, Inc., in Durham, North Carolina.
1. M. Saag, L. Alldredge, M. Kilby, and others. A Short-Term Assessment of the Safety, Pharmacokinetics, and Antiviral Activity of T-20, An Inhibitor of gp41 Mediated Membrane Fusion. IDSA 35th Annual Meeting, San Francisco, September 16, 1997 [abstract #771].
IDSA '97: Conference Without Activists
by John S. James
About 3500 doctors, mostly infectious-disease specialists, attended the 35th Annual Meeting of the Infectious Diseases Society of America, in San Francisco, September 13-16 (IDSA '97). We only saw three AIDS activists, including this writer, registered for the meeting, and three others who managed to attend some sessions. Many more wanted to go, but were kept out by rules apparently designed to prevent community participation.
Activists often attend conferences as press, covering the meeting for AIDS or other publications. This year the IDSA meeting gave press credentials only to "broadcast media or general-circulation magazines," clearly excluding treatment newsletters like AIDS Treatment News. There were no scholarships for people with AIDS. You could pay to go, as we did -- $240 at the door, $180 with early registration. But most people with AIDS and most treatment organizations cannot easily afford that cost, and most reporters refuse on principle to pay for the right to cover news. Few journalists of any sort came to this meeting, where much information important for public health was presented. We saw only one press badge in our four days there.
The issue matters because access and AIDS reporting at major conferences is essential if people with HIV and their advocates -- and those working on other diseases also -- are going to be well enough informed to continue contributing leadership in making clinical research productive, workable, and ethical. AIDS has been a model for patient empowerment -- which is much of the reason for rapid medical progress in HIV disease. Those whose lives are at stake bring an immediacy and practicality to the table that few others do. Without their influence, medical research is guided less by medicine or science than by money -- within a system of market distortions where capitalism can seldom force the efficiency it does in some other areas. Neither the public nor most professionals yet appreciate the lost opportunities and lack of productivity that result, and the countless lives lost that could otherwise be saved.
The access to meetings issue in AIDS had been settled several years ago. Now there is a backlash toward the ivory tower and the old-boy networks.
It is important to understand that almost all of the backlash involves only two conferences (the annual Retroviruses conference, and now the IDSA San Francisco meeting). And almost all of it is due to no more than four people, perhaps considerably fewer. Three of the four members of the steering committee which ran this year's Retroviruses conference were also on the steering committee for the San Francisco meeting. One or two people who are hostile to community participation can have much influence, since most physicians and scientists have little interest in meeting arrangements.
There are many smaller closed meetings in AIDS; this is seldom an issue. The problem arises when some of the world's major conferences, which report research largely funded by taxpayers, arbitrarily exclude community participation, refusing to negotiate workable arrangements with groups which have a legitimate stake in the research and reasons for being there. Organizers of the IDSA '97 meeting repeatedly said it was not an AIDS conference. But 240 of the published abstracts use the word 'HIV', 8 of the 31 session tapes for sale are clearly AIDS-related, and even the program book's cover is illustrated with a picture of HIV. And many other infectious-disease issues, such as antibiotic resistance, are vitally important to persons with HIV disease.
Much of the credit for public funding of AIDS research belongs to activists. Most organizations sweat and pray for greater public involvement in their cause. AIDS has people devoting their lives to supporting medical research. Excluding them from the information they need is a formula for stagnation.
IDSA '97: What It Did Rightby John S. James
Despite the problems of community and press access, the IDSA '97 meeting management did some things well.
IDSA '97: Excellent Medical Summaries on Tape
by John S. James
While some of the oral sessions at the IDSA '97 conference in San Francisco presented new research findings, most were reviews or summaries of existing knowledge in different fields of infectious disease. Most of these can be purchased on tape. Some of the speakers used slides -- but usually these were text summaries of the main points, and were read verbatim in the talk. Most of the talks, therefore, can be followed fairly well from the tapes without the slides. (Some of the slides will be available through the IDSA Web site.)
These talks were not written for beginners, but for physicians in other specialties who want to learn something about AIDS. Patients who are familiar with the disease will be able to follow most of them.
The tapes cost $11 each, with the Symposium sessions each including several lectures and requiring two tapes. The session numbers (IDSA97-002, etc.) can be used for ordering.
Thirty one sessions were recorded. Here are the ones most likely to interest our readers:
Symposium: The Evolving Role of Cytokines in the Immunocompromised Host (IDSA97-002, two tapes, includes four lectures):
Symposium: Pharmacodynamics of Antiviral Drugs (IDSA97- 003, two tapes, includes five lectures):
Plenary: STD [sexually transmitted diseases]-HIV Interactions: From Epidemiological Synergy to Patient Management and Public Healthy Policy, Judith Wasserheit, U.S. CDC (IDSA97-023).
Symposium: STDs and HIV Prevention Strategies: From Biology to Clinical Intervention (IDSA97-035, two tapes, includes four lectures):
Plenary: Progress Towards Eradication of Vertical HIV Infection, John Sullivan, University of Massachusetts Medical School (IDSA97-085)
Pitting Off Against HIV: Advances in Antiretroviral Chemotherapy (IDSA97-095, two tapes, includes three lectures):
Plenary: Fresh Perspectives on HIV-1 Infection: Immune Depletion and Repletion in Lymphoid Tissue Reservoirs, Ashley Haase, University of Minnesota Medical School (IDSA97-124).
Symposium: Opportunistic Infections in HIV: State-of-the- Art and Critical Issues for the Future (IDSA97-126, two tapes, includes three lectures):
Antimicrobial Resistance: Evolution and Control (IDSA97- 128, 2 tapes, includes four lectures):
These tapes can be ordered from Sound Images, Inc., 7388 South Revere Parkway, #806, Englewood, CO 80112, phone 303- 649-1811, fax 303-790-4230, email SoundImages@compuserve.com. A 12th tape is free if 11 are purchased. Same-day rush service is available. There is a small shipping charge. Call or fax for more information.