Antibodies and HIV: New Evidence Interview with Ruth Ruprecht, M.D., Ph.D.

Background

HIV infection causes the body to produce large amounts of antibodies -- specialized proteins produced by the immune system to fight infecting bacteria or other organisms. But most of the antibodies produced in response to HIV infection are not effective in stopping the virus -- and some of them may even increase HIV infection. So in recent years, many scientists have given up on antibody approaches to HIV vaccines or treatments. (Instead they are working with the other major branch of the immune system, cellular immunity, which now looks very promising for control of HIV. However, cellular immunity by itself cannot clear most HIV infections.)

At a recent conference on immune research in HIV, held April 27-29 at the Institute of Human Virology at the University of Maryland in Baltimore, Ruth M. Ruprecht, M.D., Ph.D., an immunologist at the DanaFarber Cancer Institute and Professor of Medicine at Harvard Medical School, presented an update on her team's ongoing work with HIV antibodies. She agrees with her colleagues that most antibodies against HIV are not effective. But some are (as other investigators and Dr. Ruprecht had shown) -- and she has selected three of them for further research. These three, injected together, have successfully prevented infection in monkeys, even when they are given large doses of HIV-like viruses.

If this approach continues to be successful, it could have huge implications:

(1) Vaccines could be engineered to cause the body to produce antibodies already known to work. Such antibody-inducing vaccines might be effective by themselves -- or might be combined with approaches that generate cellular immunity to produce vaccines more effective than either kind alone. Vaccine development could be greatly accelerated, because it would be possible to test quickly, in volunteers, whether or not a candidate vaccine induced production of the desired antibodies. Problems could be found and fixed quickly, before the vaccine went into a large, multi-year trial.

(2) Antibodies might also be able to prevent mother-to-infant transmission -- without the side effects or potential toxicities of antiretrovirals, without the risk of producing drug-resistant virus, and possibly without requiring the mothers to avoid breast feeding.

(3) It is possible that selected antibodies might help in the treatment of persons already infected. So far there are no data, as this has not been tried even in animals.

But many years ago there were experiments with "passive immunotherapy" for HIV -- collecting serum donated from persons who were doing well for a long time despite HIV infection, and transfusing this serum into persons who were sick. Despite some promising results, this work did not continue. From the modern perspective, these early attempts do make some sense -- Dr. Ruprecht explained that a few patients do produce antibodies that are effective in stopping HIV. But today we also know that some people are slow progressors for different reasons, some of which have nothing to do with antibodies, so there is no reason to think that transfusing their plasma would be beneficial to others. Using rationally selected, engineered antibodies would appear more promising.

Incidentally, passive immunotherapy has long been used to treat certain other infectious diseases. And recently it was found effective in animal tests in both preventing and treating ebola virus infection. [1]

Dr. Ruprecht uses monoclonal antibodies (pure antibodies produced by genetically modified cells) rather than serum or immunoglobulins prepared from serum, that deliver a variable mixture of many different antibodies. So far, monoclonal antibodies have been much too expensive to use as treatments. But now it is becoming possible to produce antibodies in plants, such as tobacco. So price need not be an obstacle -- if it is found that antibodies could work as treatment for someone already infected with HIV, which today is not known.

Note: David Scondras interviewed Dr. Ruprecht on April 28, and prepared a transcript. Since he then had to leave for AIDS work in Malawi, John S. James, who was present at the interview, edited the transcript and wrote the background section above. Dr. Ruprecht made corrections before the interview was published.

Interview with Dr. Ruprecht

Scondras: What is the goal of your work?

Ruprecht: We want to develop an immunological approach to prevent mother-to-child transmission of HIV. Simultaneously, we are also looking for a way to rationally design an HIV vaccine.

The idea came from how we manage hepatitis B. To prevent mother-to-child transmission, pregnant women are screened for the virus. If they are positive, their infants get two inoculations: the first consists of hepatitis B immunoglobulins [which contain antibodies against the hepatitis B virus, providing passive immunity], and the second is the hepatitis B vaccine.

Used together, the vaccine plus immunoglobulins confer 98% 'effective protection to the baby. If you use the immunoglobulins alone, they are only 70% effective.

Turning to HIV, people who have HIV infection make very little neutralizing [effective] antibody compared to people with other viral infections. Instead, with HIV, the body makes lots of antibodies to parts of the virus that are not important. This kind of antibody does not stop the virus from infecting cells and damaging the immune system. Indeed, it is now known that HIV makes the body produce antibodies that may even help the virus infect cells.

That was part of the reason I decided to stay away from polyclonal sera [such as antibody preparations made from the blood of persons whose HIV was progressing slowly]. You cannot do a rational analysis of the specific antibodies.

Scondras: Hasn't this approach of looking at antibodies been tried before?

Ruprecht: Every once in a while, a patient develops relatively high titers of neutralizing antibodies [meaning that they produce antibodies that effectively block HIV]. It is also known that monoclonal antibodies can be made from these people. But in scientific research, the pendulum had swung away from antibodies.

Scondras: How did you think that antibodies could play an important role anyway?

Ruprecht: I knew that antibodies help prevent hepatitis B virus infection. I also knew that the hepatitis B virus has some similarities to HIV. So I decided to focus on finding potent antibodies from HIV-infected people. Other investigators have succeeded in engineering cultured cells to produce just a single antibody, called monoclonal antibody. My colleagues kept isolating B cells [the cells in the blood that produce antibodies], and kept screening until they found cells that produced antibodies that successfully neutralized HIV. Then we could learn to mass produce the monoclonal antibodies. Today this is possible; in fact, tobacco plants can be engineered to produce these antibodies.

The Animal Tests

Ruprecht: We decided to combine antibodies that worked against HIV, in the hope that a cocktail of antibodies would be more effective than one antibody alone. We looked for overall potency of triple combinations, picked a combination that stopped HIV in the test tube, and then tested if that combination would stop a virus similar to HIV that can grow in animals.

The three antibodies that we picked are human monoclonal antibodies, targeting conserved epitopes of the envelope of HIV. [The "envelope" is the outside part of the virus, that antibodies can get to. "Epitopes" are particular shapes of parts of HIV; antibodies target foreign substances by being shaped just right to fit them. "Conserved" epitopes means ones that do not change much from one strain of HIV to another (probably because when they do change as a result of mutations, the virus is not able to survive).]

This kind of therapy that uses antibodies is called "passive immunotherapy." It is important for babies, in particular, because it may be able to protect babies from getting HIV from their mothers, and also protect them from getting HIV from breast milk from the infected mother. Antibodies stay in the blood for a fairly long time [so it might be possible to protect babies with only a few injections, instead of shots or pills every day].

Scondras: Is there any connection between this and developing a vaccine to protect people from HIV?

Ruprecht: Yes. We have antibodies now that are completely characterized [meaning that we know to what part of HIV they bind]. If these antibodies can provide complete protection from HIV transmission, then a vaccine that elicits these antibodies should be protective.

Scondras: Is it possible that these antibodies could be a therapy for people who have HIV?

Ruprecht: We just do not know yet -- no experiments have been conducted to test this approach.

Scondras: Why do you think you may have found the right antibodies?

Ruprecht: We have data showing that these three antibodies can completely protect against SHIV challenge in adult rhesus monkeys. [SHIV is a virus which combines parts of SIV, which infects monkeys, and parts of human HIV.] We have also shown that newborn monkeys could be protected completely with the triple combination of antibodies against mucosal SHIV infection. Then we tried a much more aggressive SHIV strain, and it was stopped in some newborn animals. We purposely infected these monkeys with much, much more virus than is usually transmitted from mothers to babies, and the antibodies worked well.

One other point: The antibodies we have identified are of the IgG subtype, not IgA, the typical mucosal antibodies. This implies that you do not need mucosal immunity to HIV to protect people from HIV.

Scondras: Dr. Ruprecht: How did you get started in AIDS research ?

Ruprecht: I was about to start a thesis in physical chemistry in Switzerland, my native country, but my real love was molecular biology. When I was in the U.S. as a summer intern in chemistry, I discovered that the U.S. graduate-school system would allow me to make this change of fields, unlike my school in Europe. So I decided on the spur of the moment to stay in the US, and went to Columbia University. I worked on cancer-causing retroviruses and studied the mechanism of reverse transcriptase.

After getting my Ph.D., I attended a two-year medical school at the University of Miami, and then completed my residency in internal medicine at UCLA. I was there when the first HIV patients came to the hospital. I started a fellowship, moved back to New York City, then got an academic position in 1984 at the Dana-Farber Cancer Institute, and have worked in AIDS research ever since.

References

(1.) M. Gupta, S. Mahanty, M. Bray, R. Ahmed and P.E. Rollin. Passive transfer of antibodies protects immunocompetent and immunodeficient mice against lethal Ebola virus infection without complete inhibition of viral replication. Journal of Virology. May 2001; volume 75, pages 4649-4654.