WEDNESDAY, April 30 (HealthDay News) — Researchers have devised a rapid and efficient method for generating protein sentinels of the immune system, called monoclonal antibodies, which mark and neutralize foreign invaders.
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The development could potentially accelerate the traditionally challenging task of generating human antibodies, which can be used both to develop faster disease diagnostics — for instance, to test for a new flu strain shortly after it emerges — as well as safer and more effective medications, including vaccines.
"I think it's an important, incremental advance in our ability to provide antigen-specific monoclonal antibodies quickly and efficiently," said Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases. He was not involved with the study, but the institute did fund some of the research.
The findings were published online April 30 in the journal Nature.
When a person is exposed to a germ or a vaccine, the immune system mounts a series of challenges to confront the foreign particles. One of those responses involves so-called B cells, which begin to secrete antibodies. Antibodies are proteins, and each binds to a specific three-dimensional shape, or antigen, on the pathogen's surface, blocking its ability to enter cells, or marking it for destruction by other immune cells.
Each B cell can make only one type of antibody. But because most antigens are relatively large, there may be several different B cells whose antibodies will bind to any given antigen. The resulting pool of antibodies is termed "polyclonal," because it arises from multiple clones of activated B cells.
A monoclonal antibody, as its name implies, is the product of a single B-cell clone, so it binds just to a single shape on the antigen's surface. Monoclonals are useful biotechnology tools and have proven effective in clinical settings, too: A handful of monoclonal-based therapeutics are commercially available, including the anti-cancer drug, Herceptin.
But few, if any, of these monoclonals are human proteins, said Patrick Wilson, of the Oklahoma Medical Research Foundation, who led the new study with Rafi Ahmed of Emory University School of Medicine. Instead, for both ethical and practical reasons, monoclonals are usually made in mice. And that's a problem, because the human immune system recognizes the mouse proteins as foreign and sometimes attacks them instead. The result can be an allergic reaction, and sometimes even death.
To get around that problem, researchers now "humanize" the antibodies, replacing some or all of mouse-derived pieces with human ones.
Wilson and Ahmed were interested in the immune response to vaccination. Conventional wisdom held that the B-cell response would be dominated by "memory" B cells. But as the study authors monitored individuals vaccinated against influenza, they found that a different population of B cells peaked about one week after vaccination, and then disappeared, before the memory cells kicked in. This population of cells, called antibody-secreting plasma cells (ASCs), is highly enriched for cells that target the vaccine, with vaccine-specific cells accounting for nearly 70 percent of all ASCs.
"That's the trick," said Wilson. "So instead of one cell in 1,000 binding to the vaccines, now it is seven in 10 cells."
All of a sudden, the researchers had access to a highly enriched pool of antibody-secreting cells, something that is relatively easy to produce in mice, but hard to come by for human B cells.
To ramp up the production and cloning of these antibodies, the researchers added a second twist. Mouse monoclonal antibodies are traditionally produced in the lab from hybridomas, which are cell lines made by fusing the antibody-producing cell with a cancer cell. But human cells don't respond well to this treatment. So Wilson and his colleagues isolated the ASC antibody genes and transferred them into an "immortalized" cell line. The result was the generation of more than 100 different monoclonals in less than a year, with each taking just a few weeks to produce.
That's a far cry from the one to two years typically required to make a single monoclonal cell line, Wilson noted.
Said Fauci: "The advance here is that now when you vaccinate someone, you can have literally within a week these very important antibody-secreting cells that can serve as the source for developing monoclonal antibodies. [ASCs] come earlier, they are in abundance, and have high-affinity antibodies. So that's a pretty important advance in cases where you need monoclonal antibodies for a pathogenic antigen."
In the event of an emerging flu pandemic, for instance, this approach could lead to faster production of human monoclonals to both diagnose and protect against the disease, he said.
SOURCES: Patrick Wilson, Ph.D., assistant member, Oklahoma Medical Research Foundation, Oklahoma City; Anthony Fauci, M.D., director, U.S. National Institute of Allergy and Infectious Diseases; April 30, 2008, Nature, online
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