Scientists are developing super-antibodies which would go right inside cells to attack bacteria and viruses.
Super-antibodies could tackle HIV
The Canadian team believe the advance could lead to a new range of treatments, New Scientist reports.
The super-antibodies may be able to target bacteria and viruses, including HIV, inside affected cells.
The downside is that antibodies have to be injected as they do not survive in the stomach, and experts said they are hard to develop.
The theory is that they could do more than the small molecules of most conventional drugs.
A cell-penetrating super-antibody would be highly discriminating, and because it can be far more specific than small-molecule drugs, and is not inherently toxic, it should have fewer side-effects.
InNexus Biotechnology, of Vancouver, Canada, which is developing the technology, said a simple chemical modification allows an antibody to move in and out of cells until it finds its target.
This modification is a short protein segment, normally found in signalling proteins such as growth factors that can enter cells.
Experiments showed the super-antibody enters all cells but only accumulates in those containing its target.
Charles Morgan, president of the company, said: "Most good targets for diseases are inside cells."
However, Andrew Bradbury, of the Los Alamos National Laboratory in New Mexico, said: "A lot of work has been done trying to make antibodies that are stable in cells.
"But it's proved far more difficult than expected."
And Dr Richard Pleass, an expert in therapeutic antibodies for malaria at the University of Nottingham, said experts would urge caution on super-antibodies.
He said: "There are far too many questions - how are they going to work? What is the killer mechanism?
"I don't realistically think there is a future in them."
He said that around 30% of all drugs currently being trialled are antibody based and that the market would be worth US$15 billion by 2005.