they have engineered an abzyme that degrades the superantigenic region of the gp120 CD4 binding site. This is the one part of the HIV virus outer coating that does not change, because it is the attachment point to T lymphocytes, the key cell in cell-mediated immunity. Once infected by HIV, patients produce antibodies to the more changeable parts of the viral coat. The antibodies are ineffective because of the virus' ability to change their coats rapidly. Because this protein gp120 is necessary for HIV to attach, it does not change across different strains and is a point of vulnerability across the entire range of the HIV variant population. The abzyme does more than bind to the site: it catalytically destroys the site, rendering the virus inert, and then can attack other HIV viruses. A single abzyme molecule can destroy thousands of HIV viruses. References Monoclonal antibodies Immune system Enzymes