Cyanovirin,

Cyanovirin, a particularly interesting HIV-cell fusion blocker, comes from blue-green algae. It was discovered in a National Cancer Institute (NCI) screening program for natural anti-HIV agents. A protein with a complicated structure, cyanovirin binds to the sugars attached to HIV envelope protein and prevents them from binding to mucosal cell surfaces in the vagina or rectum. This mechanism would be active whether the HIV is binding to DC-SIGN or the CD4 and chemokine receptors. Cyanovirin is also active against herpes viruses.

As with carrageenan, development of cyanovirin has been exceedingly slow-paced. The chief of the NCI cyanovirin program, Michael Boyd, described it as "languishing." Apparently the NCI's production facilities, based on genetically manipulated cell cultures, have been diverted to other projects that the agency considers of higher priority. This is unfortunate: cyanovirin is of particular interest because of its relative safety. It is 10,000 times more toxic to HIV than it is to cells.