Now 100% Sensitive at Detecting CXCR4 HIV-1 Levels as Low as 0.3%

South San Francisco, Calif., June 5, 2008 -- Monogram Biosciences, Inc. (Nasdaq: MGRM) today announced immediate availability of enhanced sensitivity in its Trofile assay.

Trofile was introduced commercially upon FDA approval of Selzentry (maraviroc), Pfizer's first in class CCR5 antagonist, in August 2007. Optimization of Monogram's Trofile HIV co-receptor tropism assay has made it substantially more sensitive at identifying very low levels of CXCR4 using virus (X4 or dual/mixed tropic) in HIV-1 patient samples while maintaining a high degree of accuracy. The assay can now detect X4 virus present at levels less than 0.3% of the total virus population, and at that level of X4 virus, the assay is 100% sensitive. This improvement in sensitivity should give physicians a greater level of confidence that the Trofile assay is selecting the most appropriate patients for CCR5 antagonist therapy.

Tropism refers to the chemokine co-receptor on the surface of CD4+ cells that a particular variant of HIV uses to enter the cell. "R5" variants use the CCR5 co-receptor, "X4" viruses use the CXCR4 co-receptor, and dual/mixed HIV uses both co-receptors. New CCR5 antagonist therapies, such as Pfizer's Selzentry block the "R5" variants of HIV from entering through the CCR5 co-receptor. CCR5 antagonists have not been shown to be effective against X4 or dual/mixed variants.

Trofile is now 100% sensitive at detecting CXCR4 minor variants as low as 0.3%, a sensitivity increase of 30-fold on average. Monogram says that with this increase in sensitivity, the assay remains highly accurate.

"Pfizer welcomes advances and innovation in tropism detection, such as the enhanced sensitivity of Trofile, which will give physicians important information when deciding whether or not to incorporate a CCR5 antagonist like Selzentry into a patient's treatment regimen," said Dr. Howard Mayer, MD, Executive Director, Pfizer Development Team Leader for HIV/AIDS. Pfizer and Monogram have a collaboration agreement for commercialization of Trofile outside of the U.S.

"Detection of CXCR4-using minority variants has been shown as an important indicator of CCR5 antagonist treatment success and Trofile is the only clinically validated assay to identify co-receptor tropism, a step the FDA and EMEA [Editor's note: European regulatory agency] has determined is critical in selecting patients for treatment with a CCR5 antagonist," said Monogram CEO William Young. "Trofile is the gold standard in tropism testing and the enhanced sensitivity version now available sets a new standard for performance so that the thousands of physicians who rely on our assay can better direct patient selection."

Trofile examines the complete gp160 coding region of the HIV-1 envelope protein, ensuring that all of the determinants of tropism are tested. In a retrospective analysis reported at the recent Conference on Retroviruses and Opportunistic Infections, the enhanced assay improved patient selection by identifying more cases of dual/mixed virus, and more accurately predicted virologic outcomes. In addition to providing patient selection for Selzentry's pivotal trials, Trofile has been used for patient selection and monitoring in all Phase II and III clinical trials of co-receptor antagonists.

About Trofile

Trofile is a clinically validated patient selection tropism assay that determines whether a patient is infected with a strain of HIV that uses either the CCR5 co-receptor, the CXCR4 co-receptor, or a combination of CCR5 and CXCR4 to enter cells. The use of CCR5, CXCR4 or both co-receptors defines the "tropism" of the virus strain. Trofile amplifies the envelope gene from a patient's HIV genome (from their blood sample) and then uses it to make HIV particles containing the patient's virus envelope protein. The resultant HIV particles are then used to infect cells that contain the CCR5 co-receptor or the CXCR4 co-receptor on the cell surface. Once the virus infects the cell, it undergoes a single round of replication. Virus replication results in the production of luciferase from a luciferase gene that is carried into the cell by the virus. The production of luciferase in either CCR5 cells, CXCR4 cells or both cell types defines the co-receptor tropism of the patient virus. Trofile is the only clinically validated tropism assay and has been used to select patients in all phase II and phase III studies of CCR5 antagonists to date.

About Monogram

Monogram is a biotechnology company advancing individualized medicine by discovering, developing and marketing innovative products to guide and improve treatment of serious infectious diseases and cancer. The company's products are designed to help doctors optimize treatment regimens for their patients that lead to better outcomes and reduced costs. The company's technology is also being used by numerous biopharmaceutical companies to develop new and improved antiviral therapeutics and vaccines as well as targeted cancer therapeutics.