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Interferon May Lead to New Option for Treating TB

By Alan McCord

September 2008

Worldwide, tuberculosis (TB) is the leading cause of death in people living with HIV. Indeed, simply having HIV is a major risk factor for developing TB. Treating it is difficult: therapy lasts 6 months, side effects interfere with treating HIV disease, and many do not complete their treatment.

Interferon gamma (IFN-g) is an important immune system chemical made by CD4 cells. It helps fight viral infections and prevent malignant cells from developing. As a medical product, IFN-g is well studied as a treatment for immune system diseases. Typical side effects include flu-like symptoms and injection site reactions.

Since CD4 cells can be depleted by HIV disease, insufficient amounts of IFN-g are present to protect the body from various infections. The Russian study looked at whether giving doses of IFN-g would improve immune responses to TB disease.

This small safety study followed 21 HIV-positive people with CD4 counts above 350. All were newly diagnosed with active TB disease of the lungs, and treatments were given to two groups. The first took standard TB drugs with 3 injections of IFN-g (500,000 IU) each week for 8 weeks. The second group took standard TB drugs and placebo injection. Lab tests were taken at weeks 0, 4 and 8.

Overall, results showed that those on IFN-g had better improvements in their general health and immune responses compared to placebo. IFN-g appeared to be well tolerated, though specific side effects were not reported. CD4 counts increased an average of 70-100 cells. HIV viral loads in the control group with IFN-g became undetectable in 11 people, while no one became undetectable in the placebo group.

Taking drugs for both TB and HIV at the same time can be challenging for many. As well, the risk for developing TB within the first 3 months on HIV therapy is quite high. Therefore, using IFN-g in people who haven't started HIV therapy may eventually provide another option for those faced with a TB diagnosis. Longer-term studies will need to be conducted to assess how durable this response remains over time.

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