Around 28% of the world’s population have been exposed to the pathogen Mycobacterium tuberculosis (MTB), with no development of active tuberculosis (TB) in over 90% of humans who are infected. They therefore have a “sleeping”, called latent, TB infection. It is already well known that an uncontrolled HIV infection harbours a high risk for the development of active TB. Conversely, little research has been conducted to date on the extent to which a latent TB infection might influence the progression of HIV.

To this end, the research group led by Katharina Kusejko analysed data from around 14,000 patients from the Swiss HIV cohort study. The subjects were divided into three groups: not infected with MTB, with a latent infection, and with active TB. The scientists correlated these groups with the patients’ corresponding course of HIV infection using a variety of statistical methods.

The main insight was that those with a latent TB infection exhibited a lower HIV viral load and fewer opportunistic infections in comparison to those who were not infected with the tuberculosis pathogen. In other words: A “sleeping” MTB infection was associated with better HIV values. In contrast, a control group of patients with active TB exhibited more copies of HIV virus in their blood and more opportunistic infections than the group that was not infected with TB.

This study allowed the research team of the Swiss HIV cohort study to describe an association between latent TB infection and a reduced HIV viral load and fewer opportunistic infections in patients infected with both HIV and TB, implying that the interactions between these infections must be significantly more complex than we have thought to date. The hypothesis on how latent infections with Mycobacterium tuberculosis affect other immune responses in humans could therefore also be further investigated in studies in the future.

Diagnosis of latent tuberculosis infection is associated with reduced HIV viral load and lower risk for opportunistic infections in people living with HIV. Katharina Kusejko, Huldrych F. Günthard, Gregory S. Olson, Kyra Zens, Katharine Darling, Nina Khanna, Hansjakob Furrer, Pauline Vetter, Enos Bernasconi, Pietro Vernazza, Matthias Hoffmann, Roger D. Kouyos, Johannes Nemeth, the Swiss HIV Cohort Study. PLoS Biol. 2020 Dec;18(12):e3000963. doi.org/10.1371/journal.pbio.3000963.