Mycobacterium tuberculosis growth inhibition by peripheral blood mononuclear cells from household contacts is not affected by previous SARS-CoV-2 infection.

Background: There is a concern that SARS-CoV-2 infection may drive poor outcomes after Mycobacterium tuberculosis Mtb exposure and infection. We performed an ex vivo Mtb killing assay using peripheral blood mononuclear cells (PBMC) from three groups: healthy household contacts of people with active TB with and without serologic evidence of previous SARS-CoV-2 infection (COV+HHC and COV-HHC), and participants with active TB and previous SARS-CoV-2 (COV+TB+).

Methods: Twenty participants per group from Cape Town, South Africa were classified according to SARS-CoV-2 anti-S and anti-N antibody tests. We infected PBMC from each participant at a MOI of 0.001 with Mtb strain H37Rv in a 4-day growth inhibition assay. Mycobacteria were quantified through inoculation into Bactec Mycobacteria Growth Indicator Tube (MGIT) liquid culture. PBMC from a subset of participants were infected in the presence of autologous time-matched serum and Mtb-uninfected control PBMCs were included.

Results: There was no difference in the time to detection of Mtb or the normalised Mtb growth ratio (log10CFUsample - log10CFUcontrol) between groups in the standard protocol, or when infected cells from the COV+HHC and COV+TB+ (n=10 each) groups were cultured with autologous time-matched serum. The group with active TB demonstrated the best Mtb growth control. Extracellular Mtb measured by culturing the supernatants of the infected cell cultures also did not show any difference between groups. Five (14.3%) uninfected controls were culture positive.

Conclusion: Our results show that previous SARS-CoV-2 does not affect the Mtb killing ability of circulating mononuclear immune cells in vitro. Previous SARS-CoV-2 is unlikely to affect the outcome of Mtb infection through this mechanism.