Mycobacterium tuberculosis-specific CD8⁺T cell recall in convalescing TB subjects with HIV co-infection

Memory T cell populations recover following phase I chemotherapy for tuberculosis (TB) and augment the effectiveness of antibiotics during the continuation phase of treatment. For those with human immunodeficiency virus (HIV), the CD8⁺T cells may have an especially important role in host defense to Mycobacterium tuberculosis (M.tb) as CD4⁺T cell function and/or numbers decline. Here we performed a preliminary study to investigate the impact of HIV infection status on CD8⁺T cell effector function during the convalescent TB period. Peripheral blood samples from convalescent HIV⁺ and HIV^- TB subjects were used to determine CD4 ⁺T cell count and monitor antigen-specific CD8⁺ T cell activation of effector function (lymphoproliferation, IFN-γ, granulysin) in response to M.tb antigen. Our preliminary results suggest that HIV co-infection is associated with moderate suppression of the M.tb-specific memory CD8⁺T cell compartment in many subjects convalescent for TB. Interestingly, highly activated CD8⁺T cells were observed in recall experiments using peripheral blood from several HIV+ subjects that had low (<200 cells/mm³) CD4⁺T cell counts. Further investigation may provide important information for development of novel approaches to target M.tb-specific CD8⁺T cell memory to protect against TB in HIV-endemic regions.