Modulation of pulmonary IL-21 expression during latent TB and Mtb/SIV co-infection

TB (Tuberculosis) and HIV co-infection remains a major global health challenge, with limited understanding of how these pathogens impact local immune responses in the lungs. This study is the first to investigate the modulation of IL-21 during LTBI and Mycobacterium tuberculosis (Mtb)/ Simian Immunodeficiency Virus (SIV) co-infection in non-human primates (NHP). We show that IL-21 expression, predominantly derived from CD4⁺ T cells, is significantly reduced in lungs of Mtb/SIV co-infected macaques, especially in the absence of cART. Although cART and cART with 3HP partially restore IL-21-producing CD4⁺ T cells, levels remain below those in LTBI, indicating ongoing immune impairment. Spatial transcriptomic analysis suggests localized alterations in immune signaling, including differences in STAT1- and STAT3-associated transcriptional profiles and reduced Mtb-specific IFN-γ responses in co-infected animals. Together, our findings indicate that IL-21-producing CD4⁺ T cells are selectively and persistently impaired in the lungs during Mtb/SIV co-infection despite antimicrobial and antiviral therapy. These results highlight a compartment-specific deficit in immune reconstitution and suggest that IL-21-associated pathways may warrant further investigation as potential targets for host-directed therapeutic strategies.