Cryptococcus neoformans responds to presence of Mycobacterium by diversifying its morphologies and remodelling its capsular material

<b>Introduction</b> <i>. Cryptococcus neoformans</i> and <i>Mycobacterium tuberculosis</i> (MTb) are opportunistic pathogens that share overlapping geographical distributions and physiological niches within the human body. Both are recognized by the World Health Organization as high-priority pathogens.<b>Gap Statement</b>. Although clinical reports of co-infections with cryptococcosis and tuberculosis are increasing, experimental studies exploring their interactions remain scarce.<b>Aim</b>. We aimed to observationally evaluate whether <i>C. neoformans</i> isolates would alter morphology when co-cultured with <i>Mycobacteria</i> spp. and observe how these changes might alter the host immune response to <i>C. neoformans</i> cells.<b>Methodology</b>. We cultured <i>C. neoformans</i> reference strain and clinical isolates in physiologically relevant growth media, in the presence or absence of <i>Mycobacterium</i> spp. Then, we generated alveolar-like macrophages and created a stimulation environment similar to a tuberculosis environment to perform phagocytic killing assays of <i>C. neoformans</i> cells.<b>Results</b>. Here, we demonstrate that <i>C. neoformans</i> can grow in the presence of either heat-killed MTb antigen or the live vaccine strain, <i>Mycobacterium bovis</i> BCG. In response to the presence of mycobacteria, <i>C. neoformans</i> increased in number and exhibited enhanced virulence-associated traits, including titan cell formation, capsule enlargement and increased survival from phagocytosis.<b>Conclusion</b>. This work provides proof of principle for a dynamic, inter-pathogen interaction that may contribute to the exacerbation of disease outcomes in settings of a co-infection.