Interference of Immunosuppressive Therapies with Cellular Antimicrobial Activity Against Mycobacterium abscessus

Immunosuppressive therapies increase the risk of infection, but there is little information regarding their effects on cellular antimycobacterial activity. In this context, the aim was to evaluate in vitro the impact of commonly used immunosuppressive drugs on the ability of peripheral blood mononuclear cells (PBMCs), neutrophils (polymorphonuclear cells, PMNs), and monocyte-derived macrophages (MDMs) to control Mycobacterium abscessus. Biofilm formation was assessed by quantifying bacterial colonies in cellular cultures (BCCCs) and bacterial viability by colony-forming units (CFUs). BCCCs showed significant differences among treatment conditions in PBMCs. The median (interquartile range) BCCC values for tacrolimus (TAC) 16.5 (41), everolimus (EVE) 11 (33), methotrexate (MTX) 12.5 (22) and leflunomide (LEF) 11 (29) were all significantly higher than the negative control (DMSO) 5 (14), indicating that these immunosuppressants impaired the ability of PBMCs to restrict BCCC formation. Log-transformed CFUs also varied across treatments in PMNs. Mycophenolic acid (MPA) 5.98 (2.61) and EVE 5.85 (2.77) increased LogCFU recovery compared with DMSO 5.58 (2.63), whereas MTX 5.18 (2.74) decreased it. In contrast, immunosuppressants had no significant overall effect in MDM cultures. Interestingly, 6-mercaptopurine (6MP) affected the size of colonies. Prednisolone, as expected, but also MTX and LEF, inhibited the expression in infected PBMCs of IL-1β, IL-1Ra, IL-6, CCL3, CCL5, CXCL8 and TIMP-2, whereas IL-10, CCL2 and CXCL7 expression remained essentially unchanged. Unexpectedly, methotrexate promoted CXCL8 expression, a chemokine for PMNs. These results show that commonly used immunosuppressive drugs can differentially modulate the antimycobacterial activity of PBMCs and innate immune cells, affecting both mycobacterial viability and biofilm formation.