Unveiling immune interference: how the dendritic cell response to co-infection with <i>Aspergillus fumigatus</i> is modulated by human cytomegalovirus and its virokine _CMV IL-10

Human cytomegalovirus (HCMV) is a master of immune evasion and a potent modulator of the human immune system. The best-characterized mechanism employed by HCMV to suppress host immunity is the production of a viral interleukin-10 homolog (_CMVIL-10). While _CMVIL-10 is known to suppress immune responses and promote viral persistence, its capacity to promote increased susceptibility to co-infecting pathogens like <i>Aspergillus fumigatus</i> remains unknown. Therefore, we studied the impact of wild-type (WT) HCMV (strain TB40), a _CMVIL-10-deficient HCMV mutant (Δ<i>UL111A</i>), and recombinant _CMVIL-10 on the immune activity of monocyte-derived dendritic cells (moDCs) during co-infection with <i>A. fumigatus</i>. Using a combination of transcriptomic and phenotypic readouts, our data revealed a strong and time-dependent immuno-paralytic effect of HCMV by suppressing pathogen recognition pathways, cytokine production, DC maturation, and expression of genes that are essential for host defense and tissue repair. Although infection with Δ<i>UL111A</i> lacking _CMVIL-10 led to stronger expression of type I interferons, IFN-γ-inducible chemokines, and proinflammatory cytokines than WT infection, interference with antifungal immune defense and fungal clearance during co-infection was largely similar between both strains. The limited effect of _CMVIL-10 on antifungal immune defense persisted even after prolonged pre-exposure of DCs to the recombinant virokine. In summary, although _CMVIL-10 contributes to shaping an anti-inflammatory environment, HCMV's suppression of antifungal immunity appears to be multifactorial, with _CMVIL-10 alone playing a rather subtle role in altering DC responses to <i>A. fumigatus</i> during viral-fungal co-infection.IMPORTANCEHuman cytomegalovirus (HCMV) is a highly prevalent herpesvirus that establishes lifelong latency and frequently reactivates in immunocompromised individuals, including hematopoietic stem cell transplant recipients. Reactivation not only causes direct disease but also increases the risk of secondary infections, such as invasive pulmonary aspergillosis caused by <i>Aspergillus fumigatus</i>. Specifically, studies estimated that about 6%-25% of critically ill HCMV-positive patients develop HCMV-associated pulmonary aspergillosis. However, the mechanisms by which HCMV creates a permissive environment for fungal superinfection remain poorly understood. HCMV encodes a viral homolog of interleukin-10 (_CMVIL-10), which mimics host IL-10 and elicits potent immunomodulatory activity. Here, we show that _CMVIL-10 dampens specific anti-viral responses, DC activation, and cytokine signaling. However, HCMV-mediated impairment of fungal control in co-infection settings occurred largely independent of _CMVIL-10 expression. These findings suggest that HCMV undermines antifungal defenses through multifactorial mechanisms beyond _CMVIL-10, highlighting the need for targeted strategies to restore immune function in high-risk patients.