Pathogenicity of Ebola and Marburg Viruses Is Associated With Differential Activation of the Myeloid Compartment in Humanized Triple Knockout-Bone Marrow, Liver, and Thymus Mice

Abstract

Ebola virus (EBOV) and Marburg virus (MARV) outbreaks are highly lethal, and infection results in a hemorrhagic fever with complex etiology. These zoonotic viruses dysregulate the immune system to cause disease, in part by replicating within myeloid cells that would normally innately control viral infection and shape the adaptive immune response. We used triple knockout (TKO)-bone marrow, liver, thymus (BLT) humanized mice to recapitulate the early in vivo human immune response to filovirus infection. Disease severity in TKO-BLT mice was dissimilar between EBOV and MARV with greater severity observed during EBOV infection. Disease severity was related to increased Kupffer cell infection in the liver, higher levels of myeloid dysfunction, and skewing of macrophage subtypes in EBOV compared with MARV-infected mice. Overall, the TKO-BLT model provided a practical in vivo platform to study the human immune response to filovirus infection and generated a better understanding of how these viruses modulate specific components of the immune system.

The Utility of Human Immune System Mice for High-Containment Viral Hemorrhagic Fever Research

“…Interestingly, the data suggested human donor-specific variations on the outcome of the disease [40], which should be considered in conjunction with the possible effects of engraftment efficiency, as was shown in hu-NSG-A2 mice [38]. In addition, flow cytometry analysis of human cells in EBOV-infected BLT humanized C57BL/6 Rag2 −/− Il2rG c −/− Cd47 −/− (TKO-BLT) mice [41], ≈60% of which succumbed to infection by 22 days post-infection (dpi), suggested that EBOV infection induced myeloid cell dysfunction and skewing of macrophage subsets in vivo at late time points, in line with prior in vitro experiments using human cells [54,55].…”

“…Studies of MARV infection in HIS mice are much more limited than ebolavirus studies. Only one report, using the TKO-BLT model, investigated MARV infection in HIS mice [41]. In humans, MARV disease is comparable in severity to EBOV disease.…”

“…While not an accurate model of VHF disease course from beginning to end, HIS mice provide a more faithful human immune system to examine specific features in a hypothesis-driven manner. For example, by comparing various viruses using the BLT system we have found that differences in dendritic cell and T cell responses exist and can be characterized even between closely related viruses [41].…”

“…Non-hematopoietic cells in these mouse models are often antigen-positive for virus. Especially common is the infection of endothelial cells [41][42][43] as well as infection of hepatocytes and Kupffer cells [41,76,77]. CD8 + T cell responses are thought to be important in the development of disease caused by VHFs [78][79][80].…”

“…Limited cross-reactivity of human and mouse cytokines [89] prevents a full assessment of causes and effects in these models, as does omitting or neglecting assessment of mouse cytokines during these studies. Unobserved parallel murine cytokine messaging from endothelial or other murine cells harboring virus could occur in HIS mouse disease models [41][42][43], but is not commonly investigated. Even less is known about the extent of human immune cell interactions with murine tissue ligands.…”