J Infect Dis. 2017 Jan 1;215(1):70-79. doi: 10.1093/infdis/jiw499. Ep

Humanized Mice Reproduce Acute and Persistent Human Adenovirus Infection.

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Humanized mice are useful tools to study human-specific diseases in a human context. They have been widely used to study cancer, autoimmune diseases, hematopoietic stem cell transplantation and infectious diseases. The use of humanized mice to model human viral infections, has been classically limited to HIV. Only in the last years, models have been established for other viruses like Epstein-Barr virus (EBV) [1], Ebola [2], and Dengue virus [3-6].


Human Adenoviruses (HAdV) usually cause asymptomatic to mild infections of the upper respiratory tract, gastrointestinal tract and conjunctiva. These infections are self-limited for the majority of the population; however, in immune-compromised patients that undergo stem cell transplantation, and especially, in children, HAdV causes life-threatening infections [7-14]. It is thought that these infections are a consequence of the reactivation of a HAdV persistent infection. Whether the virus comes from the donor bone marrow or from the recipient still remains unknown.


It has been widely studied that HAdV can persistent in tonsils, adenoids and lymphocytes of the gastro-intestinal tract [15-20]; however, little is known about he mechanisms of viral persistence and reactivation. Although several studies have used cultured cell lines to model HAdV persistence [21, 22], there are no good in vivo models that would mimic HAdV persistence and pathogenesis because HAdVs are highly species-specific, meaning that they can only infect human cells.


In our recent publication, we have shown the establishment of a humanized mouse model for HAdV infections. We generated these animals using NSG mice that express human HLA-A2, which were then transplanted with HLA-matching human hematopoietic stem cells (HSC) isolated from umbilical cord blood. This allows for the reconstitution of a broad range of blood cell subpopulations, including mature T-cells.



Infection of these animals with HAdV-C2, which is the most commonly HAdV strain found in immune-compromised patients, induced two different phenotypes (Fig. 1). On one hand, one third of the animals developed acute infection, shown by progressive weight loss, ruffled fur and lethargy. These physical symptoms were a consequence of an Adenovirus-induced hepatitis, which was shown by the presence of liver steatosis (Fig. 2), hepatocyte vacuolization, fibrosis and infiltration of human immune cells (Fig. 2), specially, of monocytes and macrophages. In these animals, viral mRNAs were detected in several organs, and both early and late viral proteins were found in the liver. Furthermore, animals showed virus dissemination as infectious particles could be rescued from the liver and peripheral blood. On the other hand, the rest of the animals remained asymptomatic, however, some of them, had developed an Adenovirus persistent infection in the bone marrow. This was shown by the presence of early viral mRNAs in this body site, however, no viral proteins or late mRNAs were found in any organ assayed. In line with this, no infectious virus could be rescued from these animals. These results indicated that HAdV had induced a persistent/latent infection in the bone marrow of humanized mice.



Additionally, our model showed establishment of primary and adaptive immune responses that served us to distinguish between acute and persistent infection.


The importance of our findings lies in the fact that a species-specific virus like HAdV is able to cause a phenotype in humanized mice, where only immune cells are human, suggesting that the immune system plays a crucial role in the pathogenesis of severe HAdV infections. We do not know yet why some animals develop acute infection and others don’t. More experiments are needed to understand which blood cell subpopulations are important for fighting these infections, which might be missing in some of our animals and also in stem cell transplanted patients that develop severe HAdV infections. The fact that a HAdV persistent infection could be found only in the bone marrow among all the other humanized hematopoietic organs in our mice, suggest that this body site might be the place for viral persistence. Intriguingly, the presence of HAdV in bone marrow donors is not routinely checked, in contrast to HIV and Hepatitis C. Further experiments are needed to prove whether a similar reservoir exists in human subjects and measures must be taken to screen for the presence of HAdV in the bone marrow of donors.



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