Comparative genomics, infectivity and cytopathogenicity of Zika viruses produced by acutely and persistently infected human hematopoietic cell lines

Comparative analysis of a Thai congenital-Zika-syndrome-associated virus with a Thai Zika-fever-associated virus

In this study, we compared the characteristics of two strains of Zika virus (ZIKV) isolated in Thailand, one isolated from a febrile patient and one isolated from tissues of a fetus medically terminated due to congenital Zika syndrome (CZS). Replication profiles showed that the isolate from the fetal tissues replicated significantly more slowly than the fever-associated isolate in human lung A549 cells during the first 24 hours postinfection but showed a similar growth profile over longer-term infection. A much smaller difference was observed in Aedes albopictus C6/36 cells. In a quasispecies analysis, a high proportion (approximately 20%) of nonfunctional genomes was identified, caused by an adenine insertion in the prM gene. This insertion was found to be present in two Thai fever strains and as such may represent a common feature of Thai endemic ZIKV. Comparison between viral RNA copy number and viral titer showed that the isolate from fetal tissues was produced more efficiently than the fever-associated isolate. Together, these results suggest that different ZIKV isolates differ in their replication capacity, and this might contribute to the fetotropic potential of a particular strain.

Zika virus infection studies with CD34+ hematopoietic and megakaryocyte-erythroid progenitors, red blood cells and platelets

BACKGROUND

To date, several cases of transfusion-transmitted ZIKV infections have been confirmed. Multiple studies detected prolonged occurrence of ZIKV viral RNA in whole blood as compared to plasma samples indicating potential ZIKV interaction with hematopoietic cells. Also, infection of cells from the granulocyte/macrophage lineage has been demonstrated. Patients may develop severe thrombocytopenia, microcytic anemia, and a fatal course of disease occurred in a patient with sickle cell anemia suggesting additional interference of ZIKV with erythroid and megakaryocytic cells. Therefore, we analyzed whether ZIKV propagates in or compartmentalizes with hematopoietic progenitor, erythroid, and megakaryocytic cells.

METHODS

ZIKV RNA replication, protein translation and infectious particle formation in hematopoietic cell lines as well as primary CD34⁺ HSPCs and ex vivo differentiated erythroid and megakaryocytic cells was monitored using qRT-PCR, FACS, immunofluorescence analysis and infectivity assays. Distribution of ZIKV RNA and infectious particles in spiked red blood cell (RBC) units or platelet concentrates (PCs) was evaluated.

RESULTS

While subsets of K562 and KU812Ep6^EPO cells supported ZIKV propagation, primary CD34⁺ HSPCs, MEP cells, RBCs, and platelets were non-permissive for ZIKV infection. In spiking studies, ZIKV RNA was detectable for 7 days in all fractions of RBC units and PCs, however, ZIKV infectious particles were not associated with erythrocytes or platelets.

CONCLUSION

Viral particles from plasma or contaminating leukocytes, rather than purified CD34⁺ HSPCs or the cellular component of RBC units or PCs, present the greatest risk for transfusion-transmitted ZIKV infections.

Comparative Genomics, Infectivity and Cytopathogenicity of American Isolates of Zika Virus that Developed Persistent Infections in Human Embryonic Kidney (HEK293) Cells

Zika virus (ZIKV) transmission can cause serious fetal neurological abnormalities. ZIKV persistence in various human cells and tissues can serve as infectious reservoirs and post serious threats to public health. The human embryonic kidney (HEK293) cell line with known neuronal developmental properties was readily infected by ZIKV in a strain-dependent fashion. Significant cytopathic effect in HEK293 cells infected by the prototype MR 766 strain of ZIKV resulted in complete loss of cells, while small numbers of HEK293 cells infected by contemporary ZIKV isolates (PRV or FLR strain) continued to survive and regrow to confluency in the culture around two months after initial infection. Most, if not all, of the cells in the two resulting persistently ZIKV-infected HEK293 cell lines tested positive for ZIKV antigen. Compared to HEK293 control cells, the persistently ZIKV-infected HEK293 cells had slower growth rates with some cells undergoing apoptosis in culture. The "persistent ZIKVs" produced constitutively by both PRV and FLR strains ZIKV-infected HEK293 cells had significantly attenuated cell infectivity and/or cytopathogenicity. Comparative genome sequence analyses between the persistent ZIKVs and the original inoculum ZIKVs showed no clonal selection with specific gene mutations in the prolonged process of establishing persistently PRV strain ZIKV-infected HEK293 cells; while selection of ZIKV subclones with mutations in the envelope, protein pr and multiple NS genes was evident in developing persistently FLR strain ZIKV-infected HEK293 cell line. Our study provides molecular insights into the complex interplays of ZIKV and human host cells in establishing ZIKV persistence.

Human Fetal Astrocytes Infected with Zika Virus Exhibit Delayed Apoptosis and Resistance to Interferon: Implications for Persistence

Zika virus (ZIKV) infection and persistence during pregnancy can lead to microcephaly and other fetal neurological disorders collectively known as Congenital Zika Syndrome. The immunological and virological events that contribute to the establishment of persistent ZIKV infection in humans are unclear though. Here we show that human fetal astrocytes (HFAs), the most abundant cell type in the central nervous system, become persistently infected with ZIKV resulting in continuous viral shedding for at least one month; a process that is facilitated by TIM/TAM receptors. HFAs are relatively resistant to ZIKV-induced apoptosis, a factor that may be important for chronic infection of these cells. Once infection was established, interferon treatment did not reduce virus replication. Moreover, the fact that the innate immune system was highly activated in persistently infected HFAs indicates that the virus can thrive in the presence of a sustained antiviral response. RNAseq analyses of persistently infected cells revealed that ZIKV alters host gene expression in a manner that could affect developmental processes. Conversely, data from sequencing of ZIKV genomes in persistently infected HFAs suggest that adaptive mutations were not required for establishing chronic infection. Based on these results, we postulate that HFAs are reservoirs for ZIKV in the fetal brain and that moderate apoptosis combined with inefficient antiviral response from these cells may contribute to the establishment of chronic brain infection associated with the ZIKV neurodevelopmental abnormalities.