Mason-Pfizer Monkey Virus Research Articles

Identification of novel simian endogenous retroviruses that are indistinguishable from simian retrovirus (SRV) on current SRV diagnostic assays.

Simian betaretroviruses include the well-known exogenous simian retroviruses (SRV-1 through SRV-8), and some closely related simian endogenous retroviruses (SERV). Here, we characterized two new viral genomes, which appear to represent novel SERVs but have characteristics of both SRV and SERV highlighting the need to develop new assays providing molecular and serologic differentiation of SERV and SRV to avoid false positives.

Optimized method for isolation of immature intracytoplasmic retroviral particles from mammalian cells

To biochemically and structurally characterize viral intracytoplasmic particles (ICAPs), a sample of high purity and homogeneity is usually required. Production of ICAPs in the system closely related to their natural host cells is crucial for the analysis of host-cell binding proteins involved in ICAPs assembly, transport and budding. However, this approach is often hampered by problems with low yield of the ICAPs due to either low expression or fast release from the host cell. Another obstacle may be a low stability or fragility of the intracellular particles. The published methods for ICAPs isolation often involved several time-consuming centrifugation steps yielding damaged particles. Other papers describe the ICAPs production in non-natural host cells. Here, we optimized the method for purification of unstable Mason-Pfizer monkey virus (M-PMV) ICAPs from non-human primate derived cells, commonly used to study MPMV replication i.e. African green monkey kidney fibroblast cell line (COS-1). Our simple and rapid procedure involved separation of the intracytoplasmic particles from the cell debris and organelles by differential, low-speed centrifugation, their purification using sucrose velocity gradient and final concentrating by low-speed centrifugation. Importantly, the method was established for unstable and fragile M-PMV intracytoplasmic particles. Therefore, it may be suitable for isolation of ICAPs of other viruses.

Evidence of simian retrovirus type D by polymerase chain reaction.

Over the past few years, there have been reports of finding Simian retrovirus type D (SRV) in macaque colonies where some animals were characterized as antibody positive but virus negative raising questions about how SRV was transmitted or whether there is a variant strain detected by antibody but not polymerase chain reaction (PCR) in current use. We developed a three-round nested PCR assay using degenerate primers targeting the pol gene to detect for SRV serotypes 1-5 and applied this newly validated PCR assay to test macaque DNA samples collected in China from 2010 to 2015. Using the nested PCR assay validated in this study, we found 0.15% of the samples archived on FTA® cards were positive. The source of SRV infection identified within domestic colonies might have originated from imported macaques. The multiplex nested PCR assay developed here may supplement the current assays for SRV.

Erratum to: High Prevalences and a Wide Genetic Diversity of Simian Retroviruses in Non-human Primate Bushmeat in Rural Areas of the Democratic Republic of Congo.

Like the majority of emerging infectious diseases, HIV and HTLV are of zoonotic origin. Here we assess the risk of cross-species transmissions of their simian counterparts, SIV and STLV, from non-human primates (NHP) to humans in the Democratic Republic of Congo (DRC). A total of 331 samples, derived from NHP bushmeat, were collected as dried blood spots (DBS, n = 283) or as tissue samples (n = 36) at remote forest sites mainly in northern and eastern DRC. SIV antibody prevalences in DBS were estimated with a novel high throughput immunoassay with antigens representing the actual known diversity of HIV/SIV lineages. Antibody-positive samples were confirmed by PCR and sequence analysis. Screening for STLV infection was done with universal primers in tax, and new strains were further characterized in LTR. SIV and STLV infection in tissue samples was done by PCR only. Overall, 5 and 15.4% of NHP bushmeat was infected with SIV and STLV, respectively. A new SIV lineage was identified in Allen's swamp monkeys (Allenopithecus nigroviridis). Three new STLV-1 subtypes were identified in Allen's swamp monkeys (Allenopithecus nigroviridis), blue monkeys (Cercopithecus mitis), red-tailed guenons (Cercopithecus ascanius schmidti) and agile mangabeys (Cercocebus agilis). SIV and STLV prevalences varied according to species and geographic region. Our study illustrates clearly, even on a small sample size from a limited number of geographic areas, that our knowledge on the genetic diversity and geographic distribution of simian retroviruses is still limited and that humans continue to be exposed to relative high proportions on infected NHP bushmeat.

High Prevalences and a Wide Genetic Diversity of Simian Retroviruses in Non-human Primate Bushmeat in Rural Areas of the Democratic Republic of Congo.

Like the majority of emerging infectious diseases, HIV and HTLV are of zoonotic origin. Here we assess the risk of cross-species transmissions of their simian counterparts, SIV and STLV, from non-human primates (NHP) to humans in the Democratic Republic of Congo (DRC). A total of 331 samples, derived from NHP bushmeat, were collected as dried blood spots (DBS, n=283) or as tissue samples (n=36) at remote forest sites mainly in northern and eastern DRC. SIV antibody prevalences in DBS were estimated with a novel high throughput immunoassay with antigens representing the actual known diversity of HIV/SIV lineages. Antibody-positive samples were confirmed by PCR and sequence analysis. Screening for STLV infection was done with universal primers in tax, and new strains were further characterized in LTR. SIV and STLV infection in tissue samples was done by PCR only. Overall, 5 and 15.4% of NHP bushmeat was infected with SIV and STLV, respectively. A new SIV lineage was identified in Allen's swamp monkeys (Allenopithecus nigroviridis). Three new STLV-1 subtypes were identified in Allen's swamp monkeys (Allenopithecus nigroviridis), blue monkeys (Cercopithecus mitis), red-tailed guenons (Cercopithecus ascanius schmidti) and agile mangabeys (Cercocebus agilis). SIV and STLV prevalences varied according to species and geographic region. Our study illustrates clearly, even on a small sample size from a limited number of geographic areas, that our knowledge on the genetic diversity and geographic distribution of simian retroviruses is still limited and that humans continue to be exposed to relative high proportions on infected NHP bushmeat.

Mechanical unfolding kinetics of the SRV-1 gag-pro mRNA pseudoknot: possible implications for -1 ribosomal frameshifting stimulation.

Minus-one ribosomal frameshifting is a translational recoding mechanism widely utilized by many RNA viruses to generate accurate ratios of structural and catalytic proteins. An RNA pseudoknot structure located in the overlapping region of the gag and pro genes of Simian Retrovirus type 1 (SRV-1) stimulates frameshifting. However, the experimental characterization of SRV-1 pseudoknot (un)folding dynamics and the effect of the base triple formation is lacking. Here, we report the results of our single-molecule nanomanipulation using optical tweezers and theoretical simulation by steered molecular dynamics. Our results directly reveal that the energetic coupling between loop 2 and stem 1 via minor-groove base triple formation enhances the mechanical stability. The terminal base pair in stem 1 (directly in contact with a translating ribosome at the slippery site) also affects the mechanical stability of the pseudoknot. The −1 frameshifting efficiency is positively correlated with the cooperative one-step unfolding force and inversely correlated with the one-step mechanical unfolding rate at zero force. A significantly improved correlation was observed between −1 frameshifting efficiency and unfolding rate at forces of 15–35 pN, consistent with the fact that the ribosome is a force-generating molecular motor with helicase activity. No correlation was observed between thermal stability and −1 frameshifting efficiency.

Transcriptional Silencing of Moloney Murine Leukemia Virus in Human Embryonic Carcinoma Cells.

Human embryonic carcinoma (EC) cells are shown to restrict the expression of murine leukemia virus genomes but not retroviral genomes of the lentiviral or betaretroviral families. The block occurs at the level of transcription and is accompanied by the deposition of repressive histone marks and methylation of the integrated proviral DNA. The host machinery required for silencing in human EC cells is distinct from that in murine EC cell lines: the histone methyltransferase SETDB1 is required, but the widely utilized corepressor TRIM28/Kap1 is not. A transcriptional enhancer element from the Mason-Pfizer monkey virus can override the silencing and promote transcription of chimeric proviral DNAs. The findings reveal novel features of human EC gene regulation not present in their murine counterparts.

Diverse activities of viral cis-acting RNA regulatory elements revealed using multicolor, long-term, single-cell imaging.

Cis-acting RNA structural elements govern crucial aspects of viral gene expression. How these structures and other posttranscriptional signals affect RNA trafficking and translation in the context of single cells is poorly understood. Herein we describe a multicolor, long-term (>24 h) imaging strategy for measuring integrated aspects of viral RNA regulatory control in individual cells. We apply this strategy to demonstrate differential mRNA trafficking behaviors governed by RNA elements derived from three retroviruses (HIV-1, murine leukemia virus, and Mason-Pfizer monkey virus), two hepadnaviruses (hepatitis B virus and woodchuck hepatitis virus), and an intron-retaining transcript encoded by the cellular NXF1 gene. Striking behaviors include "burst" RNA nuclear export dynamics regulated by HIV-1's Rev response element and the viral Rev protein; transient aggregations of RNAs into discrete foci at or near the nuclear membrane triggered by multiple elements; and a novel, pulsiform RNA export activity regulated by the hepadnaviral posttranscriptional regulatory element. We incorporate single-cell tracking and a data-mining algorithm into our approach to obtain RNA element-specific, high-resolution gene expression signatures. Together these imaging assays constitute a tractable, systems-based platform for studying otherwise difficult to access spatiotemporal features of viral and cellular gene regulation.

Histones Are Rapidly Loaded onto Unintegrated Retroviral DNAs Soon after Nuclear Entry.

Chromosomal structure of nuclear DNA is usually maintained by insertion of nucleosomes into preexisting chromatin, both on newly synthesized DNA atreplication forks and at sites of DNA damage. But during retrovirus infection, a histone-free DNA copy of the viral genome is synthesized that must be loaded with nucleosomes de novo. Here, we show that core histones are rapidly loaded onto unintegrated Moloney murine leukemia virus DNAs. Loading of nucleosomes requires nuclear entry, but does not require viral DNA integration. The histones associated with unintegrated DNAs become marked by covalent modifications, with a delay relative to thetime of core histone loading. Expression from unintegrated DNA can be enhanced by modulation of the histone-modifying machinery. The data show that histone loading onto unintegrated DNAs occurs very rapidly after nuclear entry and does not require prior establishment of an integrated provirus.

Membrane Interactions of the Mason-Pfizer Monkey Virus Matrix Protein and Its Budding Deficient Mutants

Matrix proteins (MAs) play a key role in the transport of retroviral proteins inside infected cells and in the interaction with cellular membranes. In most retroviruses, retroviral MAs are N-terminally myristoylated. This modification serves as a membrane targeting signal and also as an anchor for membrane interaction.The aim of this work was to characterize the interactions anchoring retroviral MA at the plasma membrane of infected cell. To address this issue, we compared the structures and membrane affinity of the Mason-Pfizer monkey virus (M-PMV) wild-type MA with its two budding deficient double mutants, that is, T41I/T78I and Y28F/Y67F. The structures of the mutants were determined using solution NMR spectroscopy, and their interactions with water-soluble phospholipids were studied. Water-soluble phospholipids are widely used models for studying membrane interactions by solution NMR spectroscopy. However, this approach might lead to artificial results due to unnatural hydrophobic interactions. Therefore, we used a new approach based on the measurement of the loss of the 1H NMR signal intensity of the protein sample induced by the addition of the liposomes containing phospholipids with naturally long fatty acids. HIV-1 MA was used as a positive control because its ability to interact with liposomes has already been described. We found that in contrast to HIV-1, the M-PMV MA interacted with the liposomes differently and much weaker. In our invivo experiments, the M-PMV MA did not co-localize with lipid rafts. Therefore, we concluded that M-PMV might adopt a different membrane binding mechanism than HIV-1.

サルレトロウイルス5型（SRV-5）のニホンザルへの感染実験

サルレトロウイルス5型（SRV-5）のニホンザルへの感染実験

Molecular aspects of the interaction between Mason-Pfizer monkey virus matrix protein and artificial phospholipid membrane.

The Mason-Pfizer monkey virus is a type D retrovirus, which assembles its immature particles in the cytoplasm prior to their transport to the host cell membrane. The association with the membrane is mediated by the N-terminally myristoylated matrix protein. To reveal the role of particular residues which are involved in the capsid-membrane interaction, covalent labelling of arginine, lysine and tyrosine residues of the Mason-Pfizer monkey virus matrix protein bound to artificial liposomes containing 95% of phosphatidylcholine and 5% phosphatidylinositol-(4,5)-bisphosphate (PI(4,5)P2 ) was performed. The experimental results were interpreted by multiscale molecular dynamics simulations. The application of these two complementary approaches helped us to reveal that matrix protein specifically recognizes the PI(4,5)P2 molecule by the residues K20, K25, K27, K74, and Y28, while the residues K92 and K93 stabilizes the matrix protein orientation on the membrane by the interaction with another PI(4,5)P2 molecule. Residues K33, K39, K54, Y66, Y67, and K87 appear to be involved in the matrix protein oligomerization. All arginine residues remained accessible during the interaction with liposomes which indicates that they neither contribute to the interaction with membrane nor are involved in protein oligomerization. Proteins 2016; 84:1717-1727. © 2016 Wiley Periodicals, Inc.

A novel simian retrovirus subtype discovered in cynomolgus monkeys (Macaca fascicularis).

A new simian retrovirus (SRV) subtype was discovered in China and the USA from Cambodian-origin cynomolgus monkeys. Histopathological examination from necropsied animals showed multifocal lymphoplasmacystic and histocytic inflammation. The complete genome sequences demonstrated that the US virus isolates were nearly identical (99.91-99.93 %) and differed only slightly (99.13-99.16 % identical) from the China isolate. Phylogenetic analysis showed that the new virus isolates formed a distinct branch of SRV-1 through -7, and therefore were named this subtype, SRV-8. This SRV-8 variant was also phylogenetically and serologically more closely related to SRV-4 than any other SRV subtype.

Functional and Structural Characterization of Novel Type of Linker Connecting Capsid and Nucleocapsid Protein Domains in Murine Leukemia Virus

The assembly of immature retroviral particles is initiated in the cytoplasm by the binding of the structural polyprotein precursor Gag with viral genomic RNA. The protein interactions necessary for assembly are mediated predominantly by the capsid (CA) and nucleocapsid (NC) domains, which have conserved structures. In contrast, the structural arrangement of the CA-NC connecting region differs between retroviral species. In HIV-1 and Rous sarcoma virus, this region forms a rod-like structure that separates the CA and NC domains, whereas in Mason-Pfizer monkey virus, this region is densely packed, thus holding the CA and NC domains in close proximity. Interestingly, the sequence connecting the CA and NC domains in gammaretroviruses, such as murine leukemia virus (MLV), is unique. The sequence is called a charged assembly helix (CAH) due to a high number of positively and negatively charged residues. Although both computational and deletion analyses suggested that the MLV CAH forms a helical conformation, no structural or biochemical data supporting this hypothesis have been published. Using an in vitro assembly assay, alanine scanning mutagenesis, and biophysical techniques (circular dichroism, NMR, microcalorimetry, and electrophoretic mobility shift assay), we have characterized the structure and function of the MLV CAH. We provide experimental evidence that the MLV CAH belongs to a group of charged, E(R/K)-rich, single α-helices. This is the first single α-helix motif identified in viral proteins.

Dual Simian Foamy Virus/Human Immunodeficiency Virus Type 1 Infections in Persons from Côte d'Ivoire.

Zoonotic transmission of simian retroviruses in West-Central Africa occurring in primate hunters has resulted in pandemic spread of human immunodeficiency viruses (HIVs) and human T-lymphotropic viruses (HTLVs). While simian foamy virus (SFV) and simian T- lymphotropic virus (STLV)-like infection were reported in healthy persons exposed to nonhuman primates (NHPs) in West-Central Africa, less is known about the distribution of these viruses in Western Africa and in hospitalized populations. We serologically screened for SFV and STLV infection using 1,529 specimens collected between 1985 and 1997 from Côte d’Ivoire patients with high HIV prevalence. PCR amplification and analysis of SFV, STLV, and HIV/SIV sequences from PBMCs was used to investigate possible simian origin of infection. We confirmed SFV antibodies in three persons (0.2%), two of whom were HIV-1-infected. SFV polymerase (pol) and LTR sequences were detected in PBMC DNA available for one HIV-infected person. Phylogenetic comparisons with new SFV sequences from African guenons showed infection likely originated from a Chlorocebus sabaeus monkey endemic to Côte d’Ivoire. 4.6% of persons were HTLV seropositive and PCR testing of PBMCs from 15 HTLV seroreactive persons identified nine with HTLV-1 and one with HTLV-2 LTR sequences. Phylogenetic analysis showed that two persons had STLV-1-like infections, seven were HTLV-1, and one was an HTLV-2 infection. 310/858 (53%), 8/858 (0.93%), and 18/858 (2.1%) were HIV-1, HIV-2, and HIV-positive but undifferentiated by serology, respectively. No SIV sequences were found in persons with HIV-2 antibodies (n = 1) or with undifferentiated HIV results (n = 7). We document SFV, STLV-1-like, and dual SFV/HIV infection in Côte d’Ivoire expanding the geographic range for zoonotic simian retrovirus transmission to West Africa. These findings highlight the need to define the public health consequences of these infections. Studying dual HIV-1/SFV infections in immunocompromised populations may provide a new opportunity to better understand SFV pathogenicity and transmissibility in humans.

Evaluation of Vero-cell-derived simian endogenous retrovirus infection in humans by detection of viral genome in clinicopathological samples and commercialized vaccines and by serology of Japanese general population

BackgroundVero cells are used in laboratories for the isolation of viruses and the production of vaccines. Recently, the sequence of simian endogenous retrovirus (SERV) was identified in Vero cells (SERVagm-Vero), with homology to exogenously transmitted, pathogenic simian retroviruses (SRVs). Although SERVagm-Vero was shown to be noninfectious to human cells in vitro, SERV infection in humans is controversial. In this study, we evaluated the status of SERV infection in humans by detecting the viral genome in clinicopathological samples and commercialized vaccines, and with a serological survey of the Japanese general population. MethodsReal-time polymerase chain reaction (PCR) and reverse transcription–PCR were used to detect the SERVagm-Vero genome. We also examined the seroprevalence of SERV in 1000 individuals in the Japanese population with an enzyme-linked immunoabsorbent assay (ELISA) using mixed SERVagm-Vero gag, pol, and env proteins as antigens. ResultsReal-time PCR failed to detect SERVagm-Vero genomic fragments in 783 human clinicopathological samples, and all 13 human cell lines tested were negative for the SERVagm-Vero genome. Thirteen commercialized vaccines, including five Vero-based vaccines, were also negative for the SERVagm-Vero genome on real-time PCR and reverse transcription–PCR. Eight (0.8%) were seropositive on ELISA, and western blotting showed that all eight sera contained anti-pol antibodies. All SERV-seropositive individuals were born before 1965, suggesting that SERV infection in Japan might not be associated with vaccine, because more than 90% of Japanese children born from 1964 to 2012 have received live poliovirus vaccines containing virus produced in Vero cells since the 1980s. ConclusionWe have confirmed that the vaccines we use today are free of SERVagm-Vero. Moreover, SERV infection in humans is very rare and unlikely to be associated with vaccines in the Japanese general population.

Packaging of Mason-Pfizer monkey virus (MPMV) genomic RNA depends upon conserved long-range interactions (LRIs) between U5 and gag sequences.

MPMV has great potential for development as a vector for gene therapy. In this respect, precisely defining the sequences and structural motifs that are important for dimerization and packaging of its genomic RNA (gRNA) are of utmost importance. A distinguishing feature of the MPMV gRNA packaging signal is two phylogenetically conserved long-range interactions (LRIs) between U5 and gag complementary sequences, LRI-I and LRI-II. To test their biological significance in the MPMV life cycle, we introduced mutations into these structural motifs and tested their effects on MPMV gRNA packaging and propagation. Furthermore, we probed the structure of key mutants using SHAPE (selective 2′hydroxyl acylation analyzed by primer extension). Disrupting base-pairing of the LRIs affected gRNA packaging and propagation, demonstrating their significance to the MPMV life cycle. A double mutant restoring a heterologous LRI-I was fully functional, whereas a similar LRI-II mutant failed to restore gRNA packaging and propagation. These results demonstrate that while LRI-I acts at the structural level, maintaining base-pairing is not sufficient for LRI-II function. In addition, in vitro RNA dimerization assays indicated that the loss of RNA packaging in LRI mutants could not be attributed to the defects in dimerization. Our findings suggest that U5-gag LRIs play an important architectural role in maintaining the structure of the 5′ region of the MPMV gRNA, expanding the crucial role of LRIs to the nonlentiviral group of retroviruses.

HIV-1 and M-PMV RNA Nuclear Export Elements Program Viral Genomes for Distinct Cytoplasmic Trafficking Behaviors.

Retroviruses encode cis-acting RNA nuclear export elements that override nuclear retention of intron-containing viral mRNAs including the full-length, unspliced genomic RNAs (gRNAs) packaged into assembling virions. The HIV-1 Rev-response element (RRE) recruits the cellular nuclear export receptor CRM1 (also known as exportin-1/XPO1) using the viral protein Rev, while simple retroviruses encode constitutive transport elements (CTEs) that directly recruit components of the NXF1(Tap)/NXT1(p15) mRNA nuclear export machinery. How gRNA nuclear export is linked to trafficking machineries in the cytoplasm upstream of virus particle assembly is unknown. Here we used long-term (>24 h), multicolor live cell imaging to directly visualize HIV-1 gRNA nuclear export, translation, cytoplasmic trafficking, and virus particle production in single cells. We show that the HIV-1 RRE regulates unique, en masse, Rev- and CRM1-dependent “burst-like” transitions of mRNAs from the nucleus to flood the cytoplasm in a non-localized fashion. By contrast, the CTE derived from Mason-Pfizer monkey virus (M-PMV) links gRNAs to microtubules in the cytoplasm, driving them to cluster markedly to the centrosome that forms the pericentriolar core of the microtubule-organizing center (MTOC). Adding each export element to selected heterologous mRNAs was sufficient to confer each distinct export behavior, as was directing Rev/CRM1 or NXF1/NXT1 transport modules to mRNAs using a site-specific RNA tethering strategy. Moreover, multiple CTEs per transcript enhanced MTOC targeting, suggesting that a cooperative mechanism links NXF1/NXT1 to microtubules. Combined, these results reveal striking, unexpected features of retroviral gRNA nucleocytoplasmic transport and demonstrate roles for mRNA export elements that extend beyond nuclear pores to impact gRNA distribution in the cytoplasm.

Nucleic Acid Binding by Mason-Pfizer Monkey Virus CA Promotes Virus Assembly and Genome Packaging.

The Gag polyprotein of retroviruses drives immature virus assembly by forming hexameric protein lattices. The assembly is primarily mediated by protein-protein interactions between capsid (CA) domains and by interactions between nucleocapsid (NC) domains and RNA. Specific interactions between NC and the viral RNA are required for genome packaging. Previously reported cryoelectron microscopy analysis of immature Mason-Pfizer monkey virus (M-PMV) particles suggested that a basic region (residues RKK) in CA may serve as an additional binding site for nucleic acids. Here, we have introduced mutations into the RKK region in both bacterial and proviral M-PMV vectors and have assessed their impact on M-PMV assembly, structure, RNA binding, budding/release, nuclear trafficking, and infectivity using in vitro and in vivo systems. Our data indicate that the RKK region binds and structures nucleic acid that serves to promote virus particle assembly in the cytoplasm. Moreover, the RKK region appears to be important for recruitment of viral genomic RNA into Gag particles, and this function could be linked to changes in nuclear trafficking. Together these observations suggest that in M-PMV, direct interactions between CA and nucleic acid play important functions in the late stages of the viral life cycle. Assembly of retrovirus particles is driven by the Gag polyprotein, which can self-assemble to form virus particles and interact with RNA to recruit the viral genome into the particles. Generally, the capsid domains of Gag contribute to essential protein-protein interactions during assembly, while the nucleocapsid domain interacts with RNA. The interactions between the nucleocapsid domain and RNA are important both for identifying the genome and for self-assembly of Gag molecules. Here, we show that a region of basic residues in the capsid protein of the betaretrovirus Mason-Pfizer monkey virus (M-PMV) contributes to interaction of Gag with nucleic acid. This interaction appears to provide a critical scaffolding function that promotes assembly of virus particles in the cytoplasm. It is also crucial for packaging the viral genome and thus for infectivity. These data indicate that, surprisingly, interactions between the capsid domain and RNA play an important role in the assembly of M-PMV.

Experimental evaluation of the zoonotic infection potency of simian retrovirus type 4 using humanized mouse model.

During 2001-2002 and 2008-2011, two epidemic outbreaks of infectious hemorrhagic disease have been found in Japanese macaques (Macaca fuscata) in Kyoto University Primate Research Institute, Japan. Following investigations revealed that the causative agent was simian retrovirus type 4 (SRV-4). SRV-4 was isolated by using human cell lines, which indicates that human cells are potently susceptible to SRV-4 infection. These raise a possibility of zoonotic infection of pathogenic SRV-4 from Japanese macaques into humans. To explore the possibility of zoonotic infection of SRV-4 to humans, here we use a human hematopoietic stem cell-transplanted humanized mouse model. Eight out of the twelve SRV-4-inoculated humanized mice were infected with SRV-4. Importantly, 3 out of the 8 infected mice exhibited anemia and hemophagocytosis, and an infected mouse died. To address the possibility that SRV-4 adapts humanized mouse and acquires higher pathogenicity, the virus was isolated from an infected mice exhibited severe anemia was further inoculated into another 6 humanized mice. However, no infected mice exhibited any illness. Taken together, our findings demonstrate that the zoonotic SRV-4 infection from Japanese macaques to humans is technically possible under experimental condition. However, such zoonotic infection may not occur in the real society.