Human norovirus cultivation systems and their use in antiviral research.

Human norovirus (HuNoV) is a major cause of acute gastroenteritis and foodborne diseases, affecting all age groups. Despite its clinical needs, no approved antiviral therapies are available. Since the discovery of HuNoV in 1972, studies on anti-norovirals, mechanism of HuNoV infection, viral inactivation, etc., have been hampered by the lack of a robust laboratory-based cultivation system for HuNoV. A recent breakthrough in the development of HuNoV cultivation systems has opened opportunities for researchers to investigate HuNoV biology in the context of de novo HuNoV infections. A tissue stem cell-derived human intestinal organoid/enteroid (HIO) culture system is one of those that supports HuNoV replication reproducibly and, to our knowledge, is most widely distributed to laboratories worldwide to study HuNoV and develop therapeutic strategies. This review summarizes recently developed HuNoV cultivation systems, including HIO, and their use in antiviral studies.

Homologous Recombination Deficiency Unrelated to Platinum and PARP Inhibitor Response in Cell Line Libraries.

While large publicly available cancer cell line databases are invaluable for preclinical drug discovery and biomarker development, the association between homologous recombination deficiency (HRD) and drug sensitivity in these resources remains unclear. In this study, we comprehensively analyzed molecular profiles and drug screening data from the Cancer Cell Line Encyclopedia. Unexpectedly, gene alterations in BRCA1/2 or homologous recombination-related genes, HRD scores, or mutational signature 3 were not positively correlated with sensitivity to platinum agents or PARP inhibitors. Rather, higher HRD scores and mutational signature 3 were significantly associated with resistance to these agents in multiple assays. These findings were consistent when analyzing exclusively breast and ovarian cancer cell lines and when using data from the COSMIC Cell Line Project. Collectively, the existing data from established cancer cell lines do not reflect the expected association between HRD status and drug response to platinum agents and PARP inhibitors in clinical tumors. This discrepancy may extend to other tumor characteristics, highlighting the importance of recognizing potential limitations in cell line data for researchers.

Interstitial lung disease caused by niraparib in ovarian cancer patient: a case report and literature review.

Drug-induced interstitial lung disease (DIILD) is one of the most common and important adverse drug reactions. Still, the details of the clinical presentation of DIILD caused by poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitors are unknown. A 73-year-old Japanese woman was started on niraparib maintenance therapy after radical surgery and adjuvant chemotherapy for high-grade serous carcinoma originating from the fallopian tube. Forty-seven days after starting niraparib, she presented to the hospital with dyspnea and was diagnosed with DIILD caused by niraparib. The drug was discontinued, and the patient was treated with steroid pulse therapy, and her condition improved. In clinical trials of PARP inhibitors, DIILD was reported in 0.13% of patients with olaparib, but no DIILDs, including pneumonia or pneumonitis, were reported in any patient with niraparib. This is the first report of DIILD caused by niraparib worldwide. In the future, the frequency of DIILD caused by niraparib should be clarified in real-world data.

Electrolyzed hypochlorous acid water exhibits potent disinfectant activity against various viruses through irreversible protein aggregation.

It is essential to employ efficient measures to prevent the transmission of pathogenic agents during a pandemic. One such method involves using hypochlorous acid (HClO) solution. The oxidative properties of HClO water (HAW) can contribute to its ability to eliminate viral particles. Here, we examined a highly purified slightly acidic hypochlorous acid water (Hp-SA-HAW) obtained from the reverse osmosis membrane treatment of an electrolytically-generated SA-HAW for its anti-viral activity and mode of action on viral proteins. Hp-SA-HAW exhibited broad-spectrum antiviral effects against various viruses, including adenovirus, hepatitis B virus, Japanese encephalitis virus (JEV), and rotavirus. Additionally, Hp-SA-HAW treatment dose-dependently resulted in irreversibly aggregated multimers of the JEV envelope and capsid proteins. However, Hp-SA-HAW treatment had no discernible effect on viral RNA, indicating that Hp-SA-HAW acts against amino acids rather than nucleic acids. Furthermore, Hp-SA-HAW substantially reduced the infectivity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), including the ancestral variant and other multiple variants. Hp-SA-HAW treatment induced the aggregation of the SARS-CoV-2 spike and nuclear proteins and disrupted the binding of the purified spike protein of SARS-CoV-2 to human ACE2. This study demonstrates that the broad-spectrum virucidal activity of highly purified HClO is attributed to viral protein aggregation of virion via protein oxidation.

Molecular Evolutionary Analyses of the RNA-Dependent RNA Polymerase (RdRp) Region and VP1 Gene in Human Norovirus Genotypes GII.P6-GII.6 and GII.P7-GII.6.

To understand the evolution of GII.P6-GII.6 and GII.P7-GII.6 strains, the prevalent human norovirus genotypes, we analysed both the RdRp region and VP1 gene in globally collected strains using authentic bioinformatics technologies. A common ancestor of the P6- and P7-type RdRp region emerged approximately 50 years ago and a common ancestor of the P6- and P7-type VP1 gene emerged approximately 110 years ago. Subsequently, the RdRp region and VP1 gene evolved. Moreover, the evolutionary rates were significantly faster for the P6-type RdRp region and VP1 gene than for the P7-type RdRp region and VP1 genes. Large genetic divergence was observed in the P7-type RdRp region and VP1 gene compared with the P6-type RdRp region and VP1 gene. The phylodynamics of the RdRp region and VP1 gene fluctuated after the year 2000. Positive selection sites in VP1 proteins were located in the antigenicity-related protruding 2 domain, and these sites overlapped with conformational epitopes. These results suggest that the GII.6 VP1 gene and VP1 proteins evolved uniquely due to recombination between the P6- and P7-type RdRp regions in the HuNoV GII.P6-GII.6 and GII.P7-GII.6 virus strains.

Diagnostic Utility of Hysteroscopic Biopsy in Cases of Suspected Lobular Endocervical Glandular Hyperplasia and Comparison with Cervical Conization.

BACKGROUND: Cervical cystic lesions encompass a range of benign and malignant pathologies. Magnetic resonance imaging or cytology alone cannot provide a definitive diagnosis, and conventional practice involves performing a cervical biopsy by conization to confirm the histology in cases exhibiting potential signs of lobular endocervical glandular hyperplasia (LEGH) or malignancy. However, as postoperative complications resulting from conization can impact future fertility and pregnancy, alternative diagnostic methods are needed for reproductive-age patients. This study aimed to establish the efficacy of a hysteroscopic biopsy for diagnosing cervical cystic lesions and compare it with conization. METHODS: Thirteen patients with cervical cystic lesions suspected of LEGH or malignancy underwent a hysteroscopic biopsy, while 23 underwent conization. Patient background information, preoperative evaluation, histology, and postoperative outcomes were collected and compared retrospectively. RESULTS: No significant differences were found between the hysteroscopy and conization groups in terms of mean patient age (45 vs. 48 years), operating time (23 vs. 35 min), blood loss (small amount vs. 43 mL), and postoperative hospitalization (1.1 vs. 1.6 days). CONCLUSION: A hysteroscopic biopsy allows for targeted resection of the cervix while maintaining diagnostic accuracy. It may serve as an efficient method for diagnosing cervical cystic lesions.

Inhibitory effect of Ephedra herba on human norovirus infection in human intestinal organoids.

Human norovirus (HuNoV) is a major cause of acute gastroenteritis and foodborne diseases worldwide with public health concern, yet no antiviral therapies have been developed. In this study, we aimed to screen crude drugs, which are components of Japanese traditional medicine, ''Kampo'' to see their effects on HuNoV infection using a reproducible HuNoV cultivation system, stem-cell derived human intestinal organoids/enteroids (HIOs). Among the 22 crude drugs tested, Ephedra herba significantly inhibited HuNoV infection in HIOs. A time-of-drug addition experiment suggested that this crude drug more preferentially targets post-entry step than entry step for the inhibition. To our knowledge, this is the first anti-HuNoV inhibitor screen targeting crude drugs, and Ephedra herba was identified as a novel inhibitor candidate that merits further study.

Development of an Algorithm to Differentiate Uterine Sarcoma from Fibroids Using MRI and LDH Levels.

BACKGROUND: This study aimed to establish an evaluation method for detecting uterine sarcoma with 100% sensitivity using MRI and serum LDH levels. METHODS: One evaluator reviewed the MRI images and LDH values of a total of 1801 cases, including 36 cases of uterine sarcoma and 1765 cases of uterine fibroids. The reproducibility of the algorithm was also examined by four evaluators with different imaging experience and abilities, using a test set of 61 cases, including 14 cases of uterine sarcoma. RESULTS: From the MRI images and LDH values of 1801 cases of uterine sarcoma and uterine fibroids, we found that all sarcomas were included in the group with a high T2WI and either a high T1WI, an unclear margin, or high LDH values. In addition, when cases with DWI were examined, all sarcomas had high DWI. Among the 36 sarcoma cases, the group with positive findings for T2WI, T1WI, margins, and serum LDH levels all had a poor prognosis (p = 0.015). The reproducibility of the algorithm was examined by four evaluators and the sensitivity of sarcoma detection ranged from 71% to 93%. CONCLUSION: We established an algorithm to distinguish uterine sarcoma if tumors in the myometrium with low T2WI and DWI are present.

Diagnosis Assistance in Colposcopy by Segmenting Acetowhite Epithelium Using U-Net with Images before and after Acetic Acid Solution Application.

Colposcopy is an essential examination tool to identify cervical intraepithelial neoplasia (CIN), a precancerous lesion of the uterine cervix, and to sample its tissues for histological examination. In colposcopy, gynecologists visually identify the lesion highlighted by applying an acetic acid solution to the cervix using a magnifying glass. This paper proposes a deep learning method to aid the colposcopic diagnosis of CIN by segmenting lesions. In this method, to segment the lesion effectively, the colposcopic images taken before acetic acid solution application were input to the deep learning network, U-Net, for lesion segmentation with the images taken following acetic acid solution application. We conducted experiments using 30 actual colposcopic images of acetowhite epithelium, one of the representative types of CIN. As a result, it was confirmed that accuracy, precision, and F1 scores, which were 0.894, 0.837, and 0.834, respectively, were significantly better when images taken before and after acetic acid solution application were used than when only images taken after acetic acid solution application were used (0.882, 0.823, and 0.823, respectively). This result indicates that the image taken before acetic acid solution application is helpful for accurately segmenting the CIN in deep learning.

Uterine angioleiomyoma with disseminated intravascular coagulation: a case report.

BACKGROUND: Uterine angioleiomyoma is benign tumor that composed of smooth muscle cells and thick-walled vessels. It is a very rare condition reported to present as lower abdominal mass, accompanied by dysmenorrhea and hypermenorrhea. However, its clinical presentation is not known. CASE PRESENTATION: We report the case of a 44-year-old Japanese woman who developed severe anemia with disseminated intravascular coagulation without obvious external bleeding. The patient had a huge abdominal mass of over 20 cm in size, which was thought to be a uterine tumor. She received daily blood transfusions and her condition improved rapidly after she underwent hysterectomy. Pathological examination of the tumor revealed spindle-shaped cells with little atypia and mitosis, and numerous large vessels with smooth muscle and thrombus in the vessels. CONCLUSIONS: Uterine angioleiomyoma was identified as the cause of the coagulation abnormality. CCND2 and AR gene amplification was detected in the tumor. Uterine tumors that present with coagulopathy despite a clinical course suggestive of benign disease should undergo differential diagnosis for uterine angioleiomyoma.

Treatment for Locally Resectable Stage IIIC1 Cervical Cancer: A Retrospective, Single-Institution Study.

According to the revision of the FIGO 2018 staging system, cervical cancer with pelvic lymph node metastases was changed to stage IIIC1. We retrospectively analyzed the prognosis and complications of locally resectable (classified as T1/T2 by TNM classification of the Union for International Cancer Control) stage IIIC1 cervical cancer. A total of 43 patients were divided into three groups: surgery with chemotherapy (CT) (ope+CT group) (T1; n = 7, T2; n = 16), surgery followed by concurrent chemoradiotherapy (CCRT), or radiotherapy (RT) (ope+RT group) (T1; n = 5, T2; n = 9), and CCRT or RT alone (RT group) (T1; n = 0, T2; n = 6). In T1 patients, recurrence was observed in three patients, but there was no difference among the treatment groups, and no patients died. In contrast, in T2 patients, recurrence and death were observed in nine patients (8 in ope+CT; 1 in ope+RT), and recurrence-free survival and overall survival were lower in the ope+CT group (p = 0.02 and 0.04, respectively). Lymphedema and dysuria were more common in the ope+RT group. A randomized controlled trial comparing CT and CCRT as an adjuvant therapy after surgery in T1/T2 patients, including those with pelvic lymph node metastases, is currently underway. However, our data suggest that performing CT alone after surgery in T2N1 patients is likely to worsen the prognosis.

Histopathological subtyping of high-grade serous ovarian cancer using whole slide imaging.

OBJECTIVE: We have established 4 histopathologic subtyping of high-grade serous ovarian cancer (HGSOC) and reported that the mesenchymal transition (MT) type has a worse prognosis than the other subtypes. In this study, we modified the histopathologic subtyping algorithm to achieve high interobserver agreement in whole slide imaging (WSI) and to characterize the tumor biology of MT type for treatment individualization. METHODS: Four observers performed histopathological subtyping using WSI of HGSOC in The Cancer Genome Atlas data. As a validation set, cases from Kindai and Kyoto Universities were independently evaluated by the 4 observers to determine concordance rates. In addition, genes highly expressed in MT type were examined by gene ontology term analysis. Immunohistochemistry was also performed to validate the pathway analysis. RESULTS: After algorithm modification, the kappa coefficient, which indicates interobserver agreement, was greater than 0.5 (moderate agreement) for the 4 classifications and greater than 0.7 (substantial agreement) for the 2 classifications (MT vs. non-MT). Gene expression analysis showed that gene ontology terms related to angiogenesis and immune response were enriched in the genes highly expressed in the MT type. CD31 positive microvessel density was higher in the MT type compared to the non-MT type, and tumor groups with high infiltration of CD8/CD103 positive immune cells were observed in the MT type. CONCLUSION: We developed an algorithm for reproducible histopathologic subtyping classification of HGSOC using WSI. The results of this study may be useful for treatment individualization of HGSOC, including angiogenesis inhibitors and immunotherapy.

Tubulovillous adenoma with high-grade dysplasia of the vulva harboring high tumor mutational burden and cancer-associated mutations: a case report.

BACKGROUND: Vulvar cancer is a rare disease, accounting for approximately 5% of gynecological malignancies. Primary adenocarcinoma of intestinal-type of the vulva or its precancerous lesion is extremely rare, and details regarding its origin, evolution and related genetic mutations are unknown. Treatment options for this cancer have not been defined. CASE PRESENTATION: A 63-year-old Japanese woman came to the hospital because she was aware of a vulvar mass. There was a 1 cm mass on the dorsal side of the vulva, just outside the remains of the hymen. Biopsy revealed suspected adenocarcinoma, and wide local excision was performed. From histopathology and immunohistochemistry, the specimen was diagnosed as tubulovillous adenoma with high-grade dysplasia of the vulva. No other primary lesions were found, and the vulva was considered the primary site. A gene panel test (FoundationOneCDx assay) showed a high tumor mutational burden and mutations in TP53, KEL, RB1, RNF43, PTEN, GNAS, and PIK3CA. CONCLUSIONS: The current case of tubulovillous adenoma with high-grade dysplasia of the vulva had a variety of cancer-associated mutations, despite being a precancerous lesion. In cases of intestinal-type neoplasms of the vulva, it may be helpful to check tumor mutational burden and gene mutations for treatment selection.

Ovarian teratoid carcinosarcoma with a PIK3CA mutation: a case report and review of the literature.

Ovarian teratoid carcinosarcoma involves an epithelial tumor of the Müllerian duct and an immature neuroepithelium, which is a characteristic of immature teratomas. Here, we describe the case of a 60-year-old woman who underwent surgery for a stage IC3 ovarian malignancy. The tumor showed a variety of histological features, including clear cell carcinoma, immature teratoma, and rhabdomyosarcoma, and a PIK3CA mutation was detected at the same locus in each. Two months after surgery and before the start of chemotherapy, multiple bone and liver metastases were found. Four courses of combination therapy with vincristine, actinomycin D and cyclophosphamide, the standard chemotherapy regimen for pediatric rhabdomyosarcoma, were administered, and a complete response was achieved. After a 2-month rest period, the patient developed recurrent peritoneal dissemination and underwent 6 courses of paclitaxel, carboplatin, and bevacizumab chemotherapy, resulting in a partial response. This is the eighth reported case of ovarian teratoid carcinosarcoma. This tumor has a very aggressive course, but initially responds to chemotherapy. However, survival over 5 years has not been reported, and elucidation of the pathogenesis and development of new treatment methods are needed. Supplementary Information: The online version contains supplementary material available at 10.1007/s13691-022-00571-w.

Risk factors for future osteoporosis in perimenopausal Japanese women.

OBJECTIVE: The aims of this study were to investigate trends in bone mineral density (BMD) loss and related factors in early postmenopausal women in Japan, identify risk factors for future osteoporosis, and predict osteoporosis before it occurs. METHODS: The study population consisted of women who were 50 to 54 years old at the time of the survey in 2002 or 2006. The study included a questionnaire and physical measurement findings (BMD, height, body weight [WT], body mass index [BMI], and handgrip strength). One hundred sixty-seven women continued to participate in the study and had BMD measurements at the 9- or 10-year follow-up of the Japanese Population-based Osteoporosis study. Statistical analyses were performed using Pearson correlation to examine each factor of physical measurement and BMD for lumbar spine (LS) and femoral neck (FN). The receiver operating characteristic curve of this data was also predictive of osteoporosis in 2011 for 2002 data; BMD at the age of 50 to 54 years was then used to predict the likelihood of being diagnosed with osteoporosis 9 and 10 years later. RESULTS: At the baseline in 2002 and 2006, WT, BMI, height, and handgrip strength were positively correlated with BMD. The optimal cutoff values for BMD in 2006 to predict osteoporosis in 2016 were LS less than 0.834 g/cm 2 and FN less than 0.702 g/cm 2 . These data were also predictive of osteoporosis in 2011 for 2002 data; applying this to the 2002 data, LS/FN had a sensitivity of 92%/100%, a specificity of 87%/81%, a positive predictive value of 55%/48%, and a negative predictive value of 98%/100%. The larger WT and BMI also resulted in a greater decrease in BMD of FN after 9 or 10 years. CONCLUSIONS: We have identified a cutoff value for BMD to predict future osteoporosis in menopausal women and found a negative correlation between WT and BMI in menopausal women and changes in BMD of the FN over the next 10 years.

Transient atypical lymphoplasmacytic proliferation of the endometrium associated with pyometra: a case report.

Plasmablastic lymphoma is a mature B-cell neoplasm with plasmablastic differentiation, often associated with human immunodeficiency virus (HIV) infection and other forms of immunosuppression. Although it is usually an aggressive disease, spontaneous regression has been seen in a few cases. Plasmablastic lymphoma of the uterus is rare. We report a case of atypical lymphoplasmacytic proliferation resembling plasmablastic lymphoma associated with pyometra that disappeared completely as the pyometra resolved. A 76-year-old HIV-negative woman presented with abnormal vaginal bleeding. Ultrasound and MRI findings were consistent with pyometra diagnosis. Endometrial biopsy revealed large plasmablastoid cells with abundant cytoplasm and prominent nucleoli proliferating in the endometrium. Immunohistochemistry showed that large cells stained positive for CD138, CD79a, and MUM1, and negative for CD20, PAX5, CD3, and CD5. Ki67 labelled at least 80% of the large cells. Epstein-Barr virus was detected in a small number of cells. The histologic picture was highly indicative of lymphoma, especially plasmablastic lymphoma, though the clinical context was unusual. As the pyometra was treated and resolved, the intrauterine abnormality disappeared completely. The patient has been well after 16 months with no sign of recurrent disease. This case underscores the sometimes blurry distinction between benign inflammation and lymphoma.

Mutation burden-orthogonal tumor genomic subtypes delineate responses to immune checkpoint therapy.

BACKGROUND: In cancer therapy, higher-resolution tumor-agnostic biomarkers that predict response to immune checkpoint inhibitor (ICI) therapy are needed. Mutation signatures reflect underlying oncogenic processes that can affect tumor immunogenicity, and thus potentially delineate ICI treatment response among tumor types. METHODS: Based on mutational signature analysis, we developed a stratification for all solid tumors in The Cancer Genome Atlas (TCGA). Subsequently, we developed a new software (Genomic Subtyping and Predictive Response Analysis for Cancer Tumor ICi Efficacy, GS-PRACTICE) to classify new tumors submitted to whole-exome sequencing. Using existing data from 973 pan-cancer ICI-treated cases with outcomes, we evaluated the subtype-response predictive performance. RESULTS: Systematic analysis on TCGA samples identified eight tumor genomic subtypes, which were characterized by features represented by smoking exposure, ultraviolet light exposure, APOBEC enzyme activity, POLE mutation, mismatch repair deficiency, homologous recombination deficiency, genomic stability, and aging. The former five subtypes were presumed to form an immune-responsive group acting as candidates for ICI therapy because of their high expression of immune-related genes and enrichment in cancer types with FDA approval for ICI monotherapy. In the validation cohort, the samples assigned by GS-PRACTICE to the immune-reactive subtypes were significantly associated with ICI response independent of cancer type and TMB high or low status. CONCLUSIONS: The new tumor subtyping method can serve as a tumor-agnostic biomarker for ICI response prediction and will improve decision making in cancer treatment.

CRISPR-Cas9-Based Technology for Studying Enteric Virus Infection.

Enteric viruses, including numerous viruses that initiate infection in enteric canal, are recognized as important agents that cause wide spectrum of illnesses in humans, depending on the virus type. They are mainly transmitted by fecal-oral route with several vector such as contaminated water or food. Infections by enteric viruses, such as noroviruses and rotaviruses, frequently cause widespread acute gastroenteritis, leading to significant health and economic burdens and therefore remain a public health concern. Like other viruses, enteric viruses ''hijack'' certain host factors (so called pro-viral factors) for replication in infected cells, while escaping the host defense system by antagonizing host anti-viral factors. Identification(s) of these factors is needed to better understand the molecular mechanisms underlying viral replication and pathogenicity, which will aid the development of efficient antiviral strategies. Recently, the advancement of genome-editing technology, especially the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 system, has precipitated numerous breakthroughs across the field of virology, including enteric virus research. For instance, unbiased genome-wide screening employing the CRISPR-Cas9 system has successfully identified a number of previously unrecognized host factors associated with infection by clinically relevant enteric viruses. In this review, we briefly introduce the common techniques of the CRISPR-Cas9 system applied to virological studies and discuss the major findings using this system for studying enteric virus infection.

Evaluation of Heat Inactivation of Human Norovirus in Freshwater Clams Using Human Intestinal Enteroids.

Foodborne disease attributed to the consumption of shellfish contaminated with human norovirus (HuNoV) is one of many global health concerns. Our study aimed to determine the conditions of the heat-inactivation of HuNoV in freshwater clams (Corbicula japonica) using a recently developed HuNoV cultivation system employing stem-cell derived human intestinal enteroids (HIEs). We first measured the internal temperature of the clam tissue in a water bath during boiling at 90 °C and found that approximately 2 min are required for the tissue to reach 90 °C. Next, GII.4 HuNoV was spiked into the center of the clam tissue, followed by boiling at 90 °C for 1, 2, 3, or 4 min. The infectivity of HuNoV in the clam tissue homogenates was evaluated using HIEs. We demonstrated that HuNoV in unboiled clam tissue homogenates replicated in HIEs, whereas infectivity was lost in all boiled samples, indicating that heat treatment at 90 °C for 1 min inactivates HuNoV in freshwater clams in our current HIE culture system. To our knowledge, this is the first study to determine the thermal tolerability of HuNoV in shellfish using HIEs, and our results could be informative for developing strategies to inactivate HuNoV in shellfish.

Atomic Structure of the Human Sapovirus Capsid Reveals a Unique Capsid Protein Conformation in Caliciviruses.

Sapovirus (SaV) is a member of the Caliciviridae family, which causes acute gastroenteritis in humans and animals. Human sapoviruses (HuSaVs) are genetically and antigenically diverse, but the lack of a viral replication system and structural information has hampered the development of vaccines and therapeutics. Here, we successfully produced a self-assembled virus-like particle (VLP) from the HuSaV GI.6 VP1 protein, and the first atomic structure was determined using single-particle cryo-electron microscopy (cryo-EM) at a 2.9-Å resolution. The atomic model of the VP1 protein revealed a unique capsid protein conformation in caliciviruses. All N-terminal arms in the A, B, and C subunits interacted with adjacent shell domains after extending through their subunits. The roof of the arched VP1 dimer was formed between the P2 subdomains by the interconnected ß strands and loops, and its buried surface was minimized compared to those of other caliciviruses. Four hypervariable regions that are potentially involved in the antigenic diversity of SaV formed extensive clusters on top of the P domain. Potential receptor binding regions implied by tissue culture mutants of porcine SaV were also located near these hypervariable clusters. Conserved sequence motifs of the VP1 protein, "PPG" and "GWS," may stabilize the inner capsid shell and the outer protruding domain, respectively. These findings will provide the structural basis for the medical treatment of HuSaV infections and facilitate the development of vaccines, antivirals, and diagnostic systems. IMPORTANCE SaV and norovirus, belonging to the Caliciviridae family, are common causes of acute gastroenteritis in humans and animals. SaV and norovirus infections are public health problems in all age groups, which occur explosively and sporadically worldwide. HuSaV is genetically and antigenically diverse and is currently classified into 4 genogroups consisting of 18 genotypes based on the sequence similarity of the VP1 proteins. Despite these detailed genetic analyses, the lack of structural information on viral capsids has become a problem for the development of vaccines or antiviral drugs. The 2.9-Å atomic model of the HuSaV GI.6 VLP presented here not only revealed the location of the amino acid residues involved in immune responses and potential receptor binding sites but also provided essential information for the design of stable constructs needed for the development of vaccines and antivirals.