Zika virus (ZIKV), a mosquito-borne flavivirus with homology to Dengue virus (DENV), has become a public health emergency. By characterizing memory lymphocytes from ZIKV-infected patients, we dissected ZIKV-specific and DENV-cross-reactive immune responses. Antibodies to nonstructural protein 1 (NS1) were largely ZIKV-specific and were used to develop a serological diagnostic tool. In contrast, antibodies against E protein domain I/II (EDI/II) were cross-reactive and, although poorly neutralizing, potently enhanced ZIKV and DENV infection in vitro and lethally enhanced DENVdisease in mice. Memory Tcells against NS1 or E proteins were poorly cross-reactive, even in donors preexposed to DENV. The most potent neutralizing antibodies were ZIKV-specific and targeted EDIII or quaternary epitopes on infectious virus. An EDIII-specific antibody protected mice from lethal ZIKV infection, illustrating the potential for antibody-based therapy.A fter its introduction into Brazil in 2015, Zika virus (ZIKV) has spread rapidly, and in February 2016, the World Health Organization (WHO) declared it a Public Health Emergency of International Concern (1-3). The main route of ZIKV infection is through bites by Aedes mosquitos, but the virus may also be sexually (4) and vertically transmitted (5). Although most of the ZIKV infections are asymptomatic or cause only mild symptoms, there is evidence that ZIKV infection can lead to neurological complications, such as Guillain-Barré syndrome in adults (6) and congenital birth defects, including microcephaly in the developing fetus (5,7,8), likely through its ability to infect human neural progenitor cells (9).Whereas flavivirus envelope (E) proteins mediate fusion and are the main target of neutralizing antibodies, the nonstructural protein 1 (NS1) is secreted by infected cells and is involved in immune evasion and pathogenesis (10). Two recent studies showed a high level of structural similarity between the E protein of ZIKV and that of other flaviviruses-such as dengue virus (DENV), yellow fever virus (YFV), and West Nile virus (WNV)-but also revealed distinct features that may be related to the ZIKV neurotropism (11,12). Similarly, the structural analysis of ZIKV NS1 revealed conserved features with NS1 of other flaviviruses, although with different electrostatic characteristics (13).A phenomenon that is characteristic of certain flaviviruses is the disease-enhancing activity of cross-reactive antibodies elicited by previous infections by heterologous viruses, termed antibodydependent enhancement (ADE). In the case of DENV, for which four serotypes are known, there is epidemiological evidence that a primary infection protects from reinfection with the same serotype but represents a risk factor for the development of severe disease upon reinfection with a different serotype (14). The exacerbated disease is triggered by E-and prM-specific antibodies that fail to neutralize the incoming virus but instead enhance its capture by Fc receptor-expressing (FcR + ) cells, leading to enhanced vi...

Human cytomegalovirus (HCMV), a ubiquitous human pathogen, is the leading cause of birth defects and morbidity in immunocompromised patients and a potential trigger for vascular disease. HCMV replicates in vascular endothelial cells and drives leukocyte-mediated viral dissemination through close endothelium-leukocyte interaction. However, the genetic basis of HCMV growth in endothelial cells and transfer to leukocytes is unknown. We show here that the UL131-128 gene locus of HCMV is indispensable for both productive infection of endothelial cells and transmission to leukocytes. The experimental evidence for this is based on both the loss-of-function phenotype in knockout mutants and natural variants and the gain-of-function phenotype by trans-complementation with individual UL131, UL130, and UL128 genes. Our findings suggest that a common mechanism of virus transfer may be involved in both endothelial cell tropism and leukocyte transfer and shed light on a crucial step in the pathogenesis of HCMV infection.

Broadly neutralizing antibodies reactive against most and even all variants of the same viral species have been described for influenza and HIV-1 (ref. 1). However, whether a neutralizing antibody could have the breadth of range to target different viral species was unknown. Human respiratory syncytial virus (HRSV) and human metapneumovirus (HMPV) are common pathogens that cause severe disease in premature newborns, hospitalized children and immune-compromised patients, and play a role in asthma exacerbations. Although antisera generated against either HRSV or HMPV are not cross-neutralizing, we speculated that, because of the repeated exposure to these viruses, cross-neutralizing antibodies may be selected in some individuals. Here we describe a human monoclonal antibody (MPE8) that potently cross-neutralizes HRSV and HMPV as well as two animal paramyxoviruses: bovine RSV (BRSV) and pneumonia virus of mice (PVM). In its germline configuration, MPE8 is HRSV-specific and its breadth is achieved by somatic mutations in the light chain variable region. MPE8 did not result in the selection of viral escape mutants that evaded antibody targeting and showed potent prophylactic efficacy in animal models of HRSV and HMPV infection, as well as prophylactic and therapeutic efficacy in the more relevant model of lethal PVM infection. The core epitope of MPE8 was mapped on two highly conserved anti-parallel β-strands on the pre-fusion viral F protein, which are rearranged in the post-fusion F protein conformation. Twenty-six out of the thirty HRSV-specific neutralizing antibodies isolated were also found to be specific for the pre-fusion F protein. Taken together, these results indicate that MPE8 might be used for the prophylaxis and therapy of severe HRSV and HMPV infections and identify the pre-fusion F protein as a candidate HRSV vaccine.

Mutations that occurred during adaptation of human cytomegalovirus to cell culture were monitored by isolating four strains from clinical samples, passaging them in various cell types and sequencing ten complete virus genomes from the final passages. Mutational dynamics were assessed by targeted sequencing of intermediate passages and the original clinical samples. Gene RL13 and the UL128 locus (UL128L, consisting of genes UL128, UL130 and UL131A) mutated in all strains. Mutations in RL13 occurred in fibroblast, epithelial and endothelial cells, whereas those in UL128L were limited to fibroblasts and detected later than those in RL13. In addition, a region containing genes UL145, UL144, UL142, UL141 and UL140 mutated in three strains. All strains exhibited numerous mutations in other regions of the genome, with a preponderance in parts of the inverted repeats. An investigation was carried out on the kinetic growth yields of viruses derived from selected passages that were predominantly non-mutated in RL13 and UL128L (RL13+UL128L+), or that were largely mutated in RL13 (RL13−UL128L+) or both RL13 and UL128L (RL13−UL128L−). RL13−UL128L− viruses produced greater yields of infectious progeny than RL13−UL128L+ viruses, and RL13−UL128L+ viruses produced greater yields than RL13+UL128L+ viruses. These results suggest strongly that RL13 and UL128L exert at least partially independent suppressive effects on growth in fibroblasts. As all isolates proved genetically unstable in all cell types tested, caution is advised in choosing and monitoring strains for experimental studies of vulnerable functions, particularly those involved in cell tropism, immune evasion or growth temperance.

Primary human cytomegalovirus (HCMV) infections during pregnancy are associated with a high risk of virus transmission to the fetus. To identify correlates of intrauterine HCMV transmission, serial serum samples from HCMV transmitter and non-transmitter pregnant women with primary HCMV infection were analyzed for the presence of neutralizing antibodies against different glycoproteins and glycoprotein complexes, which are known to mediate entry into distinct types of host cells. Neutralizing activity was detected in the sera early after primary infection; absorption with a soluble pentameric complex formed by gH/gL/pUL128-131, but not with gH/gL dimer or with gB, abolished the capacity of sera to neutralize infection of epithelial cells. Importantly, an early, high antibody response to pentamer antigenic sites was associated with a significantly reduced risk of HCMV transmission to the fetus. This association is consistent with the high in vitro inhibition of HCMV infection of epithelial/endothelial cells as well as cell-to-cell spreading and virus transfer to leukocytes by anti-pentamer antibodies. Taken together, these findings indicate that the HCMV pentamer complex is a major target of the antibody-mediated maternal immunity.

We evaluated SARS-CoV-2 RNA and neutralising antibodies in blood donors (BD) residing in the Lodi Red Zone, Italy. Of 390 BDs recruited after 20 February 2020 − when the first COVID-19 case in Lombardy was identified, 91 (23%) aged 19-70 years were antibody positive. Viral RNA was detected in an additional 17 (4.3%) BDs, yielding ca 28% (108/390) with evidence of virus exposure. Five stored samples collected as early as 12 February were seropositive.

A panel of human sera exhibited a ¢128-fold higher neutralizing potency against a human cytomegalovirus (HCMV) clinical isolate propagated and tested in endothelial (or epithelial) cells than against the same virus infecting human fibroblasts. In a group of 18 primary infections, the reverse geometric mean titre was in the range of 10-15 in human fibroblasts within the first 3 months after the onset of infection, whereas the endothelial cell infection-neutralizing activity was already present within the first 10 days, reaching median levels of 122, 320 and 545 at respectively 30, 60 and 90 days after onset, then declining slowly. This difference was also confirmed in the majority of reactivated and remote HCMV infections, as well as in a hyperimmune globulin preparation. The antibody response to HCMV pUL131A, pUL130 and pUL128 locus products, which are required for endothelial/epithelial cell infection, provided a potential molecular basis for such a differential neutralizing activity. In addition, monoclonal/monospecific antibodies raised against the pUL131A, pUL130 and pUL128 proteins were found to display an inhibitory activity on HCMV plaque formation and HCMV leukocyte transfer from HCMV-infected cells. Hence, conventional determination of the neutralizing activity of human sera in fibroblasts is misleading. Antibodies to pUL131A, pUL130 and pUL128 appear to display a major HCMV-neutralizing and dissemination-inhibiting activity.

Fourteen heart transplant recipients were monitored for human cytomegalovirus (HCMV) infection based on determination of antigenemia, viremia, and DNAemia (by polymerase chain reaction [PCR]) in peripheral blood polymorphonuclear leukocytes (PMNL). Three patients had symptomatic primary, 10 had recurrent (3 asymptomatic), and 1 (seronegative) had no HCMV infection. Severe clinical symptoms appeared when levels of viremia/antigenemia were greater than 50 infected PMNL/2 x 10(5) cells examined. Of 200 blood samples examined, 93 (46.5%) were positive for viremia/antigenemia and DNAemia, whereas 48 (24.0%) were positive for DNAemia only; 59 (29.5%) were negative in all assays. Follow-up of HCMV infections in heart transplant recipients showed that PCR can detect viral appearance in blood 7-10 days earlier than assays for antigenemia/viremia. On the other hand, viral disappearance from blood, as assessed by PCR, occurred weeks or months later than revealed by other assays. Detection of virus by PCR only was never associated with overt HCMV-related clinical symptoms. Of the 8 symptomatic patients treated with ganiclovir, 2 became PCR-negative at the end of treatment and 1 cleared virus from blood in the following weeks, whereas 5 showed persistent or recurrent infection.