Thus, we analyzed the relationship between antibodies HCDR3 or LCDR3 with their functions (Fig

Thus, we analyzed the relationship between antibodies HCDR3 or LCDR3 with their functions (Fig. of the viral antigens important for protective antibodies. Receptor-mediated viral entry to endothelial/epithelial cells requires a glycoprotein H (gH) complex comprising five viral proteins (gH, gL, UL128, UL130, and UL131). This gH complex is notably missing from RFC37 HCMV laboratory strains as well as HCMV vaccines previously evaluated in the clinic. To support a unique vaccine concept based on the pentameric gH complex, we established a panel of 45 monoclonal antibodies (mAbs) from a rabbit immunized with an experimental vaccine virus in which the expression of the pentameric gH complex was restored. Over one-half (25 of 45) of the mAbs have neutralizing activity. Interestingly, affinity for an antibody to bind virions was not correlated Huzhangoside D with its ability to neutralize the virus. Genetic analysis of the 45 mAbs based on their heavy- and light-chain sequences identified at least 26 B-cell linage groups characterized by distinct binding or neutralizing properties. Moreover, neutralizing antibodies possessed longer complementarity-determining region 3 for both heavy and light chains than those with no neutralizing activity. Importantly, potent neutralizing mAbs reacted to the pentameric gH complex but not to gB. Thus, the pentameric gH complex is the primary target for antiviral antibodies by vaccination. Human cytomegalovirus (HCMV) is an important pathogen in transplant patients (1C5), and its infection can Huzhangoside D lead to invasive end-organ diseases, such as pneumonitis and hepatitis, as well as vascular pathology contributing Huzhangoside D to graft failure (4, 6, 7). Huzhangoside D HCMV is also the most common cause of in utero viral infections in North America and Europe, affecting 0.5C2% of newborns annually (8C10). Congenital HCMV infection can lead to symptomatic diseases at birth and also cause developmental disabilities in children (10, 11). Maternal seropositivity before conception protects against congenital transmission (12, 13), and both maternal humoral and cellular immunity are likely to contribute to the protection (14C16). Antibodies in particular are important for preventing congenital infection, serving as the first line of defense against maternal infection. It may also play a role in preventing transmission to the fetus, supported by the results of a small, nonrandomized study in pregnant women with primary HCMV infection, in which the passive immunity of monthly infusions of HCMV hyperimmune human IgG (HCMV-HIG) (200 mg/kg maternal weight) was 60% effective in protecting against congenital HCMV infection (17, 18). These studies suggest that it is feasible to develop a vaccine for preventing congenital HCMV infection and its sequelae. However, despite the fact that the Institute of Medicine has identified development of an effective vaccine for prevention of congenital HCMV as a top priority since 1999 (19), progress toward this goal has only been incremental (8, 20, 21). One of the hurdles to the efforts is our limited understanding of component of natural immunity associated with protection against HCMV infection. HCMV is a large, complex virus, with a Huzhangoside D genome capable of encoding >150 proteins (22C26). Because of the strict species specificity, options of animal models for HCMV research are limited (27). Thus, the functions of most HCMV antigens in viral infection in vivo and their roles as targets for host immunity are poorly understood. Furthermore, culture systems of single cell types have limitations for studying HCMV pathogenesis. Immunohistochemistry studies showed that HCMV can infect varieties of cells in vivo, including endothelial, epithelial cells, fibroblasts, and leukocytes (28C36). Many HCMV end-organ diseases, such as pneumonitis and gastroenteritis, are due to infection of the epithelial/endothelial cells in the affected organ (35C39). However, common laboratory strains, such as AD169 and Towne, were culture-adapted in fibroblast cells, with genomic mutations (22, 24, 40) and, more importantly, have lost their tropism to endothelial and epithelial cells, in contrast to pathogenic clinical isolates (32, 33, 41, 42). Loss of viral tropism to endothelial and epithelial.