Tchikaev, O
Tchikaev, O. antibodies (mean PRNT50 = 1:3,760). Importantly, H3L-immunized mice were subsequently guarded against lethal intranasal challenges with 1 or 5 50% lethal doses (LD50) of pathogenic vaccinia virus strain WR, demonstrating the in vivo value of an anti-H3L response. To formally demonstrate that neutralizing anti-H3L antibodies are protective in vivo, we performed anti-H3L serum passive-transfer experiments. Mice receiving H3L-neutralizing antiserum were guarded from a lethal challenge with 3 LD50 of vaccinia virus strain WR (5/10 versus 0/10; < 0.02). Together, these data show that H3L is usually a major target of the human anti-poxvirus antibody response and is likely to be a key contributor to protection against poxvirus contamination and disease. Vaccines are one of the most cost-effective medical treatments in modern civilization (51). A smallpox vaccine was the first human vaccine, and vaccinia virus (VV) is considered the most successful human vaccine, having brought about the worldwide eradication of smallpox disease (20). Nevertheless, the mechanisms of adaptive immune protection elicited by the smallpox vaccine in humans generally remain unclear. There is currently greatly renewed interest in smallpox immunity due to the possible threat of bioterrorism (29). Given this concern, there has been much discussion about both the mechanisms of protection afforded by the smallpox vaccine and the possible development of safer alternatives to Dryvax, the current U.S. licensed Azaguanine-8 human smallpox vaccine. Our goal is to identify key antigenic targets of VV that are recognized by vaccinated humans and that are critical for protection Azaguanine-8 against disease. These efforts are important for developing a clear understanding of the mechanisms of protection afforded by this prototypic vaccine. In addition, knowledge of key antigenic targets will be instructive for ongoing efforts to design alternative smallpox vaccines, as development and assessment of novel smallpox vaccines will be dependent on a detailed understanding of correlates of immunity. Vaccines elicit three major types of immune responses that are each considered important in protective long-term immunity: antibodies, memory T cells, and memory B cells (11, 49, 56). Humans with either cellular or humoral immune deficiencies exhibit heightened susceptibility to poxvirus contamination (38, 41). Antibodies are the body’s first line of defense against contamination, and circulating antibodies are the primary indicator of immunity for most human vaccines (11, 49). Antibodies can be protective against smallpox (variola virus) contamination of humans (20, 39), presumably both by neutralizing the initial virus inoculum and by limiting the spread of virus particles within the host after contamination is initiated. It is now clear from many studies that memory T cells (CD8, CD4, or a combination) are valuable for protection against a variety of infectious diseases (63), including poxviruses (4, 58, 60, 68). The smallpox vaccine is known to elicit T-cell responses in humans (12, 16, 22, 27), and VV-specific memory T cells are likely to be important components of the vaccine-mediated protection against smallpox virus Rabbit Polyclonal to ARG1 (38, 41, 56). Memory B cells are also likely contributors to human immunity to smallpox, both by their ability to rapidly respond to contamination with an anamnestic antibody response and by their potential ability to replenish long-lived plasma cells to maintain long-term serum antibody levels (5, 12). Given the renewed interest in smallpox, recent research efforts by a number of groups have focused on identifying the smallpox vaccine targets recognized by the different arms of the adaptive immune system, in both mice and humans (3, 21, 45, 58-60), to obtain information regarding potential correlates of immunity. A variety of immunogenic VV antigens eliciting antibody responses have been identified in the literature, but the vast majority of that work was done in animal models. We have focused our efforts on understanding the human humoral immune response to VV. These efforts have centered on identifying the antigen specificities of the human anti-VV antibody response and determining which antibody targets are likely to be functionally valuable in protection. To do this, we utilized a novel proteomics approach to first globally identify the VV antigens recognized by sera from human Dryvax vaccinees. We found that H3L was a dominant antigen in the human antibody response. That observation led us to focus on understanding the biological relevance of H3L as a major target of human anti-VV antibody responses. We exhibited that Azaguanine-8 affinity-purified human anti-H3L exhibited VV-neutralizing activity in vitro. We then showed that mice immunized with recombinant H3L protein generated.