Antibodies are an integral part of the immune system’s defenses against invading pathogens. Produced by B cells, antibodies are able to prevent infection by blocking the invasion of host cells by the pathogen, by marking pathogens for destruction, or by assisting in the destruction of infected host cells. The overwhelming majority of licensed vaccines elicit protective antibody responses, and they have a long history of providing safe and durable protection from infection from a variety of pathogens. Our goal is to develop antibody-inducing vaccines against HIV-1 and malaria-causing parasites. However, despite intensive research efforts, the development of protective vaccines for these diseases remains elusive. Our approach involves developing a fundamental understanding of the mechanisms by which these pathogens interact with the host immune system and by evaluating the mechanisms of protective immunity. By deciphering how the pathogen interacts with the host and how the host can defeat the pathogen, we will be able to identify and exploit targets to be developed as antibody-inducing vaccines.
One of the major areas of study for the Sather Lab is the natural development of broadly neutralizing anti-HIV-1 antibodies (bNAbs). These bNAb provide a natural prototype that we hope to re-elicit by vaccination. This research involves a “feedback loop,” in which we study anti-HIV-1 antibody responses generated during the course of natural infection with the goal of informing the design and production of novel HIV-1 immunogens. Our studies have keyed in on the early immunological and viral events that occur as broadly neutralizing activity develops during natural infection within the first several years after infection. We are evaluating the interaction between host humoral responses and Envelope protein evolution (mediating viral escape) throughout this process. Recently, we discovered that in several HIV-1 positive subjects, the progenitor, immature bNAbs were present in the serum long before neutralizing activity became evident. Further, we found that viral escape did not occur until after the appearance of neutralizing activity, months after the initial appearance of the pre-bNAbs. Thus, there exists a time period early during infection when immature pre-bNAbs are circulating and being stimulated by viral antigen, and it is unclear why in some subjects those mature into full bNAbs. Our focus moving forward is to delve into understanding bNAb progenitor B cell population dynamics and their relationship to an evolving viral infection. In addition to studying antibodies generated during natural HIV-1 infection, the Sather lab is also engaged in understanding vaccine-elicited antibody responses. We are focused on understanding how vaccination with HIV-1 Envelope (Env) immunogens drives evolution of specific antibody gene families and on assessing vaccination-driven antibody maturation using non-human primates and humanized mice as our primary pre-clinical models. We have deployed Illumina deep sequencing as a tool to understand vaccine-elicited B cell receptor (BCR) responses at the sequence repertoire level. With these capabilities, we are able to define the pre-immune BCR repertoire to establish a base-line population prior to immunization with HIV-1 Envelope immunogens. This allows us to study in great detail the types of naïve BCRs that are available for stimulation by our vaccine immunogens and to track which of those BCRs were stimulated by vaccination with Env immunogens. In addition to tracking BCR stimulation, we are able to track in great detail how far we are able to drive somatic hypermutation by vaccination and whether we are driving somatic hypermutation in directions that may be advantageous for anti-HIV-1 neutralization. We are working toward using this system to monitor responses to our vaccines in near real time, in order to relay feedback into our immunogen design efforts. In total, this platform allows us to delve deeper than ever before to understand vaccine-elicited B cell responses against HIV-1 and to understand whether our vaccines elicit antibodies that could potentially develop into broadly neutralizing antibodies.
Themes in HIV-1 research:
- The genesis of bNAbs during natural infection.
- The interaction between host humoral immunity and viral evolution.
- Pre-clinical vaccine testing in non-human primates.
- B cell receptor population dynamics in response to vaccination.
The other major research focus in the Sather lab is the development of antibody-inducing vaccines against Malaria-causing parasites. Our vaccine development efforts focus on Plasmodium falciparum, the primary cause of severe malaria disease and the most deadly form of the parasite. The Plasmodium life cycle is complex, involving multiple stages in both humans and mosquito vectors, with each stage having a unique genetic program. This diversity makes the malaria parasite a difficult vaccine target. We target the pre-erythrocytic stages of malaria, the infectious form of the parasite. The sporozoite develops in the salivary glands of the mosquito and is injected into the skin when the mosquito bites the skin to take a blood meal. After entering the skin, the sporozoite makes its way to the blood stream, eventually invading the liver to being the next stage of infection. Stopping the sporozoite prior to entering liver cells is a primary goal of vaccine-elicited immunity, as it will prevent productive blood stage infection. Our goal is the identification, characterization, and development as vaccine immunogens of protein antigens expressed on the surface of the infectious sporozoite. In collaboration with Dr. Stefan Kappe, we have identified a number of potential protein antigens that are located on the surface of the sporozoite. We are in the process of developing these proteins as vaccine immunogens, and several promising candidates are in the vaccine pipeline.
Despite a tremendous body of research on malaria infection, little is known about the specific host-pathogen receptor/ligand interactions that are necessary for parasitic invasion. Our studies provide an unprecedented opportunity to define at the molecular level the host-pathogen interactions necessary for parasitic invasion, which will have both clinical and vaccine implications. Thus, in parallel to our antigen design efforts, we are leveraging our capabilities to begin to define the potential interactions of Plasmodium proteins with host receptors in the pre-erythrocytic and blood stages. In a sense, this creates a vaccine development/host-pathogen interaction feedback loop, similar to what we have in our HIV-1 studies. These efforts have already begun to pay dividends. In collaboration with Dr. Alexis Kaushansky, we have begun to identify potential Plasmodium protein-host receptor interactions that may be necessary for liver cell invasion. Subsequent to these findings, we have already advanced some of these Plasmodium targets into pre-clinical vaccine studies. Overall, these studies will be very informative toward the selection of potential vaccine targets and will fill in significant holes in our understanding of the molecular mechanisms of Plasmodium invasion and infection.
Themes in malaria research:
- Pre-erythrocytic and blood stage vaccine candidate development
- Isolation and evaluation of anti-malarial monoclonal antibodies
- Identification of the correlates of protection from Plasmodium invasion