Adaptive Immunity: Focus on B cell immunology
Program leader: James Crowe
SE-RP-013: Genetic and structural determinants of neutralization by naturally-occurring human monoclonal antibodies to dengue virus
Vanderbilt University
Dengue is expanding globally with an estimated 50 million to 100 million cases of dengue world-wide annually, and more than 20,000 deaths. The virus is carried by mosquitoes and causes severe flu-like symptoms that can lead to a life threatening hemorrhagic fever. The pathogenesis of dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) of course is of central importance to those interested in developing vaccines. The simple overview of current concepts of pathogenesis suggests that an initial infection with dengue virus occurs and induces antibodies, followed in some cases with a second infection with a different serotype during which pre-existing cross-reactive antibodies form non-neutralized antigen-antibody complexes that enter cells expressing Fc receptors such as monocytes, resulting in increased release of cytokines and the release of vasoactive mediator that increase vascular permeability. This process has been termed antibody-dependent enhancement (ADE) of infection, and has been demonstrated clearly to occur using cells in culture. A better understanding of the molecular, genetic, and structural basis for recognition of dengue viruses by human antibodies is sorely needed, and could lead to the rational design of vaccines that enhance the induction of neutralizing antibodies while lowering the risk of DHF. Fortunately, significant progress has been made in the field recently that lays a solid foundation for the proposed studies.
We are isolating human monoclonal antibodies to dengue virus, and then studying the genetic and structural features that mediate high neutralizing potency or enhancement of infection. The approach uses naturally-occurring human antibodies that are obtained using human hybridoma technology.
The project is structured around five specific aims, as follows:
Specific Aim 1: To isolate large panels of type 3-specific human monoclonal antibodies to dengue viruses.
Specific Aim 2: To determine the neutralizing activity of the mAbs and map the antigenic sites recognized by potent dengue virus neutralizing human mAbs.
Specific Aim 3: To determine the critical somatic mutations in the antibody variable genes of immunodominant antibodies that optimize affinity, neutralization, and serotype specificity.
Specific Aim 4: To determine the structure of human mAb-dengue E protein complexes.
Specific Aim 5: To engineer novel human mAbs to E proteins that are highly avid, potent, and type-specific.
SE-RP-014: Regulatory B cell inhibition of immune responses to pathogens
Duke University
B cells are the central source of long-term humoral immune responses to viral pathogens, but also serve critical regulatory functions during adaptive CD4+ T cell responses to artificial antigens and autoantigens. It remains substantially unknown whether B cells contribute significantly to viral immune responses beyond antibody production or whether their manipulation can hasten or enhance immune responses. Important for emerging infections and biodefense, we have recently shown that B cells are essential for optimal CD4+ T cell priming during intracellular bacteria challenge. By contrast, monoclonal antibody (mAb)-induced B cell depletion augments Th1-type cellular immune responses in other models. This unexpected observation is explained by the identification of a subpopulation of potent regulatory B cells that dramatically attenuates Th1type immune responses and autoimmunity. We have labeled this phenotypically unique B cell subset that also secretes IL-10 as "B10" cells, which represent -1% of total spleen B cells in young mice, and <1% of circulating human B cells. B10 cell numbers within tissues increase significantly in mice with autoimmunity and age. Thus, humoral and CD4+ T cell immune responses are balanced by differing positive and negative B cell responses. We have also identified a critical signaling pathway that is required for B10 cell survival in vivo. MAbs that inhibit this B cell-restricted survival signal induce rapid and semi-selective B10 cell depletion in vivo, which has an adjuvant-like effect that enhances humoral antibody responses to T cell-dependent model antigens and Th1-type CD4+ T cell immune responses. Thus, B10 cells regulate both humoral and Th1 immune responses. We have also developed a humanized mAb to the same survival target and generated transgenic mice expressing the human survival receptor that will facilitate translation of these basic studies into future human studies. Undoubtedly, the ability to manipulate B cell contributions to humoral and cell-mediated immune responses by mAb treatment offers a new strategy for accelerating immune responses during acute pathogen challenge. The focus of the proposed studies is to identify the extent that B cells and the B10 subset modulate humoral and CD4+ T cell immune responses to alphaviruses and dengue, aiming in the intermediate-to-longer term towards understanding how B cells can be manipulated for therapeutic benefit and vaccine development, and leading to the future identification of new drug targets or new drugs for depleting B10 cells and enhancing immunity.
