Increasing the protective capacity of antibodies by enhancing Fc-mediated responses - Project Summary Vaccines are powerful tools against microbial pathogens; however, it has not been possible to elicit antibodies that neutralize each pathogen nor to generate sufficient neutralizing antibodies in each person. Along with neutralizing antibodies, vaccines and infection often generate non-neutralizing antibodies that can provide protection through cell-dependent and cell-independent mechanisms. Mechanisms that require the Fc portion of IgG antibodies include antibody-dependent cell-mediated cytotoxicity and phagocytosis (ADCC and ADCP, respectively) and complement-dependent cytotoxicity (CDC). Unfortunately, protection from non-neutralizing antibodies often proves inferior compared to neutralizing antibodies, especially against viral pathogens, limiting the efficacy of vaccines as well as antibodies treating bacterial pathogens that likewise do not neutralize. Additionally, even many broadly neutralizing antibodies in vitro require Fc functions for efficacy in vivo. Currently, the complete protective potential of the entire antibody repertoire is not realized because factors affecting Fc- mediated immune responses are not fully understood, and thus cannot be fully tuned to the host’s advantage. We expect that defining general principles of Fc-mediated immune responses will promote the design of efficacious vaccines and antibody treatments for many pathogens. In this proposal, we will investigate multiple factors that modulate the Fc-mediated responses to antibodies, to increase the potency of protection resulting from antibodies requiring Fc functions for influenza virus or antibodies against Streptococcus pneumoniae. Multiple groups have defined a set of factors that affect the Fc-mediated immune response. These include location of the epitope, antibody glycosylation, antibody oligomerization, and properties of the responding immune cell, including glycosylation of the Fcγ receptors (FcγRs). We will evaluate the hypothesis that the success of Fc-mediated protection results from the contribution of multiple factors that affect the endogenous recognition of the antibody and the resulting immune response. Thus, we expect that a potent immune response can be elicited by identifying an optimal combination of key regulatory factors. In Specific Aim 1 of this proposal, we will quantify how the potency of ADCC, ADCP, and CDC responses in vitro change by modulating epitope location, antibody glycosylation, and oligomerization. Optimal combinations of these factors will be evaluated for improved protection against influenza virus infection and S. pneumoniae infection in mice. In Specific Aim 2, we will quantify how different natural killer (NK) cell factors, including N-glycan composition and FcγRIIIa affinity, affect ADCC in vitro and protection from influenza virus using antibodies in a mouse model with infused NK cells. With these Aims, we expect to advance the field by defining both positive and negative interactions between these factors during the immune response, and to define conditions to use with both neutralizing and non- neutralizing antibodies that improve protection from infection.
