Abstract
Antibodies are widely considered to be a frequent primary and often mechanistic correlate of protection of approved vaccines; thus evaluating the antibody response is of critical importance in attempting to understand and predict the efficacy of novel vaccine candidates. Historically, antibody responses have been analyzed by determining the titer of the humoral response using measurements such as an ELISA, neutralization, or agglutination assays. In the simplest case, sufficiently high titers of antibody against vaccine antigen(s) are sufficient to predict protection. However, antibody titer provides only a partial measure of antibody function, which is dependent on both the variable region (Fv) to bind the antigen target, and the constant region (Fc) to elicit an effector response from the innate arm of the immune system. In the case of some diseases, such as HIV, for which an effective vaccine has proven elusive, antibody effector function has been shown to be an important driver of monoclonal antibody therapy outcomes, of viral control in infected patients, and of vaccine-mediated protection in preclinical and clinical studies. We sought to establish a platform for the evaluation of the Fc domain characteristics of antigen-specific antibodies present in polyclonal samples in order to better develop insights into Fc receptor-mediated antibody effector activity, more fully understand how antibody responses may differ in association with disease progression and between subject groups, and differentiate protective from non-protective responses. To this end we have developed a high throughput biophysical platform capable of simultaneously evaluating many dimensions of the antibody effector response.
Highlights
Evaluation of antibody responses to vaccines has traditionally focused primarily on antibody titer, the amount of antibody present that recognizes a specific antigen or epitope
Computational analysis used include both unsupervised methods (Fig. 1D), such as hierarchical clustering and Principal Component Analysis (PCA), which aim to reveal non-obvious patterns and relationships in high-dimension data that may be missed in lower-dimensional analysis, as well as supervised methods (Fig. 1E) such as Regularized Random Forest (RRF) and Least Angle Regression (LARS), which attempt to predictively model outcomes or parameters of interest based on previous observations (Choi et al, 2015)
Prior attempts to measure these functions have generally focused on resource and time intensive cell-based assays measuring features such as antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), complement-dependent cytotoxicity (CDC) and ADCDC, which can yield relatively variable results, and do not allow inspection of the linkage between specific types of antibodies and specific antibody activities
Summary
Evaluation of antibody responses to vaccines has traditionally focused primarily on antibody titer, the amount of antibody present that recognizes a specific antigen or epitope. As researchers focus on understanding immune pathways and developing vaccines for challenging pathogens, such as HIV, the role of other antibody functions are coming into focus as important drivers of protection or viral control (Rerks-Ngarm et al, 2009; Hessell et al, 2007; Hidajat et al, 2009; Florese et al, 2009; French et al, 2010; Ackerman et al, 2012; Xiao et al, 2010; Chung et al, 2014; Yates et al, 2014; Ackerman et al, 2013a; Ackerman et al, 2013b) These roles are dependent on the constant region (Fc) of the antibody, which can be recognized by Ig receptors on innate immune cells, and trigger several types of productive responses including antibody-dependent cellular phagocytosis (ADCP) (Ackerman et al, 2011), antibody-dependent cellular cytotoxicity (ADCC) (Gomez-Roman et al, 2006a), antibody-dependent cellular viral inhibition (ADCVI) (Forthal et al, 1999) and complement-dependent cytotoxicity (CDC) (Hezareh et al, 2001). Recent efforts have begun to focus on eliciting antibodies that protect by similar mechanisms in vaccine settings through the use of different adjuvant preparations (Moody, 2014; Moody et al, 2014; Barnett et al, 2010), delivery methods (Barouch et al, 2015), or routes of administration (Brekke et al, 2014; Singh et al, 2014; Maeto et al, 2014)
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