Impact of biophysical tradeoffs on antibody affinity maturation against SARS-CoV-2

PROJECT SUMMARY/ABSTRACT The objective of the proposed research is to determine the extent to which biophysical properties constrain the evolution of B-cell receptors (i.e., membrane-bound antibodies) to bind divergent SARS-CoV-2 variants. While it is known that mutations acquired during affinity maturation change antibody expression (i.e., the confluence of antibody folding, stability, and trafficking to the B-cell surface) and antigen affinity, it is unknown how these properties impact their maturation into broadly neutralizing antibodies (bnAbs) that bind divergent SARS-CoV-2 variants. Because most mutations are deleterious to protein stability, many mutations that increase antigen affinity likely reduce antibody expression, resulting in tradeoffs that could limit bnAb maturation. The proposed work aims to test the hypothesis that tradeoffs between antibody expression and affinity to divergent antigens constrain the evolution of SARS-CoV-2 bnAbs. Aim 1 will quantify the effects of mutations on antibody expression and spike binding affinity for libraries of ~500,000 anti-SARS-CoV-2 spike antibodies, including: bnAbs that target distinct spike epitopes, all possible evolutionary intermediates between these bnAbs and their ancestral germline sequences, and systematically mutagenized bnAbs. Aim 2 will quantify the relationship between antibody expression and affinity on the fitness of the corresponding B-cell lineage by measuring the expression and spike affinity for antibody sequences isolated from longitudinally sampled patient B-cells following SARS-CoV-2 exposure. These biophysical measurements will be integrated with B-cell lineage fitness measurements to construct biophysical models that predict the outcomes of affinity maturation. Completion of these aims will quantify 1) the prevalence of tradeoffs between antibody expression and antigen affinity and 2) the relative importance of these properties in determining B-cell lineage fitness. Together, these data will transform our understanding of the biophysical mechanisms that drive antibody evolution against rapidly evolving viruses like SARS-CoV-2. This work will empower efforts to design broadly protective vaccines against these viruses and improve our understanding of protein evolution and biophysics. The objective of the proposed training is to ensure the Mr. Tharp (applicant) can accomplish the proposed research and prepare for a career as an academic principal investigator. In pursuing this work, Mr. Tharp will improve his 1) interdisciplinary knowledge and research skills through seminars, coursework, and collaboration with quantitative immunologists, 2) scientific communication skills through constructing scientific manuscripts and presenting at seminars and conferences, and 3) mentorship capabilities by mentoring high school, undergraduate, and graduate students. The collaborative, interdisciplinary, and well-funded nature of the Mr. Tharp's sponsoring lab, graduate program, and institution ensures Mr. Tharp access to the necessary tools, opportunities, and mentorship required to accomplish his research and training objectives.