Abstract
Mapping polyclonal serum responses is critical to rational vaccine design. However, most high-resolution mapping approaches involve isolating and characterizing individual antibodies, which incompletely defines the polyclonal response. Here we use two complementary approaches to directly map the specificities of the neutralizing and binding antibodies of polyclonal anti-HIV-1 sera from rabbits immunized with BG505 Env SOSIP trimers. We used mutational antigenic profiling to determine how all mutations in Env affected viral neutralization and electron microscopy polyclonal epitope mapping (EMPEM) to directly visualize serum Fabs bound to Env trimers. The dominant neutralizing specificities were generally only a subset of the more diverse binding specificities. Additional differences between binding and neutralization reflected antigenicity differences between virus and soluble Env trimer. Furthermore, we refined residue-level epitope specificity directly from sera, revealing subtle differences across sera. Together, mutational antigenic profiling and EMPEM yield a holistic view of the binding and neutralizing specificity of polyclonal sera.
Highlights
Mapping polyclonal antibody responses is central to understanding antigen-specific humoral immunity
Since there were a number of instances in which subdominant neutralizing responses to the glycan hole (GH) or C3/V5 epitope identified with TZM-bl point-mutant mapping did not appear in either electron microscopy polyclonal epitope mapping (EMPEM) or mutational antigenic profiling (e.g., GH response for 5727 is absent in mutational antigenic profiling, and a C3/V5 response for 2214 is absent in EMPEM), we examined if there were additional unobserved subdominant responses
We have used mutational antigenic profiling to map the dominant neutralizing antibody specificities in polyclonal rabbit sera elicited with Env trimer immunization
Summary
Mapping polyclonal antibody responses is central to understanding antigen-specific humoral immunity. It is difficult to disentangle the multiple epitope specificities within polyclonal responses. Serum neutralization assays or ELISAs with variant antigens are used to crudely map epitope specificities. These and other traditional serological mapping approaches do not provide high-resolution, residue-level information for the multiple components of polyclonal serum responses. Further advances in understanding polyclonal sera have been made through techniques that rely on high-throughput B-cell receptor sequencing (Kreer et al, 2020), mass spectrometry-based approaches to directly sequence
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