Fig. 2. Design strategies to enhance ‘on-target’ epitope responses.

a Stem- and head-only HAs indicating locations of engineered prolines (left, red spheres) and inter-HA cysteines (right, yellow spheres) to stabilize the prefusion conformation. b Selective removal of native glycans to expose neoepitopes (red circle). c Computational design of HA antigens based on overall subtype diversity increases cross-reactive responses. To illustrate the COBRA approach, HA is arbitrarily colored in gray shading to show variation in amino acid identity that ultimately contributes to the consensus sequence; for a complete description see Huang et al.¹³¹. d Optimization of a single epitope for a specific class of B cell precursors increases initial antigen affinity. HA receptor binding site (RBS) is shown in green as an example. e Resurfacing of a complex conformational-specific epitope allows for heterologous boosting of subdominant responses within memory. S1–S4 segments of the grafted RBS shown in red, orange, green, and blue, respectively. f Chimeric HAs where head domain (purple) of an antigenically distinct non-circulating HA is transplanted onto a conserved circulating stem domain (gray) to preferentially target stem-directed responses. All images created in PyMol using PDB 5UGY.