Optimizing immunization protocols to elicit broadly neutralizing antibodies

Sprenger, Kayla G.; Louveau, Joy E.; Chakraborty, Arup K.

Natural infections and vaccination with a pathogen typically stimulates the production of potent antibodies specific for the pathogen through a Darwinian evolutionary process known as affinity maturation. Such antibodies provide protection against reinfection by the same strain of a pathogen. A highly mutable virus, like HIV or influenza, evades recognition by these strain-specific antibodies via the emergence of new mutant strains. A vaccine that elicits antibodies that can bind to many diverse strains of the virus – known as broadly neutralizing antibodies (bnAbs) – could protect against highly mutable pathogens. Despite much work, the mechanisms by which bnAbs emerge remain uncertain. Using a computational model of affinity maturation, we studied a wide variety of vaccination strategies. Our results suggest that an effective strategy to maximize bnAb evolution is through a sequential immunization protocol, wherein each new immunization optimally increases the pressure on the immune system to target conserved antigenic sites, thus conferring breadth. We describe the mechanisms underlying why sequentially driving the immune system increasingly further from equilibrium, in an optimal fashion, is effective. The optimal protocol allows many evolving B cells to become bnAbs via diverse evolutionary paths. Significance Statement The global health burden could be substantially alleviated by the creation of universal vaccines against highly mutable pathogens like HIV and influenza. Broadly-neutralizing antibodies (bnAbs) are encouraging targets for such vaccines, because they can bind to diverse strains of highly mutable pathogens. BnAbs typically develop only rarely upon natural infection, after the immune system has been exposed to many mutated versions of a pathogen. Thus, sequentially administering multiple different pathogen-like proteins (antigens) is a promising strategy to elicit bnAbs through vaccination. However, it remains unclear how best to design and administer these antigens. We explore this matter using physics-based simulations, and provide new mechanistic insights into antibody evolution that could guide the creation of universal vaccines against highly mutable pathogens.