Reducing affinity as a strategy to boost immunomodulatory antibody agonism

Antibody responses during infection and vaccination typically undergo affinity maturation to achieve high-affinity binding for efficient neutralization of pathogens(1,2). Similarly, high affinity is routinely the goal for therapeutic antibody generation. However, in contrast to naturally occurring or direct-targeting therapeutic antibodies, immunomodulatory antibodies, which are designed to modulate receptor signalling, have not been widely examined for their affinity-function relationship. Here we examine three separate immunologically important receptors spanning two receptor superfamilies: CD40, 4-1BB and PD-1. We show that low rather than high affinity delivers greater activity through increased clustering. This approach delivered higher immune cell activation, in vivo T cell expansion and antitumour activity in the case of CD40. Moreover, an inert anti-4-1BB monoclonal antibody was transformed into an agonist. Low-affinity variants of the clinically important antagonistic anti-PD-1 monoclonal antibody nivolumab also mediated more potent signalling and affected T cell activation. These findings reveal a new paradigm for augmenting agonism across diverse receptor families and shed light on the mechanism of antibody-mediated receptor signalling. Such affinity engineering offers a rational, efficient and highly tuneable solution to deliver antibody-mediated receptor activity across a range of potencies suitable for translation to the treatment of human disease.

Automated summary

Low affinity of immunomodulatory antibodies leads to greater activity through increased clustering, resulting in higher immune cell activation, T cell expansion, and antitumor activity. This discovery reveals a new mechanism for enhancing receptor activation across diverse receptor families and sheds light on the mechanism of antibody-mediated receptor signaling. Affinity engineering offers a rational, efficient, and tunable solution for delivering antibody-mediated receptor activity for the treatment of human disease.