Modulating antigen-specific humoral immunity with non-differentiating B cells

Abstract

Antibody-derived inhibitors pose an ongoing challenge to the treatment of patients with inherited protein deficiency disorders, limiting the efficacy of both protein replacement therapy and corrective gene therapy. Beyond their central role as producers of serum antibody, B cells also exhibit many unique properties that could be exploited in cell therapy applications, notably including antigen-specific recognition and the linked capacity for antigen presentation. Here we employed CRISPR/Cas9 to demonstrate that ex vivo antigen-primed Blimp1-knockout “decoy” B cells, incapable of differentiation into plasma cells, participated in and downregulated host antigen-specific humoral responses after adoptive transfer. Following ex vivo antigen pulse, adoptively transferred high affinity antigen-specific decoy B cells were diverted into germinal centers en masse, thereby reducing participation by endogenous antigen-specific B cells in T-dependent humoral responses and suppressing both cognate and linked antigen-specific IgG following immunization with conjugated antigen. This effect was dose-dependent and, importantly, did not impact concurrent unrelated antibody responses. We demonstrated the therapeutic potential of this approach by treating factor VIII (FVIII)-knockout mice with antigen-pulsed decoy B cells prior to immunization with a FVIII conjugate protein, thereby blunting the production of serum FVIII-specific IgG by an order of magnitude as well as reducing the proportion of animals exhibiting functional FVIII inhibition by 6-fold. Finally, we demonstrated that these Blimp1-deficient decoy B cells can be simultaneously gene-edited to enable constitutive secretion of the regulatory cytokine IL 10. Together, these results suggest that it will be possible to generate engineered regulatory B cells capable of modulating the activation and differentiation of antigen-specific CD4 T cells.