Bispecific antibody shuttles targeting CD98hc mediate efficient and long-lived brain delivery of IgGs

Abstract

The inability of antibodies and other biologics to penetrate the blood-brain barrier (BBB) is a key limitation to their use in diagnostic, imaging, and therapeutic applications. One promising strategy is to deliver IgGs using a bispecific BBB shuttle, which involves fusing an IgG with a second affinity ligand that engages a cerebrovascular endothelial target and facilitates transport across the BBB. Nearly all prior efforts have focused on the transferrin receptor (TfR-1) as the prototypical endothelial target despite inherent delivery and safety challenges. Here we report bispecific antibody shuttles that engage CD98hc (also known as 4F2 and SLC3A2), the heavy chain of the large neutral amino acid transporter (LAT1), and efficiently transport IgGs into the brain parenchyma. Notably, CD98hc shuttles lead to much longer-lived brain retention of IgGs than TfR-1 shuttles while enabling more specific brain targeting due to limited CD98hc engagement in the brain parenchyma. We demonstrate the broad utility of the CD98hc shuttles by reformatting three existing IgGs as CD98hc bispecific shuttles and delivering them to the mouse brain parenchyma that either agonize a neuronal receptor (TrkB) or target other endogenous antigens on specific types of brain cells (neurons and astrocytes).

Exit pathways of therapeutic antibodies from the brain and retention strategies

“…This requires a bior multispecific antibody format, such as the modular brain shuttle system. 38 , 40 A similar engineering approach is necessary for IR, 41 LRP1, 42 CD98hc 43 or other targets. (D) Bypassing: Direct delivery via the olfactory epithelium 44 or by direct injection into the CSF 45 or the brain parenchyma.…”

“…With only 1–10% of antibodies detected in the CNS parenchyma after systemic dosing, the fraction of biologics that pass the BBB with RMT still remains substantially lower compared to what the body periphery is exposed to. 38 , 39 , 40 , 41 , 42 , 43 Bypassing the BBB via direct CNS delivery ( Figure 1 D). Another option is to circumvent the BBB altogether and to directly administer biologics into the CNS.…”

“…This requires a bior multispecific antibody format, such as the modular brain shuttle system. 38 , 40 A similar engineering approach is necessary for IR, 41 LRP1, 42 CD98hc 43 or other targets.…”

“…With only 1–10% of antibodies detected in the CNS parenchyma after systemic dosing, the fraction of biologics that pass the BBB with RMT still remains substantially lower compared to what the body periphery is exposed to. 38 , 39 , 40 , 41 , 42 , 43 …”

“…Compared to TfR, CD98hc may in this regard confer longer CNS exposure of transcytosed antibodies. 43 …”