Antibody-Drug Conjugates (ADCs) as Adaptors for Universal CAR T cells

Introduction/Rationale: Antibody–drug conjugates (ADCs) and chimeric antigen receptor (CAR) T cells are powerful cancer therapeutics, but each faces limitations. ADCs often fail to yield durable responses due to drug payload resistance or poor internalization. CAR T cells are often thwarted by challenges including immune suppression and poor persistence. To overcome these challenges, we developed a universal CAR T cell platform in which ADCs act as antigen-targeting “adaptors” that direct CAR T cell activity. In this system CAR T cells are co-administered with one or more ADCs. Instead of the CAR directly binding to a tumor antigen, ADCs bind to antigens, thus activating CAR signaling in addition to drug payload delivery.

Methods: We used our previously generated SNAP-CAR, a universal CAR that covalently binds to antibodies with a benzylguanine (BG) tag. We generated ADC adaptors by conjugating BG to several FDA-approved ADCs targeting HER2 and FOLR1. In parallel, we designed a novel universal anti-DM1/DM4 CAR that directly binds DM1 and DM4 drug payloads. Primary human CAR T cells were co-incubated with antigen-positive or -negative tumor cells and various adaptors, followed by flow cytometric assessment of T cell activation, target cell lysis, and bystander killing.

Results: SNAP-CAR T cells with ADC–BG adaptors showed strong, adaptor dose-dependent T cell activation and tumor lysis, outperforming unconjugated ADCs or BG-labeled antibodies. Additionally, these adaptors enabled bystander killing of antigen-negative tumor cells. Anti-DM1/DM4 CAR T cells were similarly effective showing dose-responsive activities induced by ADCs and in a HER2+ human tumor xenograft mouse models. Excitingly, both approaches were capable of potent killing of DM1/DM4-resistant cells, demonstrating their ability to overcome drug resistance limiting ADC therapies.

Conclusion: ADC-directed universal CAR T cells represent a highly modular approach that synergizes cytotoxic drug activity with immune function to overcome therapeutic resistance.