CD72 Nanobody-Based CAR-T Cells Have Potent Anti-Tumor Efficacy in B Cell Malignancies

Background: Approximately 50% of pediatric B-ALL patients treated with clinically approved CD19-targeting CAR-T cells do not remain in remission one year after therapy. CD22-targeting CAR-T cells appear to be curative in only a small fraction of CD19-refractory patients and this therapeutic strategy is primarily used as a bridge to stem cell transplant. Additional immunotherapeutic targets thus remain urgently needed. Our laboratory recently used cell surface proteomics to identify CD72 as a B-cell specific marker especially upregulated on poor prognosis, KMT2A/MLL-rearranged B-ALL (Nix et al., Cancer Discovery (2021)). In this published work, we used a best-in-class nanobody library displayed on yeast to develop binders to CD72. We demonstrated for the first time that fully synthetic nanobodies can generate CAR-T cells that are highly potent in vitro and in vivo. While we previously focused on these “nanoCARs” in KMT2A/MLLr B-ALL, in this follow-up study we aimed to 1) further expand our nanoCAR indications to other CD72-expressing B-cell malignancies; 2) biophysically characterize our synthetic nanobodies; 3) evaluate the potential for further humanization of the nanobody binder amino acid sequence while retaining anti-tumor efficacy; and 4) characterize the potency and T-cell immunophenotypes in the context of our lead nanobody binder (“NbD4”) placed on different CAR backbones.