Engineering scFv immunotherapies: From CAR T cells to bispecific antibodies

Single-chain variable fragments (scFvs) have become indispensable tools in cancer immunotherapy due to their high specificity, modularity, and cost-effective production. These engineered antibody fragments enable precise targeting of tumor antigens, driving innovations in chimeric antigen receptor (CAR) T cell therapy, bispecific T-cell engagers, immune checkpoint blockade, and nanoparticle delivery systems. Their compact size enhances tumor penetration compared to full-length antibodies, while recombinant production allows rapid customization. This review examines the expanding therapeutic applications of scFvs across multiple modalities, including their critical role in CAR-T cell engineering where scFv affinity determines efficacy and safety. We explore bispecific engagers that redirect T cells to tumors, checkpoint inhibitors that restore antitumor immunity, and targeted drug delivery platforms. Clinical successes in hematologic malignancies are highlighted alongside ongoing challenges in solid tumors, particularly regarding antigen heterogeneity and immunosuppressive microenvironments. Key advances in scFv optimization are discussed, focusing on half-life extension strategies, stability engineering, and combinatorial approaches to overcome limitations like rapid clearance and on-target/off-tumor toxicity. By synthesizing recent preclinical and clinical developments, this review demonstrates how scFv-based therapies continue to transform precision oncology through targeted immune modulation.