A recombinant antibody fragment directed to the thymic stromal lymphopoietin receptor (CRLF2) efficiently targets pediatric Philadelphia chromosome-like acute lymphoblastic leukemia.

Antibody fragments are promising building blocks for developing targeted therapeutics, thus improving treatment efficacy while minimising off-target toxicity. Despite recent advances in targeted therapeutics, patients with Philadelphia-like acute lymphoblastic leukemia (Ph-like ALL), a high-risk malignancy, lack specific and effective targeted treatments. Cytokine receptor-like factor 2 (CRLF2) is overexpressed in 50% of Ph-like ALL cases, conferring the survival of leukemia blasts through activation of the JAK/STAT signalling pathway. Targeting such a vital cell-surface protein could result in potent anti-leukaemic efficacy and reduce the likelihood of relapse associated with antigen loss. Herein, we developed a novel single-chain variable fragment (scFv) against CRLF2 based on a monoclonal antibody raised against the recombinant extracellular domain of human TSLPRα chain. The scFv fragment demonstrated excellent binding affinity with CRLF2 protein in the nanomolar range. Cellular association studies in vitro using an inducible CRLF2 knockdown cell line and ex vivo using patient-derived xenografts revealed the selective association of the scFv with CRLF2. The fragment exhibited significant receptor antagonistic effects on STAT5 signalling, suggesting possible therapeutic implications in vivo. This study is the first to describe the potential use of a novel scFv for targeting Ph-like ALL.