Engineered antibodies preserve structural and functional recognition of Plasmodium falciparum circumsporozoite...

Long-lasting and highly effective malaria vaccines or monoclonal antibodies (mAbs) remain urgently needed, as current interventions show age-dependent benefits rather than broad protection across all ages. Recently, two highly protective human mAbs 224 (IGHV3-49/IGLV1-40) and 7088 (IGHV3-33/IGKV1-5), encoded by distinct germline genes, were re-engineered and renamed MAM01 and MS-1805, respectively, to extend serum half-life and enable low-cost, large-scale manufacturing in alignment with WHO guidelines. MAM01 completed Phase I and IIb clinical trials (safety/PK/challenge) in US healthy naive adults and is now in Phase I trials (age-de-escalation studies) in Uganda. Here, we determined crystal structures of the antigen-binding fragments (Fabs) of engineered MAM01, MS-1805, and 7088 in complex with different regions of the Plasmodium falciparum circumsporozoite protein (PfCSP), including junctional, minor, and major repeat regions. Notably, Fab 7088 features an extended CDRL3 comprising 10 amino acids (CDRL3:10) instead of the canonical 8 amino acid CDRL3 (CDRL3:8) typically observed in V_H3-33/V_K1-5-encoded mAbs, indicating unique folding within its germline context. In addition, cryo-EM structures of Fabs 7088 and MS-1805, in complex with recombinant shortened CSP (rsCSP), revealed a regular spiral configuration stabilized by homotypic Fab-Fab interactions, whereas 224 and MAM01 did not form such assemblies. Structural comparisons demonstrated that engineered antibodies retained key molecular and hydrogen-bond interactions without significant conformational changes, thereby maintaining antigen recognition and preserving binding affinity. These findings demonstrate that targeted framework engineering can enhance therapeutic potential while preserving structural integrity and function, providing insights for next-generation antibody-based interventions against malaria.