Surface chemistry governs sex-dependent responses to PEG and zwitterionic siRNA nanocarriers in primary macrophages

Nanoparticle carriers are widely used for nucleic acid delivery, with poly(ethylene glycol) (PEG)-conjugated nanoparticles emerging as a frontrunner in the field. Growing concerns surrounding PEG immunogenicity have generated interest in zwitterionic polymers as alternative biocompatible surface grafts. At present, there exists a paucity of data regarding zwitterion-conjugated nanoparticle performance in primary immune cells and across biological sexes. Here, we synthesized pH-responsive PEG- and zwitterion-grafted cationic nanoparticles, including PEG methyl ether methacrylate (PEGMMA), carboxybetaine methacrylate (CBMA), sulfobetaine methacrylate (SBMA), and polymeric SBMA, and assessed their cytotoxicity and small interfering RNA (siRNA) delivery in primary male and female murine macrophages. All formulations enabled intracellular siRNA uptake and suppressed tumor necrosis factor-α expression. Sex-dependent effects varied by nanoparticle formulation and biological end point. Zwitterionic nanoparticles exhibited sex-specific effects in cytotoxicity and gene knockdown despite similar uptake, whereas PEGMMA showed higher uptake in females but comparable knockdown across sexes. These findings demonstrate that uptake alone does not predict functional efficacy and highlight the importance of sex-informed evaluation when developing nanomedicines.