Scientists engineered stem cells to make a version of the antimicrobial peptide LL-37 called SE-33 and gave these cells to mice. The peptide showed predictable behavior, building up mainly in the liver and lungs and staying there for up to two days, especially at higher doses. Re‑dosing increased the amount of peptide in those organs. This work is still early‑stage animal research and not ready for personal use.

The genetic modification of mesenchymal stromal/stem cells (MSCs) to express antimicrobial peptides may provide a promising strategy for developing advanced cell-based therapies for bacterial infections, including those caused or complicated by antibiotic-resistant bacteria. We have previously demonstrated that genetically modified Wharton's jelly-derived MSCs expressing an antimicrobial peptide SE-33 (WJ-MSC-SE33) effectively reduce bacterial load, inflammation, and mortality in a mouse model of <i>Staphylococcus aureus</i>-induced pneumonia compared with native WJ-MSCs. The present study aimed to evaluate the pharmacokinetics and tissue distribution of the SE-33 peptide expressed by WJ-MSC-SE33 following administration to animals. WJ-MSC-SE33 were administered to C57BL/6 mice at therapeutic and excess doses. The biodistribution and pharmacokinetics of the SE-33 peptide were analyzed in serum, lungs, liver, and spleen using chromatographic methods after single and repeated administrations. The SE-33 peptide exhibited dose-dependent pharmacokinetics. The highest levels of SE-33 peptide were detected in the liver and lungs, with persistence in tissues for up to 48 h at medium and high doses of administered WJ-MSC-SE33. A repeated administration of WJ-MSC-SE33 increased SE-33 levels in target organs. The SE-33 peptide expressed by genetically modified WJ-MSCs demonstrated predictable pharmacokinetics and effective biodistribution. These findings, together with the previously established safety profile of WJ-MSC-SE33, support its potential as a promising cell-based therapy for bacterial infections, particularly those associated with antibiotic resistance.