BACKGROUND RLS-0071 is a dual-targeting peptide developed for the regulation of humoral and cellular inflammation via inhibition of neutrophil effectors, including myeloperoxidase and neutrophil extracellular trap formation (NETosis). The safety, pharmacokinetics, and pharmacodynamics of single and multiple doses of RLS-0071 were evaluated in a first-in-human clinical trial in healthy volunteers. Myeloperoxidase is the major peroxidase enzyme present in neutrophilic granules and contributes to cellular inflammation. Extracellular myeloperoxidase has been associated with chronic inflammation in a variety of diseases, including atherosclerosis. RLS-0071 has previously been shown to inhibit extracellular myeloperoxidase function both in vitro and in vivo in animal disease models. CASE REPORT Healthy subjects participating in the RLS-0071-101 study were screened for baseline myeloperoxidase level, leading to the identification of a 21-year-old woman with elevated baseline levels. After randomization, the subject received 9 intravenous infusions of 10 mg/kg RLS-0071. The subject tolerated the peptide infusions well with no adverse changes in vital signs, significantly abnormal clinical laboratory results, or severe adverse events. Analysis of this subject's myeloperoxidase plasma concentrations demonstrated that her myeloperoxidase levels decreased by 43% and myeloperoxidase activity levels decreased 49% after infusions of RLS-0071. The reduction in the patient's plasma myeloperoxidase levels demonstrated a partial return to baseline levels 24 hours after cessation of dosing. There were no other clinically meaningful safety observations for this subject. CONCLUSIONS This observation suggests RLS-0071 has the therapeutic potential to moderate plasma myeloperoxidase levels and activity and modulate diseases in which myeloperoxidase contributes to pathogenesis.