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A small but significant proportion of COVID‐19 patients develop life‐threatening cytokine storm. We have developed a new anti‐inflammatory drug, EXO‐CD24, a combination of an immune checkpoint (CD24) and a delivery platform (exosomes). CD24 inhibits the NF‐kB pathway and the production of cytokines/chemokines. EXO‐CD24 discriminates damage‐from pathogen‐associated molecular patterns (DAMPs and PAMPs) therefore does not interfere with viral clearance. EXO‐CD24 was produced and purified from CD24‐expressing 293‐TREx™ cells. Exosomes displaying murine CD24 (mCD24) were also created. EXO‐CD24/mCD24 were characterized and examined, for safety and efficacy, in vitro and in vivo . In a phase Ib/IIa study, 35 patients with moderate–high severity COVID‐19 were recruited and given escalating doses, 10 8 –10 10 , of EXO‐CD24 by inhalation, QD, for 5 days. No adverse events related to the drug were observed up to 443–575 days. EXO‐CD24 effectively reduced inflammatory markers and cytokine/chemokine, although randomized studies are required. EXO‐CD24 may be a treatment strategy to suppress the hyper‐inflammatory response in the lungs of COVID‐19 patients and further serve as a therapeutic platform for other pulmonary and systemic diseases characterized by cytokine storm.

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