In a severe PA 103 pneumonia in mice, we demonstrated that intravenous administration of MSC EV decreased alveolar and systematic inflammation and increased bacterial clearance, which was further enhanced with HMW HA (1.0 MDa) primed MSC EV (Fig. 4) and which was again significantly reduced with CD44 siRNA pretreatment of the MSC EV (Supplementary Figure 2). The gene discussed is CD44; the disease is susceptibility to pneumonia measurement.