Rodent studies of asthma demonstrate that MSC induction of CD4 regulatory T cells (Tregs), which are immunomodulatory CD4 cells, is critical in decreasing Th2 responses25, 26 and Th2 cytokines interleukin‐4 (IL‐4), IL‐5, and IL‐13 as well as immunoglobulin E levels to ameliorate disease severity27, 28; one recent study implicated MSC transfer of mitochondria in this process.29 Here, CD4 is linked to asthma.