IL2 and macrophage activation syndrome: Early cytokine release syndrome (CRS) in CAR therapies has been related to multiple factors including γ-interferon (IFNγ, TNFα, IL1, IL2 and IL6, and may contribute to anti-leukaemic effects, but consequential inflammation and macrophage activation syndrome (MAS) can mimic sepsis with hypotension, fever rigours and vascular leak syndromes (Brentjens et al, 2013).