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). Here, IFNG is linked to macrophage activation syndrome.