The accumulation of clinical cases suggests that CRS could be affected by a combination of factors, including tumour burden, individual immune status, the peak number of CAR T cells, IL-6 level, lymphodepletion and the gut flora.9,12,37,58–63 Clarifying how these factors interact will help us better understand the general progression pattern of CRS and thus more effectively predict and manage the related toxicity.41 This evidence concerns the gene IL6 and congenital rubella syndrome.