PRF1 and hemophagocytic syndrome: Conversely, cytokine elevations in patients with CAR T-associated severe CRS, while reaching similar peak levels, were transient and rapidly decreased, indicating a potential association between more severe CRS and CAR HLH.444 Recent findings by researchers have revealed a perforin-deficient homozygous mouse model in which antigen-independent CAR-T cell expansion is linked to HLH-like toxicity.