AbstractBackgroundThough the efficacy of anti C‐type lectin‐like molecule‐1 (CLL1) CAR T‐cells in refractory/relapsed acute myeloid leukemia (R/R‐AML) have been occasionally reported, the influence of co‐stimulatory domain CAR T‐cells is not investigated so far.MethodSeven R/R‐AML children treated with anti‐CLL1 CAR T‐cells were enrolled onto this preliminary comparison study. Among these seven patients, four received CD28/CD27‐based CAR T‐cells therapy, and three received 4‐1BB‐based CAR T‐cells therapy.ResultThe overall response rates were 75% and 66.7% in CD28/CD27 and 4‐1BB group respectively. All patients experienced grade 1 to 2 cytokine release syndrome, with only one patient experiencing grade 2 immune effector cell‐associated neurotoxicity syndrome. The maximum CAR T‐cells durations were 156 and 274 days for CD28/CD27 group and 4‐1BB group respectively. The 1‐yr overall survival rate was 57.1%.ConclusionsA preliminary similar efficacy/safety index was observed in anti‐CLL1‐based CAR T‐cells with 4‐1BB or CD28/CD27 co‐stimulatory elements in treating pediatric R/R‐AML.