In contrast, intermediate phenotype, mixed B/myeloid post-CAR leukaemia, with complete loss of CD19 gene expression but residual expression of B-cell markers (CD22 or B220), regain of CD19 occurred in some secondary and the majority of tertiary recipients suggestive of a persistent pre-B cell developmental program despite partial phenotypic change (Fig. 3c). This evidence concerns the gene PTPRC and leukemia.