CD19 expression (CD19-positive)

CD19 is read by flow cytometry on blood or marrow blasts, or by immunohistochemistry on lymphoma tissue. Blinatumomab (Blincyto) is labelled for CD19-positive B-cell precursor ALL (in remission with MRD of 0.1 percent or more, in consolidation, and relapsed or refractory); tisagenlecleucel, axicabtagene ciloleucel, lisocabtagene maraleucel and brexucabtagene autoleucel are CD19-directed CAR-T products whose labels describe the disease by histology rather than by a CD19 threshold; tafasitamab and loncastuximab tesirine are CD19-directed antibodies for DLBCL. Antigen loss or lineage switch after CD19-directed therapy is documented in the labels' clinical sections and is the reason CD22- and CD20-directed options exist.

Part ofCD19· CD19 All readouts

CD19: what it is and how drugs act on it · animated schematic, not to scale

Target · the protein and the cell it sits on
Drug · antibody, small molecule, cell or radioligand
Effect · signal, damage or kill

In plain words · CD19 is a marker on B cells and B-cell cancers, and was the target of the first CAR-T therapies ever approved.

IHC score 1 approval threshold

What it means for a patient

Almost every B-cell leukaemia and lymphoma is CD19-positive, so a positive result mainly confirms that blinatumomab, CAR-T cells and the CD19 antibodies are options. If the disease comes back after one of these treatments, CD19 is re-checked, because a CD19-negative relapse needs a treatment aimed at a different target such as CD22.

Written only from the label or guideline text cited on this page. Not medical advice; your own report and the reading your team gives it come first.

Scoring rule

CD19 detected on leukaemia blasts by flow cytometry (the label states CD19-positive without a percentage); for CAR-T and lymphoma antibodies no measurement is required.

“CD19-positive B-cell precursor acute lymphoblastic leukemia (ALL) in first or second complete remission with minimal residual disease (MRD) greater than or equal to 0.1%.”
BLINCYTO prescribing information

Thresholds used in approvals

Threshold	Drug	Cancer	Regulator	Source
CD19-positive (flow cytometry, no percentage stated)	Blinatumomab	Acute lymphoblastic leukaemia	FDA	label

Drugs whose label names it

Blinatumomab

Trials that name this readout

Matched on the name and aliases of the readout in the title, setting and summary of each trial; a match is a mention, not proof the readout was an entry criterion.

Notes

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Lymphoma: CD19 is not tested before a CD19-directed treatment, because expression is close to universal in B-cell lymphoma; the reason to measure it is after treatment, not before. Relapse with loss of the CD19 epitope follows 10 to 20% of paediatric responses to CD19 CAR-T in B-cell acute lymphoblastic leukaemia, through deletion of the locus, exon 2 mutation, or selection for an alternatively spliced transcript that skips exon 2 and makes a protein the CAR cannot see (Sotillo 2015). Target evasion is also documented after axicabtagene ciloleucel in large B-cell lymphoma (Plaks 2021), but the published lymphoma series are small and the reported shares do not agree, so OnCo holds no figure for it. The cost of hitting the antigen is B-cell aplasia and low immunoglobulin, deeper and longer after CAR-T than after an antibody.