# CD19 expression (CD19-positive)

Source: https://onco.cc/biomarkers/cd19-expression/  
OnCo record `cd19-expression` (Biomarker). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

CD19 is the B-cell surface protein that blinatumomab, CAR-T cells and several antibodies aim at. Blinatumomab's label requires CD19-positive leukaemia; the CAR-T labels assume it, and losing CD19 is the commonest way the disease escapes.

## Summary

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.

## Fields

- Kind: Biomarker
- Last checked: 2026-09-23
- Also known as: CD19-positive; CD19+; CD19 expression; CD19 positive B-ALL; CD19 loss; CD19-negative relapse
- Tags: biomarker; surface-antigen

## Notes

- 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.

## Sources

- BLINCYTO prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=38b482a8-960b-4591-9857-5031ecb830aa
- Sotillo et al., Cancer Discov 2015: acquired mutations and alternative splicing of CD19 enable resistance to CART-19: https://doi.org/10.1158/2159-8290.CD-15-1020
- Plaks et al., Blood 2021: CD19 target evasion as a mechanism of relapse after axicabtagene ciloleucel in large B-cell lymphoma: https://doi.org/10.1182/blood.2021010930

## Connected records

- biomarkers: [CD20 expression (CD20-positive)](https://onco.cc/biomarkers/cd20-expression/), [CD22 expression (CD22-positive)](https://onco.cc/biomarkers/cd22-expression/), [CD30 expression (CD30-positive)](https://onco.cc/biomarkers/cd30-expression/)
- cancers: [Acute lymphoblastic leukaemia](https://onco.cc/cancers/all-leukemia/), [Diffuse large B-cell lymphoma](https://onco.cc/cancers/dlbcl/), [Follicular lymphoma](https://onco.cc/cancers/follicular-lymphoma/), [Mantle cell lymphoma](https://onco.cc/cancers/mantle-cell-lymphoma/), [Non-Hodgkin lymphoma (all types)](https://onco.cc/cancers/non-hodgkin-lymphoma/), [Relapsed and refractory acute lymphoblastic leukaemia in children](https://onco.cc/cancers/all-paediatric-relapsed/)
- drugs: [Axicabtagene ciloleucel](https://onco.cc/drugs/axicabtagene-ciloleucel/), [Blinatumomab](https://onco.cc/drugs/blinatumomab/), [Brexucabtagene autoleucel](https://onco.cc/drugs/brexucabtagene-autoleucel/), [Lisocabtagene maraleucel](https://onco.cc/drugs/lisocabtagene-maraleucel/), [Loncastuximab tesirine](https://onco.cc/drugs/zynlonta/), [Tafasitamab](https://onco.cc/drugs/tafasitamab/), [Tisagenlecleucel](https://onco.cc/drugs/tisagenlecleucel/)
- terms: [Antigen escape (antigen loss, lineage switch)](https://onco.cc/terms/antigen-escape/), [Antigen escape: how a lymphoma loses the thing the drug was aimed at](https://onco.cc/terms/lymphoma-bio-antigen-escape/), [Flow cytometry (immunophenotyping)](https://onco.cc/terms/flow-cytometry/), [Minimal / molecular residual disease (MRD)](https://onco.cc/terms/mrd/), [What it costs to aim at a lineage antigen](https://onco.cc/terms/lymphoma-bio-lineage-antigen-cost/)
- targets: [CD19](https://onco.cc/targets/cd19/)

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