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Gene Ther. 2015 May;22(5):391-403. doi: 10.1038/gt.2015.4. Epub 2015 Feb 5.

Inclusion of an IgG1-Fc spacer abrogates efficacy of CD19 CAR T cells in a xenograft mouse model.

Author information

1
Section for Cell Therapy, Department of Oncology, Oslo University Hospital Radiumhospitalet, Oslo, Norway.
2
1] Department of Immunology, Oslo University Hospital Radiumhospitalet, Oslo, Norway [2] Department of Cancer Biology, Scripps Research Institute, Jupiter, FL, USA.
3
1] Department of Tumor Biology, Oslo University Hospital Radiumhospitalet, Oslo, Norway [2] KG Jebsen Center for Breast Cancer Research, Institute for Clinical Medicine, University of Oslo, Oslo, Norway.
4
1] Centre for Immune Regulation and Department of Immunology, Oslo University Hospital Rikshospitalet, Oslo, Norway [2] Institute of Clinical Medicine, University of Oslo, Oslo, Norway.
5
Centre for Immune Regulation and Department of Immunology, Oslo University Hospital Rikshospitalet, Oslo, Norway.
6
Department of Immunology, Oslo University Hospital Radiumhospitalet, Oslo, Norway.

Abstract

Cancer therapy with T cells expressing chimeric antigen receptors (CARs) has produced remarkable clinical responses in recent trials, but also severe side effects. Whereas most protocols use permanently reprogrammed T cells, we have developed a platform for transient CAR expression by mRNA electroporation. This approach may be useful for safe clinical testing of novel receptors, or when a temporary treatment period is desirable. Herein, we investigated therapy with transiently redirected T cells in vitro and in a xenograft mouse model. We constructed a series of CD19-specific CARs with different spacers and co-stimulatory domains (CD28, OX40 or CD28-OX40). The CAR constructs all conferred T cells with potent CD19-specific activity in vitro. Unexpectedly, the constructs incorporating a commonly used IgG1-CH2CH3 spacer showed lack of anti-leukemia activity in vivo and induced severe, partly CD19-independent toxicity. By contrast, identical CAR constructs without the CH2-domain eradicated leukemia in vivo, without notable toxicity. Follow-up studies demonstrated that the CH2CH3-spacer bound soluble mouse Fcγ-receptor I and mediated off-target T-cell activation towards murine macrophages. Our findings highlight the importance of non-signalling CAR elements and of in vivo studies. Finally, the results show that transiently redirected T cells control leukemia in mice and support the rationale for developing an mRNA-CAR platform.

PMID:
25652098
DOI:
10.1038/gt.2015.4
[Indexed for MEDLINE]

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