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Published on: August 13, 2013
Epigenetic Suppression of Transgenic T-cell Receptor Expression via Gamma-Retroviral Vector Methylation in Adoptive
Theodore S Nowicki1,2,3, Colin Farrell4, Marco Morselli5,6
1Division of Pediatric Hematology-Oncology, Department of Pediatrics, University of California, Los Angeles, Los Angeles, California. tnowicki@mednet.ucla.edu.
Abstract:
Transgenic T-cell receptor (TCR) adoptive cell therapies recognizing tumor antigens are associated with robust initial response rates, but frequent disease relapse. This usually occurs in the setting of poor long-term persistence of cells expressing the transgenic TCR, generated using murine stem cell virus (MSCV) γ-retroviral vectors. Analysis of clinical transgenic adoptive cell therapy products in vivo revealed that despite strong persistence of the transgenic TCR DNA sequence over time, its expression was profoundly decreased over time at the RNA and protein levels. Patients with the greatest degrees of expression suppression displayed significant increases in DNA methylation over time within the MSCV promoter region, as well as progressive increases in DNA methylation within the entire MSCV vector over time. These increases in vector methylation occurred independently of its integration site within the host genomes. These results have significant implications for the design of future viral vector gene-engineered adoptive cell transfer therapies. SIGNIFICANCE: Cellular immunotherapies' reliance on retroviral vectors encoding foreign genetic material can be vulnerable to progressive acquisition of DNA methylation and subsequent epigenetic suppression of the transgenic product in TCR adoptive cell therapy. This must be considered in the design of future generations of cellular immunotherapies for cancer.This article is highlighted in the In This Issue feature, p. 1611.
Insights
Transgenic T-cell receptor (TCR) adoptive cell therapies often relapse due to poor cell persistence. Epigenetic silencing via DNA methylation of the retroviral vector limits long-term expression of engineered T cells.
Area of Science:
- Immunology
- Molecular Biology
- Cancer Therapy
Background:
- Transgenic T-cell receptor (TCR) adoptive cell therapies show initial promise but suffer from frequent relapses.
- Poor long-term persistence of engineered T cells is a key factor contributing to treatment failure.
Purpose of the Study:
- To investigate the mechanisms underlying the decreased expression of transgenic TCRs in adoptive cell therapy.
- To understand the role of epigenetic modifications in the long-term efficacy of TCR-engineered T cells.
Main Methods:
- Analysis of clinical TCR adoptive cell therapy products in vivo.
- Assessment of transgenic TCR DNA, RNA, and protein expression over time.
- Quantification of DNA methylation in the murine stem cell virus (MSCV) promoter and vector regions.
Main Results:
- Transgenic TCR DNA persisted, but RNA and protein expression significantly decreased over time.
- Increased DNA methylation in the MSCV promoter and vector correlated with suppressed TCR expression.
- Vector methylation occurred independently of integration site, suggesting an intrinsic vulnerability.
Conclusions:
- Epigenetic silencing through DNA methylation of retroviral vectors limits the sustained expression of transgenic TCRs.
- This epigenetic suppression poses a significant challenge for the long-term efficacy of TCR adoptive cell therapies.
- Future generations of gene-engineered cell therapies must address this vector-mediated epigenetic vulnerability.
