Reversible transgene expression reduces fratricide and permits 4-1BB Costimulation of CAR T cells directed to T-cell malignancies

Maksim Mamonkin, Malini Mukherjee, Madhuwanti Srinivasan, Sandhya Sharma, Diogo Gomes-Silva, Feiyan Mo, Giedre Krenciute, Jordan S. Orange, Malcolm Brenner

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


T cells expressing second-generation chimeric antigen receptors (CARs) specific for CD5, a T-cell surface marker present on normal and malignant T cells, can selectively kill tumor cells. We aimed to improve this killing by substituting the CD28 costimulatory endodomain (28.z) with 4-1BB (BB.z), as 28.z CD5 CART cells rapidly differentiated into short-lived effector cells. In contrast, 4-1BB costimulation is known to promote development of the central memory subpopulation. Here, we found BB.z CD5 CAR T cells had impaired growth compared with 28.z CD5.CAR T cells, due to increased T-cell-T-cell fratricide. We demonstrate that TRAF signaling from the 4-1BB endodomain upregulated the intercellular adhesion molecule 1, which stabilized the fratricidal immunologic synapse between CD5 CAR T cells. As the surviving BB.z CD5 CAR T cells retained the desired central memory phenotype, we aimed to circumvent the 4-1BB-mediated toxicity using a regulated expression system that reversibly inhibits CAR expression. This system minimized CAR signaling and T-cell fratricide during in vitro expansion in the presence of a small-molecule inhibitor, and restored CAR expression and antitumor function of transduced T cells in vivo. These studies reveal a mechanism by which 4-1BB costimulation impairs expansion of CD5 CAR T cells and offer a solution to mitigate this toxicity.

Original languageEnglish (US)
Pages (from-to)47-58
Number of pages12
JournalCancer immunology research
Issue number1
StatePublished - Jan 2018

ASJC Scopus subject areas

  • Immunology
  • Cancer Research


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