Abstract
The number and position of CD3ζ ITAMs in CD19 CAR 19-28ζ T cells controls T-cell fate.
Major finding: The number and position of CD3ζ ITAMs in CD19 CAR 19-28ζ T cells controls T-cell fate.
Concept: Redundancy CD28 and CD3ζ signaling drives both CD19 CAR 19-28ζ T-cell activation and exhaustion.
Impact: Optimizing the balance between T-cell effector function and memory functions is critical for CAR design.
CD19-targeting chimeric antigen receptor (CAR) T cells have been highly efficacious in patients with hematologic cancers; recently, it has been shown that the CD19 CAR 19-28ζ construct, which encodes for a single CD28 signaling domain and 3 CD3ζ immunoreceptor tyrosine-based activation motifs (ITAM), results in strong effector functions and limited life span of T cells. To ascertain whether modulating the redundancy of CD28- and CD3ζ-mediated signaling enhances T-cell life span without affecting potency, Feucht, Sun, and colleagues performed mutagenesis to inactivate 1 or 2 of the CD3ζ ITAMs (X) from the membrane-proximal to membrane-distal CD3ζ ITAM1/2/3 and generate the mutant CD19 CAR 19-28ζ constructs termed 1XX, X2X, XX3, and X23. Compared to parental CAR T cells, mutant 1XX T cells were more efficacious and induced long-term remission in a xenograft model of pre-B acute lymphoblastic leukemia whereas mutant X2X and X23 T cells exhibited similar antitumor efficacy, and mutant XX3 T cells were the least efficacious of all CARs evaluated. In vitro, XX3 CAR T cells exhibited diminished effector function compared with the other mutant and parental CAR T cells, but all single ITAM mutants exhibited increased persistence and delayed T-cell differentiation in vivo. CAR constructs encoding for ITAM1 or ITAM3 in the ITAM1 position exhibited similar cytotoxicity activity, decreased T-cell differentiation, and increased antitumor efficacy. 1XX-engineered naïve T cells acquired a persistent stem-like state, whereas those engineered with the parental CAR rapidly exhibited a gene signature associated with exhausted T cells, while 1XX T cells exhibited a gene signature associated with a less-differentiated T-cell state, and XX3 T cells preserved expression of naïve/memory–associated genes but failed to activate sufficient effector programs. These results suggest that defined mutations in the CD3ζ chain of the 19-28ζ CAR construct control the balance between T-cell differentiation and effector activity and suggest potential approaches to improve the efficacy of CD28-based CAR constructs.
Note: Research Watch is written by Cancer Discovery editorial staff. Readers are encouraged to consult the original articles for full details. For more Research Watch, visit Cancer Discovery online at http://cancerdiscovery.aacrjournals.org/CDNews.
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