Understanding that T cells require cytokine engagement for optimal activation following antigen stimulation, Kagoya et al. added a truncated cytoplasmic STAT5 signaling domain from IL-2Rβ and a YXXQ STAT3-recruiting motif to a CD19-CAR construct. T cells expressing this modified CAR construct showed enhanced in vivo antitumor efficacy mediated by antigen-specific activation of the JAK-STAT pathway, which promoted proliferation and persistence and prevented terminal differentiation.

The adoptive transfer of T cells engineered with a chimeric antigen receptor (CAR) (hereafter referred to as CAR-T cells) specific for the B lymphocyte antigen CD19 has shown impressive clinical responses in patients with refractory B cell malignancies. However, the therapeutic effects of CAR-T cells that target other malignancies have not yet resulted in significant clinical benefit. Although inefficient tumor trafficking and various immunosuppressive mechanisms can impede CAR-T cell effector responses, the signals delivered by the current CAR constructs may still be insufficient to fully activate antitumor T cell functions. Optimal T cell activation and proliferation requires multiple signals, including T cell receptor (TCR) engagement (signal 1), co-stimulation (signal 2) and cytokine engagement (signal 3). However, CAR constructs currently being tested in the clinic contain a CD3z (TCR signaling) domain and co-stimulatory domain(s) but not a domain that transmits signal 3 (refs. 13, 14, 15, 16, 17, 18). Here we have developed a novel CAR construct capable of inducing cytokine signaling after antigen stimulation. This new-generation CD19 CAR encodes a truncated cytoplasmic domain from the interleukin (IL)-2 receptor beta-chain (IL-2Rbeta) and a STAT3-binding tyrosine-X-X-glutamine (YXXQ) motif, together with the TCR signaling (CD3z) and co-stimulatory (CD28) domains (hereafter referred to as 28-DeltaIL2RB-z(YXXQ)). The 28-DeltaIL2RB-z(YXXQ) CAR-T cells showed antigen-dependent activation of the JAK kinase and of the STAT3 and STAT5 transcription factors signaling pathways, which promoted their proliferation and prevented terminal differentiation in vitro. The 28-DeltaIL2RB-z(YXXQ) CAR-T cells demonstrated superior in vivo persistence and antitumor effects in models of liquid and solid tumors as compared with CAR-T cells expressing a CD28 or 4-1BB co-stimulatory domain alone. Taken together, these results suggest that our new-generation CAR has the potential to demonstrate superior antitumor effects with minimal toxicity in the clinic and that clinical translation of this novel CAR is warranted.

Author Info: (1) Tumor Immunotherapy Program, Campbell Family Institute for Breast Cancer Research, Campbell Family Cancer Research Institute, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario

Author Info: (1) Tumor Immunotherapy Program, Campbell Family Institute for Breast Cancer Research, Campbell Family Cancer Research Institute, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada. (2) Tumor Immunotherapy Program, Campbell Family Institute for Breast Cancer Research, Campbell Family Cancer Research Institute, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada. Takara Bio, Inc., Kusatsu, Japan. (3) Tumor Immunotherapy Program, Campbell Family Institute for Breast Cancer Research, Campbell Family Cancer Research Institute, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada. Department of Immunology, University of Toronto, Toronto, Ontario, Canada. (4) Tumor Immunotherapy Program, Campbell Family Institute for Breast Cancer Research, Campbell Family Cancer Research Institute, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada. Department of Immunology, University of Toronto, Toronto, Ontario, Canada. (5) Tumor Immunotherapy Program, Campbell Family Institute for Breast Cancer Research, Campbell Family Cancer Research Institute, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada. Department of Immunology, University of Toronto, Toronto, Ontario, Canada. (6) Tumor Immunotherapy Program, Campbell Family Institute for Breast Cancer Research, Campbell Family Cancer Research Institute, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada. (7) Tumor Immunotherapy Program, Campbell Family Institute for Breast Cancer Research, Campbell Family Cancer Research Institute, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada. Department of Immunology, University of Toronto, Toronto, Ontario, Canada. Department of Medicine, University of Toronto, Toronto, Ontario, Canada. (8) Department of Hematology-Oncology, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada. (9) Tumor Immunotherapy Program, Campbell Family Institute for Breast Cancer Research, Campbell Family Cancer Research Institute, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada. Department of Immunology, University of Toronto, Toronto, Ontario, Canada.

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