Tumor-Targeted Human T Cells Expressing CD28-Based Chimeric Antigen Receptors Circumvent CTLA-4 Inhibition

Abstract

Adoptive T cell therapy represents a promising treatment for cancer. Human T cells engineered to express a chimeric antigen receptor (CAR) recognize and kill tumor cells in a MHC-unrestricted manner and persist in vivo when the CAR includes a CD28 costimulatory domain. However, the intensity of the CAR-mediated CD28 activation signal and its regulation by the CTLA-4 checkpoint are unknown. We investigated whether T cells expressing an anti-CD19, CD3 zeta and CD28-based CAR (19-28z) displayed the same proliferation and anti-tumor abilities than T cells expressing a CD3 zeta-based CAR (19z1) costimulated through the CD80/CD28, ligand/receptor pathway. Repeated in vitro antigen-specific stimulations indicated that 19-28z+ T cells secreted higher levels of Th1 cytokines and showed enhanced proliferation compared to those of 19z1+ or 19z1-CD80+ T cells. In an aggressive pre-B cell leukemia model, mice treated with 19-28z+ T cells had 10-fold reduced tumor progression compared to those treated with 19z1+ or 19z1-CD80+ T cells. shRNA-mediated CTLA-4 down-regulation in 19z1-CD80+ T cells significantly increased their in vivo expansion and anti-tumor properties, but had no effect in 19-28z+ T cells. Our results establish that CTLA-4 down-regulation may benefit human adoptive T cell therapy and demonstrate that CAR design can elude negative checkpoints to better sustain T cell function.

A Chimeric Switch-Receptor Targeting PD1 Augments the Efficacy of Second-Generation CAR T Cells in Advanced Solid Tumors

“…In contrast, modifying SS1BBZ CAR T-cells with PD1CD28 led to reduction in both LAG3 expression and TIM3/CEACAM1 co-expression. This phenomenon, i.e., PD1CD28 allowing adoptively transferred T-cells to circumvent inhibition by IRs other than PD1, was also demonstrated in a murine study looking at CTLA-4 (50). Further investigations to understand the underlying mechanisms are planned, but one leading hypothesis is that the PD1CD28 modified TILs that are exposed to significantly higher levels of IL2 represent “younger” T-cells whose chronicity of activation and exposure to the TME is substantially less than their unmodified counterparts.…”

Structural Design of Engineered Costimulation Determines Tumor Rejection Kinetics and Persistence of CAR T Cells

“…Thus, 4-1BBL is more likely to find its cognate receptor than CD80, while 1928z may compensate for the loss of endogenous CD28, unlike 19BBz for endogenous 4-1BB. Additionally, the activity of CD80 may be further constrained by CTLA-4, which is not the case for the CD28 signal delivered through the 1928z CAR (Condomines et al, 2015). These differences in the engagement of CD28 and 4-1BB signaling pathways likely account for or contribute to the greater efficacy of 1928z-41BBL relative to 19BBz-CD80.…”

Therapeutic T cell engineering

“…The Btk inhibitor ibrutinib, which is active against CLL, has also been found to improve CAR T cell function in preclinical models 113 . Checkpoint blockade may sustain function and persistence of engineered T cells in some instances 114–116 , albeit not universally 117 . Multiple approaches have been used to interfere with immune checkpoints, including the use of blocking antibodies 114,116 , dominant-negative receptors 114 and targeted gene disruption 118 .…”