From the loading dock to the boardroom: a new job for Akt kinase

A metabolic switch to memory CAR T cells: Implications for cancer treatment

Therapeutic efficacy of chimeric antigen receptor (CAR) T cells is associated with their expansion, persistence and effector function. Although CAR T cell therapy has shown remarkable therapeutic effects in hematological malignancies, its therapeutic efficacy has been limited in some types of cancers - in particular, solid tumors - partially due to the cells' inability to persist and the acquisition of T cell dysfunction within a harsh immunosuppressive tumor microenvironment. Therefore, it would be expected that generation of CAR T cells with intrinsic properties for functional longevity, such as the cells with early-memory phenotypes, could beneficially enhance antitumor immunity. Furthermore, because the metabolic pathways of CAR T cells help determine cellular differentiation and lifespan, therapies targeting such pathways like glycolysis and oxidative phosphorylation, can alter CAR T cell fate and durability within tumors. Here we discuss how reprogramming of CAR T cell metabolism and metabolic switch to memory CAR T cells influences their antitumor activity. We also offer potential strategies for targeting these metabolic circuits in the setting of adoptive CAR T cell therapy, aiming to better unleash the potential of adoptive CAR T cell therapy in the clinic.

The PDL1-inducible GTPase Arl4d controls T effector function by limiting IL-2 production

Interleukin-2 (IL-2) is a key regulator of adaptive immune responses but its regulation is incompletely understood. We previously found that PDL1-dependent signals were pivotal for liver sinusoidal endothelial cell-mediated priming of CD8 T cells, which have a strongly reduced capacity to produce IL-2. Here, we show that the expression of the ARF-like GTPase Arl4d is PD-L1-dependently induced in such LSEC-primed T cells, and is associated with reduced IL-2 secretion and Akt phosphorylation. Conversely, Arl4d-deficient T cells overproduced IL-2 upon stimulation. Arl4d-deficiency in CD8 T cells also enhanced their expansion and effector function during viral infection in vivo. Consistent with their increased IL-2 production, Arl4d-deficient T cells showed enhanced development into KLRG1⁺CD127⁻ short-lived effector cells (SLEC), which is dependent on IL-2 availability. Thus, our data reveal a PD-L1-dependent regulatory circuitry that involves the induction of Arl4d for limiting IL-2 production in T cells.

Signal integration by Akt regulates CD8 T cell effector and memory differentiation

During a T cell response, the effector CTL pool contains two cellular subsets: short-lived effector cells (SLECs), a majority of which are destined for apoptosis, and the memory precursor effector cells, which differentiate into memory cells. Understanding the mechanisms that govern the differentiation of memory CD8 T cells is of fundamental importance in the development of effective CD8 T cell-based vaccines. The strength and nature of TCR signaling, along with signals delivered by cytokines like IL-2 and IL-12, influence differentiation of SLECs and memory precursor effector cells. A central question is, how are signals emanating from multiple receptors integrated and interpreted to define the fate of effector CTLs? Using genetic and pharmacological tools, we have identified Akt as a signal integrator that links distinct facets of CTL differentiation to the specific signaling pathways of FOXO, mTOR, and Wnt/β-catenin. Sustained Akt activation triggered by convergent extracellular signals evokes a transcription program that enhances effector functions, drives differentiation of terminal effectors, and diminishes the CTLs' potential to survive and differentiate into memory cells. Whereas sustained Akt activation severely impaired CD8 T cell memory and protective immunity, in vivo inhibition of Akt rescued SLECs from deletion and increased the number of memory CD8 T cells. Thus, the cumulative strength of convergent signals from signaling molecules such as TCR, costimulatory molecules, and cytokine receptors governs the magnitude of Akt activation, which in turn controls the generation of long-lived memory cells. These findings suggest that therapeutic modulation of Akt might be a strategy to augment vaccine-induced immunity.