Promoting Thiol Expression Increases the Durability of Antitumor T-cell Functions

Abstract

Ex vivo-expanded CD8+ T cells used for adoptive immunotherapy generally acquire an effector memory-like phenotype (TEM cells). With regard to therapeutic applications, two undesired features of this phenotype in vivo are limited persistence and reduced anti-tumor efficacy, relative to CD8+ T cells with a central memory-like phenotype (TCM cells). Further, there is incomplete knowledge about all the differences between TEM and TCM cells that may influence tumor treatment outcomes. Given that TCM cells survive relatively longer in oxidative tumor microenvironments, we investigated the hypothesis that TCM possess relatively greater anti-oxidative capacity than TEM cells. Here we report that TCM cells exhibit a relative increase compared to TEM cells in expression of cell surface thiols, a key target of cellular redox controls, along with other antioxidant molecules. Increased expression of redox regulators in TCM cells inversely correlated with the generation of reactive oxygen and nitrogen species, proliferative capacity and glycolytic enzyme levels. Notably, TCR-transduced T cells pretreated with thiol donors, such as N-acetyl cysteine or rapamycin, up-regulated thiol levels and antioxidant genes. A comparison of anti-tumor CD8+ T cell populations on the basis of surface thiol expression showed that thiol-high cells persisted longer in vivo and exerted superior tumor control. Our results suggest that higher levels of reduced cell surface thiols are a key characteristic of T cells that can control tumor growth, and that profiling this biomarker may have benefits to T cell adoptive immunotherapy protocols.

Lack ofp53Augments Antitumor Functions in Cytolytic T Cells

“…The expression of cyclin dependent kinase inhibitors CDKn1a , CDKn2a , and CDKn2b , which are regulated by p53 were also significantly reduced in h3T- p53 KO cells as compared to h3T T cells (Figure 1C). In addition, higher proliferation rate could lead the T cells close to replicative senescence with increased CD62L lo phenotype and susceptibility to cell death (3). A recent study has also shown p53 isoform switching regulates tumor associated replicative senescence T cells (17).…”

“…Since Tcm phenotype is associated with higher anti-oxidant capacity and reduced cell death (3), we determined ROS/RNS levels and AICD levels between h3T- p53 KO vs. h3T T cells. Upon TCR restimulation with cognate tyrosinase antigen h3T- p53 KO T cells secreted less ROS (measured using DCFDA dye), and RNS (measured using DAF dye), as compared to h3T T cells (Figure 2A).…”

“…However, susceptibility to immunosuppression and reduced survival of effector T cells in an oxidative tumor microenvironment are the key confounding factors in immunotherapy (2,3). We have previously shown that reactive oxygen species (ROS) scavengers can inhibit repetitive TCR stimulation mediated activation induced cell death (AICD) of tumor reactive T cells without interfering with cytokine production (4), a measure of CTL function, placing redox regulation at a central point for therapeutic intervention.…”

IL-15 activates mTOR and primes stress-activated gene expression leading to prolonged antitumor capacity of NK cells

“…35,36 This agrees with studies showing that IL-15-activated human NK cells are functionally resistant to steroid inhibition 37 and sustain their superior in vivo proliferation. 1,35,38 In T cells, IL-15 promotes survival via upregulating Bcl-2 39,40 and antioxidant proteins 41,42 and limiting proapoptotic caspase-3. 43 In addition, we show that the expression of activating NK-cell receptors is upregulated on IL-2-expanded NK cells after short-term incubation with IL-15, possibly contributing to the result that, upon injection into immunodeficient mice, the frequency of IL-15-expanded NK cells in the liver was higher as compared with IL-2-expanded NK cells.…”

Anti-oxidant capacity and anti-tumor T cell function: A direct correlation

“…2 Our study highlights that using Rapamycin -a drug that is known to enhance CD62L expression, 3 also increases anti-oxidant capacity of the T cells. It is likely that in addition to its role as mTOR inhibitor and regulating metabolic commitment of a T cell, rapamycin pre-treated T cells persist better in a tumor microenvironment and exhibit improved anti-tumor function because increased capacity to resist oxidative stress.…”