Differential cytokine withdrawal-induced death sensitivity of effector T cells derived from distinct human CD8+ memory subsets

Abstract

CD8+ central memory (CM) and effector memory (EM) T-cell subsets exhibit well-established differences in proliferative and protective capacity after infectious challenge. However, their relative sensitivity to apoptosis has been largely overlooked, despite the importance of programmed cell death in regulating effector T-cell homeostasis. Here we demonstrate that primary human effector T cells derived from the CD8+ EM subset exhibit significantly higher sensitivity to cytokine withdrawal-induced cell death (CWID), a critical intrinsic apoptosis program responsible for culling cells once an infection is cleared and interleukin-2 (IL-2) levels diminish. Interestingly, we found no differences in the expression of IL-2 or IL-2 receptor components in cells originating from either subset. Relative to CM-derived effectors, however, EM-derived T cells displayed more mitochondrial instability and greater caspase activity. Indeed, we found that heightened CWID sensitivity in EM-derived effectors coincided with higher expression of the pro-apoptotic Bcl-2 family protein BIM, both at steady state and with de novo induction following withdrawal of exogenous IL-2. These data point to ‘imprinted’ differences in BIM protein regulation, preserved by CD8+ CM and EM progeny, which govern their relative sensitivity to CWID. In addition, we detected a burst of autophagy after IL-2 withdrawal, which was better maintained in CM-derived T cells. Both subsets showed increased, equivalent CWID sensitivity upon treatment with autophagy inhibitors, suggesting sustained autophagy could preferentially protect CM-derived T cells from apoptosis. These findings offer new insight into how CM CD8+ T cells display superior effector cell expansion and more persistent memory responses in vivo relative to EM-derived T cells, based in part on decreased CWID sensitivity.

Metabolic reprogramming and apoptosis sensitivity: Defining the contours of a T cell response

“…During the contraction phase of the T cell response triggered by cytokine withdrawal, T cells also increase autophagic activity to cope with the stress of growth factor deprivation [43, 44]. Macroautophagy, referred to here as autophagy, is a catabolic process by which cellular proteins and organelles are degraded to provide free amino acids and allows T cells to maintain ATP production.…”

“…Inhibition of NOTCH1 signaling induces metabolic shutdown and triggers autophagy for survival in T cell acute lymphoblastic leukemia (T-ALL); co-inhibition of autophagy synergistically enhanced anti-NOTCH treatment efficacy in eliminating T-ALL cells [52]. Additionally, we recently demonstrated that secondary effector T cells derived from sorted human memory CD8 + T cell subsets (central and effector memory) are differentially sensitive to CWID [43]. Effectors derived from the central memory (CM) pool are more resistant to RICD than their effector memory (EM)-derived counterparts, due to more sustained protective autophagy and reduced BIM expression [43].…”

“…Additionally, we recently demonstrated that secondary effector T cells derived from sorted human memory CD8 + T cell subsets (central and effector memory) are differentially sensitive to CWID [43]. Effectors derived from the central memory (CM) pool are more resistant to RICD than their effector memory (EM)-derived counterparts, due to more sustained protective autophagy and reduced BIM expression [43]. Hence, disparate rates of autophagy and subsequent apoptosis in memory T cell subsets likely influence the magnitude of a secondary immune response, which is an important consideration for adoptive T cell transfer strategies.…”

“…The importance of apoptosis sensitivity extends to adoptive T cell therapies for tumor eradication, for which the selection of appropriate T cell subsets for expansion and autologous transfer is imperative for sustained anti-tumor responses. Our finding that human effector CD8 + T cells derived from the CM vs. EM subset survive better after IL-2 withdrawal may help to explain their superior expansion and protective capacity in vivo [43] and may help explain why CM T cells give rise to longer-lived, more robust and efficacious effector T cell responses. Furthermore, RICD sensitization must also be considered carefully when engineering such T cells for precision targeting using chimeric antigen receptors (CARs).…”

IL2 enhances ex-vivo expanded regulatory T cell persistence after adoptive transfer

“…IL2 complexes also stabilize the expression of the Treg-lineage master transcription factor, FOXP3 in TGF-B-induced pTregs 30 . We hypothesized that ex-vivo expanded Tregs' exposure to high IL2 concentrations may render them particularly sensitive to cytokine withdrawalinduced death 31 (CWID) after adoptive transfer, a sensitivity that could be ameliorated with systemic IL2 therapy. Given proven IL2 and rapamycin (IL2+rapa) advantages in supporting endogenous Treg expansion in small animal models 32,33 and patients 34 , we tested IL2+rapa for its capacity to prolong the half-life of autologously-derived, ex-vivoexpanded Tregs after adoptive transfer in an outbred, NHP model and performed flow cytometry and single cell transcriptomics to explore underlying mechanisms and correlations with lifespan and Treg subset dynamics after transfer.…”