Acidity suppresses CD8 + T-cell function by perturbing IL-2, mTORC1, and c-Myc signaling.

CD8 + T cells have critical roles in tumor control, but a range of factors in their microenvironment such as low pH can suppress their function. Here, we demonstrate that acidity restricts T-cell expansion mainly through impairing IL-2 responsiveness, lowers cytokine secretion upon re-activation, and reduces the cytolytic capacity of CD8 + T cells expressing low-affinity TCR. We further find decreased mTORC1 signaling activity and c-Myc levels at low pH. Mechanistically, nuclear/cytoplasmic acidification is linked to mTORC1 suppression in a Rheb-, Akt/TSC2/PRAS40-, GATOR1- and Lkb1/AMPK-independent manner, while c-Myc levels drop due to both decreased transcription and higher levels of proteasome-mediated degradation. In addition, lower intracellular levels of glutamine, glutamate, and aspartate, as well as elevated proline levels are observed with no apparent impact on mTORC1 signaling or c-Myc levels. Overall, we suggest that, due to the broad impact of acidity on CD8 + T cells, multiple interventions will be required to restore T-cell function unless intracellular pH is effectively controlled.

Cystathionine-gamma-lyase overexpression in T cells enhances antitumor effect independently of cysteine autonomy.

T cells could be engineered to overcome the aberrant metabolic milieu of solid tumors and tip the balance in favor of a long-lasting clinical response. Here, we explored the therapeutic potential of stably overexpressing cystathionine-gamma-lyase (CTH, CSE, or cystathionase), a pivotal enzyme of the transsulfuration pathway, in antitumor CD8+ T cells with the initial aim to boost intrinsic cysteine metabolism. Using a mouse model of adoptive cell transfer (ACT), we found that CTH-expressing T cells showed a superior control of tumor growth compared to control T cells. However, contrary to our hypothesis, this effect was not associated with increased T cell expansion in vivo or proliferation rescue in the absence of cysteine/cystine in vitro. Rather than impacting methionine or cysteine, ACT with CTH overexpression unexpectedly reduced glycine, serine, and proline concentration within the tumor interstitial fluid. Interestingly, in vitro tumor cell growth was mostly impacted by the combination of serine/proline or serine/glycine deprivation. These results suggest that metabolic gene engineering of T cells could be further investigated to locally modulate amino acid availability within the tumor environment while avoiding systemic toxicity.

Phenotypic switch of CD8(+) T cells reactivated under hypoxia toward IL-10 secreting, poorly proliferative effector cells.

CD8(+) T cells controlling pathogens or tumors must function at sites where oxygen tension is frequently low, and never as high as under atmospheric culture conditions. However, T-cell function in vivo is generally analyzed indirectly, or is extrapolated from in vitro studies under nonphysiologic oxygen tensions. In this study, we delineate the role of physiologic and pathologic oxygen tension in vitro during reactivation and differentiation of tumor-specific CD8(+) T cells. Using CD8(+) T cells from pmel-1 mice, we observed that the generation of CTLs under 5% O2, which corresponds to physioxia in lymph nodes, gave rise to a higher effector signature than those generated under atmospheric oxygen fractions (21% O2). Hypoxia (1% O2) did not modify cytotoxicity, but decreasing O2 tensions during CTL and CD8(+) tumor-infiltrating lymphocyte reactivation dose-dependently decreased proliferation, induced secretion of the immunosuppressive cytokine IL-10, and upregulated the expression of CD137 (4-1BB) and CD25. Overall, our data indicate that oxygen tension is a key regulator of CD8(+) T-cell function and fate and suggest that IL-10 release may be an unanticipated component of CD8(+) T cell-mediated immune responses in most in vivo microenvironments.

Transplant tolerance is associated with reduced expression of cystathionine-γ-lyase that controls IL-12 production by dendritic cells and TH-1 immune responses.

Antigen-activated T lymphocytes undergo an immune or tolerogeneic response in part according to the activation status of their antigen-presenting cells. However, factors controlling the activation of antigen-presenting cells are not fully understood. In this study, we demonstrate that immune tolerance after organ allotransplantation in the rat is associated with a repressed intragraft expression of several enzymes of the trans-sulfuration pathway, including cystathionine γ-lyase (CSE). The pharmacologic blockade of CSE with propargylglycine delayed heart allograft rejection and abrogated type IV hypersensitivity but did not modify antibody responses, and was associated with a selective inhibition of the TH-1 type factors T-bet, IL-12, and IFN-γ. IL-12 repression could also be induced by propargylglycine in vitro in monocytes and dendritic cells (DCs), a phenomenon not mediated by changes to nuclear factor-κ B or hydrogen sulfide but that occurred together with a modulation of intracellular cysteine content. Intracellular cysteine levels were predominantly controlled in DCs by CSE activity, together with extracellular import via the X(c)(-) transporter. Our results indicate that CSE plays a critical role in regulating IL-12 in monocytes and DCs and is down-modulated in transplant tolerance, presumably participating in the maintenance of the tolerant state.

A lentiviral vector for the production of T cells with an inducible transgene and a constitutively expressed tumour-targeting receptor.

Vectors that facilitate the engineering of T cells that can better harness endogenous immunity and overcome suppressive barriers in the tumour microenvironment would help improve the safety and efficacy of T-cell therapies for more patients. Here we report the design, production and applicability, in T-cell engineering, of a lentiviral vector leveraging an antisense configuration and comprising a promoter driving the constitutive expression of a tumour-directed receptor and a second promoter enabling the efficient activation-inducible expression of a genetic payload. The vector allows for the delivery of a variety of genes to human T cells, as we show for interleukin-2 and a microRNA-based short hairpin RNA for the knockdown of the gene coding for haematopoietic progenitor kinase 1, a negative regulator of T-cell-receptor signalling. We also show that a gene encoded under an activation-inducible promoter is specifically expressed by tumour-redirected T cells on encountering a target antigen in the tumour microenvironment. The single two-gene-encoding vector can be produced at high titres under an optimized protocol adaptable to good manufacturing practices.

Enforcing GLUT3 expression in CD8+ T cells improves fitness and tumor control by promoting glucose uptake and energy storage.

Despite the tremendous success of adoptive T-cell therapies (ACT) in fighting certain hematologic malignancies, not all patients respond, a proportion experience relapse, and effective ACT of most solid tumors remains elusive. In order to improve responses to ACT suppressive barriers in the solid tumor microenvironment (TME) including insufficient nutrient availability must be overcome. Here we explored how enforced expression of the high-affinity glucose transporter GLUT3 impacted tumor-directed T cells. Overexpression of GLUT3 in primary murine CD8+ T cells enhanced glucose uptake and increased glycogen and fatty acid storage, and was associated with increased mitochondrial fitness, reduced ROS levels, higher abundance of the anti-apoptotic protein Mcl-1, and better resistance to stress. Importantly, GLUT3-OT1 T cells conferred superior control of B16-OVA melanoma tumors and, in this same model, significantly improved survival. Moreover, a proportion of treated mice were cured and protected from re-challenge, indicative of long-term T cell persistence and memory formation. Enforcing expression of GLUT3 is thus a promising strategy to improve metabolic fitness and sustaining CD8+ T cell effector function in the context of ACT.

Anti-Ly6G binding and trafficking mediate positive neutrophil selection to unleash the anti-tumor efficacy of radiation therapy.

The anti-Ly6G antibody is used to deplete Ly6Gpos neutrophils and study their role in diverse pathologies. However, depletion is never absolute, as Ly6Glow neutrophils resistant to depletion rapidly emerge. Studying the functionality of these residual neutrophils is necessary to interpret anti-Ly6G-based experimental designs. In vitro, we found anti-Ly6G binding induced Ly6G internalization, surface Ly6G paucity, and primed the oxidative burst of neutrophils upon TNF α co-stimulation. In vivo, we found neutrophils resistant to anti-Ly6G depletion exhibited anti-neutrophil-cytoplasmic-antibodies. In the pre-clinical KrasLox-STOP-Lox-G12D/WT; Trp53Flox/Flox mouse lung tumor model, abnormal neutrophil accumulation and aging was accompanied with an N2-like SiglecFpos polarization and ly6g downregulation. Consequently, SiglecFpos neutrophils exposed to anti-Ly6G reverted to Ly6Glow and were resistant to depletion. Noting that anti-Ly6G mediated neutrophil depletion alone had no anti-tumor effect, we found a long-lasting rate of tumor regression (50%) by combining anti-Ly6G with radiation-therapy, in this model reputed to be refractory to standard anticancer therapies. Mechanistically, anti-Ly6G regulated neutrophil aging while radiation-therapy enhanced the homing of anti-Ly6G-boundSiglecFneg neutrophils to tumors. This anti-tumor effect was recapitulated by G-CSF administration prior to RT and abrogated with an anti-TNFα antibody co-administration. In summary, we report that incomplete depletion of neutrophils using targeted antibodies can intrinsically promote their oxidative activity. This effect depends on antigen/antibody trafficking and can be harnessed locally using select delivery of radiation-therapy to impair tumor progression. This underutilized aspect of immune physiology may be adapted to expand the scope of neutrophil-related research.

Engineering Chimeric Antigen Receptor T-Cells for Racing in Solid Tumors: Don't Forget the Fuel.

T-cells play a critical role in tumor immunity. Indeed, the presence of tumor-infiltrating lymphocytes is a predictor of favorable patient prognosis for many indications and is a requirement for responsiveness to immune checkpoint blockade therapy targeting programmed cell death 1. For tumors lacking immune infiltrate, or for which antigen processing and/or presentation has been downregulated, a promising immunotherapeutic approach is chimeric antigen receptor (CAR) T-cell therapy. CARs are hybrid receptors that link the tumor antigen specificity and affinity of an antibody-derived single-chain variable fragment with signaling endodomains associated with T-cell activation. CAR therapy targeting CD19 has yielded extraordinary clinical responses against some hematological tumors. Solid tumors, however, remain an important challenge to CAR T-cells due to issues of homing, tumor vasculature and stromal barriers, and a range of obstacles in the tumor bed. Protumoral immune infiltrate including T regulatory cells and myeloid-derived suppressor cells have been well characterized for their ability to upregulate inhibitory receptors and molecules that hinder effector T-cells. A critical role for metabolic barriers in the tumor microenvironment (TME) is emerging. High glucose consumption and competition for key amino acids by tumor cells can leave T-cells with insufficient energy and biosynthetic precursors to support activities such as cytokine secretion and lead to a phenotypic state of anergy or exhaustion. CAR T-cell expansion protocols that promote a less differentiated phenotype, combined with optimal receptor design and coengineering strategies, along with immunomodulatory therapies that also promote endogenous immunity, offer great promise in surmounting immunometabolic barriers in the TME and curing solid tumors.

Hypoxia and antitumor CD8+ T cells: An incompatible alliance?

T Lymphocytes face pathologically low O2 tensions within the tumor bed at which they will have to function in order to impact on the malignancy. Recent studies highlighting the importance of O2 and hypoxia-inducible factors for CD8+ T-cell function and fate must now be integrated into tumor immunology concepts if immunotherapies are to progress. Here, we discuss, reinterpret, and reconcile the many apparent contradictions in these data and we propose that O2 is a master regulator of the CD8+ T-cell response. Certain T cell functions are enhanced, others suppressed, but on balance, hypoxia is globally detrimental to the antitumor response.

Decitabine Treatment of Glioma-Initiating Cells Enhances Immune Recognition and Killing.

Malignant gliomas are aggressive brain tumours with very poor prognosis. The majority of glioma cells are differentiated (glioma-differentiated cells: GDCs), whereas the smaller population (glioma-initiating cells, GICs) is undifferentiated and resistant to conventional therapies. Therefore, to better target this pool of heterogeneous cells, a combination of diverse therapeutic approaches is envisaged. Here we investigated whether the immunosensitising properties of the hypomethylating agent decitabine can be extended to GICs. Using the murine GL261 cell line, we demonstrate that decitabine augments the expression of the death receptor FAS both on GDCs and GICs. Interestingly, it had a higher impact on GICs and correlated with an enhanced sensitivity to FASL-mediated cell death. Moreover, the expression of other critical molecules involved in cognate recognition by cytotoxic T lymphocytes, MHCI and ICAM-1, was upregulated by decitabine treatment. Consequently, T-cell mediated killing of both GDCs and GICs was enhanced, as was T cell proliferation after reactivation. Overall, although GICs are described to resist classical therapies, our study shows that hypomethylating agents have the potential to enhance glioma cell recognition and subsequent destruction by immune cells, regardless of their differentiation status. These results support the development of combinatorial treatment modalities including epigenetic modulation together with immunotherapy in order to treat heterogenous malignancies such as glioblastoma.

Myeloid-derived suppressor cells: mechanisms of action and recent advances in their role in transplant tolerance.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature hematopoietic precursors known to suppress immune responses in infection, chronic inflammation, cancer, and autoimmunity. In this paper, we review recent findings detailing their mode of action and discuss recent reports that suggest that MDSC are also expanded during transplantation and that modulation of MDSC can participate in preventing graft rejection as well as graft-versus-host disease.

Myeloid-derived suppressor cells accumulate in kidney allograft tolerance and specifically suppress effector T cell expansion.

The immune tolerance to rat kidney allografts induced by a perioperative treatment with anti-CD28 Abs is associated with a severe unresponsiveness of peripheral blood cells to donor Ags. In this model, we identified an accumulation in the blood of CD3(-)class II(-)CD11b(+)CD80/86(+) plastic-adherent cells that additionally expressed CD172a as well as other myeloid markers. These cells were able to inhibit proliferation, but not activation, of effector T cells and to induce apoptosis in a contact-dependent manner. Their suppressive action was found to be under the control of inducible NO synthase, an enzyme also up-regulated in tolerated allografts. Based on these features, these cells can be defined as myeloid-derived suppressor cells (MDSC). Interestingly, CD4(+)CD25(high)FoxP3(+) regulatory T cells were insensitive in vitro to MDSC-mediated suppression. Although the adoptive transfer of MDSC failed to induce kidney allograft tolerance in recently transplanted recipients, the maintenance of tolerance after administration of anti-CD28 Abs was found to be dependent on the action of inducible NO synthase. These results suggest that increased numbers of MDSC can inhibit alloreactive T cell proliferation in vivo and that these cells may participate in the NO-dependent maintenance phase of tolerance.