Mimicking homeostatic proliferation in vitro generates T cells with high anti-tumor function in non-lymphopenic hosts

Narcissistic T cells: reactivity to self makes a difference

It has been appreciated for more than three decades that the interactions between the T-cell antigen receptor and self-antigens are the major determinants of the cell fates of developing thymocytes and the establishment of central tolerance. However, recent evidence shows that the level of self-reactivity substantially contributes to fate choices of positively selected mature T cells in homeostasis, as well as during immune responses. This implies that individual clones of peripheral T cells are predisposed to specific functional properties based on the self-reactivity of their antigen receptors. Overall, the relative difference in the self-reactivity among peripheral T cells is an important factor contributing to the diversity of T-cell responses to foreign antigens.

Co-transfer of tumor-specific effector and memory CD8+ T cells enhances the efficacy of adoptive melanoma immunotherapy in a mouse model

BACKGROUND

Adoptive cell transfer (ACT) is a promising cancer immunotherapeutic strategy that remains ineffective for a large subset of patients. ACT with memory CD8+ T cells (T_mem) has been shown to have superior efficacy compared to traditional ACT with effector CD8+ T cells (T_eff). T_eff and T_mem have complementary physiological advantages for immunotherapy, but previous publications have not examined ACT using a combination of T_eff and T_mem.

METHODS

Splenocytes harvested from Ly5.1+/C57BL/6 mice during and after infection with lymphocytic choriomeningitis virus (LCMV) were used to generate bona fide effector and memory CD8+ T cells specific for the LCMV epitope peptide GP33. Congenic Ly5.2+/C57BL/6 mice were inoculated with B16F10 melanoma cells transfected to express very low levels of GP33, then treated with ACT 7 days later with GP33-specific T_eff, T_mem, or a combination of T_eff + T_mem.

RESULTS

Inhibition of melanoma growth was strongest in mice receiving combinatorial ACT. Although combinatorial ACT and memory ACT resulted in maximal intratumoral infiltration of CD8+ T cells, combinatorial ACT induced stronger infiltration of endogenous CD8+ T cells than T_mem ACT and a stronger systemic T cell responsiveness to tumor antigen. In vitro assays revealed rapid but transient melanoma inhibition with T_eff and gradual but prolonged melanoma inhibition with T_mem; the addition of T_mem enhanced the ability of T_eff to inhibit melanoma in a manner that could be reproduced using conditioned media from activated T_mem and blocked by the addition of anti-IL-2 blocking antibody.

CONCLUSIONS

These findings suggest that a novel combinatorial approach that takes advantage of the unique and complementary strengths of tumor-specific T_eff and T_mem may be a way to optimize the efficacy of adoptive immunotherapy.

Chemotherapy and immunotherapy: A close interplay to fight cancer?

In theory, the immunotherapy of cancer should induce the selective destruction of cancer cells and a long-term specific protection, based on the specificity and memory of immunity. This contrasts with the collateral damages of conventional therapies and their toxic effects on host tissues. However, recent data suggest that chemotherapy may potentiate ongoing immune responses, through homeostatic mechanisms. Massive tumor death, empty "immune" niches and selected cytokines may act as a danger signal, alerting the immune system and amplifying pre-existing antitumor reactivity.

IL-15 signaling promotes adoptive effector T-cell survival and memory formation in irradiation-induced lymphopenia

Background

Lymphopenia promotes naïve T-cell homeostatic proliferation and adoptive effector T-cell survival and memory formation. IL-7 plays a critical role in homeostatic proliferation, survival and memory formation of naïve T-cells in lymphopenia, and its underlying molecular mechanism has also been well studied. However, the mechanism for adoptively transferred effector T-cell survival and memory formation is not fully understood. Here, we transferred in vitro-activated transgenic OT-I CD8⁺ effector T-cells into irradiation (600 rads)-induced lymphopenic C57BL/6, IL-7 knockout (KO) and IL-15 KO mice, and investigated the survival and memory formation of transferred T-cells in lymphopenia.

Results

We demonstrate that transferred T-cells prolong their survival and enhance their memory in lymphopenic mice, in a manner that depends on IL-15 signaling, but not IL-7. We determine that in vitro stimulation of naïve or effector T-cells with IL-7 and IL-15 reduces IL-7Rα, and increases and/or maintains IL-15Rβ expression, respectively. Consistent with these findings, the expression of IL-7Rα and IL-15Rβ is down- and up-regulated, respectively, in vivo on transferred T-cells in an early phase post T-cell transfer in lymphopenia. We further show that in vitro IL-15 restimulation-induced memory T-cells (compared to IL-2 restimulation-induced effector T-cells) and in vivo transferred T-cells in irradiated IL-15-sufficient C57BL/6 mice (compared to IL-15-deficient IL-15 KO mice) have increased mitochondrial content, but less NADH and lower mitochondrial potential (ΔΨm), and demonstrate greater phosphorylation of signal transducers and activators of transcription-5 (STAT5) and Unc-51-like kinase-1 (ULK1), and higher expression of B-cell leukemia/lymphoma-2 (Bcl2) and memory-, autophagy- and mitochondrial biogenesis-related molecules.

Conclusion

Irradiation-induced lymphopenia promotes effector T-cell survival via IL-15 signaling the STAT5/Bcl2 pathway, enhances T-cell memory formation via IL-15 activation of the forkhead-box family of transcription factor (FOXO)/eomesodermin (Eomes) memory and ULK1/autophagy-related gene-7 (ATG7) autophagy pathways, and via IL-15 activation of the mitochondrial remodeling. Our data thus identify some important targets to consider when designing potent adoptive T-cell immunotherapies of cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13578-016-0098-2) contains supplementary material, which is available to authorized users.

Enhanced local and systemic anti-melanoma CD8+ T cell responses after memory T cell-based adoptive immunotherapy in mice

Adoptive cell transfer (ACT) melanoma immunotherapy typically employs acutely activated effector CD8+ T cells for their ability to rapidly recognize and clear antigen. We have previously observed that effector CD8+ T cells are highly susceptible to melanoma-induced suppression, whereas memory CD8+ T cells are not. Although memory T cells have been presumed to be potentially advantageous for ACT, the kinetics of local and systemic T cell responses after effector and memory ACT have not been compared. B16F10 melanoma cells stably transfected to express very low levels of the lymphocytic choriomeningitis virus (LCMV) peptide GP33 (B16GP33) were inoculated into syngeneic C57BL/6 mice. Equal numbers of bona fide naïve, effector, or memory phenotype GP33-specific CD8+ T cells were adoptively transferred into mice 1 day after B16GP33 inoculation. The efficacy of ACT immunotherapy was kinetically assessed using serial tumor measurements and flow cytometric analyses of local and systemic CD8+ T cell responses. Control of B16GP33 tumor growth, persistence of adoptively transferred CD8+ cells, intratumoral infiltration of CD8+ T cells, and systemic CD8+ T cell responsiveness to GP33 were strongest after ACT of memory CD8+ T cells. Following surgical tumor resection and melanoma tumor challenge, only mice receiving memory T cell-based ACT immunotherapy exhibited durable tumor-specific immunity. These findings demonstrate how the use of non-expanded memory CD8+ T cells may enhance ACT immunotherapeutic efficacy.

Elevated endoplasmic reticulum stress reinforced immunosuppression in the tumor microenvironment via myeloid-derived suppressor cells

The role of endoplasmic reticulum (ER) stress in cancer has been studied in detail, and ER stress is known to increase tumor cell apoptosis, and thus, reduce tumor growth. However, in our study, persistent ER stress induced by multiple administrations of low-dose thapsigargin (Tg) accelerated tumor growth in mice. Tg-mediated ER stress increased the generation of Ly6G⁺CD11b⁺ myeloid cells, but did not alter anti-tumor effector T cells. 4-Phenylbutyric acid (4-PBA), a chemical chaperone widely used as an ER stress reducer, attenuated Tg-induced myeloid-derived suppressor cell (MDSC) expansion and tumor growth. Tg-mediated ER stress enhanced the immunosuppressive capacity of tumor-infiltrating MDSCs by increasing expression of ARG1, iNOS, and NOX2, although splenic MDSCs were not affected. Consistent with these results, 4-PBA restored the anti-tumor immune response by regulating inflammatory cytokines such as TNF-α and CXCL1/KC, and activated tumor-infiltrating CD8⁺ T cells that were inhibited by Tg-mediated ER stress. These results suggest that significant ER stress in a tumor-bearing host might induce tumor growth mediated by enhancement of MDSC-mediated suppression. Therefore, ER stress reducers such as 4-PBA could restore anti-tumor immunity by inhibiting suppressive MDSCs that are exacerbated by ER stress.

Case Report of a Fatal Serious Adverse Event Upon Administration of T Cells Transduced With a MART-1-specific T-cell Receptor

Here, we describe a fatal serious adverse event observed in a patient infused with autologous T-cell receptor (TCR) transduced T cells. This TCR, originally obtained from a melanoma patient, recognizes the well-described HLA-A*0201 restricted 26-35 epitope of MART-1, and was not affinity enhanced. Patient 1 with metastatic melanoma experienced a cerebral hemorrhage, epileptic seizures, and a witnessed cardiac arrest 6 days after cell infusion. Three days later, the patient died from multiple organ failure and irreversible neurologic damage. After T-cell infusion, levels of IL-6, IFN-γ, C-reactive protein (CRP), and procalcitonin increased to extreme levels, indicative of a cytokine release syndrome or T-cell-mediated inflammatory response. Infused T cells could be recovered from blood, broncho-alveolar lavage, ascites, and after autopsy from tumor sites and heart tissue. High levels of NT-proBNP indicate semi-acute heart failure. No cross reactivity of the modified T cells toward a beating cardiomyocyte culture was observed. Together, these observations suggest that high levels of inflammatory cytokines alone or in combination with semi-acute heart failure and epileptic seizure may have contributed substantially to the occurrence of the acute and lethal event. Protocol modifications to limit the risk of T-cell activation-induced toxicity are discussed.

Homeostatic expansion as a barrier to lymphocyte depletion strategies

PURPOSE OF REVIEW

Following lymphodepletion, lymphocytes repopulate the immune space both through enhanced thymopoiesis and proliferation of residual nondepleted peripheral lymphocytes. The term homeostatic proliferation (alternatively homeostatic expansion or lymphopenia-induced proliferation) refers to the latter process. Homeostatic proliferation is especially relevant to reconstitution of the lymphocyte compartment following immunodepletion therapy in transplantation. Repopulating lymphocytes can skew toward an effector memory type capable of inducing graft rejection, autoimmunity, or, in the case of allogeneic bone marrow transplantation, graft versus host disease. Here we review recent studies exploring the biologic mechanisms underlying homeostatic proliferation and explore implications for therapy in transplantation.

RECENT FINDINGS

Two immune-depleting agents, alemtuzumab and rabbit antithymocyte globulin, have been well characterized in their abilities to induce an effector-memory phenotype in repopulating lymphocytes. Additionally, we have gained new understandings of the mechanisms by which the cytokines interleukin-7 and interleukin-15 regulate this process. Recent studies have also explored the functions of noncytokine and signaling molecules in lymphopenia-induced proliferation. Finally, we have seen the promise and limitations of several therapeutic approaches, including recombinant interleukin-7 therapy, CD8-targeted antibodies, and peri-transplant cyclophosphamide, to treat posttransplant lymphopenia and reduce the risks of immune dysregulation following homeostatic proliferation.

SUMMARY

Immune dysfunction following homeostatic proliferation is a special challenge in transplantation. A deeper understanding of the underlying biology has led to a number of promising new therapies to overcome this problem.

IL-18 synergizes with IL-7 to drive slow proliferation of naive CD8 T cells by costimulating self-peptide-mediated TCR signals

Naive T cell populations are maintained in the periphery at relatively constant levels via mechanisms that control expansion and contraction and are associated with competition for homeostatic cytokines. It has been shown that in a lymphopenic environment naive T cells undergo expansion due, at least in part, to additional availability of IL-7. We have previously found that T cell-intrinsic deletion of TNFR-associated factor (TRAF) 6 (TRAF6ΔT) in mice results in diminished peripheral CD8 T cell numbers. In this study, we report that whereas naive TRAF6ΔT CD8 T cells exhibit normal survival when transferred into a normal T cell pool, proliferation of naive TRAF6ΔT CD8 T cells under lymphopenic conditions is defective. We identified IL-18 as a TRAF6-activating factor capable of enhancing lymphopenia-induced proliferation (LIP) in vivo, and that IL-18 synergizes with high-dose IL-7 in a TRAF6-dependent manner to induce slow, LIP/homeostatic-like proliferation of naive CD8 T cells in vitro. IL-7 and IL-18 act synergistically to upregulate expression of IL-18R genes, thereby enhancing IL-18 activity. In this context, IL-18R signaling increases PI3K activation and was found to sensitize naive CD8 T cells to a model noncognate self-peptide ligand in a way that conventional costimulation via CD28 could not. We propose that synergistic sensitization by IL-7 and IL-18 to self-peptide ligand may represent a novel costimulatory pathway for LIP.