Immunomodulatory Functions of BTLA and HVEM Govern Induction of Extrathymic Regulatory T Cells and Tolerance by Dendritic Cells.

Dendritic cells (DCs) initiate immunity and also antigen-specific tolerance mediated by extrathymic regulatory T (Treg) cells, yet it remains unclear how DCs regulate induction of such tolerance. Here, we report that efficient induction of Treg cells was instructed by BTLA+DEC205+CD8+CD11c+ DCs and the immunomodulatory functions of BTLA. In contrast, T cell activation in steady state by total CD11c+ DCs that include a majority of DCs that do not express BTLA did not induce Treg cells and had no lasting impact on subsequent immune responses. Engagement of HVEM, a receptor of BTLA, promoted Foxp3 expression in T cells through upregulation of CD5. In contrast, T cells activated in the absence of BTLA and HVEM-mediated functions remained CD5lo and therefore failed to resist the inhibition of Foxp3 expression in response to effector cell-differentiating cytokines. Thus, DCs require BTLA and CD5-dependent mechanisms to actively adjust tolerizing T cell responses under steady-state conditions.

Single-cell analysis of peripheral CD8+ T cell responses in patients receiving checkpoint blockade immunotherapy for cancer.

Checkpoint blockade immunotherapy has become a first-line treatment option for cancer patients, with success in increasingly diverse cancer types. Still, many patients do not experience durable responses and the reasons for clinical success versus failure remain largely undefined. Investigation of immune responses within the tumor microenvironment can be highly informative but access to tumor tissue is not always available, highlighting the need to identify biomarkers in the blood that correlate with clinical success. Here, we used single-cell RNA sequencing coupled with T cell receptor sequencing to define CD8+ T cell responses in peripheral blood of two patients with melanoma before and after immunotherapy with either anti-PD-1 (nivolumab) alone or the combination of anti-PD-1 and CTLA-4 (ipilimumab). Both treatment regimens increased transcripts associated with cytolytic effector function and decreased transcripts associated with naive T cells. These responses were further evaluated at the protein level and extended to a total of 53 patients with various cancer types. Unexpectedly, the induction of CD8+ T cell responses associated with cytolytic function was variable and did not predict therapeutic success in this larger patient cohort. Rather, a decrease in the frequency of T cells with a naive-like phenotype was consistently observed after immunotherapy and correlated with prolonged patient survival. In contrast, a more detailed clonotypic analysis of emerging and expanding CD8+ T cells in the blood revealed that a majority of individual T cell clones responding to immunotherapy acquired a transcriptional profile consistent with cytolytic effector function. These results suggest that responses to checkpoint blockade immunotherapy are evident and traceable in patients' blood, with outcomes predicted by the simultaneous loss of naive-like CD8+ T cells and the expansion of mostly rare and diverse cytotoxic CD8+ T cell clones.

Checkpoint blockade immunotherapy enhances the frequency and effector function of murine tumor-infiltrating T cells but does not alter TCRß diversity.

Checkpoint blockade immunotherapy is now a first-line treatment option for patients with melanoma. Despite achieving objective responses in about half of patients, the exact immune mechanisms elicited and those required for therapeutic success have not been clearly identified. Insight into these mechanisms is key for improving outcomes in a broader range of cancer patients. We used a murine melanoma model to track responses by different subsets of tumor-infiltrating lymphocytes (TIL) during checkpoint blockade immunotherapy. Tumors from treated mice had increased frequencies of both CD4+ and CD8+ T cells, which also showed evidence of functional reinvigoration and elevated effector cytokine production after immunotherapy. We predicted that increased T cell numbers and function within tumors reflected either infiltration by new T cells or clonal expansion by a few high-affinity tumor-reactive T cells. To address this, we compared TIL diversity before and after immunotherapy by sequencing the complementarity determining region 3 (CDR3) of all T cell receptor beta (TCRß) genes. While checkpoint blockade effectively slowed tumor progression and increased T cell frequencies, the diversity of intratumoral T cells remained stable. This was true when analyzing total T cells and when focusing on smaller subsets of effector CD4+ and CD8+ TIL as well as regulatory T cells. Our study suggests that checkpoint blockade immunotherapy does not broaden the T cell repertoire within murine melanoma tumors, but rather expands existing T cell populations and enhances effector capabilities.

Adapting Cancer Immunotherapy Models for the Real World.

Early experiments in mice predicted the success of checkpoint blockade immunotherapy in cancer patients. However, these same animal studies failed to accurately predict many of the limitations and toxicities of treatment. One of the likely reasons for this discrepancy is the nearly universal use of young healthy mice, which stand in stark contrast to diverse patient populations varying in age, weight, diet, and hygiene. Because these variables impact immunity and metabolism, they also influence outcomes during immunotherapy and should be incorporated into the study design of preclinical experiments. Here, we discuss recent findings that highlight how efficacy and toxicity of cancer immunotherapy are affected by patient variation, and how distinct host environments can be better modeled in animal studies.

Peripheral CD8+ T cell tolerance to self-proteins is regulated proximally at the T cell receptor.

CD8(+) T cell tolerance, although essential for preventing autoimmunity, poses substantial obstacles to eliciting immune responses to tumor antigens, which are generally overexpressed normal proteins. Development of effective strategies to overcome tolerance for clinical applications would benefit from elucidation of the immunologic mechanism(s) regulating T cell tolerance to self. To examine how tolerance is maintained in vivo, we engineered dual-T cell receptor (TCR) transgenic mice in which CD8(+) T cells recognize two distinct antigens: a foreign viral-protein and a tolerizing self-tumor protein. Encounter with peripheral self-antigen rendered dual-TCR T cells tolerant to self, but these cells responded normally through the virus-specific TCR. Moreover, proliferation induced by virus rescued function of tolerized self-tumor-reactive TCR, restoring anti-tumor activity. These studies demonstrate that peripheral CD8(+) T cell tolerance to self-proteins can be regulated at the level of the self-reactive TCR complex rather than by central cellular inactivation and suggest an alternate strategy to enhance adoptive T cell immunotherapy.

T-cell expression of CXCL13 is associated with immunotherapy response in a sex-dependent manner in patients with lung cancer.

Emerging evidence in preclinical models demonstrates that antitumor immunity is not equivalent between males and females. However, more investigation in patients and across a wider range of cancer types is needed to fully understand sex as a variable in tumor immune responses. We investigated differences in T-cell responses between male and female patients with lung cancer by performing sex-based analysis of single cell transcriptomic datasets. We found that the transcript encoding CXC motif chemokine ligand 13 (CXCL13), which has recently been shown to correlate with T-cell tumor specificity, is expressed at greater levels in T cells isolated from female compared to male patients. Furthermore, increased expression of CXCL13 was associated with response to PD-1-targeting immunotherapy in female but not male patients. These findings suggest that there are sex-based differences in T-cell function required for response to anti-PD-1 therapy in lung cancer that may need to be considered during patient treatment decisions.

Obesity-related T cell dysfunction impairs immunosurveillance and increases cancer risk.

Obesity is a well-established risk factor for human cancer, yet the underlying mechanisms remain elusive. Immune dysfunction is commonly associated with obesity but whether compromised immune surveillance contributes to cancer susceptibility in individuals with obesity is unclear. Here we use a mouse model of diet-induced obesity to investigate tumor-infiltrating CD8 + T cell responses in lean, obese, and previously obese hosts that lost weight through either dietary restriction or treatment with semaglutide. While both strategies reduce body mass, only dietary intervention restores T cell function and improves responses to immunotherapy. In mice exposed to a chemical carcinogen, obesity-related immune dysfunction leads to higher incidence of sarcoma development. However, impaired immunoediting in the obese environment enhances tumor immunogenicity, making the malignancies highly sensitive to immunotherapy. These findings offer insight into the complex interplay between obesity, immunity and cancer, and provide explanation for the obesity paradox observed in clinical immunotherapy settings.

CD8+ T cell exhaustion during persistent viral infection is regulated independently of the virus-specific T cell receptor.

During chronic viral infections, responses by virus-specific CD8(+) T cells become marginalized by the acquisition of functional defects and reduced cell numbers in a process defined as T cell exhaustion. Similarly, T cell tolerance to self-antigen is also characterized by impaired effector function and eventual deletion of self-reactive T cells. Induction of both tolerance and exhaustion involve many shared inhibitory mechanisms, thus similar therapeutic approaches have proven effective in these distinct environments. We previously demonstrated that tolerant self-reactive CD8(+) T cells expressing dual-T cell receptors (i.e., dual-TCR) could be rescued by immunization through a second TCR specific for a foreign antigen. These data revealed that T cell tolerance was regulated at the level of the self-reactive TCR. Here, dual-TCR CD8(+) T cells were used to examine if exhaustion during persistent viral infection could be rescued by an analogous strategy of immunization through a second TCR not involved in recognition of virus. In direct contrast to the rescue achievable in tolerant CD8(+) T cells, exhausted T cells were equally impaired through both TCR. These findings suggest that exhaustion is maintained by defects downstream of the virus-specific TCR, and establish that exhaustion and tolerance are distinctly regulated states of T cell dysfunction.

Antigen-specific TGF-ß-induced regulatory T cells secrete chemokines, regulate T cell trafficking, and suppress ongoing autoimmunity.

The ability to regulate ongoing inflammation using regulatory T cells (Tregs) is under intense investigation. Strategies to induce and expand Ag-specific Tregs are being developed, and whether various types of Tregs are suppressive in the inflammatory conditions associated with ongoing disease needs to be determined. In this study, we report that TGF-ß-induced Tregs (iTregs) and expanded Tregs specific for a major self-Ag in autoimmune gastritis suppress inflammation and associated pathology when administered late in the process of ongoing disease. Transferred iTregs localized to the stomach, maintained Foxp3 and suppressor functions, and engaged several distinct mechanisms to alleviate disease progression. In addition to suppressing the production of inflammatory cytokines in the stomach and preventing the destruction of parietal cells, we show that iTregs secrete numerous chemokines and regulate both iTreg and effector T cell trafficking into the stomach. These data support efforts to use iTregs in therapies to treat autoimmunity and inflammatory diseases and provide novel insight into the biological mechanisms of iTreg-mediated immune suppression.

Interleukin-15 rescues tolerant CD8+ T cells for use in adoptive immunotherapy of established tumors.

CD8+ T cells can mediate eradication of established tumors, and strategies to amplify tumor-reactive T-cell numbers by immunization or ex vivo expansion followed by adoptive transfer are currently being explored in individuals with cancer. Generating effective CD8+ T cell-mediated responses to tumors is often impeded by T-cell tolerance to relevant tumor antigens, as most of these antigens are also expressed in normal tissues. We examined whether such tolerant T cells could be rescued and functionally restored for use in therapy of established tumors. We used a transgenic T-cell receptor (TCR) mouse model in which peripheral CD8+ T cells specific for a candidate tumor antigen also expressed in liver are tolerant, failing to proliferate or secrete interleukin (IL)-2 in response to antigen. Molecular and cellular analysis showed that these tolerant T cells expressed the IL-15 receptor alpha chain, and could be induced to proliferate in vitro in response to exogenous IL-15. Such proliferation abrogated tolerance and the rescued cells became effective in treating leukemia. Therefore, high-affinity CD8+ T cells are not necessarily deleted by encounter with self-antigen in the periphery, and can potentially be rescued and expanded for use in tumor immunotherapy.

Interactions of azole-based inhibitors with human heme oxygenase.

Human heme oxygenase-1 (hHO-1) plays a crucial role in human physiology because of its ability to metabolize free heme. The heme degradation products, biliverdin and bilirubin, were shown to have protective antioxidant properties in cells. In the context of cancer, hHO-1 function grants cancer cells defense from standard chemotherapy treatments, leading to the development of azole-based inhibitors that target hHO-1 for potential anticancer therapy. This work reports experimental and theoretical characterization of interactions between three azole-based inhibitors and the active site of hHO-1. It was found that all three compounds have Kd values within the µM order. The electronic absorption and resonance Raman (rR) spectra indicated that they bind to the ferric heme and coordinate through a nitrogen atom. rR measurements revealed varying effects of inhibitors on the geometry of heme vinyl groups in the ferric form of hHO-1. Changes in peripheral group orientation are known to affect heme redox potential, and consequently can reflect the inhibitory properties of studied azoles. The subsequent docking studies showed that inhibitors with lower Kd values are located close to two vinyl groups, while the compound with higher Kd is situated near only one, consistent with the rR studies. Finally, the rR studies of the CO adducts showed that the inhibitors bind to the heme in a reversible manner. Altogether, the combination of ligand binding studies, UV-Vis and rR spectroscopies, as well as computational approach revealed an importance of the steric hindrance imposed by the inhibitor's side chain.

Survival in Metastatic Renal Cell Carcinoma Treated With Immunotherapy and Stereotactic Radiation Therapy or Immunotherapy Alone: A National Cancer Database Analysis.

Purpose: Immunotherapy (IO) has significantly improved outcomes in metastatic renal cell carcinoma (mRCC). Preclinical evidence suggests that responses to IO may be potentiated via immunomodulatory effects of stereotactic radiation therapy (SRT). We hypothesized that clinical outcomes from the National Cancer Database (NCDB) would demonstrate improved overall survival (OS) in patients with mRCC receiving IO + SRT versus IO alone. Methods and Materials: Patients with mRCC receiving first-line IO ± SRT were identified from the NCDB. Conventional radiation therapy was allowed in the IO alone cohort. The primary endpoint was OS stratified by the receipt of SRT (IO + SRT vs IO alone). Secondary endpoints included OS stratified by the presence of brain metastases (BM) and timing of SRT (before or after IO). Survival was estimated using Kaplan-Meier methodology and compared via the log-rank test. Results: Of 644 eligible patients, 63 (9.8%) received IO + SRT, and 581 (90.2%) received IO alone. Median follow-up time was 17.7 months (range, 2-24 months). Sites treated with SRT included the brain (71.4%), lung/chest (7.9%), bones (7.9%), spine (6.3%), and other (6.3%). OS was 74.4% versus 65.0% at 1 year and 71.0% versus 59.4% at 2 years for the IO + SRT and IO alone groups, respectively, although this difference did not reach statistical significance (log-rank P = .1077). In patients with BM, however, 1-year OS (73.0% vs 54.7%) and 2-year OS (70.8% vs 51.4%) was significantly higher in those receiving IO + SRT versus IO alone, respectively (pairwise P = .0261). Timing of SRT (before or after IO) did not influence OS (log-rank P = .3185). Conclusions: Patients with BM secondary to mRCC had prolonged OS with the addition of SRT to IO. Factors such as International mRCC Database Consortium risk stratification, oligometastatic tumor burden, SRT dose/fractionation, and utilization of doublet therapy should be considered in future analyses to better identify patients who may benefit from combined IO + SRT. Further prospective studies are warranted.

Overall survival in advanced hepatocellular carcinoma treated with concomitant systemic therapy and stereotactic body radiation therapy or systemic therapy alone.

Introduction: First-line systemic therapy (ST) options for advanced hepatocellular carcinoma (HCC) include tyrosine kinase inhibitors and immunotherapy (IO). Evolving data suggest prolonged overall survival (OS) when ST is combined with stereotactic body radiation therapy (SBRT), although evidence is significantly limited in HCC populations. We hypothesized that advanced HCC patients in the National Cancer Database (NCDB) would have improved OS when receiving ST+SBRT vs ST alone. Methods: Stage III/IV HCC patients diagnosed from 2010-2020 and treated with first-line ST±SBRT were identified from the NCDB. The primary endpoint was OS from date of diagnosis stratified by the receipt of SBRT (ST+SBRT vs ST alone). Survival was estimated using Kaplan-Meier methodology and compared via log-rank. Multivariate analysis (MVA) was performed by Cox regression. Results: Of 10,505 eligible patients with stage III disease, 115 (1.1%) received ST+SBRT and 10,390 (98.9%) received ST alone. Of 9,617 eligible patients with stage IV disease, 127 (1.3%) received ST+SBRT and 9,490 (98.7%) received ST alone. Median follow-up time was 6.8 months. Baseline characteristics were similar between cohorts. Patients with stage III disease receiving ST+SBRT had improved median OS (12.62 months vs 8.38 months) and higher rates of survival at 1-year (53.0% vs 38.7%) and 2-years (27.0% vs 20.7%) compared to those receiving ST alone (log-rank P=0.0054). Similarly, patients with stage IV disease receiving ST+SBRT had improved median OS (11.79 months vs 5.72 months) and higher rates of survival at 1-year (49.6% vs 26.2%) and 2-years (23.6% vs 12.0%) (log-rank P<0.0001). On MVA, receipt of SBRT predicted improved OS (HR=0.748, 95%CI 0.588-0.951; P=0.0178) and receipt of IO trended towards improved OS (HR=0.859, 95%CI 0.735-1.003; P=0.0538). Conclusion: In advanced HCC, patients receiving ST+SBRT had improved OS compared to those receiving ST alone. Prospective clinical trials are warranted to better identify HCC populations which may benefit from combined modality therapy.

Immune responses to SARS-CoV-2 in vaccinated patients receiving checkpoint blockade immunotherapy for cancer.

Vaccination against SARS-CoV-2 has been successful in protecting patients with cancer from severe infections, but how immune responses against COVID-19 vaccination interact with those elicited during cancer immunotherapy has not been fully described. Immune checkpoint blockade (ICB) disrupts inhibitory pathways in immune cells to improve function and induce tumor immunity but can often cause serious immune related adverse events (IRAEs). Because COVID-19 vaccination and ICB both boost immune responses, it is imperative to understand if combining these regimens causes synergistic enhancement of the immune system. Specifically, whether ICB impacts anti-vaccine immunity in previously vaccinated patients is important since a large percentage of newly diagnosed cancer patients eligible for immunotherapy will have already been vaccinated against COVID-19. To address this, we investigated the influence of ICB on SARS-CoV-2-spike protein (SP) antibody titers and T cell responses in cancer patients previously vaccinated against COVID-19. Human blood samples were collected from 29 vaccinated patients and 12 unvaccinated control patients at baseline (prior to ICB) and following two rounds of ICB infusion. Anti-SARS-CoV-2-SP IgG titers and T cell responses were quantified. Compared to responses at baseline, there was no significant difference in these immune responses after immunotherapy in vaccinated individuals (P=0.4583, P=0.4571, respectively). We interpret these results as evidence that ICB immunotherapy does not significantly enhance SARS-CoV-2-specific antibody titers or T cell responses. Although our study lacks corresponding IRAE rates, the results provide humoral and cellular immunological data that support recent reports documenting the clinical safety and efficacy of COVID-19 vaccination in patients receiving ICB. Additional longitudinal prospective studies, such as the VOICE study (ClinicalTrials.gov identifier NCT04715438) and CAPTURE study (ClinicalTrials.gov identifier NCT03226886), are warranted and will provide broader safety and immunological data defining the effect of systemic cancer therapies on COVID-19 immunity.

Oxidized Lipoproteins Promote Resistance to Cancer Immunotherapy Independent of Patient Obesity.

Antitumor immunity is impaired in obese mice. Mechanistic insight into this observation remains sparse and whether it is recapitulated in patients with cancer is unclear because clinical studies have produced conflicting and controversial findings. We addressed this by analyzing data from patients with a diverse array of cancer types. We found that survival after immunotherapy was not accurately predicted by body mass index or serum leptin concentrations. However, oxidized low-density lipoprotein (ox-LDL) in serum was identified as a suppressor of T-cell function and a driver of tumor cytoprotection mediated by heme oxygenase-1 (HO-1). Analysis of a human melanoma gene expression database showed a clear association between higher HMOX1 (HO-1) expression and reduced progression-free survival. Our in vivo experiments using mouse models of both melanoma and breast cancer revealed HO-1 as a mechanism of resistance to anti-PD1 immunotherapy but also exposed HO-1 as a vulnerability that could be exploited therapeutically using a small-molecule inhibitor. In conclusion, our clinical data have implicated serum ox-LDL as a mediator of therapeutic resistance in patients with cancer, operating as a double-edged sword that both suppressed T-cell immunity and simultaneously induced HO-1-mediated tumor cell protection. Our studies also highlight the therapeutic potential of targeting HO-1 during immunotherapy, encouraging further translational development of this combination approach.See article by Kuehm et al., p. 227.

Fructose Promotes Cytoprotection in Melanoma Tumors and Resistance to Immunotherapy.

Checkpoint blockade immunotherapy relies on the empowerment of the immune system to fight cancer. Why some patients fail to achieve durable clinical responses is not well understood, but unique individual factors such as diet, obesity, and related metabolic syndrome could play a role. The link between obesity and patient outcomes remains controversial and has been mired by conflicting reports and limited mechanistic insight. We addressed this in a C57BL/6 mouse model of diet-induced obesity using a Western diet high in both fats and sugars. Obese mice bearing B16 melanoma or MC38 carcinoma tumors had impaired immune responses to immunotherapy and a reduced capacity to control tumor progression. Unexpectedly, these compromised therapeutic outcomes were independent of body mass and, instead, were directly attributed to dietary fructose. Melanoma tumors in mice on the high-fructose diet were resistant to immunotherapy and showed increased expression of the cytoprotective enzyme heme oxygenase-1 (HO-1). This increase in HO-1 protein was recapitulated in human A375 melanoma cells exposed to fructose in culture. Induced expression of HO-1 shielded tumor cells from immune-mediated killing and was critical for resistance to checkpoint blockade immunotherapy, which could be overcome in vivo using a small-molecule inhibitor of HO-1. This study reveals dietary fructose as a driver of tumor immune evasion, identifying HO-1 expression as a mechanism of resistance and a promising molecular target for combination cancer immunotherapy.See article by Khojandi et al., p. 214.

Adoptive immunotherapy of disseminated leukemia with TCR-transduced, CD8+ T cells expressing a known endogenous TCR.

Adoptive T-cell immunotherapy has shown promise in the treatment of human malignancies, but the challenge of isolating T cells with high avidity for tumor antigens in each patient has limited application of this approach. The transfer into T cells of T-cell receptor (TCR) genes encoding high-affinity TCRs recognizing defined tumor-associated antigens can potentially circumvent this obstacle. Using a well-characterized murine model of adoptive T-cell immunotherapy for widely disseminated leukemia, we demonstrate that TCR gene-modified T cells can cure mice of disseminated tumor. One goal of such adoptive therapy is to establish a persistent memory response to prevent recurrence; however, long-term function of transferred TCR-transduced T cells is limited due to reduced expression of the introduced TCR in vivo in quiescent resting T cells. However, by introducing the TCR into a cell with a known endogenous specificity, activation of these T cells by stimulation through the endogenous TCR can be used to increase expression of the introduced TCR, potentially providing a strategy to increase the total number of tumor-reactive T cells in the host and restore more potent antitumor activity.

Interleukin 27 Protects From Gastric Atrophy and Metaplasia During Chronic Autoimmune Gastritis.

BACKGROUND & AIMS: The association between chronic inflammation and gastric carcinogenesis is well established, but it is not clear how immune cells and cytokines regulate this process. We investigated the role of interleukin 27 (IL27) in the development of gastric atrophy, hyperplasia, and metaplasia (preneoplastic lesions associated with inflammation-induced gastric cancer) in mice with autoimmune gastritis. METHODS: We performed studies with TxA23 mice (control mice), which express a T-cell receptor against the H+/K+ adenosine triphosphatase α chain and develop autoimmune gastritis, and TxA23xEbi3-/- mice, which develop gastritis but do not express IL27. In some experiments, mice were given high-dose tamoxifen to induce parietal cell atrophy and spasmolytic polypeptide-expressing metaplasia (SPEM). Recombinant IL27 was administered to mice with mini osmotic pumps. Stomachs were collected and analyzed by histopathology and immunofluorescence; we used flow cytometry to measure IL27 and identify immune cells that secrete IL27 in the gastric mucosa. Single-cell RNA sequencing was performed on immune cells that infiltrated stomach tissues. RESULTS: We identified IL27-secreting macrophages and dendritic cell in the corpus of mice with chronic gastritis (TxA23 mice). Mice deficient in IL27 developed more severe gastritis, atrophy, and SPEM than control mice. Administration of recombinant IL27 significantly reduced the severity of inflammation, atrophy, and SPEM in mice with gastritis. Single-cell RNA sequencing showed that IL27 acted almost exclusively on stomach-infiltrating CD4+ T cells to suppress expression of inflammatory genes. CONCLUSIONS: In studies of mice with autoimmune gastritis, we found that IL27 is an inhibitor of gastritis and SPEM, suppressing CD4+ T-cell-mediated inflammation in the gastric mucosa.

Rescue of Tolerant CD8+ T Cells during Cancer Immunotherapy with IL2:Antibody Complexes.

Interleukin-2 (IL2) was among the earliest reagents used for cancer immunotherapy due to its ability to support the survival and function of tumor-reactive T cells. However, treatment with IL2 is accompanied by off-target toxicity and low response rates in patients. In mouse models, these issues are largely overcome when IL2 is administered as a cytokine/antibody complex (IL2c). The complex has a longer serum half-life and can be designed for preferential cytokine delivery to specific cells of interest. Early studies showed IL2c could boost antitumor immunity in mice by activating tumor-reactive CD8+ T cells. But such functional T cells are often limited in the tumor microenvironment, where instead unresponsive tolerant T cells are eventually eliminated by apoptosis, representing a major obstacle to the success of cancer immunotherapy. We found that IL2c treatment rescued tumor-specific CD8+ T cells from a state of established tolerance, providing effective immunotherapy in tumor-bearing mice. Expression of the transcription factor T-bet was necessary to drive intratumoral IFNγ production and effector activity by T cells rescued with IL2c. Furthermore, IL2c promoted T-bet expression in human CD4+ and CD8+ T cells in humanized tumor-bearing mice, but also increased the frequency of Foxp3+ regulatory T cells. Our study reveals a novel role for IL2c as a powerful immunotherapeutic reagent capable of reversing tolerance in tumor-reactive T cells, and provides the first evidence that IL2c influences human T cells in vivo, highlighting the translational potential to modulate human antitumor immune responses. Cancer Immunol Res; 4(12); 1016-26. ©2016 AACR.

Checkpoint blockade immunotherapy relies on T-bet but not Eomes to induce effector function in tumor-infiltrating CD8+ T cells.

Coinhibitory receptor blockade is a promising strategy to boost T-cell immunity against a variety of human cancers. However, many patients still do not benefit from this treatment, and responders often experience immune-related toxicities. These issues highlight the need for advanced mechanistic understanding to improve patient outcomes and uncover clinically relevant biomarkers of treatment efficacy. However, the T-cell-intrinsic signaling pathways engaged during checkpoint blockade treatment are not well defined, particularly for combination approaches. Using a murine model to study how effector CD8(+) T-cell responses to tumors may be enhanced in a tolerizing environment, we identified a critical role for the T-box transcription factor T-bet. Combination blockade of CTLA-4, PD-1, and LAG-3 induced T-bet expression in responding tumor/self-reactive CD8(+) T cells. Eradication of established leukemia using this immunotherapy regimen depended on T-bet induction, which was required for IFNγ production and cytotoxicity by tumor-infiltrating T cells, and for efficient trafficking to disseminated tumor sites. These data provide new insight into the success of checkpoint blockade for cancer immunotherapy, revealing T-bet as a key transcriptional regulator of tumor-reactive CD8(+) T-cell effector differentiation under otherwise tolerizing conditions.