Preclinical evaluation and first-in-dog clinical trials of PBMC-expanded natural killer cells for adoptive immunotherapy in dogs with cancer

BACKGROUND

Natural killer (NK) cells are cytotoxic cells capable of recognizing heterogeneous cancer targets without prior sensitization, making them promising prospects for use in cellular immunotherapy. Companion dogs develop spontaneous cancers in the context of an intact immune system, representing a valid cancer immunotherapy model. Previously, CD5 depletion of peripheral blood mononuclear cells (PBMCs) was used in dogs to isolate a CD5dim-expressing NK subset prior to co-culture with an irradiated feeder line, but this can limit the yield of the final NK product. This study aimed to assess NK activation, expansion, and preliminary clinical activity in first-in-dog clinical trials using a novel system with unmanipulated PBMCs to generate our NK cell product.

METHODS

Starting populations of CD5-depleted cells and PBMCs from healthy beagle donors were co-cultured for 14 days, phenotype, cytotoxicity, and cytokine secretion were measured, and samples were sequenced using the 3'-Tag-RNA-Seq protocol. Co-cultured human PBMCs and NK-isolated cells were also sequenced for comparative analysis. In addition, two first-in-dog clinical trials were performed in dogs with melanoma and osteosarcoma using autologous and allogeneic NK cells, respectively, to establish safety and proof-of-concept of this manufacturing approach.

RESULTS

Calculated cell counts, viability, killing, and cytokine secretion were equivalent or higher in expanded NK cells from canine PBMCs versus CD5-depleted cells, and immune phenotyping confirmed a CD3-NKp46+ product from PBMC-expanded cells at day 14. Transcriptomic analysis of expanded cell populations confirmed upregulation of NK activation genes and related pathways, and human NK cells using well-characterized NK markers closely mirrored canine gene expression patterns. Autologous and allogeneic PBMC-derived NK cells were successfully expanded for use in first-in-dog clinical trials, resulting in no serious adverse events and preliminary efficacy data. RNA sequencing of PBMCs from dogs receiving allogeneic NK transfer showed patient-unique gene signatures with NK gene expression trends in response to treatment.

CONCLUSIONS

Overall, the use of unmanipulated PBMCs appears safe and potentially effective for canine NK immunotherapy with equivalent to superior results to CD5 depletion in NK expansion, activation, and cytotoxicity. Our preclinical and clinical data support further evaluation of this technique as a novel platform for optimizing NK immunotherapy in dogs.

Para-infectious brain injury in COVID-19 persists at follow-up despite attenuated cytokine and autoantibody responses

To understand neurological complications of COVID-19 better both acutely and for recovery, we measured markers of brain injury, inflammatory mediators, and autoantibodies in 203 hospitalised participants; 111 with acute sera (1-11 days post-admission) and 92 convalescent sera (56 with COVID-19-associated neurological diagnoses). Here we show that compared to 60 uninfected controls, tTau, GFAP, NfL, and UCH-L1 are increased with COVID-19 infection at acute timepoints and NfL and GFAP are significantly higher in participants with neurological complications. Inflammatory mediators (IL-6, IL-12p40, HGF, M-CSF, CCL2, and IL-1RA) are associated with both altered consciousness and markers of brain injury. Autoantibodies are more common in COVID-19 than controls and some (including against MYL7, UCH-L1, and GRIN3B) are more frequent with altered consciousness. Additionally, convalescent participants with neurological complications show elevated GFAP and NfL, unrelated to attenuated systemic inflammatory mediators and to autoantibody responses. Overall, neurological complications of COVID-19 are associated with evidence of neuroglial injury in both acute and late disease and these correlate with dysregulated innate and adaptive immune responses acutely.

Regulation of human and mouse bystander T cell activation responses by PD-1

Bystander activation of memory T cells occurs via cytokine signaling alone in the absence of T cell receptor (TCR) signaling and provides a means of amplifying T cell effector responses in an antigen-nonspecific manner. While the role of Programmed Cell Death Protein 1 (PD-1) on antigen-specific T cell responses is extensively characterized, its role in bystander T cell responses is less clear. We examined the role of the PD-1 pathway during human and mouse non-antigen-specific memory T cell bystander activation and observed that PD-1+ T cells demonstrated less activation and proliferation than activated PD-1- populations in vitro. Higher activation and proliferative responses were also observed in the PD-1- memory population in both mice and patients with cancer receiving high-dose IL-2, mirroring the in vitro phenotypes. This inhibitory effect of PD-1 could be reversed by PD-1 blockade in vivo or observed using memory T cells from PD-1-/- mice. Interestingly, increased activation through abrogation of PD-1 signaling in bystander-activated T cells also resulted in increased apoptosis due to activation-induced cell death (AICD) and eventual T cell loss in vivo. These results demonstrate that the PD-1/PD-Ligand 1 (PD-L1) pathway inhibited bystander-activated memory T cell responses but also protected cells from AICD.

Intratumoral NKp46+ natural killer cells are spatially distanced from T and MHC-I+ cells with prognostic implications in soft tissue sarcoma

Introduction

Soft tissue sarcomas (STS) are rare, heterogenous malignancies with an unmet need for novel immunotherapies. Tumor infiltrating lymphocytes (TILs) have been linked with favorable outcomes in STS patients, though the contribution of natural killer (NK) cells and spatial relationships of TILs with MHC-I expressing cells lacks detailed characterization.

Experimental design

Using archived and prospectively collected specimens, we evaluated intratumoral NK cells by immunohistochemistry (IHC), flow cytometry, and immunofluorescence (IF). We assessed spatial localization of NK and T cells by multiplex IF, analyzing the effects of MHC-I expression status on NK and T cell clustering.

Results

Both intratumoral NKp46 and CD56dim expression were associated with significantly improved overall survival (P=0.05), while higher infiltrates of CD56bright NK cells predicted a worse prognosis (P=0.05). The presence of intratumoral NK cells was inversely proportional to CD3+ T cells. Spatial analyses showed NK cells preferentially clustering close to other NK cells with sparse CD3+ T and CD8+ T cells in range (P<0.0001). Additionally, CD3+ T and CD8+ T cells showed significantly greater co-localization with MHC-I+ cells, compared to NK cells (P<0.0001). After neoadjuvant radiotherapy, there was greater CD8 clustering, while after neoadjuvant chemotherapy, there was overall lower TIL clustering.

Conclusion

Intratumoral NK cells are prognostic in STS and localize closer to MHC-I- cells than T cells. Although both NK and T cells are associated with improved survival in STS, their differential distribution in the TME based on MHC-I expression status may serve as a biomarker for improved immunotherapy treatment selection.

Aging augments obesity-induced thymic involution and peripheral T cell exhaustion altering the "obesity paradox"

Introduction

The incidence of obesity, a condition characterized by systemic chronic inflammation, has reached pandemic proportions and is a poor prognostic factor in many pathologic states. However, its role on immune parameters has been diverse and at times contradictory. We have previously demonstrated that obesity can result in what has been called the "obesity paradox" which results in increased T cell exhaustion, but also greater efficacy of immune checkpoint blockade in cancer treatment.

Methods

The role of obesity, particularly in the context of aging, has not been robustly explored using preclinical models. We therefore evaluated how age impacts the immune environment on T cell development and function using diet-induced obese (DIO) mice.

Results

We observed that DIO mice initially displayed greater thymopoiesis but then developed greater thymic involution over time compared to their lean counterparts. Both aging and obesity resulted in increased T cell memory conversion combined with increased expression of T cell exhaustion markers and Treg expansion. This increased T cell immunosuppression with age then resulted in a loss of anti-tumor efficacy by immune checkpoint inhibitors (ICIs) in older DIO mice compared to the younger DIO counterparts.

Discussion

These results suggest that both aging and obesity contribute to T cell dysfunction resulting in increased thymic involution. This combined with increased T cell exhaustion and immunosuppressive parameters affects immunotherapy efficacy reducing the advantage of obesity in cancer immunotherapy responses.

Brain injury in COVID-19 is associated with dysregulated innate and adaptive immune responses

COVID-19 is associated with neurological complications including stroke, delirium and encephalitis. Furthermore, a post-viral syndrome dominated by neuropsychiatric symptoms is common, and is seemingly unrelated to COVID-19 severity. The true frequency and underlying mechanisms of neurological injury are unknown, but exaggerated host inflammatory responses appear to be a key driver of COVID-19 severity. We investigated the dynamics of, and relationship between, serum markers of brain injury [neurofilament light (NfL), glial fibrillary acidic protein (GFAP) and total tau] and markers of dysregulated host response (autoantibody production and cytokine profiles) in 175 patients admitted with COVID-19 and 45 patients with influenza. During hospitalization, sera from patients with COVID-19 demonstrated elevations of NfL and GFAP in a severity-dependent manner, with evidence of ongoing active brain injury at follow-up 4 months later. These biomarkers were associated with elevations of pro-inflammatory cytokines and the presence of autoantibodies to a large number of different antigens. Autoantibodies were commonly seen against lung surfactant proteins but also brain proteins such as myelin associated glycoprotein. Commensurate findings were seen in the influenza cohort. A distinct process characterized by elevation of serum total tau was seen in patients at follow-up, which appeared to be independent of initial disease severity and was not associated with dysregulated immune responses unlike NfL and GFAP. These results demonstrate that brain injury is a common consequence of both COVID-19 and influenza, and is therefore likely to be a feature of severe viral infection more broadly. The brain injury occurs in the context of dysregulation of both innate and adaptive immune responses, with no single pathogenic mechanism clearly responsible.

Acute seizure risk in patients with encephalitis: development and validation of clinical prediction models from two independent prospective multicentre cohorts

Objective

In patients with encephalitis, the development of acute symptomatic seizures is highly variable, but when present is associated with a worse outcome. We aimed to determine the factors associated with seizures in encephalitis and develop a clinical prediction model.

Methods

We analysed 203 patients from 24 English hospitals (2005-2008) (Cohort 1). Outcome measures were seizures prior to and during admission, inpatient seizures and status epilepticus. A binary logistic regression risk model was converted to a clinical score and independently validated on an additional 233 patients from 31 UK hospitals (2013-2016) (Cohort 2).

Results

In Cohort 1, 121 (60%) patients had a seizure including 103 (51%) with inpatient seizures. Admission Glasgow Coma Scale (GCS) ≤8/15 was predictive of subsequent inpatient seizures (OR (95% CI) 5.55 (2.10 to 14.64), p<0.001), including in those without a history of prior seizures at presentation (OR 6.57 (95% CI 1.37 to 31.5), p=0.025).A clinical model of overall seizure risk identified admission GCS along with aetiology (autoantibody-associated OR 11.99 (95% CI 2.09 to 68.86) and Herpes simplex virus 3.58 (95% CI 1.06 to 12.12)) (area under receiver operating characteristics curve (AUROC) =0.75 (95% CI 0.701 to 0.848), p<0.001). The same model was externally validated in Cohort 2 (AUROC=0.744 (95% CI 0.677 to 0.811), p<0.001). A clinical scoring system for stratifying inpatient seizure risk by decile demonstrated good discrimination using variables available on admission; age, GCS and fever (AUROC=0.716 (95% CI 0.634 to 0.798), p<0.001) and once probable aetiology established (AUROC=0.761 (95% CI 0.6840.839), p<0.001).

Conclusion

Age, GCS, fever and aetiology can effectively stratify acute seizure risk in patients with encephalitis. These findings can support the development of targeted interventions and aid clinical trial design for antiseizure medication prophylaxis.

Transcriptome Analysis of Tumor-Infiltrating Lymphocytes Identifies NK Cell Gene Signatures Associated With Lymphocyte Infiltration and Survival in Soft Tissue Sarcomas

Purpose

Clinical successes using current T-cell based immunotherapies have been limited in soft tissue sarcomas (STS), while pre-clinical studies have shown evidence of natural killer (NK) cell activity. Since tumor immune infiltration, especially tumor-infiltrating lymphocytes, is associated with improved survival in most solid tumors, we sought to evaluate the gene expression profile of tumor and blood NK and T cells, as well as tumor cells, with the goal of identifying potential novel immune targets in STS.

Experimental Design

Using fluorescence-activated cell sorting, we isolated blood and tumor-infiltrating CD3^-CD56⁺ NK and CD3⁺ T cells and CD45^- viable tumor cells from STS patients undergoing surgery. We then evaluated differential gene expression (DGE) of these purified populations with RNA sequencing analysis. To evaluate survival differences and validate primary DGE results, we also queried The Cancer Genome Atlas (TCGA) database to compare outcomes stratified by bulk gene expression.

Results

Sorted intra-tumoral CD3⁺ T cells showed significant upregulation of established activating (CD137) and inhibitory genes (TIM-3) compared to circulating T cells. In contrast, intra-tumoral NK cells did not exhibit upregulation of canonical cytotoxic genes (IFNG, GZMB), but rather significant DGE in mitogen signaling (DUSP4) and metabolic function (SMPD3, SLC7A5). Tumors with higher NK and T cell infiltration exhibited significantly increased expression of the pro-inflammatory receptor TLR4 in sorted CD45^- tumor cells. TCGA analysis revealed that tumors with high TLR4 expression (P = 0.03) and low expression of STMN1 involved in microtubule polymerization (P < 0.001) were associated with significantly improved survival.

Conclusions

Unlike T cells, which demonstrate significant DGE consistent with upregulation of both activating and inhibiting receptors in tumor-infiltrating subsets, NK cells appear to have more stable gene expression between blood and tumor subsets, with alterations restricted primarily to metabolic pathways. Increased immune cell infiltration and improved survival were positively correlated with TLR4 expression and inversely correlated with STMN1 expression within tumors, suggesting possible novel therapeutic targets for immunotherapy in STS.

Inhaled recombinant human IL-15 in dogs with naturally occurring pulmonary metastases from osteosarcoma or melanoma: a phase 1 study of clinical activity and correlates of response

PURPOSE

Although recombinant human interleukin-15 (rhIL-15) has generated much excitement as an immunotherapeutic agent for cancer, activity in human clinical trials has been modest to date, in part due to the risks of toxicity with significant dose escalation. Since pulmonary metastases are a major site of distant failure in human and dog cancers, we sought to investigate inhaled rhIL-15 in dogs with naturally occurring lung metastases from osteosarcoma (OSA) or melanoma. We hypothesized a favorable benefit/risk profile given the concentrated delivery to the lungs with decreased systemic exposure.

EXPERIMENTAL DESIGN

We performed a phase I trial of inhaled rhIL-15 in dogs with gross pulmonary metastases using a traditional 3+3 cohort design. A starting dose of 10 µg twice daily × 14 days was used based on human, non-human primate, and murine studies. Safety, dose-limiting toxicities (DLT), and maximum tolerated dose (MTD) were the primary objectives, while response rates, progression-free and overall survival (OS), and pharmacokinetic and immune correlative analyses were secondary.

RESULTS

From October 2018 to December 2020, we enrolled 21 dogs with 18 dogs reaching the 28-day response assessment to be evaluable. At dose level 5 (70 μg), we observed two DLTs, thereby establishing 50 µg twice daily × 14 days as the MTD and recommended phase 2 dose. Among 18 evaluable dogs, we observed one complete response >1 year, one partial response with resolution of multiple target lesions, and five stable disease for an overall clinical benefit rate of 39%. Plasma rhIL-15 quantitation revealed detectable and sustained rhIL-15 concentrations between 1-hour and 6 hour postnebulization. Decreased pretreatment lymphocyte counts were significantly associated with clinical benefit. Cytotoxicity assays of banked peripheral blood mononuclear cells revealed significant increases in peak cytotoxicity against canine melanoma and OSA targets that correlated with OS.

CONCLUSIONS

In this first-in-dog clinical trial of inhaled rhIL-15 in dogs with advanced metastatic disease, we observed promising clinical activity when administered as a monotherapy for only 14 days. These data have significant clinical and biological implications for both dogs and humans with refractory lung metastases and support exploration of combinatorial therapies using inhaled rhIL-15.

Immune-Mediated Mechanisms of COVID-19 Neuropathology

Although SARS-CoV-2 causes a respiratory viral infection, there is a large incidence of neurological complications occurring in COVID-19 patients. These range from headaches and loss of smell to encephalitis and strokes. Little is known about the likely diverse mechanisms causing these pathologies and there is a dire need to understand how to prevent and treat them. This review explores recent research from the perspective of investigating how the immune system could play a role in neurological complications, including cytokines, blood biomarkers, immune cells, and autoantibodies. We also discuss lessons learnt from animal models. Overall, we highlight two key points that have emerged from increasing evidence: (1) SARS-CoV-2 does not invade the brain in the majority of cases and so the associated neurological complications might arise from indirect effects, such as immune activation (2) although the immune system plays a critical role in controlling the virus, its dysregulation can cause pathology.

Killers on the loose: Immunotherapeutic strategies to improve NK cell-based therapy for cancer treatment

Natural killer (NK) cells are innate lymphocytes that control tumor progression by not only directly killing cancer cells, but also by regulating other immune cells, helping to orchestrate a coordinated anti-tumor response. However, despite the tremendous potential that this cell type has, the clinical results obtained from diverse NK cell-based immunotherapeutic strategies have been, until recent years, rather modest. The intrinsic regulatory mechanisms that are involved in the control of their activation as well as the multiple mechanisms that tumor cells have developed to escape NK cell-mediated cytotoxicity likely account for the unsatisfactory clinical outcomes. The current approaches to improve long-term NK cell function are centered on modulating different molecules involved in both the activation and inhibition of NK cells, and the latest data seems to advocate for combining strategies that target multiple aspects of NK cell regulation. In this review, we summarize the different strategies (such as engineered NK cells, CAR-NK, NK cell immune engagers) that are currently being used to take advantage of this potent and complex immune cell.

Characterization of the Tumor Immune Microenvironment in Soft Tissue Sarcoma Patients Undergoing Surgery

Tumor infiltrating lymphocytes (TILs) have been shown to predict survival in soft tissue sarcomas (STS), but the specific contribution of natural killer (NK) and CD8+ T cells to outcomes is undefined. Therefore, we sought to characterize the extent of NK and CD8+ T cell infiltration in STS.

Prospectively, we evaluated 15 patients using fresh tumor from surgery for flow cytometric analysis. Retrospectively, we evaluated archived tumor tissue from 90 STS patients by immunohistochemistry (IHC) for CD3, CD8, CD45RO, NKp46, TIGIT, MHC-I, and p53. We analyzed metastasis-free survival (MFS) and overall survival (OS) by Kaplan-Meier method and log-rank test.

By flow cytometry, we observed significant variability in CD45+ leukocytes in the STS TME (mean 29±24% of total live cells) with low percentages of tumor-infiltrating CD3-CD56+ NK cells (1.7±1.9% of total live cells and 5.3±3.0% of live CD45+ cells) and CD8+ T cells (1.6±1.6% of total live cells and 29.6±30.5% of live CD45+ cells). By IHC, NK and T cell infiltrates were low (median H score 0, range 0–66.5 and 2.7, range 0–110, respectively). We confirmed a positive correlation between CD8+ T cell infiltration and significantly improved OS (P&lt;0.05) and a trend for improved MFS. We also observed a trend for improved OS among patients with higher NKp46 scores (P=0.07). MHC-I expression positively correlated with both T and NK cell infiltration (P&lt;0.05), whereas TIGIT expression positively correlated with T cell infiltration (P&lt;0.05), but not NK infiltration.

Infiltration of NK and CD8+ T cells is overall low in STS patients undergoing surgery but associated with superior OS. Further characterization of the immune infiltrate in STS may yield better biomarkers of prognosis and immune targeting.

Supported by the following grants: NIH/NCI 1R03CA252793 NIH/NCI T32 CA251007-01

Tissue resident lung natural killer (NK) cells demonstrate enhanced responses to IL-15 compared to peripheral populations

Tissue resident NK cells with unique phenotype and function have been identified in organs such as the lung and liver. We have shown that inhaled (IH) rhIL-15 can lead to durable clinical responses in dogs with naturally occurring osteosarcoma or melanoma lung metastases, suggesting that lung NK populations can be targeted therapeutically. Thus, we set out to evaluate the phenotype of resting and rhIL-15-stimulated lung NK cells isolated from murine and human lung. C57BL/6 and BALB/c mice were exposed to IH or systemic IL-15 at escalating doses, and NK cells were isolated by negative selection from lungs and spleen of wild type mice for co-culture. In human patients undergoing surgery for malignancy, non-tumor lung tissue was isolated for flow cytometry and ex vivo stimulation with IL-15. Using mouse spleen or human blood as controls, we observed a higher proportion of lung NK cells per live CD45+ cells in baseline mouse and human samples. Lung NK also had higher expression of activation markers CD69 and HLA-DR (human), but lower expression of the inhibitory receptor TIGIT. Ex vivo culture with IL-15 also resulted in greater upregulation of Ki67 on lung NK cells. Compared to systemic delivery of IL-15, IH IL-15 resulted in greater upregulation of Ki67 and lower upregulation of TIGIT in lung NK cells. Subset analysis of CD49a+ lung NK cells showed similar results in both mouse and human models for activation marker and Ki67 expression after IL-15. Taken together, our results suggest that lung NK cells possess a more active baseline phenotype and exhibit preferential stimulation in response to rhIL-15 compared to circulating NK cells. Ultimately, targeting of lung resident NK cells may be a viable therapeutic strategy in patients with lung metastases.

Supported by NIH/ NCI 1R03CA252793 NIH/NCI U01 CA224166-01 NIH/NCI T32 CA251007-01

Optimization of expansion techniques for adoptive NK cell transfer in dogs with cancer

Natural killer (NK) cells can recognize heterogeneous cancer cell targets without prior sensitization, making them promising prospects for use in immunotherapy. We have completed first-in-dog feasibility clinical trials in dogs with cancer using both autologous and allogeneic NK cells expanded from peripheral blood mononuclear cells (PBMCs). Previously, CD5 depletion of PBMCs has been used to enrich for a CD5dim expressing subset prior to NK co-culture with an irradiated feeder line, but this can limit the yield of the final NK product. The purpose of this study was to compare ex vivo culture conditions using standard CD5 depletion versus unmanipulated PBMCs plus feeder line co-culture with 100 IU/mL rhIL-2 in matched healthy donors, hypothesizing that PBMCs plus feeder cells would generate an equivalent or superior NK product to CD5 depletion. Cell count, fold change, and viability data were collected for both techniques in 12 dogs across five time points up to day 14. A mixed-effects model analysis showed no statistical difference in calculated cell counts, overall fold change, and viability (p&gt;0.05 all) between PBMCs with feeders and CD5 depleted cells with feeders. PBMCs had a higher mean than CD5 depleted cells at day 14 in all three categories, reaching a peak mean of 677 million cells from 5 million PBMCs at day 0. Flow phenotype showed similar upregulation of NKp46 and Granzyme B expression. Killing assays against melanoma and osteosarcoma targets demonstrated comparable results among PBMCs plus feeders versus CD5 depleted NK cells (p&gt;0.05). Overall, these findings support the use of unmanipulated PBMCs plus feeder line coculture as an equivalent method to CD5 depletion in the expansion of canine NK cells for adoptive immunotherapy.

Supported by grants from National Institutes of Health/National Cancer Institute (U01 CA224166-01, 1R03CA252793, T32 CA251007-01)

Increased efficacy of dual proinflammatory cytokine blockade on acute GVHD while maintaining GVT effects

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains a potential curative option for treating a variety of hematologic diseases, but acute and chronic graft-versus-host disease (GVHD) remain major barriers limiting efficacy. Acute gut GVHD occurs with marked increases in proinflammatory cytokines (including TNF and IL-6), which we recently demonstrated was exacerbated in obesity resulting in severe gastrointestinal pathology. Given the pleiotropic and overlapping effects of these 2 cytokines, we assessed the impact of dual TNF and IL-6R blockade on GVHD as well as graft-versus tumor (GVT) effects in different mouse GVHD models. Early administration of combined blockade resulted in greater protection and survival from acute gut GVHD compared with single blockade regimens and even development of later chronic skin GVHD. Importantly, double cytokine blockade preserved GVT effects reinforcing that GVT and GVHD can be delineated and may result in greater efficacy in allo-HSCT.

Mechanisms by Which Obesity Promotes Acute Graft-Versus-Host Disease in Mice

The efficacy of allogeneic hematopoietic stem cell transplantation (allo-HSCT) is limited by the occurrence of acute and chronic graft-versus-host disease (GVHD). We have recently demonstrated that obesity results in exacerbated acute gastrointestinal GVHD in both mouse models and clinical outcomes due to increased pro-inflammatory cytokine responses and microbiota alterations. We therefore wanted to delineate the role of the various parameters in obesity, adiposity, effects of high-fat (HF) diet, and the role of microbiome on GVHD pathogenesis, by taking advantage of a mouse strain resistant to diet-induced obesity (DIO). Female BALB/c mice are resistant to DIO phenotype with approximately 50% becoming DIO under HF diets. The DIO-susceptible recipients rapidly succumb to acute gut GVHD, whereas the DIO-resistant recipient littermates, which do not become obese, are partially protected from GVHD, indicating that being on HF diet alone contributes to but is not the primary driver of GVHD. Microbiome assessment revealed restricted diversity in both cohorts of mice, but coprophagy normalizes the microbiota in mice housed together. We then individually housed DIO-resistant, DIO-susceptible, and lean control mice. Notably, each of the individually housed groups demonstrates marked restricted diversity that has been shown to occur from the stress of single housing. Despite the restricted microbiome diversity, the GVHD pathogenesis profile remains consistent in the group-housed mice, with the lean control single-housed mice exhibiting no acute GVHD and DIO-resistant recipients showing again partial protection. These results demonstrate that the deleterious effects of obesity on acute gut GVHD are critically dependent on adiposity with the HF diet also playing a lesser role, and the microbiome alterations with obesity instead appear to fuel ongoing acute GVHD processes.

Obesity induces gut microbiota alterations and augments acute graft-versus-host disease after allogeneic stem cell transplantation

The efficacy of allogeneic hematopoietic stem cell transplantation (allo-HSCT) is limited by acute and chronic graft-versus-host disease (GVHD). The impact of obesity on allo-HSCT outcomes is poorly understood. Here, we report that obesity had a negative and selective impact on acute gut GVHD after allo-HSCT in mice with diet-induced obesity (DIO). These animals exhibited increased gut permeability, endotoxin translocation across the gut, and radiation-induced gastrointestinal damage after allo-HSCT. After allo-HSCT, both male and female DIO mouse recipients showed increased proinflammatory cytokine production and expression of the GVHD marker ST2 (IL-33R) and MHC class II molecules; they also exhibited decreased survival associated with acute severe gut GVHD. This rapid-onset, obesity-associated gut GVHD depended on donor CD4⁺ T cells and occurred even with a minor MHC mismatch between donor and recipient animals. Retrospective analysis of clinical cohorts receiving allo-HSCT transplants from unrelated donors revealed that recipients with a high body mass index (BMI, >30) had reduced survival and higher serum ST2 concentrations compared with nonobese transplant recipients. Assessment of both DIO mice and allo-HSCT recipients with a high BMI revealed reduced gut microbiota diversity and decreased Clostridiaceae abundance. Prophylactic antibiotic treatment protected DIO mouse recipients from endotoxin translocation across the gut and increased inflammatory cytokine production, as well as gut pathology and mortality, but did not protect against later development of chronic skin GVHD. These results suggest that obesity-induced alterations of the gut microbiota may affect GVHD after allo-HSCT in DIO mice, which could be ameliorated by prophylactic antibiotic treatment.

Gene expression analysis of sarcoma-infiltrating NK cells identifies signatures correlating with favorable prognosis and potential new targets for augmenting NK function

Success of current T-cell based immunotherapies in soft tissue sarcomas (STS) is limited while pre-clinical and clinical studies have shown evidence of NK activity in STS. To investigate the effects of the tumor microenvironment (TME) on tumor-infiltrating NK cell gene expression, we isolated circulating and tumor-infiltrating NK and CD3 T cells from sarcoma patients undergoing surgery (N=4) and performed RNA sequencing analysis. Comparing Differential Gene Expression (DGE) of flow-sorted intra-tumoral NK cells to circulating NK cells, we identified upregulation of genes involved in mitogen signaling inhibition (DUSP4) and metabolic function (SMPD3, SLC7A5), but not of genes typically associated with cytotoxic function (e.g. IFNG, GZMB). In contrast, intra-tumoral T cells showed significant upregulation of both activating (CD137) and inhibitory genes (TIM-3) compared to circulating T cells. We then queried the TCGA STS dataset and stratified cases into “NK Activating TME” and “NK Suppressing TME” based on the CIBERSORT NK signature analysis program (based on high or low proportion of activated NK cells, respectively). Patients with NK Activating TME had significantly improved survival compared to NK Suppressive TME (log-rank p = 0.03). DGE identified unique tumor-associated gene ontology between NK activated versus suppressive subsets with upregulation of the retinoic acid pathway. Unlike T cells which demonstrate significant DGE between circulating and tumor-infiltrating subsets, NK cells appear to have similar gene expression between blood and tumor. Therefore, although NK cells appear to be prognostic in STS, their anti-tumor effects may be dictated by systemic rather than local factors.

Mouse Preclinical Cancer Immunotherapy Modeling Involving Anti-PD-1 Therapies Reveals the Need to Use Mouse Reagents to Mirror Clinical Paradigms

Immune checkpoint inhibition (ICI) has emerged as one of the most powerful tools to reverse cancer induced immune suppression. Monoclonal antibodies (mAbs) targeting programmed cell death 1/programmed cell death ligand 1(PD-1/PD-L1) are FDA-approved and their clinical use is rapidly expanding. As opposed to the clinical paradigm, which can result in significant responses and toxicities, it has been difficult to reproduce these effects preclinically using mouse models. In large part, this is due to models, which employ rapidly growing ex vivo cultured transplantable tumor cell lines engrafted into young naïve inbred laboratory mice. However, another issue concerns the use and repeated application of xenogeneic reagents in mice (i.e., rat or hamster mAbs directed against mouse antigens at variance with clinical use of human or humanized mAbs). Building on our previous studies demonstrating that repeated administration of commonly used xenogeneic anti-PD-1 mAbs derived from both rat and hamster can induce fatal hypersensitivity in some tumor-bearing mice, we sought to compare these result with the effects of a mouse anti-mouse PD-1 mAb. Application of a murine anti-mouse PD-1 (clone: MuDX400) did not result in lethal anaphylaxis in the 4T1 tumor model. It also displayed superior antitumor effects in this and other tumor models, as it did not induce neutralizing antibody responses against the anti-PD-1 mAb, such as were observed when using xenogeneic anti-PD1 mAbs. These results demonstrate that more accurate preclinical modeling necessitates the use of mouse reagents mirroring the clinical scenario to ascertain long-term effects or toxicities, while avoiding xenogeneic responses, which do not occur clinically. Furthermore, these studies suggest a direct mechanism, whereby preclinical murine studies have often failed to recapitulate the clinical efficacy and toxicity of single agent checkpoint inhibition.

PD-1 Blockade Reverses Obesity-Mediated T Cell Priming Impairment

Despite obesity reaching pandemic proportions, its impact on antigen-specific T cell responses is still unclear. We have recently demonstrated that obesity results in increased expression of PD-1 on T cells, and checkpoint blockade targeting PD-1/PD-L1 surprisingly resulted in greater clinical efficacy in cancer therapy. Adverse events associated with this therapy center around autoimmune reactions. In this study, we examined the impact of obesity on T cell priming and on autoimmune pathogenesis using the mouse model experimental autoimmune encephalomyelitis (EAE), which is mediated by autoreactive myelin-specific T cells generated after immunization. We observed that diet-induced obese (DIO) mice had a markedly delayed EAE onset and developed milder clinical symptoms compared to mice on control diet (CD). This delay was associated with impaired generation of myelin-specific T cell numbers and concurrently correlated with increased PD-L1 upregulation on antigen-presenting cells in secondary lymphoid organs. PD-1 blockade during the priming stage of EAE restored disease onset and severity and increased numbers of pathogenic CD4+ T cells in the central nervous system (CNS) of DIO mice to similar levels to those of CD mice. Administration of anti-PD-1 after onset of clinical symptoms did not increase EAE pathogenesis demonstrating that initial priming is the critical juncture affected by obesity. These findings demonstrate that obesity impairs antigen-specific T cell priming, but this can be reversed with PD-1 blockade. Our results further suggest that PD-1 blockade may increase the risk of autoimmune toxicities, particularly in obesity.

Analysis of tumor-infiltrating NK and T cells highlights IL-15 stimulation and TIGIT blockade as a combination immunotherapy strategy for soft tissue sarcomas

Purpose

Given the unmet need for novel immunotherapy in soft tissue sarcoma (STS), we sought to characterize the phenotype and function of intratumoral natural killer (NK) and T cells to identify novel strategies to augment tumor-infiltrating lymphocyte (TIL) function.

Experimental design

Using prospectively collected specimens from dogs and humans with sarcomas, archived specimens, and The Cancer Genome Atlas (TCGA) data, we evaluated blood and tumor NK and T cell phenotype and function and correlated those with outcome. We then assessed the effects of interleukin 15 (IL-15) stimulation on both NK and T cell activation and TIGIT upregulation. Finally, we evaluated cytotoxic effects of IL-15 combined with TIGIT blockade using a novel anti-TIGIT antibody.

Results

TILs were strongly associated with survival outcome in both archived tissue and TCGA, but higher TIL content was also associated with higher TIGIT expression. Compared with blood, intratumoral NK and T cells showed significantly higher expression of both activation and exhaustion markers, in particular TIGIT. Ex vivo stimulation of blood and tumor NK and T cells from patients with STS with IL-15 further increased both activation and exhaustion markers, including TIGIT. Dogs with metastatic osteosarcoma receiving inhaled IL-15 also exhibited upregulation of activation markers and TIGIT. Ex vivo, combined IL-15 and TIGIT blockade using STS blood and tumor specimens significantly increased cytotoxicity against STS targets.

Conclusion

Intratumoral NK and T cells are prognostic in STS, but their activation is marked by significant upregulation of TIGIT. Our data suggest that combined IL-15 and TIGIT blockade may be a promising clinical strategy in STS.

IL-2 and Anti-TGF-β Promote NK Cell Reconstitution and Anti-tumor Effects after Syngeneic Hematopoietic Stem Cell Transplantation

Simple Summary

Hematopoietic stem cell transplantation (HSCT) causes early immune deficiency and susceptibility to both opportunistic infections and cancer relapse. In this study, using a mouse model where donor cells can be tracked over time, we have observed that the combination of IL-2 (a cytokine which activates the immune system) combined with the blockade of TGF-β (a cytokine which suppresses the immune system) increased immune recovery and resulted in greater anti-tumor efficacy. The combination of IL-2 and anti-TGF-β accelerated NK cell and myeloid cell reconstitution after HSCT.

Abstract

The failure of autologous hematopoietic stem cell transplantation (HSCT) has been associated with a profound immunodeficiency that follows shortly after treatment, which renders patients susceptible to opportunistic infections and/or cancer relapse. Thus, given the additional immunosuppressive pathways involved in immune evasion in cancer, strategies that induce a faster reconstitution of key immune effector cells are needed. Natural killer (NK) cells mediate potent anti-tumor effector functions and are the first immune cells to repopulate after HSCT. TGF-β is a potent immunosuppressive cytokine that can impede both the development and function of immune cells. Here, we evaluated the use of an immunotherapeutic regimen that combines low dose of IL-2, an NK cell stimulatory signal, with TGF-β neutralization, in order to accelerate NK cell reconstitution following congenic HSCT in mice by providing stimulatory signals yet also abrogating inhibitory ones. This therapy led to a marked expansion of NK cells and accelerated NK cell maturation. Following HSCT, mature NK cells from the treated recipients displayed an activated phenotype and enhanced anti-tumor responses both in vitro and in vivo. No overt toxicities or adverse effects were observed in the treated recipients. However, these stimulatory effects on NK cell recovery were predicated upon continuous treatment as cessation of treatment led to return to baseline levels and to no improvement of overall immune recovery when assessed at later time-points, indicating strict regulatory control of the NK cell compartment. Overall, this study still demonstrates that therapies that combine positive and negative signals can be plausible strategies to accelerate NK cell reconstitution following HSCT and augment anti-tumor efficacy.

Minimal PD-1 expression in mouse and human NK cells under diverse conditions

PD-1 expression is a hallmark of both early antigen-specific T cell activation and later chronic stimulation, suggesting key roles in both naive T cell priming and memory T cell responses. Although significant similarities exist between T cells and NK cells, there are critical differences in their biology and functions reflecting their respective adaptive and innate immune effector functions. Expression of PD-1 on NK cells is controversial despite rapid incorporation into clinical cancer trials. Our objective was to stringently and comprehensively assess expression of PD-1 on both mouse and human NK cells under multiple conditions and using a variety of readouts. We evaluated NK cells from primary human tumor samples, after ex vivo culturing, and from multiple mouse tumor and viral models using flow cytometry, quantitative reverse-transcriptase PCR (qRT-PCR), and RNA-Seq for PD-1 expression. We demonstrate that, under multiple conditions, human and mouse NK cells consistently lack PD-1 expression despite the marked upregulation of other activation/regulatory markers, such as TIGIT. This was in marked contrast to T cells, which were far more prominent within all tumors and expressed PD-1. These data have important implications when attempting to discern NK from T cell effects and to determine whether PD-1 targeting can be expected to have direct effects on NK cell functions.

Differences in NK and Memory CD8 T cell responses to antigen-nonspecific stimulation by interleukin-15

Natural killer (NK) cells are innate lymphoid cells that exert immediate functions which can be further augmented and sustained with immunostimulatory cytokines. Memory CD8 T cells, due to expression of CD132 and CD122, can be activated by similar cytokines in the absence of TCR engagement (termed “bystander” activation). This results in activation and proliferation but necessitates high amounts of cytokine as high-affinity IL2R complexes (CD25) are not induced. Interestingly, both cell types can then elicit similar effector functions via NKG2D-mediated target cell recognition. As these cell types can fill a similar immunologic niche, we set out to compare NK and memory CD8 T cell responses following IL-15 exposure in vitro from healthy human donors. Cell analysis was performed by flow cytometry and qRT-PCR. At baseline, CD25 expression is negligible at &lt;5% on both human NK and memory CD8 T cells. Surprisingly, culture with rhIL-15 (10 ng/mL) for 4–6 days resulted in marked CD25 upregulation on CD56+CD3− NK cells but not bystander-activated CD45RA-CD95+ CD8 T cells (72±9.2% vs 11±3.8%, P=0.003) despite comparable expansion. Additionally, cytokine-activated NK cells expressed higher levels of inhibitory receptor TIGIT (85±4% vs 57±2%, P=0.01) and activation marker CD69 (99±1% vs 27±9%, P=0.008). Functionally, NK cells had increased expression of granzyme B compared to bystander-activated CD8 T cells. Thus, although NK and bystander CD8 T cells can fill a similar immunologic niche regarding target cell killing, there are significant differences in expression of critical markers following activation. These differences may have consequences in the regulation of these cell types and impact anti-viral and anti-tumor responses.

The effect of mouse cytomegalovirus infection on natural killer cell development following hematopoietic stem cell transplant

Hematopoietic stem cell transplant (HSCT) is a treatment for patients with hematological malignancies who are not eligible to receive intensive cytoreductive therapy. Cytomegalovirus (CMV) is an extremely prevalent infection and in immune-compromised patients, it is a significant cause of morbidity and mortality. Approximately two-thirds of seropositive patients experience CMV reactivation following HSCT. There have been reports that CMV reactivation causes increased activation of NK cells which actually benefits graft-versus-tumor effects. Our study objective is to delineate the kinetics of this effect and determine whether there are long-term functional differences in NK cells. We hypothesized that immune reconstitution is impacted by CMV infection and that the lymphopenic and inflammatory environment post-HSCT detrimentally affects the immune response to CMV infection. Using a syngeneic HSCT model in C57BL/6 mice, we studied de novo NK cell repopulation. At day 8 post-transplant, mice were inoculated with a low dose of mouse CMV. We found a significantly higher viral burden in the HSCT recipients compared to control mice. We found that CMV-specific NK cells (Ly49H+) rapidly expanded following CMV infection post-HSCT, but experienced a population collapse after two weeks. This is possibly due to exposure to a primary virus infection early on in development and/or the increased viral burden. There was a higher frequency of mature NK cells and IFN-gamma producing NK cells following CMV infection in the HSCT environment, suggestive of increased activation and accelerated differentiation. The disproportionate loss of the Ly49H+ NK cells may cause long-term functional defects in the HSCT recipient immune response.

Adiposity augments toxicity of mouse cytomegalovirus

Obesity, a meta-inflammatory state defined by BMI≥30kg/m2, is reaching pandemic proportions. Generally, the impact of obesity on immune responses is poorly understood. Obesity is associated with chronic low-grade systemic pro-inflammatory cytokines. Similar to aging, obesity can affect immune responses and cause susceptibility to infection and pathology. Cytomegalovirus (CMV) is a prevalent herpes virus that can remain asymptomatic for years but causes significant morbidity and mortality in immunosuppressed patients. Our goal was to evaluate the impact of obesity on immune responses to CMV infection with a focus on toxicity. We reported that systemic immunotherapy results in elevated levels of pro-inflammatory cytokines in obese mice, leading to TNF-mediated pathological responses and death. We hypothesized that obesity will augment toxicity in mouse CMV (MCMV) infection as a consequence of heightened pro-inflammatory cytokine production. C57BL/6 and Balb/c were fed either a 60% fat (DIO) or 10% fat (Control) diet starting at 6-weeks old until 6-months old. DIO mice had significantly more subcutaneous and visceral adipose tissue than control mice assessed by MRI. Although ob/ob mice were fed a regular diet, they were significantly fatter than WT mice. Mice (DIO vs control and ob/ob vs WT) infected with 1–5×104 p.f.u. MCMV were assessed for clinical symptoms, serum cytokines, and survival. We observed that 50% of both DIO and ob/ob mice succumbed starting 2 days post-infection, which was associated with increased pro-inflammatory cytokine production. The augmented toxicity induced by MCMV in obese models demonstrates that adiposity is a critical factor in immune-mediated pathological responses to infections.

PD-1 is not expressed on highly activated Natural Killer cells in human and murine models

PD-1 expression is a hallmark of acute T cell priming and response to chronic antigen exposure with a key role in T cell exhaustion. Though identified on NK cells in select populations, the role of PD-1 on NK cells is less clear. Our objective was to determine the expression of PD-1 on resting and activated NK cells in human and murine models. Human NK cells were isolated and expanded ex vivo using a feeder line or cytokine culture. Murine NK cells were evaluated in vivo in tumor-bearing mice and post-MCMV infection in both immunocompetent and immunodeficient mice. We assessed NK cell surface phenotype, activation markers, and intracellular cytokine by flow cytometry and qRT-PCR. Throughout ex vivo human NK activation and proliferation, NK PD-1+ frequency was consistently less than 1% by flow cytometry and negligible by PCR, with upregulation of TIGIT by PCR and flow cytometry (P&lt;0.05). In cytokine stimulated human PBMCs, NK PD-1 expression was 0–2%. In vivo studies with 4T1-bearing mice showed negligible PD-1 from intra-tumoral and splenic NK cells. NK cells isolated from livers in C57BL/6 mice after acute MCMV infection showed high activation by CD69 (&gt;90% positive) but &lt;2% PD-1 expressing NK cells, while T cells exhibited high activation and a 5-fold increase in PD-1 expression. In Rag2−/− mice exposed to MCMV, NK cells isolated from the liver on post-infection day 3 showed minimal PD-1 expression, but positive PD-L1 and TIGIT expression. Unlike T cells, our results show that highly activated human and murine NK cells do not significantly upregulate PD-1. Our data suggest that PD-1 is not a consistent marker for NK exhaustion, though TIGIT appears to demonstrate consistent upregulation and may represent a more useful marker for NK exhaustion.

PD-1 regulates response to bystander activation of memory CD8 T cells

Inflammatory cytokines, released in virally infected tissues, activate bystander memory T cells, expressing CD132 and CD122, in an antigen non-specific manner through signal 3 alone to provide early anti-viral protection in an NKG2D-dependent manner. We have previously observed that IL-2 stimulation expands bystander memory CD8 T cells that are NKG2D+/Programmed cell death protein 1(PD-1)-/CD25-. However, it is unclear if the presence of PD-1 regulates the ability of memory T cells to respond to signal 3 alone. In our study, IL-2 in vitro culture for 3 days results in proliferation of memory T cells in human PBMCs and preferential expansion of memory CD8 over CD4 T cells. PD-1- CD8 T cells had greater cycling of proliferation compared to PD-1+ CD8 T cells, as observed by dilution of CPeFluor670 staining. Similarly, mouse splenocytes proliferate in response to IL-2 in vitro. Ki67+ CD8 T cells were found to be predominantly PD-1−, while ConA-stimulated Ki67+ CD8 T cells were predominantly PD-1+. Adoptively transferred memory OTI CD8 T cells but not naïve OTI CD8 T cells expanded in vivo in the liver at 3–4 days post-infection with 2×10^3 PFU murine cytomegalovirus (MCMV), and a greater percentage of PD-1− OTI CD8 T cells were Ki67 positive compared to PD-1+ OTI CD8 T cells. We conclude that the expression of PD-1 on memory CD8 T cells can regulate response to signal 3 alone. Future studies will examine the impact of PD-1 blockade on the bystander response in anti-viral protection.

Assessment of PD-1 expression in human resting and activated natural killer cells and murine tumor models

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Background: Blockade of the PD-1/PD-L1/2 axis has revolutionized cancer therapy. Although reinvigorated PD-1+ T cells are the main effectors in the response to checkpoint blockade, the contribution of Natural Killer (NK) cells to PD-1/PD-L1 inhibition is under debate. While PD-1 has been identified on NK cells, this appears to be restricted to small populations under limited conditions. We sought to evaluate the extent of PD-1 expression in mouse and human resting and activated NK cells. Methods: Human NK cells were isolated from healthy donor PBMCs and cancer patients. Ex vivo activation and proliferation techniques included recombinant human cytokine and feeder line co-culture. Murine NK cells were isolated from splenocytes, and PBMCs from wild type and immunodeficient mice. We assessed NK cell surface markers and intracellular cytokine by flow cytometry, and gene expression by quantitative RT-PCR. Results: Over 21-days of ex vivo expansion, expression of PD-1 or PD-L1 on human NK cells was < 1% at all time points, while TIGIT+ expression increased to > 85%. Conversely, ConA stimulation of T cells increased PD-1 expression with no change in TIGIT expression. QRT-PCR demonstrated absent PD-1 expression in purified NK cells compared to a 5-fold increase in PD-1 gene expression in ConA stimulated PBMCs. PD-1/PD-L1 was also < 1% in the NK92 cell line and < 2.5% in peripheral CD56+CD3- NK cells from patients with soft tissue sarcoma (STS). NK cells from digested freshly resected STS show variable PD-1 ( < 10%) and minimal PD-L1 ( < 1%) expression with a small, but measurable population of intra-tumoral NK cells (1% of immune cells). In vivo mouse studies showed < 5% PD-1+ NK cells in spleen and tumor of CT26 tumor-bearing mice, while PD-L1+ NK cells increased in frequency from spleen (5-35%) to tumor (40-95%) in both wild type BALB/C and SCID mice. Conclusions: In contrast to prior studies, we did not observe a substantial PD-1+ population on human or murine NK cells after multiple activation strategies compared to T cells. Contrary to its application in T cells, our data suggest that PD-1 is not a useful marker for NK cell exhaustion/dysfunction. PD-L1 on NK cells may represent an important link between NK and T cell immunotherapy.

NK cells for PD-1/PD-L1 blockade immunotherapy: pinning down the NK cell

In spite of a very robust body of literature and definitive data demonstrating the importance of the programmed cell death receptor-1 (PD-1) pathway in T cells and their function, the data on NK cell PD-1 expression have been highly variable and, particularly in the case of mouse NK cells, scarce. In this issue of the JCI, Hsu et al. present data demonstrating PD-1 expression on mouse NK cells only within tumors and show that PD-1 blockade elicits an antitumor NK cell-mediated response. This study indicates that, given the complexity of both the biology and study of NK cells, further work is needed to more clearly determine the role of the PD-1/PD-1 ligand (PD-L1) on NK cells.

Obesity results in marked increases in gut permeability, inflammatory cytokines, and acute gut graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) remains the most applicable curative option for treating hematologic diseases. In this study, we assessed the impact of obesity on recipient graft-versus-host disease (GVHD) outcome post allogeneic HSCT using a minor histocompatibility antigens (miHA)-mismatched mouse model. Control or diet-induced obese (DIO) BALB/c mice received HSCT from H2-identical B10.D2 mice which is known for resulting in chronic skin GVHD. Strikingly, DIO mice rapidly succumbed to gut GVHD while control mice survived and developed sclerodermatous GVHD much later post-HSCT. The DIO recipient mice had higher expression of pro-inflammatory cytokines (IL-6 and TNF-α) in the gut and serum, as well as higher serum ST2. There were increased numbers of donor CD4+ T cells in the mesenteric lymph nodes of DIO mice compared to control mice. Untreated DIO mice also displayed increased gut permeability and lipopolysaccharide translocation, as well as having less-diverse microbiota which potentially contributed to the severe GVHD post-HSCT. Importantly, administration of anti-IL-6R monoclonal antibody and Enbrel significantly protected DIO mice from lethal gut GVHD, correlating with lower pro-inflammatory cytokine concentrations (IL-6 and TNF-α) and ST2 in the serum. In an initial evaluation, treating DIO mice with broad-spectrum antibiotics 2 weeks before HSCT also ameliorated GVHD. Taken together, these results indicate that obesity exacerbates GVHD, manifested primarily as gut pathology, and therapeutic intervention by blockade of pro-inflammatory cytokine signaling ameliorates GVHD post-HSCT.

Diet-induced obesity impairs induction of Experimental Autoimmune Encephalomyelitis and is restored by PD-1 blockade

Obesity has marked effects on immune function and is associated with increased infection susceptibility and decreased adaptive immune response. We examined the effects of obesity on adaptive autoimmune responses using a diet-induced obesity mouse model. The pathogenesis of experimental autoimmune encephalomyelitis (EAE), a model of autoimmune demyelinating disease of CNS, is mediated by autoreactive Th1 and Th17 CD4 T cell subsets. 8–9-month-old C57Bl/6 male mice were fed 60% fat or 10% fat control diet starting at 6–8 weeks old and were immunized with 300 μg of rodent myelin oligodendrocyte glycoprotein (MOG)35–55 peptide in complete Freund’s adjuvant (CFA) containing 5 mg/ml heat-killed M. tuberculosis. Control diet mice exhibited onset of severe clinical symptoms of hind limb paralysis similarly to young wild-type controls, while diet-induced obese mice experienced a significantly delayed onset. Clinical scores correlated with greater number of MOG-specific tetramer-positive CD4 T cells and number of IFN-gamma and IL-17a-expressing CD4 T cells in the CNS of control mice compared to obese mice. Decreased functional cytokine expression and proliferation called into question the exhaustive nature of T cells in obese mice through the upregulation of the PD-1/PD-L1 pathway, a known regulator of EAE. We treated EAE-induced mice on control and high-fat diet with anti-PD-1 blockade (29F.1A12) and restored EAE induction in both clinical score and number of pathologic CD4 T cells in the CNS of obese mice. Our findings may indicate an impairment of the adaptive immune system through the PD-1/PD-L1 pathway in obesity, possibly indicating an augmentation of the checkpoint pathway in settings of systemic inflammation.

Obesity results in higher PD-1-mediated T-cell suppression but greater T-cell effector functions following blockade

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Background: Obesity is increasingly prevalent and viewed as a critical co-factor in many pathologic conditions due to metabolic, inflammatory and immune perturbations. We performed a multi-species evaluation of the impact of obesity T cell effector functions and markers of immune exhaustion. Methods: We examined the impact of obesity on PD-1 and T cell-mediated responses across different pre-clinical models (tumor, infection, and autoimmune encephalomyelitis [EAE]) and species (mouse, dog, non-human primate, and human). Results: CD4 and CD8 T cells from obese mice, dogs, non-human primates and humans displayed increases in memory T cells and PD-1 expression, as well as impaired proliferative responses compared to lean controls, indicating a greater degree of T cell exhaustion at baseline. Following immunization with myelin oligodendrocyte glycoprotein, obese mice were resistant to induction of EAE, correlating with reduced antigen-specific CD4 T cells in the central nervous system. Administration of anti-PD-1 resulted in restoration of EAE and increased antigen-specific T cell numbers in obese mice. Tumors in obese mice exhibited accelerated growth compared to lean mice, and T cells displayed higher PD-1 expression correlating with RNAseq/molecular signatures of exhaustion compared to tumor-bearing lean mice. PD-1 blockade resulted in marked anti-tumor effects only in obese mice, and not lean. Impaired viral resistance to murine cytomegalovirus (MCMV) resulted was seen in obese mice, associated with increased PD-1/PD-L1 expression, which was reversible by PD-1/PD-L1 blockade. Conclusions: Obesity results in an increase in PD-1/PD-L1 expression and inhibition of T cell responses across species, and blockade not only reverses this inhibition but also leads to markedly augmented T cell effector responses compared to lean counterparts where no effects were observed. These results highlight how the immune system has evolved to control T cell responses using checkpoints contingent on dynamic host conditions and have translational relevance for predicting both efficacy and toxicity in clinical immuno-oncology.

Licensing delineates helper and effector NK cell subsets during viral infection

Natural killer (NK) cells can be divided into phenotypic subsets based on expression of receptors that bind self-MHC-I molecules, a concept termed licensing or education. Here we show NK cell subsets with different migratory, effector, and immunoregulatory functions in dendritic cell and antigen (ag)-specific CD8+ T cell responses during influenza and murine cytomegalovirus infections. Shortly after infection, unlicensed NK cells localized in draining lymph nodes and produced GM-CSF, which correlated with the expansion and activation of dendritic cells, and resulted in greater and sustained ag-specific T cell responses. In contrast, licensed NK cells preferentially migrated to infected tissues and produced IFN-γ. Importantly, human NK cell subsets exhibited similar phenotypic characteristics. Collectively, our studies demonstrate a critical demarcation between the functions of licensed and unlicensed NK cell subsets, with the former functioning as the classical effector subset and the latter as the stimulator of adaptive immunity helping to prime immune responses.

Obesity predisposes to rapid gastrointestinal graft-versus-host disease lethality after allogeneic hematopoietic stem cell transplantation in mice

Obesity is a form of chronic inflammation, termed “meta-inflammation”, resulting in the development of many chronic diseases such as diabetes and cancer. In this study, we assessed the impact of obesity on recipient graft-versus-host disease (GVHD) outcome post allogeneic HSCT using mouse models. In a model of sclerodermatous chronic GVHD, lean or diet-induced obese (DIO) BALB/c mice received 800 cGy total body irradiation (TBI), bone marrow cells, and splenocytes from H2-identical but minor MHC-mismatched B10.D2 mice. To mimic major MHC mismatch transplant which results in acute GVHD impacting gut, skin and liver, lean or DIO C57BL/6 mice received 1050 cGy TBI, bone marrow cells, and different doses of purified T cells from BALB/c mice. Strikingly, after the minor mismatch HSCT, all DIO mice succumbed to gut pathology while all lean mice survived and developed sclerodermatous GVHD at week 3 post transplant. In both models, pathological assessment indicated marked gut pathology in DIO mice correlating with lethality. Lean mice in the major MHC mismatch strain combination had significantly increased survival and less severe gut pathology compared to the DIO mice. The DIO mice had higher expression of pro-inflammatory cytokines in the gut, liver, visceral fat, and serum post-HSCT. Flow cytometric analysis demonstrated increased numbers of donor CD8+ T cells in the gut of DIO mice compared to lean mice. In an initial evaluation, untreated DIO mice displayed increased gut permeability as well as having limited diversity in their microbiome which would contribute to severe GVHD post-HSCT. Taken together, these results indicate that obesity exacerbates GVHD after allogeneic HSCT primarily affecting the gastrointestinal tract.

The immune environment dictates the dominance of licensed versus unlicensed natural killer cell subsets during viral infection

Natural Killer (NK) cells are innate lymphocytes involved in anti-viral and anti-cancer responses. They can be functionally and phenotypically divided based on expression of inhibitory receptors capable of binding to self-MHC class I, a concept termed licensing/education. NK cells capable of binding to self-MHC (licensed) have been shown to be more functionally competent compared to those that cannot (unlicensed). It is still unclear which subset is more critical during an anti-viral response. Using two models of murine cytomegalovirus infection (MCMV), we show distinct subsets of NK cells that can both directly and indirectly contribute to the anti-viral response. We have previously shown that after hematopoietic stem cell transplantation (HSCT), the licensed effector NK population was predominantly responsible for resistance to MCMV, which was in part due to the absence of T cells present immediately after transplant. However, MCMV infection in non-HSCT mice yielded an opposite pattern with the unlicensed NK subset augmenting resistance to MCMV. We found preferential localization patterns of the different NK subsets which correlated with increased antigen specific T cell expansion and viral clearance. Interestingly, by depleting the different NK subsets in HSCT vs non-HSCT mice, we demonstrated differences in subset roles. The unlicensed NK cells, which promote antigen specific T cells, are more critical during normal conditions, while the licensed NK cells serve a better direct anti-viral role following HSCT where T cells take longer to repopulate. Thus, the contributions of these different NK subsets and their dependence on the immune environment should be taken into consideration when applying NK cells therapeutically.