A Phase Ib Expansion Cohort Evaluating Aurora A Kinase Inhibitor Alisertib and Dual TORC1/2 Inhibitor Sapanisertib in Patients with Advanced Solid Tumors

BACKGROUND

This study further evaluated the safety and efficacy of the combination of alisertib and sapanisertib in an expansion cohort of patients, including a subset of patients with refractory pancreatic adenocarcinoma, with further evaluation of the pharmacodynamic characteristics of combination therapy.

METHODS

Twenty patients with refractory solid tumors and 11 patients with pancreatic adenocarcinoma were treated at the recommended phase 2 dose of alisertib and sapanisertib. Adverse events and disease response were assessed. Patients in the expansion cohort were treated with a 7-day lead-in of either alisertib or sapanisertib prior to combination therapy, with tumor tissue biopsy and serial functional imaging performed for correlative analysis.

RESULTS

Toxicity across treatment groups was overall similar to prior studies. One partial response to treatment was observed in a patient with ER positive breast cancer, and a patient with pancreatic cancer experienced prolonged stable disease. In an additional cohort of pancreatic cancer patients, treatment response was modest. Correlative analysis revealed variability in markers of apoptosis and immune cell infiltrate according to lead-in therapy and response.

CONCLUSIONS

Dual targeting of Aurora A kinase and mTOR resulted in marginal clinical benefit in a population of patients with refractory solid tumors, including pancreatic adenocarcinoma, though individual patients experienced significant response to therapy. Correlatives indicate apoptotic response and tumor immune cell infiltrate may affect clinical outcomes.

VDX-111, a novel small molecule, induces necroptosis to inhibit ovarian cancer progression

Epithelial ovarian cancers that are nonhomologous recombination deficient, as well as those that are recurrent and in a platinum-resistant state, have limited therapeutic options. The objectives of this study were to characterize the mechanism of action and investigate the therapeutic potential of a small molecule, VDX-111, against ovarian cancer. We examined the ability of VDX-111 to inhibit the growth of a panel of ovarian cancer cell lines, focusing on BRCA wild-type lines. We found that VDX-111 causes a dose-dependent loss of cell viability across ovarian cancer cell lines. Reverse phase protein array (RPPA) analysis was used to identify changes in cell signaling in response to VDX-111 treatment. An RPPA analysis performed on cells treated with VDX-111 detected changes in cell signaling related to autophagy and necroptosis. Immunoblots of OVCAR3 and SNU8 cells confirmed a dose-dependent increase in LC3A/B and RIPK1. Incucyte live cell imaging was used to measure cell proliferation and death in response to VDX-111 alone and with inhibitors of apoptosis, necroptosis, and autophagy. Annexin/PI assays suggested predominantly nonapoptotic cell death, while real-time kinetic imaging of cell growth indicated the necroptosis inhibitor, necrostatin-1, attenuates VDX-111-induced loss of cell viability, suggesting a necroptosis-dependent mechanism. Furthermore, VDX-111 inhibited tumor growth in patient-derived xenograft and syngeneic murine models. In conclusion, the cytotoxic effects of VDX-111 seen in vitro and in vivo appear to occur in a necroptosis-dependent manner and may promote an antitumor immune response.

Targeting Tryptophan Catabolism in Ovarian Cancer to Attenuate Macrophage Infiltration and PD-L1 Expression

High-grade serous carcinoma (HGSC) of the fallopian tube, ovary, and peritoneum is the most common type of ovarian cancer and is predicted to be immunogenic because the presence of tumor-infiltrating lymphocytes conveys a better prognosis. However, the efficacy of immunotherapies has been limited because of the immune-suppressed tumor microenvironment (TME). Tumor metabolism and immune-suppressive metabolites directly affect immune cell function through the depletion of nutrients and activation of immune-suppressive transcriptional programs. Tryptophan (TRP) catabolism is a contributor to HGSC disease progression. Two structurally distinct rate-limiting TRP catabolizing enzymes, indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2), evolved separately to catabolize TRP. IDO1/TDO2 are aberrantly expressed in carcinomas and metabolize TRP into the immune-suppressive metabolite kynurenine (KYN), which can engage the aryl hydrocarbon receptor to drive immunosuppressive transcriptional programs. To date, IDO inhibitors tested in clinical trials have had limited efficacy, but those inhibitors did not target TDO2, and we find that HGSC cell lines and clinical outcomes are more dependent on TDO2 than IDO1. To identify inflammatory HGSC cancers with poor prognosis, we stratified patient ascites samples by IL6 status, which correlates with poor prognosis. Metabolomics revealed that IL6-high patient samples had enriched KYN. TDO2 knockdown significantly inhibited HGSC growth and TRP catabolism. The orally available dual IDO1/TDO2 inhibitor, AT-0174, significantly inhibited tumor progression, reduced tumor-associated macrophages, and reduced expression of immune-suppressive proteins on immune and tumor cells. These studies demonstrate the importance of TDO2 and the therapeutic potential of AT-0174 to overcome an immune-suppressed TME.

SIGNIFICANCE

Developing strategies to improve response to chemotherapy is essential to extending disease-free intervals for patients with HGSC of the fallopian tube, ovary, and peritoneum. In this article, we demonstrate that targeting TRP catabolism, particularly with dual inhibition of TDO2 and IDO1, attenuates the immune-suppressive microenvironment and, when combined with chemotherapy, extends survival compared with chemotherapy alone.

SARS-CoV-2 Vaccine-Elicited Immunity after B Cell Depletion in Multiple Sclerosis

The impact of B cell deficiency on the humoral and cellular responses to SARS-CoV2 mRNA vaccination remains a challenging and significant clinical management question. We evaluated vaccine-elicited serological and cellular responses in 1) healthy individuals who were pre-exposed to SARS-CoV-2 (n = 21), 2) healthy individuals who received a homologous booster (mRNA, n = 19; or Novavax, n = 19), and 3) persons with multiple sclerosis on B cell depletion therapy (MS-αCD20) receiving mRNA homologous boosting (n = 36). Pre-exposure increased humoral and CD4 T cellular responses in immunocompetent individuals. Novavax homologous boosting induced a significantly more robust serological response than mRNA boosting. MS-α CD20 had an intact IgA mucosal response and an enhanced CD8 T cell response to mRNA boosting compared with immunocompetent individuals. This enhanced cellular response was characterized by the expansion of only effector, not memory, T cells. The enhancement of CD8 T cells in the setting of B cell depletion suggests a regulatory mechanism between B and CD8 T cell vaccine responses.

A platform-independent framework for phenotyping of multiplex tissue imaging data

Multiplex imaging is a powerful tool to analyze the structural and functional states of cells in their morphological and pathological contexts. However, hypothesis testing with multiplex imaging data is a challenging task due to the extent and complexity of the information obtained. Various computational pipelines have been developed and validated to extract knowledge from specific imaging platforms. A common problem with customized pipelines is their reduced applicability across different imaging platforms: Every multiplex imaging technique exhibits platform-specific characteristics in terms of signal-to-noise ratio and acquisition artifacts that need to be accounted for to yield reliable and reproducible results. We propose a pixel classifier-based image preprocessing step that aims to minimize platform-dependency for all multiplex image analysis pipelines. Signal detection and noise reduction as well as artifact removal can be posed as a pixel classification problem in which all pixels in multiplex images can be assigned to two general classes of either I) signal of interest or II) artifacts and noise. The resulting feature representation maps contain pixel-scale representations of the input data, but exhibit significantly increased signal-to-noise ratios with normalized pixel values as output data. We demonstrate the validity of our proposed image preprocessing approach by comparing the results of two well-accepted and widely-used image analysis pipelines.

Combination CDC-like kinase inhibition (CLK)/Dual-specificity tyrosine-regulated kinase (DYRK) and taxane therapy in CTNNB1-mutated endometrial cancer

SM08502 (cirtuvivint) is a novel pan CDC-like kinase (CLK) and Dual specificity tyrosine kinase (DYRK) inhibitor that targets mRNA splicing and is optimized for Wnt pathway inhibition. Previous evaluation of single agent CLK/DYRK inhibition (SM04690) demonstrated inhibition of tumor progression and β-catenin/TCF transcriptional activity in CTNNB1-mutant endometrial cancer (EC). In-vitro analysis of SM08502 similarly decreases Wnt transcriptional activity and cellular proliferation while increasing cellular apoptosis. SM08502 is an active single-agent therapy with IC50's in the nanomolar range for all EC cell lines evaluated. Combination of SM08502 with paclitaxel has synergistic effect in vitro, as demonstrated by Combination Index <1, and inhibits tumor progression in four endometrial cancer models (HEC265, Ishikawa, Ishikawa-S33Y, and SNGM). In our in vivo mouse models, Ishikawa demonstrated significantly lower tumor volumes of combination vs SM08502 alone (Repeated Measures one-way ANOVA, p = 0.04), but not vs paclitaxel alone. HEC265, SNGM, and Ishikawa-S33Y tumors all had significantly lower tumor volumes with combination SM08502 and paclitaxel compared to single-agent paclitaxel (Repeated Measures one-way ANOVA, p = 0.01, 0.004, and 0.0008, respectively) or single-agent SM08502 (Repeated Measures one-way ANOVA, p = 0.002, 0.005, and 0.01, respectively) alone. Mechanistically, treatment with SM08502 increases alternative splicing (AS) events compared to treatment with paclitaxel. AS regulation is an important post-transcriptional mechanism associated with the oncogenic process in many cancers, including EC. Results from these studies have led to a Phase I evaluation of this combination in recurrent EC.

Targeting MDSC Differentiation Using ATRA: A Phase I/II Clinical Trial Combining Pembrolizumab and All-Trans Retinoic Acid for Metastatic Melanoma

PURPOSE

A phase Ib/II clinical trial was conducted to evaluate the safety and efficacy of the combination of all-trans retinoic acid (ATRA) with pembrolizumab in patients with stage IV melanoma.

PATIENTS AND METHODS

Anti-PD-1 naïve patients with stage IV melanoma were treated with pembrolizumab plus supplemental ATRA for three days surrounding each of the first four pembrolizumab infusions. The primary objective was to establish the MTD and recommended phase II dose (RP2D) of the combination. The secondary objectives were to describe the safety and toxicity of the combined treatment and to assess antitumor activity in terms of (i) the reduction in circulating myeloid-derived suppressor cell (MDSC) frequency and (ii) progression-free survival (PFS).

RESULTS

Twenty-four patients were enrolled, 46% diagnosed with M1a and 29% with M1c stage disease at enrollment. All patients had an ECOG status ≤1, and 75% had received no prior therapies. The combination was well tolerated, with the most common ATRA-related adverse events being headache, fatigue, and nausea. The RP2D was established at 150 mg/m2 ATRA + 200 mg Q3W pembrolizumab. Median PFS was 20.3 months, and the overall response rate was 71%, with 50% of patients experiencing a complete response, and the 1-year overall survival was 80%. The combination effectively lowered the frequency of circulating MDSCs.

CONCLUSIONS

With a favorable tolerability and high response rate, this combination is a promising frontline treatment strategy for advanced melanoma. Targeting MDSCs remains an attractive mechanism to enhance the efficacy of immunotherapies, and this combination merits further investigation. See related commentary by Olson and Luke, p. 1167.

Expression and T cell regulatory action of the PD-1 immune checkpoint in the ovary and fallopian tube

PROBLEM

Immune cell trafficking and surveillance within the ovary and fallopian tube are thought to impact fertility and also tumorigenesis in those organs. However, little is known of how native cells of the ovary and fallopian tube interact with resident immune cells. Interaction of the Programmed Cell Death Protein-1 (PD-1/PDCD-1/CD279) checkpoint with PD-L1 is associated with downregulated immune response. We have begun to address the question of whether PD-1 ligand or its receptors (PD-L1/-L2) can regulate immune cell function in these tissues of the female reproductive tract.

METHOD OF STUDY

PD-1 and ligand protein expression was evaluated in human ovary and fallopian tube specimens, the latter of which included stages of tubal cell transformation and early tumorigenesis. Ovarian expression analysis included the determination of the proteins in human follicular fluid (HFF) specimens collected during in vitro fertilization procedures. Finally, checkpoint bioactivity of HFF was determined by treatment of separately-isolated human T cells and the measurement of interferon gamma (IFNγ).

RESULTS

We show that membrane bound and soluble variants of PD-1 and ligands are expressed by permanent constituent cell types of the human ovary and fallopian tube, including granulosa cells and oocytes. PD-1 and soluble ligands were present in HFF at bioactive levels that control T cell PD-1 activation and IFNγ production; full-length checkpoint proteins were found to be highly enriched in HFF exosome fractions.

CONCLUSION

The detection of PD-1 checkpoint proteins in the human ovary and fallopian tube suggests that the pathway is involved in immunomodulation during folliculogenesis, the window of ovulation, and subsequent egg and embryo immune-privilege. Immunomodulatory action of receptor and ligands in HFF exosomes is suggestive of an acute checkpoint role during ovulation. This is the first study in the role of PD-1 checkpoint proteins in human tubo-ovarian specimens and the first examination of its potential regulatory action in the contexts of normal and assisted reproduction.

Combinatory EHMT and PARP inhibition induces an interferon response and a CD8 T cell-dependent tumor regression in PARP inhibitor-resistant models

Euchromatic histone lysine methyltransferases 1 and 2 (EHMT1/2), which catalyze demethylation of histone H3 lysine 9 (H3K9me2), contribute to tumorigenesis and therapy resistance through unknown mechanisms of action. In ovarian cancer, EHMT1/2 and H3K9me2 are directly linked to acquired resistance to poly-ADP-ribose polymerase (PARP) inhibitors and are correlated with poor clinical outcomes. Using a combination of experimental and bioinformatic analyses in several PARP inhibitor resistant ovarian cancer models, we demonstrate that combinatory inhibition of EHMT and PARP is effective in treating PARP inhibitor resistant ovarian cancers. Our in vitro studies show that combinatory therapy reactivates transposable elements, increases immunostimulatory dsRNA formation, and elicits several immune signaling pathways. Our in vivo studies show that both single inhibition of EHMT and combinatory inhibition of EHMT and PARP reduces tumor burden, and that this reduction is dependent on CD8 T cells. Together, our results uncover a direct mechanism by which EHMT inhibition helps to overcome PARP inhibitor resistance and shows how an epigenetic therapy can be used to enhance anti-tumor immunity and address therapy resistance.

On clustering for cell-phenotyping in multiplex immunohistochemistry (mIHC) and multiplexed ion beam imaging (MIBI) data

OBJECTIVE

Multiplex immunohistochemistry (mIHC) and multiplexed ion beam imaging (MIBI) images are usually phenotyped using a manual thresholding process. The thresholding is prone to biases, especially when examining multiple images with high cellularity.

RESULTS

Unsupervised cell-phenotyping methods including PhenoGraph, flowMeans, and SamSPECTRAL, primarily used in flow cytometry data, often perform poorly or need elaborate tuning to perform well in the context of mIHC and MIBI data. We show that, instead, semi-supervised cell clustering using Random Forests, linear and quadratic discriminant analysis are superior. We test the performance of the methods on two mIHC datasets from the University of Colorado School of Medicine and a publicly available MIBI dataset. Each dataset contains a bunch of highly complex images.

Specialized interferon action in COVID-19

The impacts of interferon (IFN) signaling on COVID-19 pathology are multiple, with both protective and harmful effects being documented. We report here a multiomics investigation of systemic IFN signaling in hospitalized COVID-19 patients, defining the multiomics biosignatures associated with varying levels of 12 different type I, II, and III IFNs. The antiviral transcriptional response in circulating immune cells is strongly associated with a specific subset of IFNs, most prominently IFNA2 and IFNG. In contrast, proteomics signatures indicative of endothelial damage and platelet activation associate with high levels of IFNB1 and IFNA6. Seroconversion and time since hospitalization associate with a significant decrease in a specific subset of IFNs. Additionally, differential IFN subtype production is linked to distinct constellations of circulating myeloid and lymphoid immune cell types. Each IFN has a unique metabolic signature, with IFNG being the most associated with activation of the kynurenine pathway. IFNs also show differential relationships with clinical markers of poor prognosis and disease severity. For example, whereas IFNG has the strongest association with C-reactive protein and other immune markers of poor prognosis, IFNB1 associates with increased neutrophil to lymphocyte ratio, a marker of late severe disease. Altogether, these results reveal specialized IFN action in COVID-19, with potential diagnostic and therapeutic implications.

The Spatial Context of Tumor-Infiltrating Immune Cells Associates with Improved Ovarian Cancer Survival

Ovarian cancer is the deadliest gynecologic malignancy. Multi-omics techniques have provided a platform for improved predictive modeling of therapy response and patient outcomes. While high-grade serous carcinoma (HGSOC) tumors are immunogenic and numerous studies have defined positive correlation to immune cell infiltration, immunotherapies in clinical trials have exhibited low efficacy rates. There is a significant need to better comprehend the role and composition of immune cells in mediating ovarian cancer therapeutic response and progression. We performed multiplex IHC with an HGSOC tissue microarray (n = 127) to characterize the immune cell composition within tumors. After analyzing the composition and spatial context of T cells (CD4/CD8), macrophages (CD68), and B cells (CD19) within the tumor, we found that increased B-cell and CD4 T-cell presence correlated with overall survival. More importantly, we observed that the proximity between tumor-associated macrophages and B cells or CD4 T cells significantly correlated with overall survival. IMPLICATIONS: The results highlight the antitumor role of B cells and CD4 T cells, and that the spatial interactions between immune cell types are a novel predictor of therapeutic response and patient outcomes.

Pembrolizumab and all-trans retinoic acid combination treatment of advanced melanoma

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Background: Myeloid-derived suppressor cells (MDSCs) are potent suppressors of antitumor immunity and are commonly associated with poor outcomes in melanoma patients treated with immune checkpoint inhibitors. Inducing the differentiation of MDSCs using all-trans retinoic acid (ATRA) reduces MDSC frequency. This analysis seeks to assess the safety and efficacy of combining ATRA and pembrolizumab in advanced melanoma patients. Methods: This single arm, single institution, phase I/II study (NCT03200847) enrolled 24 patients diagnosed with stage IV melanoma. Eligible patients were over the age of 18 and had not been previously treated anti-PD-1 therapy. Treatment consisted of 200mg Q3W pembrolizumab plus the supplemental treatment of 150 mg/m2 ATRA orally for 3 days surrounding each of the first four infusions of pembrolizumab, with patients continuing pembrolizumab for up to two years until confirmed disease progression or unacceptable toxicity. The primary endpoints were safety and reduction in circulating MDSCs. Secondary endpoints were overall response rate (ORR), disease control rate (DCR), progression free survival (PFS) according to RECIST v1.1. Results: At data cut off (Feb, 2021) 22 patients were evaluable for tumor response. Median follow-up was 1.0 years (0.3-2 years). In general, the combination of pembrolizumab and ATRA was well tolerated. The most common treatment-related adverse events (AEs) were grade 1 or 2, including headache (22 pts, 92%), fatigue (18 pts, 75%), rash (16 pts, 66%), and nausea (8 pts, 33%), most of which corresponded with the 3-day course of ATRA treatment. Ten patients had grade 3 or higher AEs with most being common ICI-related AEs. The ORR was 60% and DCR was 83%. Six-month PFS rate was 62%. Excluding patients diagnosed with uveal melanoma (n = 2) the ORR was 72%, DCR was 86%, and the six-month PFS rate was 68%. Paired analysis showed sustained decreases in absolute numbers ( p = 0.002) and percentage ( p = 0.007) of circulating MDSCs (CD3-CD19-CD56-CD11b+CD33+HLA-DR-/low) 4-6 weeks after stopping ATRA. The study is ongoing and further data will be presented in the future. Conclusions: This study demonstrates that the combination of ATRA and pembrolizumab is well tolerated and suggests that reducing MDSCs with ATRA may enhance the efficacy of pembrolizumab. This strategy of targeting MDSCs in combination with pembrolizumab warrants further development. Research Funding: Merck. Clinical trial information: NCT03200847.

Adamantinomatous craniopharyngioma associated with a compromised blood–brain barrier: patient series

BACKGROUND

Adamantinomatous craniopharyngioma (ACP) is a highly morbid adult and pediatric brain tumor derived from epithelial remnants of the craniopharyngeal canal (Rathke’s pouch), which gives rise to the anterior pituitary gland. Standard therapy includes maximal safe resection with or without radiation therapy. Systemic antitumor therapy remains elusive. Immune-related paracrine signaling involving the interleukin-6 receptor (IL-6R) may contribute to ACP pathogenesis. Tocilizumab, a recombinant humanized monoclonal antibody against IL-6R, is approved by the US Food and Drug Administration but does not cross an intact blood–brain barrier.

OBSERVATIONS

In a phase 0 trial design, a single dose of tocilizumab was delivered intravenously before clinically indicated surgical intervention in 3 children with ACP. The presence of tocilizumab was assayed in plasma, tumor tissue, tumor cyst fluid, and cerebrospinal fluid (n = 1) using a novel enzyme-linked immunosorbent assay. Tocilizumab reached ACP tumor tissue and/or cyst fluid after one systemic dose in every patient.

LESSONS

This finding helps explain extant data that indicate tocilizumab may contribute to ACP therapy. It further indicates that ACP does not reside behind an intact blood–brain barrier, dramatically broadening the range of potential antitumor therapies against this tumor. This has substantial implications for the design of future clinical trials for novel therapies against ACP in both children and adults.

Seroconversion stages COVID19 into distinct pathophysiological states

COVID19 is a heterogeneous medical condition involving diverse underlying pathophysiological processes including hyperinflammation, endothelial damage, thrombotic microangiopathy, and end-organ damage. Limited knowledge about the molecular mechanisms driving these processes and lack of staging biomarkers hamper the ability to stratify patients for targeted therapeutics. We report here the results of a cross-sectional multi-omics analysis of hospitalized COVID19 patients revealing that seroconversion status associates with distinct underlying pathophysiological states. Low antibody titers associate with hyperactive T cells and NK cells, high levels of IFN alpha, gamma and lambda ligands, markers of systemic complement activation, and depletion of lymphocytes, neutrophils, and platelets. Upon seroconversion, all of these processes are attenuated, observing instead increases in B cell subsets, emergency hematopoiesis, increased D-dimer, and hypoalbuminemia. We propose that seroconversion status could potentially be used as a biosignature to stratify patients for therapeutic intervention and to inform analysis of clinical trial results in heterogenous patient populations.

The COVIDome Explorer Researcher Portal

COVID-19 pathology involves dysregulation of diverse molecular, cellular, and physiological processes. In order to expedite integrated and collaborative COVID-19 research, we completed multi-omics analysis of hospitalized COVID-19 patients including matched analysis of the whole blood transcriptome, plasma proteomics with two complementary platforms, cytokine profiling, plasma and red blood cell metabolomics, deep immune cell phenotyping by mass cytometry, and clinical data annotation. We refer to this multidimensional dataset as the COVIDome. We then created the COVIDome Explorer, an online researcher portal where the data can be analyzed and visualized in real time. We illustrate here the use of the COVIDome dataset through a multi-omics analysis of biosignatures associated with C-reactive protein (CRP), an established marker of poor prognosis in COVID-19, revealing associations between CRP levels and damage-associated molecular patterns, depletion of protective serpins, and mitochondrial metabolism dysregulation. We expect that the COVIDome Explorer will rapidly accelerate data sharing, hypothesis testing, and discoveries worldwide.

Induction of ADAM10 by Radiation Therapy Drives Fibrosis, Resistance, and Epithelial-to-Mesenchyal Transition in Pancreatic Cancer

Stromal fibrosis activates prosurvival and proepithelial-to-mesenchymal transition (EMT) pathways in pancreatic ductal adenocarcinoma (PDAC). In patient tumors treated with neoadjuvant stereotactic body radiation therapy (SBRT), we found upregulation of fibrosis, extracellular matrix (ECM), and EMT gene signatures, which can drive therapeutic resistance and tumor invasion. Molecular, functional, and translational analysis identified two cell-surface proteins, a disintegrin and metalloprotease 10 (ADAM10) and ephrinB2, as drivers of fibrosis and tumor progression after radiation therapy (RT). RT resulted in increased ADAM10 expression in tumor cells, leading to cleavage of ephrinB2, which was also detected in plasma. Pharmacologic or genetic targeting of ADAM10 decreased RT-induced fibrosis and tissue tension, tumor cell migration, and invasion, sensitizing orthotopic tumors to radiation killing and prolonging mouse survival. Inhibition of ADAM10 and genetic ablation of ephrinB2 in fibroblasts reduced the metastatic potential of tumor cells after RT. Stimulation of tumor cells with ephrinB2 FC protein reversed the reduction in tumor cell invasion with ADAM10 ablation. These findings represent a model of PDAC adaptation that explains resistance and metastasis after RT and identifies a targetable pathway to enhance RT efficacy. SIGNIFICANCE: Targeting a previously unidentified adaptive resistance mechanism to radiation therapy in PDAC tumors in combination with radiation therapy could increase survival of the 40% of PDAC patients with locally advanced disease.See related commentary by Garcia Garcia et al., p. 3158 GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/12/3255/F1.large.jpg.

Seroconversion stages COVID19 into distinct pathophysiological states

COVID19 is a heterogeneous medical condition involving a suite of underlying pathophysiological processes including hyperinflammation, endothelial damage, thrombotic microangiopathy, and end-organ damage. Limited knowledge about the molecular mechanisms driving these processes and lack of staging biomarkers hamper the ability to stratify patients for targeted therapeutics. We report here the results of a cross-sectional multi-omics analysis of hospitalized COVID19 patients revealing that seroconversion status associates with distinct underlying pathophysiological states. Seronegative COVID19 patients harbor hyperactive T cells and NK cells, high levels of IFN alpha, gamma and lambda ligands, markers of systemic complement activation, neutropenia, lymphopenia and thrombocytopenia. In seropositive patients, all of these processes are attenuated, observing instead increases in B cell subsets, emergency hematopoiesis, increased markers of platelet activation, and hypoalbuminemia. We propose that seroconversion status could potentially be used as a biosignature to stratify patients for therapeutic intervention and to inform analysis of clinical trial results in heterogenous patient populations.

Extracellular vesicles from young women's breast cancer patients drive increased invasion of non-malignant cells via the Focal Adhesion Kinase pathway: a proteomic approach

Background

Extracellular vesicles (EVs) are small membrane particles that contribute to cancer progression and metastases by transporting biologically significant proteins and nucleic acids. They may also serve as biomarkers of various disease states or important therapeutic targets. Breast cancer EVs have the potential to change the behavior of other cells in their microenvironment. However, the proteomic content of EVs isolated from young women’s breast cancer patients and the mechanisms underlying the influence of EVs on tumor cell behavior have not yet been reported.

Methods

In our current translational studies, we compared the proteomic content of EVs isolated from invasive breast cancer cell lines and plasma samples from young women’s breast cancer (YWBC) patients and age-matched healthy donors using mass spectrometry. We analyzed the functionality of EVs in two dimensional tumor cell invasion assays and the gene expression changes in tumor cells after incubation with EVs.

Results

We found that treatment with EVs from both invasive breast cancer cell lines and plasma of YWBC patients altered the invasive properties of non-invasive breast cancer cells. Proteomics identified differences between EVs from YWBC patients and healthy donors that correlated with their altered function. Further, we identified gene expression changes in non-invasive breast cancer cells after treatment with EVs that implicate the Focal Adhesion Kinase (FAK) signaling pathway as a potential targetable pathway affected by breast cancer-derived EVs.

Conclusions

Our results suggest that the proteome of EVs from breast cancer patients reflects their functionality in tumor motility assays and may help elucidate the role of EVs in breast cancer progression.

Mass Cytometry Reveals Global Immune Remodeling with Multi-lineage Hypersensitivity to Type I Interferon in Down Syndrome

People with Down syndrome (DS; trisomy 21) display a different disease spectrum relative to the general population, including lower rates of solid malignancies and higher incidence of neurological and autoimmune conditions. However, the mechanisms driving this unique clinical profile await elucidation. We completed a deep mapping of the immune system in adults with DS using mass cytometry to evaluate 100 immune cell types, which revealed global immune dysregulation consistent with chronic inflammation, including key changes in the myeloid and lymphoid cell compartments. Furthermore, measurement of interferon-inducible phosphorylation events revealed widespread hypersensitivity to interferon-α in DS, with cell-type-specific variations in downstream intracellular signaling. Mechanistically, this could be explained by overexpression of the interferon receptors encoded on chromosome 21, as demonstrated by increased IFNAR1 surface expression in all immune lineages tested. These results point to interferon-driven immune dysregulation as a likely contributor to the developmental and clinical hallmarks of DS.

The Capacity of the Ovarian Cancer Tumor Microenvironment to Integrate Inflammation Signaling Conveys a Shorter Disease-free Interval

PURPOSE

Ovarian cancer has one of the highest deaths to incidence ratios across all cancers. Initial chemotherapy is effective, but most patients develop chemoresistant disease. Mechanisms driving clinical chemo-response or -resistance are not well-understood. However, achieving optimal surgical cytoreduction improves survival, and cytoreduction is improved by neoadjuvant chemotherapy (NACT). NACT offers a window to profile pre- versus post-NACT tumors, which we used to identify chemotherapy-induced changes to the tumor microenvironment.

EXPERIMENTAL DESIGN

We obtained matched pre- and post-NACT archival tumor tissues from patients with high-grade serous ovarian cancer (patient, n = 6). We measured mRNA levels of 770 genes (756 genes/14 housekeeping genes, NanoString Technologies), and performed reverse phase protein array (RPPA) on a subset of matched tumors. We examined cytokine levels in pre-NACT ascites samples (n = 39) by ELISAs. A tissue microarray with 128 annotated ovarian tumors expanded the transcriptional, RPPA, and cytokine data by multispectral IHC.

RESULTS

The most upregulated gene post-NACT was IL6 (16.79-fold). RPPA data were concordant with mRNA, consistent with elevated immune infiltration. Elevated IL6 in pre-NACT ascites specimens correlated with a shorter time to recurrence. Integrating NanoString (n = 12), RPPA (n = 4), and cytokine (n = 39) studies identified an activated inflammatory signaling network and induced IL6 and IER3 (immediate early response 3) post-NACT, associated with poor chemo-response and time to recurrence.

CONCLUSIONS

Multiomics profiling of ovarian tumor samples pre- and post-NACT provides unique insight into chemo-induced changes to the tumor microenvironment. We identified a novel IL6/IER3 signaling axis that may drive chemoresistance and disease recurrence.

HITM-SURE: Hepatic immunotherapy for metastases phase Ib anti-CEA CAR-T study utilizing pressure enabled drug delivery

In recent years, cell therapy technologies have resulted in impressive results in hematologic malignancies. Treatment of solid tumors with chimeric antigen receptor T-cells (CAR-T) has been less successful. Solid tumors present challenges not encountered with hematologic cancers, including high intra-tumoral pressure and ineffective CAR-T trafficking to the site of disease. Novel delivery methods may enable CAR-T therapies for solid tumor malignancies. A patient with liver metastases secondary to pancreatic adenocarcinoma received CAR-T targeting carcinoembryonic antigen (CEA). Previously we reported that Pressure-Enabled Drug Delivery (PEDD) enhanced CAR-T delivery to liver metastases 5.2-fold. Three doses of anti-CEA CAR-T were regionally delivered via hepatic artery infusion (HAI) using PEDD technology to optimize the therapeutic index. Interleukin-2 was systemically delivered by continuous intravenous infusion to support CAR-T in vivo. HAI of anti-CEA CAR-T was not associated with any serious adverse events (SAEs) above grade 3 and there were no on-target/off-tumor SAEs. Following CAR-T treatment, positron emission tomography-CT demonstrated a complete metabolic response within the liver, which was durable and sustained for 13 months. The response was accompanied by normalization of serum tumor markers and an abundance of CAR+ cells found within post-treatment tumor specimens. The findings from this report exhibit biologic activity and safety of regionally infused CAR-T for an indication with limited immune-oncology success to date. Further studies will determine how HAI of CAR-T may be included in multidisciplinary treatment plans for patients with liver metastases. ClinicalTrials.gov number, NCT02850536.

Abstract 5305: Characterization of the ovarian tumor transcriptome and microenvironment in pre and post-chemotherapy treated patients

Purpose: Ovarian cancer has one of the highest deaths to incidence ratios across all cancers. Initial chemotherapy is typically effective, but most patients will experience recurrence and enter a cycle of response and recurrence, ultimately developing resistant disease. Importantly, the understanding of mechanisms contributing to clinical chemoresistance in ovarian cancer is limited. Achieving optimal cytoreduction improves survival. Gynecologic oncologists therefore perform laparoscopy to evaluate resectability and collect tumor biopsies. Patients identified with un-resectable tumor receive three cycles of neoadjuvant platinum/taxane-based chemotherapy (NACT) to improve the likelihood of optimal cytoreductive surgery. NACT offers a previously unavailable window for identifying therapy-induced remodeling of the tumor, potentially providing insight into drivers of chemo-resistance.

Experimental Design: We accessed formalin fixed (FFPE) tumor tissue from high-grade serous ovarian cancer NACT patients (n=6) pre- and post-chemotherapy. RNA was extracted and the mRNA transcript levels were examined for 791 genes via the Immunoncology 360 NanoString panel. Further, using the pre-treated ascites fluid we examined the cytokine environment through MesoScale Discovery multiplex ELISA. Transcriptional and cytokine profiles were correlated to clinical outcomes, such as days to recurrence.

Results: Component analysis found that transcriptional profiles separated based on pre- and post-chemotherapy status. Comparing the pre- (n=6) and post-chemotherapy (n=6), the most upregulated gene following therapy was IL6 (4.1 log2 fold change, adj. p = 0.045) and the most downregulated gene was UBE2C (-3.9 log2 fold change, adj. p = 0.001). Elevated IL-6 within ascites correlated to a shorter time to recurrence. On the patient-by-patient basis we compared transcriptional changes between pre- and post therapy. We correlated these changes to IL6 expression and time to recurrence uncovered that an increase in Immediate Early Response 3 (IER3) is a poor prognostic indicator. IER3/IEX-1 is a NF-κB target gene involved in apoptosis and potentiates MAPK activation.

Conclusion: Using ovarian cancer tumors from NACT patients provides a unique insight into chemo-induced transcriptional changes. To-date little is known of IER3's function in ovarian cancer thus future work will focus on a potential novel IL-6/IER3 signaling axis that protects tumors from chemotherapy-induced apoptosis. Also, computer modeling and integration of transcriptional and cytokine date could also provide an approach to predict recurrence.

Citation Format: Kimberly R. Jordan, Jill Slansky, Angela Minic, Jennifer K. Richer, James C. Costello, Aaron J. Clauset, Rajendra T. Kumar, Kian Behbakht, Matthew J. Sikora, Benjamin G. Bitler. Characterization of the ovarian tumor transcriptome and microenvironment in pre and post-chemotherapy treated patients [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5305.

Abstract 6647: Sensitizing microsatellite stable colorectal cancer to immune checkpoint therapy utilizing Wnt pathway inhibition

Immunotherapies that target immune regulatory checkpoints such as CTLA-4 and PD-1 are widely used among many cancer types and have shown positive results in CRC with high microsatellite instability. However, in microsatellite stable (MSS) CRC there is a dismal response rate of 0%. The limited efficacy has shown to be partially due to the lack of T-cells in the tumor microenvironment and/or no activation/regulation of paramount cells in the immune system. The Wnt pathway is the most commonly altered pathway in CRC and is highly involved in driving tumor initiation and progression. Recent evidence also demonstrates the Wnt pathway is involved in T-lymphocyte development, maturation/activation of CD8+ effector T cells and recruitment of dendritic cells. Therefore, targeting the Wnt pathway utilizing a Porcupine (PORCN) inhibitor (ETC-159) in MSS CRC may be a promising strategy to sensitize tumors to immune checkpoint inhibition.

Human Immune System BRGS (BALB/c, Rag2−/−, IL2RγC−/−, NODSIRPα) mice were engrafted with MSS CRC PDX (hPDX). The hPDX were randomized according to human chimerism into the following drug treatments groups: Vehicle, ETC-159, nivolumab, and the combination. Treatments began when tumors reached 100-300mm3 and tumors were measured twice weekly. At the end of study, sera, lymph nodes, spleen, and tumor tissue were collected for immunohistochemistry, single cell suspensions, and flow cytometry analysis.

Combination therapy resulted in a significant decrease in tumor volume compared to both single agents and vehicle. Flow cytometric analysis demonstrated an increase in human immune cells, in particular human CD4 and CD8 cells in the combination compared to the vehicle and nivolumab treated groups. Additionally, these T-cells showed increased signs of activation and effector function, as indicated by increased CD69+ expression, effector memory subsets, and granzyme B+ cells in the TILs, with a further reduction in Treg populations, suggesting an overall increase in inflammation. An increase in MHC II expression on tumor cells was observed in the ETC-159 single agent with a statistically significant increase in the combination treated tumors demonstrating enhanced antigen presentation. Furthermore, PD-1 expression was upregulated on CD4+ T-cells in the ETC-159 single agent. Lastly, VECTRA analysis corroborates the flow cytometry data showing a changing tumor immune landscape through an increase in CD4+ and CD8+ T cells in the tumor and surrounding stroma.

Our data demonstrates the combination treatment of ETC-159 + nivolumab in MSS CRC hPDX show increased tumor infiltration of human immune cells. Further preclinical data is compulsory but these results support further development of this combination in clinical trials.

Citation Format: Stacey M. Bagby, Sarah J. Hartman, Natalie M. Navarro, Betelehem W. Yacob, Jeremy Shulman, Jessica Barkow, Christopher H. Lieu, S. Lindsey Davis, Alexis D. Leal, Wells A. Messersmith, Angela Minic, Kimberly R. Jordan, Julie Lang, Todd M. Pitts. Sensitizing microsatellite stable colorectal cancer to immune checkpoint therapy utilizing Wnt pathway inhibition [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6647.

Early pulmonary function changes associated with brigatinib initiation

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Background: Phase I-III studies reported symptomatic pulmonary toxicity within the first week of initiating brigatinib in 6% patients post-crizotinib and 3% in TKI naive patients with standard dosing (90mg QD for 7 days then 180mg QD as tolerated). A prospective observational study of pulmonary function testing (PFT) on initiating brigatinib was conducted. Methods: Patients PS≤2, with resting O2 sats on RA ≥90% and Hg ≥10 g/dL, without significant heart/lung disease or steroid use initiating brigatinib 90 mg QD were eligible. PFT with DLCO, Borg dyspnea and 6-minute walk tests were performed at baseline (prior to brigatinib), and on day 2 (D2), 8 (D8), and 15 (D15) of brigatinib. D15 analyses were initially as clinically indicated but became mandatory if DLCO had not returned to baseline by D8. Peripheral blood was collected at baseline, D2 and D8 for CyTOF analysis. The primary endpoint was the incidence of Early Onset Pulmonary Events (EOPEs), defined as a DLCO reduction of ≥ 20% from baseline. An interim analysis was performed on the first 10 patients due to a higher than expected incidence of DLCO reduction. Results: D2 and D8 measurements were captured in all 10 patients, D15 in 7 patients. Ninety percent (9/10) of patients experienced DLCO reduction with nadir occurring on D2 in 4/9 and on D8 in 5/9 patients. Median DLCO nadir was −13.33% from baseline (range: −34.44 to −5.00). Three patients (30%) met EOPE criteria, all on D8, all without symptoms. Brigatinib was not held and all 10 patients escalated to 180mg on D8. Despite continued dosing, 4/9 patients recovered DLCO to baseline or above by D15 (2/3 EOPEs cases), 2/9 recovered above nadir but below baseline by D15 (1/3 EOPE case), and 3/9 did not have improvement from nadir values but no D15 assessment was performed. Dyspnea and 6-minute walk test did not correlate with DLCO changes. Patients who experienced an EOPE had significantly higher levels of activated neutrophils (pERKhi) at baseline. On the day of the EOPE event, patients who met EOPE criteria had significantly higher levels of activated neutrophils and fewer activated CD4+ effector memory T cells. Conclusions: Modest DLCO reduction occurred in 90% (9/10) patients during the first 8 days of brigatinib-dosing without associated symptoms. When rechecked on D15, DLCO improved in 100% patients (6/6) despite continued dosing and standard dose escalation at D8. Patients unlikely to tolerate even this modest, short-lived change should consider shallower step-up dosing or alternative drugs. CyTOF analysis suggests levels of pretreatment neutrophils may be a biomarker for developing EOPEs. Clinical trial information: NCT03389399 .

High-Dimensional Analysis of Postsplenectomy Peripheral Immune Cell Changes

Although the consequences of splenectomy are well understood in mice, much less is known about the immunologic changes that occur following splenectomy in humans. We sought to characterize the circulating immune cell populations of patients before and after elective splenectomy to determine if these changes are related to postsplenectomy survival outcomes. Retrospective clinical information was collected from 95 patients undergoing elective splenectomy compared with 91 patients undergoing pancreaticoduodenectomy (Whipple procedure). We further analyzed peripheral blood from five patients in the splenectomy group, collected before and after surgery, using single-cell cytometry by time-of-flight mass spectrometry. We compared pre- and postsplenectomy data to characterize both the major and minor immune cell populations in significantly greater detail. Compared with patients undergoing a Whipple procedure, splenectomized patients had significant and long-lasting elevated counts of lymphocytes, monocytes, and basophils. Cytometry by time-of-flight mass spectroscopy analysis demonstrated that the elevated lymphocytes primarily consisted of naive CD4⁺ T cells and a population of activated CD25⁺CD56⁺CD4⁺ T cells, whereas the elevated monocyte counts were mainly mature, activated monocytes. We also observed a significant increase in the expression of the chemokine receptors CCR6 and CCR4 on several cellular populations. Taken together, these data indicate that significant immunological changes take place following splenectomy. Whereas other groups have compared splenectomized patients to healthy controls, this study compared patients undergoing elective splenectomy to those undergoing a similar major abdominal surgery. Overall, we found that splenectomy results in significant long-lasting changes in circulating immune cell populations and function.

Development of an Adrenocortical Cancer Humanized Mouse Model to Characterize Anti-PD1 Effects on Tumor Microenvironment

CONTEXT

Although the development of immune checkpoint inhibitors has transformed treatment strategies of several human malignancies, research models to study immunotherapy in adrenocortical carcinoma (ACC) are lacking.

OBJECTIVE

To explore the effect of anti-PD1 immunotherapy on the alteration of the immune milieu in ACC in a newly generated preclinical model and correlate with the response of the matched patient.

DESIGN, SETTING, AND INTERVENTION

To characterize the CU-ACC2-M2B patient-derived xenograft in a humanized mouse model, evaluate the effect of a PD-1 inhibitor therapy, and compare it with the CU-ACC2 patient with metastatic disease.

RESULTS

Characterization of the CU-ACC2-humanized cord blood-BALB/c-Rag2nullIl2rγnullSirpaNOD model confirmed ACC origin and match with the original human tumor. Treatment of the mice with pembrolizumab demonstrated significant tumor growth inhibition (60%) compared with controls, which correlated with increased tumor infiltrating lymphocyte activity, with an increase of human CD8+ T cells (P < 0.05), HLA-DR+ T cells (P < 0.05) as well as Granzyme B+ CD8+ T cells (<0.001). In parallel, treatment of the CU-ACC2 patient, who had progressive disease, demonstrated a partial response with 79% to 100% reduction in the size of target lesions, and no new sites of metastasis. Pretreatment analysis of the patient's metastatic liver lesion demonstrated abundant intratumoral CD8+ T cells by immunohistochemistry.

CONCLUSIONS

Our study reports the first humanized ACC patient-derived xenograft mouse model, which may be useful to define mechanisms and biomarkers of response and resistance to immune-based therapies, to ultimately provide more personalized care for patients with ACC.

IL-6 and IL-8 Are Linked With Myeloid-Derived Suppressor Cell Accumulation and Correlate With Poor Clinical Outcomes in Melanoma Patients

We sought to identify tumor-secreted factors that altered the frequency of MDSCs and correlated with clinical outcomes in advanced melanoma patients. We focused our study on several of the many factors involved in the expansion and mobilization of MDSCs. These were identified by measuring circulating concentrations of 13 cytokines and growth factors in stage IV melanoma patients (n = 55) and healthy controls (n = 22). Based on these results, we hypothesized that IL-6 and IL-8 produced by melanoma tumor cells participate in the expansion and recruitment of MDSCs and together would be predictive of overall survival in melanoma patients. We then compared the expression of IL-6 and IL-8 in melanoma tumors to the corresponding plasma concentrations and the frequency of circulating MDSCs. These measures were correlated with clinical outcomes. Patients with high plasma concentrations of either IL-6 (40%) or IL-8 (63%), or both (35%) had worse median overall survival compared to patients with low concentrations. Patients with low peripheral concentrations and low tumoral expression of IL-6 and IL-8 showed decreased frequencies of circulating MDSCs, and patients with low frequencies of MDSCs had better overall survival. We have previously shown that IL-6 is capable of expanding MDSCs, and here we show that MDSCs are chemoattracted to IL-8. Multivariate analysis demonstrated an increased risk of death for subjects with both high IL-6 and IL-8 (HR 3.059) and high MDSCs (HR 4.265). Together these results indicate an important role for IL-6 and IL-8 in melanoma patients in which IL-6 potentially expands peripheral MDSCs and IL-8 recruits these highly immunosuppressive cells to the tumor microenvironment. This study provides further support for identifying potential therapeutics targeting IL-6, IL-8, and MDSCs to improve melanoma treatments.

Mass-cytometry reveals global immune remodeling with multi-lineage hypersensitivity to Type I Interferon in Down syndrome

People with Down syndrome (DS), the genetic condition caused by trisomy of chromosome 21 (chr21), have an altered disease spectrum. For example, adults with DS are largely protected from solid tumors while predisposed to various autoimmune disorders, early-onset Alzheimer’s disease, and severe respiratory infection. While the immune system is known to play a key role in these comorbidities among the disomic population, there is a dearth of immune studies in adults with DS. Here, we applied the single-cell, systems-level approach of mass-cytometry, or Cytometry by Time-Of-Flight (CyTOF), to broadly define phenotypic and functional alterations in immune homeostasis in adults with DS that are relevant to the potentiation of comorbidities associated with T21. We developed an innovative strategy to analyze CyTOF data, by incorporating techniques commonly used in genomics and even topography to eliminate batch bias and efficiently resolve ~100 immune cell types. This approach revealed that adults with DS have global immune dysregulation reminiscent of various inflammatory and autoimmune states enriched among older individuals of the disomic population. Upon stimulation directly ex vivo with Type I Interferon (IFN) and simultaneous detection of diverse phosphorylation events across the lymphoid and myeloid lineages, all immune subsets from individuals with T21 were hyper-responsive, but the degree of response and signaling pathways used varied among specific cell types. Notably, 4 of the 6 IFN receptor subunits for Types I, II, and III IFNs are encoded on chr21. Altogether, these results establish a critical foundation to pursue immune dysregulation and IFN hyperactivity as a driver of the altered disease spectrum in adults with DS.

Pancreatic Tumor Microenvironment Modulation by EphB4-ephrinB2 Inhibition and Radiation Combination

PURPOSE

A driving factor in pancreatic ductal adenocarcinoma (PDAC) treatment resistance is the tumor microenvironment, which is highly immunosuppressive. One potent immunologic adjuvant is radiotherapy. Radiation, however, has also been shown to induce immunosuppressive factors, which can contribute to tumor progression and formation of fibrotic tumor stroma. To capitalize on the immunogenic effects of radiation and obtain a durable tumor response, radiation must be rationally combined with targeted therapies to mitigate the influx of immunosuppressive cells and fibrosis. One such target is ephrinB2, which is overexpressed in PDAC and correlates negatively with prognosis.Experimental Design: On the basis of previous studies of ephrinB2 ligand-EphB4 receptor signaling, we hypothesized that inhibition of ephrinB2-EphB4 combined with radiation can regulate the microenvironment response postradiation, leading to increased tumor control in PDAC. This hypothesis was explored using both cell lines and in vivo human and mouse tumor models.

RESULTS

Our data show this treatment regimen significantly reduces regulatory T-cell, macrophage, and neutrophil infiltration and stromal fibrosis, enhances effector T-cell activation, and decreases tumor growth. Furthermore, our data show that depletion of regulatory T cells in combination with radiation reduces tumor growth and fibrosis.

CONCLUSIONS

These are the first findings to suggest that in PDAC, ephrinB2-EphB4 interaction has a profibrotic, protumorigenic role, presenting a novel and promising therapeutic target.

Characterization of immune responses to anti-PD-1 mono and combination immunotherapy in hematopoietic humanized mice implanted with tumor xenografts

Background

The success of agents that reverse T-cell inhibitory signals, such as anti-PD-1/PD-L1 therapies, has reinvigorated cancer immunotherapy research. However, since only a minority of patients respond to single-agent therapies, methods to test the potential anti-tumor activity of rational combination therapies are still needed. Conventional murine xenograft models have been hampered by their immune-compromised status; thus, we developed a hematopoietic humanized mouse model, hu-CB-BRGS, and used it to study anti-tumor human immune responses to triple-negative breast cancer (TNBC) cell line and patient-derived colorectal cancer (CRC) xenografts (PDX).

Methods

BALB/c-Rag2^nullIl2rγ^nullSIRPα^NOD (BRGS) pups were humanized through transplantation of cord blood (CB)-derived CD34+ cells. Mice were evaluated for human chimerism in the blood and assigned into experimental untreated or nivolumab groups based on chimerism. TNBC cell lines or tumor tissue from established CRC PDX models were implanted into both flanks of humanized mice and treatments ensued once tumors reached a volume of ~150mm³. Tumors were measured twice weekly. At end of study, immune organs and tumors were collected for immunological assessment.

Results

Humanized PDX models were successfully established with a high frequency of tumor engraftment. Humanized mice treated with anti-PD-1 exhibited increased anti-tumor human T-cell responses coupled with decreased Treg and myeloid populations that correlated with tumor growth inhibition. Combination therapies with anti-PD-1 treatment in TNBC-bearing mice reduced tumor growth in multi-drug cohorts. Finally, as observed in human colorectal patients, anti-PD-1 therapy had a strong response to a microsatellite-high CRC PDX that correlated with a higher number of human CD8+ IFNγ+ T cells in the tumor.

Conclusion

Hu-CB-BRGS mice represent an in vivo model to study immune checkpoint blockade to human tumors. The human immune system in the mice is inherently suppressed, similar to a tumor microenvironment, and thus allows growth of human tumors. However, the suppression can be released by anti-PD-1 therapies and inhibit tumor growth of some tumors. The model offers ample access to lymph and tumor cells for in-depth immunological analysis. The tumor growth inhibition correlates with increased CD8 IFNγ+ tumor infiltrating T cells. These hu-CB-BRGS mice provide a relevant preclinical animal model to facilitate prioritization of hypothesis-driven combination immunotherapies.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0518-z) contains supplementary material, which is available to authorized users.

Abstract A117: Tumor-produced IL-6 and IL-8 are associated with MDSC accumulation and correlate with long-term clinical outcomes in melanoma patients

Background: Recruitment and expansion of immunosuppressive myeloid cells present a significant barrier to the successful treatment of melanoma. We aimed to identify tumor-secreted factors that altered the frequency of MDSCs and correlated with clinical outcomes in advanced melanoma patients. We hypothesized that production of IL-6 and IL-8 by melanoma tumors would lead to expansion and accumulation of MDSCs and correlate with long-term clinical outcomes. Methods: Expression of IL-6 and IL-8 in melanoma tumors as well as the plasma concentration of IL-6 and IL-8 were measured and compared with the frequency of circulating MDSCs in a total of 52 stage IV melanoma patients. These measures were correlated with tumor burden, BRAF status, lactic acid dehydrogenase (LDH) levels and with clinical outcomes. Samples were collected beginning in January 2011 and clinical follow-up was collected through January 2018. Results: The plasma concentration of both IL-6 and IL-8 correlated with tumor burden (p &lt; 0.0001 and p= 0.0122, respectively). Patients with high plasma concentrations of either IL-6 (40%) or IL-8 (63%) had worse median overall survival (MOS) (7.5 months, p &lt; 0.0001 and 9.2 months, p = 0.0015, respectively) compared to patients with low concentrations, where MOS was not reached. Patients with high plasma concentrations of both IL-6 and IL-8 (35%) had even worse MOS (6.7 months) than patients with low levels of both cytokines (MOS not reached, 31%) p &lt; 0.0001. We observed that patients with lower circulating concentrations and lower tumoral expression of IL-6 and IL-8 showed decreased frequencies of circulating MDSCs. Furthermore, patients with low frequencies of MDSCs (MOS not reached) had better overall survival than patients with high frequencies of these cells (MOS 11.9 months) p = 0.0224. Multivariable analysis showed that when adjusting for variables BRAF status and LDH in the model, the hazard for the event of death for subjects with both high IL-6 and IL-8 is 4.46 times (95% CI, 1.4, 14.2) that of the hazard for the subjects with low IL-6 and IL-8 (p = 0.01). Additionally, the hazard of death for subjects with higher total MDSCs is 3.3 times (95% CI, 1.2, 9.0) that for subjects with low total MDSCs. Conclusions: The durability of the nearly 7-year follow-up time for these advanced melanoma patients further strengthens the implied importance of IL-6 and IL-8 in the accumulation of MDSC’s in melanoma patients. These data provide clues for potential therapeutic targets in advanced melanoma patients.

Citation Format: Richard P. Tobin, Kimberly R. Jordan, Dana Davis, Victoria M. Vorwald, Kasey Couts, Dexiang Gao, Derek E Smith, William A Robinson, Virginia Borges, Martin D McCarter. Tumor-produced IL-6 and IL-8 are associated with MDSC accumulation and correlate with long-term clinical outcomes in melanoma patients [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A117.

Characterization of clinical grade CD19 chimeric antigen receptor T cells produced using automated CliniMACS Prodigy system

BACKGROUND

Chimeric antigen receptor (CAR) T-cell therapy is highly effective for treating acute lymphoblastic leukemia and non-Hodgkin's lymphoma with high rate complete responses. However, the broad clinical application of CAR T-cell therapy has been challenging, largely due to the lack of widespread ability to produce and high cost of CAR T-cell products using traditional methods of production. Automated cell processing in a closed system has emerged as a potential method to increase the feasibility of producing CAR T cells locally at academic centers due to its minimal reliance on experienced labor, thereby making the process less expensive and more consistent than traditional methods of production.

METHOD

In this study, we describe the successful production of clinical grade CD19 CAR T cells using the Miltenyi CliniMACS Prodigy Automated Cell Processor at University of Colorado Anschutz Medical Campus in a rapid manner with a high frequent CD19 CAR expression.

RESULTS

The final CAR T-cell product is highly active, low in immune suppression, and absent in exhaustion. Full panel cytokine assays also showed elevated production of Th1 cytokines upon IL-2 stimulation when specifically killing CD19+ target cells.

CONCLUSION

These results demonstrate the feasibility of producing CAR T cells locally in a university hospital setting using automated cell processor for future clinical applications.

Targeting myeloid-derived suppressor cells using all-trans retinoic acid in melanoma patients treated with Ipilimumab

BACKGROUND

Immune checkpoint inhibitors have improved overall survival rates for many cancers, yet the majority of patients do not respond to treatment and succumb to disease progression. One tumor-related mechanism limiting the efficacy of immunotherapies in melanoma is the recruitment and expansion of myeloid-derived suppressor cells (MDSCs). Therefore, targeting MDSCs in combination with immunotherapies is an attractive strategy to improve response rates and effectiveness.

METHODS

We tested this strategy by designing a randomized phase II clinical trial treating advanced melanoma patients with either Ipilimumab monotherapy or Ipilimumab plus all-trans retinoic acid (ATRA). Clinicaltrails.gov identifier (NCT02403778). The frequency of circulating MDSCs and the activation of CD8(+) T cells was measured by flow cytometry. Expression of immunosuppressive genes was measured with quantitative real time-PCR. T cell suppressive functions were measured by mixed lymphocyte reaction.

RESULTS

Here we show that in vitro treatment with ATRA decreases immunosuppressive function of MDSCs in mixed lymphocyte reactions. Additionally, ATRA reduces the expression of immunosuppressive genes including PD-L1, IL-10, and indoleamine 2,3‑dioxygenase by MDSCs. Furthermore, the addition of ATRA to standard of care Ipilimumab therapy appears safe, as ATRA did not increase the frequency of grade 3 or 4 adverse events. Finally, ATRA significantly decreased the frequency of circulating MDSCs compared to Ipilimumab treatment alone in advanced-stage melanoma patients.

CONCLUSIONS

These results illustrate the importance of MDSCs in immunotherapy resistance and provide evidence that targeting MDSCs in cancer patients may augment immunotherapeutic approaches.

Effects of in vitro ATRA treatment on human MDSC expansion and function

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Background: Myeloid derived suppressor cells (MDSCs) are a heterogeneous population of immature immunosuppressive myeloid cells that are expanded in tumor bearing hosts. Melanoma patients with high frequencies of MDSCs have decreased overall survival and an increased risk of death and disease progression, as well as impaired responses to ipilimumab. Targeting MDSCs to decease their frequency or suppressive activity may provide an effective means to improve the efficacy of anti-cancer therapies. All-trans retinoic acid (ATRA) is a vitamin A derivative currently used to treat APL that may target MDSCs. ATRA differentiates immature myeloid cells into macrophages, dendritic cells, or granulocytes. ATRA has been tested as an MDSC targeting agent in two completed caner clinical trials and is being investigated in several other open and completed trials. Methods: We purified myeloid cells from LRS chambers collected from normal donors. The purified cells were treated with GM-CSF+IL-6, GM-CSF+IL-4, or melanoma conditioned media with or without ATRA. After 5 days of incubation, PCR was used to determine the expression of immunoregulatory genes. Additionally, we used a MLR to determine the effect of ATRA on MDSC’s T cell suppressive function. Results: Here we report that in vitro ATRA treatment decreases the expression of ARG1, NOX1, INOS, and PD-L1. Further, we report that ATRA treatment improved T cell proliferation. Conclusions: Controlling MDSC suppressive function and accumulation may provide a mechanism to improve the efficacy of many current cancer therapies. Here we show that ATRA reduces the expression of the immunosuppressive genes ARG1, NOX1, INOS, and PD-L1 in MDSCs. Additionally, we show that treatment of MDSCs with ATRA decreases MDSC’s ability to suppress T cell proliferation. These results indicate that ATRA may improve the efficacy of conventional and immnunotherapeutic treatments.

Abstract P4-12-05: Extracellular vesicles from young women's and postpartum breast cancer display unique proteomic content, alter breast cancer aggressive behavior, and influence immune cell function

Background: Young women's breast cancer[YWBC] affects 27,000 US women age ≤45 annually. Half of these cancers occur within 5-10 years of a prior childbirth, a postpartum breast cancer[PPBC], incurring a 3 fold increased risk for metastasis and death. Recently, extracellular vesicles[EV] have been identified in human circulation, released from cancer cells, that have paracrine and autocrine effects, alter the tumor microenvironment and establish metastatic niches. EVs isolated from breast cancer lines increase proliferation and invasion of other breast cancer cells in vitro. However, the impact of EVs isolated from primary breast cancer patients on tumor invasion, metastasis and their role in tumor immune suppression is largely unknown. We hypothesized that EVs from YWBC/PPBC patients may contain unique pro-metastatic cargo, influence aggressive breast cancer cell behavior and may demonstrate the ability to alter immune cell function.

Method: We isolated EVs using size-exclusion chromatography [SEC] from the plasma of 10 unaffected young women and 20 YWBC patients balanced for parity, age, subtype and stage. We compared the breast cancer-specific EV proteins within various clinical groups of YWBC and PPBC to identify significant proteomic differences by parity, sub-type, stage, and disease recurrence. We determined the functional impact of these EVs on tumor cell motility and proliferation, and analyzed the effect of breast cancer derived EVs on immune cell phenotype, function, and T cell proliferation assays.

Results: Of the 582 proteins, 22 proteins are significantly increased in the EVs of YWBC compared to unaffected donors. The protein set includes breast cancer antigens [MUC 1, 2, 5b], transcriptional regulators [Myc target protein], enzymes [catalase, MMP inhibitor 1], and signaling molecules [Annexin 1, latent TGFb binding protein 1], among others. Several identified proteins specifically track with those YWBC cases with subsequent metastases. Furthermore, 8 unique proteins track with PPBC, including cartilage oligomeric matrix protein, a novel breast cancer biomarker that correlates with increased invasiveness, and decreased recurrence-free survival. EVs isolated from the plasma of newly diagnosed YWBC increase breast cancer invasion and EVs derived from breast cancer are engulfed by the majority of monocytic immune cells, including dendritic cells, classical and activated monocytes, but not by lymphocytes. Specifically, CD14+ monocytic myeloid derived suppressor cells engulfed the EVs while the CD15+ granulocytic subset did not. Once engulfed, phenotypic changes occurr in the EV containing monocytes and a significantly reduction in T cell stimulation in standard mixed-lymphocyte reactions is observed.

Conclusion: EVs isolated from YWBC & PPBC cases have unique protein content and increase breast cancer invasiveness, which suggests potential mechanistic roles for EVs as increasing metastatic risk and provides novel candidate biomarkers. We identified an immunomodulatory effect of breast cancer EVs on human monocytes that may contribute to immunosuppression in breast cancer and a role for EVs as directly modulating the host and tumor microenvironment.

Citation Format: Borges VF, Jordan KR, Hall JK, Schedin T, Hansen K, Schedin P. Extracellular vesicles from young women's and postpartum breast cancer display unique proteomic content, alter breast cancer aggressive behavior, and influence immune cell function [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-12-05.

The clinical evidence for targeting human myeloid-derived suppressor cells in cancer patients

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that represent a formidable obstacle to the successful treatment of cancer. Patients with high frequencies of MDSCs have significantly decreased progression-free survival (PFS) and overall survival (OS). Whereas there is experimental evidence that the reduction of the number and/or suppressive function of MDSCs in mice improves the efficacy of anti-cancer therapies, there is notably less evidence for this therapeutic strategy in human clinical trials. Here, we discuss currently available data concerning MDSCs from human clinical trials and explore the evidence that targeting MDSCs may improve the efficacy of cancer therapies.

Immunosuppressive myeloid-derived suppressor cells are increased in splenocytes from cancer patients

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells that are increased in the peripheral blood of cancer patients and limit productive immune responses against tumors. Immunosuppressive MDSCs are well characterized in murine splenic tissue and are found at higher frequencies in spleens of tumor-bearing mice. However, no studies have yet analyzed these cells in parallel human spleens. We hypothesized that MDSCs would be increased in the spleens of human cancer patients, similar to tumor-bearing mice. We compared the frequency and function of MDSC subsets in dissociated human spleen from 16 patients with benign pancreatic cysts and 26 patients with a variety of cancers. We found that total MDSCs (Lin^neg CD11b^pos CD33^pos HLA-DR^neg), granulocytic MDSCs (additional markers CD14^neg CD15^pos), and monocytic MDSCs (CD14^pos CD15^neg) were identified in human spleen. The monocytic subset was the most prominent in both spleen and peripheral blood and the granulocytic subset was expanded in the spleen relative to matched peripheral blood samples. Importantly, the frequency of CD15^pos MDSCs in the spleen was increased in patients with cancer compared to patients with benign pancreatic cysts and was associated with a significantly increased risk of death and decreased overall survival. Finally, MDSCs isolated from the spleen suppressed T cell responses, demonstrating for the first time the functional capacity of human splenic MDSCs. These data suggest that the human spleen is a potential source of large quantities of cells with immunosuppressive function for future characterization and in-depth studies of human MDSCs.

Improving antigenic peptide vaccines for cancer immunotherapy using a dominant tumor-specific T cell receptor

Vaccines that incorporate peptide mimics of tumor antigens, or mimotope vaccines, are commonly used in cancer immunotherapy and function by eliciting increased numbers of T cells that cross-react with the native tumor antigen. Unfortunately, they often elicit T cells that do not cross-react with or that have low affinity for the tumor antigen. Using a high affinity tumor-specific T cell clone, we identified a panel of mimotope vaccines for the dominant peptide antigen from a mouse colon tumor that elicits a range of tumor protection following vaccination. The TCR from this high affinity T cell clone was rarely identified in ex vivo evaluation of tumor-specific T cells elicited by mimotope vaccination. Conversely, a low affinity clone found in the tumor and following immunization was frequently identified. Using peptide libraries, we determined if this frequently identified TCR improved the discovery of efficacious mimotopes. We demonstrated that the representative TCR identified more protective mimotopes than the high affinity TCR. These results suggest that targeting a dominant fraction of tumor-specific T cells generates potent immunity and that consideration of the available T cell repertoire is necessary for targeted T cell therapy. These results have important implications when optimizing mimotope vaccines for cancer immunotherapy.

Influence of human immune cells on cancer: studies at the University of Colorado

There will be over half a million cancer-related deaths in the United States in 2012, with lung cancer being the leader followed by prostate in men and breast in women. There is estimated to be more than one and a half million new cases of cancer in 2012, making the development of effective therapies a high priority. As tumor immunologists, we are interested in the development of immunotherapies because the immune response offers exquisite specificity and the potential to target tumor cells without harming normal cells. In this review, we highlight the current advances in the field of immunotherapy and the current work being completed by laboratories at University of Colorado School of Medicine in multiple malignancies, including breast cancer, lung cancer, melanoma, thyroid cancer, and glioblastoma. This work focuses on augmenting the anti-tumor response of CD8 T cells in the blood, lymph nodes, and tumors of patients, determining biomarkers for patients who are more likely to respond to immunotherapy, and identifying additional anti-tumor and immunosuppressive cells that influence the overall response to tumors. These collaborative efforts will identify mechanisms to improve immune function, which may elucidate therapeutic targets for clinical trials to improve patient health and survival.

Augmenting antitumor T-cell responses to mimotope vaccination by boosting with native tumor antigens

Vaccination with antigens expressed by tumors is one strategy for stimulating enhanced T-cell responses against tumors. However, these peptide vaccines rarely result in efficient expansion of tumor-specific T cells or responses that protect against tumor growth. Mimotopes, or peptide mimics of tumor antigens, elicit increased numbers of T cells that crossreact with the native tumor antigen, resulting in potent antitumor responses. Unfortunately, mimotopes may also elicit cells that do not crossreact or have low affinity for tumor antigen. We previously showed that one such mimotope of the dominant MHC class I tumor antigen of a mouse colon carcinoma cell line stimulates a tumor-specific T-cell clone and elicits antigen-specific cells in vivo, yet protects poorly against tumor growth. We hypothesized that boosting the mimotope vaccine with the native tumor antigen would focus the T-cell response elicited by the mimotope toward high affinity, tumor-specific T cells. We show that priming T cells with the mimotope, followed by a native tumor-antigen boost, improves tumor immunity compared with T cells elicited by the same prime with a mimotope boost. Our data suggest that the improved tumor immunity results from the expansion of mimotope-elicited tumor-specific T cells that have increased avidity for the tumor antigen. The enhanced T cells are phenotypically distinct and enriched for T-cell receptors previously correlated with improved antitumor immunity. These results suggest that incorporation of native antigen into clinical mimotope vaccine regimens may improve the efficacy of antitumor T-cell responses.

Abstract 5376: Immunosuppressive T regs and MDSCs in human melanoma

Despite the ability to elicit active immune responses, most immunotherapies fail to eliminate tumors in human cancer patients. One reason immunotherapy has not met expectations may be due to immunosuppression in the local environment of the tumor. We have previously reported that untreated advanced-stage melanoma patients have increased numbers of peripheral T regs. In addition, exposure to melanoma cells in vitro expands T regs from normal human peripheral blood mononuclear cells (PBMCs). We have shown that melanoma-conditioned media have increased levels of TGF-beta, which may be responsible for the expansion of these suppressive cells in culture. Here we show that the number of peripheral T regs directly correlates with the amount of TGF-beta in the plasma of late-stage melanoma patients. We also show that melanoma patients have increased numbers of other suppressive cells, known as myeloid-derived suppressor cells (MDSCs). These MDSCs may further contribute to immunosuppression in advanced-stage melanoma patients. Finally, we show that the tumor-induced T regs and the T regs and MDSCs from the peripheral blood of melanoma patients suppress T cell responses in vitro, including proliferation, cytokine production, and cytotoxic activity. We are currently investigating whether MDSCs from melanoma patients contribute to the accumulation of T regs and whether immunotherapies used in the treatment of advanced-stage melanoma patients, particularly IL-2 and ipilimumab, affect their frequency or function. An understanding of the potential interaction between melanoma, MDSCs, and regulatory T cells will further our goal in identifying ways of blocking the function of these suppressive cells in melanoma patients to improve the effectiveness of future therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5376. doi:1538-7445.AM2012-5376

TCR hypervariable regions expressed by T cells that respond to effective tumor vaccines

A major goal of immunotherapy for cancer is the activation of T cell responses against tumor-associated antigens (TAAs). One important strategy for improving antitumor immunity is vaccination with peptide variants of TAAs. Understanding the mechanisms underlying the expansion of T cells that respond to the native tumor antigen is an important step in developing effective peptide-variant vaccines. Using an immunogenic mouse colon cancer model, we compare the binding properties and the TCR genes expressed by T cells elicited by peptide variants that elicit variable antitumor immunity directly ex vivo. The steady-state affinity of the natural tumor antigen for the T cells responding to effective peptide vaccines was higher relative to ineffective peptides, consistent with their improved function. Ex vivo analysis showed that T cells responding to the effective peptides expressed a CDR3β motif, which was also shared by T cells responding to the natural antigen and not those responding to the less effective peptide vaccines. Importantly, these data demonstrate that peptide vaccines can expand T cells that naturally respond to tumor antigens, resulting in more effective antitumor immunity. Future immunotherapies may require similar stringent analysis of the responding T cells to select optimal peptides as vaccine candidates.

DC maturation and function are not altered by melanoma-derived immunosuppressive soluble factors

BACKGROUND

Although melanoma can elicit robust tumor antigen-specific immune responses, advanced melanoma is associated with immune tolerance. We have previously described several mechanisms of melanoma-induced immunosuppression, including the skewing of the immune response towards a Th2 cytokine profile and the induction of regulatory T cells. Since dendritic cells (DCs) are potentially important players that can direct other cells of the immune system towards a cytotoxic, humoral, or regulatory phenotype, we hypothesized that melanoma-produced factors directly affect the maturation and function of DCs, influencing the nature and magnitude of the resulting immune response.

MATERIALS AND METHODS

To test this hypothesis, immature myeloid-derived DCs (mdDCs) were derived with cytokines from CD14+ peripheral blood mononuclear cells (PBMCs) and exposed to 20% melanoma-conditioned media (MCM). After 2 d, the expression of maturation markers and the function of these mdDCs, measured by cytokine production, the amount of endocytosis, expression of the inhibitory molecule indoleamine 2,3-dioxygenase (IDO), and the ability to stimulate T cells were determined.

RESULTS

We found that incubation with MCM did not inhibit the expression of maturation markers or IDO, the production of cytokines, the amount of antigen uptake, or the ability to induce T cell proliferation in mixed-lymphocyte reactions by mdDC.

CONCLUSIONS

These results suggest that the immunosuppressive effects of melanoma-produced factors are independent of directly measurable changes in mdDC function or maturation in vitro.

Vaccination of mice with baculovirus-infected insect cells expressing antigenic proteins

Methods to induce antigen-specific immune responses in mice using insect cells infected with recombinant baculoviruses are described in this unit. Although this vaccine strategy has been used to generate both antibody and T cell responses, it has been more thoroughly characterized for the peptide-specific cytotoxic T cell responses. Nonspecific responses to the vaccine vehicle are controlled for by vaccinating with insect cells infected with baculoviruses encoding irrelevant antigens or no antigen. The baculovirus-infected insect cells alone are an effective immune adjuvant to elicit antigen-specific T cells. Overall, immune responses generated using this approach are similar to those generated by more conventional vaccine strategies.

Vaccination with Mimotopes Prevents Tumor Growth by Enhancing the Activation of T cells that Respond to Natural Tumor Antigens (41.40)

Vaccination with mimotopes, or peptide mimics of self-tumor antigens, is a potential strategy for antigen-specific immunotherapy of cancer. We tested mimotopes with substitutions in residues involved in T cell interactions, rather than in conventional MHC-anchor residues, for protection against the transplantable tumor, CT26. Although vaccination with all of the mimotopes elicited tumor-specific T cells more effectively than the wild type tumor antigen, AH1, only some mimotopes prevented tumor growth. Vaccination with the protective mimotopes generated considerably more cross-reactive T cells that produced the cytokine IFNgamma after stimulation with lower concentrations of the AH1 peptide. These T cells expressed TCR molecules with a more restricted Vbeta repertoire ex vivo, but were similar in CDR3 sequence to the T cells generated by vaccination with the AH1 peptide. Importantly, the T cells responding to the non-effective mimotopes did not inhibit the antitumor responses of the protective mimotopes. These results suggest that protective mimotopes generate antitumor immunity, in part, by enhancing the activation and differentiation of a subset of T cells that naturally respond to the tumor, not a new repertoire of T cells only elicited by the mimotope.

Baculovirus-infected insect cells expressing peptide-MHC complexes elicit protective antitumor immunity

Evaluation of T cell responses to tumor- and pathogen-derived peptides in preclinical models is necessary to define the characteristics of efficacious peptide vaccines. We show in this study that vaccination with insect cells infected with baculoviruses expressing MHC class I linked to tumor peptide mimotopes results in expansion of functional peptide-specific CD8+ T cells that protect mice from tumor challenge. Specific peptide mimotopes selected from peptide-MHC libraries encoded by baculoviruses can be tested using this vaccine approach. Unlike other vaccine strategies, this vaccine has the following advantages: peptides that are difficult to solublize can be easily characterized, bona fide peptides without synthesis artifacts are presented, and additional adjuvants are not required to generate peptide-specific responses. Priming of antitumor responses occurs within 3 days of vaccination and is optimal 1 wk after a second injection. After vaccination, the Ag-specific T cell response is similar in animals primed with either soluble or membrane-bound Ag, and CD11c+ dendritic cells increase expression of maturation markers and stimulate proliferation of specific T cells ex vivo. Thus, the mechanism of Ag presentation induced by this vaccine is consistent with cross-priming by dendritic cells. This straightforward approach will facilitate future analyses of T cells elicited by peptide mimotopes.

Use of baculovirus MHC/peptide display libraries to characterize T-cell receptor ligands

Peptide/protein display libraries are powerful tools for identifying and manipulating receptor/ligand pairs. While the large size of bacterial phage display libraries has made them the platform of choice in many applications, often considerable engineering has been required to achieve display of properly folded and active eukaryotic proteins, such as antibodies. This problem has been partially solved in several eukaryotic display systems, e.g. using yeast or retroviruses, but these systems have their own limitations. Recently, baculovirus has been developed as a display system using the virus itself or infected insect cells as the display platform. Here, we review the development and use of baculovirus-infected cells as a platform for display libraries of peptides bound to major histocompatibility complex (MHC) class I (MHCI) or class II (MHCII). We have used fluorescent multimeric soluble T-cell receptors (TCRs) to screen these libraries and to identify peptide antigen mimotopes. We also present some improvements to this system that allow very large libraries to be constructed and screened. We have used these libraries to examine the role of MHCII-bound peptides in the presentation of the staphylococcal enterotoxin A (SEA) and to manipulate an MHCI tumor-associated antigen.

Relating TCR-peptide-MHC affinity to immunogenicity for the design of tumor vaccines

One approach to enhancing the T cell response to tumors is vaccination with mimotopes, mimics of tumor epitopes. While mimotopes can stimulate proliferation of T cells that recognize tumor-associated antigens (TAAs), this expansion does not always correlate with control of tumor growth. We hypothesized that vaccination with mimotopes of optimal affinity in this interaction will improve antitumor immunity. Using a combinatorial peptide library and a cytotoxic T lymphocyte clone that recognizes a TAA, we identified a panel of mimotopes that, when complexed with MHC, bound the TAA-specific TCR with a range of affinities. As expected, in vitro assays showed that the affinity of the TCR-peptide-MHC (TCR-pMHC) interaction correlated with activity of the T cell clone. However, only vaccination with mimotopes in the intermediate-affinity range elicited functional T cells and provided protection against tumor growth in vivo. Vaccination with mimotopes with the highest-affinity TCR-pMHC interactions elicited TAA-specific T cells to the tumor, but did not control tumor growth at any of the peptide concentrations tested. Further analysis of these T cells showed functional defects in response to the TAA. Thus, stimulation of an antitumor response by mimotopes may be optimal with peptides that increase but do not maximize the affinity of the TCR-pMHC interaction.

Peripheral blood-derived bovine dendritic cells promote IgG1-restricted B cell responses in vitro

Regulation of humoral responses involves multiple cell types including the requirements for cognate interactions between T and B cells to drive CD40-dependent responses to T-dependent antigens. A third cell type has also been shown to play an essential role, the dendritic cell (DC). We demonstrate that bovine peripheral blood-derived (PB)-DC are similar in function to features described for human interstitial DC including the production of signature type 2 cytokines [interleukin (IL)-13, IL-10]. PB-DC express moderate-to-high costimulatory molecule expression, and major histocompatibility complex class II is negative for CD14 expression and has low or no expression of CD11c. Consistent with the interstitial phenotype is the ability of PB-DC to influence B cell activation and differentiation via direct expression of CD40L and type 2 cytokines. Collectively, these results suggest that direct B cell-DC interactions may promote an immunoglobulin-isotype expression pattern consistent with type 2 responses, independent of direct T cell involvement.