Clinical and molecular effects of oral CCR4 antagonist RPT193 in atopic dermatitis: A Phase 1 study

BACKGROUND

RPT193 is an orally administered small molecule antagonist of the human C-C motif chemokine receptor 4 (CCR4) that inhibits the migration and downstream activation of T-helper Type 2 (Th2) cells. We investigated single- and multiple-ascending doses of RPT193 in healthy subjects, and multiple doses of RPT193 in subjects with moderate-to-severe atopic dermatitis (AD).

METHODS

This was a first-in-human randomized, placebo-controlled Phase 1a/1b monotherapy study (NCT04271514) to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and CCR4 surface receptor occupancy in eligible healthy subjects and subjects with moderate-to-severe AD. Clinical efficacy and skin biomarker effects of RPT193 monotherapy were assessed as exploratory endpoints in AD subjects.

RESULTS

In healthy (n = 72) and AD subjects (n = 31), once-daily RPT193 treatment was generally well tolerated, with no serious adverse events reported and all treatment-emergent adverse events reported as mild/moderate. In AD subjects, numerically greater improvements in clinical efficacy endpoints were observed with RPT193 monotherapy versus placebo up to the end of the treatment period (Day 29), with statistically significant improvement, compared to Day 29 and placebo, observed 2 weeks after the end of treatment (Day 43) on several endpoints (p < .05). Moreover, significant changes in the transcriptional profile were seen in skin biopsies of RPT193-treated versus placebo-treated subjects at Day 29, which were also significantly correlated with improvements in clinical efficacy measures.

CONCLUSIONS

To our knowledge, this is the first clinical study with an oral CCR4 antagonist that showed clinical improvement coupled with modulation of the cutaneous transcriptomic profile in an inflammatory skin disease.

Potent GCN2 Inhibitor Capable of Reversing MDSC-Driven T Cell Suppression Demonstrates In Vivo Efficacy as a Single Agent and in Combination with Anti-Angiogenesis Therapy

General control nonderepressible 2 (GCN2) protein kinase is a cellular stress sensor within the tumor microenvironment (TME), whose signaling cascade has been proposed to contribute to immune escape in tumors. Herein, we report the discovery of cell-potent GCN2 inhibitors with excellent selectivity against its closely related Integrated Stress Response (ISR) family members heme-regulated inhibitor kinase (HRI), protein kinase R (PKR), and (PKR)-like endoplasmic reticulum kinase (PERK), as well as good kinome-wide selectivity and favorable PK. In mice, compound 39 engages GCN2 at levels ≥80% with an oral dose of 15 mg/kg BID. We also demonstrate the ability of compound 39 to alleviate MDSC-related T cell suppression and restore T cell proliferation, similar to the effect seen in MDSCs from GCN2 knockout mice. In the LL2 syngeneic mouse model, compound 39 demonstrates significant tumor growth inhibition (TGI) as a single agent. Furthermore, TGI mediated by anti-VEGFR was enhanced by treatment with compound 39 demonstrating the complementarity of these two mechanisms.

EBV+ tumors exploit tumor cell-intrinsic and -extrinsic mechanisms to produce regulatory T cell-recruiting chemokines CCL17 and CCL22

The Epstein-Barr Virus (EBV) is involved in the etiology of multiple hematologic and epithelial human cancers. EBV+ tumors employ multiple immune escape mechanisms, including the recruitment of immunosuppressive regulatory T cells (Treg). Here, we show some EBV+ tumor cells express high levels of the chemokines CCL17 and CCL22 both in vitro and in vivo and that this expression mirrors the expression levels of expression of the EBV LMP1 gene in vitro. Patient samples from lymphoblastic (Hodgkin lymphoma) and epithelial (nasopharyngeal carcinoma; NPC) EBV+ tumors revealed CCL17 and CCL22 expression of both tumor cell-intrinsic and -extrinsic origin, depending on tumor type. NPCs grown as mouse xenografts likewise showed both mechanisms of chemokine production. Single cell RNA-sequencing revealed in vivo tumor cell-intrinsic CCL17 and CCL22 expression combined with expression from infiltrating classical resident and migratory dendritic cells in a CT26 colon cancer mouse tumor engineered to express LMP1. These data suggest that EBV-driven tumors employ dual mechanisms for CCL17 and CCL22 production. Importantly, both in vitro and in vivo Treg migration was effectively blocked by a novel, small molecule antagonist of CCR4, CCR4-351. Antagonism of the CCR4 receptor may thus be an effective means of activating the immune response against a wide spectrum of EBV+ tumors.

Tumors establish resistance to immunotherapy by regulating Treg recruitment via CCR4

BACKGROUND

Checkpoint inhibitors (CPIs) such as anti-PD(L)-1 and anti-CTLA-4 antibodies have resulted in unprecedented rates of antitumor responses and extension of survival of patients with a variety of cancers. But some patients fail to respond or initially respond but later relapse as they develop resistance to immune therapy. One of the tumor-extrinsic mechanisms for resistance to immune therapy is the accumulation of regulatory T cells (T_reg) in tumors. In preclinical and clinical studies, it has been suggested that tumor trafficking of T_reg is mediated by CC chemokine receptor 4 (CCR4). Over 90% of human T_reg express CCR4 and migrate toward CCL17 and CCL22, two major CCR4 ligands that are either high at baseline or upregulated in tumors on CPI treatment. Hence, CCR4 antagonism has the potential to be an effective antitumor treatment by reducing the accumulation of T_reg into the tumor microenvironment (TME).

METHODS

We developed in vitro and in vivo models to assess T_reg migration and antitumor efficacy using a potent and selective CCR4 antagonist, CCR4-351. We used two separate tumor models, Pan02 and CT26 mouse tumors, that have high and low CCR4 ligand expression, respectively. Tumor growth inhibition as well as the frequency of tumor-infiltrating T_reg and effector T cells was assessed following the treatment with CCR4 antagonist alone or in combination with CPI.

RESULTS

Using a selective and highly potent, novel small molecule inhibitor of CCR4, we demonstrate that migration of CCR4⁺ T_reg into the tumor drives tumor progression and resistance to CPI treatment. In tumor models with high baseline levels of CCR4 ligands, blockade of CCR4 reduced the number of T_reg and enhanced antitumor immune activity. Notably, in tumor models with low baseline level of CCR4 ligands, treatment with immune CPIs resulted in significant increases of CCR4 ligands and T_reg numbers. Inhibition of CCR4 reduced T_reg frequency and potentiated the antitumor effects of CPIs.

CONCLUSION

Taken together, we demonstrate that CCR4-dependent T_reg recruitment into the tumor is an important tumor-extrinsic mechanism for immune resistance. Blockade of CCR4 led to reduced frequency of T_reg and resulted in increased antitumor activity, supporting the clinical development of CCR4 inhibitors in combination with CPI for the treatment of cancer.

STATEMENT OF SIGNIFICANCE

CPI upregulates CCL17 and CCL22 expression in tumors and increases T_reg migration into the TME. Pharmacological antagonism of the CCR4 receptor effectively inhibits T_reg recruitment and results in enhanced antitumor efficacy either as single agent in CCR4 ligand^high tumors or in combination with CPIs in CCR4 ligand^low tumors.

Abstract 3153: Targeting the stress response kinase GCN2 to restore immunity in the tumor microenvironment

Recent advances in cancer metabolism suggest that targeting amino acid metabolism represents a promising strategy for the development of novel therapeutic agents. Tumor, stromal and myeloid-derived suppressor cells (MDSC) within the tumor microenvironment (TME) create a nutrient-poor environment that inhibit immune function and support tumor growth. GCN2 (general control nonderepressible 2), a stress response kinase, plays a key role in maintaining cellular homeostasis under a wide range of stressors. Phosphorylation of GCN2 (pGCN2) in response to stress leads to inhibition of global protein synthesis and subsequently leads to 1) T cell anergy and apoptosis, 2) enhanced MDSC-dependent immune suppression and 3) tumor cell survival. Collectively, these roles suggest that GCN2 inhibition could have both a direct anticancer and an immune-activating effect. Treating nutrient-deprived T cells in vitro with a RAPT GCN2 inhibitor (RPT-GCN2i) rescued CD4+ and CD8+ T cell proliferation and effector functions. The RPT-GCN2i also reversed T cell suppression mediated by MDSCs derived from healthy donors or cancer patients. Using syngeneic mouse tumor models, we demonstrated that translational induction of activating transcription factor 4 (ATF4) is a strong marker of GCN2 pathway activation in vivo. Oral administration of an RPT-GCN2i exhibited notable drug-target occupancy and potently inhibited GCN2 kinase and ATF4 in the TME. RPT-GCN2i as a single agent and in combination with checkpoint blockade or angiogenesis inhibitor (anti-VEGFR) led to delays in tumor growth rate in various syngeneic tumor models. In addition, GCN2 inhibition redirected MDSC within the TME from a suppressive to inflammatory phenotype through downregulation of Arg1 and iNOS. Our results show that inhibition of GCN2 is an attractive approach for enhancing antitumor immune response and therefore GCN2 is a promising therapeutic target for the treatment of cancer.

Citation Format: Lisa Marshall, Buvana Ravishankar, Urvi Kolhatkar, Mengshu Xu, Lavanya Adusumilli, Deepa Pookot, Thant Zaw, Chandru Ramana, Raashi Sreenivasan, Mikhail Zibinsky, Jeffrey Jackson, Grant Shibuya, Paul Leger, Omar Robles, Anqi Ma, Andrew Ng, Anton Shakhmin, Justy Guagua, Scott Jacobson, Steve Wong, Delia Bradford, Tracy L. McGaha, M Teresa Ciudad, James E. Talmadge, Holly C. Britton, George Katibah, Gene Cutler, David Wustrow, Paul D. Kassner, Dirk G. Brockstedt. Targeting the stress response kinase GCN2 to restore immunity in the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3153.

Abstract 1585: T-regulatory cells impair CAR T cell-mediated antitumor activity in a murine solid tumor model

Introduction: Chimeric antigen receptor (CAR) T cell immunotherapy has had only modest success in solid malignancies due in part to tumor antigen heterogeneity and the immunosuppressive tumor microenvironment. We have previously demonstrated that administration of cyclophosphamide (CTX) prior to CAR T infusion promoted the eradication of solid tumors that lacked homogenous expression of the CAR target antigen. Although CTX has multiple effects, we hypothesized that one potential mechanism was depletion of T-regulatory cells (Treg). To test this, we used a genetic model of Treg depletion involving mice with FOXP3-driven diphtheria toxin receptor expression (FOXP3-DTR) and an orally administered chemokine receptor 4 (CCR4) antagonist called CCR4-351. Treg express CCR4 and migrate toward CCL17 and CCL22 which are frequently upregulated by tumors. We have previously shown that the tool compound CCR4-351 decreases Treg accumulation in tumors.

Methods: Transgenic FOXP3-DTR C57BL/6 mice were injected s.c. in the flank with a syngeneic murine mesothelioma cell line expressing human mesothelin. When tumors reached ~85 mm3, diphtheria toxin was given i.p. and 24 hours later, 2 doses of 107 transduced human anti-mesothelin CAR T cells (M11) were injected i.v. 2 days apart. In our pharmacologic study, wild type, tumor-bearing C57BL/6 mice were given CCR4-351 daily at 50 mg/kg by oral gavage. Mice were treated with M11 CAR T cells as above, starting one day after CCR4-351 therapy. Tumor growth and mouse survival were determined.

Results: Genetic depletion of Treg alone did not significantly slow tumor growth compared to untreated control. However, the combination of M11 CAR T cells plus genetic depletion of Treg significantly slowed tumor growth compared to vehicle control (p&lt;0.05, one-way ANOVA). Compared to untreated controls, treatment with CCR4-351 (p&lt;0.04, log rank) or M11 CAR T cells (p&lt;0.001, log rank) alone significantly improved survival, however there was no significant difference in survival between CAR and CCR4-351 only treated mice. In contrast, the combination of M11 CAR T cells with CCR4-351 resulted in enhanced antitumor activity with 4/9 mice cured and significantly increased survival compared to CAR (p&lt;0.01, log rank) and CCR4-351 (p&lt;0.006, log rank) monotherapies.

Conclusions: Treg depletion via systemic ablation or inhibition of trafficking, resulted in augmentation of the antitumor effects of CAR T cells in our pre-clinical immunocompetent solid tumor model. If generalizable, these data support further investigation as to whether the orally bioavailable CCR4 antagonist currently in clinical development, FLX475, may be used to augment human CAR T cell therapy for solid tumors.

Citation Format: Michael S. Leibowitz, Nicholas S. Olimpo, Liqing Wang, Aparna Jorapur, Deepa Pookot, Maria Liousia, Evguenia Arguiri, Jing Sun, Astero Klampatsa, Dirk G. Brockstedt, Wayne W. Hancock, Steven M. Albelda. T-regulatory cells impair CAR T cell-mediated antitumor activity in a murine solid tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1585.

Novel Piperidinyl-Azetidines as Potent and Selective CCR4 Antagonists Elicit Antitumor Response as a Single Agent and in Combination with Checkpoint Inhibitors

The C-C chemokine receptor 4 (CCR4) is broadly expressed on regulatory T cells (T_reg) as well as other circulating and tissue-resident T cells. T_reg can be recruited to the tumor microenvironment (TME) through the C-C chemokines CCL17 and CCL22. T_reg accumulation in the TME has been shown to dampen the antitumor immune response and is thought to be an important driver in tumor immune evasion. Preclinical and clinical data suggest that reducing the T_reg population in the TME can potentiate the antitumor immune response of checkpoint inhibitors. We have developed small-molecule antagonists of CCR4, featuring a novel piperidinyl-azetidine motif, that inhibit the recruitment of T_reg into the TME and elicit antitumor responses as a single agent or in combination with an immune checkpoint blockade. The discovery of these potent, selective, and orally bioavailable CCR4 antagonists, and their activity in in vitro and in vivo models, is described herein.

Evaluation of Cyclophosphamide/GVAX Pancreas Followed by Listeria-Mesothelin (CRS-207) with or without Nivolumab in Patients with Pancreatic Cancer

PURPOSE

Two studies in previously treated metastatic pancreatic cancer have been completed combining GVAX pancreas vaccine (GM-CSF-secreting allogeneic pancreatic tumor cells) with cyclophosphamide (Cy) and CRS-207 (live, attenuated Listeria monocytogenes-expressing mesothelin). In the current study, we compared Cy/GVAX followed by CRS-207 with (Arm A) or without nivolumab (Arm B).

PATIENTS AND METHODS

Patients with pancreatic adenocarcinoma who received one prior therapy for metastatic disease and RECIST measurable disease were randomized 1:1 to receive treatment on Arm A or Arm B. The primary objective was to compare overall survival (OS) between the arms. Additional objectives included assessment of progression-free survival, safety, tumor responses, CA19-9 responses, and immunologic correlates.

RESULTS

Ninety-three patients were treated (Arm A, 51; Arm B, 42). The median OS in Arms A and B were 5.9 [95% confidence interval (CI), 4.7-8.6] and 6.1 (95% CI, 3.5-7.0) months, respectively, with an HR of 0.86 (95% CI, 0.55-1.34). Objective responses were seen in 3 patients using immune-related response criteria (4%, 2/51, Arm A; 2%, 1/42, Arm B). The grade ≥3 related adverse event rate, whereas higher in Arm A (35.3% vs. 11.9%) was manageable. Changes in the microenvironment, including increase in CD8+ T cells and a decrease in CD68+ myeloid cells, were observed in long-term survivors in Arm A only.

CONCLUSIONS

Although the study did not meet its primary endpoint of improvement in OS of Arm A over Arm B, the OS was comparable with standard therapy. Objective responses and immunologic changes in the tumor microenvironment were evident.

Single-Cell Immune Competency Signatures Associate with Survival in Phase II GVAX and CRS-207 Randomized Studies in Patients with Metastatic Pancreatic Cancer

The identification of biomarkers for patient stratification is fundamental to precision medicine efforts in oncology. Here, we identified two baseline, circulating immune cell subsets associated with overall survival in patients with metastatic pancreatic cancer who were enrolled in two phase II randomized studies of GVAX pancreas and CRS-207 immunotherapy. Single-cell mass cytometry was used to simultaneously measure 38 cell surface or intracellular markers in peripheral blood mononuclear cells obtained from a phase IIa patient subcohort (N = 38). CITRUS, an algorithm for identification of stratifying subpopulations in multidimensional cytometry datasets, was used to identify single-cell signatures associated with clinical outcome. Patients with a higher abundance of CD8⁺CD45RO^-CCR7^-CD57⁺ cells and a lower abundance of CD14⁺CD33⁺CD85j⁺ cells had improved overall survival [median overall survival, range (days) 271, 43-1,247] compared with patients with a lower abundance of CD8⁺CD45RO^-CCR7^-CD57⁺ cells and higher abundance of CD14⁺CD33⁺CD85j⁺ cells (77, 24-1,247 days; P = 0.0442). The results from this prospective-retrospective biomarker analysis were validated by flow cytometry in 200 patients with pancreatic cancer enrolled in a phase IIb study (P = 0.0047). The identified immune correlates provide potential prognostic or predictive signatures that could be employed for patient stratification.

Clinical Response of Live-Attenuated, Listeria monocytogenes Expressing Mesothelin (CRS-207) with Chemotherapy in Patients with Malignant Pleural Mesothelioma

PURPOSE

Malignant pleural mesothelioma (MPM) is an aggressive cancer associated with poor prognosis. CRS-207 is a live-attenuated Listeria monocytogenes engineered to express mesothelin, a tumor-associated antigen highly expressed in MPM. CRS-207 induces antitumor immune responses and increases susceptibility of neoplastic cells to immune-mediated killing.

PATIENTS AND METHODS

Patients with unresectable MPM, ECOG 0 or 1, and adequate organ and pulmonary function were enrolled in this multicenter, open-label phase Ib study. They received two priming infusions of 1 × 109 CFU CRS-207, followed by pemetrexed/cisplatin chemotherapy, and CRS-207 booster infusions. Primary objectives were safety and induction of immune response. Secondary/exploratory objectives included tumor response, progression-free survival (PFS), overall survival (OS), immune subset analysis, and gene-expression profiling of tumor.

RESULTS

Of 35 evaluable patients, 89% (31/35) had disease control with one complete response (3%), 19 partial responses (54%), and 10 stable disease (29%). The estimated median duration of response was 5.0 months (95% CI, 3.9-11.5). The median PFS and OS were 7.5 (95% CI, 7.0-9.9) and 14.7 (95% CI, 11.2-21.9) months, respectively. Tumor size reduction was observed post-CRS-207 infusion prior to chemotherapy in 11 of 35 (31%) patients. No unexpected treatment-related serious adverse events or deaths were observed. IHC analysis of pre- and post-CRS-207 treatment tumor biopsies revealed possible reinvigoration and proliferation of T cells, increased infiltration of dendritic and natural killer cells, increased CD8:Treg ratio, and a shift from immunosuppressive M2-like to proinflammatory M1-like macrophages following CRS-207 administration.

CONCLUSIONS

Combination of CRS-207 and chemotherapy induced significant changes in the local tumor microenvironment and objective tumor responses in a majority of treated patients.

Results from a Phase IIb, Randomized, Multicenter Study of GVAX Pancreas and CRS-207 Compared with Chemotherapy in Adults with Previously Treated Metastatic Pancreatic Adenocarcinoma (ECLIPSE Study)

PURPOSE

Limited options exist for patients with advanced pancreatic cancer progressing after 1 or more lines of therapy. A phase II study in patients with previously treated metastatic pancreatic cancer showed that combining GVAX pancreas (granulocyte-macrophage colony-stimulating factor-secreting allogeneic pancreatic tumor cells) with cyclophosphamide (Cy) and CRS-207 (live, attenuated Listeria monocytogenes expressing mesothelin) resulted in median overall survival (OS) of 6.1 months, which compares favorably with historical OS achieved with chemotherapy. In the current study, we compared Cy/GVAX + CRS-207, CRS-207 alone, and standard chemotherapy in a three-arm, randomized, controlled phase IIb trial.

PATIENTS AND METHODS

Patients with previously treated metastatic pancreatic adenocarcinoma were randomized 1:1:1 to receive Cy/GVAX + CRS-207 (arm A), CRS-207 (arm B), or physician's choice of single-agent chemotherapy (arm C). The primary cohort included patients who had failed ≥2 prior lines of therapy, including gemcitabine. The primary objective compared OS between arms A and C in the primary cohort. The second-line cohort included patients who had received 1 prior line of therapy. Additional objectives included OS between all treatment arms, safety, and tumor responses.

RESULTS

The study did not meet its primary efficacy endpoint. At the final study analysis, median OS [95% confidence interval (CI)] in the primary cohort (N = 213) was 3.7 (2.9-5.3), 5.4 (4.2-6.4), and 4.6 (4.2-5.7) months in arms A, B, and C, respectively, showing no significant difference between arm A and arm C [P = not significant (NS), HR = 1.17; 95% CI, 0.84-1.64]. The most frequently reported adverse events in all treatment groups were chills, pyrexia, fatigue, and nausea. No treatment-related deaths occurred.

CONCLUSIONS

The combination of Cy/GVAX + CRS-207 did not improve survival over chemotherapy. (ClinicalTrials.gov ID: NCT02004262)See related commentary by Salas-Benito et al., p. 5435.

A phase 2 trial of CRS-207 and pembrolizumab in adults with recurrence of metastatic gastric, gastroesophageal junction (GEJ), or esophageal adenocarcinomas

TPS200

Background: CRS-207 is a live, attenuated, double-deleted Listeria monocytogenes (LADD) strain with a mesothelin expression cassette inserted. CRS-207 has a well-established, manageable toxicity profile and can elicit mesothelin-specific cell-mediated immunity. Clinical activity of CRS-207 has been shown in a separate Phase 1 trial of mesothelioma. In gastroesophageal (GE) cancers, mesothelin expression is estimated between 30% – 50% and has been correlated with poor prognosis. Preclinical models suggest the combination of LADD-based immunotherapeutics and a PD1 inhibitor may induce more sustained anti-tumor responses than either LADD or PD1 inhibitor monotherapy. GE cancers are responsive to PD1 inhibitors in a subset of patients; this trial proposes to evaluate the efficacy of CRS-207 combined with pembrolizumab in patients with relapsed GE cancer, and to correlate clinical activity with mesothelin expression level. Methods: This Phase 2, open-label, single-arm, multicenter clinical study (NCT 03122548) will enroll approximately 79 subjects at 20 sites. Adults with histologically-confirmed, advanced gastric, GEJ, or esophageal adenocarcinomas are eligible. Subjects must have received 1 or 2 prior treatment regimens, which must have included a platinum and a fluoropyrimidine. Subjects must have disease progression with measurable tumors. A pre-treatment biopsy of either the primary tumor or metastatic site is required prior to dosing. Subjects with prior exposure to checkpoint inhibitors or other immunotherapies are excluded. From cycle 1 to 4 during the treatment and evaluation period, pembrolizumab (IV 200 mg) and CRS-207 (IV 1 x 109 CFU) are both administered in 3-week cycles. Afterward, pembrolizumab will be administered once every 3 weeks; CRS-207 will be given once every 6 weeks. CT scans will be performed every 6 weeks to monitor disease status. The primary endpoint is objective response rate defined by RECIST 1.1. Clinical trial information: NCT03122548.

Mismatch repair deficiency in cholangiocarcinoma

269

Background: Cholangiocarcinoma (CC) is a fatal malignancy with an unmet treatment need. With the approval of immunotherapy for solid tumors with mismatch repair (MMR) deficiency, there is a renewed interest in MMR testing. Little is known about the incidence of MMR deficiency in CC or its correlation to survival, immune cell infiltration, PD-L1 and other proteins expressed in CC such as mesothelin. Methods: CC tumors were identified from patients treated at the University of Virginia from 2000-2014. Tissue microarrays (TMAs) were constructed of 3-4 cores from each tumor and were stained by immunohistochemistry for MMR genes (MLH1, PMS2, MSH2, MSH6), mesothelin, PD-L1 and immune cells. TMAs were scanned using the Leica SCN400 and analyzed using the Digital Image Hub software. Stain intensity thresholds for defining positive cells were determined by two users and recorded as an average of all cores from each tumor. Mesothelin and PD-L1 expression were measured as a percentage of positive tumor cells. Correlation with overall survival was assessed using log-rank tests and classification and regression trees, with p values < 0.05 considered significant. Results: Ninety-one tumors were analyzed: 24 intrahepatic, 33 hilar, and 34 distal. MMR deficiency was found in 20 tumors (22%). None of the MMR deficient tumors co-expressed PD-L1 (>1%), which was found in 15% of the remaining tumors. T cell infiltration (CD4, CD8 and FoxP3) did not differ between MMR deficient or proficient tumors. Patients with MMR deficiency had a trend towards worse survival compared to those with proficiency (median OS: 19.2 vs. 28.1 months, p = 0.07). MMR deficient tumors showed a lower mesothelin expression compared to MMR proficient tumors, median 8 vs. 129 positive cells per TMA (p = 0.08). Patients with MMR deficiency and low mesothelin expression had a worse outcome compared to patients with MMR proficiency and high mesothelin expression (median OS: 14.5 vs. 30.0 months, p = 0.05). Conclusions: Given the high rate of MMR deficiency, all CC tumors should be tested and may benefit from anti-PD-1 therapy. The poor prognosis of MMR deficient CC may be independent of T-cell infiltration and additional studies are needed to better characterize the genetic and molecular landscape of this subset of tumors.

Correlation of mesothelin expression and CD8 tumor infiltrating lymphocytes with prognosis in cholangiocarcinoma

e15650

Background: Cholangiocarcinoma (CC) is a rapidly progressing malignancy with an unmet treatment need. Little is known about the CC tumor immune microenvironment or about relevant antigenic targets. We hypothesized that lack of T cell infiltration or PD-L1 expression may identify patients at high risk of death, and that mesothelin may be a relevant antigenic target. Methods: A retrospective analysis was conducted of CC tumors at the University of Virginia from 2000-2014. TMAs were constructed of 3-4 cores from each tumor and were stained by IHC for CD4 and CD8 tumor infiltrating lymphocytes (TILs), mesothelin and PD-L1. TMAs were scanned using the Leica SCN400 and analyzed using the Digital Image Hub software. Stain intensity thresholds for defining positive cells were determined by two users and recorded as an average of all cores from each tumor. Mesothelin and PD-L1 expression were measured as a percentage of positive tumor cells. TILs and protein expression were analyzed for association with overall survival, grouped as high or low expression based either on the median or the 33rdpercentile. Correlation with overall survival was assessed using a log rank test and a classification and regression tree with p-values < 0.05 being considered statistically significant. Results: Ninety-nine tumors were available for analysis: 26 intrahepatic, 37 hilar, and 36 distal. PD-L1 and mesothelin expression > 1% of tumor cells were found in 16% and 92% of tumors, respectively. CD4 and CD8 TILs were found in nearly all tumors (98% and 96%), with the majority showing intraepithelial CD4 and CD8 infiltration (73% and 68%). There were no significant associations between survival and PD-L1, mesothelin, or CD4 and CD8 infiltration. However when considered together, the group with low mesothelin/low CD8 (each below 33rdpercentile) had worse survival (9.1 months) compared to high mesothelin/high CD8 (25 months), high mesothelin/low CD8 (30.1 months) and low mesothelin/high CD8 (26.1 months), p = 0.015. Conclusions: CC tumors that lack CD8 infiltration and mesothelin expression have a poor prognosis. Mesothelin represents an attractive target in cholangiocarcinoma, opening the door for future immunotherapy for CC.

Results from a phase 2b, randomized, multicenter study of GVAX pancreas and CRS-207 compared to chemotherapy in adults with previously-treated metastatic pancreatic adenocarcinoma (ECLIPSE Study)

345

Background: GVAX is composed of irradiated, allogeneic pancreatic cancer cells modified to express GM-CSF and induce broad tumor antigen responses. Low-dose cyclophosphamide (CY) is administered with GVAX to inhibit regulatory T cells. CRS-207 is live, attenuated, double-deleted Listeria monocytogenes(LADD) engineered to express mesothelin. CRS-207 boosts T cell responses against mesothelin and stimulates innate and adaptive immunity. In an earlier Phase 2 study in patients with mPDA, CY/GVAX + CRS-207 resulted in a significant improvement in overall survival (OS) compared to CY/GVAX alone. Methods: Patients with previously-treated mPDA were randomized 1:1:1 to receive 2 doses of CY/GVAX + 4 doses of CRS-207 (Arm A), 6 doses of CRS-207 alone (Arm B), or physician’s choice of single-agent chemotherapy (Arm C). Two cohorts were included based on number of prior lines of therapy; the primary cohort (PC) represented those with ≥ 2 prior lines. The primary objective was to compare OS between Arms A and C in the PC. Additional objectives include OS analyses between all treatment arms, safety, tumor responses and immune analyses. Results: 303 patients were enrolled: 213 in the PC and 90 in an exploratory 2nd-line cohort (SC). Common AEs associated with CRS-207 treatment included transient fevers, chills, and nausea. High dropout rates were observed in Arm C prior to treatment (40% in PC, 63% in SC). Clinical trial information: NCT02004262 . Subset and immune analyses, as well as OS data from SC, will be presented at the meeting. Conclusions: The combination of CY/GVAX + CRS-207 did not show a survival benefit over chemotherapy in patients with previously-treated mPDA, although survival of patients receiving CRS-207 alone appeared similar to chemotherapy. The regimens were well tolerated with no new significant safety findings. The high dropout rate in the chemotherapy arm demonstrates a potential challenge for conventional controls in immunotherapy trials. [Table: see text]

Abstract A013: Favorable changes in tumor microenvironment following intravenous dosing with live attenuated Listeria monocytogenes-based immunotherapy

Modification of the tumor microenvironment (TME) to promote immune-mediated tumor cell destruction is considered to be an essential step for effective immunotherapy. We are evaluating recombinant live-attenuated, double deleted Listeria monocytogenes (LADD) as an immunotherapy platform for the treatment of cancer in several clinical trials in diverse indications. One LADD strain, known as CRS-207, has been engineered to express the tumor-associated antigen mesothelin and is being tested in pancreatic, ovarian and mesothelioma malignancies. Using multi-dimensional immunohistochemistry of paired biopsies from three patients with mesothelioma, we demonstrate the recruitment and expansion of effector tumor-infiltrating lymphocytes, including CD8+ T cells, mature DCs, CD163− macrophages and NK cells, following two prime infusions of CRS-207. In several different syngeneic mouse tumor models, we demonstrate that treatment with LADD engineered to express endogenous tumor antigens also induced significant changes in the TME that were consistent with changes observed in cancer patients, including enhanced CD8+ T cell effector function, recruitment of critical antigen presenting cells and reduction of regulatory T cells, and these changes correlated with significant therapeutic benefit in the mouse. LADD-induced changes to the TME were required for synergistic therapeutic antitumor efficacy combined with immune checkpoint blockade, including targeting MC38 tumor-specific neoantigens. Together, these findings demonstrate that intravenous administration of recombinant LADD therapy induces favorable changes in the tumor microenvironment in mice and humans with promise for effective outcomes in human clinical trials.

Citation Format: Weiwen Deng, Takahiro Tsujikawa, Nitya Nair, Thomas Hudson, Weiqun Liu, Chris S. Rae, Edward E. Lemmens, Anthony W. Desbien, William Hanson, Peter Lauer, Lisa M. Coussens, Dirk G. Brockstedt, Thomas W. Dubensky, Jr., Meredith L. Leong. Favorable changes in tumor microenvironment following intravenous dosing with live attenuated Listeria monocytogenes-based immunotherapy [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A013.

Tumor-Specific T Cell Dysfunction Is a Dynamic Antigen-Driven Differentiation Program Initiated Early during Tumorigenesis

CD8(+) T cells recognizing tumor-specific antigens are detected in cancer patients but are dysfunctional. Here we developed a tamoxifen-inducible liver cancer mouse model with a defined oncogenic driver antigen (SV40 large T-antigen) to follow the activation and differentiation of naive tumor-specific CD8(+) T (TST) cells after tumor initiation. Early during the pre-malignant phase of tumorigenesis, TST cells became dysfunctional, exhibiting phenotypic, functional, and transcriptional features similar to dysfunctional T cells isolated from late-stage human tumors. Thus, T cell dysfunction seen in advanced human cancers may already be established early during tumorigenesis. Although the TST cell dysfunctional state was initially therapeutically reversible, it ultimately evolved into a fixed state. Persistent antigen exposure rather than factors associated with the tumor microenvironment drove dysfunction. Moreover, the TST cell differentiation and dysfunction program exhibited features distinct from T cell exhaustion in chronic infections. Strategies to overcome this antigen-driven, cell-intrinsic dysfunction may be required to improve cancer immunotherapy.

Randomized phase II study of the safety, efficacy, and immune response of GVAX pancreas (with cyclophosphamide) and CRS-207 with or without nivolumab in patients with previously treated metastatic pancreatic adenocarcinoma (STELLAR)

TPS486

Background: A heterologous prime-boost vaccination strategy using GVAX pancreas and CRS-207 is showing promise in patients with pancreatic adenocarcinoma (PDA) (Le, JCO 2015). Furthermore, blockade of the immune checkpoint programmed death-1 (PD-1) is active in some cancers. Combinatorial strategies aimed at priming tumor antigen-specific T cells while simultaneously blocking negative checkpoints may be necessary to improve outcomes in PDA. GVAX is composed of allogeneic pancreatic cancer cells modified to express GM-CSF and induces a broad response against multiple tumor antigens. GVAX is given with low-dose cyclophosphamide (CY) to inhibit regulatory T cells. CRS-207 is live-attenuated Listeria monocytogenes engineered to express the tumor-associated antigen mesothelin. CRS-207 boosts responses against mesothelin and is unique in its capacity to stimulate both innate and adaptive immunity by activating T cells and NK cells. Nivolumab is an antibody against PD-1. Methods: This is a phase 2 study comparing CY/GVAX and CRS-207 with or without nivolumab in subjects with PDA who failed only one chemotherapy regimen for metastatic disease. Subjects are randomized in a 1:1 ratio to receive either 2 doses of CY/nivolumab/GVAX and 4 doses of nivolumab/CRS-207 (Arm A) or 2 doses of CY/GVAX and 4 doses of CRS-207 (Arm B). The primary objective is to compare OS between Arms A and B. Secondary/exploratory objectives include: assessment of safety and clinical responses (tumor assessments and CA19-9 levels) and correlation of Lm- and mesothelin-specific T cell and other immunological responses with OS, progression-free survival and best overall response. Clinical trial information: NCT02243371.

Clinical and immune characteristics of rapid dropout and long-term survival in a phase II safety and efficacy study of combination CRS-207/GVAX immunotherapy in pancreatic cancer

459

Background: Baseline patient characteristics may impact duration on study and survivorship of patients in immunotherapy trials. In this study, GVAX pancreas (GM-CSF–secreting allogeneic pancreatic tumor cells) was administered with low-dose cyclophosphamide (Cy), with or without subsequent CRS-207 (live-attenuated Listeria monocytogenes–expressing mesothelin) infusion. Baseline clinical and immunological data were examined for two patient subsets based on duration on study. Methods: Previously treated patients with metastatic pancreatic adenocarcinoma were randomly assigned at a ratio of 2:1 to 2 doses of Cy/GVAX followed by 4 doses of CRS-207 or 6 doses of Cy/GVAX every 3 weeks. Stable patients were offered additional courses. Patients were evaluated for post-randomization duration on study of < 60 days (rapid dropouts, RD) and > 18 months (long-term survivors, LTS). Baseline characteristics of these subsets were examined. Results: A total of 93 patients were randomized. Fifteen patients were RD; 13 were LTS. More RDs versus LTS had liver metastasis and lymph node involvement. On average, fewer RD patients had radiotherapy prior to randomization and fewer had prior surgical intervention. RD averaged 1.73 prior metastatic cancer treatment regimens versus 1.31 in LTS. RD also had higher average baseline CA 19-9 levels. Immune analysis showed higher circulating terminal effector CD8+ T cells and lower serum IL-6 in LTS compared to RD. Serum IL-6 concentration remained lower in LTS at four weeks following initiation of treatment. For patients who received CRS-207, CD8+ T cells specific to listeriolysin O (LLO) and mesothelin were higher in LTS than RD, as determined by ELISPOT. Conclusions: Baseline clinical and immunological characteristics may impact patient duration on immunotherapy trials. Immune monitoring and biomarker analysis in this study is ongoing to identify circulating cellular, tumor biomarkers and genomic (miRNA and mRNA) signatures that may correlate with survival. These findings warrant continued exploration of patient characteristics to identify best candidates for immunotherapy trials. Clinical trial information: NCT01417000.

Systemic Tolerance Mediated by Melanoma Brain Tumors Is Reversible by Radiotherapy and Vaccination

PURPOSE

Immune responses to antigens originating in the central nervous system (CNS) are generally attenuated, as collateral damage can have devastating consequences. The significance of this finding for the efficacy of tumor-targeted immunotherapies is largely unknown.

EXPERIMENTAL DESIGN

The B16 murine melanoma model was used to compare cytotoxic responses against established tumors in the CNS and in the periphery. Cytokine analysis of tissues from brain tumor-bearing mice detected elevated TGFβ secretion from microglia and in the serum and TGFβ signaling blockade reversed tolerance of tumor antigen-directed CD8 T cells. In addition, a treatment regimen using focal radiation therapy and recombinant Listeria monocytogenes was evaluated for immunologic activity and efficacy in this model.

RESULTS

CNS melanomas were more tolerogenic than equivalently progressed tumors outside the CNS as antigen-specific CD8 T cells were deleted and exhibited impaired cytotoxicity. Tumor-bearing mice had elevated serum levels of TGFβ; however, blocking TGFβ signaling with a small-molecule inhibitor or a monoclonal antibody did not improve survival. Conversely, tumor antigen-specific vaccination in combination with focal radiation therapy reversed tolerance and improved survival. This treatment regimen was associated with increased polyfunctionality of CD8 T cells, elevated T effector to T regulatory cell ratios, and decreased TGFβ secretion from microglia.

CONCLUSIONS

These data suggest that CNS tumors may impair systemic antitumor immunity and consequently accelerate cancer progression locally as well as outside the CNS, whereas antitumor immunity may be restored by combining vaccination with radiation therapy. These findings are hypothesis-generating and warrant further study in contemporary melanoma models as well as human trials.

A phase IIb, randomized, controlled, multicenter, open-label study of the efficacy and immune response of GVAX pancreas vaccine and CRS-207 compared to chemotherapy or to CRS-207 alone in adults with previously treated metastatic pancreatic adenocarcinoma (ECLIPSE Study)

TPS489

Background: A prime-boost vaccination strategy using GVAX pancreas vaccine and CRS-207 is showing activity in patients with metastatic pancreatic adenocarcinoma (PDA). GVAX is composed of lethally-irradiated, allogeneic pancreatic cancer cells modified to express GM-CSF. GVAX induces a response against multiple tumor antigens and is given after low-dose cyclophosphamide (CY) to inhibit regulatory T cells. CRS-207 is live-attenuated Listeria monocytogenes engineered to express the tumor-associated antigen mesothelin. CRS-207 boosts responses against mesothelin and stimulates both innate and adaptive immunity by activating T cells and NK cells. Results from a phase 2 study demonstrated CY/GVAX plus CRS-207 improved overall survival (OS) compared to CY/GVAX alone (p-value<0.05; Le, GI ASCO 2014). Methods: This is a phase 2b study comparing CY/GVAX and CRS-207 to chemotherapy or to CRS-207 alone in patients with previously-treated metastatic PDA. Patients will be enrolled in two cohorts: 150 patients into a primary cohort of patients with at least two prior chemotherapy regimens for metastatic disease (third + line) and 90 patients into an exploratory cohort of patients with only one prior chemotherapy regimen for metastatic disease (second line). Patients will be randomized in a 1:1:1 ratio to receive 2 doses of CY/GVAX and 4 doses of CRS-207 (Arm A), six doses of CRS-207 (Arm B) or physician’s choice of single-agent chemotherapy (Arm C). The primary objective is to compare OS between Arms A and C in the primary cohort. Secondary/exploratory objectives include: comparison of OS in both primary and exploratory cohorts between all treatment arms, assessment of safety and clinical responses (tumor assessments and CA19-9 levels) and correlation of Lm- and mesothelin-specific T cell and other immunological responses with clinical responses. Updated enrollment will be reported. (Sponsor: Aduro BioTech, Inc.; NCT02004262). Clinical trial information: NCT02004262.

Phase II, randomized study of GVAX pancreas and CRS-207 immunotherapy in patients with metastatic pancreatic cancer: Clinical update on long term survival and biomarker correlates to overall survival

261

Background: In a phase 2a randomized study, metastatic pancreatic ductal adenocarcinoma (PDA) patients treated sequentially with two vaccine-based immunotherapies showed extended overall survival (OS) with tolerable side effects. Treatment included low-dose cyclophosphamide (CY) to inhibit T-regulatory cells prior to GVAX, an irradiated GM-CSF-secreting allogeneic PDA cell vaccine, which activates a broad antigenic response, followed by CRS-207, a live-attenuated, mesothelin-expressing Listeria monocytogenes vaccine which stimulates innate and adaptive immunity. Methods: Patients were enrolled with metastatic PDA who received or refused ≥1 prior chemotherapy, had ECOG ≤1 and adequate organ function. Patients were randomized 2:1 to receive 2 doses of CY/GVAX followed by 4 doses of CRS-207 (Arm A) or 6 doses of CY/GVAX (Arm B). PBMC and serum were collected over the course of treatment for immune and biomarker analyses. CyTOF, ELISPOT, and luminex were used to identify biomarker correlates of OS. Results: We previously reported phase 2a results demonstrating median OS in patients treated in arm A was 6.1 months compared to 3.9 months for those in arm B (HR=0.54, one-sided p=0.011). As of August 2014, 8 patients are still alive (median time on study: 768 days; range: 596-880), with 3 subjects on combination treatment. Mesothelin-specific CD8+T cell responses following CY/GVAX correlated with improved OS in both arms. Elevated frequencies of T cell subsets and a panel of baseline serum cytokines also correlated with longer OS. Strikingly, hierarchical clustering based on expression of biomarkers showed significant clustering of patients according to OS. Conclusions: Treatment with CY/GVAX and CRS-207 was well-tolerated and resulted in improved OS compared to CY/GVAX alone. A larger phase 2b, 3-arm, randomized trial is ongoing and plans to treat 240 adults with previously-treated metastatic PDA with CY/GVAX and CRS-207, CRS-207 alone, or standard chemotherapy. Preliminary results using patients’ PBMCs and sera revealed potential biomarkers for OS. Clinical trial information: NCT01417000. Clinical trial information: NCT01417000.

Safety and survival with GVAX pancreas prime and Listeria Monocytogenes-expressing mesothelin (CRS-207) boost vaccines for metastatic pancreatic cancer

PURPOSE

GVAX pancreas, granulocyte-macrophage colony-stimulating factor-secreting allogeneic pancreatic tumor cells, induces T-cell immunity to cancer antigens, including mesothelin. GVAX is administered with low-dose cyclophosphamide (Cy) to inhibit regulatory T cells. CRS-207, live-attenuated Listeria monocytogenes-expressing mesothelin, induces innate and adaptive immunity. On the basis of preclinical synergy, we tested prime/boost vaccination with GVAX and CRS-207 in pancreatic adenocarcinoma.

PATIENTS AND METHODS

Previously treated patients with metastatic pancreatic adenocarcinoma were randomly assigned at a ratio of 2:1 to two doses of Cy/GVAX followed by four doses of CRS-207 (arm A) or six doses of Cy/GVAX (arm B) every 3 weeks. Stable patients were offered additional courses. The primary end point was overall survival (OS) between arms. Secondary end points were safety and clinical response.

RESULTS

A total of 90 patients were treated (arm A, n = 61; arm B, n = 29); 97% had received prior chemotherapy; 51% had received ≥ two regimens for metastatic disease. Mean number of doses (± standard deviation) administered in arms A and B were 5.5 ± 4.5 and 3.7 ± 2.2, respectively. The most frequent grade 3 to 4 related toxicities were transient fevers, lymphopenia, elevated liver enzymes, and fatigue. OS was 6.1 months in arm A versus 3.9 months in arm B (hazard ratio [HR], 0.59; P = .02). In a prespecified per-protocol analysis of patients who received at least three doses (two doses of Cy/GVAX plus one of CRS-207 or three of Cy/GVAX), OS was 9.7 versus 4.6 months (arm A v B; HR, 0.53; P = .02). Enhanced mesothelin-specific CD8 T-cell responses were associated with longer OS, regardless of treatment arm.

CONCLUSION

Heterologous prime/boost with Cy/GVAX and CRS-207 extended survival for patients with pancreatic cancer, with minimal toxicity.

Attenuated Listeria monocytogenes vectors overcome suppressive plasma factors during HIV infection to stimulate myeloid dendritic cells to promote adaptive immunity and reactivation of latent virus

HIV-1 infection is characterized by myeloid dendritic cell (DC) dysfunction, which blunts the responsiveness to vaccine adjuvants. We previously showed that nonviral factors in HIV-seropositive plasma are partially responsible for mediating this immune suppression. In this study we investigated recombinant Listeria monocytogenes (Lm) vectors, which naturally infect and potently activate DCs from seronegative donors, as a means to overcome DC dysfunction associated with HIV infection. Monocyte-derived DCs were cocultured with plasma from HIV-infected donors (HIV-moDCs) to induce a dysregulated state and infected with an attenuated, nonreplicative vaccine strain of Lm expressing full length clade B consensus gag (KBMA Lm-gag). Lm infection stimulated cytokine secretion [interleukin (IL)-12p70, tumor necrosis factor (TNF)-α, and IL-6] and Th-1 skewing of allogeneic naive CD4 T cells by HIV-moDCs, in contrast to the suppressive effects observed by HIV plasma on moDCs on toll-like receptor ligand stimulation. Upon coculture of "killed" but metabolically active (KBMA) Lm-gag-infected moDCs from HIV-infected donors with autologous cells, expansion of polyfunctional, gag-specific CD8(+) T cells was observed. Reactivation of latent proviruses by moDCs following Lm infection was also observed in models of HIV latency in a TNF-α-dependent manner. These findings reveal the unique ability of Lm vectors to contend with dysregulation of HIV-moDCs, while simultaneously possessing the capacity to activate latent virus. Concurrent stimulation of innate and adaptive immunity and disruption of latency may be an approach to reduce the pool of latently infected cells during HIV infection. Further study of Lm vectors as part of therapeutic vaccination and eradication strategies may advance this evolving field.

Radiation therapy combined with Listeria monocytogenes-based cancer vaccine synergize to enhance tumor control in the B16 melanoma model

Conceptually, the immune system may profoundly influence the efficacy of radiation therapy. Compelling evidence has recently emerged revealing the capacity of local radiation therapy (RT) to induce antitumor immune responses and sparked interest in combining RT with immunotherapy to promote tumor-specific immunity. A Listeria monocytogenes (Lm)-based cancer vaccine engineered to express tumor-associated antigen has been shown to effectively retard tumor growth by cell-mediated immune mechanisms. We hypothesized that combining RT and Lm vaccine will result in synergistic effects that enhance tumor control. Collectively, our data demonstrate that combination therapy significantly delayed B16 melanoma tumor growth by a mechanism partly dependent on CD8⁺ T cells. Radiotherapy and Lm vaccine each induce different aspects of antitumor immunity, resulting in an overall increase in intratumoral numbers of activated T cells, antigen-specific CD8⁺ T cells, natural killer (NK) cells and levels of effector molecules, such as interferon γ (IFNγ) and granzyme B. Thus, radiation and Lm vaccine combination therapy is a promising new strategy for the treatment of malignant disease, and further understanding of the mechanisms that underlie efficacy is required to optimize the dosage and schedule for administering the two treatments.

A Listeria vaccine and depletion of T-regulatory cells activate immunity against early stage pancreatic intraepithelial neoplasms and prolong survival of mice

BACKGROUND & AIMS

Premalignant lesions and early stage tumors contain immunosuppressive microenvironments that create barriers for cancer vaccines. Kras(G12D/+);Trp53(R172H/+);Pdx-1-Cre (KPC) mice, which express an activated form of Kras in pancreatic tissues, develop pancreatic intraepithelial neoplasms (PanIN) that progress to pancreatic ductal adenocarcinoma (PDA). We used these mice to study immune suppression in PDA.

METHODS

We immunized KPC and Kras(G12D/+);Pdx-1-Cre mice with attenuated intracellular Listeria monocytogenes (which induces CD4(+) and CD8(+) T-cell immunity) engineered to express Kras(G12D) (LM-Kras). The vaccine was given alone or in sequence with an anti-CD25 antibody (PC61) and cyclophosphamide to deplete T-regulatory (Treg) cells. Survival times were measured; pancreatic and spleen tissues were collected and analyzed by histologic, flow cytometry, and immunohistochemical analyses.

RESULTS

Interferon γ-mediated, CD8(+) T-cell responses were observed in KPC and Kras(G12D/+);Pdx-1-Cre mice given LM-Kras, but not in unvaccinated mice. Administration of LM-Kras to KPC mice 4-6 weeks old (with early stage PanINs), depleted of Treg cells, significantly prolonged survival and reduced PanIN progression (median survival, 265 days), compared with unvaccinated mice (median survival, 150 days; P = .002), mice given only LM-Kras (median survival, 150 days; P = .050), and unvaccinated mice depleted of Treg cells (median survival, 170 days; P = .048). In 8- to 12-week-old mice (with late-stage PanINs), LM-Kras, alone or in combination with Treg cell depletion, did not increase survival time or slow PanIN progression. The combination of LM-Kras and Treg cell depletion reduced numbers of Foxp3(+)CD4(+) T cells in pancreatic lymph nodes, increased numbers of CD4(+) T cells that secrete interleukin 17 and interferon γ, and caused CD11b(+)Gr1(+) cells in the pancreas to acquire an immunostimulatory phenotype.

CONCLUSIONS

Immunization of KPC mice with Listeria monocytogenes engineered to express Kras(G12D), along with depletion of Treg cells, reduces progression of early stage, but not late-stage, PanINs. This approach increases infiltration of the lesion with inflammatory cells. It might be possible to design immunotherapies against premalignant pancreatic lesions to slow or prevent progression to PDA.

Attenuated Listeria monocytogenes reprograms M2-polarized tumor-associated macrophages in ovarian cancer leading to iNOS-mediated tumor cell lysis

A principal mechanism by which tumors evade immune-mediated elimination is through immunosuppression. Previous approaches to tumor immunotherapy have focused on modifying the immunosuppressive environment with immune checkpoint inhibitors, cytokine therapy, and other modalities with the intent to generate T-cell based anti-tumor immunity. We hypothesized that transformation of the suppressive ovarian cancer microenvironment could be achieved by introduction of the attenuated ΔactA/ΔinlB strain of Listeria monocytogenes. ΔactA/ΔinlB introduced into the microenvironment of the aggressive ID8-Defb29/Vegf-A murine ovarian carcinoma is preferentially phagocytosed by tumor-associated macrophages (TAMs) and reprograms that population from one of suppression to immunostimulation. TAMs in the peritoneum upregulated their co-stimulatory molecules CD80 and CD86, increased transcription of inflammatory cytokines, and downregulated transcription of suppressive effector molecules. Surprisingly, therapeutic benefit was not mediated by T- or NK-cell activity. ΔactA/ΔinlB-induced repolarization of TAMs activated direct tumor cell lysis via Nos2 production of nitric oxide. Modulation of the immunosuppressive nature of the ID8-Defb29/Vegf-A microenvironment, specifically by reprogramming of the TAM suppressive population from M2 to M1 polarization, is critical for our observed immune-mediated survival benefit.

Enhanced virus-specific CD8+ T cell responses by Listeria monocytogenes-infected dendritic cells in the context of Tim-3 blockade

In this study, we engineered Listeria monocytogens (Lm) by deleting the LmΔactA/ΔinlB virulence determinants and inserting HCV-NS5B consensus antigens to develop a therapeutic vaccine against hepatitis C virus (HCV) infection. We tested this recombinant Lm-HCV vaccine in triggering of innate and adaptive immune responses in vitro using immune cells from HCV-infected and uninfected individuals. This live-attenuated Lm-HCV vaccine could naturally infect human dendritic cells (DC), thereby driving DC maturation and antigen presentation, producing Th1 cytokines, and triggering CTL responses in uninfected individuals. However, vaccine responses were diminished when using DC and T cells derived from chronically HCV-infected individuals, who express higher levels of inhibitory molecule Tim-3 on immune cells. Notably, blocking Tim-3 signaling significantly improved the innate and adaptive immune responses in chronically HCV-infected patients, indicating that novel strategies to enhance the potential of antigen presentation and cellular responses are essential for developing an effective therapeutic vaccine against HCV infection.

A phase 2, randomized trial of GVAX pancreas and CRS-207 immunotherapy versus GVAX alone in patients with metastatic pancreatic adenocarcinoma: Updated results

177^

Background: Immunotherapy for pancreatic ductal adenocarcinoma (PDA) is likely to require synergistic combinations. One approach is to use heterologous prime boost vaccinations to capitalize on immunostimulatory features of distinct vectors. GVAX is irradiated, GM-CSF-secreting allogeneic pancreatic cell lines given intradermally to elicit a broad antigenic response. Low-dose cyclophosphamide (CY) is given prior to GVAX to inhibit regulatory T-cells. CRS-207 is live-attenuated Listeria monocytogenes (Lm) which expresses mesothelin and stimulates innate and adaptive immunity. In mouse tumor models, Lm/GVAX vaccines are synergistic and in the Phase 1 study of CRS-207, 3 PDA patients who had received prior GVAX lived ≥15 months (mos). Methods: Metastatic PDA patients (ECOG 0-1; adequate organ function) who received or refused ≥1 prior chemotherapy were randomized 2:1 to receive either 2 doses of CY/GVAX followed by 4 doses of CRS-207 (Arm A) or 6 doses of CY/GVAX (Arm B) every 3 weeks. Courses could be repeated. The primary endpoint was to compare overall survival (OS) between the arms. Secondary endpoints were safety, clinical and immune responses. One-sided p-values are reported. Results: 90 patients (Full Analysis Set [FAS]; A: 61, B: 29), of which 51% had received ≥2 chemotherapy regimens for metastatic PDA, were treated. After a median follow-up of 7.8 mos, median OS in FAS was 6.1 vs 3.9 mos (A vs B; HR=0.54, p=0.011). Median OS in patients who received ≥3 doses (per protocol [PP] set: 2 doses of CY/GVAX and ≥1 dose of CRS-207 in A or ≥3 doses of CY/GVAX in B) was 9.7 vs 4.6 mos (A vs B; HR=0.44, p=0.0074). The treatment effect was particularly evident in patients who received ≥2 prior regimens for metastatic PDA with median OS of 5.1 vs 3.7 mos (A vs B; HR=0.34, p=0.001). OS in the PP set was 8.2 vs 4.0 mos (A vs B; HR=0.23, p=0.0003). CA19-9 stabilization was seen in 32% vs 13% of patients (A vs B; p=0.06). Toxicities included local reactions after GVAX and transient fevers, rigors and lymphopenia after CRS-207. Conclusions: CY/GVAX followed by CRS-207 shows extended survival with manageable toxicity in previously-treated metastatic PDA and warrants further study. Clinical trial information: NCT01417000.

CRS-207 vaccine plus chemotherapy as front-line treatment for subjects with malignant pleural mesothelioma (MPM)

TPS7607

Background: CRS-207 is a live-attenuated Listeria monocytogenes (Lm) vaccine expressing the tumor-associated antigen mesothelin which is overexpressed in MPM. CRS-207 was well tolerated and induced Lm- and mesothelin-specific T cell immunity in a phase 1 study in adults with mesothelin-expressing cancers (Le et al., Clin. Cancer Res. 2012). Preclinical and clinical studies suggest that vaccines and chemotherapies work synergistically and augment anti-tumor effectiveness of subsequent chemotherapies. Methods: This phase 1B study is evaluating the safety and induction of mesothelin-specific immune responses by CRS-207 plus chemotherapy with pemetrexed (P) and cisplatin (C) in adults with newly diagnosed, unresectable MPM. Two doses of 1×109colony forming units (CFU) CRSE207 are administered intravenously two weeks apart followed two weeks later by up to six cycles of P (500 mg/m2) and C (75 mg/m2) given every 3 weeks. Two booster vaccinations of CRS-207 are administered three weeks apart 4 weeks after completing PC. Secondary and exploratory endpoints will assess objective tumor response, time to progression, overall survival and immune correlates. This is one of the first trials to assess the synergy between vaccines and chemotherapy in newly diagnosed patients with MPM. Sponsor: Aduro BioTech, Inc. ClinicalTrials.gov ID: NCT01675765. Clinical trial information: NCT01675765.

Interim safety and efficacy analysis of a phase II, randomized study of GVAX pancreas and CRS-207 immunotherapy in patients with metastatic pancreatic cancer

4040^

Background: GVAX is composed of GM-CSF-secreting allogeneic pancreas cancer cell lines and administered with low-dose cyclophosphamide (CY) to inhibit regulatory T cells. In prior studies, GVAX induced mesothelin-specific T cell responses that correlated with survival. CRS-207 is a live-attenuated Listeria monocytogenes engineered to express human mesothelin. CRS-207 stimulates potent innate and adaptive immunity and has shown synergy with GVAX in mouse tumor models. Anecdotal survival benefit was observed in the CRS-207 phase I study in patients who received prior GVAX. Methods: Patients were enrolled with metastatic pancreatic ductal adenocarcinoma (PDA) who received or refused ≥ 1 prior chemotherapy, had ECOG ≤ 1 and adequate organ function. Patients were randomized 2:1 to receive 2 doses of CY/GVAX followed by 4 doses of CRS-207 (Arm A) or 6 doses of CY/GVAX (Arm B) every 3 weeks. Clinically stable patients were offered additional 20-week courses. The primary endpoint was comparison of OS between treatment arms. Secondary endpoints were to evaluate safety, clinical and immune responses. Results: 90 patients were treated (Arm A: 61, Arm B: 29). As of Jan 2013, 27 patients completed 1 course (A: 24, B: 3) and 17 patients (A: 15, B: 2) initiated a 2nd course. Median age was 63. Median number of prior regimens was 3. No treatment-related serious adverse events (SAEs) or unexpected toxicities were observed. The most frequent Grade (G) 3/4 related toxicities were fever, lymphopenia, hypophosphatemia, elevated liver enzymes, and fatigue following CRS-207 in <5% of subjects. Of 51 patients evaluated post-treatment, 34% had stable disease in Arm A vs. 19% in Arm B. OS for all patients treated was 6 months in Arm A vs. 3.4 months in Arm B (two-sided, p=0.0114). Conclusions: Combined CY/GVAX pancreas and CRS-207 was generally well-tolerated with no treatment-related SAEs or unexpected G3/4 toxicities. The significant difference in OS between treatment arms met the criteria for early stopping. This indicates that the combination immunotherapy may extend OS for metastatic PDA patients with minimal toxicity and should continue to be developed as an effective therapy. Clinical trial information: NCT01417000.

Abstract 2837: Combined targeting of antigens expressed in prostate cancer and prostate stem cells using Listeria-based cancer vaccines for the treatment of prostate cancer

Immune-based therapies have demonstrated benefit in multiple clinical trials, and as we gain better knowledge of the mechanisms by which tumors avoid immune detection, new strategies can be designed to more effectively target tumor-specific antigens. Aduro BioTech, Inc. has engineered attenuated Listeria monocytogenes (Lm), to be safe for human use and to also induce potent and broad innate and adaptive immune responses including CD4 and CD8 T cells specific for tumor-associated antigens. Aduro's lead therapeutic, CRS-207, is now being evaluated in a randomized, controlled Phase 2 study in patients with metastatic pancreas cancer. Prostate cancer is the only type of cancer for which a targeted therapeutic cancer vaccine has been approved by the U.S. Food and Drug Administration (FDA). Provenge®, an autologous cellular vaccine targeting prostatic acid phosphatase (PAP) developed by the Dendreon Corporation, was approved in 2010 for patients with metastatic, castrate-resistant prostate cancer (CRPC), validating the benefits of immunotherapy and providing a new treatment for CRPC with significantly less toxicity than chemotherapy. We have developed a candidate therapeutic vaccine strain for prostate cancer, named Lm-PCaVx, in which Aduro's proprietary Lm platform has been engineered to express three antigens, PAP, NY-ESO-1 and NKX3.1. The goal is to concurrently target antigens that are expressed by tumor cells (PAP and NY-ESO-1) as well as an antigen that can be expressed by cancer stem cells (NKX3.1). PAP has been clinically validated as the target of the Provenge® vaccine; NY-ESO-1 has been shown to a tumor-associated immunological target by other vaccine approaches; and NKX3.1 is over-expressed in prostate tissue that regenerates after castration therapy. In this study, we report the construction of an Lm vaccine strain encoding these three antigens and demonstrate expression of the encoded antigens in Lm-infected antigen-presenting cells. Immunization with Lm-PCaVx induced PAP-, NY-ESO-1- and NKX3.1-specific T-cell responses in mice as well as anti-tumor-type responses in HLA-A2/HLA-DR1 transgenic mice. Together these findings support the further development of a multivalent Lm-based vaccine targeting cell-mediated immune responses against multiple tumor-associated antigens as a novel, cost-effective and rational approach for the treatment of patients with prostate cancer.

Citation Format: Douglas McNeel, Marcella Fasso, Laura Johnson, Ed Lemmens, Bill Hanson, Pete Lauer, Steven Bodovitz, Charles Drake, Dirk G. Brockstedt. Combined targeting of antigens expressed in prostate cancer and prostate stem cells using Listeria-based cancer vaccines for the treatment of prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2837. doi:10.1158/1538-7445.AM2013-2837

Clinical development of Listeria monocytogenes-based immunotherapies

Active immunotherapy targeting dendritic cells (DCs) has shown great promise in preclinical models and in human clinical trials for the treatment of malignant disease. Sipuleucel-T (Provenge, Dendreon, Seattle, WA), which consists of antigen-loaded dendritic cells (DCs), recently became the first targeted therapeutic cancer vaccine to be approved by the US Food and Drug Administration (FDA). However, ex vivo therapies such as Provenge have practical limitations and elicit an immune response with limited scope. By contrast, live-attenuated Listeria monocytogenes (Lm) naturally targets DCs in vivo and stimulates both innate and adaptive cellular immunity. Lm-based vaccines engineered to express cancer antigens have demonstrated striking efficacy in several animal models and have resulted in encouraging anecdotal survival benefit in early human clinical trials. Two different Lm-based vaccine platforms have advanced into phase II clinical trials in cervical and pancreatic cancer. Future Lm-based clinical vaccine candidates are expected to feature polyvalent antigen expression and to be used in combination with other immunotherapies or conventional therapies such as radiotherapy and chemotherapy to augment efficacy.

Killed but metabolically active vaccines

Beginning in the 20th century and continuing into the new millennia, vaccines against numerous diseases have had an unquestioned principal role of both enhancing the quality of life and increasing life expectancy (Rappuoli R, Mandl CW, Black S, De Gregorio E: Vaccines for the twenty-first century society. Nat Rev Immunol 2011, 11:865-872). Despite this success and the development of sophisticated new vaccine technologies, there remain multiple infectious diseases including tuberculosis, malaria and AIDS that await an effective prophylactic vaccine. In addition, there have been recent clinical successes among individuals with cancer using vaccine treatment strategies-so-called therapeutic vaccines-that stimulate tumor specific immunity and increase survival (Kantoff PW, Higano CS, Shore ND, Berger ER, Small EJ, Penson DF, Redfern CH, Ferrari AC, Dreicer R, Sims RB, et al.: Sipuleucel-T immunotherapy for castration-resistant prostate cancer. New Engl J Med 2010, 363:411-422). Here we summarize a new class of vaccines termed Killed But Metabolically Active (KBMA). KBMA vaccines are whole pathogenic or attenuated organisms killed through photochemical inactivation and cannot cause disease, yet retain sufficient metabolic activity to initiate a potent immune response. KBMA vaccines have two broad applications. First, recombinant KBMA vaccines encoding selected antigens relevant to infectious disease or cancer can be used to elicit a desired immune response. In the second application, KBMA vaccines can be derived from attenuated forms of a targeted pathogen, allowing for the presentation of the entire antigenic repertoire to the immune system, of particular importance when the correlates of protection are unknown.