Phase Ib Trial of the Toll-like Receptor 8 Agonist, Motolimod (VTX-2337), Combined with Cetuximab in Patients with Recurrent or Metastatic SCCHN

Purpose: As Toll-like receptors (TLR) are key mediators of immune responses, TLR agonists may be important for augmenting the efficacy of therapies for squamous cell carcinoma of the head and neck (SCCHN). Motolimod (VTX-2337), a selective small-molecule agonist of TLR8, stimulates natural killer (NK) cells, dendritic cells, and monocytes. A phase Ib clinical trial assessed the safety and antitumor activity of motolimod in combination with cetuximab in patients with SCCHN. Correlative biomarkers of immune activity were explored.Experimental Design: Thirteen patients with recurrent or metastatic SCCHN were enrolled in this open-label, dose-escalation study using a standard 3 + 3 design. Doses of motolimod (2.5, 3.0, or 3.5 mg/m²) were given on days 1, 8, and 15, in combination with fixed weekly doses of cetuximab in 28-day cycles.Results: There were no protocol-defined dose-limiting toxicities, drug-related deaths, or evidence of synergistic toxicities between motolimod and cetuximab. Clinical tolerability at the 3.5 mg/m² dose level was not optimal for repeated dosing and 3.0 mg/m² was identified as the MTD. Two patients achieved partial responses for an overall response rate of 15%. Five patients had disease stabilization equating to a disease control rate of 54%. Statistically significant increases in plasma cytokines and in the frequency and activation of circulating NK cells were observed.Conclusions: Motolimod can be safely administered in combination with cetuximab with an acceptable toxicity profile. Encouraging antitumor activity and robust pharmacodynamic responses were observed. Motolimod is being further investigated in a phase II trial in patients with SCCHN (ClinicalTrials.gov ID: NCT01836029). Clin Cancer Res; 23(10); 2442-50. ©2016 AACR.

Epidermal growth factor receptor derived peptide vaccination to prevent lung adenocarcinoma formation: An in vivo study in a murine model of EGFR mutant lung cancer

The ability to prevent disease is the holy grail of medicine. For decades, efforts have been made to extend the successes seen with vaccination against infectious diseases to cancer. In some instances, preventive vaccination against viruses (prototypically HPV) has successfully prevented tumorigenesis and will make a major impact on public health in the decades to come. However, the majority of cancers that arise are a result of genetic mutation within the host, or non-viral environmental exposures. We present compelling evidence that vaccination against an overexpressed self-tumor oncoprotein has the potential to prevent tumor development. Vaccination against the Epidermal Growth Factor Receptor (EGFR) using a multipeptide vaccine in a preventive setting decreased EGFR-driven lung carcinogenesis by 76.4% in a mouse model of EGFR-driven lung cancer. We also demonstrate that anti-EGFR vaccination primes the development of a robust immune response in vivo. This study provides proof of concept for the first time that targeting tumor drivers in a preventive setting in lung cancer using peptide vaccination can inhibit tumorigenesis and may provide useful clinical insights into the development of strategies to vaccinate against EGFR in populations where EGFR-mutant disease is highly prevalent. © 2015 Wiley Periodicals, Inc.

Clinical significance of tumor-infiltrating lymphocytes in breast cancer

Tumor infiltrating lymphocytes (TIL) play an essential role in mediating response to chemotherapy and improving clinical outcomes in all subtypes of breast cancer. Triple negative breast cancers (TN) are most likely to have tumors with >50 % lymphocytic infiltrate, termed lymphocyte predominant breast cancer, and derive the greatest survival benefit from each 10 % increase in TIL. The majority of HER2+ breast cancers have similar level of immune infiltrate as TN breast cancer yet the presence of TILs has not shown the same survival benefit. For HER2+ breast cancers, type 1 T-cells, either increased TBET+ tumor infiltration or increased type 1 HER2-specific CD4+ T-cells in the peripheral blood, are associated with better outcomes. Hormone receptor positive HER2 negative tumors tend to have the least immune infiltrate yet are the only breast cancer subtype to show worse prognosis with increased FOXP3 regulatory T-cell infiltrate. Notably, all breast cancer subtypes have tumors with low, intermediate, or high TIL infiltrate. Tumors with high TILs may also have increased PD-L1 expression which might be the reason that TN breast cancer seems to demonstrate the most robust clinical response to immune checkpoint inhibitor therapy but further investigation is needed. Tumors with intermediate or low levels of pre-treatment immune infiltrate, on the other hand, may benefit from an intervention that may increase TIL, particularly type 1 T-cells. Examples of these interventions include specific types of cytotoxic chemotherapy, radiation, or vaccine therapy. Therefore, the systematic evaluation of TIL and specific populations of TIL may be able to both guide prognosis and the appropriate sequencing of therapies in breast cancer.

Concurrent SPECT/PET-CT imaging as a method for tracking adoptively transferred T-cells in vivo

Background

The ability of T-cells to traffic to and penetrate tumors impacts the clinical efficacy of T-cell therapy therefore methods to track transferred T-cells in vivo are needed. In this preliminary report, we evaluated the use of concurrent SPECT/PET-CT imaging to monitor the egress of HER-2/neu specific T-cells in a breast cancer patient with extensive bone-only metastatic disease.

Findings

Indium (In-111) labeled T-cells demonstrated similar or greater viability than unlabeled T-cells at either a low or high dose of In-111 over a 24-h incubation period in vitro. The function of labeled or unlabeled T-cells was not significantly different (p > 0.05) at either dose. T-cells trafficked to all sites of metastatic disease and infiltrated the tumor as assessed by SPECT imaging. In-111 uptake at 24 h after infusion varied from 3.8 (right proximal humerus) to 6.3 (right sacrum) background corrected counts per pixel and remained elevated at 48 h. Concurrent PET-CT imaging demonstrated a fluorodeoxyglucose flare, measured by increase in tumor site uptake as high as 32 % and at most sites of disease at 48 h. This flare was associated with focal pain after T-cell infusion at metastatic sites. The patient had stable disease for 18 months after completion of T-cell therapy.

Conclusion

Concurrent SPECT/PET-CT imaging, over a 48-h period after T-cell infusion, provided evidence of T-cell homing to all disease sites as well as a tumor metabolism flare response. This technique may be useful for monitoring T-cell trafficking after autologous as well as chimeric antigen receptor T-cell infusion.

Trial Registraion

Trial registered at ClinicalTrials.gov registration number NCT00791037, registered 13 November 2008.

CITN11-02 phase I trial of subcutaneous recombinant human IL-15 (rhIL-15) is associated with expansion of circulating CD56+ NK cells and CD8+ T cells

Background

IL-15 is a high priority for clinical development because of its homeostatic effects on both NK cells and CD8+ T cells, and minimal effect on regulatory T cells. The Cancer Immunotherapy Trials Network is conducting a phase I dose-escalation study of subcutaneous (SQ) rhIL-15 in advanced melanoma, renal cell, non-small cell lung and squamous cell head and neck carcinoma patients.

Methods

A cycle consists of 5 daily SQ injections of rhIL-15 (E.coli-derived, NCI) given Monday-Friday for two weeks, then 2 weeks observation. The absolute lymphocyte count is tested every injection day, and whole blood flow cytometric analyses are conducted on Days 1, 11 and 15 of each cycle.

Results

Three patients each were treated at the 0.25, 0.5, 1.0 and 3.0 mcg/kg dose levels and six patients at 2.0 mcg/kg/dose (N=18). Seventeen patients completed ≥1 cycle, with one dose limiting toxicity (DLT) at 3.0 mcg/kg and one serious adverse event at 2.0 mcg/kg. Flow cytometric data indicate a consistent increase in the frequency of CD56+CD3− NK cell frequencies peaking at Day 15 of Cycle 1 (Day 12=last dose), with lesser increases in subsequent cycles. The median fold-increase in circulating NK cells during Cycle 1 demonstrated dose responsiveness and peaked at 11.5-fold with 3.0 mcg/kg. By contrast, the maximum fold-increase in circulating CD8+ T cells was 2.6-fold.

Conclusion

SQ rhIL-15 has been well tolerated and the 3.0 mcg/kg dose cohort is being expanded. Higher doses of rhIL-15 were associated with profound increases in circulating NK cells with significant but smaller increases in CD8+ T cells. Outpatient use of SQ rhIL-15 is safe and will be combined with other cancer immunotherapies.

Study support: NIH 1U01 CA154967-01 (Clinical Trials.gov NCT01727076).

Immunodynamics: a cancer immunotherapy trials network review of immune monitoring in immuno-oncology clinical trials

The efficacy of PD-1/PD-L1 targeted therapies in addition to anti-CTLA-4 solidifies immunotherapy as a modality to add to the anticancer arsenal. Despite raising the bar of clinical efficacy, immunologically targeted agents raise new challenges to conventional drug development paradigms by highlighting the limited relevance of assessing standard pharmacokinetics (PK) and pharmacodynamics (PD). Specifically, systemic and intratumoral immune effects have not consistently correlated with standard relationships between systemic dose, toxicity, and efficacy for cytotoxic therapies. Hence, PK and PD paradigms remain inadequate to guide the selection of doses and schedules, both starting and recommended Phase 2 for immunotherapies. The promise of harnessing the immune response against cancer must also be considered in light of unique and potentially serious toxicities. Refining immune endpoints to better inform clinical trial design represents a high priority challenge. The Cancer Immunotherapy Trials Network investigators review the immunodynamic effects of specific classes of immunotherapeutic agents to focus immune assessment modalities and sites, both systemic and importantly intratumoral, which are critical to the success of the rapidly growing field of immuno-oncology.

Coordinated Activation of Toll-Like Receptor8 (TLR8) and NLRP3 by the TLR8 Agonist, VTX-2337, Ignites Tumoricidal Natural Killer Cell Activity

VTX-2337 (USAN: motolimod) is a selective toll-like receptor 8 (TLR8) agonist, which is in clinical development as an immunotherapy for multiple oncology indications, including squamous cell carcinoma of the head and neck (SCCHN). Activation of TLR8 enhances natural killer cell activation, increases antibody-dependent cell-mediated cytotoxicity, and induces Th1 polarizing cytokines. Here, we show that VTX-2337 stimulates the release of mature IL-1β and IL-18 from monocytic cells through coordinated actions on both TLR8 and the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome complex. In vitro, VTX-2337 primed monocytic cells to produce pro-IL-1β, pro-IL-18, and caspase-1, and also activated the NLRP3 inflammasome, thereby mediating the release of mature IL-1β family cytokines. Inhibition of caspase-1 blocked VTX-2337-mediated NLRP3 inflammasome activation, but had little impact on production of other TLR8-induced mediators such as TNFα. IL-18 activated natural killer cells and complemented other stimulatory pathways, including FcγRIII and NKG2D, resulting in IFNγ production and expression of CD107a. NLRP3 activation in vivo was confirmed by a dose-related increase in plasma IL-1β and IL-18 levels in cynomolgus monkeys administered VTX-2337. These results are highly relevant to clinical studies of combination VTX-2337/cetuximab treatment. Cetuximab, a clinically approved, epidermal growth factor receptor-specific monoclonal antibody, activates NK cells through interactions with FcγRIII and facilitates ADCC of tumor cells. Our preliminary findings from a Phase I open-label, dose-escalation, trial that enrolled 13 patients with recurrent or metastatic SCCHN show that patient NK cells become more responsive to stimulation by NKG2D or FcγRIII following VTX-2337 treatment. Together, these results indicate that TLR8 stimulation and inflammasome activation by VTX-2337 can complement FcγRIII engagement and may augment clinical responses in SCCHN patients treated with cetuximab.

Trial Registration: ClinicalTrials.gov NCT01334177

Abstract PD3-08: Modulation of immunity with 2-fluorofucose (2FF) for breast cancer treatment and prevention

The majority of patients with breast cancer have robust Type II immune responses directed against their tumors with little to no Type I immunity. The dominance of a Type II microenvironment is established early in breast tumorigenesis with a Type II immune signature prevalent even in pre-invasive lesions such as ductal carcinoma in situ. As a result, breast cancer is associated with abundant autoantibodies directed against tumor associated antigens and few infiltrating T-cells in the majority of patients. A recently reported inhibitor of protein and cellular fucosylation, 2-fluorofucose (2FF) has been shown to enhance immune cell function, in part through the generation of fucose-deficient antibodies which result in enhanced antibody dependent cell mediated cytotoxicity, as well as apparent modulation of T-cell dependent activity [Ca Res, Oct 1, 2014 74;2890].

For treatment studies, TgMMTV-neu (MMTVneu; luminal) and C31-Tag (C3T; triple negative) mice were treated orally with vehicle alone and 20mM 2FF when spontaneous tumor volume reached 75-100mm3 until sacrifice (n=20/grp). To assess the ability to prevent breast cancer development, mice were treated orally with vehicle alone, 20 or 50mM 2FF for up to 200 days starting at 6-8 weeks of age (n=20/grp). Tumor kinetics, disease free survival, and overall survival were calculated. Immune responses were evaluated by both DTH and IFN-gamma ELISPOT. To determine immune mechanism of action, NK, B, CD4, or CD8 cells were depleted concurrently with tumor implant.

When tumor bearing mice were treated with 2FF, tumor growth was significantly inhibited in both groups over the course of therapy (MMTVneu p<0.0001 and C3T p<0.0001 compared to controls). In addition, survival was significantly prolonged in both models (MMTVneu p<0.0001 and C3T p=0.0014). In the prevention setting, 2FF significantly delayed the average age of tumor onset in both models at both doses with the higher does showing greater efficacy; MMTVneu 20mM, p=0.001, 50mM, p=0.0002. At the time of study termination (300d), 45% of 2FF-treated MMTVneu mice had no evidence of mammary tumors. 2FF also significantly improved the average age of tumor onset in C3T mice when comparing untreated to 20mM (p=0.007), and 50mM (p=0.0007) treated mice. At study termination, 33% of all 2FF-treated C3T animals were disease free. 2FF anti-tumor activity was associated with the induction of tumor antigen specific immunity. After treatment both the MMTVneu (p<0.0001) and C3T (p<0.0001) developed a DTH response to syngeneic tumor lysates. Of note, the DTH response was inversely associated with the rate of tumor growth (p<0.0001). 2FF anti-tumor activity was associated with the induction of tumor antigen specific immunity. Depletion of immune cell subsets using targeting antibodies demonstrated that the anti-tumor response was mediated in large part by CD4 T-cells which are involved in stimulating both humoral and CD8 T-cell responses.

2FF, a novel inhibitor of fucosylation has potent anti-tumor effects in 2 transgenic models of breast cancer; luminal and triple negative mammary tumors. The agent is active in these mouse models in both the treatment and prevention setting and thus may represent a rational therapeutic approach to evaluate in breast cancer patients.

Citation Format: Disis ML, Rastetter L, Gad E, Koehnlein M, Senter PD, Gardai S, Okeley NM. Modulation of immunity with 2-fluorofucose (2FF) for breast cancer treatment and prevention. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr PD3-08.

Triple-negative breast cancer: immune modulation as the new treatment paradigm

Recent studies of tumor lymphocytic immune infiltrates in breast cancer have suggested an improved prognosis associated with increasing levels of tumor-infiltrating lymphocytes (TIL). Triple-negative breast cancer (TNBC) is the breast cancer subtype that has the greatest incidence of patients with a robust tumor immune infiltrate, although it is still a minority of patients. Elevated levels of either intratumoral or stromal T cells are associated with an improved overall survival (OS) and disease-free survival (DFS) in TNBC as compared with other breast cancer subtypes. TNBC may be immunogenic for several reasons. Subtypes of TNBC have a significant number of genetic mutations, and the immune system may see the aberrant proteins encoded by these mutations as foreign. Moreover, TNBC is associated with a prognostic gene signature that also includes B cells. Antibodies secreted by B cells may bind to tumor antigens and amplify the adaptive immune response that has already been initiated in the tumor. New immune modulatory agents, including immune checkpoint inhibitors, have shown activity in immunogenic tumors such as melanoma and bladder cancer and have recently been tested in TNBC. The clinical response rates observed, patterns of response, and adverse event profiles are similar to what has been described in melanoma where this class of agents has already been approved for clinical use in some cases. Lessons learned in assessing the immunogenicity of TNBC, potential mechanisms of immune stimulation, and response to immune modulatory drugs lay the foundation for the development of immune-based therapies in all subtypes of the disease.

Abstract P2-11-05: Overall survival in inflammatory breast cancer patients receiving Her-2 Neu directed tumor vaccine therapy: Matched comparison with SEER registry patients

Background

Patients with inflammatory breast cancer (IBC) have a poor prognosis, primarily due to distant dissemination. Additionally, IBC patients have an increased rate of HER2 overexpression when compared to patients with non-inflammatory breast cancer. The forms the rationale for HER2 directed tumor vaccine therapy in these patients. The purpose of this study was to examine overall survival in IBC patients receiving HER2 directed tumor vaccine therapy when compared with matched control patients from the SEER Registry.

Methods

Patients with diagnosis of Stage III or IV HER2 positive IBC having completed standard initial therapy and without evidence of disease received HER2 vaccinations after being enrolled on 5 prospective clinical trials. Overall survival data were pooled and analyzed. A control group of matched IBC patients were identified by querying the SEER database from 1997-2011. The control group was identified as any individual in the database with a code for IBC. A secondary analysis comparing survival in HER2 positive IBC vs HER2 negative IBC patients was performed by querying the SEER database from 2010 onwards, the time point when the HER2 status was coded in the database. Propensity score adjustment were made to the control group to account for any imbalances between groups in measured covariates such as stage, race, age, sex, and era of enrollment and the time interval from diagnosis to enrollment on vaccine trial (median ∼2 years).

Results

A total of 37 IBC patients received HER2 directed vaccine therapy and 676 patients were identified for the SEER control group; Stage at enrollment: stage IIIB: 30 patients in the vaccine group and 639 patients in the control group; stage IIIC: 1 patient in the vaccine group and 15 patients in the control group; stage IV 6 patients in the vaccine group and 22 in the control group. The median survival of the overall population was 112 months for the vaccine group and 47 months for the control group (p=0.04). After using propensity scores to adjust the control for imbalances in measured covariates, the median survival for the overall population was 112 months for the vaccine group and 37 months for the control group (p=0.03). There was no difference in survival between HER2 positive and HER2 negative IBC patients in the control group (p=0.6).

Conclusion

These results demonstrate promising overall survival in HER2 positive IBC patients receiving HER2 directed vaccine therapy after initial therapy. Propensity matching was performed to adjust for imbalances in measured covariates and resulted in a modest decrease in survival of the control group after adjustment, suggesting that the vaccine trial group had relatively unfavorable pre-treatment characteristics. Despite these unfavorable characteristics, patients receiving vaccine had a median survival of 112 months. These results must be further confirmed in a prospective randomized trial.

Citation Format: Rengan R, Baker K, Salazar L, Childs J, Higgins D, Redman M, Reichow J, Disis ML. Overall survival in inflammatory breast cancer patients receiving Her-2 Neu directed tumor vaccine therapy: Matched comparison with SEER registry patients. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-11-05.

The Antitumor Efficacy of IL2/IL21-Cultured Polyfunctional Neu-Specific T Cells Is TNFα/IL17 Dependent

PURPOSE

Infusion of HER2-specific T cells, derived from vaccine-primed patients and expanded with IL2/IL12, has induced tumor regression in a minority of patients with metastatic treatment-refractory HER2(+) breast cancer. We questioned whether alteration of cytokine growth factors used to culture vaccine-primed T cells could improve antitumor activity.

EXPERIMENTAL DESIGN

Using the TgMMTV-neu murine mammary tumor model, we cultured T cells derived from mice immunized with a previously defined neu class II peptide, p98-114 (neu p98), and evaluated different cytokine combinations for expansion.

RESULTS

Infusion of neu p98-specific T-cell lines derived from all cytokine conditions evaluated resulted in significant antitumor activity compared with infused naïve splenocytes (P < 0.05). T cells cultured with IL2/IL21 could uniquely mediate complete regression of spontaneous mammary tumors. IL2/IL21 cultured neu-specific T cells demonstrated a different cytokine secretion pattern as compared with other cultured T cells; secreting high levels of TNFα and IL17 (P < 0.05). Moreover, tumor-infiltrating CD8(+) cells were significantly increased after the infusion of IL2/IL21 cultured T cells as compared with tumors treated with T cells expanded under other cytokine conditions (P < 0.001). The antitumor effect of the infusion of IL2/IL21 cultured cells was mediated by CD8 T cells. Depletion of TNFα or IL17, but not IFNγ, abrogated the tumor growth inhibition induced by the IL2/IL21 T cells and markedly decreased the influx of CD8 into tumors. Finally, IL2/IL21-cultured human antigen specific T cells also displayed a similar polyfunctional Th1/Th17 phenotype.

CONCLUSIONS

Expansion of HER2 vaccine-primed T cells with IL2/IL21 may have the potential to effectively mediate tumor regression when used in adoptive transfer. Clin Cancer Res; 22(9); 2207-16. ©2015 AACR.

Abstract 3135: HER2 specific adoptive T cells shown to localize and infiltrate all sites of disease using combined SPECT and PET imaging

Adoptive T cell therapy has been shown to stimulate anti-tumor response in multiple cancers, however these responses have not been robust or durable. In previous studies, indium-111 labeled T cells have functioned normally but were either not present at all sites of metastatic disease or not able to infiltrate the sites of disease. In breast cancer, adoptive HER2 targeted T cells were unable to penetrate visceral metastases. Previous work in our laboratory has demonstrated that HER2 vaccine-primed autologous adoptive T cells were safe and well tolerated. In this phase I study, HER2 positive breast cancer patients received three HER2 peptide vaccines before plasmapheresis and ex-vivo expansion of HER2 specific autologous T cells to evaluate the immune and clinical response to adoptive T cell therapy in breast cancer. In one patient, the trafficking of indium-111 labeled T cells was also evaluated using SPECT and PET imaging.

An aliquot of 1×107 expanded T cells were labeled with 300 uCi of indium-111 and given with the third T cell infusion. Prior in vitro studies had demonstrated that labeled HER2 expanded T had similar viability (at 24 hours 97±1% viability with unlabeled cells and 90.9±1.1% viability with 480 uCI labeled cells) and interferon gamma release (263±8 pg/mL released in unlabeled cells and 208.5±11 released in 480 uCi labeled cells) as unlabeled HER2 expanded T cells when stimulated by IL2. SPECT imaging demonstrated that the T cells trafficked to all the metastatic sites of disease by 24 hours and completely infiltrated the tumor. The patient studied had metastases to her skull, left axilla, sternum, bilateral proximal humeri, and sacrum. The corrected indium-111 uptake at 24 hours varied from 2.27 counts per pixel in the R proximal humerus to 6.28 counts per pixel in the R sacrum and remained elevated at 48 hours (for example a continued 6.9 counts/pixel signal at the R sacrum). Concurrent PET CT imaging demonstrated FDG flare at 48 hours at all sites of metastatic disease including a 1.3 fold increase in the R proximal humerus and a 1.3 fold increase in the L proximal humerus signal over baseline scans. This increased FDG uptake had resolved 1 month after therapy. After this study, the patient had stable disease for 18 months. She had a robust response to each T cell infusion and the booster vaccines, including fevers, headaches, and increased pain at the sites of metastatic disease. These symptoms have been associated with a disease specific T cell response. This study demonstrates by a novel method of concurrent SPECT and PET imaging that the ex-vivo expanded HER2 specific T cells were able to traffic to and fully infiltrate all sites of metastatic disease causing an acute FDG-PET flare and prolonged stable disease in a HER2 positive breast cancer patient with bone-only metastatic disease. Further studies are now needed to confirm if this imaging method can be used universally in adoptive T cell studies.

Citation Format: Sasha E. Stanton, Janet Eary, Edmond Marzbani, David Mankoff, Lupe Salazar, Doreen Higgins, Jessica Reichow, Yushe Dang, Mary L. Disis. HER2 specific adoptive T cells shown to localize and infiltrate all sites of disease using combined SPECT and PET imaging. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3135. doi:10.1158/1538-7445.AM2015-3135

Abstract 273: TLR8 agonist VTX-2337 (motolimod) decreases monocytic myeloid-derived suppressor cells by inducing differentiation to mature antigen-presenting cells

There is increasing evidence that myeloid-derived suppressor cells (MDSCs) contribute to the progression of cancer by inhibiting tumor-directed immune responses and producing mediators that promote the growth and survival of tumor cells. While present at low numbers in the peripheral blood of healthy individuals, levels of circulating MDSC increase in cancer patients as tumors produce factors that drive both the expansion and recruitment of these immune cells. MDSCs are a heterogeneous population and include both granulocytic MDSC (G-MDSC) and monocytic MDSC (M-MDSC) sub-populations, each of which can inhibit T cell function through arginase activity and the production of nitric oxide. Novel approaches to decrease MDSC expansion, or inhibit their immunosuppressive functions, hold great promise for augmenting anti-tumor immunity. In this study, we examined the effect of VTX-2337, a selective TLR8 agonist, on MDSC function. We initially measured the expression of TLR8 in RNA extracted from FACS-sorted MDSC isolated from peripheral blood mononuclear cells (PBMCs) of three healthy donors. TLR8 levels found in the M-MDSC subpopulation were comparable to those found in monocytes and myeloid dendritic cells (mDC), and are known to express high levels of TLR8 protein. To assess the M-MDSC response to TLR8 activation, PBMCs from healthy donors, were treated overnight in medium alone, low dose (167 nM) or high dose (500 nM) VTX-2337. Treatment with VTX-2337 resulted in a significant loss of the M-MDSC (HLA-DR-CD14+) population. Interestingly, we also observed that older (&gt;45 years) donors demonstrated a greater loss of the M-MDSC sub-population than younger (&lt;45 years) donors. In contrast, there was no significant difference in the recovery of the G-MDSC subtype (Lin-HLA-DR-CD33+) following VTX-2337 treatment. Additionally, treatment with either the TLR7 agonist imiquimod, or TLR9 agonist CpG ODN2006, did not result in a loss of the M-MDSC population. We hypothesized that the selective decrease in the M-MDSC subpopulation following TLR8 activation may be attributed to their differentiation into mature antigen-presenting cells. To test this hypothesis, we cultured CFSE-labelled MACS-separated HLA-DR-CD14+ M-MDSC and autologous PBMC with VTX-2337 or medium only (control). TLR8 activation of labelled M-MDSC cells resulted in HLA-DR expression and promoted their differentiation into HLA-DR+CD14+ monocytes. Whether VTX-2337 activation can also decrease the immunosuppressive and/or tumor-promoting activities of MDSC is currently under investigation. Our finding, where TLR8-activated M-MDSC can differentiate into mature antigen-presenting cells is highly novel, and suggests the potential for using VTX-2337 to modulate MDSCs in cancer patients and enable a more effective, immune response to tumors.

Citation Format: Zina J. Rutnam, Yushe Dang, Gregory Diestch, Hailing Lu, Yi Yang, Robert Hershberg, Mary L. Disis. TLR8 agonist VTX-2337 (motolimod) decreases monocytic myeloid-derived suppressor cells by inducing differentiation to mature antigen-presenting cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 273. doi:10.1158/1538-7445.AM2015-273

Abstract 286: Coordinated activation of TLR8 and NLRP3 by VTX-2337 (motolimod) ignites tumoricidal NK cell activity

VTX-2337 (motolimod) is a selective toll-like receptor 8 (TLR8) agonist in clinical development as an immunotherapy for multiple oncology indications, including squamous cell carcinomas of the head and neck (SCCHN). Activation of TLR8 has been found to enhance natural killer (NK) cell activation, increase antibody-dependent cell-mediated cytotoxicity (ADCC), and induce Th1 polarizing cytokines. Further characterization of VTX-2337 reveals the release of mature IL-1β and IL-18 from monocyte cell populations through coordinated actions on both TLR8 and NLRP3. In vitro, VTX-2337 primes monocytes to produce pro-IL-1β, pro-IL-18 and caspase 1, while activating the NLRP3 inflammasome, leading to the release of mature IL-1 family cytokines. Inflammasome activation by VTX-2337 is blocked by inhibiting caspase 1, with little impact on the production of other TLR8 induced mediators such as TNFα. The release of IL-18 stimulates NK cells, and augments other activation pathways including: FcγRIII and NKG2D receptors, resulting in IFNγ production and induction of CD107α. NLRP3 activation in vivo was confirmed by a dose-related increase in plasma levels of IL-1β and IL-18 in cynomolgus monkeys administered VTX-2337. This pathway for NK activation was subsequently assessed in SCCHN patients treated with VTX-2337 in combination with cetuximab, a clinically approved epidermal growth factor receptor (EGFR) specific monoclonal antibody (mAb). Cetuximab can activate NK cells through an interaction with FcγRIII, and facilitate ADCC of tumor cells. Preliminary data from a Phase I clinical trial found that prior to treatment, patient NK cells did not effectively activate in response to ex vivo stimulation by NKG2D or FcγRIII. However, following VTX-2337 treatment, patient NK cells become more responsive to these activating signals. These results show that TLR8 stimulation and inflammasome activation by VTX-2337, can complement FcγRIII engagement, and may augment clinical responses in SCCHN patients treated with cetuximab.

Citation Format: Greg Dietsch, Haling Lu, Yi Yang, Chihiro Morishima, Laura Q. Chow, Mary L. Disis, Robert Hershberg. Coordinated activation of TLR8 and NLRP3 by VTX-2337 (motolimod) ignites tumoricidal NK cell activity. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 286. doi:10.1158/1538-7445.AM2015-286

Current methods of epitope identification for cancer vaccine design

The importance of the immune system in tumor development and progression has been emerging in many cancers. Previous cancer vaccines have not shown long-term clinical benefit possibly because were not designed to avoid eliciting regulatory T-cell responses that inhibit the anti-tumor immune response. This review will examine different methods of identifying epitopes derived from tumor associated antigens suitable for immunization and the steps used to design and validate peptide epitopes to improve efficacy of anti-tumor peptide-based vaccines. Focusing on in silico prediction algorithms, we survey the advantages and disadvantages of current cancer vaccine prediction tools.