Abstract 1516: Deep profiling of T-cell repertoire and tumor heterogeneity in chronic lymphocytic leukemia patients following allogeneic T-cell therapy

Chemotherapy/ targeted therapy are both known to trigger evolution of treatment resistant clones that can lead to relapse. Allogeneic stem cell transplant (alloSCT) for refractory Chronic Lymphocytic Leukemia (CLL) patients is associated with better outcomes. We hypothesized that allogeneic T-cell immunotherapies, including alloSCT and donor lymphocyte infusion (DLI) would impact tumor evolution through the application of selective immunologic pressure with reciprocal changes in the T-cell compartment. Here, we tested a cohort of 24 heavily pre-treated CLL patients treated. Treatments consisted of alloSCT alone, or with follow-up DLI, which are two established mediators of effective Graft versus Leukemia (GVL). Our cohort included 11 patients who relapsed (denoted as non-responder, NR) after alloSCT and 13 patients who had complete response (CR) after alloSCT, with 11/13 patients showing durable CR with a median post-transplant overall survival (OS) of 9.8 years. We mapped the evolutionary trajectories of tumor cells by whole exome sequencing (WES) of sort purified CLL in post-transplant relapsed patients. To investigate changes in immune repertoire and gene expression post-transplant, CD3 positive T-cells from peripheral blood and bone marrows of CLL patients at complete donor chimerism were analyzed both at bulk and at the single cell level. We found evidence of subclonal leukemic evolution in the majority of our CLL patient cohort after nonmyeloablative HLA-matched alloSCT. Different patterns of CLL evolution were observed, and these changes included putative CLL drivers in every case. In all of the 11 patients with longitudinal post-alloSCT samples available, we observed branched CLL evolution in 4 patients, linear evolution in 4 patients, and no evolution in 3 patients. These data suggest that differential sensitivity of leukemic subclones to allogeneic T cell killing may underlie the branched and linear evolution that we observed, and therefore can shape leukemic subclonal architecture after transplant. Of note, we found that clonal CLL was more responsive to alloSCT in comparison to CLL with subclonal disease architecture.To identify T-cells with GVL potential, we first cataloged potential neoantigens by screening mutated regions in CLL with in silico HLA binding prediction models. Neoantigen specific T-cells were then sorted from longitudinal peripheral blood samples using tetramers, followed by identification of GVL specific TCR in both bulk and single cell setting. We were able to identify T-cells that coevolved with specific tumorigenic lesions in a subset of CLL patients. Taken together, our results suggest that donor-derived antigen-specific T-cells mediate clonal selection of CLL with concurrent changes in allogeneic T-cells, and that these changes can be monitored in longitudinal patient samples.

Citation Format: Celine Kerros, John P. Miller, Xizeng Mao, Haven R. Garber, Hannah C. Beird, Jianhua Zhang, Jason Roszik, Paul Leonard, Li Zhao, Sahil Seth, Pei Lin, Huandong Sun, William G. Wierda, Issa F. Khouri, Karen Clise-Dwyer, Andrew Futreal, Shoudan Liang, Koppikar Priya, Jeffrey Molldrem. Deep profiling of T-cell repertoire and tumor heterogeneity in chronic lymphocytic leukemia patients following allogeneic T-cell therapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1516.

Fucosylation Enhances the Efficacy of Adoptively Transferred Antigen-Specific Cytotoxic T Lymphocytes

PURPOSE

Inefficient homing of adoptively transferred cytotoxic T lymphocytes (CTLs) to tumors is a major limitation to the efficacy of adoptive cellular therapy (ACT) for cancer. However, through fucosylation, a process whereby fucosyltransferases (FT) add fucose groups to cell surface glycoproteins, this challenge may be overcome. Endogenously fucosylated CTLs and ex vivo fucosylated cord blood stem cells and regulatory T cells were shown to preferentially home to inflamed tissues and marrow. Here, we show a novel approach to enhance CTL homing to leukemic marrow and tumor tissue.

EXPERIMENTAL DESIGN

Using the enzyme FT-VII, we fucosylated CTLs that target the HLA-A2-restricted leukemia antigens CG1 and PR1, the HER2-derived breast cancer antigen E75, and the melanoma antigen gp-100. We performed in vitro homing assays to study the effects of fucosylation on CTL homing and target killing. We used in vivo mouse models to demonstrate the effects of ex vivo fucosylation on CTL antitumor activities against leukemia, breast cancer, and melanoma.

RESULTS

Our data show that fucosylation increases in vitro homing and cytotoxicity of antigen-specific CTLs. Furthermore, fucosylation enhances in vivo CTL homing to leukemic bone marrow, breast cancer, and melanoma tissue in NOD/SCID gamma (NSG) and immunocompetent mice, ultimately boosting the antitumor activity of the antigen-specific CTLs. Importantly, our work demonstrates that fucosylation does not interfere with CTL specificity.

CONCLUSIONS

Together, our data establish ex vivo CTL fucosylation as a novel approach to improving the efficacy of ACT, which may be of great value for the future of ACT for cancer.

Membrane-Associated Proteinase 3 on Granulocytes and Acute Myeloid Leukemia Inhibits T Cell Proliferation

Proteinase 3 (P3), a serine protease expressed by myeloid cells, localized within azurophil granules, and also expressed on the cellular membrane of polymorphonuclear neutrophils (PMN), is the target of autoimmunity in granulomatosis with polyangiitis. PR1, an HLA-A2 restricted nonameric peptide derived from P3, has been targeted effectively in myeloid leukemia. We previously showed (Molldrem et al. 2003. JClinInvest 111: 639-647) that overexpression of P3 in chronic myeloid leukemia induces apoptosis of high-affinity PR1-specific T cells, leading to deletional tolerance and leukemia outgrowth. In this study, we investigated the effect of membrane P3 (mP3)-expressing PMN and acute myeloid leukemia (AML) blasts on the proliferation of CD4 and CD8 T cells in vitro. We demonstrate that mP3-expressing PMN significantly inhibits autologous healthy donor T cell proliferation but does not affect cytokine production in activated T cells and that this effect requires cell proximity and was abrogated by P3 blockade. This inhibition required P3 enzyme activity. However, suppression was not reversed by either the addition of catalase or the inhibition of arginase I. In addition to P3 blockade, anti-low density lipoprotein receptor-related protein 1 (LRP1) Ab also restored T cells' capacity to proliferate. Last, we show dose-dependent inhibition of T cell proliferation by mP3-expressing AML blasts. Together, our findings demonstrate a novel mechanism whereby PMN- and AML-associated mP3 inhibits T cell proliferation via direct LRP1 and mP3 interaction, and we identify P3 as a novel target to modulate immunity in myeloid leukemia and autoimmune disease.

Targeting the Leukemia Antigen PR1 with Immunotherapy for the Treatment of Multiple Myeloma

Purpose: PR1 is a human leukocyte antigen (HLA)-A2 nonameric peptide derived from neutrophil elastase (NE) and proteinase 3 (P3). We have previously shown that PR1 is cross-presented by solid tumors, leukemia, and antigen-presenting cells, including B cells. We have also shown that cross-presentation of PR1 by solid tumors renders them susceptible to killing by PR1-targeting immunotherapies. As multiple myeloma is derived from B cells, we investigated whether multiple myeloma is also capable of PR1 cross-presentation and subsequently capable of being targeted by using PR1 immunotherapies.Experimental Design: We tested whether multiple myeloma is capable of cross-presenting PR1 and subsequently becomes susceptible to PR1-targeting immunotherapies, using multiple myeloma cell lines, a xenograft mouse model, and primary multiple myeloma patient samples.Results: Here we show that multiple myeloma cells lack endogenous NE and P3, are able to take up exogenous NE and P3, and cross-present PR1 on HLA-A2. Cross-presentation by multiple myeloma utilizes the conventional antigen processing machinery, including the proteasome and Golgi, and is not affected by immunomodulating drugs (IMiD). Following PR1 cross-presentation, we are able to target multiple myeloma with PR1-CTL and anti-PR1/HLA-A2 antibody both in vitro and in vivoConclusions: Collectively, our data demonstrate that PR1 is a novel tumor-associated antigen target in multiple myeloma and that multiple myeloma is susceptible to immunotherapies that target cross-presented antigens. Clin Cancer Res; 24(14); 3386-96. ©2018 AACR.

Cathepsin G Is Expressed by Acute Lymphoblastic Leukemia and Is a Potential Immunotherapeutic Target

Cathepsin G (CG) is a myeloid azurophil granule protease that is highly expressed by acute myeloid leukemia (AML) blasts and leukemia stem cells. We previously identified CG1 (FLLPTGAEA), a human leukocyte antigen-A2-restricted nonameric peptide derived from CG, as an immunogenic target in AML. In this report, we aimed to assess the level of CG expression in acute lymphoid leukemia (ALL) and its potential as an immunotherapeutic target in ALL. Using RT-PCR and western blots, we identified CG mRNA and protein, respectively, in B-ALL patient samples and cell lines. We also examined CG expression in a large cohort of 130 patients with ALL via reverse-phase protein array (RPPA). Our data show that CG is widely expressed by ALL and is a poor prognosticator. In addition to endogenous expression, we also provide evidence that CG can be taken up by ALL cells. Finally, we demonstrate that patient ALL can be lysed by CG1-specific cytotoxic T lymphocytes in vitro. Together, these data show high expression of CG by ALL and implicate CG as a target for immunotherapy in ALL.

Abstract 3984: Neuropilin-1 mediates neutrophil elastase uptake and antigen cross-presentation in breast cancer cells

We previously showed that soluble neutrophil elastase (NE) is rapidly taken up by tumor cells that lack endogenous NE expression, including breast cancer (BrCa). NE uptake led to cross-presentation of PR1, an NE-derived HLA-A2-restricted peptide that is an immunotherapeutic target in hematologic malignancies. The mechanism of NE uptake, however, remains unknown. Here, we demonstrated that NE internalization was temperature- and time-sensitive, dose-saturation was observed, and uptake was partially blocked by chlorpromazine (CPZ) and wortmannin, supporting a receptor-mediated process and suggesting a role for clathrin- and PI3K-dependent mechanisms. To identify a candidate NE receptor, we performed mass spectrometry (MS) of proteins after anti-NE co-immunoprecipitation of NE-pulsed MDA-MB-231 BrCa cells and we identified neuropilin-1 (NRP1) as an NE co-associated protein. Binding of NE to NRP1 was confirmed by ELISA, and peptide epitope mapping studies indicated NE bound via it consensus sequence RRXR, which is also known to bind the b1b2 domain of NRP1. NE bound to NRP1 with high affinity (Kd=38.7 nM) as measured with biolayer interferometry. To confirm the role of NRP1 in cellular uptake of NE, we transfected MDA-MB-231 BrCa cells with siRNA or shRNA against NRP1 and showed that NRP1 knockdown resulted in a 2-fold decrease in NE uptake as determined with flow cytometry. Similarly, blocking with an NRP1-neutralizing antibody decreased NE uptake by 60% vs. isotype control antibody, an effect that was also observed in other breast cancer cell lines that expressed NRP1. Conversely, transient expression of NRP1 in the NRP1-deficient T47D BrCa cell line was sufficient to induce uptake of NE. Importantly, knockdown of NRP1 expression in MDA-231 cells also prevented PR1 cross-presentation as determined with the anti-PR1/HLA-A2 monoclonal antibody 8F4. This was confirmed by the loss of susceptibility of NE-pulsed MDA-MB-231 cells to lysis by PR1-specific cytotoxic T cells following knockdown of NRP1 expression. Our data support a novel function of NRP1 in the uptake and cross-presentation of neutrophil-derived proteins by

non-hematopoietic cancer cells. Because 8F4 mediates killing of PR1/HLA-A2+ leukemia and NRP1 is broadly expressed on many tumors, our results suggest a role for immunotherapy strategies that target NE-derived peptides on NRP1+ tumors.

Citation Format: Celine Kerros, Satyendra C. Tripathi, Dongxing Zha, Sergeeva Anna, Haley L. Peters, Hiroyuki Katayama, Pariya Sukhumalchandra, Kathryn R. Cox, Alexander A. Perakis, Lisa S. St John, Gheath Alatrash, Elizabeth A. Mittendorf, Karen C. Dwyer, Samir M. Hanash, Jeffrey J. Molldrem. Neuropilin-1 mediates neutrophil elastase uptake and antigen cross-presentation in breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3984. doi:10.1158/1538-7445.AM2017-3984

Neuropilin-1 mediates neutrophil elastase uptake and cross-presentation in breast cancer cells

Neutrophil elastase (NE) can be rapidly taken up by tumor cells that lack endogenous NE expression, including breast cancer, which results in cross-presentation of PR1, an NE-derived HLA-A2-restricted peptide that is an immunotherapy target in hematological and solid tumor malignancies. The mechanism of NE uptake, however, remains unknown. Using the mass spectrometry-based approach, we identify neuropilin-1 (NRP1) as a NE receptor that mediates uptake and PR1 cross-presentation in breast cancer cells. We demonstrated that soluble NE is a specific, high-affinity ligand for NRP1 with a calculated K_d of 38.7 nm Furthermore, we showed that NRP1 binds to the RRXR motif in NE. Notably, NRP1 knockdown with interfering RNA or CRISPR-cas9 system and blocking using anti-NRP1 antibody decreased NE uptake and, subsequently, susceptibility to lysis by PR1-specific cytotoxic T cells. Expression of NRP1 in NRP1-deficient cells was sufficient to induce NE uptake. Altogether, because NRP1 is broadly expressed in tumors, our findings suggest a role for this receptor in immunotherapy strategies that target cross-presented antigens.

Serine Proteases Enhance Immunogenic Antigen Presentation on Lung Cancer Cells

Immunotherapies targeting immune checkpoints have proven efficacious in reducing the burden of lung cancer in patients; however, the antigenic targets of these reinvigorated T cells remain poorly defined. Lung cancer tumors contain tumor-associated macrophages (TAM) and neutrophils, which release the serine proteases neutrophil elastase (NE) and proteinase 3 (P3) into the tumor microenvironment. NE and P3 shape the antitumor adaptive immune response in breast cancer and melanoma. In this report, we demonstrate that lung cancer cells cross-presented the tumor-associated antigen PR1, derived from NE and P3. Additionally, NE and P3 enhanced the expression of human leukocyte antigen (HLA) class I molecules on lung cancer cells and induced unique, endogenous peptides in the immunopeptidome, as detected with mass spectrometry sequencing. Lung cancer patient tissues with high intratumoral TAMs were enriched for MHC class I genes and T-cell markers, and patients with high TAM and cytotoxic T lymphocyte (CTL) infiltration had improved overall survival. We confirmed the immunogenicity of unique, endogenous peptides with cytotoxicity assays against lung cancer cell lines, using CTLs from healthy donors that had been expanded against select peptides. Finally, CTLs specific for serine proteases-induced endogenous peptides were detected in lung cancer patients using peptide/HLA-A2 tetramers and were elevated in tumor-infiltrating lymphocytes. Thus, serine proteases in the tumor microenvironment of lung cancers promote the presentation of HLA class I immunogenic peptides that are expressed by lung cancer cells, thereby increasing the antigen repertoire that can be targeted in lung cancer. Cancer Immunol Res; 5(4); 319-29. ©2017 AACR.

Neutrophil elastase enhances antigen presentation by upregulating human leukocyte antigen class I expression on tumor cells

Neutrophil elastase (NE) is an innate immune cell-derived inflammatory mediator that we have shown increases the presentation of tumor-associated peptide antigens in breast cancer. In this study, we extend these observations to show that NE uptake has a broad effect on enhancing antigen presentation by breast cancer cells. We show that NE increases human leukocyte antigen (HLA) class I expression on the surface of breast cancer cells in a concentration and time-dependent manner. HLA class I upregulation requires internalization of enzymatically active NE. Western blots of NE-treated breast cancer cells confirm that the expression of total HLA class I as well as the antigen-processing machinery proteins TAP1, LMP2, and calnexin does not change following NE treatment. This suggests that NE does not increase the efficiency of antigen processing; rather, it mediates the upregulation of HLA class I by stabilizing and reducing membrane recycling of HLA class I molecules. Furthermore, the effects of NE extend beyond breast cancer since the uptake of NE by EBV-LCL increases the presentation of HLA class I-restricted viral peptides, as shown by their increased sensitivity to lysis by EBV-specific CD8+ T cells. Together, our results show that NE uptake increases the responsiveness of breast cancer cells to adaptive immunity by broad upregulation of membrane HLA class I and support the conclusion that the innate inflammatory mediator NE enhances tumor cell recognition and increases tumor sensitivity to the host adaptive immune response.

Abstract 4049: Neutrophil elastase induces post-transcriptional increase of surface MHC class I expression on lung cancer cells

Neutrophil infiltration and the presence of the neutrophil-associated serine protease neutrophil elastase (NE) is a poor prognosis factor for lung cancer patients. NE protein contains the nonomeric epitope for PR1, an immunogenic leukemia associated antigen recognized by a circulating population of functional cytotoxic T lymphocytes (CTL) in healthy individuals. As previously reported by our laboratory, solid tumor cells such as breast cancer cells internalize NE and cross-present PR1 in the context of the CTL ligand, MHC class I molecules, specifically HLA-A2. Internalization of NE by lung cancer cell lines has previously been reported by other groups. Therefore, we hypothesized that lung cancer cells internalize NE and cross-present PR1 on HLA-A2. A panel of lung cancer cell lines did not endogenously express proteins containing the PR1 epitope, NE and proteinase 3, at the transcript or protein level, using RT-PCR, western blot analysis and flow cytometry. Intracellular staining of NE was detected in lung cancer cell lines by flow cytometry after pulsing overnight with 10 μg/mL purified soluble NE. Subsequently, elevated surface expression of PR1:HLA-A2 complexes was determined using the PR1:HLA-A2-specific antibody generated within our laboratory (A. Sergeeva, et al., Blood 2011). Furthermore, an enhancement of HLA-A2 (antibody clone BB7.2) and pan-HLA-I (antibody clone W6/32) was observed. Through RT-PCR analysis, MHC class I genes (heavy chains HLA-A, -B, -C and the β2-microglobulin light chain) were not altered by NE exposure. Additionally, genes associated with the antigen processing machinery remained unchanged (tapasin, calnexin, calreticulin, and the Transporter associated with Antigen Processing 1 and 2). Thus exposure of lung cancer cells to NE enhances surface MHC class I molecules beyond the transcript level.

MHC class I molecules serve as ligands for the T cell receptor of cytotoxic T lymphocytes, which can cause direct lysis of the target cell presenting a foreign or tumor-associated antigen. In these studies, we have detected enhanced expression of surface MHC class I molecules on lung cancer cells after exposure to NE. Thus these studies indicate that immunotherapies augmenting CTL activation could have the greatest efficacy for the poor prognosis lung cancer patients with high neutrophil infiltration or elevated plasma NE. NE contains the immunogenic PR1 epitope, and our studies have detected its cross-presentation on lung cancer cells. Therefore, anti-PR1 immunotherapies that have been developed for treatment of leukemia and lymphoma, could seamlessly be translated into lung cancer patients, and remains an area of active investigation in our laboratory.

Citation Format: Haley L. Peters, Satyendra C. Tripathi, Hiro Katayama, Celine Kerros, Alex Perakis, Lisa S. St. John, Gheath Al-Atrash, Samir Hanash, Jeffrey J. Molldrem. Neutrophil elastase induces post-transcriptional increase of surface MHC class I expression on lung cancer 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 4049. doi:10.1158/1538-7445.AM2015-4049

Abstract 2351: Characterization of Neutrophil elastase uptake in breast cancer: implications for immunotherapy

Neutrophil Elastase (NE)_a serine protease released by neutrophils in the tumor microenvironment_induces invasion and metastasis. We demonstrated that while NE is not endogenously expressed in breast cancer cells, breast cancer cells (BrCA) take up exogenous NE derived from tumor-associated neutrophils. NE uptake results in the expression of the HLA-A2-restricted peptides CCNE1 and PR1, derived from cyclin E and NE, respectively, on the surface of triple-negative (TN) BrCA cells (MDA-MB-231). Expression of these peptides/HLA-A2 molecules induces BrCA cell susceptibility to cytolysis by CCNE1- and PR1-specific cytotoxic T lymphocytes (CTLs), and to 8F4, a monoclonal antibody that binds specifically to the PR1/HLA-A2 complex. We hypothesize that NE uptake is a receptor-mediated process that results in cross-presentation of NE-derived peptides on HLA molecules of BrCA cells.

In this study, we found that NE uptake in BrCA is specific, time and dose-dependent, and become saturated, suggesting a receptor-mediated uptake mechanism. We showed that MDA-MB-231 did not take up cathepsin G, a related serine protease, suggesting specificity of NE receptor uptake. NE internalization was partially blocked by chlorpromazine and by wortmannin, implicating clathrin-dependent uptake and PI3Kinase-dependence, respectively. Confocal microscopy showed that NE was co-localized with the early endosome marker, EEA-1, as early as 10 minutes after uptake. Flow cytometry indicated that surface-bound NE on MDA-MB-231 cells decreased after five minutes, and Western blot showed a simultaneous decrease of MAPKinases phosphorylation (p-Erk, p-p38) and loss of IRS-1 signaling. Inhibition of NE enzyme activity by serine proteases inhibitors, such as elafin or PMSF, potentiated NE uptake in BrCA cells, indicating that enzyme activity is not required for uptake. Conclusion: The results support a novel mechanism of rapid receptor-mediated uptake of soluble exogenous NE by TN BrCA. NE uptake is efficient, PI3 kinase-dependent, sensitive to clathrin inhibition, and associated with down-regulation of Erk phosphorylation and IRS-1. In addition, uptake does not require NE enzyme activity. Following uptake, NE co-localizes to an early endosomal compartment, an organelle associated with HLA class I peptide loading. Since we previously linked NE uptake to CCNE1 and PR1 peptide presentation on MDA-MB-231 cells, which enhanced BrCA susceptibility to immunotherapies that target CCNE1 and PR1, our results here strongly suggest receptor-mediated NE uptake that could regulate HLA class I peptide presentation. Understanding the mechanisms that regulate NE uptake and peptide presentation on the surface of BrCA will help us develop new strategies to enhance peptide presentation by BrCA, potentially improving the response of BrCA and other tumor types to antigen-specific immunotherapies.

Citation Format: Celine Kerros, Satyendra C. Tripathi, Anne V. Philips, Gheath Al-Atrash, Kathryn E. Ruisaard, Karen C. Dwyer, Elizabeth A. Mittendorf, Samir Hanash, Jeffrey J. Molldrem. Characterization of Neutrophil elastase uptake in breast cancer: implications for immunotherapy. [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 2351. doi:10.1158/1538-7445.AM2015-2351

Abstract P5-04-09: Characterization of neutrophil elastase receptor in breast cancer: Implication for immunotherapy

Neutrophil Elastase (NE), a serine protease released by tumor-associated neutrophils in the tumor microenvironment induces invasion and metastasis. We have demonstrated that NE is not endogenously expressed in breast cancer (BrCA), but is taken up by BrCA cells. NE uptake results in the expression of the HLA-A2-bound peptides CCNE1 and PR1, derived from cyclin E and NE, respectively, on the surface of triple-negative (TN) BrCA cells (MDA-MB-231). Expression of these peptide/HLA-A2 molecules induces BrCA cell susceptibility to cytolysis by CCNE1- and PR1-specific cytotoxic T lymphocytes (CTLs), and to 8F4, a monoclonal antibody that binds specifically to the PR1/HLA-A2 complex. We hypothesize that NE uptake is a receptor-mediated process that results in cross-presentation of NE-derived peptides on HLA molecules of BrCA cells.

Here, we found that NE uptake is specific, time- and dose-dependent, and saturable, suggesting a receptor-mediated uptake mechanism. We showed that MDA-MB-231 did not take up cathepsin G, a related serine protease, suggesting specificity of receptor uptake. NE internalization was partially blocked by chlorpromazine and by wortmannin, suggesting clathrin-dependent uptake and PI3Kinase-dependence, respectively. Confocal microscopy showed that NE was colocalized with the early endosome marker, EEA-1, as early as 10 min after uptake. Flow cytometry indicated that surface-bound NE on MDA-MB-231 cells decreased after 5 minutes, and both flow cytometry and Western blot showed a simultaneous decrease of phospho-Erk and loss of IRS-1 signaling. Inhibition of NE enzyme activity by elafin or PMSF potentiated NE uptake in BrCA cells, thus enzyme activity is not required for uptake. Conclusion: The results support a novel mechanism of rapid receptor-mediated uptake of soluble exogenous NE by TN BrCA. NE uptake is efficient, PI3 kinase-dependent, sensitive to clathrin inhibition, and associated with down-regulation of Erk phosphorylation and IRS-1. In addition, uptake does not require NE enzyme activity. Following uptake, NE colocalizes to an early endosomal compartment, an organelle associated with peptide loading of MHC-I molecules for expression of the cell surface. We previously showed that the NE-derived peptide PR1 is cross-presented on MDA-MB-231 cells after NE uptake, leading to susceptibility to immunotherapies that target PR1/HLA-A2. Taken together, our results demonstrate receptor-mediated NE uptake, which is a potentially novel paradigm that could vastly expand the number of tumor-associated antigens that could be targeted on BrCA. An understanding of the mechanism that mediates NE uptake will help us develop strategies to increase expression of immunogenic peptides on cancer cells and to guide the design of targeted immunotherapies against CCNE1 and PR1 as new clinical therapies for BrCA.

Citation Format: Celine Kerros, Satyendra C Tripathi, Anne V Philips, Gheath Al-Atrash, Kathryn E Ruisaard, Karen C Dwyer, Elizabeth A Mittendorf, Samir M Hanash, Jeffrey J Molldrem. Characterization of neutrophil elastase receptor in breast cancer: Implication for immunotherapy [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-04-09.

Abstract 4843: Neutrophil elastase enhances adaptive immunity via increase of peptide presentation and downregulation of T cell inhibitory molecules

Introduction: Neutrophil elastase (NE) is an inflammatory mediator that is taken up by breast cancer cells. We have previously shown that NE uptake increases susceptibility to lysis by cytotoxic T lymphocytes (CTL) targeting the tumor antigens PR1 and cyclin E. We investigated whether NE uptake alters adaptive immunity by affecting MHC class I antigen presentation and T cell inhibitory molecules.

Methods: MDA-MB-231 breast cancer cells were maintained in standard media ± NE. Healthy donor HLA-A2+ peripheral blood mononuclear cells were used to generate antigen specific CTL by pulsing dendritic cells with E75, a HER2-derived epitope we are currently investigating as a vaccine in clinical trials. Calcein-AM cytotoxicity assays evaluated E75-specific lysis. Flow cytometry was used to show NE uptake, HLA-A2, pan-HLA class I (HLA-ABC) and PD-L1 surface expression. Western blot analysis was used to show total MHC class I heavy chain, B2M, LMP2, TAP1, calnexin and tapasin expression. Relative PD-L1 mRNA levels were determined using qPCR.

Results: NE uptake enhanced tumor cell lysis by E75-specific CTL at all effector to target (E:T) ratios (lysis for 20 to 1 E:T ratio was 50% ± 7 for NE treated vs 28% ± 7 for untreated, p < 0.05), and led to an increase in HLA-A2 and HLA-ABC surface expression (p < 0.05; Table). However, NE uptake did not change total expression of MHC class I or components of the MHC class I pathway. Additionally, NE uptake led to a decrease in PD-L1 surface expression and transcript levels (p < 0.05; Table).

Conclusion: NE increases tumor antigen presentation as well as MHC class I on the cell surface. However, NE uptake does not change total MHC class I expression or expression of MHC class I antigen processing components, suggesting that NE increases peptide availability as a mechanism of increased MHC class I antigen presentation. NE also leads to the downregulation of PD-L1. Together, our data indicate that NE uptake enhances adaptive immune responses.

HLA-A2 Surface Expression (MFI)HLA-ABC Surface Expression (MFI)PD-L1 Surface Expression (MFI)PD-L1 mRNA Expression (RQ)NE Treated (Mean ± SD)7341 ± 8671317 ± 1201723 ± 550.274 ± 0.02Untreated (Mean ± SD)5144 ± 272802 ± 1336966 ± 4511

Citation Format: Akhil Chawla, Anne V. Philips, Na Qiao, Pariya Sukhumalchandra, Celine Kerros, Gheath Alatrash, Jeffrey J. Molldrem, Elizabeth A. Mittendorf. Neutrophil elastase enhances adaptive immunity via increase of peptide presentation and downregulation of T cell inhibitory molecules. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4843. doi:10.1158/1538-7445.AM2014-4843

The peptide derived from the Ig-like domain of human herpesvirus 8 K1 protein induces death in hematological cancer cells

BACKGROUND

Although significant progress has been made in the treatment of lymphomas, many lymphomas exhibit resistance to cell death, suggesting a defective Fas signaling, which remains poorly understood. We previously reported that cells expressing the K1 protein of human herpesvirus 8 (HHV-8) resist death through the complex formation of the Ig-like domain of K1 with Fas. Recently, we investigated whether peptides derived from the Ig-like domain of the K1 protein may affect cell death.

METHODS

K1 positive and negative cell lines were incubated with the K1-derived peptides, and cell death (apoptotic and necrotic) was assessed by flow cytometry and LDH assay. Activation of caspases was assessed by fluorometric assay and flow cytometry. Fas receptor-independent, peptide-mediated cell killing was tested in the Fas-resistant Daudi cell line and Jurkat cell clones deficient in caspase-8 and FADD functionality. Activation of TNF receptors I and II was blocked by pre-incubation with corresponding blocking antibodies. The effect of the K1 peptide in vivo was tested in a mouse xenograft model.

RESULTS

We observed that the peptide S20-3 enhanced cell death in K1-positive BJAB cells and HHV-8 positive primary effusion lymphoma (PEL) cell lines. Similar effects of this peptide were observed in B-cell lymphoma and T-lymphoblastic leukemia cells without K1 expression but not in normal human peripheral blood mononuclear cells. A single intratumoral injection of the S20-3 peptide decreased the growth of Jurkat xenografts in SCID mice. The mechanism of tumor cell death induced by the S20-3 peptide was associated with activation of caspases, but this activity was only partially inhibited by the pan-caspase inhibitor z-VAD. Furthermore, the K1 peptide also killed Fas-resistant Daudi cells, and this killing effect was inhibited by pre-incubation of cells with antibodies blocking TNFRI.

CONCLUSION

Taken together, these findings indicate that the S20-3 peptide can selectively induce the death of malignant hematological cell lines by Fas- and/or TNFRI-dependent mechanisms, suggesting the K1-derived peptide or peptidomimetic may have promising therapeutic potential for the treatment of hematological cancers.

Abstract 4965: Oncoprotein PMLRARα directly suppresses Fas-mediated apoptosis through forming an apoptotic inhibitory complex with c-FLIP in vivo

Objective: Many genotoxic therapies, including radiation, depend on intact Fas signaling to eradicate cancer cells. Defective Fas signaling is an important cause of cancer resistance to therapy. Restoring Fas apoptosis or sensitizing cancer cells to Fas-mediated apoptosis would improve the efficacy of many cancer therapies. To elucidate a role for specific regulators of Fas signaling in cancer cells, we sought to identify potential modulators of Fas expressed in cancers and target them to selectively sensitize cancer cells to Fas-mediated apoptosis as a component of chemotherapy. Methods: Liquid chromatography tandem mass spectrometry was used to identify Fas-associated proteins; co-immunoprecipitation and Western blot were used to detect interactions of PMLRARα, PML, c-FLIP and Fas, and to examine the components of death-inducing signaling complex (DISC) and caspase-8 cleavage. Deletional mutagenesis was used to map the interaction domains. PML shRNA lentivirus and As2O3 were used to knock down PML and PMLRARα. Flow cytometry analysis of propidium iodide- and Annexin-V-stained cells was used to detect apoptosis. Mice were transfected with PMLRARα, monitored for survival, and tissues were analyzed for apoptosis by staining for cleaved caspase-3 and TUNEL. Results: We identified promyelocytic leukemia protein (PML) as a Fas-interacting protein using mass spectrometry analysis. The function of PML is blocked by its dominant-negative form PMLRARα. We found PMLRARα interaction with Fas in acute promyelocytic leukemia (APL)-derived cells and APL primary cells, and PML-Fas complexes in normal tissues. Binding of PMLRARα to Fas was mapped to the B-box domain of PML moiety and death domain of Fas. PMLRARα blockage of Fas apoptosis was demonstrated in U937/PR9 cells, human APL cells and transgenic mouse APL cells, in which PMLRARα recruited c-FLIPL/S and excluded procaspase-8 from Fas death signaling complex. PMLRARα expression in mice protected the mice against a lethal dose of agonistic anti-Fas antibody (P<.001) and the protected tissues contained Fas-PMLRARα-cFLIP complexes. Livers from PMLRARα-transfected mice contained fewer cleaved caspase-3 positive/apoptotic cells when compared with control vector-transfected mice. Conclusions: PMLRARα binds to Fas and blocks Fas-mediated apoptosis in APL by forming an apoptotic inhibitory complex with c-FLIP. These data suggest that PMLRARα is a cancer specific Fas-binding inhibitor of Fas-mediated apoptosis and thus, can contribute to cancer development and resistance to therapy. The newly discovered PMLRARα-Fas and PML-Fas complexes can be sites for modulation of apoptosis. By neutralizing the effect of death receptor inhibitors, such as PMLRARα, we can improve responses to many chemotherapeutic treatments that depend on activation of death receptors for effective elimination of cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4965. doi:1538-7445.AM2012-4965