Improving Chimeric Antigen Receptor-Modified T Cell Function by Reversing the Immunosuppressive Tumor Microenvironment of Pancreatic Cancer

The adoptive transfer of T cells redirected to tumor-associated antigens via transgenic expression of chimeric antigen receptors (CARs) has produced tumor responses, even in patients with refractory diseases. To target pancreatic cancer, we generated CAR T cells directed against prostate stem cell antigen (PSCA) and demonstrated specific tumor lysis. However, pancreatic tumors employ immune evasion strategies such as the production of inhibitory cytokines, which limit CAR T cell persistence and function. Thus, to protect our cells from the immunosuppressive cytokine IL-4, we generated an inverted cytokine receptor in which the IL-4 receptor exodomain was fused to the IL-7 receptor endodomain (4/7 ICR). Transgenic expression of this molecule in CAR-PSCA T cells should invert the inhibitory effects of tumor-derived IL-4 and instead promote T cell proliferation. We now demonstrate the suppressed activity of CAR T cells in tumor-milieu conditions and the ability of CAR/ICR T cells to thrive in an IL-4-rich microenvironment, resulting in enhanced antitumor activity. Importantly, CAR/ICR T cells remained both antigen and cytokine dependent. These findings support the benefit of combining the 4/7 ICR with CAR-PSCA to treat pancreatic cancer, a PSCA-expressing tumor characterized by a dense immunosuppressive environment rich in IL-4.

Fine-tuning the CAR spacer improves T-cell potency

The adoptive transfer of genetically engineered T cells expressing chimeric antigen receptors (CARs) has emerged as a transformative cancer therapy with curative potential, precipitating a wave of preclinical and clinical studies in academic centers and the private sector. Indeed, significant effort has been devoted to improving clinical benefit by incorporating accessory genes/CAR endodomains designed to enhance cellular migration, promote in vivo expansion/persistence or enhance safety by genetic programming to enable the recognition of a tumor signature. However, our efforts centered on exploring whether CAR T-cell potency could be enhanced by modifying pre-existing CAR components. We now demonstrate how molecular refinements to the CAR spacer can impact multiple biological processes including tonic signaling, cell aging, tumor localization, and antigen recognition, culminating in superior in vivo antitumor activity.

Enhancing the Potency and Specificity of Engineered T Cells for Cancer Treatment

The adoptive transfer of chimeric antigen receptor (CAR)-modified T cells has produced tumor responses even in patients with refractory diseases. However, the paucity of antigens that are tumor selective has resulted, on occasion, in "on-target, off-tumor" toxicities. To address this issue, we developed an approach to render T cells responsive to an expression pattern present exclusively at the tumor by using a trio of novel chimeric receptors. Using pancreatic cancer as a model, we demonstrate how T cells engineered with receptors that recognize prostate stem cell antigen, TGFβ, and IL4, and whose endodomains recapitulate physiologic T-cell signaling by providing signals for activation, costimulation, and cytokine support, produce potent antitumor effects selectively at the tumor site. In addition, this strategy has the benefit of rendering our cells resistant to otherwise immunosuppressive cytokines (TGFβ and IL4) and can be readily extended to other inhibitory molecules present at the tumor site (e.g., PD-L1, IL10, and IL13).Significance: This proof-of-concept study demonstrates how sophisticated engineering approaches can be utilized to both enhance the antitumor efficacy and increase the safety profile of transgenic T cells by incorporating a combination of receptors that ensure that cells are active exclusively at the tumor site. Cancer Discov; 8(8); 972-87. ©2018 AACR.See related commentary by Achkova and Pule, p. 918This article is highlighted in the In This Issue feature, p. 899.

CAR T cell therapy for breast cancer: harnessing the tumor milieu to drive T cell activation

BACKGROUND

The adoptive transfer of T cells redirected to tumor via chimeric antigen receptors (CARs) has produced clinical benefits for the treatment of hematologic diseases. To extend this approach to breast cancer, we generated CAR T cells directed against mucin1 (MUC1), an aberrantly glycosylated neoantigen that is overexpressed by malignant cells and whose expression has been correlated with poor prognosis. Furthermore, to protect our tumor-targeted cells from the elevated levels of immune-inhibitory cytokines present in the tumor milieu, we co-expressed an inverted cytokine receptor linking the IL4 receptor exodomain with the IL7 receptor endodomain (4/7ICR) in order to transform the suppressive IL4 signal into one that would enhance the anti-tumor effects of our CAR T cells at the tumor site.

METHODS

First (1G - CD3ζ) and second generation (2G - 41BB.CD3ζ) MUC1-specific CARs were constructed using the HMFG2 scFv. Following retroviral transduction transgenic expression of the CAR±ICR was assessed by flow cytometry. In vitro CAR/ICR T cell function was measured by assessing cell proliferation and short- and long-term cytotoxic activity using MUC1+ MDA MB 468 cells as targets. In vivo anti-tumor activity was assessed using IL4-producing MDA MB 468 tumor-bearing mice using calipers to assess tumor volume and bioluminescence imaging to track T cells.

RESULTS

In the IL4-rich tumor milieu, 1G CAR.MUC1 T cells failed to expand or kill MUC1+ tumors and while co-expression of the 4/7ICR promoted T cell expansion, in the absence of co-stimulatory signals the outgrowing cells exhibited an exhausted phenotype characterized by PD-1 and TIM3 upregulation and failed to control tumor growth. However, by co-expressing 2G CAR.MUC1 (signal 1 - activation + signal 2 - co-stimulation) and 4/7ICR (signal 3 - cytokine), transgenic T cells selectively expanded at the tumor site and produced potent and durable tumor control in vitro and in vivo.

CONCLUSIONS

Our findings demonstrate the feasibility of targeting breast cancer using transgenic T cells equipped to thrive in the suppressive tumor milieu and highlight the importance of providing transgenic T cells with signals that recapitulate physiologic TCR signaling - [activation (signal 1), co-stimulation (signal 2) and cytokine support (signal 3)] - to promote in vivo persistence and memory formation.

Selectively targeting myeloid-derived suppressor cells through TRAIL receptor 2 to enhance the efficacy of CAR T cell therapy for treatment of breast cancer

BACKGROUND

Successful targeting of solid tumors such as breast cancer (BC) using chimeric antigen receptor (CAR) T cells has proven challenging, largely attributed to the immunosuppressive tumor microenvironment (TME). Myeloid-derived suppressor cells (MDSCs) inhibit CAR T cell function and persistence within the breast TME. To overcome this challenge, we have developed CAR T cells targeting tumor-associated mucin 1 (MUC1) with a novel chimeric costimulatory receptor that targets tumor necrosis factor-related apoptosis-inducing ligand receptor 2 (TR2) expressed on MDSCs.

METHODS

The function of the TR2.41BB costimulatory receptor was assessed by exposing non-transduced (NT) and TR2.41BB transduced T cells to recombinant TR2, after which nuclear translocation of NFκB was measured by ELISA and western blot. The cytolytic activity of CAR.MUC1/TR2.41BB T cells was measured in a 5-hour cytotoxicity assay using MUC1+ tumor cells as targets in the presence or absence of MDSCs. In vivo antitumor activity was assessed using MDSC-enriched tumor-bearing mice treated with CAR T cells with or without TR2.41BB.

RESULTS

Nuclear translocation of NFκB in response to recombinant TR2 was detected only in TR2.41BB T cells. The presence of MDSCs diminished the cytotoxic potential of CAR.MUC1 T cells against MUC1+ BC cell lines by 25%. However, TR2.41BB expression on CAR.MUC1 T cells induced MDSC apoptosis, thereby restoring the cytotoxic activity of CAR.MUC1 T cells against MUC1+ BC lines. The presence of MDSCs resulted in an approximately twofold increase in tumor growth due to enhanced angiogenesis and fibroblast accumulation compared with mice with tumor alone. Treatment of these MDSC-enriched tumors with CAR.MUC1.TR2.41BB T cells led to superior tumor cell killing and significant reduction in tumor growth (24.54±8.55 mm³) compared with CAR.MUC1 (469.79±81.46 mm³) or TR2.41BB (434.86±64.25 mm³) T cells alone. CAR.MUC1.TR2.41BB T cells also demonstrated improved T cell proliferation and persistence at the tumor site, thereby preventing metastases. We observed similar results using CAR.HER2.TR2.41BB T cells in a HER2+ BC model.

CONCLUSIONS

Our findings demonstrate that CAR T cells that coexpress the TR2.4-1BB receptor exhibit superior antitumor potential against breast tumors containing immunosuppressive and tumor promoting MDSCs, resulting in TME remodeling and improved T cell proliferation at the tumor site.

Association mapping of North American spring wheat breeding germplasm reveals loci conferring resistance to Ug99 and other African stem rust races

BACKGROUND

The recently identified Puccinia graminis f. sp. tritici (Pgt) race TTKSK (Ug99) poses a severe threat to global wheat production because of its broad virulence on several widely deployed resistance genes. Additional virulences have been detected in the Ug99 group of races, and the spread of this race group has been documented across wheat growing regions in Africa, the Middle East (Yemen), and West Asia (Iran). Other broadly virulent Pgt races, such as TRTTF and TKTTF, present further difficulties in maintaining abundant genetic resistance for their effective use in wheat breeding against this destructive fungal disease of wheat. In an effort to identify loci conferring resistance to these races, a genome-wide association study was carried out on a panel of 250 spring wheat breeding lines from the International Maize and Wheat Improvement Center (CIMMYT), six wheat breeding programs in the United States and three wheat breeding programs in Canada.

RESULTS

The lines included in this study were grouped into two major clusters, based on the results of principal component analysis using 23,976 SNP markers. Upon screening for adult plant resistance (APR) to Ug99 during 2013 and 2014 in artificial stem rust screening nurseries at Njoro, Kenya and at Debre Zeit, Ethiopia, several wheat lines were found to exhibit APR. The lines were also screened for resistance at the seedling stage against races TTKSK, TRTTF, and TKTTF at USDA-ARS Cereal Disease Laboratory in St. Paul, Minnesota; and only 9 of the 250 lines displayed seedling resistance to all the races. Using a mixed linear model, 27 SNP markers associated with APR against Ug99 were detected, including markers linked with the known APR gene Sr2. Using the same model, 23, 86, and 111 SNP markers associated with seedling resistance against races TTKSK, TRTTF, and TKTTF were identified, respectively. These included markers linked to the genes Sr8a and Sr11 providing seedling resistance to races TRTTF and TKTTF, respectively. We also identified putatively novel Sr resistance genes on chromosomes 3B, 4D, 5A, 5B, 6A, 7A, and 7B.

CONCLUSION

Our results demonstrate that the North American wheat breeding lines have several resistance loci that provide APR and seedling resistance to highly virulent Pgt races. Using the resistant lines and the SNP markers identified in this study, marker-assisted resistance breeding can assist in development of varieties with elevated levels of resistance to virulent stem rust races including TTKSK.

Croix B. Cancer cell survival depends on collagen uptake into tumor-associated stroma

Collagen I, the most abundant protein in humans, is ubiquitous in solid tumors where it provides a rich source of exploitable metabolic fuel for cancer cells. While tumor cells were unable to exploit collagen directly, here we show they can usurp metabolic byproducts of collagen-consuming tumor-associated stroma. Using genetically engineered mouse models, we discovered that solid tumor growth depends upon collagen binding and uptake mediated by the TEM8/ANTXR1 cell surface protein in tumor-associated stroma. Tumor-associated stromal cells processed collagen into glutamine, which was then released and internalized by cancer cells. Under chronic nutrient starvation, a condition driven by the high metabolic demand of tumors, cancer cells exploited glutamine to survive, an effect that could be reversed by blocking collagen uptake with TEM8 neutralizing antibodies. These studies reveal that cancer cells exploit collagen-consuming stromal cells for survival, exposing an important vulnerability across solid tumors with implications for developing improved anticancer therapy.

Secreted Fas Decoys Enhance the Antitumor Activity of Engineered and Bystander T Cells in Fas Ligand-Expressing Solid Tumors

T-cell immunotherapy has demonstrated remarkable clinical outcomes in certain hematologic malignancies. However, efficacy in solid tumors has been suboptimal, partially due to the hostile tumor microenvironment composed of immune-inhibitory molecules. One such suppressive agent abundantly expressed in solid tumors is Fas ligand (FasL), which can trigger apoptosis of Fas-expressing effector cells such as T cells and natural killer (NK) cells. To alleviate this FasL-induced suppression of tumor-specific immune cells in solid tumors, we describe here the development of a Fas decoy that is secreted by engineered cells upon activation and sequesters the ligand, preventing it from engaging with Fas on the surface of effector cells. We further improved the immune-stimulatory effects of this approach by creating a Fas decoy and IL15 cytokine fusion protein, which enhanced the persistence and antitumor activity of decoy-engineered as well as bystander chimeric-antigen receptor (CAR) T cells in xenograft models of pancreatic cancer. Our data indicate that secreted Fas decoys can augment the efficacy of both adoptively transferred and endogenous tumor-specific effector cells in FasL-expressing solid tumors.

Overcoming the breast tumor microenvironment by targeting MDSCs through CAR-T cell therapy

1032

Background: Successful targeting of solid tumors such as breast cancer (BC) using CAR T cells (CARTs) has proven challenging, largely due to the immune suppressive tumor microenvironment (TME). Myeloid derived suppressor cells (MDSCs) inhibit CART’s function and persistence within the breast TME. We generated CAR T cells targeting tumor-expressed mucin 1 (MUC1) (Bajgain P et al, 2018) for BC. To potentiate expansion and persistence of MUC1 CARTs and modulate the suppressive TME, we developed a novel chimeric co-stimulatory receptor, TR2.4-1BB, encoding a ScFv derived from a TNF-related apoptosis-inducing ligand receptor 2 (TR2) mAb followed by a 4-1BB endodomain. We hypothesize that engagement with TR2 expressed on TME-resident MDSCs, will lead to both MDSC apoptosis and CART co-stimulation, promoting T cell persistence and expansion at tumor site. Methods: Function of the novel TR2.4-1BB receptor, was assessed by exposing non-transduced (NT) and TR2.4-1BB transduced T cells to recombinant TR2 and nuclear translocation of NFκB was measured by ELISA. Functionality of in vitro generated MDSCs was determined by the suppression assay. In vitro CART/costimulatory receptor T cell function was measured by cytotoxicity assays using MUC1+ tumor targets in presence or absence of MDSCs. In vivo anti-tumor activity was assessed using MDSC enriched tumor-bearing mice using calipers to assess tumor volume and bioluminescence imaging to track T cells. Results: Nuclear translocation of NFκB was detected only in TR2.4-1BB T cells. MDSCs significantly attenuated T cell proliferation by 50±5% and IFNγ production by half compared with T cells cultured alone. Additionally, presence of MDSCs, diminished cytotoxic potential of MUC1 CARTs against MUC1+ BC cell lines by 25%. However, TR2.4-1BB expression on CAR.MUC1 T cells induced MDSC apoptosis thereby restoring the cytotoxic activity of CAR.MUC1 against MUC1+ BC lines in presence of TR2.4-1BB (67±8.5%). There was an approximate two-fold increase in tumor growth due enhanced angiogenesis and fibroblast accumulation in mice receiving tumors + MDSCs compared to tumors alone. Treatment of these MDSC-enriched tumors with MUC1.TR2.4-1BB CARTs led to superior tumor cell killing and significant reduction in tumor growth (24.54±8.55 mm3) compared to CAR.MUC1 (469.79.9±81.46mm3) or TR2.4-1BB (434.86±64.25 mm3) T cells alone (Day 28 after T cell injection). The treatment also improved T cell proliferation and persistence at the tumor site. Thereby, leading to negligible metastasis demonstrating ability of CARTs to eliminate tumor and prevent dissemination. We observed similar results using HER2.TR2.4-1BB CARTs in a HER2+ BC model. Conclusions: Our findings demonstrate that CARTs co-expressing our novel TR2.4-1BB receptor have higher anti-tumor potential against BC tumors and infiltrating MDSCs, resulting in TME remodeling and improved T cell proliferation at the tumor site.

Abstract 4703: Improving CAR T cell function by reversing the immunosuppressive tumor microenvironment of pancreatic cancer

Adoptive transfer of T cells redirected to tumor-associated antigens (TAAs) by expression of chimeric antigen receptors (CARs) can produce tumor responses, even in patients with resistant malignancies. To target pancreatic ductal adenocarcinoma (PDAC), we generated T cells expressing a CAR directed to the TAA prostate stem cell antigen (PSCA). T cells expressing this CAR were able to kill PSCA(+) tumor cell lines CAPAN1 and K562-PSCA but not PSCA(-)293T cells (74±4%, 73±6% and 9±3% specific lysis, respectively, 10:1 E:T, n = 3). Although these CAR-T cells had potent anti-tumor activity, pancreatic tumors employ immune evasion strategies such as the production of inhibitory cytokines, which limit in vivo CAR-T cell persistence and effector function. Indeed, when we examined the serum of patients with pancreatic cancer (n = 8) we found the levels of the immunosuppressive cytokine IL4 to be elevated relative to patients with benign pancreatic disorders or normal healthy controls (14.25±19.48 pg/mL vs 7.28±9.03 vs 1.13±1.42 pg/mL). Thus, to protect our CAR-PSCA T cells from the negative influences of IL-4, we generated a chimeric cytokine receptor in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (IL4/7 ChR). Transgenic expression of this molecule in CAR-PSCA T cells should invert the inhibitory effects of tumor-derived IL4 and instead promote the proliferation of the effector CAR T cells. In preliminary experiments we successfully co-expressed both CAR-PSCA and IL4/7 ChR (47.5±12.3% double-positive cells, n = 4) on primary T cells. These T cells retained their tumor-specific activity (80±8% specific lysis against CAPAN1, 10:1 E:T, n = 3) and when cultured in conditions that mimic the tumor milieu (IL4 12.5 ng/ml), CAR-PSCA 4/7R ChR-modified T cells continued to expand (increase from 2×10e6 cells on day 0 to 5.53±8.46×10e10 cells on day 28), unlike unmodified CAR-PSCA T cells which plateaued at 3.84±5.43×10e8 cells (n = 4). Indeed, in the presence of IL4, transgenic cells had a selective advantage (comprising 44.8±11.0% of the population on day 0 and 87.6±10.0% on day 28; n = 4). However, even after prolonged cytokine exposure these T cells remained both antigen- and cytokine-dependent. In conclusion, CAR-PSCA 4/7 ChR-modified tumor-specific T cells can effectively target pancreatic cancer cells and should be equipped to expand, persist, and retain their cytotoxic function even in the presence of high levels of IL4 in the tumor microenvironment.

Citation Format: Somala Mohammed, Sujita Sukumaran, Pradip Bajgain, Usanarat Anurathapan, Helen E. Heslop, Cliona M. Rooney, Malcolm K. Brenner, Ann M. Leen, Juan F. Vera. Improving CAR T cell function by reversing the immunosuppressive tumor microenvironment of pancreatic cancer. [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 4703. doi:10.1158/1538-7445.AM2015-4703

Abstract 3501: Binary control of CAR-CTL by transgenic IL-7 and IL-7R expression

While adoptive transfer of cytotoxic T lymphocytes (CTLs) engrafted with chimeric antigen receptors (CAR) has produced objective clinical responses in vivo, the infused cells usually fail to persist long-term, limiting benefit. We have recently demonstrated that CTL persistence can be improved by engineering cells to express the IL-7 receptor alpha chain (IL-7R) which is physiologically absent on CTLs. However, this approach requires access to clinical grade cytokine and biodistribution to T lymphocytes at tumor sites may be insufficient. To circumvent these problems we have prepared two CTL products: one expressing a tumor-specific CAR in combination with IL-7R (product #1), and the second engineered to co-express the same CAR and produce IL-7 cytokine (product #2). In this way, both products have anti-tumor activity mediated through the CAR, while cytokine produced from CTL#2 should support the survival and persistence of the IL-7R-expressing CTL#1. A binary system such as this should be intrinsically safer than incorporating a positive feedback loop of both cytokine and receptor in a single cell. As a proof of this principle, we used the SFG-CAR that targets the ≤ light chain expressed on B cell malignancies: SFG-CAR/IL-7R-GFP(#1) and SFG-CAR/IL-7cyto-mOrange(#2). EBV-CTLs from 3 donors were transduced with each vector. FACS analysis of transgene expression indicated that all were expressed at approximately equivalent levels: CTL#1 (CAR, IL-7Rα, and GFP; 58%±15, 53%±18, 57.8%±12) and CTL#2 (CAR and mOrange; 54%±18 and 52%±20). The modified CTL were functional, and cells transduced with either vector were able to kill the α+ B cell tumors Daudi as evaluated by Cr51 assay (72%±13 and 69%±25, respectively) at an R:S of 40:1. Preliminary data indicates that CTLs#1 were able to proliferate in response to exogenous IL-7 administration, and IL-7 cytokine production from CTLs#2 was directly proportional to the antigenic stimulation provided to the cells. In addition, when CTLs#1 and #2 were cultured together we observed that CTLs#2 were capable of promoting the expansion of their CTL counterpart in a more efficient way than that compared to exogenous administration of IL-7 or IL-2. These results indicate that binary control of CAR modified CTLs is possible through transgenic expression of IL-7R and IL-7 cytokine in two different CTL populations.

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 3501. doi:1538-7445.AM2012-3501

Engineering CD276/B7-H3-targeted antibody-drug conjugates with enhanced cancer-eradicating capability

CD276/B7-H3 represents a promising target for cancer therapy based on widespread overexpression in both cancer cells and tumor-associated stroma. In previous preclinical studies, CD276 antibody-drug conjugates (ADCs) exploiting a talirine-type pyrrolobenzodiazepine (PBD) payload showed potent activity against various solid tumors but with a narrow therapeutic index and dosing regimen higher than that tolerated in clinical trials using other antibody-talirine conjugates. Here, we describe the development of a modified talirine PBD-based fully human CD276 ADC, called m276-SL-PBD, that is cross-species (human/mouse) reactive and can eradicate large 500-1,000-mm3 triple-negative breast cancer xenografts at doses 10- to 40-fold lower than the maximum tolerated dose. By combining CD276 targeting with judicious genetic and chemical ADC engineering, improved ADC purification, and payload sensitivity screening, these studies demonstrate that the therapeutic index of ADCs can be substantially increased, providing an advanced ADC development platform for potent and selective targeting of multiple solid tumor types.

Croix B. Uncovering receptor-ligand interactions using a high-avidity CRISPR activation screening platform

The majority of clinically approved drugs target proteins that are secreted or cell surface bound. However, further advances in this area have been hindered by the challenging nature of receptor deorphanization, as there are still many secreted and cell-bound proteins with unknown binding partners. Here, we developed an advanced screening platform that combines CRISPR-CAS9 guide-mediated gene activation (CRISPRa) and high-avidity bead-based selection. The CRISPRa platform incorporates serial enrichment and flow cytometry-based monitoring, resulting in substantially improved screening sensitivity for well-known yet weak interactions of the checkpoint inhibitor family. Our approach has successfully revealed that siglec-4 exerts regulatory control over T cell activation through a low affinity trans-interaction with the costimulatory receptor 4-1BB. Our highly efficient screening platform holds great promise for identifying extracellular interactions of uncharacterized receptor-ligand partners, which is essential to develop next-generation therapeutics, including additional immune checkpoint inhibitors.

Croix B, Leen AM, Bajgain P. A dual-luciferase bioluminescence system for the assessment of cellular therapies

Bioluminescence imaging is a well-established platform for evaluating engineered cell therapies in preclinical studies. However, despite the discovery of new luciferases and substrates, optimal combinations to simultaneously monitor two cell populations remain limited. This makes the functional assessment of cellular therapies cumbersome and expensive, especially in preclinical in vivo models. In this study, we explored the potential of using a green bioluminescence-emitting click beetle luciferase, CBG99, and a red bioluminescence-emitting firefly luciferase mutant, Akaluc, together to simultaneously monitor two cell populations. Using various chimeric antigen receptor T cells and tumor pairings, we demonstrate that these luciferases are suitable for real-time tracking of two cell types using 2D and 3D cultures in vitro and experimental models in vivo. Our data show the broad compatibility of this dual-luciferase (duo-luc) system with multiple bioluminescence detection equipment ranging from benchtop spectrophotometers to live animal imaging systems. Although this study focused on investigating complex CAR T cells and tumor cell interactions, this duo-luc system has potential utility for the simultaneous monitoring of any two cellular components-for example, to unravel the impact of a specific genetic variant on clonal dominance in a mixed population of tumor cells.

Abstract B63: Improving CAR T cell function by reversing the immunosuppressive tumor environment of pancreatic cancer

Background: Adoptive transfer of T cells redirected to tumor-associated antigens (TAAs) by expression of chimeric antigen receptors (CARs) can produce tumor responses, even in patients with resistant malignancies. Although these CAR-T cells have potent anti-tumor activity in vitro and in vivo, pancreatic tumors employ immune evasion mechanisms, such as the production of inhibitory cytokines, which limit in vivo CAR-T cell persistence and effector function.

Methods: To target pancreatic ductal adenocarcinoma (PDAC), we generated T cells expressing a CAR directed to the TAA prostate stem cell antigen (PSCA). We also engineered a chimeric cytokine receptor in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (IL4/7 ChR). Expansion and selection profiles and short- and long-term anti-tumor activity of these transgenic T cells were assessed.

Results: T cells expressing CAR-PSCA kill PSCA(+) tumor cell lines CAPAN1 and K562-PSCA but not PSCA(-) targets, such as 293T (74±4%, 73±6% and 9±3% specific lysis, respectively, 10:1 E:T, n=3). Although these CAR-T cells had potent anti-tumor activity in vitro and in vivo, pancreatic tumors employ immune evasion mechanisms, such as the production of inhibitory cytokines, which limit in vivo CAR-T cell persistence and effector function. Indeed, when the serum of patients with pancreatic cancer (n=8) was examined, we found the levels of the immunosuppressive cytokine IL4 to be elevated relative to patients with benign pancreatic disorders or normal healthy controls (14.25±19.48 pg/mL vs 7.28±9.03 vs 1.13±1.42 pg/mL). Thus, to protect the CAR-PSCA T cells from the negative influences of IL-4, we generated a chimeric cytokine receptor in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (IL4/7 ChR). Transgenic expression of this molecule in CAR-PSCA T cells should invert the inhibitory effects of tumor-derived IL4 and instead promote the proliferation of the effector CAR T cells. In preliminary experiments we successfully co-expressed both CAR-PSCA and IL4/7 ChR (47.5±12.3% double-positive cells, n=4) on primary T cells. These T cells retained their tumor-specific activity (80±8% specific lysis against CAPAN1, 10:1 E:T, n=3) and when cultured in conditions that mimic the tumor milieu (IL4 12.5 ng/ml), CAR-PSCA 4/7R ChR-modified T cells continued to expand unlike unmodified CAR-PSCA T cells (from 2x106 cells on day 0 to 5.53x1010±8.46x1010 cells (CAR-PSCA 4/7R ChR) on day 28, in comparison to CAR-PSCA T cells that reached only 3.84x108±5.43x108 cells, n=4). Indeed, in the presence of IL4, transgenic cells had a selective advantage (comprising 44.8±11.0% of the population on day 0 and 87.6±10.0% on day 28, n=4), but even after prolonged cytokine exposure these T cells remained both antigen- and cytokine-dependent.

Conclusions: CAR-PSCA 4/7 ChR-modified tumor-specific T cells can effectively target pancreatic cancer cells and should be equipped to expand, persist, and retain their cytotoxic function even in the presence of high levels of IL4 in the tumor microenvironment.

Citation Format: Somala Mohammed, Sujita Sukumaran, Usanarat Anurathapan, Pradip Bajgain, Helen E. Heslop, Cliona M. Rooney, Malcolm K. Brenner, Ann M. Leen, Juan F. Vera. Improving CAR T cell function by reversing the immunosuppressive tumor environment of pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B63.

Abstract P3-05-07: Improving CAR T cell function by reversing the immunosuppressive tumor environment of breast cancer

Adoptive transfer of T cells redirected to tumor-associated antigens (TAAs) by expression of chimeric antigen receptors (CARs) can produce tumor responses, even in patients with resistant malignancies. To target breast cancer, we generated T cells expressing a CAR directed to the TAA mucin-1 (MUC1). T cells expressing this CAR (86±1.9%, n=5) specifically killed MUC1-expressing cells (MDA-MB-468 – 45.9±7.3%, MCF-7 – 36.8±3.6) but not MUC1(-) 293T cells (3.7±1.6% specific lysis, 20:1 E:T, n=3). Although these CAR T cells had potent anti-tumor activity against breast cancer cells, when exposed to the Th2-polarizing cytokine IL4 [which is upregulated in tumor samples (Oncomine, p<0.05)] we observed a dramatic reduction in their cytolytic potential [IL2 - 45.9±7.3% vs IL4 - 11.3±3.7% specific lysis, 20:1 E:T ratio, n=4]. Thus, to protect our CAR.MUC1 T cells from the negative influences of IL4, we generated an inverted cytokine receptor (ICR) in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (4/7 ICR). Transgenic expression of this molecule in CAR.MUC1 T cells (55±4.8% double positive cells, n=5), restored the cytolytic function of CAR T cells (30.9±8.1% specific lysis, 20:1 E:T, n=3). Next, to determine the long term effects of this modification we co-cultured transgenic T cells with MUC1+ tumor cells and measured tumor and T cells numbers. In the presence of IL4, only double positive (CAR.MUC1-4/7) T cells expanded and eliminated the tumors in vitro and in vivo. However, upon tumor elimination, transgenic T cells rapidly contracted, demonstrating the antigen- and cytokine-dependence of the product. In conclusion, CAR.MUC1-4/7 T cells can effectively target breast cancer cells and retain their cytotoxic function even in the IL4-rich tumor microenvironment.

Citation Format: Bajgain P, Tawinwung S, Watanabe N, Sukumaran S, Anurathapan U, Heslop HE, Rooney CM, Brenner M, Leen AM, Vera JF. Improving CAR T cell function by reversing the immunosuppressive tumor environment of breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-05-07.

Mapping and characterization of the recessive leaf rust resistance gene Lr83 on wheat chromosome arm 1DS

KEY MESSAGE

The leaf rust resistance gene in Thatcher wheat derivative 78-1 was mapped to chromosome 1DS with SNP markers and designated as Lr83. 'Thatcher' wheat near isogenic line RL6149, a putative derivative of Triticum dicoccoides, was previously determined to carry leaf rust resistance gene Lr64 on chromosome arm 6AL and a second gene temporarily named LrX on chromosome arm 1DS. The objective of this study was to map and characterize LrX in a population of recombinant inbred lines (RILs) that segregated for a single gene. Thatcher line 78-1 with LrX was crossed with Thatcher and individual F₂ seedlings and F₆ RILs were evaluated for leaf rust response. The 208 F₂ plants segregated for a single recessive gene and 148 F₆ lines for a single gene. The RILs and parents were characterized by genotyping by sequencing (GBS). Six GBS markers and five Kompetitive Allele-Specific PCR (KASP) markers were used to map LrX on the distal region of chromosome arm 1DS. LrX was 1 centiMorgan (cM) proximal to marker K-IWB38437 and 0.4 cM distal to GBS marker 1D_9037138. Line 78-1 was crossed with Thatcher wheat lines with Lr21, Lr42, and Lr60 for allelism tests. LrX mapped 19.49 cM from Lr21 and 11.93 cM from Lr42. In the cross of line 78-1 with the Thatcher line with Lr60, one recombinant in 1,003 F₂ plants was found. LrX and Lr60 are at tightly linked loci on the distal region of chromosome arm 1DS. The gene in line 78-1 was designated as Lr83. Cytological examination of RL6149 provided no evidence of transfer of a chromosome segment of an A- or B-genome chromosome to chromosome 1D.