Cell Redirection Research Articles

PF439 EXPLORING THE THERAPEUTIC POTENTIAL OF T‐CELL‐RECEPTOR REDIRECTED CD3+ NATURAL KILLER CELLS FOR ADOPTIVE CELLULAR THERAPY TO ACUTE MYELOID LEUKEMIA

Background:Adoptive cellular therapy (ACT) with redirected T cells expressing a chimeric antigen receptor (CAR) or transgenic T‐cell‐receptor (tTCR) has revolutionized cellular immunotherapy to hematological neoplasia, in particular to acute lymphoid leukemia, and also shows great promise as therapy for solid tumors. While CARs can only detect fully cell surface expressed target structures, TCR‐mediated recognition is not limited to surface antigens, but covers processed tumor neoantigens derived from the whole proteome. However, mispairing of transgenic and endogenous TCRs and restriction to patient‐derived, autologous T lymphocytes with variable “fitness” and T cell subsets due to individual health conditions and age of the patient exemplify the current limitations encountered in TCR‐redirected ACT. The natural killer (NK) cell line NK92 elicits lytic activity comparable to T cells, has been approved by the FDA for ACT and shown not to cause graft‐vs‐host disease. Since NK cell redirection is currently limited to CARs, NK92 cells engineered to express a CD3/TCR or CD3/CD8/TCR complex might evolve as an attractive, standardized cellular source for off‐the‐shelf TCR‐based ACT.Aims:Thus, the goal of this study was to explore NK92‐CD3+ and NK92‐CD3+CD8+ variants redirected to acute myeloid leukemia (AML) by expression of different AML‐reactive TCRs for antileukemic immunity in vitro and in vivo.Methods:NK92 cells expressing the γδεζ‐chains of the CD3 complex (NK92CD3+) were kindly provided by Dr. C. Wölfel (III. Dept. of Medicine) and further genetically engineered to express different human CD8 isoforms. Upon retroviral transfer (RT) of 3 different codon‐optimized and murinized TCRs obtained from AML‐specific CD8+CTL clones into NK92‐CD3+cells TCR expression was examined by flow cytometry (FC). NK92CD3+TCR+as well as NK92CD3+CD8+TCR+cells (together referred to as NK92TCR+) were enriched using antibiotic selection and immunomagnetic cell sorting (MACS®). Biological reactivity of redirected NK92TCR+cells to patient‐derived (primary) AML blasts was tested in vitro by IFN‐γ ELISPOT and 51Cr‐release assays. Comparable expression‐profiling of checkpoint molecules on NK92 and NK92TCR+cells such as e.g. CD80/86, PD1/PDL1, NKG2A, TIM3, TIGIT and HLA‐E was performed by FC. A patient‐derived AML‐xenograft (PDX) model in NSG mice has been already established.Results:Following RT and enrichment >80% of NK92‐CD3+cells expressed a given TCR, and >90% of NK92CD3+CD8+TCR+cells could be obtained. Upon coculture with different primary AML samples and corresponding EBV‐LCL blasts as controls NK92CD3+TCR+ elicited TCR dependent IFN–γ release and exhibited cytolytic activity to some but not all AML samples. CD8 coexpression slightly increased reactivity as measured by IFN‐γ release. Interestingly, as TCR‐redirected NK92 antileukemic responses appeared to be inhibited to some but not all AML samples we found high expression of HLA‐E on these AML blasts and of NGK2A on NK92TCR+ cells. Current blocking studies to examine whether a HLA‐E/NKG2A interaction might impair NK92TCR+ mediated AML reactivity are ongoing and will be presented. Moreover, first preliminary in vivo experiments of adoptively transferred NK92TCR+ cells into a NSG‐AML PDX model indicated biological activity but further studies are in progress to evaluate this point in more detail.Summary/Conclusion:These studies demonstrate that the established and FDA approved NK92 cell line can be redirected to elicit TCR‐mediated antitumoral immunity to AML. NK92TCR+ cells might thus represent a promising universal tool for an ‘off‐the‐shelf’ ACT product

Local activator and T cell engager (LocATE) selectively blocks PD-L1 at the cytolytic synapse for deeper responses in multiple myeloma.

8045 Background: The BCMA-targeting bispecific T-cell engager AMG420 emerged as the first bispecific that achieved responses similar to CAR-T therapies in patients with relapsed/refractory (RR) multiple myeloma (MM). Despite improved ORR, the median duration until relapse is currently limited to approximately 12 months. Persistent minimal residual disease drives relapse and is characterized by increased expression of PD-1/PD-L1. Efficacy with checkpoint inhibitors is compromised by 1) their activity not been targeted specifically to the immune synapse between T cells and cancer cells, and 2) dose-limiting broadly distributed immune-related adverse events, which has halted several clinical trials. This underscores the need for localized checkpoint inhibition within the cytolytic synapse. We developed a Local Activator and T cell Engager (LocATE) antibody that combines binding to CD3 and BCMA with selective blockade of PD-L1 at the immune synapse in just one scaffold. Selectivity is achieved via low afffinity for PD-L1 and high affinity for BCMA. Methods: Antibody mediated Cytotoxicity (LDH assay) and T cell activation (IL-2 release) was measured in vitro using MM cell lines together with isolated human CD3+ T cells. Human ex vivo T cell activity and redirection was evaluated on fresh bone marrow biopsies from MM patients with different disease stages by automated microscopy (pharmacoscopy) and image analysis. Results: The LocATE antibody showed a 5-fold increase in T cell activation and MM cell killing in vitro compared to a BCMAxCD3 BiTE. Furthermore, patient-derived MM cells showed up to a 19-fold increase in T cell activation as compared to a BCMAxCD3 BiTE or a combination of BiTE and PD-L1 inhibitor, while no activity was observed on healthy cells. Conclusions: These results suggest that T cell redirection with simultaneous checkpoint inhibition in the synapse is highly potent while minimizing off-tumor toxicity, therefore, has high therapeutic potential for patients with relapsed MM.

Pharmacodynamic effect of IMCgp100 (TCR–CD3 bispecific) on peripheral cytokines and association with overall survival in patients with advanced melanoma.

9523 Background: ImmTAC molecules are unique TCR–anti-CD3 bispecifics that redirect T cells against intracellular antigens. IMCgp100, an ImmTAC targeting melanocyte-expressed gp100 antigen, has demonstrated monotherapy activity in advanced melanoma and can cause rash and cytokine-mediated AEs, hypothesized to be on-target (gp100) or effector (CD3) mediated. A preclinical MoA for T cell bispecifics suggests chemokine CXCL10 redirection of CXCR3+ T cells from blood into antigen-positive tissues; this has not been clinically validated. Methods: 84 HLA-A2+ pts with advanced melanoma (n = 61 cutaneous [CM], n = 19 uveal [UM], n = 4 other) received IMCgp100 (NCT01211262). Serum (n = 40) and PBMC (n = 22) samples were taken pre- and post-infusion to analyze changes in cytokines and circulating T cells. Pre- (n = 16) and post-treatment (n = 11) tumor biopsies were analyzed by IHC for CD3, PD-L1 and gp100 expression; tumor RNA (n = 12) was analyzed for gene expression. Results: IMCgp100 induced a transient increase in IFNg-inducible cytokines, most prominently CXCL10. A greater increase in serum CXCL10 was associated with longer OS (p = 0.0002), tumor shrinkage (p = 0.003), and greater transient reduction in peripheral CXCR3+CD8+ T cells (p = 0.001). Reduction in CXCR3+ CD8+ T cells also trended with longer OS (p = 0.02), and tumor shrinkage (p = 0.03). 3/16 pre-treatment biopsies had < 1% gp100 expression (all progressive disease). 8/11 biopsies post-IMCgp100 had increased CD3+ T cells compared with matched pre-treatment samples (associated with baseline gp100 but not PD-L1 expression). Based on tumor biopsy gene expression analysis, IMCgp100 increased T cell markers, IFNg-inducible and cytotoxicity-related genes. Conclusions: The association of clinical benefit with increased serum CXCL10 and decreased peripheral CXCR3+ T cells supports the MoA of IMCgp100-induced T cell redirection and activation. Tumor biopsy results support IMCgp100 redirection of T cells to antigen-positive tumor. A Phase II trial in CM (NCT02535078), a Phase I/II trial in UM (NCT02570308), and a Pivotal RCT in UM (NCT03070392) are ongoing. Clinical trial information: NCT01211262.

Development of a Bifunctional Checkpoint Inhibitory T Cell Engager (CiTE) to Reverse Adaptive Immune Escape in AML

The CD33-targeting bispecific T cell engager (BiTE®) AMG 330 proved to be highly efficient in mediating cytotoxicity of AML cells in vitro and in mouse models (Krupka et al, Blood 2014). Yet, T cell activation is correlated with the upregulation of PD-L1 and other inhibitory checkpoint molecules on AML cells that confer adaptive immune resistance (Krupka et al, Leukemia 2016). PD-1/PD-L1 blocking agents may counteract T cell dysfunction, however, at the expense of broadly distributed immune-related adverse events (irAEs). We developed a checkpoint inhibitory T cell engaging (CiTE) antibody that combines T cell redirection to CD33 on AML cells with locally restricted immune checkpoint blockade.CiTE constructs were generated by first fusing a high-affinity CD33 single-chain variable fragment (scFv) to a CD3ε scFv in one polypeptide chain. Next, this single-chain chain was fused to the extracellular domain of PD-1 (PD-1ex), which naturally holds a low affinity to PD-L1. Antigen binding of CiTE constructs as well as CiTE mediated cytotoxicity of AML cell lines and primary AML cells were done using multiparameter flow cytometry. T cell activation and cytotoxicity assays were complemented by cytometric bead arrays. Murine AML xenograft studies using non-obese diabetic (NOD) scid gamma mice were used for engraftment of primary AML cells and assessment of CiTE mediated cytotoxicity in vivo.CiTE antibody constructs were successfully generated by fusing the bispecific CD33-CD3ε scFv to the endogenous extracellular domain of human PD-1 (PD-1ex). The CiTE was compared to a single chain triplebody (sctb), in which PD-1ex was replaced by a high-affinity PD-L1 scFv. The BiTE-like molecule, PD-1ex.αCD3 and αPD-L1.αCD3, as well as a non-targeting molecule served as controls. When investigating CiTE and sctb as whole molecules, both bound with similar affinities to CD33+PD-L1+ AML cell lines and HD T cells. CiTE- and sctb-induced upregulation of CD69 and CD25 on healthy donor T cells in the presence of MOLM-13-PD-L1 cells. By a synergistic effect of checkpoint blockade and avidity-dependent binding, the PD-1ex attachment increased T cell activation (3.3-fold elevation of IFN-γ release) and lead to efficient and highly selective cytotoxicity of CD33+PD-L1+ cells (EC50 = 2.3 pM to 26.9 pM) as well as primary AML patient samples (n=8). CiTE induced preferential lysis of CD33+PD-L1+ cells and had no activity against CD33-PD-L1+ cells. This was supported by the observation that the CiTE molecule was able to selectively induce elimination of CD33+PD-L1+ cells in the presence of PD-L1+ cells. In a murine xenograft model, the CiTE induced complete AML eradication without causing leukemia-unrelated T cell activation or body weight loss. Notably, murine and human PD-L1 bind with similar affinities to PD-1.We conclude that our molecule preferentially targets CD33+PD-L1+ AML cells, whereas high-affinity blocking agents also address PD-L1+ non-AML cells. Based on these findings, we expect to reverse adaptive immune escape mechanisms of T cell recruiting antibody formats and avoid irAEs associated with systemic checkpoint blockade, suggesting efficient therapeutic potential particularly for patients with relapsed or refractory AML. Future studies will need to further examine efficiency and tolerance in advanced in vivo models before applying the CiTE format into a clinical setting. DisclosuresLindl:Amgen: Research Funding. Metzeler:Celgene: Consultancy, Research Funding; Novartis: Consultancy. Subklewe:Gilead: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria; Roche: Consultancy, Research Funding; Celgene: Consultancy, Honoraria.

Abstract 2777: Antigen Seeding Technology by Engineered Toxin Bodies provides a targeted immuno-oncology approach for treatment of cancers

Abstract Engineered Toxin Bodies (ETBs) are a distinct class of targeted immunotoxins in development by Molecular Templates as anti-cancer therapeutics. ETBs drive a potent and targeted response mediated by antibody-like binding, cellular internalization, and enzymatic ribosomal inhibition via the delivery of a Shiga-like toxin subunit A (SLTA) that has been proprietarily modified to avoid innate and adaptive immune recognition. In addition to this primary mechanism of action (MOA), the intrinsic ability of ETBs to induce internalization in a targeted fashion, present a unique delivery platform for next generation MOAs in the immuno-oncological (IO) space. Recent advances in IO such as checkpoint inhibitors, bi-specific T cell engagers, and CAR-T cells now provide direct clinical evidence that restoration of T cell functionality or re-direction of fully functional T cells drive significant clinical benefit to patients that have failed traditional standard of care. Molecular Templates has developed the Antigen Seeding Technology (AST) platform, rendering next generation ETBs with the unique ability to deliver foreign protein antigen to the cytoplasm of targeted populations of tumor cells. This MOA allows for the intracellular processing of antigen and subsequent surface MHC-I presentation required for activation of a re-directed T lymphocyte response and the capacity to restore a functional immune clearance program against the tumor. Our first generation AST molecule has been engineered as a PD-L1 targeted ETB carrying the immunodominant HLA:A02 restricted peptide (NLVPMVATV) from the Cytomegalovirus (CMV) tegument protein-pp65. This design takes advantage of targeting of PD-L1 expressing tumor cells, which are components of multiple cancers responsive to current IO modalities. Furthermore, the incorporation of an immunodominant CMV-peptide allows for the appropriation of a highly functional and non-exhausted CMV-specific lymphocyte response that is highly prevalent in the human population. Pre-clinical data demonstrate a potent ability for AST to trigger ETB-mediated T cell responses and tumor cell clearance of multiple PD-L1+ tumor targets. This response is highly specific, as treatment of PD-L1+ positive but not negative cell lines leads to detectable surface expression of NLVPMVATV in an HLA:A02 dependent manner. Furthermore, this result correlates with activation of effector T cells and subsequent eradication of multiple PD-L1/A02+ tumor targets after co-culture with healthy T cells from A02/CMV+ donors. Together, our POC data shows that using our AST-platform, we can deliver a targeted antigenic response to re-direct CMV-T cell responses to various tumor cell lines, trigger a T cell-mediated response and targeted-tumor cell clearance. Molecular Templates intends on extending the AST platform to clinical lead programs in 2018. Citation Format: Brigitte Brieschke, Sangeetha Rajagopalan, Garrett L. Robinson, Jack P. Higgins, Erin K. Willert, Hilario J. Ramos. Antigen Seeding Technology by Engineered Toxin Bodies provides a targeted immuno-oncology approach for treatment of cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2777.

Abstract 3092: Redirection of human HER2-positive breast cancer cells

Abstract Breast cancer is the most common form of cancer among women, affecting one eigth of the female population. While advances in clinical management and therapeutic modalities have been achieved, serious limitations in the improvement of outcomes after the diagnosis remain, largely due to the complexity of the underlying biology. Studying the mechanism that makes cancer cells tumorigenic and how they can lose the ability to cause malignant formations is the first step towards understanding complex mechanisms of this disease. The normal mammary microenvironment can redirect cells to assume a normal mammary epithelial phenotype. This phenomenon also applies to tumorigenic cells; cancer cells lose their tumor-forming capacity and differentiate, assuming a normal, non-tumorigenic phenotype. This phenomenon has been termed “cancer cell redirection.” Comparing cells that went through this transformation with original cancer cells, features that identify tumorigenic activity can be acknowledged. We have established an in vitro model of cancer cell redirection, in which HER2+ breast cancer cells are grown alone or in co-culture with normal human breast epithelial cells. The ratios of cells used in co-cultures, 1:1 and 1:50 (cancer: normal) were previously established through in vivo and in vitro studies. Redirection was confirmed by immunostaining. The metric used to determine cancer cell redirection was the absence of receptor tyrosine kinase phosphorylation without a change in surface expression of the receptor. HER2 and P-HER2 expression were both present in the HER2+ cancer cells and in the: MCF10A and 1:1 co-cultures. However, HER2 expression was observed in 1:50 co-cultures, but an absence of P-HER2 was noted. Based on attenuation of receptor phosphorylation in the 1:50 co-cultures we can confirm the breast cancer cell redirection, which matches our previous results. Furthermore, alteration of HER2 dimerization patterns in redirected cells were investigated. The capacity of cancer and redirected cells to form tumors was examined with use of mammosphere assay. Formation of mammospheres has correlated to stem cell function and tumor-initiation capacity. The HER2+ breast cancer cell lines formed significantly higher numbers of spheres compared to the non-tumorigenic breast epithelial cells. Mammosphere formation is decreased in redirected cancer cells. Breast cancer stem cells are HER2+ regardless of pathological or genetic classification. This suggests that HER2 expression is not only a target in HER2+ breast cancer but should be targeted in all breast cancers to prevent breast cancer stem cells from recapitulating tumors following treatment. Our data demonstrates that by attenuating activity of HER2 theses cancer cells lose the capacity to form tumors in vivo and lose their cancer phenotype in vitro. Citation Format: Anastasia Frank-Kamenetskii, Julia M. Mook, Brian W. Booth. Redirection of human HER2-positive breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3092.

In vivo reprogramming of non-mammary cells to an epithelial cell fate is independent of amphiregulin signaling

AREG-/- mice demonstrate impaired mammary development and form only rudimentary ductal epithelial trees, however, AREG-/- glands are still capable of undergoing alveologenesis and lactogenesis during pregnancy. Transplantation of AREG-/- mammary epithelial cells into cleared mouse mammary fat pads results in a diminished capacity for epithelial growth (∼15%) as compared to wild type mammary epithelial cells. To determine whether ERα and/or AREG signaling were necessary for non-mammary cell redirection, we inoculated either ERα-/- or AREG-/- mammary cells with non-mammary progenitor cells (WapCre/Rosa26LacZ+ male testicular cells or GFP+ embryonic neuronal stem cells). ERα-/- cells possessed a limited ability to grow or reprogram non-mammary cells in transplanted mammary fat pads. AREG-/- mammary cells were capable of redirecting both types of non-mammary cell populations to mammary phenotypes in regenerating mammary outgrowths. Transplantation of fragments from AREG-reprogrammed chimeric outgrowths resulted in secondary outgrowths in 6 out of 10 fat pads, demonstrating the self-renewing capacity of the redirected non-mammary cells to contribute new progeny to chimeric outgrowths. Nestin was detected at the leading edges of developing alveoli suggesting its expression may be essential for lobular expansion.

Cancer cell redirection biomarker discovery using a mutual information approach.

Introducing tumor-derived cells into normal mammary stem cell niches at a sufficiently high ratio of normal to tumorous cells causes those tumor cells to undergo a change to normal mammary phenotype and yield normal mammary progeny. This phenomenon has been termed cancer cell redirection. We have developed an in vitro model that mimics in vivo redirection of cancer cells by the normal mammary microenvironment. Using the RNA profiling data from this cellular model, we examined high-level characteristics of the normal, redirected, and tumor transcriptomes and found the global expression profiles clearly distinguish the three expression states. To identify potential redirection biomarkers that cause the redirected state to shift toward the normal expression pattern, we used mutual information relationships between normal, redirected, and tumor cell groups. Mutual information relationship analysis reduced a dataset of over 35,000 gene expression measurements spread over 13,000 curated gene sets to a set of 20 significant molecular signatures totaling 906 unique loci. Several of these molecular signatures are hallmark drivers of the tumor state. Using differential expression as a guide, we further refined the gene set to 120 core redirection biomarker genes. The expression levels of these core biomarkers are sufficient to make the normal and redirected gene expression states indistinguishable from each other but radically different from the tumor state.

RNA Expression Profiling Reveals Differentially Regulated Growth Factor and Receptor Expression in Redirected Cancer Cells.

Tumorigenic cells can be redirected to adopt a normal phenotype when transplanted into cleared mammary fat pads of juvenile female mice in specific ratios with normal epithelial cells. The redirected tumorigenic cells enter stem cell niches and provide progeny that differentiate into all mammary epithelial subtypes. We have developed an in vitro model that mimics the in vivo phenomenon. The shift in phenotype to redirection should be accomplished through a return to a normal gene expression state. To measure this shift, we interrogated the transcriptome of various in vitro model states in search for casual genes. For this study, expression of growth factors, cytokines, and their associated receptors was examined. In all, we queried 251 growth factor and cytokine-related genes. We found numerous growth factor and cytokine genes whose expression levels switched from expression levels seen in cancer cells to expression levels observed in normal cells. The comparisons of gene expression between normal mammary epithelial cells, tumor-derived cells, and redirected cancer cells have revealed insight into active and inactive growth factors and cytokines in cancer cell redirection.

In vivo reprogramming of non-mammary cells to an epithelial cell fate is independent of amphiregulin signaling.

Amphiregulin (AREG)-/- mice demonstrate impaired mammary development and form only rudimentary ductal epithelial trees; however, AREG-/- glands are still capable of undergoing alveologenesis and lactogenesis during pregnancy. Transplantation of AREG-/- mammary epithelial cells into cleared mouse mammary fat pads results in a diminished capacity for epithelial growth (∼15%) as compared to that of wild-type mammary epithelial cells. To determine whether estrogen receptor α (ERα, also known as ESR1) and/or AREG signaling were necessary for non-mammary cell redirection, we inoculated either ERα-/- or AREG-/- mammary cells with non-mammary progenitor cells (WAP-Cre/Rosa26LacZ+ male testicular cells or GFP-positive embryonic neuronal stem cells). ERα-/- cells possessed a limited ability to grow or reprogram non-mammary cells in transplanted mammary fat pads. AREG-/- mammary cells were capable of redirecting both types of non-mammary cell populations to mammary phenotypes in regenerating mammary outgrowths. Transplantation of fragments from AREG-reprogrammed chimeric outgrowths resulted in secondary outgrowths in six out of ten fat pads, demonstrating the self-renewing capacity of the redirected non-mammary cells to contribute new progeny to chimeric outgrowths. Nestin was detected at the leading edges of developing alveoli, suggesting that its expression may be essential for lobular expansion.

The Impact of the Bone Marrow Microenvironment on T Cell Redirection Therapeutics

Redirecting T cells to specifically target and kill malignant cells has been validated as an effective anti-cancer strategy in the clinic with the approval of CD19xCD3 BiTE (Blincyto) for acute lymphoblastic leukemia. However, the immunosuppressive nature of the tumor microenvironment potentially poses a significant hurdle to T cell therapies. For instance, the bone marrow (BM) niche is appreciated to be a site of immune privilege at steady state to allow for normal hematopoiesis and immune cell generation. Additionally, in hematological malignancies, the BM niche is protective to leukemic stem cells, a phenomenon that has minimized the efficacy of several anti-cancer drugs including chemotherapy, targeted small molecule inhibitors and antibody based therapies.In this study, we investigated the impact of the BM microenvironment on T cell redirection. Using antibodies made with the Genmab DuoBody® technology targeting specific tumor antigens (CD123 and BCMA) and CD3, we observed that co-culture of acute myeloid leukemia (AML; KG-1, MOLM-13 and OCI-AML5) or multiple myeloma (MM; H929 and RPMI8226) cell lines with bone marrow stromal cell lines (HS-5 and HS-27a) significantly protected leukemic cells from DuoBody®-T cell mediated lysis in vitro. Specifically, co-culture of bone marrow stromal cells in killing assays led to a 20-50% decrease in the maximum observed cytotoxicity and a 3-10 fold weaker EC50, reflecting an impact on both the efficacy and potency of bispecific DuoBody® antibodies. Similar results were also observed with primary stromal cells obtained from healthy donors. Furthermore, presence of stromal cells in a humanized xenograft AML model attenuated tumor growth inhibition (TGI) observed with DuoBody® treatment (78% TGI with MOLM-13 vs 15% TGI with MOLM-13+HS-5). Impaired TGI correlated with reduced T cell activation (7 fold decrease in CD25 upregulation) and production of granzyme B (8 fold reduction), providing one potential mechanism to explain loss of activity of the DuoBody® antibody. In vitro trans-well redirection assays revealed that cell-cell contact with stromal cells was crucial for reduced T cell activation and target cell survival relative to controls. Additionally, leukemic cells not killed by T cells were observed to preferentially cluster around stromal cells. We propose that target cells can evade T cell death by a stromal cell dependent mechanism involving activation of multiple pro-survival and anti-apoptotic pathways in leukemic cells in addition to suppressed activation of T cells. We are currently studying pathways mediating the cross-talk between cancer, immune and stromal cells. A better understanding of the mechanisms underlying the protective and immunosuppressive nature of the BM microenvironment will be instrumental to the design of more effective CD3 redirected therapeutics or novel combinatorial regimens for robust anti-cancer responses. DisclosuresNair-Gupta:Janssen: Employment. Rudnick:Janssen Pharmaceuticals R&D: Employment. Luistro:Janssen: Employment. Chin:Janssen: Employment. Smith:Janssen Research & Development, LLC: Employment, Equity Ownership. McDaid:Janssen Pharmaceuticals Research and Development: Employment. Li:Janssen: Employment. Pillarisetti:Janssen Research and Development, LLC: Employment. Baldwin:Janssen: Employment. Packman:Janssen: Employment. Elsayed:Janssen: Employment. Attar:Janssen: Employment. Gaudet:Janssen Pharmaceuticals R&D: Employment, Other: Stock options, Patents & Royalties: pending, not yet issued.

PS2 - 172 Preclinical Validation of a Novel CD33/CD3 Bispecific T-Cell Engager (BiTE) Antibody to Target Patient-Derived Glioblastoma Cells

Glioblastoma (GBM), an aggressive primary adult brain tumor, is feared for its near uniformly fatal prognosis. Despite the use of aggressive treatment including surgical resection, radiotherapy and chemotherapy, the outcome of patients with GBM has failed to improve significantly. Numerous studies have implicated CD133+GBM subpopulation as driver of chemo- and radio-resistance. CD133 expression correlates with disease progression, recurrence, and poor overall survival of GBM patients. Here, we describe the preclinical evaluation of a recombinant CD133xCD3 bispecific T-cell engager (BiTE) antibody that redirects human polyclonal T cells to CD133+GBM cells, inducing very potent anti-tumor response. CD133-specific BiTE was constructed; with one arm recognizing the tumor antigen (CD133) while the second is specific to CD3 antigen. Using CD133high and CD133low primary GBM lines, we validated the binding of BiTEs to CD133+GBMs and CD3+T cells. In order to test the ability of BiTEs to functionally elicit CD133-specific cytotoxic responses in vitro, we performed killing assays. We observed CD133-specific BiTE mediated T cell activation and redirection to kill CD133-expressing GBM cells in a co-culture of T cells and GBM cells. The killing was more efficient in CD133high GBMs compared to CD133low GBMs, validating its specificity to target CD133+BTICs. Treatment with BiTEs yielded significant reductions in brain tumor burden in vivo. These data offers compelling evidence that BiTE-mediated cytotoxicity against treatment-resistant CD133+GBMs could provide a very potent, specific and can be a novel therapeutic strategy for GBM patients.

Abstract 1492: Development of a CD123xCD3 bispecific antibody to treat acute myeloid leukemia (AML)

Abstract AML is a heterogeneous disease characterized by uncontrolled clonal expansion of leukemic stem cells (LSCs). Current therapies for AML are not curative, in part due to their inability to eradicate LSCs from the bone marrow. T cell redirection has been shown to be effective in heme malignancies and represents a promising approach to treat AML by targeting markers differentially expressed on the cell surface of cancer cells. One marker, CD123 (α-chain of the interleukin-3 receptor) is often present on AML LSCs and blasts. We developed a human bispecific antibody (CD123xCD3; Ab-178) capable of binding to the extracellular domain of CD123 and the ϵ chain of CD3 on T cells to induce T cell–mediated tumor cell killing. This bispecific IgG4 antibody can recruit T cells to CD123+ AML cells (MOLM-13, KG-1 and OCI-AML5) and induce T cell activation as evidenced by CD69 and CD25 up-regulation on T cells. Ab-178 potently killed these CD123+ AML cell lines in vitro (EC50 = 0.51-0.91 nM) but not a CD123− cell line (JIM3). Ab-178 was also able to induce tumor inhibition (MOLM-13 cells) and regression (KG-1 cells) in murine xenograft CD123+ AML models in the presence of human PBMCs. Furthermore, this antibody was able to kill AML blasts in primary AML blood samples ex vivo in the absence of exogenous T cells (autologous setting; EC50 = 0.83 nM). Related bispecific antibodies directed against a viral epitope (nullxCD3 or CD123xnull) did not activate T cells or cause tumor cell killing in the various assays tested. Ab-178 had no impact on T cell activation when incubated with T cells alone. These results indicate that Ab-178 can potently and specifically activate T cells in the presence of CD123+ AML cells and induce their killing. Furthermore, because of the antibody format, this molecule is expected to have a longer half-life compared to smaller bispecific biologic scaffolds. Ab-178 is currently being evaluated pre-clinically for its potential to treat patients with AML. Citation Format: Francois Gaudet, Jennifer F. Nemeth, Ronan McDaid, Yingzhe Li, Benjamin Harman, Hillary Millar, Alexey Teplyakov, John Wheeler, Jinquan Luo, Susan Tam, Sheng-Jiun Wu, Emily Chen, Alexander Babich, Yusri Elsayed, Ricardo Attar. Development of a CD123xCD3 bispecific antibody to treat acute myeloid leukemia (AML). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1492.

Validation of an in vitro model of erbB2(+) cancer cell redirection.

Overexpression of the oncoprotein erbB2/HER2 is present in 20-30% of breast cancer patients and inversely correlates with patient survival. Reports have demonstrated the deterministic power of the mammary microenvironment where the normal mammary microenvironment redirects cells of non-mammary origin or tumor-derived cells to adopt a mammary phenotype in an in vivo model. This phenomenon is termed tumor cell redirection. Tumor-derived cells that overexpress the erbB2 oncoprotein lose their tumor-forming capacity in this model. In this model, phosphorylation of erbB2 is attenuated thus reducing the tumor cell's tumor-forming potential. In this report, we describe our results using an in vitro model based on the in vivo model mentioned previously. Tumor-derived cells are mixed in predetermined ratios with normal mammary epithelial cells prior to seeding in vitro. In this in vitro model, the tumor-derived cells are redirected as determined by attenuated phosphorylation of the receptor and reduced sphere and colony formation. These results match those observed in the in vivo model. This in vitro model will allow expanded experimental options in the future to determine additional aspects of tumor cell redirection that can be translated to other types of cancer.

Redirection of Antigen-Specific T Cells to Tumor Cells Using Nanoparticle-Based Antigen-Specific Redirectors (ATRs)

Immunotherapy is the modulation of a patient’s immune system to treat illness. Unfortunately many T cell based attempts have failed due to the fact that existing tumor-specific T cells are mostly anergic or tolerized and ex vivo generated T cells are often already of exhausted phenotype. Therefore, investigators have developed alternative approaches including bispecific antibody technology to redirect fully functional non-tumor specific T cells to the tumor. This has been primarily accomplished through targeting CD3 which is expressed on all T cells to engage and redirect them towards a molecule that is expressed on the tumor cells. Here we present a novel nanoparticle based approach to selectively target cytotoxic T cells (CTL) and re-direct them to kill tumors, termed ATR (Antigen-specific T cell Redirectors).ATR were generated by coupling either MHC-Ig dimer or clonotypic anti-TCR antibody 1B2 to target the effector T cell population and an anti-CD19 to re-direct those to CD19+ tumor target cells onto 50-100nm nanoparticles. Flow cytometry and microscope based data confirm that the described ATR phenotype efficiently and stably stain tumor and T cells in a dose dependent manner and ATR mediate antigen-specific conjugate formation of effector T cells and tumor target cells. We further developed two clinically relevant protocols to test and optimize our ATR in vitro. First a pre-treatment approach in which the effector T cells are pre-incubated with ATR mimicking an adoptive transfer approach and second a co-culture protocol that mimics an active immunotherapy approach of direct ATR injection. Antigen-specific ATR mediated re-direction of T cells to tumor target cells was demonstrated in 51Cr-release killing assays at low E:T ratios. Variation of ATR target-cell : effector-cell targeting molecule ratio could further increase efficacy. Finally, intra tumoral ATR injection induced T cell re-direction and reduced tumor growth in a s.c. Raji/SCIDbeige treatment model.In summary this data demonstrates that ATR target and redirect antigen-specific CTL to tumor cells that would otherwise not be recognized and mediates their lysis. ATR can be used to develop new innovative immunotherapeutic approaches for all cancers that can be targeted with antibodies or antibody-like molecules. Furthermore, ATR could also be used in conjunction with virus-specific immunization to specifically increase the targeted CTL population. Ultimately, we expect ATR and their potential for clinical applications to increase our understanding of tumor immunotherapy through T cell redirection. DisclosuresOelke:NextImmune: Equity Ownership. Schneck:NextImmune: Equity Ownership.

Antigen-specific T cell redirectors (ATR) for antigen-specific redirection of T cells to tumors

Immunotherapy is the modulation of a patient's immune system to treat illness. Unfortunately many T cell based attempts have failed due to the fact that existing tumor-specific T cells are mostly anergic or tolerized and ex vivo generated T cells are often already of exhausted phenotype. Therefore, investigators have developed alternative approaches including bispecific antibody technology to redirect fully functional non-tumor specific T cells to the tumor. This has been primarily accomplished through targeting CD3, which is expressed on all T cells to engage and redirect them towards a molecule that is expressed on the tumor cells. Here we present a novel nanoparticle based approach to selectively target cytotoxic T cells (CTL) and re-direct them to kill tumors, termed ATR (Antigen-specific T cell Redirectors). ATR were generated by coupling either MHC-Ig dimer or clonotypic anti-TCR antibody 1B2 to target the effector T cell population and an anti-CD19 to re-direct those to CD19+ tumor target cells onto 50-100nm nanoparticles. Flow cytometry and microscope based data confirm that the described ATR phenotype efficiently and stably stain tumor and T cells in a dose dependent manner, and ATR mediate antigen-specific conjugate formation of effector T cells and tumor target cells. We further developed two clinically relevant protocols to test and optimize our ATR in vitro. First a pre-treatment approach in which the effector T cells are pre-incubated with ATR mimicking an adoptive transfer approach and second a co-culture protocol that mimics an active immunotherapy approach of direct ATR injection. Antigen-specific ATR mediated re-direction of T cells to tumor target cells was demonstrated in 51Cr-release killing assays at low E:T ratios. Variation of ATR target-cell: effector-cell targeting molecule ratio could further increase efficacy. Finally, intra tumoral ATR injection induced T cell re-direction and reduced tumor growth in a s.c. Raji/SCIDbeige treatment model. In summary this data demonstrates that ATR target and redirect antigen-specific CTL to tumor cells that would otherwise not be recognized and mediates their lysis. ATR can be used to develop new innovative immunotherapeutic approaches for all cancers that can be targeted with antibodies or antibody-like molecules. Furthermore, ATR could also be used in conjunction with virus-specific immunization to specifically increase the targeted CTL population. Ultimately, we expect ATR and their potential for clinical applications to increase our understanding of tumor immunotherapy through T cell redirection.

P64. T cell re-direction against Glypican-3 for immunotherapy of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) represents the third most common cause of cancer related death worldwide. A new therapeutic approach is the adoptive T-cell therapy. Glypican-3 (GPC3) as a tumour associated antigen is expressed in 75% of all HCC but not in healthy liver or other organs. In the present study we have identified and cloned the GPC3-specific T-cell receptor P1-1. The functionality of the isolated TCR P1-1 towards human hepatoma cells was demonstrated in vitro and in vivo. GPC3-directed T-cell therapy shows great promise for the treatment of HCC.

ImmTAC-redirected tumour cell killing induces and potentiates antigen cross-presentation by dendritic cells.

Antigen cross-presentation by dendritic cells (DCs) is thought to play a critical role in driving a polyclonal and durable T cell response against cancer. It follows, therefore, that the capacity of emerging immunotherapeutic agents to orchestrate tumour eradication may depend on their ability to induce antigen cross-presentation. ImmTACs [immune-mobilising monoclonal TCRs (T cell receptors) against cancer] are a new class of soluble bi-specific anti-cancer agents that combine pico-molar affinity TCR-based antigen recognition with T cell activation via a CD3-specific antibody fragment. ImmTACs specifically recognise human leucocyte antigen (HLA)-restricted tumour-associated antigens, presented by cancer cells, leading to T cell redirection and a potent anti-tumour response. Using an ImmTAC specific for a HLA-A*02-restricted peptide derived from the melanoma antigen gp100 (termed IMCgp100), we here observe that ImmTAC-driven melanoma-cell death leads to cross-presentation of melanoma antigens by DCs. These, in turn, can activate both melanoma-specific T cells and polyclonal T cells redirected by IMCgp100. Moreover, activation of melanoma-specific T cells by cross-presenting DCs is enhanced in the presence of IMCgp100; a feature that serves to increase the prospect of breaking tolerance in the tumour microenvironment. The mechanism of DC cross-presentation occurs via 'cross-dressing' which involves the rapid and direct capture by DCs of membrane fragments from dying tumour cells. DC cross-presentation of gp100-peptide-HLA complexes was visualised and quantified using a fluorescently labelled soluble TCR. These data demonstrate how ImmTACs engage with the innate and adaptive components of the immune system enhancing the prospect of mediating an effective and durable anti-tumour response in patients.

Abstract 3528: IMCmage1: A novel bi-specific biologic re-directing T cells to kill MAGE-A3/A6 presenting cancers

Abstract In a minority of cancer patients immunotherapy has shown the capacity to eradicate tumours leading to clinical remission and the promise of a cure. In the majority of patients however, a cure remains elusive due to active immune evasion by cancers; HLA-down-regulation and immunosuppression are two of the known mechanisms adopted by cancers to promote their survival and proliferation. To overcome these challenges we have developed bi-specific soluble biologics termed ImmTACs (Immune mobilising mTCR against cancer) to re-direct the immune system to recognise and kill cancers. Antigenic peptide fragments presented by HLA molecules on the surface of cancer cells constitute the largest class of cancer associated targets. T cells scan the HLA-peptide (pHLA) antigens being presented to them; sufficient recognition by the harboured T Cell Receptor (TCR) will result in T cell activation and killing of the antigen presenting cell. In cancer patients this process is inefficient partly due to the low affinity TCRs expressed by tumour specific T cells and the low abundance of pHLA on cancers. ImmTACs comprise a soluble TCR with an enhanced affinity for cancer associated pHLA (targeting end) fused to an anti-CD3 scfv, enabling potent T cell re-direction (effector end). Our pipeline constitutes a number of ImmTACs targeting various antigen pHLA complexes relevant to numerous cancer indications. IMCmage1 is a novel ImmTAC targeting MAGE-A3168-176 in the context of HLA-A1. MAGE-A3 is a well validated cancer testis antigen expressed in a variety of cancers including myeloma, NSCLC, prostate cancer, melanoma, bladder cancer, oesophageal cancer and others. IMCmage1 re-directs T cells from cancer patients or healthy donors to kill a range of MAGE positive cell-lines in vitro; this activity is observed against cells presenting as few as 40 epitopes per cell and is coupled with the release of pro-inflammatory cytokines including IFNα, TNFα, IL-2, MIP1α and others. We also demonstrate that IMCmage1 specifically targets and kills the myeloma associated population within CD138+ cells extracted from the marrow of a stage III myeloma patient. IMCmage1 specificity was confirmed by exposure to a panel of HLA-A1 MAGE negative primary cells derived from various organs such as the heart, skin, lung and others; no significant activity was detected. A phase I clinical trial in multiple myeloma to assess tolerability and establish a maximum tolerated dose is planned to commence in Q2 2012. 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 3528. doi:1538-7445.AM2012-3528

Costimulatory blockade with monoclonal antibodies to induce alloanergy in donor lymphocytes

Alloreactive donor T cells are central to the pathogenesis of Graft-versus-Host Disease (GvHD). Non-specific T cell depletion of donor grafts reduces GvHD, but increases infection and disease relapse. Several strategies are, therefore, in development to selectively remove alloreactive donor T cells prior to transplant while retaining beneficial donor T cells. An alternative approach is ex vivo alloanergization of donor T cells via allostimulation and blockade of costimulatory signals with fusion proteins or monoclonal antibodies. This strategy, which selectively inactivates alloreactive donor T cells, has been tested with some success in previous clinical trials of HLA-mismatched bone marrow transplantation. To build on the findings of these early trials, the strategy is now being tested in a multi-center clinical study of alloanergized donor lymphocyte infusion after HLA-mismatched stem cell transplantation. Recent advances in the understanding of alloanergization include the recognition of the central role played by CD4(+) regulatory T cells and new applications include the combination of alloanergization with T cell redirection to maximize anti-tumor activity. This mini-review will give an overview of the immunological basis for alloanergization, the previous and current clinical applications, and how new pre-clinical data have helped to create exciting new avenues of translational research in this area.