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A major challenge in adoptive T cell immunotherapy is the discovery of natural T cell receptors (TCRs) with high activity and specificity to tumor antigens. Engineering synthetic TCRs for increased tumor antigen recognition is complicated by the risk of introducing cross-reactivity and by the poor correlation that can exist between binding affinity and activity of TCRs in response to antigen (peptide-MHC). Here, we developed TCR-Engine, a method combining genome editing, computational design, and deep sequencing to engineer the functional activity and specificity of TCRs on the surface of a human T cell line at high throughput. We applied TCR-Engine to successfully engineer synthetic TCRs for increased potency and specificity to a clinically relevant tumor-associated antigen (MAGE-A3) and validated their translational potential through multiple in vitro and in vivo assessments of safety and efficacy. Thus, TCR-Engine represents a valuable technology for engineering of safe and potent synthetic TCRs for immunotherapy applications., Immunity, 55 (10)

BackgroundCancer-associated neoantigens (neoAg) derived from tumor genomic sequencing and predictive algorithms for mutated peptides are a promising basis for therapeutic vaccines under investigation. Although these are generally designed to bind major histocompatibility complex class I and induce CD8 cytolytic T lymphocyte (CTL) activity, results from preclinical and clinical studies demonstrate that the majority of neoAg vaccines efficiently induce CD4 T helper (Th) responses but not CTL. Despite this, these vaccines have demonstrated clinical efficacy. Therefore, understanding the mechanisms of CD4 + T cell-mediated tumor protection is critical to optimizing this immunotherapeutic strategy.MethodsWe investigated this phenomenon in the mineral oil-induced plasmacytoma (MOPC).315.BM (MOPC315) mouse model of multiple myeloma, a malignancy of plasma cells. MOPC315 cells express in their lambda chain a unique tumor-specific neoAg, an idiotypic (Id) peptide. We generated a vaccine formulated with this Id peptide fused to a heat shock protein HSC70 binding (HSB) motif co-delivered with poly (I:C). The immunogenicity of the Id-vaccine was measured in splenocytes by ELISpot. Mice were challenged with MOPC315 cells and antitumor immunity was assessed by co-incubating splenocytes and bone marrow mononuclear cells derived from vaccinated mice and controls, with the Id antigen and irradiated MOPC315 cells. The frequency of activated CD4 and CD8 T cells and their phenotype were characterized by flow cytometry.ResultsId-vaccine efficiently induced antigen-specific CD4 Th activity and antitumor immunity, protecting mice from MOPC315 tumor growth. CD4 cytolytic activity was not detected under these conditions. Polyfunctional CD8 T cells homed to the bone marrow microenvironment of protected mice and preferentially expanded only when restimulated ex vivo with both Id peptide and MOPC315 cells. Protective activity was abrogated by depletion of either CD4 or CD8 lymphocytes.ConclusionThese results demonstrate that Id-HSB +poly (I:C) vaccine protects against MOPC315 growth by priming Id-specific CD4 Th cells that confer protection against tumor but are not directly cytotoxic. These data indicate that activation of CD8 CTL against MOPC315-associated antigens not present in the vaccine is one of the major mechanisms of tumor immunity.

Purpose: The type I Melanoma Antigen GEnes (MAGEs) are commonly expressed in cancers, fueling speculation that they may be therapeutic targets with oncogenic potential. They form complexes with RING domain proteins that have E3 ubiquitin ligase activity and promote p53 degradation. MAGE-A3 was detected in tumor specimens from patients with multiple myeloma and its expression correlated with higher frequencies of Ki-67+ malignant cells. In this report, we examine the mechanistic role of MAGE-A in promoting survival of proliferating multiple myeloma cells. Experimental Design: The impact of MAGE-A3 expression on survival and proliferation in vivo was examined by immunohistochemical analysis in an independent set of tumor specimens segregated into two groups: newly diagnosed, untreated patients and patients who had relapsed after chemotherapy. The mechanisms of MAGE-A3 activity were investigated in vitro by silencing its expression by short hairpin RNA interference in myeloma cell lines and primary cells and assessing the resultant effects on proliferation and apoptosis. Results: MAGE-A3 was detected in a significantly higher percentage of relapsed patients compared with newly diagnosed, establishing a novel correlation with progression of disease. Silencing of MAGE-A showed that it was dispensable for cell cycling, but was required for survival of proliferating myeloma cells. Loss of MAGE-A led to apoptosis mediated by p53-dependent activation of proapoptotic Bax expression and by reduction of survivin expression through both p53-dependent and -independent mechanisms. Conclusions: These data support a role for MAGE-A in the pathogenesis and progression of multiple myeloma by inhibiting apoptosis in proliferating myeloma cells through two novel mechanisms. Clin Cancer Res; 17(13); 4309–19. ©2011 AACR.

Type I Melanoma Antigen Genes of the MAGE-A family are commonly expressed in multiple myeloma (MM). Their frequency of expression is higher in patients who have relapsed after chemotherapy compared to newly diagnosed patients, with a significant association with progression of disease. MAGE were also associated with high-risk disease in gene expression profiling studies. They belong to the Cancer-Testis group of oncofetal genes that are normally restricted to germ cells and trophoblastic tissue, and are aberrantly expressed in a broad range of human cancers. Type I MAGE proteins partner with the RING domain protein Kap1 to form ubiquitin ligase complexes, and in laboratory models of solid tumors they ubiquitinylate cancer-associated targets involved in metabolism, autophagy, and metastasis. We demonstrated that expression of MAGE-A genes, especially MAGE-A3, was correlated with progression of disease in MM and that MAGE-A inhibit p53-dependent and independent apoptosis in MM cells. These results lead us to investigate the hypothesis that MAGE-A promote resistance to chemotherapy-induced apoptosis in MM cells. We performed gene expression profiling by RNAseq of primary tumor specimens from an open label phase 2 clinical trial of panobinostat, a pan-HDAC inhibitor approved for treatment of relapsed MM, in combination with lenalidomide and dexamethasone (NCT01651039). These GEP data were analyzed for differential expression based on progression free survival (PFS) < 90 days (short PFS) versus PFS > 90 days (long PFS). MAGE-A1 was the most overexpressed gene in the short PFS group compared to long (p Disclosures Cho: Ludwig Institute for Cancer Research: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Research Funding; Agenus, Inc.: Research Funding; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding. Chari:Takeda: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Amgen Inc.: Honoraria, Research Funding; Celgene: Consultancy, Research Funding; Array Biopharma: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Pharmacyclics: Research Funding. Jagannath:Celgene: Consultancy; Bristol-Myers Squibb: Consultancy; Janssen: Consultancy; Novartis: Consultancy; Merck: Consultancy.

Abstract 1807 The type I Melanoma Antigen GEnes MAGE-A3 and CT7 (MAGE-C1) are detected in more than 75% of primary multiple myeloma specimens, and their expression is correlated with proliferation and progression of disease. We previously showed that MAGE-A3 inhibits apoptosis in human myeloma cell lines (HMCL) and primary cells in part through ubiquitinylation of the prototypical tumor suppressor p53, which targets it for proteasomal degradation and inhibits its pro-apoptotic transcriptional program (Nardiello et al, Clin Cancer Res, 2011; 17:4309). However, silencing of MAGE-A3 in HMCL and primary cells that lacked functional p53, either through deletions or mutations, also resulted in apoptosis. Silencing of CT7 alone did not affect survival of HMCL that lacked p53, but it did increase their sensitivity to chemotherapy-induced apoptosis. Many type I MAGE proteins, including MAGE-A3, bind to the RING domain protein TRIM28/Kap1 through their highly conserved MAGE Homology Domain (MHD) to form E3 ubiquitin ligase complexes, but it was unknown if CT7 also associated with TRIM28. These results lead to the hypothesis that CT7 is a survival factor for myeloma cells that can act through p53-independent mechanisms. To investigate the biochemical activity of CT7 and identify non-p53 pathways regulated by type I MAGE in myeloma cells, we analyzed protein-protein interactions with CT7 by two methods. We immunoprecipitated (IP'ed) CT7 from lysates of HMCL followed by sequencing of co-IP'ed proteins by mass spectroscopy and we performed yeast two-hybrid screening with a bait construct containing the MHD of CT7. CT7 was reciprocally co-IP'ed from HMCL lysates with TRIM28, demonstrating that it, too, associated with this RING domain protein. These methods also revealed two novel interactions with CT7. CT7 reciprocally co-IP'ed with STAT1, a transcription factor that plays a critical role in receptor-mediated signaling for cytokines such as interferon α/β. CT7 also interacted with Protein Inhibitor of Activated STAT y (PIASy), a modified RING domain protein that negatively regulates STAT proteins through its Small Ubiquitin-like MOdifier (SUMO) ligase activity, which sequesters target proteins out of the nucleus and into the cytoplasm. Surprisingly, phosphorylated STAT1 (pSTAT1) was detected in lysates from unstimulated HMCL, indicating a tonic level of activation, but most or all of the pSTAT1 was in the cytoplasm, suggesting that its transcriptional activity was being blocked through exclusion from the nucleus. Phospho-STAT1 also appeared to preferentially associate with the CT7/TRIM28 complex. Phospho-STAT1 did not appear to be ubiquitinylated in these HMCL, but SUMO2/3 modification of pSTAT1 was detected. These results suggest that CT7 negatively regulates pSTAT1 activity in HMCL by sequestering the transcription factor out of the nucleus through SUMO modification. This may be a direct result of CT7-mediated SUMOylation in partnership with PIASy, or indirectly due to CT7/TRIM28-mediated ubiquitinylation events that result in activation of a SUMO ligase such as PIASy. These findings suggest the possibility that complexes containing type I MAGE proteins may also have SUMO ligase activity and identify STAT1 as a novel non-p53 biochemical pathway regulated by these genes. Disclosures: No relevant conflicts of interest to declare.

Abstract 785 The type I Melanoma Antigen GEne (MAGE) MAGE-A3 is commonly present in primary multiple myeloma cells and its expression is correlated with advanced disease and proliferation. MAGE-A3 belongs to the Cancer-Testis antigen (CTAg) family of tumor-associated proteins, which are present in many cancers, but their normal expression is limited to developing germ cells and placental trophoblast. This unique expression pattern fuels speculation on a role for CTAg in oncogenesis; however, very little is known about their function. In gene expression analyses of primary myeloma cells, CTAg were associated with proliferative gene signatures and poor clinical outcome, suggesting they contribute to the pathogenesis or progression of this disease through effects on survival and/or proliferation of myeloma cells. To investigate this, we examined the impact of MAGE-A on disease progression, proliferation, and apoptosis in primary myeloma specimens and human myeloma cell lines (HMCL). MAGE-A3 protein expression was examined by immunohistochemistry in a new, independent set of myeloma bone marrow specimens from two critical clinical milestones, newly diagnosed, untreated patients and patients who relapsed after chemotherapy. MAGE-A3 was detected in a higher percentage of tumor specimens from relapsed patients (77%) compared to those from newly diagnosed patients (36%, p=0.0003). The percentage of proliferating myeloma cells, as measured by staining for the proliferation marker Ki-67, was significantly higher in relapsed specimens (19.0 ± 3.5%) compared to newly diagnosed (6.9 ± 1.3%, p=0.0002), demonstrating a correlation between MAGE-A3, progression of disease and proliferation. The mechanisms for MAGE-A3 activity were investigated by silencing this gene in primary myeloma cells and HMCL by shRNA interference. Targeted lentiviral shRNA transduction efficiently knocked down MAGE-A3 mRNA and protein in MM.1r (p53+/+) and ARP-1 (p53−/−) HMCL and in primary myeloma cells by 48 hours, and this effect was maintained up to 96 hours. Silencing of MAGE-A did not affect cell cycling, as this intervention did not affect the phosphorylation of the Retinoblastoma gene product (Rb) that is required for progression through the G1 cell cycle checkpoints and entry into S phase. In contrast, MAGE-A was required for survival of proliferating myeloma cells. Silencing of MAGE-A led to a precipitous loss of viable cells within 48–72 hrs compared to controls. This was due to activation of intrinsic apoptosis, as demonstrated by increased annexin V staining, loss of mitochondrial membrane polarization, and cleavage/activation of caspase-9. These effects of MAGE-A knock-down were completely reversed by the pan-caspase inhibitor Quinoline-Val-Asp-CH2-OPh. Apoptosis after MAGE-A silencing appeared to be mediated by at least two distinct mechanisms; p53-dependent activation of pro-apoptotic Bax and Bak expression and reduced expression of the Inhibitor of Apoptosis Protein survivin through both p53-dependent and independent mechanisms. These results demonstrate that MAGE-A plays a role in the survival of proliferating multiple myeloma cells through the regulation of two critical apoptotic mechanisms. Disclosures: No relevant conflicts of interest to declare.