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CD19-specific KIR-CAR/Dap12 shows antigen-specific cytotoxicity in vitro.

SS1-KIRS2 does not affect endogenous TCR expression.

Figure legends for supplemental data.

SS1-KIRS2/DAP12 T cells mediate robust anti-tumor activity in vivo.

Chimeric antigen receptors (CAR) bearing an antigen-binding domain linked in cis to the cytoplasmic domains of CD3ζ and costimulatory receptors have provided a potent method for engineering T-cell cytotoxicity toward B-cell leukemia and lymphoma. However, resistance to immunotherapy due to loss of T-cell effector function remains a significant barrier, especially in solid malignancies. We describe an alternative chimeric immunoreceptor design in which we have fused a single-chain variable fragment for antigen recognition to the transmembrane and cytoplasmic domains of KIR2DS2, a stimulatory killer immunoglobulin-like receptor (KIR). We show that this simple, KIR-based CAR (KIR-CAR) triggers robust antigen-specific proliferation and effector function in vitro when introduced into human T cells with DAP12, an immunotyrosine-based activation motifs-containing adaptor. T cells modified to express a KIR-CAR and DAP12 exhibit superior antitumor activity compared with standard first- and second-generation CD3ζ-based CARs in a xenograft model of mesothelioma highly resistant to immunotherapy. The enhanced antitumor activity is associated with improved retention of chimeric immunoreceptor expression and improved effector function of isolated tumor-infiltrating lymphocytes. These results support the exploration of KIR-CARs for adoptive T-cell immunotherapy, particularly in immunotherapy-resistant solid tumors. Cancer Immunol Res; 3(7); 815–26. ©2015 AACR.

Cytotoxicity induced by SS1-KIRS2, but not receptor expression at the cell surface, depends upon DAP12 co-expression.

Mesothelin-specific CD3ζ CARs and SS1-KIRS2/Dap12 show comparable antigen-specific in vitro cytotoxicity toward EM-meso cells.

FAP-specific KIR-CAR/Dap12 T cells induce bone marrow hypocellularity and loss of body weight.

Prior to adoptive transfer, CAR T cells are activated, lentivirally infected with CAR transgenes, and expanded over 9 to 11 days. An unintended consequence of this process is the progressive differentiation of CAR T cells over time in culture. Differentiated T cells engraft poorly, which limits their ability to persist and provide sustained tumor control in hematologic as well as solid tumors. Solid tumors include other barriers to CAR T cell therapies, including immune and metabolic checkpoints that suppress effector function and durability. Sialic acids are ubiquitous surface molecules with known immune checkpoint functions. The enzyme C. perfringens neuraminidase (CpNA) removes sialic acid residues from target cells, with good activity at physiologic conditions. In combination with galactose oxidase (GO), NA has been found to stimulate T cell mitogenesis and cytotoxicity in vitro. Here we determine whether CpNA alone and in combination with GO promotes CAR T cell antitumor efficacy. We show that CpNA restrains CAR T cell differentiation during ex vivo culture, giving rise to progeny with enhanced therapeutic potential. CAR T cells expressing CpNA have superior effector function and cytotoxicity in vitro. In a Nalm-6 xenograft model of leukemia, CAR T cells expressing CpNA show enhanced antitumor efficacy. Arming CAR T cells with CpNA also enhanced tumor control in xenograft models of glioblastoma as well as a syngeneic model of melanoma. Given our findings, we hypothesize that charge repulsion via surface glycans is a regulatory parameter influencing differentiation. As T cells engage target cells within tumors and undergo constitutive activation through their CARs, critical thresholds of negative charge may impede cell-cell interactions underlying synapse formation and cytolysis. Removing the dense pool of negative cell-surface charge with CpNA is an effective approach to limit CAR T cell differentiation and enhance overall persistence and efficacy.

Central to protective humoral immunity is the activation of B cells and their terminal differentiation into antibody-secreting plasma cells. Long-lived plasma cells (LLPC) may survive for years to decades. Such long-lived plasma cells are also responsible for producing pathogenic antibodies that cause a variety of challenges such as autoimmunity, allograft rejection, and drug neutralization. Up to now, various therapeutic strategies aimed at durably eliminating pathogenic antibodies have failed, in large part due to their inability to efficiently target LLPCs. Several antibody-based therapies have recently gained regulatory approval or are in clinical phases of development for the treatment of multiple myeloma, a malignancy of plasma cells. We discuss the exciting potential of using these emerging cancer immunotherapies to solve the antibody problem.

CD19-directed chimeric antigen receptor (CAR) T cells show characteristic proliferation kinetics after infusion that correlate with response. Clearance of circulating disease, B-cell aplasia (BCA), and cytokine release syndrome (CRS) are used to observe CAR T-cell function, given the lack of commercial CAR T-cell measurement assays. We investigated the utility of common hematology laboratory parameters in 166 patients with B-cell acute lymphoblastic leukemia (B-ALL) who were treated with CAR T-cell therapy targeting CD19. CAR T-cell infusion was followed by disappearance of circulating blasts in 86% of patients at a median of 6 days. After a lag phase, there was a rapid expansion in absolute lymphocyte count (ALC) in the second week that coincided with the appearance of atypical lymphocytes. The expansion phase was followed by a contraction phase with a concomitant decrease in atypical lymphocytes. In vitro CAR T-cell studies showed similar kinetics and morphological changes. Peak ALC and overall expansion was greater in sustained responders compared with that in nonresponders. Patients with early loss of BCA and those with eventual CD19+ minimal residual disease/relapse showed lower overall lymphocyte expansion compared with the controls. Pleomorphic lymphocytosis was noted in the cerebrospinal fluid at post-CAR time points. We conclude that lymphocyte counts and differential can also be used to evaluate CAR T-cell expansion after infusion, along with BCA and CRS. This is the first report to characterize the morphology of CAR T cells and determine the utility of lymphocyte kinetics.

Introduction: B-cell depletion has been shown to be an effective strategy for the majority of patients with membranous nephropathy (MN), and in PLA2R-positive MN, immunologic remission (improvement or elimination of measurable serum anti-PLA2R antibodies) precedes renal remission. Yet, cases exist of patients who do not achieve immunologic remission despite achieving peripheral B-cell depletion. This has led to the hypothesis that some patients have plasma cells that are responsible for producing anti-PLA2R antibodies. Case Presentation: A 66-year-old man with a past medical history of hypertension, hyperlipidemia, and cerebrovascular disease presented with nephrotic syndrome and was diagnosed with PLA2R-positive MN on kidney biopsy. He was refractory to multiple therapies including tacrolimus, and was resistant to rituximab despite having achieved B-cell depletion. He also did not enter into remission with plasmapharesis and cyclophosphamide. He then achieved immediate immunologic remission after treatment with the proteasome inhibitor bortezomib, which is used as first-line therapy for multiple myeloma. Discussion/Conclusion: This case suggests that considering the source of PLA2R antibody production could lead to individualized and targeted therapies for MN.

Key Points HLA-specific alloantibodies can be maintained despite profound CD19+ cell aplasia, likely due to production by CD19− plasma cells.

This cohort study examines the ability of patients receiving chimeric antigen receptor T-cell treatments to mount T-cell immunity in response to messenger RNA vaccines for severe acute respiratory syndrome coronavirus 2 despite substantial B-cell depletion.

Chimeric antigen receptor (CAR) T cells have induced remarkable antitumor responses in B cell malignancies. Some patients do not respond because of T cell deficiencies that hamper the expansion, persistence, and effector function of these cells. We used longitudinal immune profiling to identify phenotypic and pharmacodynamic changes in CD19-directed CAR T cells in patients with chronic lymphocytic leukemia (CLL). CAR expression maintenance was also investigated because this can affect response durability. CAR T cell failure was accompanied by preexisting T cell-intrinsic defects or dysfunction acquired after infusion. In a small subset of patients, CAR silencing was observed coincident with leukemia relapse. Using a small molecule inhibitor, we demonstrated that the bromodomain and extra-terminal (BET) family of chromatin adapters plays a role in downregulating CAR expression. BET protein blockade also ameliorated CAR T cell exhaustion as manifested by inhibitory receptor reduction, enhanced metabolic fitness, increased proliferative capacity, and enriched transcriptomic signatures of T cell reinvigoration. BET inhibition decreased levels of the TET2 methylcytosine dioxygenase, and forced expression of the TET2 catalytic domain eliminated the potency-enhancing effects of BET protein targeting in CAR T cells, providing a mechanism linking BET proteins and T cell dysfunction. Thus, modulating BET epigenetic readers may improve the efficacy of cell-based immunotherapies.

Pre-existing allo-antibodies (allo-Abs), that preclude transplant due to the risk of hyperacute rejection, lead to prolonged wait times and high mortality rates. Current desensitization approaches are ineffective as they do not adequately deplete allo-specific B cells and plasma cells (PCs). We hypothesize that stringent depletion of these cells is required to eliminate pre-existing allo-Abs. We leverage the exquisite ability of CAR T cells to eliminate target cells to desensitize transplant candidates. We constructed CARs targeting murine CD19 or BCMA, which cover the entire B cell-PC continuum. We first evaluated the function of CAR T cells against B cells and PCs in vitro. C57BL/6 mice were sensitized with BALB/c skin grafts. After skin rejection, sensitized mice received total body irradiation followed by treatment with either control T cells, CART-19 T cells, or a combination of CART-19 and CART-BCMA T cells (combo-CART). Allo-Abs, total Ig, and B cells were measured over 13 weeks. Functional desensitization was then assessed by induction of diabetes followed by BALB/c-derived islet cell transplant and glucose were measured to assess graft survival. CD19- and BCMA-targeted CARs effectively depleted primary B cells and PCs in vitro and in vivo. Control and CART-19 T cells were ineffective at desensitizing mice, but combo-CART treatment resulted in significant decrease of allo-Abs. Islet cell grafts succumbed to hyperacute rejection in 80% of control and CART-19 treated mice. However, combo-CART treatment resulted in prolonged graft survival in all mice (mean 35 days, range 16–60). Thus, CAR T cells targeting B cell and PC antigens represent a promising approach to desensitization and could enable lifesaving transplantation.

Adoptive transfer of chimeric antigen receptor regulatory T cells (CAR Tregs) is a promising way to prevent allograft loss without the morbidity associated with current therapies. Non-human primates (NHPs) are a clinically relevant model to develop transplant regimens, but manufacturing and engraftment of NHP CAR Tregs have not been demonstrated yet. Here, we describe a culture system that massively expands CAR Tregs specific for the Bw6 alloantigen. In vitro, these Tregs suppress in an antigen-specific manner without pro-inflammatory cytokine secretion or cytotoxicity. In vivo, Bw6-specific CAR Tregs preferentially traffic to and persist in bone marrow for at least 1 month. Following transplant of allogeneic Bw6

Though islet transplantation has emerged as a promising therapeutic for type 1 diabetes, the immunosuppressive agents that prevent rejection carry significant risk of morbidity. Adoptive transfer of chimeric antigen receptor (CAR) Tregs has the potential to protect allografts and transform transplantation medicine in the way that CAR T cells have revolutionized the treatment of cancer. However, there lacks a large animal model in which to optimize the safety and efficacy of CAR Treg therapy. Therefore, we developed methods to sort, transduce, and expand Cynomolgus macaque CAR Tregs recognizing the human/non-human primate cross-reactive alloantigen Bw6. Our novel pan-primate artificial antigen presenting cells expanded Tregs to clinical sized doses of >500 million cells from as few as 25k sorted cells. Expanded Tregs expressed protein and epigenetic markers indicative of stable CAR Tregs and displayed suppressor function without cytotoxicity. CAR Tregs transferred into an antigen negative recipient could be detected for 7 days in peripheral blood and 1 month in bone marrow. When transferred to a diabetic recipient simultaneously with allogeneic Bw6+ islets, islets were partially protected from rejection as measured by increased control of blood glucose with insulin treatment. Transferred Tregs persisted in peripheral blood for >34 days while displaying markers of stable, activated Tregs including CAR, FoxP3, and Helios. Importantly, we could not detect CAR+ FoxP3− effector T cells which would target the graft and expedite graft rejection. Our results provide a proof of concept for CAR Treg adoptive therapy in a large animal model and establish a framework for optimization of therapy before a clinical trial in humans.

Approaches to harness the immune system to alleviate disease have become remarkably sophisticated since the crude, yet impressively-effective, attempts using live bacteria in the late 1800s. Recent evidence that engineered T cell therapy can deliver durable results in patients with cancer has spurred frenzied development in the field of T cell therapy. The myriad approaches include an innumerable variety of synthetic transgenes, multiplex gene-editing, and broader application to diseases beyond cancer. In this article, we review the preclinical studies and over a decade of clinical experience with engineered conventional T cells that have paved the way for translating engineered regulatory T cell therapies.

Metastatic medullary thyroid cancer (MTC) is a rare but often aggressive thyroid malignancy with a 5-year survival rate of less than 40% and few effective therapeutic options. Adoptive T cell immunotherapy using chimeric antigen receptor (CAR)-modified T cells (CAR Ts) is showing encouraging results in the treatment of cancer, but development is challenged by the availability of suitable target antigens. We identified glial-derived neurotrophic factor (GDNF) family receptor alpha 4 (GFRα4) as a putative antigen target for CAR-based therapy of MTC. We show that GFRα4 is highly expressed in MTC, in parafollicular cells within the thyroid from which MTC originates, and in normal thymus. We isolated two single-chain variable fragments (scFvs) targeting GFRα4 isoforms a and b by antibody phage display. CARs bearing the CD3ζ and the CD137 costimulatory domains were constructed using these GFRα4-specific scFvs. GFRα4-specific CAR Ts trigger antigen-dependent cytotoxicity and cytokine production in vitro, and they are able to eliminate tumors derived from the MTC TT cell line in an immunodeficient mouse xenograft model of MTC. These data demonstrate the feasibility of targeting GFRα4 by CAR T and support this antigen as a promising target for adoptive T cell immunotherapy and other antibody-based therapies for MTC., Graphical Abstract, Metastatic medullary thyroid carcinoma (MTC) is a rare but aggressive malignancy with no curative options. By sequencing mRNA from a patient’s tumor, Siegel and colleagues identified and characterized GFRα4 as a promising tumor target antigen and demonstrated that CAR T immunotherapy targeting this antigen controlled MTC in tumor xenograft models.

Vaccine-mediated immunity often relies on the generation of protective antibodies and memory B cells, which commonly stem from germinal center (GC) reactions. An in-depth comparison of the GC responses elicited by SARS-CoV-2 mRNA vaccines in healthy and immunocompromised individuals has not yet been performed due to the challenge of directly probing human lymph nodes. Herein, through a fine-needle-aspiration-based approach, we profiled the immune responses to SARS-CoV-2 mRNA vaccines in lymph nodes of healthy individuals and kidney transplant recipients (KTXs). We found that, unlike healthy subjects, KTXs presented deeply blunted SARS-CoV-2-specific GC B cell responses coupled with severely hindered T follicular helper cell, SARS-CoV-2 receptor-binding-domain-specific memory B cell and neutralizing antibody responses. KTXs also displayed reduced SARS-CoV-2-specific CD4 and CD8 T cell frequencies. Broadly, these data indicate impaired GC-derived immunity in immunocompromised individuals, and suggest a GC-origin for certain humoral and memory B cell responses following mRNA vaccination., Graphical Abstract, Fine needle aspiration of lymph nodes in humans, reveals that SARS-CoV-2 vaccination induces neutralizing antibody-producing germinal centers, enhanced by repeated vaccination. Conversely, in patients receiving immunosuppressant medication, this process is disrupted resulting in stunted protective immune responses highlighting issues about vaccine and booster efficacy in patients with compromised immune systems.

Adoptive cellular therapy using T cells with tumor specificity derived from either natural T cell receptors (TCRs) or an artificial chimeric antigen receptor (CAR) has reached late phase clinical testing, with two CAR T cell therapies achieving regulatory approval within the United States in 2017. The effective use of these therapies depends upon an understanding of their pharmacology, which is quite divergent from traditional small molecule or biologic drugs. We review the different types of T cell therapy under clinical development, the factors affecting cellular kinetics following infusion, and the relationship between these cellular kinetics and anti-cancer activity. We also discuss the toxicity associated with T cell therapies, with an emphasis on cytokine release syndrome and neurotoxicity, and the gaps in knowledge regarding these frequent and unique adverse effects.

Abstract Background: The two FDA approved mRNA-based SARS-CoV2 vaccines have shown >90% efficacy at preventing COVID and eliciting protective immunity in nearly all healthy individuals. However, the extent of vaccine induced antibody and T cell immunity in immunocompromised patients is not well known. Our study objective is to determine if patients with hematologic malignancies treated with B-cell targeting chimeric antigen receptor (CAR) T cell therapies can mount antibody and T cell immune responses to SARS-CoV2 vaccines. A prospective single-center study to evaluate the SARS-CoV2 immune responses in immunocompromised individuals (COVAX Study) was initiated at University of Pennsylvania following the IRB guidelines. The study enrolled 8 healthy adults,12 patients are in remission after treatment (average of 40.6 months) with CART cells targeting either CD19 or CD19+CD22 and received both doses of SARS-CoV2 vaccine. Methods and Results: Serology to SARS-CoV2 spike-receptor binding domain (RBD) IgG, RBD-IgA, RBD-IgM and spike-specific T cell responses were measured prior to vaccination and serially up to 28 days after booster vaccination. RBD-IgG and RBD-IgA were detected in 8/8 and 7/8 healthy subjects compared to 5/12 and 2/12 CART patients, respectively (Figure A). In the CART cohort, several patients who demonstrated an induction of RBD-IgG (57.2/uL +/- 20.2) compared to those who were RBD-IgG-negative (9/uL +/- 10.1, ANOVA with multiple comparisons test p=0.017) have higher level of circulating B cells. No association was found with time since CART infusion, age, disease type, or vaccine manufacturer. All 8 healthy subjects demonstrated induction of SARS-Cov2 spike-specific CD4 + T cell immunity compared to 7 out of 11 CART patients (Figure B). RBD-IgG responses were not correlated with CD4 + T cell activation (Pearson correlation, R=0.21, p=0.53). Indeed, 3 CART patients demonstrated robust CD4 + T cell activation despite absence of antibody induction. Overall, 8/12 CART patients demonstrated induction of either or both humoral and T cell immune responses. Conclusions: We show that immune responses to SARS-CoV2 mRNA vaccines are induced in majority of patients who have been treated with CART therapies targeting B-cell lineage antigens. Induction of vaccine-specific antibody was strongly associated with the level of circulating B cells. However, in CART cohort patients despite severe humoral immune deficiency, strong CD4 + T cell responses were observed suggestive of a sufficient protective immunity. Figure 1 Figure 1. Disclosures Frey: Novartis: Research Funding; Sana Biotechnology: Consultancy; Kite Pharma: Consultancy; Syndax Pharmaceuticals: Consultancy. Garfall: Amgen: Honoraria; CRISPR Therapeutics: Research Funding; GlaxoSmithKline: Honoraria; Janssen: Honoraria, Research Funding; Novartis: Research Funding; Tmunity: Research Funding. Porter: American Society for Transplantation and Cellular Therapy: Honoraria; Genentech: Current equity holder in publicly-traded company, Ended employment in the past 24 months; ASH: Membership on an entity's Board of Directors or advisory committees; DeCart: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Kite/Gilead: Membership on an entity's Board of Directors or advisory committees; National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Tmunity: Patents & Royalties; Wiley and Sons Publishing: Honoraria. June: AC Immune, DeCART, BluesphereBio, Carisma, Cellares, Celldex, Cabaletta, Poseida, Verismo, Ziopharm: Consultancy; Tmunity, DeCART, BluesphereBio, Carisma, Cellares, Celldex, Cabaletta, Poseida, Verismo, Ziopharm: Current equity holder in publicly-traded company; Novartis: Patents & Royalties.

The development of inhibitors to Factor VIII (FVIII) is a major complication of hemophilia A (HA) treatment. Most preclinical studies in HA animals have been limited to a xenoprotein response, e.g., evaluating the murine immune response to human FVIII (hFVIII). Severe HA dogs are a naturally occurring outbred model that recapitulates the spontaneous bleeding phenotype of the disease; their severe HA is due to intron 22 inversion (INV22) of the canine F8 gene, analogous to the INV22 found in 45% of severe HA patients. Importantly, similar to HA INV22 patients, about 20% of these animals develop an anti-canine FVIII (cFVIII) inhibitor response. This ability of the HA dogs to develop inhibitors in a species-specific manner provides an opportunity to probe the molecular ontogeny of an alloimmune anti-FVIII response. Here, we use antibody phage display to capture the humoral anti-cFVIII IgG repertoire in a dog with severe HA. This dog developed and maintained high titers of cFVIII inhibitor (89 Bethesda Units, BU) after exposure to cFVIII protein. The dog then received AAV liver-directed gene therapy encoding a cFVIII transgene, and after an initial anamnestic response characterized by rapid increase of cFVIII inhibitor titer (peak titer of 182 BU), the dog exhibited successful inhibitor eradication and immune tolerance induction, similar to our previous report (Finn et al., Blood 2010). Canine peripheral blood mononuclear cells were used to construct a single-chain variable fragment (scFv) phage display library which was sequentially selected four times against immobilized recombinant B-domain deleted (BDD) cFVIII protein. The amount of enrichment per round of selection plateaued during the third round from which 55 scFv/phage clones were isolated for characterization. Individual phage clones were sequenced by Sanger sequencing and screened for binding to both canine and human BDD-FVIII by ELISA. ScFv/phage clones were tested for inhibitory activity in a modified Bethesda assay. We identified 26 distinct scFv clones binding cFVIII based on heavy chain/light chain composition comprising 16 distinct CDRH3 sequences and 23 distinct CDRL3 sequences. The heavy chains of the 26 clones were derived from six canine germline IGHV genes, namely IGHV3-2, IGHV3-5, IGHV3-9, IGHV3-19, IGHV3-38, and IGHV3-41. The 16 distinct CDRH3 sequences had a mean length of 10.1 ± 3.6 amino acids, shorter than the 13.5 ± 3.6 amino acids previously reported for total canine CDRH3 repertoires (Steiniger et al., Mol. Immunol. 2014). Only 10 of the 26 FVIII-specific clones contained a lambda light chain, despite canine IgG repertoires dominated by the use of lambda light chains (Steiniger et al.). Eight of the 26 clones exhibited inhibitory activity. Although this dog was never exposed to hFVIII, 12/26 (46%) clones bound both cFVIII and hFVIII, consistent with the high degree of homology between the two orthologues with 85% identity. For three clones, framework region mutations and different light chain pairings resulted in altered inhibitory activity and hFVIII binding. Interestingly, one clone in particular comprised the majority of randomly screened scFv from the third and fourth rounds of phage library selection. These results suggest that cFVIII-specific B cells arise from multiple germline VH genes and exhibit high CDRH3 diversity. While the IgG-FVIII interaction has previously been suggested to be mostly influenced by the IgG heavy chain, our data suggest that for some antibodies, the IgG light chain may influence both inhibitory activity and epitope reactivity. Future studies will assess B cell clonal evolution via deep sequencing and longitudinal epitope specificity during multi-year immune tolerance induction by continuous exposure to cBDD-FVIII gene therapy. This is the first in-depth assessment of FVIII immunogenicity in a large HA model that avoids the use of a non-species specific antigen. Direct comparison with ongoing studies in HA inhibitor patients will inform the immunodominant epitopes of FVIII across species and thus provide insights on FVIII immunogenicity. Disclosures Doshi: Janssen: Consultancy; Spark Therapeutics: Speakers Bureau. Samelson-Jones: Spark: Research Funding; Pfizer: Consultancy, Research Funding. Siegel: Verismo Therapeutics, Inc: Other: Co-Founder and Equity Holder; Vetigenics, LLC: Other: Co-Founder and Equity Holder.

Background: Chimeric Antigen Receptor (CAR) T cell immunotherapy has revolutionized the treatment of B-cell malignancies. However, a significant subset of these patients either fails to respond or eventually relapses. Moreover, in solid cancers, CAR T immunotherapy has had little to no success in the clinic so far. In recent years, several studies have shown the influence of commensal gut microbes on T cell function, in particular in the setting of checkpoint immunotherapy. Our group has recently demonstrated that modulation of the gut microbiota using antibiotics such as oral vancomycin (vanco) can enhance the efficacy of tumor-specific T cells in animal models. In this study, we sought to study the effect of vanco-induced dysbiosis on CART immunotherapy using murine models and clinical correlates. Methods and Results: We used the CD19+ A20 lymphoma and the B16 melanoma (transduced with CD19) murine models. Lymphoma- and melanoma-bearing mice were randomized to received oral vanco or vehicle alone (CTR), or in combination with either control untransduced murine T cells (UTD) or murine CART19 (4-1BB). Oral vanco or vehicle treatments started on the day of A20 cells injection and throughout the duration of the experiment (40-45 days). A20-bearing mice treated with CART19+vanco showed strikingly improved tumor control compared to either vanco alone or UTD+vanco (day 40 tumor volume in mm 3 (mean ± s.e.m): CTR=1,678.8±279.4, UTD=1,803.2±180, UTD+vanco=1,477±174, CART19=1,219±208, CART19+vanco=439.5±122.5 , CART versus CART+vanco Two Way Anova P Conclusions: These results suggest that the modulation of the gut microbiota using vancomycin affects the outcome of CART therapy in preclinical models with better anti-tumor effect via cross-priming and enhanced CART expansion in tumor samples. In a retrospective cohort of patients with B-ALL receiving vancomycin after CART19 therapy, we observed higher CART expansion and serum inflammatory cytokines. Based on these observations, a clinical trial of oral vanco in patients receiving CD19-directed CAR T cells for B-cell lymphomas is planned. Disclosures Ruella: viTToria biotherapeutics: Research Funding; Tmunity: Patents & Royalties; Novartis: Patents & Royalties; BMS, BAYER, GSK: Consultancy; AbClon: Consultancy, Research Funding. Frey: Novartis: Research Funding; Sana Biotechnology: Consultancy; Kite Pharma: Consultancy; Syndax Pharmaceuticals: Consultancy. June: Tmunity, DeCART, BluesphereBio, Carisma, Cellares, Celldex, Cabaletta, Poseida, Verismo, Ziopharm: Current equity holder in publicly-traded company; AC Immune, DeCART, BluesphereBio, Carisma, Cellares, Celldex, Cabaletta, Poseida, Verismo, Ziopharm: Consultancy; Novartis: Patents & Royalties. Porter: American Society for Transplantation and Cellular Therapy: Honoraria; ASH: Membership on an entity's Board of Directors or advisory committees; DeCart: Membership on an entity's Board of Directors or advisory committees; Genentech: Current Employment, Current equity holder in publicly-traded company; Incyte: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Kite/Gilead: Membership on an entity's Board of Directors or advisory committees; National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Unity: Patents & Royalties; Wiley and Sons Publishing: Honoraria. Schuster: TG Theraputics: Research Funding; Incyte: Research Funding; Adaptive Biotechnologies: Research Funding; Pharmacyclics: Research Funding; Merck: Research Funding; Genentech/Roche: Consultancy, Research Funding; Tessa Theraputics: Consultancy; Loxo Oncology: Consultancy; Juno Theraputics: Consultancy, Research Funding; BeiGene: Consultancy; Alimera Sciences: Consultancy; Acerta Pharma/AstraZeneca: Consultancy; Novartis: Consultancy, Honoraria, Patents & Royalties, Research Funding; Abbvie: Consultancy, Research Funding; Nordic Nanovector: Consultancy; Celgene: Consultancy, Honoraria, Research Funding.

Tisagenlecleucel, a chimeric antigen receptor (CAR) T-cell product targeting CD19 is approved for relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL). However, the impact of pretreatment variables, such as CD19 expression level, on leukemic blasts, the presence of CD19(–) subpopulations, and especially prior CD19-targeted therapy, on the response to CAR T-cell therapy has not been determined. We analyzed 166 patients treated with CAR T-cell therapy at our institution. Eleven patients did not achieve a minimal residual disease (MRD)(–) deep remission, whereas 67 patients had a recurrence after achieving a MRD(–) deep remission: 28 patients with CD19(+) leukemia and 39 patients with CD19(–) leukemia. Return of CD19(+) leukemia was associated with loss of CAR T-cell function, whereas CD19(–) leukemia was associated with continued CAR T-cell function. There were no significant differences in efficacy of CAR T cells in CD19-dim B-ALL, compared with CD19-normal or -bright B-ALL. Consistent with this, CAR T cells recognized and lysed cells with very low levels of CD19 expression in vitro. The presence of dim CD19 or rare CD19(–) events by flow cytometry did not predict nonresponse or recurrence after CAR T-cell therapy. However, prior therapy with the CD19-directed, bispecific T-cell engager blinatumomab was associated with a significantly higher rate of failure to achieve MRD(–) remission or subsequent loss of remission with antigen escape. Finally, immunophenotypic heterogeneity and lineage plasticity were independent of underlying clonotype and cytogenetic abnormalities.

CD19-directed immunotherapies are clinically effective for treating B cell malignancies but also cause a high incidence of neurotoxicity. A subset of patients treated with chimeric antigen receptor (CAR) Tcells or bispecific Tcell engager (BiTE) antibodies display severe neurotoxicity, including fatal cerebral edema associated with Tcell infiltration into the brain. Here, we report that mural cells, which surround the endothelium and are critical for blood-brain-barrier integrity, express CD19. We identify CD19 expression in brain mural cells using single-cell RNA sequencing data and confirm perivascular staining at the protein level. CD19 expression in the brain begins early in development alongside the emergence of mural cell lineages and persists throughout adulthood across brain regions. Mouse mural cells demonstrate lower levels of Cd19 expression, suggesting limitations in preclinical animal models of neurotoxicity. These data suggest an on-target mechanism for neurotoxicity in CD19-directed therapies and highlight the utility of human single-cell atlases for designing immunotherapies.

We report a patient relapsing 9 months after CD19-targeted CAR T cell (CTL019) infusion with CD19(-) leukemia that aberrantly expressed the anti-CD19 CAR. The CAR gene was unintentionally introduced into a single leukemic B cell during T cell manufacturing, and its product bound in cis to the CD19 epitope on the surface of leukemic cells, masking it from recognition by and conferring resistance to CTL019.

The thrombotic microangiopathy (TMA) Registry Network of North America (TRNA) is a collaborative network organized for the purpose of developing a multi-institutional registry and network to conduct clinical studies in a rare patient population. The TRNA was founded in 2013 by four academic medical centers (Columbia University Medical Center, Duke University Medical Center, University of Alabama at Birmingham, and University of Pennsylvania) to develop a national and demographically diverse dataset of patients with TMA. A clinical database was developed by network members using REDCap (Research Electronic Data Capture), a web-based database developed for clinical research. To facilitate rapid Institutional Review Board (IRB) approval at multiple sites, the TRNA utilized IRBshare, a streamlined IRB process to allow patient recruitment and enrollment into the TMA registry. This article reviews the process used to establish the TRNA network and discusses the significance of the first multi-institutional clinical apheresis network developed in the United States. J. Clin. Apheresis 31:448-453, 2016. © 2015 Wiley Periodicals, Inc.

Patients with diffuse large B-cell lymphoma or follicular lymphoma that is refractory to or that relapses after immunochemotherapy and transplantation have a poor prognosis. High response rates have been reported with the use of T cells modified by chimeric antigen receptor (CAR) that target CD19 in B-cell cancers, although data regarding B-cell lymphomas are limited.We used autologous T cells that express a CD19-directed CAR (CTL019) to treat patients with diffuse large B-cell lymphoma or follicular lymphoma that had relapsed or was refractory to previous treatments. Patients were monitored for response to treatment, toxic effects, the expansion and persistence of CTL019 cells in vivo, and immune recovery.A total of 28 adult patients with lymphoma received CTL019 cells, and 18 of 28 had a response (64%; 95% confidence interval [CI], 44 to 81). Complete remission occurred in 6 of 14 patients with diffuse large B-cell lymphoma (43%; 95% CI, 18 to 71) and 10 of 14 patients with follicular lymphoma (71%; 95% CI, 42 to 92). CTL019 cells proliferated in vivo and were detectable in the blood and bone marrow of patients who had a response and patients who did not have a response. Sustained remissions were achieved, and at a median follow-up of 28.6 months, 86% of patients with diffuse large B-cell lymphoma who had a response (95% CI, 33 to 98) and 89% of patients with follicular lymphoma who had a response (95% CI, 43 to 98) had maintained the response. Severe cytokine-release syndrome occurred in 5 patients (18%). Serious encephalopathy occurred in 3 patients (11%); 2 cases were self-limiting and 1 case was fatal. All patients in complete remission by 6 months remained in remission at 7.7 to 37.9 months (median, 29.3 months) after induction, with a sustained reappearance of B cells in 8 of 16 patients and with improvement in levels of IgG in 4 of 10 patients and of IgM in 6 of 10 patients at 6 months or later and in levels of IgA in 3 of 10 patients at 18 months or later.CTL019 cells can be effective in the treatment of relapsed or refractory diffuse large B-cell lymphoma and follicular lymphoma. High rates of durable remission were observed, with recovery of B cells and immunoglobulins in some patients. Transient encephalopathy developed in approximately one in three patients and severe cytokine-release syndrome developed in one in five patients. (Funded by Novartis and others; ClinicalTrials.gov number, NCT02030834 .).

The mechanisms underlying the maintenance of long-lasting humoral immunity are not well understood. Studies in mice indicate that plasma cells (PCs) can survive up to a lifetime, even in the absence of regeneration by B cells, implying the presence of long-lived PCs as a mechanism for long-lasting immunity. Evidence from humans treated with anti-CD20, which depletes circulating B cells, also suggests B-cell-independent long-term survival of some PCs. On the other hand, antibody responses may be sustained solely by short-lived PCs with repopulation from clonally related memory B cells. To explore PC longevity and humoral immunity in humans, we investigated the fate of PCs and their antibodies in adult and pediatric patients who received chimeric antigen receptor-based adoptive T-cell immunotherapy targeting CD19 to treat B-cell lineage malignancies (CTL019). Treatment with CTL019 is frequently associated with B-cell aplasia that can persist for years. Serum antibody titers to vaccine-related antigens were measured, and quantitative assessment of B cells and PCs in blood and bone marrow was performed at various time points before and after CTL019 therapy. While total serum immunoglobulin concentrations decline following CTL019-induced B-cell aplasia, several vaccine/pathogen-specific serum immunoglobulin G and A (IgG and IgA) titers remain relatively stable for at least 6 and 12 months posttreatment, respectively. Analysis of bone marrow biopsies after CTL019 revealed 8 patients with persistence of antibody-secreting PCs at least 25 months post-CTL019 infusion despite absence of CD19(+)CD20(+) B cells. These results provide strong evidence for the existence of memory B-cell-independent, long-lived PCs in humans that contribute to long-lasting humoral immunity.

Hemophilia A (HA) is a X-linked bleeding disorder caused by deficiency of coagulation factor VIII (FVIII). Optimal clinical management centers on FVIII protein concentrate replacement. However, up to 30% of patients with severe HA develop neutralizing antibodies to FVIII (inhibitors) upon exposure to therapeutic FVIII. Inhibitors neutralize the infused FVIII and, thus, pose a significant challenge in the management of these patients. Immune tolerance induction (ITI) using high-dose FVIII infusions can eliminate inhibitors but is not effective at generating long-term eradication in all patients. Thus, we developed an immunotherapy to more effectively eliminate FVIII-specific B cells to induce lasting eradication of inhibitors. Adoptive T cell immunotherapies using chimeric antigen receptor (CAR)-modified T cells (CARTs) are showing encouraging results in the treatment of cancer. We previously reported a proof-of-concept CART approach to eliminate autoantibodies to desmoglein-3, implicated in pemphigus vulgaris, by targeting non-malignant B cells. Here, using a similar strategy, we constructed two FVIII-based CARs using isolated FVIII A2 and C2 domains, which are commonly targeted by inhibitors Both FVIII fragments were used as the CAR extracellular domain followed by CD8a-derived hinge and transmembrane domains and intracellular signaling domains derived from 4-1BB and CD3z (BBz), as has been used in a recently FDA-approved CD19-targeted CAR (CART19) that have shown efficacy in patients. A2- and C2-CARs were introduced into primary human T cells using lentivirus vectors and were found to express on the cell surface. Primary expansion following anti-CD3/CD28 activation and lentivirus transduction yielded comparable population doublings of CART19 and A2-CARTs over 9-11 days (mean, 4.3 vs. 3.7; p=0.16). However, C2-CARTs consistently achieved fewer doublings compared to CART19 (mean 4.3 vs. 2.6; p=0.01). Additionally, C2-CARTs maintained larger cell volumes following initial activation compared to A2 and CART19, reminiscent of other CARs that demonstrate a high-level of ligand-independent basal activation. Consistent with hyper-activation and activation-induced cell death, flow cytometric analysis of C2-CART cultures showed prolonged expression of CD69, increased levels of cell death, and gradual loss of CAR+ cells compared to A2 and CART19 cultures. The FVIII C2 domain contains hydrophobic surfaces involved in binding to phospholipid membranes and von Willebrand Factor. We hypothesized that these hydrophobic regions may cause unfavorable interactions that result in CAR clustering and, in-turn, ligand-independent signaling. However, since these regions are also targeted by FVIII inhibitors, mutation of hydrophobic residues to improve CAR function would likely result in loss of binding to intended targets. Thus, we tested two independent strategies to improve function of C2-CARTs, both of which maintain native FVIII domain sequences. First, to block unfavorable interactions with C2 hydrophobic surfaces, we tested whether addition of C2 domain specific antibodies to the CART culture would improve expansion. Indeed, addition of anti-C2 antibodies improved C2-CART expansion by approximately one population doubling and reduced both cell volume and CD69 expression in C2-CARTs. As an alternate and perhaps more easily translatable approach, we replaced the BBz CAR signaling domain with a killer immunoglobulin receptor (KIR)-based multi-chain signaling system, which we previously utilized to improve function of a mesothelin-targeted CAR. KIR-based signaling effectively "rescued" the C2 CAR, and showed an expansion and activation profile comparable to CART19. Lastly, KIR-based FVIII CARs, demonstrated specific lysis of and cytokine response to target cells engineered to express surface anti-FVIII, even in the presence of soluble inhibitors. These data indicate that unfavorable interactions may be ameliorated directly by blocking agents or, indirectly, by altering intracellular signal transduction domains. These strategies have allowed us to construct optimized FVIII-based CARTs to target FVIII-specific B cells that are responsible for producing FVIII inhibitors in patients with HA. Disclosures Doshi: Bayer Hemophilia Awards Program: Research Funding. Milone:Novartis: Patents & Royalties.

Protein ubiquitylation has emerged as a key mechanism that regulates immune responses. Much like phosphorylation, ubiquitylation is a reversible covalent modification that regulates the stability, activity and localization of target proteins. As such, ubiquitylation regulates the development of the immune system and many phases of the immune response, including its initiation, propagation and termination. Recent work has shown that several ubiquitin ligases help to prevent the immune system from attacking self tissues. The dysfunction of several ubiquitin ligases has been linked to autoimmune diseases.

Skin keratinocytes provide a first line of defense against invading microorganisms in two ways: (i) by acting as a physical barrier to pathogen entry and (ii) by initiating a vigorous innate immune response upon sensing danger signals. How keratinocytes detect virus infections and generate antiviral immune responses is not well understood. Orthopoxviruses are dermatotropic DNA viruses that cause lethal disease in humans. Virulence in animal models depends on the virus-encoded bifunctional Z-DNA/double-stranded RNA (dsRNA)-binding protein E3. Here, we report that infection of mouse primary keratinocytes with a vaccinia ΔE3L mutant virus triggers the production of beta interferon (IFN-β), interleukin-6 (IL-6), CCL4, and CCL5. None of these immune mediators is produced by keratinocytes infected with wild-type vaccinia virus. The dsRNA-binding domain of E3 suffices to prevent activation of the innate immune response. ΔE3L induction of IFN-β, IL-6, CCL4, and CCL5 secretion requires mitochondrial antiviral signaling protein (MAVS; an adaptor for the cytoplasmic viral RNA sensors RIG-I and MDA5) and the transcription factor IRF3. IRF3 phosphorylation is induced in keratinocytes infected with ΔE3L, an event that depends on MAVS. The response of keratinocytes to ΔE3L is unaffected by genetic ablation of Toll-like receptor 3 (TLR3), TRIF, TLR9, and MyD88.

Lipoprotein apheresis is an extracorporeal therapy whereby apo B-containing lipoproteins (LDL, vLDL, and Lp(a)) are selectively removed from the plasma of a patient. It is a variation of plasma exchange, which non-selectively removes all plasma proteins. Lipoprotein apheresis is most commonly used to treat patients with familial hypercholesterolemia, but is also often used for other hyperlipidemic patients, including those with elevated Lp(a), to limit and/or reverse the atherosclerotic complications of high cholesterol. Herein, we provide an overview of lipoprotein apheresis including indications, techniques, efficacy, and adverse events, as well as guidelines and other considerations important for selection of patients for this therapy.

Chimeric antigen receptors (CAR) bearing an antigen-binding domain linked in cis to the cytoplasmic domains of CD3ζ and costimulatory receptors have provided a potent method for engineering T-cell cytotoxicity toward B-cell leukemia and lymphoma. However, resistance to immunotherapy due to loss of T-cell effector function remains a significant barrier, especially in solid malignancies. We describe an alternative chimeric immunoreceptor design in which we have fused a single-chain variable fragment for antigen recognition to the transmembrane and cytoplasmic domains of KIR2DS2, a stimulatory killer immunoglobulin-like receptor (KIR). We show that this simple, KIR-based CAR (KIR-CAR) triggers robust antigen-specific proliferation and effector function in vitro when introduced into human T cells with DAP12, an immunotyrosine-based activation motifs-containing adaptor. T cells modified to express a KIR-CAR and DAP12 exhibit superior antitumor activity compared with standard first- and second-generation CD3ζ-based CARs in a xenograft model of mesothelioma highly resistant to immunotherapy. The enhanced antitumor activity is associated with improved retention of chimeric immunoreceptor expression and improved effector function of isolated tumor-infiltrating lymphocytes. These results support the exploration of KIR-CARs for adoptive T-cell immunotherapy, particularly in immunotherapy-resistant solid tumors. Cancer Immunol Res; 3(7); 815–26. ©2015 AACR.

In the setting of autoimmunity, one of the goals of successful therapeutic immune modulation is the induction of peripheral tolerance, a large part of which is mediated by regulatory/suppressor T cells. In this report, we demonstrate a novel immunomodulatory mechanism by an FDA-approved, exogenous peptide-based therapy that incites an HLA class I-restricted, cytotoxic suppressor CD8+ T cell response. We have shown previously that treatment of multiple sclerosis (MS) with glatiramer acetate (GA; Copaxone) induces differential up-regulation of GA-reactive CD8+ T cell responses. We now show that these GA-induced CD8+ T cells are regulatory/suppressor in nature. Untreated patients show overall deficit in CD8+ T cell-mediated suppression, compared with healthy subjects. GA therapy significantly enhances this suppressive ability, which is mediated by cell contact-dependent mechanisms. CD8+ T cells from GA-treated patients and healthy subjects, but not those from untreated patients with MS, exhibit potent, HLA class I-restricted, GA-specific cytotoxicity. We further show that these GA-induced cytotoxic CD8+ T cells can directly kill CD4+ T cells in a GA-specific manner. Killing is enhanced by preactivation of target CD4+ T cells and may depend on presentation of GA through HLA-E. Thus, we demonstrate that GA therapy induces a suppressor/cytotoxic CD8+ T cell response, which is capable of modulating in vivo immune responses during ongoing therapy. These studies not only explain several prior observations relating to the mechanism of this drug but also provide important insights into the natural immune interplay underlying this human immune-mediated disease.

Innate cellular production of IFN-γ is suppressed after repeated exposure to LPS, whereas CpG-containing DNA potentiates IFN-γ production. We compared the modulatory effects of LPS and CpG on specific cellular and cytokine responses necessary for NK-cell dependent IFN-γ synthesis. C3H/HeN mice pretreated with LPS for 2 days generated 5-fold less circulating IL-12 p70 and IFN-γ in response to subsequent LPS challenge than did challenged control mice. In contrast, CpG-pretreated mice produced 10-fold more circulating IFN-γ without similar changes in IL-12 p70 levels, but with 10-fold increases in serum IL-18 relative to LPS-challenged control or endotoxin-tolerant mice. The role of IL-18 in CpG-induced immune potentiation was studied in splenocyte cultures from control, LPS-conditioned, or CpG-conditioned mice. These cultures produced similar amounts of IFN-γ in response to rIL-12 and rIL-18. However, only CpG-conditioned cells produced IFN-γ when cultured with LPS or CpG, and production was ablated in the presence of anti-IL-18R Ab. Anti-IL-18R Ab also reduced in vivo IFN-γ production by >2-fold in CpG-pretreated mice. Finally, combined pretreatment of mice with LPS and CpG suppressed the production of circulating IFN-γ, IL-12 p70, and IL-18 after subsequent LPS challenge. We conclude that CpG potentiates innate IFN-γ production from NK cells by increasing IL-18 availability, but that the suppressive effects of LPS on innate cellular immunity dominate during combined LPS and CpG pretreatment. Multiple Toll-like receptor engagement in vivo during infection can result in functional polarization of innate immunity dominated by a specific Toll-like receptor response.

This chapter discusses one's current knowledge of the properties of mitochondrial antiviral signaling (MAVS), its role in signaling, as well as its role in the in vivo host response to infection with RNA viruses. MAVS was discovered independently by four different groups, and so it is also called IPS-1, VISA, and Cardif. Importantly, the mitochondrial localization of MAVS is critical for it to induce interferons I (IFN-I). The chapter provides a more detailed description of tumor receptor associated factor (TRAF) and their role in the retinoic acid-inducible gene I (RIG-I)/melanoma differentiation associated gene 5 (MDA-5) pathway. The mitochondrial localization of MAVS is crucial for antiviral signaling because removal of the C-terminal mitochondrial targeting domain (TM) of MAVS abolishes its ability to induce IFNs. The chapter summarizes the current knowledge of MAVS signaling, and points out some outstanding questions that demand further dissection. In summary, an outline that emerges from the recent studies is that MAVS activates IKB kinase (IKK) and TBK1 through TRAF proteins as well as several kinase adaptors. To date, two studies have examined the activation of adaptive immune parameters in MAVS-/- mice. It is now well established that MAVS serves as an essential signaling adaptor in the cytosolic antiviral signaling pathway.

Detection of nucleic acids and induction of type I interferons (IFNs) are principal elements of antiviral defense, but can cause autoimmunity if misregulated. Cytosolic DNA detection activates a potent, cell-intrinsic antiviral response through a poorly defined pathway. In a screen for proteins relevant to this interferon-stimulatory DNA (ISD) response, we identify 3’ repair exonuclease 1 (Trex1). Mutations in the human trex1 gene cause Aicardi-Goutieres Syndrome (AGS) and chilblain lupus, but the molecular basis of these diseases is unknown. We define Trex1 as an essential negative regulator of the ISD response and delineate the genetic pathway linking Trex1 deficiency to lethal autoimmunity. We show that single-stranded DNA derived from endogenous retroelements accumulates in Trex1-deficient cells and that Trex1 can metabolize reverse-transcribed DNA. These findings reveal a cell-intrinsic mechanism for initiation of autoimmunity, implicate the ISD pathway as the cause of AGS, and suggest an unanticipated contribution of endogenous retroelements to autoimmunity.

Metastatic medullary thyroid cancer (MTC) is a rare, but often aggressive, thyroid malignancy with a 5-year survival rate of 28% and few effective therapeutic options. Adoptive T-cell immunotherapy using chimeric antigen receptor (CAR)-modified T cells (CARTs) is showing encouraging results in the treatment of cancer, but development is challenged by the availability of suitable target antigens. We identified glial-derived neurotrophic factor (GDNF) family receptor alpha 4 (GFRα4), which associates with the RET receptor tyrosine kinase, as a putative antigenic target for CAR-based therapy of MTC. Using RNA in situ hybridization (RNAscope) and quantitative RT-PCR, we show that GFRα4 is highly expressed in MTC. Normal tissue expression of GFRα4 mRNA is restricted to parafollicular cells (C-cells) within the thyroid, the normal cell type from which MTC originates, and normal thymus.Based upon the highly restricted expression, we generated two high affinity single chain variable fragments (scFvs) targeting GFRα4 isoforms a and b by selecting a naïve rabbit antibody library by phage display. Second generation CARs bearing the CD137 costimulatory domain were constructed using these GFRα4-specific scFvs. GFRα4-specific CARTs trigger antigen-dependent cytotoxicity and cytokine production in vitro, and they are able to control pre-established TT cell tumors in an immunodeficient mouse xenograft model of MTC. These data demonstrate the feasibility of targeting GFRα4 by CARTs, and support this molecule as a promising target for adoptive T cell immunotherapy and other antibody-based therapy of MTC. Citation Format: Vijay G. Bhoj, Selene Nunez-Cruz, Kenneth Zhou, Dimitrios Arhontoulis, Michael Feldman, Keith Mansfield, Haiyong Peng, Christoph Rader, Don L. Siegel, Michael C. Milone. GDNF family receptor alpha 4 (GFRa4)-targeted adoptive T-cell immunotherapy for medullary thyroid carcinoma. [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 2295.

7564Background: Autologous T cells genetically modified to express a chimeric antigen receptor with an external anti-CD19 antibody domain, and CD3ζ and 4-1BB signaling domains (CTL019) can achieve remissions in patients (pts) with relapsed/refractory (r/r) CD19+ non-Hodgkin lymphomas (NHL). We studied the effect of this therapy on humoral immunity. Methods: Serial immunoglobulin (Ig) levels were measured in pts with complete response (CR) to CTL019 on a phase II trial. Pts had r/r CD19+ follicular lymphoma (FL), diffuse large B cell lymphoma (DLBCL), or mantle cell lymphoma (MCL). After collection of lymphocytes, pts received lymphodepleting chemotherapy followed 1 - 4 days later by 1 - 5 x 108CTL019 cells intravenously. Response was assessed every 3 months (mo) for 24 mo. Enrollment is reported from Feb 2014 – Nov 2015, survival analyses through Jan 2016. Results: 43 pts enrolled: median age 56 years (range 25-77); female: male ratio 17:26; median prior therapies 4 (range 1-19); prior ASCT 14 (33%). 30 p...

The CAR-T platform has provided an exceptionally potent means to treat cancers that have proven resistant to standard treatments. This potency, however, can work against normal tissue as well. Some clinical trials have identified adverse consequences as a result of CAR-T cell targeting of critical normal tissue. To enable as many targets as possible using the CAR-T cell approach, it is important to understand the potential liabilities of those targets in normal tissues prior to initiating clinical trials. CD123, the IL-3 receptor alpha subunit, is a viable target for treatment of acute myeloid leukemia, as it is expressed highly on primary AML blasts. We have previously shown that, in mice transplanted with human hematopoietic stem cells, CD123 targeting CAR T-cells eradicated these precursors and, in turn, normal hematopoiesis (Gill et al 2014xPreclinical targeting of human acute myeloid leukemia and myeloablation using chimeric antigen receptor-modified T cells. Gill, Saar, Tasian, Sarah K., Ruella, Marco, Shestova, Olga, Li, Yong, Porter, David L., Carroll, Martin, Danet-Desnoyers, Gwenn, Scholler, John, Grupp, Stephan A., June, Carl H., and Kalos, Michael. Blood. 2014; 123: 2343–2354Crossref | PubMed | Scopus (120)See all ReferencesGill et al 2014). Here, we describe an animal model developed to address the potential effects of targeting CD123 on non-hematopoietic tissue, namely endothelial cells that are found to express significant levels of CD123. An scFv that bound cynomolgus monkey CD123 was identified and a chimeric lentivirus that efficiently transduced monkey PBMCs was developed. Cells were demonstrated to be active in vitro and dosed into monkeys, after which cellular expansion was observed. In vivo safety assessments and histopathology results will be discussed.

Respiratory syncytial virus (RSV) infection is the leading cause of hospitalization in infants and young children worldwide [1, 2]. In addition to the acute morbidity [3], the association between RSV lower respiratory tract infection and the development of recurrent wheezing has been clearly established in several well-controlled prospective studies [4–7]. In fact, among children hospitalized for RSV bronchiolitis, studies indicate that >30% will develop persistent wheezing until 13 years of age, which may extend into early adulthood [4, 5]. The nature of this association is not well understood, and both the host and the virus likely contribute to the development of RSV-induced long-term airway disease [8, 9]. Recent evidence derived from in vitro experiments [10], animal models [11–14], and studies in adults [15] suggests that RSV may persist “latently” or at a low level of viral replication in immunologically privileged sites in the lung, avoiding immune detection and elimination [16]. However, questions have arisen regarding the significance, if any, of RSV persistence. This study was designed to characterize the significance of RSV RNA persistence in the lungs by using a mouse model of RSV infection. To this end, we determined whether the establishment of RSV RNA persistence in the lungs required active viral replication and whether RSV RNA persistence correlated with the development of RSV-induced chronic pulmonary disease.

Chimeric antigen receptors (CARs) based upon a single chimeric molecule bearing an antigen binding domain linked in cis to the cytoplasmic domains of CD3ζ and costimulatory receptors CD28 or 4-1BB provide a potent method for engineering T cell cytotoxicity towards tumors. We describe a simple chimeric multichain receptor based upon a killer immunoglobulin-like receptors (KIRs) normally expressed by natural killer (NK) cells and T cells. Constructed by fusing a single chain variable fragment (scFv) to the transmembrane and cytoplasmic domain of a KIR, we show that a KIR-based CAR targeting mesothelin (SS1-KIR) triggers antigen-specific cytotoxic activity and cytokine production that is comparable to CD3ζ-based CARs with antigen-induced proliferation that is independent of additional costimulation. Using a xenograft model of mesothelioma resistant to T cell immunotherapy, we further demonstrate that a KIR-based CAR targeting mesothelin exhibits more potent anti-tumor activity compared with T cells bearing mesothelin-specific CD3ζ-based CARs with costimulation despite in vivo persistence of the latter CAR-modified T cells. Evaluation of tumor infiltrating lymphocytes demonstrate that KIR-based CAR+ T cells show resistance to acquired hypofunction within the tumor microenivornment compared with CD3ζ-based CARs with costimulatory receptor domains. The ability of a KIR-based CAR to induce regression of a tumor in which second generation CD3ζ-based CARs show limited activity supports the future clinical evaluation of a KIR-based CAR in mesothelioma and other tumors. Citation Format: Enxiu Wang, Liang-Chuan Wang, Ching-Yi Tsai, Vijay Bhoj, Steven Albelda, Edmund Moon, Michael C. Milone. A chimeric antigen receptor (CARs) based upon a killer immunoglobulin-like receptor (KIR) triggers robust cytotoxic activity in solid tumors. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B22.