BET bromodomain protein inhibition reverses chimeric antigen receptor extinction and reinvigorates exhausted T cells in chronic lymphocytic leukemia.

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.

Engineered CAR T Cells Targeting the Cancer-Associated Tn-Glycoform of the Membrane Mucin MUC1 Control Adenocarcinoma.

Genetically modified T cells expressing chimeric antigen receptors (CARs) demonstrate robust responses against lineage restricted, non-essential targets in hematologic cancers. However, in solid tumors, the full potential of CAR T cell therapy is limited by the availability of cell surface antigens with sufficient cancer-specific expression. The majority of CAR targets have been normal self-antigens on dispensable hematopoietic tissues or overexpressed shared antigens. Here, we established that abnormal self-antigens can serve as targets for tumor rejection. We developed a CAR that recognized cancer-associated Tn glycoform of MUC1, a neoantigen expressed in a variety of cancers. Anti-Tn-MUC1 CAR T cells demonstrated target-specific cytotoxicity and successfully controlled tumor growth in xenograft models of T cell leukemia and pancreatic cancer. These findings demonstrate the therapeutic efficacy of CAR T cells directed against Tn-MUC1 and present aberrantly glycosylated antigens as a novel class of targets for tumor therapy with engineered T cells.

Ebola virus mediated infectivity is restricted in canine and feline cells.

Ebolaviruses and marburgviruses belong to the Filoviridae family and often cause severe, fatal hemorrhagic fever in humans and non-human primates. The magnitude of the 2014 outbreak in West Africa and the unprecedented emergence of Ebola virus disease (EVD) in the United States underscore the urgency to better understand the dynamics of Ebola virus infection, transmission and spread. To date, the susceptibility and possible role of domestic animals and pets in the transmission cycle and spread of EVD remains unclear. We utilized infectious VSV recombinants and lentivirus pseudotypes expressing the EBOV surface glycoprotein (GP) to assess the permissiveness of canine and feline cells to EBOV GP-mediated entry. We observed a general restriction in EBOV-mediated infection of primary canine and feline cells. To address the entry mechanism, we used cells deficient in NPC1, a host protein implicated in EBOV entry, and a pharmacological blockade of cholesterol transport, to show that an NPC1-dependent mechanism of EBOV entry is conserved in canine and feline cells. These data demonstrate that cells of canine and feline origin are susceptible to EBOV GP mediated infection; however, infectivity of these cells is reduced significantly compared to controls. Moreover, these data provide new insights into the mechanism of EBOV GP mediated entry into cells of canine and feline origin.

Chinese hamster ovary cell lines selected for resistance to ebolavirus glycoprotein mediated infection are defective for NPC1 expression.

Ebolavirus causes severe hemorrhagic fever in humans and non-human primates. Entry of ebolavirus is mediated by the viral glycoprotein, GP; however, the required host factors have not been fully elucidated. A screen utilizing a recombinant Vesicular Stomatitis Virus (VSV) encoding Zaire ebolavirus GP identified four Chinese Hamster Ovary (CHO) cell lines resistant to GP-mediated viral entry. Susceptibility to vectors carrying SARS coronavirus S or VSV-G glycoproteins suggests that endocytic and processing pathways utilized by other viruses are intact in these cells. A cathepsin-activated form of the ebolaviral glycoprotein did not overcome the entry restriction, nor did expression of several host factors previously described as important for ebolavirus entry. Conversely, expression of the recently described ebolavirus host entry factor Niemann-Pick Type C1 (NPC1) restored infection. Resistant cells encode distinct mutations in the NPC1 gene, resulting in loss of protein expression. These studies reinforce the importance of NPC1 for ebolavirus entry.

Constitutive non-canonical NFkappaB signaling in pancreatic cancer cells.

Constitutive classical NFkappaB activation has been implicated in the development of pancreatic cancer, and inhibition of classical NFkappaB signaling sensitizes pancreatic cancer cells to apoptosis. However, the role of the more recently described non-canonical NFkappaB pathway has not been specifically addressed in pancreatic cancer. The non-canonical pathway requires stabilization of NIK and IKKalpha-dependent phosphorylation and processing of NFkappaB2/p100 to p52. This leads to the activation of p52-RelB heterodimers that regulate genes encoding lymphoid-specific chemokines and cytokines. We performed qRT-PCR to detect gene expression in a panel of pancreatic ductal adenocarcinoma cell lines (BxPC-3, PCA-2, PANC-1, Capan-1, Hs-766T, AsPC-1, MiaPACA-2) and found only modest elevation of classical NFkappaB-dependent genes. In contrast, each of the tumor cell lines displayed dramatically elevated levels of subsets of the non-canonical NFkappaB target genes CCL19, CCL21, CXCL12, CXCL13 and BAFF. Consistent with activation of the non-canonical pathway, p52 and RelB co-localized in adenocarcinoma cells in sections of pancreatic tumor tissue, and each of the tumor cell lines displayed elevated p52 levels. Furthermore, p52 and RelB co-immunoprecipitated from pancreatic cancer cells and immunoblotting revealed that NIK was stabilized and p100 was constitutively phosphorylated in a subset of the cell lines. Finally, stable overexpression of dominant negative IKKalpha significantly inhibited non-canonical target gene expression in BxPC-3 cells. These findings therefore demonstrate that the non-canonical NFkappaB pathway is constitutively active and functional in pancreatic cancer cells.

Control of large, established tumor xenografts with genetically retargeted human T cells containing CD28 and CD137 domains.

Mesothelin is a cell-surface molecule over-expressed on a large fraction of carcinomas, and thus is an attractive target of immunotherapy. A molecularly targeted therapy for these cancers was created by engineering T cells to express a chimeric receptor with high affinity for human mesothelin. Lentiviral vectors were used to express a single-chain variable fragment that binds mesothelin and that is fused to signaling domains derived from T-cell receptor zeta, CD28, and CD137 (4-1BB). When stimulated by mesothelin, lentivirally transduced T cells were induced to proliferate, express the antiapoptotic gene Bcl-X(L), and secrete multiple cytokines, all features characteristic of central memory T cells. When transferred intratumorally or intravenously into NOD/scid/IL2rgamma(-/-) mice engrafted with large pre-established tumors, the engineered T cells reduced the tumor burden, and in some cases resulted in complete eradication of the tumors at low effector-to-target ratios. Incorporation of the CD137 signaling domain specifically reprogrammed cells for multifunctional cytokine secretion and enhanced persistence of T cells. These findings have important implications for adoptive immunotherapy of cancer, especially in the context of poorly immunogenic tumors. Genetically redirected T cells have promise of targeting T lymphocytes to tumor antigens, confer resistance to the tumor microenvironment, and providing immunosurveillance.

Characterization of the contribution of spliced RNAs of hepatitis B virus to DNA synthesis in transfected cultures of Huh7 and HepG2 cells.

Hepatitis B virus synthesizes multiple spliced RNAs that can be reverse transcribed into viral DNA. We thoroughly characterized the contribution of spliced RNAs to DNA synthesis in transfected cultures of Huh7 and HepG2 cells. We found that up to 50% of DNA within intracellular capsids is derived from five spliced RNAs. Expressing HBV P protein and pgRNA from separate plasmids and the use of the CMV-IE promoter contributes to these high levels of encapsidated DNA derived from spliced RNA. A spliced RNA called Sp1 was the predominant species expressed in both cell lines. All spliced RNAs support the synthesis minus-strand DNA and duplex linear DNA. Only one of the spliced RNAs, Sp14, supported the synthesis of relaxed circular DNA because splicing removed an important cis-acting sequence (hM) in the other four RNAs. Additionally, we created a variant that was deficient in the synthesis of spliced RNA and supported DNA synthesis at wild-type levels. Our results reinforce and extend the idea that a significant fraction of HBV DNA synthesized under common experimental conditions is derived from spliced RNA. It is important that their presence be considered when analyzing HBV DNA replication in transfected cell cultures.

The sequence of the RNA primer and the DNA template influence the initiation of plus-strand DNA synthesis in hepatitis B virus.

For hepadnaviruses, the RNA primer for plus-strand DNA synthesis is generated by the final RNase H cleavage of the pregenomic RNA at an 11 nt sequence called DR1 during the synthesis of minus-strand DNA. This RNA primer initiates synthesis at one of two distinct sites on the minus-strand DNA template, resulting in two different end products; duplex linear DNA or relaxed circular DNA. Duplex linear DNA is made when initiation of synthesis occurs at DR1. Relaxed circular DNA, the major product, is made when the RNA primer translocates to the sequence complementary to DR1, called DR2 before initiation of DNA synthesis. We studied the mechanism that determines the site of the final RNase H cleavage in hepatitis B virus (HBV). We showed that the sites of the final RNase H cleavage are always a fixed number of nucleotides from the 5' end of the pregenomic RNA. This finding is similar to what was found previously for duck hepatitis B virus (DHBV), and suggests that all hepadnaviruses use a similar mechanism. Also, we studied the role of complementarity between the RNA primer and the acceptor site at DR2 in HBV. By increasing the complementarity, we were able to increase the level of priming at DR2 over that seen in the wild-type virus. This finding suggests that the level of initiation of plus-strand DNA synthesis at DR2 is sub-maximal for wild-type HBV. Finally, we studied the role of the sequence at the 5' end of the RNA primer that is outside of the DR sequence. We found that substitutions or insertions in this region affected the level of priming at DR1 and DR2.

A role for PKC-delta and PI 3-kinase in TNF-alpha-mediated antiapoptotic signaling in the human neutrophil.

The proinflammatory cytokine tumor necrosis factor (TNF)-alpha has been implicated in the attenuation of neutrophil spontaneous apoptosis during sepsis. Antiapoptotic signaling is principally mediated through the p60TNF receptor (p60TNFR). In neutrophils, TNF-alpha is an incomplete secretagogue and requires input from a ligated integrin(s) for neutrophil activation. In adherent neutrophils, TNF-alpha triggers association of both protein kinase C (PKC)-delta and phosphatidylinositol (PI) 3-kinase with the p60TNFR. In this study, a role for PKC-delta and PI 3-kinase in TNF-alpha-mediated antiapoptotic signaling was examined. TNF-alpha inhibited spontaneous apoptosis in fibronectin-adherent neutrophils, and this antiapoptotic signaling was blocked by the PKC-delta inhibitor rottlerin, but not by an inhibitor of Ca(2+)-dependent PKC isotypes, Go-6976. Inhibition of PI 3-kinase by LY-294002 also inhibited TNF-alpha-mediated antiapoptotic signaling. Cycloheximide blocked TNF-alpha-mediated antiapoptotic signaling, suggesting protein synthesis is required. Inhibition of either PKC-delta or PI 3-kinase attenuated TNF-alpha-mediated activation of the antiapoptotic transcription factor NFkappaB. Thus both PKC-delta and PI 3-kinase have essential roles in TNF-alpha-mediated antiapoptotic signaling in adherent neutrophils.