William K. Decker

Functionally active virus-specific T cells that target CMV, adenovirus, and EBV can be expanded from naive T-cell populations in cord blood and will target a range of viral epitopes

The naive phenotype of cord blood (CB) T cells may reduce graft-versus-host disease after umbilical cord blood transplantation, but this naivety and their low absolute numbers also delays immune reconstitution, producing higher infection-related mortality that is predominantly related to CMV, adenovirus (Adv), and EBV. Adoptive immunotherapy with peripheral blood-derived virus-specific cytotoxic T lymphocytes (CTLs) can effectively prevent viral disease after conventional stem cell transplantation, and we now describe the generation of single cultures of CTLs from CB that are specific for multiple viruses. Using EBV-infected B cells transduced with a clinical-grade Ad5f35CMVpp65 adenoviral vector as sources of EBV, Adv, and CMV antigens, we expanded virus-specific T cells even from CB T cells with a naive phenotype. After expansion, each CTL culture contained both CD8(+) and CD4(+) T-cell subsets, predominantly of effector memory phenotype. Each CTL culture also had HLA-restricted virus-specific cytotoxic effector function against EBV, CMV, and Adv targets. The CB CTLs recognized multiple viral epitopes, including CD4-restricted Adv-hexon epitopes and immunosubdominant CD4- and CD8-restricted CMVpp65 epitopes. Notwithstanding their naive phenotype, it is therefore possible to generate trivirus-specific CTLs in a single culture of CB, which may be of value to prevent or treat viral disease in CB transplant recipients. This study is registered at www.clinicaltrials.gov as NCT00078533.

Superior ex vivo cord blood expansion following co-culture with bone marrow-derived mesenchymal stem cells

One factor limiting the therapeutic efficacy of cord blood (CB) hematopoietic progenitor cell (HPC) transplantation is the low cell dose of the graft. This is associated with an increased incidence of delayed or failed engraftment. Cell dose can be increased and the efficacy of CB transplantation potentially improved, by ex vivo CB expansion before transplantation. Two ex vivo CB expansion techniques were compared: (1) CD133+ selection followed by ex vivo liquid culture and (2) co-culture of unmanipulated CB with bone-marrow-derived mesenchymal stem cells (MSCs). Ex vivo culture was performed in medium supplemented with granulocyte colony-stimulating factor, stem cell factor and either thrombopoietin or megakaryocyte growth and differentiation factor. Expansion was followed by measuring total nucleated cell (TNC), CD133+ and CD34+ cell, colony-forming unit and cobblestone area-forming cell output. When compared to liquid culture, CB-MSC co-culture (i) required less cell manipulation resulting in less initial HPC loss and (ii) markedly improved TNC and HPC output. CB-MSC co-culture therefore holds promise for improving engraftment kinetics in CB transplant recipients.

Mouse VDAC isoforms expressed in yeast: channel properties and their roles in mitochondrial outer membrane permeability.

Abstract. The channel-forming protein called VDAC forms the major pathway in the mitochondrial outer membrane and controls metabolite flux across that membrane. The different VDAC isoforms of a species may play different roles in the regulation of mitochondrial functions. The mouse has three VDAC isoforms (VDAC1, VDAC2 and VDAC3). These proteins and different versions of VDAC3 were expressed in yeast cells (S. cerevisiae) missing the major yeast VDAC gene and studied using different approaches. When reconstituted into liposomes, each isoform induced a permeability in the liposomes with a similar molecular weight cutoff (between 3,400 and 6,800 daltons based on permeability to polyethylene glycol). In contrast, electrophysiological studies on purified proteins showed very different channel properties. VDAC1 is the prototypic version whose properties are highly conserved among other species. VDAC2 also has normal gating activity but may exist in 2 forms, one with a lower conductance and selectivity. VDAC3 can also form channels in planar phospholipid membranes. It does not insert readily into membranes and generally does not gate well even at high membrane potentials (up to 80 mV). Isolated mitochondria exhibit large differences in their outer membrane permeability to NADH depending on which of the mouse VDAC proteins was expressed. These differences in permeability could not simply be attributed to different amounts of each protein present in the isolated mitochondria. The roles of these different VDAC proteins are discussed.

Each mammalian mitochondrial outer membrane porin protein is dispensable: effects on cellular respiration

Voltage-dependent anion channels (VDACs, also known as mitochondrial porins) are small pore-forming proteins of the mitochondrial outer membrane found in all eukaryotes. Mammals harbor three distinct VDAC isoforms, with each protein sharing 65-70% sequence identity. Deletion of the yeast VDAC1 gene leads to conditional lethality that can be partially or completely complemented by the mammalian VDAC genes. In vitro, VDACs conduct a variety of small metabolites and in vivo they serve as a binding site for several cytosolic kinases involved in intermediary metabolism, yet the specific physiologic role of each isoform is unknown. Here we show that mouse embryonic stem cells lacking each isoform are viable but exhibit a 30% reduction in oxygen consumption. VDAC1 and VDAC2 deficient cells exhibit reduced cytochrome c oxidase activity, whereas VDAC3 deficient cells have normal activity. These results indicate that VDACs are not essential for cell viability and we speculate that reduced respiration in part reflects decreased outer membrane permeability for small metabolites necessary for oxidative phosphorylation.

Ex vivo fucosylation improves human cord blood engraftment in NOD-SCID IL-2Rγ null mice

Delayed engraftment remains a major hurdle after cord blood (CB) transplantation. It may be due, at least in part, to low fucosylation of cell surface molecules important for homing to the bone marrow microenvironment. Because fucosylation of specific cell surface ligands is required before effective interaction with selectins expressed by the bone marrow microvasculature can occur, a simple 30-minute ex vivo incubation of CB hematopoietic progenitor cells with fucosyltransferase-VI and its substrate (GDP-fucose) was performed to increase levels of fucosylation. The physiologic impact of CB hematopoietic progenitor cell hypofucosylation was investigated in vivo in NOD-SCID interleukin (IL)-2Rγ(null) (NSG) mice. By isolating fucosylated and nonfucosylated CD34(+) cells from CB, we showed that only fucosylated CD34(+) cells are responsible for engraftment in NSG mice. In addition, because the proportion of CD34(+) cells that are fucosylated in CB is significantly less than in bone marrow and peripheral blood, we hypothesize that these combined observations might explain, at least in part, the delayed engraftment observed after CB transplantation. Because engraftment appears to be correlated with the fucosylation of CD34(+) cells, we hypothesized that increasing the proportion of CD34(+) cells that are fucosylated would improve CB engraftment. Ex vivo treatment with fucosyltransferase-VI significantly increases the levels of CD34(+) fucosylation and, as hypothesized, this was associated with improved engraftment. Ex vivo fucosylation did not alter the biodistribution of engrafting cells or pattern of long-term, multilineage, multi-tissue engraftment. We propose that ex vivo fucosylation will similarly improve the rate and magnitude of engraftment for CB transplant recipients in a clinical setting.

Antigen presenting cell-mediated expansion of human umbilical cord blood yields log-scale expansion of natural killer cells with anti-myeloma activity.

Natural killer (NK) cells are important mediators of anti-tumor immunity and are active against several hematologic malignancies, including multiple myeloma (MM). Umbilical cord blood (CB) is a promising source of allogeneic NK cells but large scale ex vivo expansion is required for generation of clinically relevant CB-derived NK (CB-NK) cell doses. Here we describe a novel strategy for expanding NK cells from cryopreserved CB units using artificial antigen presenting feeder cells (aAPC) in a gas permeable culture system. After 14 days, mean fold expansion of CB-NK cells was 1848-fold from fresh and 2389-fold from cryopreserved CB with >95% purity for NK cells (CD56+/CD3−) and less than 1% CD3+ cells. Though surface expression of some cytotoxicity receptors was decreased, aAPC-expanded CB-NK cells exhibited a phenotype similar to CB-NK cells expanded with IL-2 alone with respect to various inhibitory receptors, NKG2C and CD94 and maintained strong expression of transcription factors Eomesodermin and T-bet. Furthermore, CB-NK cells formed functional immune synapses with and demonstrated cytotoxicity against various MM targets. Finally, aAPC-expanded CB-NK cells showed significant in vivo activity against MM in a xenogenic mouse model. Our findings introduce a clinically applicable strategy for the generation of highly functional CB-NK cells which can be used to eradicate MM.

Mutual regulation of tumour vessel normalization and immunostimulatory reprogramming

Blockade of angiogenesis can retard tumour growth, but may also paradoxically increase metastasis. This paradox may be resolved by vessel normalization, which involves increased pericyte coverage, improved tumour vessel perfusion, reduced vascular permeability, and consequently mitigated hypoxia. Although these processes alter tumour progression, their regulation is poorly understood. Here we show that type 1 T helper (TH1) cells play a crucial role in vessel normalization. Bioinformatic analyses revealed that gene expression features related to vessel normalization correlate with immunostimulatory pathways, especially T lymphocyte infiltration or activity. To delineate the causal relationship, we used various mouse models with vessel normalization or T lymphocyte deficiencies. Although disruption of vessel normalization reduced T lymphocyte infiltration as expected, reciprocal depletion or inactivation of CD4+ T lymphocytes decreased vessel normalization, indicating a mutually regulatory loop. In addition, activation of CD4+ T lymphocytes by immune checkpoint blockade increased vessel normalization. TH1 cells that secrete interferon-γ are a major population of cells associated with vessel normalization. Patient-derived xenograft tumours growing in immunodeficient mice exhibited enhanced hypoxia compared to the original tumours in immunocompetent humans, and hypoxia was reduced by adoptive TH1 transfer. Our findings elucidate an unexpected role of TH1 cells in vasculature and immune reprogramming. TH1 cells may be a marker and a determinant of both immune checkpoint blockade and anti-angiogenesis efficacy.

Reduction of Regulatory T Cells by Mogamulizumab, a Defucosylated Anti-CC Chemokine Receptor 4 Antibody, in Patients with Aggressive/Refractory Mycosis Fungoides and Sézary Syndrome

Purpose: The CC chemokine receptor 4 (CCR4) is expressed on malignant T cells in cutaneous T-cell lymphoma (CTCL) as well as on regulatory T cells (Treg). When mogamulizumab, a defucosylated monoclonal antibody, binds to CCR4, it induces antibody-dependent cellular cytotoxicity against CCR4+ malignant T cells. The goal of this study was to determine the effect of mogamulizumab on CCR4+ Tregs in patients with CTCL. Experimental Design: Peripheral blood of 24 patients with CTCL participating in a phase I/II trial was analyzed for CCR4 expression on different T-cell subsets by flow cytometry, before and after one course of mogamulizumab. The number and function of natural killer (NK) cells were also analyzed. Lesional biopsies were examined for CCR4, Foxp3, and CD16 expression by immunohistochemistry. Results: Malignant T cells in peripheral blood were 20.8%–100% positive for CCR4 at baseline. Fourteen patients who achieved a response in blood had high baseline CCR4 expression on malignant T cells. Tregs in blood were 58.6% to 100% positive for CCR4 at baseline and showed decreased numbers and CCR4 expression after treatment. CD8+ T cells in blood were 3.2% to 23.2% positive for CCR4 at baseline and showed limited reduction of CCR4 expression with increased percentages of CD8+ T cells after treatment. Of 14 patients tested for NK cells in blood, 10 showed increased percentages after treatment. Four of 6 patients tested showed increased NK cell cytotoxicity. Sixteen of 18 patients who had CCR4+ lymphocytes in baseline lesions showed decreased numbers after treatment. Conclusions: Mogamulizumab reduces levels of CCR4+ malignant T cells and also CCR4+ Tregs in patients with CTCL, which may in turn improve immune profiles. Clin Cancer Res; 21(2); 274–85. ©2014 AACR.

A Novel Isoform of the Mitochondrial Outer Membrane Protein VDAC3 via Alternative Splicing of a 3-Base Exon FUNCTIONAL CHARACTERISTICS AND SUBCELLULAR LOCALIZATION

Voltage-dependent anion channels (VDACs) are pore-forming proteins found in the outer mitochondrial membrane of all eucaryotes. VDACs are the major pathway for metabolites through the outer mitochondrial membrane and, in mammals, bind several cytosolic carbohydrate kinases. Whereas yeast contain a single VDAC (YVDAC), to date three isoforms have been described in the mouse that constitute a gene family. We have observed an additional isoform of VDAC3 that appears to be generated via the tissue-specific alternative splicing of a 3-base exon (ATG). The exon is predicted to introduce a methionine 39 amino acids downstream of the amino terminus of the polypeptide. Between exons 3 and 4 is an intronic sequence that potentially encodes the exon, with flanking splice enhancer elements. Expression of this alternative form in the mouse is limited to brain, heart, and skeletal muscle. Complementation ofYVDAC-deficient yeast by the two isoforms and with other sequence variants of VDAC3 suggests this residue is an important modulator of VDAC3 function. In transfected mammalian cells both isoforms localize to mitochondria. A similar variant is present in humans.

Cord blood natural killer cells exhibit impaired lytic immunological synapse formation that is reversed with IL-2 exvivo expansion.

Peripheral blood natural killer (NK) cell therapy for acute myeloid leukemia has shown promise in clinical trials after allogeneic stem cell transplantation. Cord blood (CB) is another potentially rich source of NK cells for adoptive immune therapy after stem cell transplantation. Tightly regulated receptor signaling between NK cells and susceptible tumor cells is essential for NK cell-mediated cytotoxicity. However, despite expressing normal surface activating and inhibitory NK receptors, CB-derived NK cells have poor cytolytic activity. In this study, we investigate the cellular mechanism and demonstrate that unmanipulated CB-NK cells exhibit an impaired ability to form F-actin immunologic synapses with target leukemia cells compared with peripheral blood-derived NK cells. In addition, there was reduced recruitment of the activating receptor CD2, integrin leukocyte function-associated antigen-1, and the cytolytic molecule perforin to the CB-NK synapse site. Exvivo interleukin (IL)-2 expansion of CB-NK cells enhanced lytic synapse formation including CD2 and leukocyte function-associated antigen-1 polarization and activity. Furthermore, the acquired antileukemic function of IL-2-expanded CB-NK cells was validated using a nonobese diabetic severe combined immunodeficient IL-2 receptor common γ-chain null mouse model. We believe our results provide important mechanistic insights for the potential use of IL-2-expanded CB-derived NK cells for adoptive immune therapy in leukemia.