Takuya Maeda

Effects of NiO on electrical properties of NiAu-based ohmic contacts for p-type GaN

Effects of a NiO layer on the electrical properties of NiAu-based ohmic contacts for p-GaN were studied by depositing a p-type NiO layer on the p-GaN using a sputter-deposition technique. NiO layers doped with Li[NiO(Li)] had a p-type conduction with sheet resistivity of around 1 Ω cm after annealing at temperatures lower than 500 °C. A variety of the NiAu-based contacts with the NiO layers such as NiO/Au, NiO(Li)/Au, Ni/NiO(Li)/Au, Ni/Li2O/NiO/Au, and Ni/Li2O/Ni/NiO/Au contacts were prepared by depositing on the p-GaN, where a slash “/” indicates the deposition sequence. However, these contacts did not provide specific contact resistances (ρc) lower than that (ρc∼10−2 Ω cm2) of the conventional Ni/Au contacts prepared by annealing in N2 ambient. From the present results, it was believed that the p-NiO layer did not act as an intermediate semiconductor layer to reduce the Schottky barrier height at the p-GaN/Au interface.

Regeneration of CD8αβ T Cells from T-cell–Derived iPSC Imparts Potent Tumor Antigen-Specific Cytotoxicity

Although adoptive transfer of cytotoxic T lymphocytes (CTL) offer a promising cancer therapeutic direction, the generation of antigen-specific CTL from patients has faced difficulty in efficient expansion in ex vivo culture. To resolve this issue, several groups have proposed that induced pluripotent stem cell technology be applied for the expansion of antigen-specific CTL, which retain expression of the same T-cell receptor as original CTL. However, in these previous studies, the regenerated CTL are mostly of the CD8αα+ innate type and have less antigen-specific cytotoxic activity than primary CTL. Here we report that, by stimulating purified iPSC-derived CD4/CD8 double-positive cells with anti-CD3 antibody, T cells expressing CD8αβ were generated and exhibited improved antigen-specific cytotoxicity compared with CD8αα+ CTL. Failure of CD8αβ T-cell production using the previous method was found to be due to killing of double-positive cells by the double-negative cells in the mixed cultures. We found that WT1 tumor antigen-specific CTL regenerated by this method prolonged the survival of mice bearing WT1-expressing leukemic cells. Implementation of our methods may offer a useful clinical tool. Cancer Res; 76(23); 6839-50. ©2016 AACR.

Temperature dependence of barrier height in Ni/n-GaN Schottky barrier diode

The temperature dependence of barrier height in a Ni/n-GaN Schottky barrier diode fabricated on a GaN homoepitaxial layer was investigated by capacitance–voltage, current–voltage, and internal photoemission measurements in the range of 223–573 K. The barrier height obtained by these methods linearly decreased with increasing temperature. The temperature coefficient was −(1.7–2.3) × 10−4 eV/K, which is about half of the temperature coefficient of the band gap reported previously. This indicates that the decrease in the barrier height may mainly reflect the shrinkage of the band gap (lowering of the conduction band edge) in GaN with increasing temperature.

NK cell alloreactivity against KIR-ligand-mismatched HLA-haploidentical tissue derived from HLA haplotype-homozygous iPSCs.

Summary HLA haplotype-homozygous (HLA-homo) induced pluripotent stem cells (iPSCs) are being prepared to be used for allogeneic transplantation of regenerated tissue into recipients carrying an identical haplotype in one of the alleles (HLA-hetero). However, it remains unaddressed whether natural killer (NK) cells respond to these regenerated cells. HLA-C allotypes, known to serve as major ligands for inhibitory receptors of NK cells, can be classified into group 1 (C1) and group 2 (C2), based on their binding specificities. We found that the T cells and vascular endothelial cells regenerated from HLA-homo-C1/C1 iPSCs were killed by specific NK cell subsets from a putative HLA-hetero-C1/C2 recipient. Such cytotoxicity was canceled when target cells were regenerated from iPSCs transduced with the C2 gene identical to the recipient. These results clarify that NK cells can kill regenerated cells by sensing the lack of HLA-C expression and further provide the basis for an approach to prevent such NK cell-mediated rejection responses.

Franz-Keldysh effect in GaN p-n junction diode under high reverse bias voltage

Photocurrent induced by sub-bandgap light absorption due to the Franz-Keldysh effect was observed in GaN p-n junction diodes under a high reverse bias voltage. The photocurrent increased with the reverse bias voltage and the increase was found to be more significant as the wavelength approached the absorption edge of GaN. The photocurrent was calculated with consideration of light absorption induced by the Franz-Keldysh effect in the depletion layer. The calculated curves showed excellent agreement with the experimental curves. The photocurrent also increased with an increase in temperature and this could be quantitatively explained by the red-shift of the GaN absorption edge with the increase in temperature.Photocurrent induced by sub-bandgap light absorption due to the Franz-Keldysh effect was observed in GaN p-n junction diodes under a high reverse bias voltage. The photocurrent increased with the reverse bias voltage and the increase was found to be more significant as the wavelength approached the absorption edge of GaN. The photocurrent was calculated with consideration of light absorption induced by the Franz-Keldysh effect in the depletion layer. The calculated curves showed excellent agreement with the experimental curves. The photocurrent also increased with an increase in temperature and this could be quantitatively explained by the red-shift of the GaN absorption edge with the increase in temperature.

Generation and Regeneration of T Cells

T cells contain a variety of lineages, each of which is formed by passing through a number of strictly regulated steps. In this article we aim to clarify essential factors and critical developmental steps during T cell development. First, we will describe the process of T cell development that occurs in vivo. Then, by presenting recent approaches in synthetic biology, we will show that, in the murine case, a feeder-free culture system using a combination of cytokines and Notch ligand is sufficient to support T cell development starting from multipotent hematopoietic progenitors to the TCR-expressing CD4+CD8+ stage. Finally, in the human case, we will show that mature functional CD8+ killer T cells can be produced in vitro starting as early as from the ES/iPS cell stage using feeder cells. These studies may help clarify “minimal requirements” for T cell development.

Abstract B126: Regeneration of tumor antigen specific CTLs utilizing iPSC technology

Current cancer immunotherapies mainly aim to activate and expand tumor antigen specific cytotoxic T lymphocytes (CTLs) in vitro or in vivo, but these methods are not so successuful because of the difficulty in preparing sufficient number of CTLs. We are trying to overcome this problem by utilizing the induced pluripotent stem cell (iPSC) technology. Our strategy is based on the concept that i) when iPSCs are produced from antigen specific T cells, the rearranged configurations of T cell receptor (TCR) genes are inherited to the iPSCs (which we call T-iPSCs), and that ii) when T cells are regenerated from such T-iPSCs, all of them should come to express the same TCR as the original one. Therefore it will become possible to obtain de novo generated tumor specific CTLs almost unlimitedly, because it is possible to make a mass-culture of cells at the iPSC level. In line with this concept, we have succeeded in establishing T-iPSCs from CTLs specific for the melanoma antigen MART-1 derived from tumor infiltarating lymphocytes, and in regenerating MART-1 specific T cells from such T-iPSCs (Vizcardo et al, Cell Stem Cell, 2013). The strategy mentioned above has been conducted in the category of autologous transplantation. Autologous transplantation setting, however, has some problems; i) high cost to establish T-iPSCs from each patients, ii) heterogeneneity of the quality as iPSCs, iii) difficulty in getting high affinity TCR. To solve these problems we are now planing to apply this method to the allogeneic transplantation setting. In allogeneic setting, we can select high quality T-iPSC clone and such a clone can be used to many other patients. It is preferable to produce T-iPSCs from a HLA haplotype homo donor, since CTLs generated from these T-iPSCs can be administerd to the patients carrying the same HLA haplotype on one allele. Thus by utilizing allogenic T-iPSCs the cost would be reduced and the quality of T-iPSCs can be ensured. Now we are trying to establish T-iPSCs from CTLs specific for various cancer antigen from healthy donors. We succeded in establishing T-iPSCs from CTLs specific for EB virus related antigen LMP2 and cancer testis antigen WT1, both of which are restricted to HLA A2402, the commonest HLA-A in the Japanese. We improved in vitro culture condition and have succeded in regenerating CD8 single positive cells expressing CD8 alpha-beta heterodimers. These regenerated CTLs exhibited very high antigen specific killing activity comparable to the original CTLs. The CTLs derived from WT1 specific T-iPSCs were able to kill some leukemia cell lines which express endogenous WT1 protein. They can be expanded more than ten thousand fold by repeated TCR stimulation without reducing their killing activity. We are now examining in vivo killing activity of these CTLs using zenograft model. This method could bring about a breakthrough in cancer immunotherapy. Citation Format: Takuya Maeda, Seiji Nagano, Hiroshi Ichise, Kyoko Masuda, Toshio Kitawaki, Akifumi Kondo-Takaori, Hiroshi Kawamoto. Regeneration of tumor antigen specific CTLs utilizing iPSC technology. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B126.