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To develop an in vivo model wherein human hematopoiesis occurs, we transplanted severe combined immunodeficiency (SCID) mice with either human fetal bone marrow (HFBM) or human fetal liver (HFL). After transplantation of SCID mice with cultured HFBM (BM-SCID-hu mice) or HFL cells (Liv-SCID-hu mice), significant engraftment of the mouse bone marrow (BM) and population of the peripheral blood with human leukocytes was detected. Human colony-forming unit–granulocyte macrophage and burst forming unit-erythroid were detected in the BM of the BM-SCID-hu and Liv-SCID-hu mice up to 8 months after transplantation. When the HFBM or HFL cells were transduced with a retroviral vector before transplantation, integrated retroviral sequences were detected in human precursor cells present in the SCID mouse BM and in leukocytes circulating in the peripheral blood (PB) up to 7 months after transplantation. The PB of the BM-SCID-hu mice also became populated with human T cells after implantation with human thymic tissue, which provided a human microenvironment wherein human pre-T cells from the BM could mature. When the HFBM was retrovirally transduced before transplantation, integrated retrovirus was detected in sorted CD4+CD8+ double positive and CD4+ single positive cells from the thymic implant and CD4+ cells from the PB. Taken together, these data indicated that the BM of our BM-SCID-hu and Liv-SCID-hu mice became engrafted with retrovirally transduced human hematopoietic precursors that undergo the normal human hematopoietic program and populate the mouse PB with human cells containing integrated retroviral sequences. In addition to being a model for studying in vivo human hematopoiesis, these mice should also prove to be a useful model for investigating in vivo gene therapy using human stem/precursor cells.

Apoptosis is an important physiological process that promotes tissue homeostasis by eliminating unnecessary or malfunctioning cells. Abnormality in this process contributes to tumorigenesis, as well as the resistance to cancer treatment by radiation and chemotherapy. Restoration of normal apoptosis would not only promote cancer cell death and halt tumor progression, but also increase the response to many current cancer therapies. Although apoptosis induction is an important principle of currently used radiation and chemotherapy treatment, uncovering the mechanisms that govern this process, and which are lost during transformation, represents an important direction for realizing improved therapies for the future. This article first briefly reviews aspects of current discovery strategies for new anticancer therapeutics based on intervening in cell death pathways, and then discusses in more detail several cancer-relevant death pathways, which are disabled during transformation and which can be targeted therapeutically. These include anoikis/cell adhesion; energy metabolism and the unfolded protein response. Finally, we introduce a new concept, which utilizes cancer-specific apoptosis induced by oncolytic viruses. The discussion of these topics involves novel targets, compounds and virotherapy.

RNAi-mediated gene inactivation has become a cornerstone of the present day gene function studies that are the foundation of mechanism and target based drug discovery and development, which could potentially shorten the otherwise long process of drug development. In particular, the coming of age of “RNAi drug” could provide new promising therapeutics bypassing traditional approaches. However, there are technological hurdles need to overcome and the biological limitations need to consider for achieving effective therapeutics. Major hurdles include the intrinsic poor pharmacokinetic property of siRNA and major biological restrictions include off-target effects, interferon response and the interference with endogenous miRNA. Recent innovations in nucleic acid chemistry, formulations and delivery methods have gradually rendered it possible to develop effective RNAi-based therapeutics. Careful design based on the newest RNAi/miRNA biology can also help to minimize the potential tissue toxicity. If successful with systemic application, RNAi drug will no doubt revolutionize the whole drug development process. This review attempts to describe the progress in this area, including applications in preclinical models and recent favorable experience in a number of human trials of local diseases, along with the discussion on the potential limitations of RNAi therapeutics.

Three members of the NR4A1/Nur77/ NGFIB orphan nuclear hormone receptor subfamily (NR4A1, NR4A2, and NR4A3) belong to the steroid nuclear hormone receptor superfamily. They share similar structural features and have no known natural ligand. They constitute immediate early genes that are induced by serum, growth factors and receptor engagement and are thus implicated in cell mitogenic responses. These nuclear receptors are transcription factors that exert their functions through activation and subsequent induction of the downstream pathways. They have been shown to play a role in complex pathways of cell survival and apoptosis. Although the expression of these genes have been shown to be pro-survival, it has also been reported that NR4A1 expression can cause apoptosis. These two opposite effects apparently result from distinct mechanisms: either transcriptional activation of genes responsible for cell survival or cell apoptosis, or translocation into the cytoplasm where they target the mitochondria and cause cell apoptosis via Bcl- 2 binding. The latter mechanism constitutes a new paradigm of cellular apoptosis. In vitro functional studies using over-expression (gain of function) or gene inactivation (loss of function) type assays, combined with transgenic or knockout animal data in vivo, have revealed these effects and their physiological roles, including thymocyte development for NR4A1/3 and prosurvival in CNS for NR4A2. Recent studies have also suggested an important role of these receptors in cell transformation and tumorigenicity via both their antiapoptotic and pro-apoptotic functions. In particular, the recent identification of a functional ligand for NR4A1 suggests that these members could potentially serve as drug targets for disease indications such as cancer. While many aspects of these receptors have been previously reviewed, this article focuses on new experimentation and discovery of their apoptotic and carcinogenic roles, and discusses their potential roles as therapeutic targets.