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Following the discovery that leukemic cells exhibit properties of hematopoietic stem cells, the prospective isolation of stem-like cells with high tumorigenicity has been reported for a variety of tumors. These ˵cancer stem cells″ (CSCs) are so named because they exhibit the capacity for sustained self-renewal and possess the ability to regenerate transplanted tumor masses resembling the primary tumor in immunodeficient mice. However, the existence of CSCs remains contentious in the field of cancer biology, in part because of the application of inconsistent and inaccurate definitions and disputes over terminology. Herein, we review the discovery of CSCs, examine in detail their physical and functional characteristics, the mechanisms that lead to their formation, and how their contribution to solid tumor formation impacts cancer therapies. [ABSTRACT FROM AUTHOR]

The first in vivo tumor models were developed in the mid-1960s. These models were mouse leukemia models grown as ascites. The growth pattern was like that of bacteria in vivo and therefore it was possible to apply similar mathematics of growth and response to these tumors as had been worked out for bacteria. Since the development of the murine leukemia models, investigators have devoted a large effort to modeling solid tumors in mice. There are now a variety of models including syngeneic mouse tumors and human tumor xenografts grown as subcutaneous nodules, syngeneic mouse tumors and human tumor xenografts grown in orthotopic sites, models of disseminated disease, ``labeled΄΄ tumor models that can be visualized using varied technologies, and transgenic tumor models. The value of these models depends upon the application of rigorous experimental design and data analysis. The endpoints used can be in situ or excision. Each of these has advantages and disadvantages to the ``drug hunter΄΄ searching for improved treatments. [ABSTRACT FROM AUTHOR]

When foreign DNA is transferred by genetic engineering to a microbe, plant or animal, a so-called transgenic organism is the result. These new life forms are created for a variety of reasons: to improve on nature, to act as ‘bioreactors’ that make useful products, or to act as models for understanding basic biology. A transgenic organism usually contains just one gene from another organism within a vast sea of its own DNA. So it is hardly surprising that transgenic sheep, for example, with a gene for a human protein, do not suddenly acquire human faces (or any other noticeably human characteristics). But however reassuringly normal transgenic organisms may appear, they are somewhat different from the creatures that have emerged during the course of evolution. How radical this difference is depends on your viewpoint. You could argue that humans have been ‘interfering’ in evolution since the dawn of agriculture, with the development of conventional plant and animal breeding, and genetic engineering is just a rather sophisticated breeding technology. You could point to nature's own ‘genetic engineering’ – the spread of antibiotic resistance, the transfer of taxol genes (see p. 74) from the yew to a fungus, and even Griffith's discovery of the transforming principle, to name but three examples. Or you may side with those who regard genetic engineering as deeply suspicious because of the way it allows the setting aside of species barriers. Inevitably, like any new technology, the creation of transgenic animals raises a number of important issues – animal welfare, environmental and ecosystem concerns and safety. [ABSTRACT FROM AUTHOR]

Chapter 96 of the book "Critical Decisions in Periodontology" is presented. It discusses various bone fill regenerative procedures that have proven to be clinically successful in treating intrabony defects. Among the procedures are extraoral autogenous bone graft, xenografts, synthetic bone substitutes and guided tissue regeneration.

A definition of the term "xenograft" is presented. It refers to the engrafment of organs, cells or tissues between individuals of different species. It is used to describe a human cancer model. Xenografts are often employed as preclinical models to study the efficacy of tumor therapeutic approaches.