Induced pluripotent stem iPS cells Cells from adult tissues reprogrammed to pluripotency Pluripotent Not patentable i. The primary source of early human stem cells was adult bone marrow, the tissue that makes red and white blood cells. Since scientists realized that bone marrow was a good source of stem cells, early transplants were initiated in the early 's to treat diseases that involved the immune system genetic immunodeficiencies and cancers of the immune system.
J Cancer ; 4 1: How to cite this article: An increasing number of studies, however, have suggested that aberrant infiltration of immune cells into tumor or normal tissues may promote tumor progression, invasion, and metastasis. Neither the primary reason for these contradictory observations, nor the mechanism for the reported diverse impact of tumor-infiltrating immune cells has been elucidated, making it difficult to judge the clinical implications of infiltration of immune cells within tumor tissues.
This mini-review presents several existing hypotheses and models that favor the promoting impact of tumor-infiltrating immune cells on tumor invasion and metastasis, and also analyzes their strength and weakness. Carcinogenesis in different organs is believed to share a similar process, i.
The significant difference in clinical prognosis between in situ and invasive or metastatic cancer results predominantly from the presence or absence of the surrounding basement membrane BM.
All normal or pre-invasive tumor epithelia are normally devoid of lymphatic ducts and blood vessels and are also physically segregated from vascular structures within the stroma by the BM. The BM consists of mainly type IV collagen, laminins, and other molecules that form a continuous sheet more commonly called the tumor capsulesurrounding the epithelial cells [ 9 - 12 ].
The basal or myoepithelial cell layer lies between the epithelial cells and the BM. In the gastrointestinal tract, the normal mucosa and in situ cancer are further separated from the submucosa by the muscularis mucosa, a dense band comprised of two layers of smooth muscle cells [ 13 ]. Due to these structural relationships, the disruption of the tumor capsule and its associated physical barriers is an absolute pre-requisite for tumor cell invasion or metastasis.
It is a commonly held belief that progression from in situ to invasive or metastatic cancer is caused by proteolytic enzymes produced by tumor cells that increase linearly in concentration with tumor progression, reaching their highest level at the in situ cancer stage.
It has been proposed that these proteolytic enzymes cause degradation or disruption of the tumor capsule and allow the in situ cancer cells to migrate into the adjacent stroma or to disseminate to distant organs [ 14 - 17 ]. The above model of tumor invasion and metastasis is consistent with results obtained from tissue culture and animal model studies [ 18 - 20 ]; however, it is hard to reconcile with a number of well-established observations: Together, these facts argue that alternative pathways may exist for tumor progression and subsequent invasion or metastasis.
Existing hypotheses of tumor infiltrating immune cells promoting tumor invasion and metastasis A great number of studies have shown that infiltration of the immune cells into tumor tissues and direct physical contact between infiltrating immune cells and tumor cells are associated with the physical destruction of tumor cells, reduction of the tumor burden, and an improved clinical prognosis [ 31 - 36 ].
On the other hand, a significant and steadily increasing number of studies have shown that increased infiltration of immune cells may promote tumor progression and invasion. For example, several studies have documented that stage- and histopathologically-matched pre-invasive prostate and esophageal tumors with increased immune cell infiltration have a significantly higher frequency of subsequent progression to invasive cancer than their counterparts without aberrant immune cell infiltration [ 37 - 39 ].
Unfortunately, the primary reasons for these contradictory observations remain elusive, making it difficult to judge the clinical implications of the infiltration of immune cells within tumor tissues. To address these issues, numerous studies [ 40 - 47 ] have been conducted, and a number of hypotheses [ 48 - 55 ] have been presented to explore the primary impact of tumor infiltrating immune cells on associated tumor tissues.
Again, the outcomes of these studies are highly contradictory and the primary impact of infiltrating immune cells on associated tumors remains elusive [ 56 - 57 ]. In this mini-review, we present several existing hypotheses that favor the promoting impact of tumor-infiltrating immune cells on tumor invasion and metastasis and analyze their strengths and weakness.
These specific hypotheses were selected for a number of reasons, including 1 they directly address the impact of tumor infiltrating immune cells on tumor cell behavior, and 2 they appear to be applicable to multiple, or perhaps all, epithelial-derived tumors.
Tumor-educated macrophages paracrine loop signaling The main concept of this hypothesis was introduced in [ 58 ] and was based on findings of a chemotaxis-based in vivo invasion assay and multiphoton-based intravital imaging on transgenic mice.
The study shows that interactions between breast tumor cells and macrophages facilitates the migration of cancer cells into the primary tumor and also that tumor cell intravasation occurs in association with perivascular macrophages [ 5960 ].
At this invasive site, macrophages enhance tumor cell migration and invasion through their secretion of chemotactic and chemokinetic factors including epidermal growth factor EGF.
They promote angiogenesis by the synthesis of angiogenic factors including vascular endothelial growth factor VEGFand they remodel the extracellular matrix and in particular, regulate collagen fibrillogenesis. The main strength of this hypothesis is that the assay system used in these studies allows direct visualization of macrophage-assisted tumor cell migration and intravasation in mammary tumors.
The primary weakness of this hypothesis is that it may not truly reflect the intrinsic events in humans for four important reasons. Previous studies have shown that human macrophages are significantly different from mouse macrophages not only in their relative ratio to other immune cell types, but also in their use of arginine for production of nitric oxide NOwhich is the most important component of the macrophage arsenal against intracellular pathogens [ 62 - 69 ].
The mouse macrophages produce large amounts of NO and L-citrulline from L-arginine via induction of the inducible form of NOS iNOSand also synthesize the obligatory cofactor tetrahydrobiopterin BH4essential for stabilization and function of the iNOS enzyme protein [ 6364 ].Stem cells have to be "successfully isolated and grown in the laboratory." This has already been accomplished: They have to be encouraged to "turn into specific cell types." This has been done for most of the cell types in the human body.
Human cloning is the creation of a genetically identical copy (or clone) of a arteensevilla.com term is generally used to refer to artificial human cloning, which is the reproduction of human cells and arteensevilla.com does not refer to the natural conception and delivery of identical arteensevilla.com possibility of human cloning has raised arteensevilla.com ethical concerns have prompted several nations to pass.
"Major roadblocks remain before human embryonic stem cells could be transplanted into humans to cure diseases or replace injured body parts, a research pioneer said Thursday night. * Legal Disclaimer: Chelation and Hyperbaric Therapy, Stem Cell Therapy, and other treatments and modalities mentioned or referred to in this web site are medical techniques that may or may not be considered “mainstream”.
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Advantages and Disadvantages of Embryonic Stem Cells.
OccupyTheory. on 4 February, at one of the largest benefits associated with embryonic stem cells is that they offer an array of medical possibilities that you can use to your advantage. Human embryos must be destroyed in the process of collecting these .