Biotechwiz

News,Views & Insights on Biotechnology

Browsing Posts published on February 25, 2010

Stem cell therapy has drawn a lot of interest lately. This therapy has shown promise in treatments of a large number of life- threatening and/or debilitating disorders that are genetic in nature. Stem cells are like base cells. They are like clay that can be molded into any desired shape. These master cells are multi potent and if given optimum conditions, they can be induced to grow into any one of the various  types of differentiated cells in our body; for example Brain or liver cells. Thus these special cells have two important attributes: 1. They can renew themselves by cell division even after relatively long periods of inaction. 2. Once they have divided, each daughter cell can either remain as a stem cell, retaining all its pluripotency or it can differentiate into any one of the different organ types in the body. Stem cells also exist in various tissue systems to serve repair functions.

Typically stem cells are divided into adult stem cells and embryonic stem cells. Embryonic stem cells are derived from the Blastocyst stage of Embryos. Embryonic stem cells can generally give rise to almost all the different cell types in the human body. Adult stem cells on the other hand, generally give rise only to all the different cells of the particular tissue from which they are derived. What does this mean? In simple terms, Hematopoetic Stem cells derived from bone marrow can give rise to all the different types of blood cells but not to cells of a very different organ system such as neurons of the brain. So in a sense they are of limited capacity. In 2006, researchers made another breakthrough by identifying conditions that would allow some specialized adult cells to be “reprogrammed” genetically to assume a stem cell-like state. This new type of stem cell is called induced pluripotent stem cells (iPSCs).

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Well, while we are on the subject of transgenics, the current news byte seems to be right on target. The latest in transgenic technology also represents a break-through in the development of animal models for testing of viral diseases. Scientists at the Salk institute in La Jola have managed to develop a mouse that has a human liver. This research was carried out principally by Dr. Inder Verma.What this means is, that the animal now sports a liver that is made up almost entirely of human hepatocytes. This will make it easier to use this mouse as a model to study human viruses affecting the liver such as Hepatitis B and C.

THe Humanised Mouse !

THe Humanised Mouse !

The problem with viruses is their host specificity. What this simply means is, viruses attacking a human being will generally have no effect on a mouse and vice versa. While this is good as the non- human viruses will not spread rapidly and infect humans, it does present substantial problems to scientists trying to study the pathology of human viruses and developing vaccines and drugs for the same. Since one cannot test therapies directly on human beings, a viable alternative needs to be provided. In the past, we have experimented with using in vitro cell cultures; liver cells grown in a Petri dish. However, this model has severe limitations due to the lack of proper organ structure and complete absence of the kind of interactions between cells and organs seen in a complete organism. Alternatives to this were to use animals such as mice that completely lacked a viable immune system (nude mice) for studying tumors of human origin. The tumors would be transplanted into these mice and their effects and probable curative measure would be studied.

However, this model has its side effects too. As Dr. Inder says, clinically speaking, a tumor does not start by acquiring millions of tumor cells from outside the system. It starts with one or two or ten cells that have lost control of their cell division cycle and hence keep on multiplying uncontrollably to give rise to a tumor. So, to that extent, transplanting a tumor into a mouse is really a fundamentally different process and may not yield real-time data as needed. However, with this new model where the mouse liver cells are literally taken over by human liver cells (Hepatocytes) so that they overgrow to give a liver that is almost entirely human, we will be able to study the actual process of tumorigenesis or viral infections along with the possible cures and vaccination methods.

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