Scientists Grow Human Thymus From Stem Cells

knight_23 writes: "The Herald Sun reports that Australian researchers have grown a functioning thymus from stem cells. The thymus is a small organ that is critical to the immune system. Human trials could begin within two years."

Comments

Little FYI on the THY:

[damu]

The functions of the thymus were not well understood until the early 1960s, when its role in the development of the body's system of immunity was discovered. Beginning during fetal development, the thymus processes many of the body's lymphocytes, which migrate throughout the body via the bloodstream, seeding lymph nodes and other lymphatic tissue. The main cells undergoing this processing are the T cells, a heterogeneous groups of cells essential in protecting the body against invasions by foreign organisms. If the thymus fails to develop or is removed early in fetal life, the immune system cannot develop completely. Normally, by the time the infant is a few months old, the immune system has sufficiently formed so as to function throughout life. However, further growth and development of lymphoid tissue still depends on intervention by the thymic cells. After the initial seeding process, the thymus releases a hormonal substance that stimulates further growth of lymphoidal tissue, although such a substance has not yet been isolated.
dam()

Re:The thymus shuts down after puberty?

[herrd0kt0r]

basically, there are T cells and B cells (i won't even get into the Mr. T-cells in this post-- though i've mentioned them in another post). the precursors for these are made very early in life, either in the fetal liver or yolk sac, or later in bone marrow.

these precursors differentiate, or "grow up" in the thymus. basically, they're "taught" how to work. hmn. i just re-read your post. i'll cut to the chase:

tons and tons of each type of cell precursor are made. the typical lifespan of T-cells is thought to be in the period of months to years. "memory" T cells, in particular, are thought to have very long lifespans in the range of "many" years.

it is important to note that production of precursors does _not_ halt: they are constantly produced in the bone marrow. also, the thymus doesn't poof entirely-- it maintains function, though it shrinks tremendously in size as we get older.

Re:The thymus shuts down after puberty?

[thesnowdog]

Your understanding of T cells is correct. However, T cells mature from the basic stem cell in the thymus during childhood. Without a thymus (or a dysfunctional thymus), the body will not have any fully-functional T cells. This results in a vulnerability to devastating viral infections that you or I would fight off in about a week.

Krishna

Re:politcal debate

[gilroy]

I am far from a biomedical expert, so I'm going on my impression from news reports and other sources. For example,

What are the ethical issues involved?

Currently, the best source for stem cells is a human embryo. But using human material, such as aborted fetuses, in research is a contensious issue because it can be construed as the sacrifice of human life for scientific progress.

source

and

Even if much of the potential of adult stem cells is realised, there are circumstances where they are unlikely to be useful.... The isolation and growth of adult stem cells have to date proved very difficult. Stem cells generally represent a very small proportion of cells in adult tissues. Unambiguous identification is difficult as their presence in a tissue or mixture of cells is generally inferred from a research observation rather than indicated by any specific biochemical marker which might aid their purification... Current understanding of the potential of adult stem cells for redifferentiation is still very limited. Although many studies suggest that such processes occur, there is often a degree of ambiguity... In their natural location in the body adult stem cells do not exhibit great potential for differentiation into new cell types but have evolved to give rise only to specific cell lineages.

House of Lords report

and

While adult stem cells hold real promise, there are some significant limitations to what we may or may not be able to accomplish with them. First of all, stem cells from adults have not been isolated for all tissues of the body. Although many different kinds of multipotent stem cells have been identified, adult stem cells for all cell and tissue types have not yet been found in the adult human. For example, we have not located adult cardiac stem cells or adult pancreatic islet stem cells in humans. Secondly, adult stem cells are often present in only minute quantities, are difficult to isolate and purify, and their numbers may decrease with age. For example, brain cells from adults that may be neuronal stem cells have only been obtained by removing a portion of the brain of epileptics, not a trivial procedure.

Stem Cells: A Primer

This is not to say that the matter is cut-and-dried, but rather, to indicate that there is solid reason for suspecting that stem cells will need to be embryonic to be (fully) useful; and hence, the debate (which was my actual point).

T cells

[aswang]

There are at least three types of T cells: Th cells (helper T cells), Tc cells (cytotoxic T cells), and TDTH cells (delayed-type hypersensitivity T cells). The existence of Ts cells (suppressor T cells) has been postulated but is apparently still controversial. In addition, Th cells are further subdivided into Th1 cells necesary for cell-mediated immunity (primarily targeting viral infections and tumors) and Th2 cells necessary for antibody production. T cells and B cells are both lymphocytes, which are a different lineage of white blood cells than macrophages.