Myoblasts appear to be good candidates for use in gene therapy because

Myoblasts appear to be good candidates for use in gene therapy because of an unusual and advantageous biological property: when injected into muscle, they fuse with nearby muscle fibers and become an integral part of the muscle tissue. Moreover, since muscle tissue is generally well supplied with nerves and blood, the therapeutic agents produced by the transgene are also accessible to nerves and the circulatory system. Thus, myoblasts may not only be useful for treating muscle disorders such as muscular dystrophy, but also nonmuscle disorders such as neurodegenerative diseases and inherited hormone deficiencies.

In a series of experiments in rodents, a team of investigators has been testing neural stem cells as vehicles for cell-based gene therapy for brain tumors known as gliomas. Gliomas are virtually impossible to treat because the tumor cells readily invade the surrounding tissue and migrate extensively into the normal brain. The researchers genetically modified human neural stem cells to produce a protein, cytosine deaminase, that converts a nontoxic precursor drug into an active form that kills cancer cells. The engineered neural stem cells were then injected into the brains of mice with human-derived gliomas. Within two weeks of the gene therapy and systemic treatment with the precursor drug, the tumors had shrunk by 80 percent. The animal studies also revealed that neural stem cells were able to quickly and accurately "find" glioma cells, regardless of whether the stem cells were implanted directly into the tumors, implanted far from the tumors (but still within the brain), or injected into circulating blood outside the brain.

Another cell-based gene therapy system under investigation involves the use of osteoblasts. In a recent preliminary study examining a gene therapy approach to bone repair and regeneration, researchers genetically engineered osteoblasts to produce a bone growth factor. The osteoblasts were added to a biodegradable matrix that could act as a "scaffold" for new bone formation. Within a month after the cell-impregnated scaffold was implanted into mice, new bone formation was detectable. Although this work is in the very early stages, it offers hope of an effective alternative to conventional bone-grafting techniques.

1. Why does the author mention that muscle tissue is generally well supplied with nerves and blood in the second sentence of the first paragraph?

(A) to offer further proof that the advantageous biological properties of myoblasts distinguish them from osteoblasts
(B) to elaborate upon the hypothesis that myoblasts can be used to treat coronary heart disease
(C) to describe how myoblasts are able to deliver therapeutic agents for the treatment of muscular dystrophy
(D) to provide evidence that myoblasts are truly integrated into the actual fibers of a recipient muscle
(E) to explain how a transgene that binds to muscle fibers can affect — other bodily systems



2. The author of this passage would most likely agree with which of the following statements?

(A) Most cell-based gene therapy systems have only been proven to work on mice and are years away from human trials.
(B) Recent research indicates that cell-based gene therapy may provide new methods of treating multiple disorders and diseases in humans.
(C) There are no gene therapy treatment methods that have been shown to be truly effective in combating gliomas.
(D) Osteoblasts, as indicated by their name, are used exclusively in the treatment of bone injuries and disorders.
(E) Nontoxic precursor drugs generally do not cause significant side effects in recipients.



3. The author suggests that neural stem cells exhibit which of the following traits?

I. the ability to consume gliomas
II. the ability to distribute themselves via the circulatory system
III. the ability to treat brain tumors

(A) I ONLY
(B) II ONLY
(C) I and II ONLY
(D) II and III ONLY
(E)I, II and III



4. The content of the passage leads most naturally to which of the following conclusions?

(A) Myoblast ‘scaffolding’ offers hope to patients currently facing painful bone-grafting operations.
(B) While neural stem cell research may appear promising, ethical debate surrounding it will likely hamper future applications of this new system
(C) Cytosine deaminase effectively reduces brain tumors formed by gliomas.
(D) Researchers are studying several methods of delivering cell-based gene therapy.
(E) Myoblasts offer the most promising mechanism for cell-based gene therapy.