试题出自试卷《中国矿业大学（北京）2012年考博英语真题》

Recombinant DNA technology allows scientists to cut segments of DNA from one type of organism and combine them with the genes of a second organism. Also called genetic engineering. Recombinant DNA technology is a method by which relatively simple organisms, such as bacteria or yeast, or even mammalian cells in culture, can be induced to make quantities of human proteins, including interferons or grow tobacco plants that produce monoclonal antibodies, and goats that secrete a clot-dissolving heart attack drug, tissue plasminogen activator (TPA), in their milk.
Another facet of recombinant DNA technology involves gene therapy. The goal of this therapy is to replace defective genes, or to endow a cell with new capabilities. In 1989, the feasibility and safety of gene transfer was demonstrated when tumor-infiltrating lymphocytes (TILS) were extracted from a patient, equipped with a marker gene (so they could be tracked and monitored), and then re-injected into patients with advanced cancer. To deliver the gene into the TILS, the scientists used a virus, exploiting its natural tendency to invade cells, before being used as a vector, the virus was altered so that it could not reproduce or cause disease. This experiment demonstrated that gene-modified cells could survive for long periods in the bloodstream and in tumor deposits without harm to the patient.
The earliest attempts to use genes therapeutically focused on a form of severe combined immunodeficiency disease (SCID), which is caused by the lack of an enzyme due to a single abnormal gene. The gene for this enzyme-adenosine deaminase (ADA)—is delivered into the patient's T cells by a modified retrovirus. When the virus splices its genes into those of the T cells, it simultaneously introduces the gene for the missing enzyme. After the treated T cells begin to produce the missing enzyme, they are injected back into the patient.
Gene therapy is now being used with some cancer patients. TILS reinforced with a gene for the antitumor cytokine known as tumor necrosis factor (TNF) have been administered to patients with advanced melanoma, a deadly form of skin cancer. Plans are under way to engineer a cancer “vaccine” designed to improve anticancer immune responses by taking small bits of tumor from patients with cancer, outfitting the tumor cells with genes for immune cell activating cytokines such as LL2, and re-injecting these gene-modified tumors into the patient. While the thought of reintroducing a cancerous tumor into a patient seems somewhat frightening, the enhanced immune response triggered by this technique may help prevent the recurrence of cancer.
1.What innate characteristic of viruses did researchers take advantage of in order to transport genes into TILS?
2.According to the passage, SCID is caused by（  ）.
3.Why might cancer patients be leery of the prospect of a cancer “vaccine” as discussed in this passage?
4.Adenosine deaminase (ADA) is transferred into the T cells of a patient via which of the following?