genetic therapy | Photo credit: Getty Images
The story so far: Scientists in the UK testing a new form of cancer treatment have reported the success of a teenage girl, Alyssia, who has a form of cancer called acute lymphoblastic T-cell leukemia.
What happens in this form of cancer?
In this form of blood cancer, T cells, which are a class of white blood cells, equipped to hunt and neutralize threats to the body, turn against the body and end up destroying healthy cells that normally contribute to immunity. . The disease is rapid and progressive and is usually treated with chemotherapy and radiotherapy.
What marked Alyssia’s treatment?
The BBC reported that 13-year-old Alyssia tried many of the standard treatments, including chemotherapy and radiotherapy, but with limited success. Just when it seemed there was no hope, she was signed up for a trial of an experimental drug. This trial was conducted by doctors and scientists from University College London and Great Ormond Street Hospital. Alyssia was the first to receive experimental gene therapy using a new technique called “base editing”.
What is the “base set?”
A person’s genetic code is made up of several permutations of four bases: adenine (A), guanine (G), cytosine (C) and thymine (T). The sequences of these bases, related to the letters of the alphabet, spell out the genes that are instructions for producing the wide range of proteins needed for the body’s functions. In Alyssia’s case, her T cells – possibly due to a misarrangement in the base sequence – had turned cancerous. One way to correct this misarrangement could mean a healthier immune system. Over the past two decades, the world of biomedical engineering has become enthusiastic about a technique that can modify genes and “correct” errors. The most popular of these approaches has been the CRISPR-cas9 system.
Inspired by the way certain bacteria defend themselves against viruses, by taking and storing pieces of their genes, the CRISPR-cas 9 system consists of an enzyme that acts like molecular scissors. It can be done to cut a piece of DNA at a specific location and guide RNA can be used to insert modified genetic code at the incision sites. Although there are several ways to effect such changes, the CRISPR-cas9 system is considered to be the fastest and most versatile system for effecting such genetic modification. David Liu, from the Broad Institute, Massachusetts improvised on the CRISPR-cas9 system to be able to directly change certain bases: thus, a C can be changed to G and a T to A.
Although still a nascent technology, base editing would be most effective in treating blood disorders caused by so-called point mutations or where a change in a single base pair can cause terminal disease.
How did the core set work for Alyssia’s therapy?
The goal of gene therapy for T-cell leukemia was to fix his immune system so that it stopped making cancerous T cells. First, healthy T cells were taken from a donor and subjected to a series of modifications. The first basic modification blocked the T-cell targeting mechanism from attacking Alyssa’s body, the second removed a chemical marker, called CD7, which is on all T-cells, and the third prevented the cells from being killed by a chemotherapy drug. Finally, the T cells were programmed to destroy any cells – cancerous or protective – with CD7 labeled on them. After spending a month in remission, she received a second donor transplant to regrow her immune system which would contain healthy T cells.
How effective was the treatment?
Three months after treatment, his cancer appeared to resurface but the most recent investigations suggest no signs of it, according to the BBC. Alyssia was one of 10 people enrolled in the trial to receive the treatment.
It has been 1.5 years since she was first diagnosed with the disease and it remains to be seen whether the treatment has reliably and completely repaired her immune system.
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