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CRISPR for Cancer?

April 28, 2019

CRISPR, the gene editing tool that sounds like something out of a fridge, is now talked about for every genetic disease and just entered a clinical trials to treat cancer.

What is it?  In a cell, a complex of proteins and RNA that can cut a gene, in some cases cutting out one gene and splicing in another. Big business, leading to mega patent disputes. Yet it all started from a relatively modest NSF grant to Jennifer Doudna about bacterial DNA.

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As Ultraphyte presented before: CRISPR stands for
Clustered (short DNA sequences)
Regularly
Interspaced (with bits inbetween)
Short
Palindromic (read the same forwards and back)
Repeats.

So where did this DNA-editing machine come from? It evolved over millions of years in bacteria, as a bacterium’s immune system. The clusters of short repeated sequences appear in the bacterial DNA. Each short sequence has been copied from the viral genome of a previously infecting virus.

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Some generations before, a bacteriophage (bacteria-infecting virus) injected its DNA into the cell. The DNA sequence was recognized as foreign by the CAS complex, which is a protein/RNA machine that makes RNA copies of the infecting DNA sequence. The CAS RNA copies then cause the cell to (1) degrade the viral genomic DNA; (2) make short copies of viral sequence and insert them into host. These short copies (the “palindromic repeats” of CRISPR) then serve to generate future CAS RNAs that recognize the virus when it infects again–a kind of bacterial immune system.

Now what molecular biologists are doing is to engineer the CAS complex (and related protein machines, from different bacteria). Incredibly, the CAS machine has been made to work inside a human cell, where it can snip and edit one gene. The CAS needs to be engineered for extreme accuracy, to cut only one place in a large human genome, and to avoid “off-target effects” (unknown other ways it could mess with a genome). For example, at Duke University researchers have found a way to modify the shape of the RNA part of the machine so as to make the cutting more specific to the DNA sequence. This is really important when you are trying to fix one gene out of 3 billion base pairs.

The first clinical trial for cancer has been approved,  at the University of Pennsylvania, for treatment of multiple myeloma. Multiple myeloma occurs in white blood cells called B lymphocytes, or B cells. These B cells develop in the bone marrow, and certain clones proliferate when stimulated by an antigen to make antibodies. Then these antibody-producing cells develop into plasma cells, which are supposed to produce antibodies in the blood to combat infection. But when regulation fails, too many plasma cells are made, and they make abnormal antibodies that clog the blood.

Normally, the body needs to make T lymphocytes to regulate the B cells, but in multiple myeloma this regulation fails. So the aim of CRISPR therapy is to restore the patient’s own T cell regulation. This is done by:

–Remove some of patient’s own T cells for engineering (by autologous donation, giving cells back to oneself afterward)

–Giving the patient’s T cells a gene called TCR that recognizes a cancer surface protein called NY-ESO-1, found on myeloma cells. Now the T cells will be able to recognize and eliminate the cancer cells.

–To give the gene to the cells require a vector DNA called a lentivector. This lentivector was engineered from a lentivirus, originally the same HIV virus that causes AIDS. Ultraphyte has discussed lentivirus before; and The Highest Frontier shows lentiviruses as a future everyday therapy like aspiring. Amazingly, lentiviruses are now a standard approach for developing new cures.

–Use CRISPR to edit three other genes of the T cells, altering their function to enable these engineered T cells to attack the myeloma cells.

If that all sounds like a mouthful, it is. The result could be a miracle cure for an incurable illness. As you might imagine, though, as such cures become routine, increasing complexity means increasing development costs, and costs to your insurer. Something to think about as we develop these cures: Who will be able to afford them?

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