New approach to build immunity against infections

Scientists have developed a novel approach to protect humans from infections by adjusting the genes of the human cells to remove the mechanism that allows pathogens to cause diseases.
The researchers decided to silence genes in human cells to discover if the loss of any single gene would confer immunity to the parasite E histolytica, which infects 50 million people and causes 40,000-110,000 deaths via severe diarrhoea worldwide.
The team used the technique called RNAi to create a library of bladder cancer cells with thousands of independent, silenced genes. Then they challenged these cultures with the parasite E histolytica.
"We do this all the time in cancer research. Commonly, we're looking for genes that, when silenced, will make cells more susceptible to chemotherapy," said Dan Theodorescu, director of the University of Colorado Cancer Centre.

In this case the analogue of chemotherapy was the infectious, dangerous pathogen.
"This amoeba is a cluster bomb - a voracious killer. In the back of my mind I was thinking the parasite was going to decimate the host cells no matter what we did with their genetics," said Chelsea Marie, postdoctoral researcher in the Petri Laboratory at University of Virginia.

For the vast majority of cells in this genome-wide screen, Marie found that E histolytica decimated many thousands of these independent cell cultures. However, a small number of cells seemed to resist the parasite.
Marie discarded the killed cells and retested the cells that had survived; again she infected these survivor cells with E histolytica.

"We did this over nine generations of cells, each time selecting the cells that survived and then re-applying the parasite. Over these generations of selection, we saw the cultures becoming more and more enriched for cells lacking specific genes," Marie said.
Marie identified the genes that conferred resistance and found that many were involved in managing the flow of potassium into and out of human cells.
A follow-up experiment showed that new intestinal cells treated with E histolytica showed potassium efflux - the flow of potassium from inside a cell out through the cell wall - directly before cell death.

"The parasite was causing potassium efflux right before cell death and cells that happened to be unable to transport potassium didn't die," said Theodorescu.
To ensure that lack of potassium transport was, in fact, causing resistance to the parasite, the group reversed the direction of their experiments.
Marie started with new cells and used drugs to block their ability to transport potassium. Blocking potassium efflux created cells that were resistant to E histolytica.
This study shows that in addition to characteristics of the parasite, mortality due to disease can be prevented by manipulating characteristics of the host.
The study was published in the journal Nature Scientific Reports.