McLean (United States) (AFP)
When a person's immune system is sabotaged by a genetic disease, a bone marrow transplant can cure it, but a temporary vulnerability then appears: during the first months, the recipient is naked in the face of viruses. A common germ can send him to the hospital.
A new type of treatment, called cell therapy, aims to fill these months during which the body's defenses are rebuilt. After two decades of therapeutic trials, the technology is refined and more and more children are being treated.
Johan is one of them.
Today he is a clever little fellow with a thick, relentless pursuit of the family puppy. Nothing betrays the three years of medical and emotional adventure from which his family emerges today, in a wealthy suburb of Washington.
The roller coaster started the pregnancy test: Johan was not planned. "It was a shock, I cried," said his mother, Maren Chamorro, 39.
She knew from her childhood that she was carrying a gene causing an often fatal disease before the age of ten, chronic granulomatosis. Her brother died at the age of seven. The laws of genetics meant that she had a one in four chance of passing it on.
For their first children, she and her husband, Ricardo, had chosen in vitro fertilization, allowing a genetic test of the embryos before implantation. Their twins Thomas and Joanna were born seven and a half years ago without the disease.
For Johan, a genetic test quickly confirmed that he had been reached. After contacting the Washington Children's Hospital, the couple made one of the most important decisions of their life: Johan would receive a bone marrow transplant, a risky procedure but one that made healing possible.
"The fact that Maren lost her younger brother to this illness played a big role," says Ricardo.
Bone marrow is our factory for red and white blood cells. That of Johan produced white blood cells unable to respond to bacteria and fungi. In him, a bacterial infection could get out of hand.
Luckily, his brother Thomas was a compatible donor. In April 2018, doctors cleaned Johan's marrow with chemotherapy. Then they took that of Thomas, then six years old, from the bones of his pelvis, with a needle.
They extracted from it "supercells", as Thomas says, stem cells, which they reinjected into Johan's veins so that they gradually make their nest in his bone marrow, and make normal white blood cells there.
- Brother's immune system -
The second step was preventive cell therapy, in an experimental program led by immunologist Michael Keller. The part of the immune system that protects against bacteria rebuilds in a few weeks, but for viruses, it takes more than three months.
From the blood of Thomas, the doctors extracted globules having already encountered six viruses, T lymphocytes. Doctor Keller multiplied them for ten days in an incubator, to create an army of hundreds of millions of specialized lymphocytes. The result is a white cream, at the bottom of a bottle.
Then the T cells were injected into Johan, immediately guarding these six viruses, preventively.
"He has his brother's immune system," says Michael Keller.
What his mother confirms: today when Thomas and Johan catch a cold, they have the same symptoms, the same duration. "It's pretty cool to have the same immunity as your big brother," she says.
The approach of boosting the immune system, from donor cells or from one's own genetically modified cells, is called immunotherapy.
The main application concerns cancer, but Michael Keller hopes that it will soon be available against viruses, for immunocompromised patients like Johan.
For Johan, a year and a half after the transplant, everything indicated that she had taken it perfectly.
"It's great to see him playing in the mud," says Maren, whose only concern, when Johan gets sick now, is that the rest of the family gets the same germ.
© 2020 AFP