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needed to be monitored and confirmed in the next few months.

Acute lymphoblastic leukaemia (ALL) is the most common kind of cancer in children and affects cells in the immune system, known as B cells and T cells, which fight and protect against viruses.

GOSH said Alyssa was the first patient known to have been given base-edited T cells, which involves chemically converting single nucleotide bases -- letters of the DNA code -- which carry instructions for a specific protein.

Researchers at GOSH and University College London helped develop the use of genome-edited T cells to treat B-cell leukaemia in 2015.

But to treat some other types of leukaemia the team had to overcome the challenge that T cells designed to recognise and attack cancerous cells had ended up killing each other during the manufacturing process.

Multiple additional DNA changes were needed to the base-edited cells to allow them to target cancerous cells without damaging each other.

“This is a great demonstration of how, with expert teams and infrastructure, we can link cutting edge technologies in the lab with real results in the hospital for patients,” said GOSH consultant immunologist and professor Waseem Qasim.

“It’s our most sophisticated cell engineering so far and paves the way for other new treatments and ultimately better futures for sick children.”