New hope for FHL treatment with CRISPR-Cas9

BioTechniques News
Beatrice Bowlby

Researchers present a novel therapeutic mechanism to treat familial hemophagocytic lymphohistiocytosis (FHL) by editing T cells with CRISPR-Cas9.

A study from researchers at the Max Delbrück Center (Berlin, Germany), led by Klaus Rajewsky, has identified a potential treatment of a serious immune disorder, FHL, that typically impacts children under 18 months old. Using CRISPR-Cas9 technology, the researchers have been able to correct an issue associated with FHL in the T cells of mice, taking the first step in validating this approach.

FHL is the result of gene mutations that ablate the function of cytotoxic T cells. When an infant with FHL is infected by a virus, their T cells are unable to eradicate the infected cells and the immune response escalates to a cytokine storm, coupled with extreme levels of inflammation. This combination can prove fatal, resulting in a high mortality rate for infants with FHL. The current standard of care involves a combination of chemotherapy and bone marrow transplantation; however, many children still die of FHL.

In order to improve the therapeutic landscape for FHL, Rajewsky and his team investigated a model of the condition in mice, engineering them to express a dysfunctional protein from the gene perforin, which is commonly mutated in people with FHL. These mice were then infected with the Epstein-Bar virus to trigger an immune response, which spiraled out of control as a result of their defective T cells, leading the mice to develop FHL.

Once this response had been triggered, the team extracted memory T cells from the infected mice and used an adeno-associated virus-based CRISPR-Cas9 system developed by the team, coupled with nonhomologous end joining inhibition, to repair the defective perforin genes within them. They then implanted the edited T cells back into the mice, where they could mature into cytotoxic T cells. This resulted in the dampening of their immune response and the relief of their symptoms.

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With the initial concept demonstrated in mice, the team then set out to determine whether the same approach could translate to humans. First author Xun Li took blood samples from two children with FHL. The team then applied their CRISPR-Cas9 editing method to correct the patients’ T cells. One child had a defective perforin gene while the other had a mutation in a different part of their genome.

Commenting on the process and their technique, Li reported that, “our gene repair technique is more precise than previous methods, and the T cells are virtually unchanged after undergoing gene editing. It was also fascinating to see how effectively the memory T cells could be multiplied and repaired from even a small amount of blood.” Using these repaired T cells in cell culture studies, Li et al demonstrated that the cells could produce effective cytotoxic responses, suggesting that the approach could well be applicable to humans.

Next, the team needs to validate this novel therapeutic mechanism in clinical trials and begin to discern how long the therapeutic effect could last. “Since the T memory stem cells remain in the body for a long time, we hope the therapy provides long-term or even permanent protection. It is also conceivable that patients could be treated with their repaired T cells over and over again,” commented Christine Kocks, one of the co-authors of the study.

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