AAV-CRISPR-Cas9: an imminent treatment for familial hemophagocytic lymphohistiocytosis?
Preclinical investigations show the success of a method to overcome genetic defects that lead to a severe immune disorder, familial hemophagocytic lymphohistiocytosis.
A research team from the Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (Berlin, Germany) has demonstrated an effective gene-edited cell therapy for the treatment of familial hemophagocytic lymphohistiocytosis (FHL) in preclinical mice models. This holds the potential to improve the current medical options for the rare disease, which currently has a 50% long-term survival rate with the best available therapy.
FHL is a rare, inherited syndrome that causes life-threatening severe and systemic hyperinflammation. It is the consequence of genetic mutations in several different genes involved in the cytotoxicity pathway, most commonly PRF1 but also UNC13D, STX11 and STXBP2, which impact either the production of perforin — a membrane perforating protein — or the attachment mechanisms of perforin-containing lytic granules to a target [1].
During an infection, the ineffective cytotoxicity of lymphocytes results in sustained activation of the immune system, leading to subsequent cytokine storms and immune-cell-mediated multi-organ damage.
Usually occurring in infants under 18 months, FHL is severe and has a high mortality rate. The longest life-preserving treatment of FHL employs combinatorial immunochemotherapy and allogeneic hematopoietic stem cell transplantation. However, even with these treatments, 50% of patients do not survive long-term. Therefore, there is an urgent clinical need for more effective therapeutic options, which the researchers sought to address in a recent paper [2].
Focusing on one of the genetic mutations — Prf1 — the researchers developed a repair strategy for faulty immune T-cells. They used CRISPR-Cas9, a powerful genome-editing molecular tool, to introduce a functional Prf1 gene using an adeno-associated viral (AAV) vector.
This was initially performed ex vivo in both primary mouse T-cells and long-lived memory T-cells — cells that give rise to active cytotoxic T-cells. Then, they infused the gene-corrected memory T-cells into in vivo mice models of FHL, which were consequently rescued from the condition.
The researchers then focused on human cells, obtained from FHL patients undergoing immunochemotherapy. AAV-CRISPR-Cas9 gene correction restored the cytotoxicity of T-cells, not only in the case of a defective PRF1 gene but also for a faulty UNC13D gene. These results demonstrate the feasibility of employing AAV-CRISPR-Cas9 gene correction for FHL, serving as a proof-of-principle study.
“It is still uncertain how long the protective effect lasts,” commented Christine Kocks, one of the authors of the study. “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.”
Alongside further research to probe the effective timescale of the therapy, the team also acknowledges the need for human clinical trials to investigate additional questions, such as whether engrafted T-cells can overcome challenges associated with the heterogeneity of the disease and what the effects of suboptimal protein expression are.