Researchers from the Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC) have developed a groundbreaking gene therapy approach that could provide hope for patients with familial hemophagocytic lymphohistiocytosis (FHL), an inherited immune deficiency characterized by severe systemic hyperinflammation.

The study, titled “Precise CRISPR-Cas9 gene repair in autologous memory T cells to treat familial hemophagocytic lymphohistiocytosis,” focuses on repairing mutations in T cells from a mouse model of FHL and two pediatric patients with the condition. The researchers utilized a CRISPR-Cas9 system based on adeno-associated virus (AAV), demonstrating successful repair and paving the way for potential clinical applications in FHL patients and other primary immunodeficiencies with monogenic T cells.

The innovative technique combines a CRISPR-Cas9-induced double-stranded DNA break (DSB), an AAV-delivered DNA donor template for homology-directed repair (HDR), and an inhibitor of nonhomologous end joining (NHEJ). The researchers introduced Cas9-sgRNA complex-containing ribonucleoprotein particles (RNPs) into cells through electroporation and used AAV infection to deliver repair templates.

In a proof-of-concept study, the team applied AAV-templated CRISPR-Cas9-mediated gene correction to restore PFR1-deficient memory T cells. They successfully developed gene correction strategies in human T cells to fix PRF1 and UNC13D mutations, restoring CD8 T cell cytotoxicity in cells isolated from pediatric patients with FHL2 and FHL3.

Given that only about half of FHL patients survive long-term with existing treatments, this novel gene therapy approach addresses an urgent clinical need to improve outcomes. The researchers highlight the potential for gene repair using autologous T cells as a therapeutic option for FHL in humans and suggest that the developed T cell gene repair strategies could be applicable to other primary immunodeficiencies based on monogenic T cells and less common types of FHL.

By Impact Lab