A groundbreaking CRISPR-based gene therapy has shown promise in treating a life-threatening immune disorder known as CD3δ-deficient severe combined immunodeficiency (SCID). In a recent Cell article, McAuley, Kohn et al. presented proof-of-principle of this innovative gene therapy approach using a CRISPR-Cas9-derived adenine-base-editor (ABE). The study demonstrated the potential impact of this therapy on the treatment of monogenic diseases, offering new tailored therapeutic options.
Severe combined immunodeficiencies (SCIDs) are rare and life-threatening disorders characterized by the absence of T-cells, as well as potential impairment of other lymphocyte populations such as B- and NK-cells. These impairments leave affected individuals with ineffective immune systems, making them vulnerable to simple infections that can be fatal. CD3δ-deficiency is a specific form of SCID, accounting for roughly 1% of all cases. It is characterized by a deficiency of T-cells while maintaining normal B- and NK-cell development.
Developing a gene therapy strategy for CD3δ-deficient SCID has been challenging due to the limited availability of primary patient cells for research purposes, caused by the rarity of the disease. To overcome this obstacle, McAuley, Kohn et al. initially created a disease model using Jurkat cells to screen for suitable ABE strategies. They then explored CD34 cells from healthy donors modified with a lentiviral vector (LV) carrying specific mutation sequences as an ABE target. The tests conducted on these modified cells showed a high on-target base editor (BE) frequency of approximately 80%. When these edited cells were engrafted in mice, they successfully generated all hematopoietic lineages and exhibited long-term persistence.
In order to proceed with targeted gene editing for CD3δ-SCID, the researchers focused on the ABEmax-NRTH variant. They utilized this variant to perform base editing on CD34 cells from an infant SCID patient with a biallelic CD3δ 202C > T nonsense mutation. The edited cells were then cultured within artificial thymic organoids (ATO), which is an advanced in vitro differentiation assay that replicates various stages of human thymopoiesis. The team made an intriguing observation during this stage: while the unedited CD3δ-SCID cells were blocked at the double positive early (DPE) stage, the BE-corrected cells developed into functional T-cells, exhibiting a diverse repertoire of T-cell receptors (TCR).
This groundbreaking study opens up new possibilities for gene therapy in the treatment of monogenic diseases, particularly severe combined immunodeficiencies. By utilizing CRISPR-Cas9-derived adenine-base-editors, researchers have demonstrated the potential to correct the underlying genetic defects responsible for CD3δ-deficient SCID. The successful engraftment and development of edited cells in mice, as well as the functional T-cell production observed in vitro, offer hope for future therapies.
In conclusion, the study conducted by McAuley, Kohn et al. serves as a proof-of-concept for a CRISPR-based gene therapy approach to address CD3δ-deficient severe combined immunodeficiency. The development of tailored therapeutic options for monogenic diseases, such as SCID, marks a significant advancement in the field of gene therapy. As further research is conducted, this groundbreaking study could potentially pave the way for life-saving treatments for individuals suffering from similar conditions.
