Reduction in Incidence and Severity of Acute Graft-Versus-Host Disease (aGVHD) via CRISPR-Cas9 Deletion of the miR-155 Host Gene (MIR155HG) in Primary Human T Cells
CRISPR/Cas 9 mediated targeting of MIR155HG in primary human T cells creates genomic deletions that disrupt transcription of mature microRNA-155 (miR-155, a miR associated with inflammation). Applying this treatment to donor T cells prior to allogenic hematopoietic stem cell transplantation (allo-HSCT) when treating hematological malignancies and other primary bone marrow disorders can prevent the development of aGVHD in patients.
More than 8,000 patients receive allo-HSCT annually in the US alone as a cure for hematologic malignancies and other primary bone marrow disorders. However, the major barrier for the success of allo-HSCT is the high incidence of aGVHD and its associated morbidity and mortality. Acute GVHD is clinically characterized by damage to the skin, liver, and gastrointestinal (GI) tract. Current preventive measures of aGVHD involve pharmacological immunosuppression or T cell depletion, but despite the use of standard GVHD prophylaxis regimens, 30-75% of patients who receive allo-HSCT eventually develop aGVHD. Despite response rates of only 40-60%, the standard first-line treatment for GVHD remains high-dose corticosteroids, which results in high rates of non-relapse mortality. Finding a novel therapeutic that could prevent the development of aGVHD would be a turning point in the global HSCT market, which is estimated to be US $2 billion in 2020 and is expected to have a CAGR of 11% 2020-2027 due to the growth in leukemia and lymphoma cases.
Researchers at the Ohio State University, led by Dr. Parvathi Ranganathan, have developed a strategy to genomically target MIR155HG using the CRISPR/Cas9 system, thereby reducing the expression of microRNA-155, which is associated with the development of aGVHD. By designing pairs of sgRNA to target certain fragments of MIR155HG, they were able to decrease, and in some cases prevent, the development of GVHD in a xenogeneic model of the disease. The research initially focused on using the sgRNA to target either the promoter or exon 3 sequences of MIR155HG. CRISPR-edited T cells were injected into NSG mice and evaluated for protection against development of GVHD in a xenogeneic model of aGVHD. Data were recorded for non-targeting, exon 3-targeting, and promoter-targeting groups. In Figure 1, fold change in miR-155 and MIR155HG expression were measured at 72 hours (C) and 7 days (D) post-transfection, showing promising results, esp. for the exon 3-targeting group. In Figure 2, the probability of survival (A) and aGVHD clinical scores (B) were compared with the non-targeting and the exon 3-targeting T cell transplants. Again the results support MIR155HG exon 3-targeting, which showed survival for the transplant group of >100 days post-transplant, and an aGVHD clinical score of 0 up to about 60 days and up to ~2 at 100 days post-transplant (compared to ~4 at 65 days post-transplant for the non-targeting group). Results indicate CRISPR/Cas9 mediated targeting of MIR155HG results in sustained downregulation of miR-155 expression in primary human T cells, no production in significant off-target effects, and protection form aGVHD in a xenogeneic model of the disease. Additionally, T cells lacking miR-155 show robust anti-tumor clearance comparable to WT T cells. These results showcase the power of genomic deletion in MIR155HG and subsequent prevention of aGVHD in mice models, with promising translation to human models. Using this strategy to engineer human donor T cells in patients undergoing allo-HSCT could be a better preventative measure against aGVHD when compared to the alternatives.