Engineering Safe Microglia Replacement Using Inhibitor-Resistant CSF1R

Hematopoietic stem cell transplantation (HSCT) is a treatment option for replacing endogenous microglia in the brain, but it is associated with high mortality. To mitigate the risks associated with HSCT and expand the potential for microglia replacement, researchers have engineered an inhibitor-resistant form of the colony stimulating factor 1 receptor (CSF1R). This new form of CSF1R, known as G795A, confers resistance to multiple inhibitors, including PLX3397 and PLX5622. Despite the modification, G795A-CSF1R has no discernible gain or loss of function compared to the wildtype form of the receptor.

G795A-expressing macrophages were able to efficiently engraft the brain of mice treated with PLX3397 and persist after cessation of inhibitor treatment. To gauge the translational potential of this new form of CSF1R, researchers engineered human induced pluripotent stem cell-derived microglia (iMG) to express G795A. 

Xenotransplantation studies demonstrate that G795A-iMG are nearly identical to wildtype iMG in terms of gene expression and similarly respond to inflammatory stimuli. In the presence of PLX3397, G795A-iMG can progressively expand and replace endogenous microglia to fully occupy the brain.

This study represents a significant advancement in our understanding of microglia replacement therapy. By engineering a form of CSF1R resistant to inhibitors, researchers have developed a non-toxic, cell type-specific, and tissue-specific method for replacing microglia in the brain. This new approach can potentially expand the use of microglia replacement therapy and could have important implications for treating a wide range of neurological disorders.

The findings of this study, published in the Journal of Experimental Medicine, demonstrate that G795A-iMG are a promising new tool for microglia replacement therapy. By engrafting efficiently in the brain and responding to inflammatory stimuli like wildtype iMG, G795A-iMG have the potential to be a safe and effective treatment for a variety of neurological disorders. Furthermore, the ability of G795A-iMG to persist after cessation of inhibitor treatment suggests that this new form of microglia replacement therapy could be long-lasting and provide sustained benefits for patients.

By demonstrating the efficacy and safety of G795A-iMG, this study represents a significant step forward in the field of microglia replacement therapy and has the potential to lead to new treatments for patients with neurological disorders.