This is a summary of Kendirli, A., de la Rosa, C., Lämmle, K.F. et al. A genome-wide in vivo CRISPR screen identifies essential regulators of T cell migration to the CNS in a multiple sclerosis model. Nat Neurosci (2023). https://doi.org/10.1038/s41593-023-01432-2

The challenge

MS is initiated when activated autoreactive T cells infiltrate the central nervous system (CNS) and trigger a cascade of tissue injury. We know from previous studies how important this T-cell infiltration is, but so far, most studies have focused on assessing and validating the roles of molecules known to be involved in T cell trafficking. Thus, we lack a comprehensive understanding of the essential molecular cues and signaling streams that enable or limit T cell entry to the CNS and may thus represent alternative targets for therapy.

Our approach

We employed genome-wide in vivo CRISPR screening in a rat model of multiple sclerosis. This gene editing approach has primarily been used in investigations relating to cancer pathogenesis but has not yet been applied to study the initiation of CNS inflammation. Here we use this approach in combination with functional in vivo validation studies, multiphoton microscopy, and in vitro mechanistic experiments to identify the essential regulators of the infiltration of autoreactive T cells to the CNS.

Our findings

We identified 5 essential inhibitors and 18 essential facilitators of T cell migration to the CNS. These regulators can be categorized into three functional categories necessary for a T cell to cross over from the blood to the brain: adhesion to blood vessel endothelium, egress from blood vessels, and regulation of attractive signals. The adhesion of T cells to the endothelium of blood vessels through the molecule alpha-4 integrin is an important process at the beginning of transmigration. In the next step, the T cells egress from the blood vessel. Their movement is controlled by messengers, which are recognized by a specific protein, the chemokine receptor CXCR3. The third functional category relates to molecules that regulate how T cells register attractive signals from the blood. Notably, several of the top hits identified in our screen are already targeted by successful disease-modifying therapies in clinical practice.

The implications

The migration of T cells into the CNS is the fundamental step in the pathogenesis of MS lesions. Our study, therefore, has two clear implications. First, it confirmed that current MS therapies already efficiently target the transmigration of autoreactive T cells – a reassuring finding for clinical practice. Secondly, our approach validated the transferability to humans. Our CRISPR-based screening of MS models is a highly versatile approach that can be easily adapted. This means our method can be applied to currently poorly understood questions, such as what happens when other harmful immune cell populations migrate from the blood to the nervous system – questions we want to explore further together with our partners in SyNergy.

Creating SyNergies

This research in SyNergy was led by the Kerschensteiner and Kawakami teams at LMU and included two SyNergy members (Gerdes and Beltrán).