@fohanc I get what you’re saying for the top cloze of c1. But it could be misinterpreted as facilitating the maturation - given how it starts out with “ensures the maturation…”; an alternative would be saying “selects for mature T-cells that can…” but this would be somewhat redundant given how the term is “positive selection”
For the bottom cloze of c1, “self-reactive” is ambiguous so something more specific will definitely be helpful. For sake of brevity, I’ve condensed what you’ve suggested to “Causes apoptosis in T-cells that bind to MHC molecules presenting no antigen or a self-antigen”