We find that a minority of TCF-1+ CD8+ T cells within BrMs co-express TOX and PD-1, two proteins also expressed on exhausted, tumor-specific CD8+ T cells.37, 38, 39,46, 47, 48 Crucially, we show that bystander cells specific for microbial antigens infiltrate BrMs, and a subset of these cells share phenotypic characteristics—such as TCF-1 expression—with exhausted progenitor CD8+ T cells. Here, TOX is linked to neoplasm.