Jonathan Hoar

Stem-like T cells promote the efficacy of immunotherapy and are heterogeneous in stemness, with long-term (LT) stem-like T cells at the apex of this hierarchy. How the stemness hierarchy is regulated in chimeric antigen receptor (CAR) T cells and how it affects antitumor function are unclear. Here we show that BACH2 dose-dependently regulates LT stem-like differentiation and antitumor immunity of CAR T cells. LT stem-like CAR T cells that appear before infusion and re-emerge after tumor clearance have superior antitumor immunity and the greatest BACH2 expression. BACH2 promotes the antitumor response of CAR T cells and the LT stem-like transcriptional program. Temporal and quantitative induction of BACH2 expression in CAR T cells during manufacturing using chemical switches fine-tunes the degree of stemness and imprints greater control of solid tumors. Together, these data show that BACH2 dosage defines stemness hierarchy in CAR T cells and can be temporally and tunably controlled to optimize differentiation and antitumor efficacy.

T cell aging increases the risk of viral infection‐related morbidity and mortality and reduces vaccine efficacy in the elderly. A major hallmark of T cell aging is the loss of quiescence and shift toward terminal differentiation during homeostasis. However, how aging impacts the differentiation program of virus‐specific T cells during infection is unclear. Here, in a murine coronavirus (MHV) infection model with age‐associated increased mortality, we demonstrate that aging impairs, instead of promoting, the terminal differentiation program of virus‐specific CD8⁺ T cells. Upon infection, CD8⁺ and CD4⁺ T cells in old mice showed marked reduction in clonal expansion and upregulation of immune checkpoints associated with T cell exhaustion. Bulk and single‐cell transcriptomics showed that aging upregulated the T cell exhaustion transcriptional program associated with TOX in virus‐specific CD8⁺ T cells and shifted the myeloid compartment from immunostimulatory to immunosuppressive phenotype. In addition, aging downregulated the transcriptional program of terminally differentiated effector CD8⁺ T cells and diminished the CX3CR1⁺ cytotoxic effector lineage. Mechanistically, virus‐specific CD8⁺ T cells from infected aged mice displayed defects in inducing transcription factors ZEB2 and KLF2, which were required for terminal differentiation of effector CD8⁺ T cells. Together, our study shows that aging impairs terminal differentiation and promotes exhaustion of virus‐specific CD8⁺ T cells responding to coronavirus infection through dysregulating expression of lineage‐defining transcription factors.