Long-lived memory CD8+ T cells are essential for the control of persistent viral infections. The mechanisms that preserve memory cells are poorly understood. Fate mapping of the transcriptional repressor GFI1 identified that GFI1 was differentially regulated in virus-specific CD8+ T cells and was selectively expressed in stem cell memory and central memory cells. Deletion of GFI1 led to reduced proliferation and progressive loss of memory T cells, which in turn resulted in failure to maintain antigen-specific CD8+ T cell populations following infection with chronic lymphocytic choriomeningitis virus or murine cytomegalovirus. Ablation of GFI1 resulted in downregulation of the transcription factors EOMES and BCL-2 in memory CD8+ T cells. Ectopic expression of EOMES rescued the expression of BCL-2, but the persistence of memory CD8+ T cells was only partially rescued. These findings highlight the critical role of GFI1 in the long-term maintenance of memory CD8+ T cells in persistent infections by sustaining their proliferative potential.
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Immune checkpoint blockade (ICB) can induce antitumor efficacy but also induces immune-related adverse events. Systemically administered ICB can activate immune cells throughout the host. Conditionally active ICB with proteolytically cleaved masking domains can potentially reduce the adverse events seen with anti-cytotoxic T-lymphocyte associated protein 4 (CTLA-4) antibody.
We examined how different formats of a conditionally activated dual variable domain IgG (DVD) that binds CTLA-4 and the tumor-associated antigen prostate stem cell antigen (PSCA) can lead to efficacy in syngeneic subcutaneous and metastatic murine tumor models. We also defined the capacity of these DVDs to modulate immune responses by multiparameter flow cytometry.
Conditionally active DVDs can uncouple antitumor efficacy from toxicity. A fully cleavable construct (symmetric DVD, sDVD), which can be released from the target tumor cells, showed superior antitumor efficacy compared with asymmetric DVD, which retains its tumor antigen binding. The sDVD elicited the highest tumor-antigen-specific T-cell responses detected in tumors and tumor-draining lymph nodes, as well as presenting the highest rate of intratumoral and splenic "non-exhausted" antigen-specific CD8 T cells. SDVD also induced the highest degrees of T-cell memory and self-renewal potential. These effects were dependent on PSCA expression by the tumors.
These findings support the notion that ICB modulation of antitumor immunity away from the tumor cells is critically important for optimal antitumor immunity. The bispecific sDVD antibody design may enable improved systemic antitumor responses than traditional ICB in both primary tumors and metastases.
© Author(s) (or their employer(s)) 2025. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ Group.