SUMMARY: UCLA researchers from the Department of Microbiology, Immunology, and Molecular Genetics have developed a novel method to increase the immune response of natural killer cells by ablating the transcriptional regulator Fli1 via CRISPR. BACKGROUND: Natural killer (NK) cells are innate immune cells that combat viral infections and serve as the first line of defense against malignant tumors. Now with increasing evidence, NK cells have been shown to constitute a heterogeneous and versatile cell subset. Of particular interest, they have been shown to also exhibit the capacity for immunological memory responses, in which the cells can remember previous encounters with pathogens and execute a specific and robust secondary response upon re-exposure. Like T and B cells, NK cells can undergo activation, expansion, and contraction in an antigen-specific manner to generate long-lived memory phenotype (MP) NK cells. Numerous studies describe the enhanced antitumor effects that are mediated by these memory-like NK cells in mice and human models. However, many of the current NK cell-based therapies are limited by short lifespans and impaired function. Currently, research is underway to understand the molecular mechanisms that regulate memory formation in NK cells. Innovating methods to modulate the biology of NK cells and increase their potency as immunotherapies could make huge strides in fighting cancer. INNOVATION: Researchers led by Dr. Timothy O’Sullivan in UCLA’s Department of Microbiology, Immunology, and Molecular Genetics have developed a method for increasing the persistence of MP NK cells and improving the immunological response against re-infection. Using single-cell RNA sequencing, the researchers first identified two distinct effector NK cell populations in mouse cytomegalovirus (MCMV)-infected murine models. They found that one of these populations shared a core epigenetic signature with MP CD8+ T cells enriched in the Fli1 transcription factor binding motif. To elucidate the role of Fli1 in MP NK cell formation, the researchers ablated Fli1 expression and saw that apoptosis of early effector NK cells decreased, suggesting that Fli1 limits MP NK formation. Building from this discovery, the O’Sullivan group used CRISPR to delete Fli1 in early effector NK cells. They demonstrated that Fli1 deletion results in increased MP NK cell persistence following viral infection. Taken together, CRISPR-mediated Fli1 deletion presents a promising immunotherapy tool to improve individual immune responses against viral infection, cancers, and other diseases. POTENTIAL APPLICATIONS: • Enhance anti-tumor properties of NK cell-based immunotherapies • Increase persistence of MP NK cells for stronger immune responses against reinfection by infectious diseases ADVANTAGES: • NK cells mediate anti-cancer effects without risk of inducing graft-versus-host disease • NK cells are active against a host of infectious diseases, including viral, bacterial, and fungal pathogens DEVELOPMENT-TO-DATE: The researchers have successfully demonstrated that deletion of Fli1 increases the persistence of MP NK cells after MCMV infection in murine models. Related Papers (from the inventors only): Riggan, L., Ma, F., Li, J.H. et al. The transcription factor Fli1 restricts the formation of memory precursor NK cells during viral infection. Nat Immunol 23, 556–567 (2022).