Transcriptional programming of CD4⁺ T_RM differentiation in viral infection balances effector- and memory-associated...

After resolution of infection, T cells differentiate into long-lived memory cells that recirculate through secondary lymphoid organs or establish residence in tissues. In contrast to CD8⁺ tissue-resident memory T cells (T_RM), the developmental origins and transcriptional regulation of CD4⁺ T_RM remain largely undefined. Here, we investigated the phenotypic, functional, and transcriptional profiles of CD4⁺ T_RM in the small intestine (SI) responding to acute viral infection, revealing a shared gene expression program and chromatin accessibility profile with circulating T_H1 and the progressive acquisition of a mature T_RM program. Single-cell RNA sequencing identified heterogeneity among established CD4⁺ T_RM, which were predominantly located in the lamina propria, and revealed a population of cells that coexpressed both effector- and memory-associated genes, including the transcriptional regulators Blimp1, Id2, and Bcl6. T_H1-associated Blimp1 and Id2 and T_FH-associated Bcl6 were required for early T_RM formation and development of a mature T_RM population in the SI. These results demonstrate a developmental relationship between T_H1 effector cells and the establishment of early T_RM, as well as highlighted differences in CD4⁺ versus CD8⁺ T_RM populations, providing insights into the mechanisms underlying the origins, differentiation, and persistence of CD4⁺ T_RM in response to viral infection.