A distinct subset of stem-cell memory is poised for the cytotoxicity program in CD4⁺ T cells in humans

The CD4⁺ cytotoxic T lymphocytes (CD4-CTLs) with cytotoxic potential are reported to be the components of protective immune response in many diseases. However, the lack of understanding about their lineage, molecular character, and cytolytic potential in comparison to CD8⁺(CD8)-CTLs has restricted their utility. Thus, here, by parallelly analyzing the human peripheral CD4-CTLs and CD8-CTLs, we demonstrate that they are indistinguishable for the cytotoxic program. Furthermore, using an integrative multiomics approach combining the transcriptome, T cell antigen-receptor repertoire, and open chromatin profile of CD4⁺ T cell memory subsets, we found a stem-cell memory subset that is precommitted to the cytotoxicity program. Through an in vitro differentiation model, we developed CD4⁺ T cells with cytolytic potential coexpressing and exhibiting progressive chromatin accessibility for cytotoxicity- and longevity-associated genes, hence generating long-lived CD4-CTL effectors of varying cytotoxic capacity. Together, our study advocates for exploring both CD4-CTLs and CD8-CTLs for vaccine development, vaccine efficacy testing, and immunotherapies and cell-based therapies for precision medicine.