Multi-omics analysis identifies progenitors of CD4-CTLs [scRNA-seq in vitro]

The CD4+ T cells expressing cytolytic molecules such as granzymes and perforins have been detected in many diseases and are shown to be enriched in the effector memory expressing CD45RA (TEMRA) in humans, but their origin remains elusive. However, their gene expression profile in comparison to classically defined cytotoxic T lymphocytes (CTLs), the CD8-CTLs has not been well demonstrated, hence their relevance remains debatable. Thus in this study by parallelly analysing the CD4-CTLs and CD8-CTLs, we demonstrate that they are indistinguishable for the cytolytic program with both showing similar gene expression profile and T cell antigen-receptor (TCR) clonal expansion. Further using an integrative multi-omics approach combining the transcriptome, TCR repertoire, and open chromatin profile of CD4+ naïve (CD4-TN) and memory subsets, we discovered a stem-cell memory subset that is pre-committed to CTL program within the CD4+ T cell lineage. Through an in vitro differentiation model we developed CD4+ T cells with cytolytic potential from CD4-TN cells. The in vitro differentiated cells followed the trajectory of different developmental memory subsets from ex vivo CD4+ T cells for transcriptomic patterns as well as open-chromatin landscape. Thus, through this model, we deciphered the molecular signatures of early commitment of CD4-TN cells to cytotoxicity program. Of particular interest was the expression of both longevity as well as cytotoxicity associated gene sets by the in vitro differentiated CD4-CTLs, hence generating long-lived CD4-CTL effectors. This specific property can be further explored for vaccine development as well as testing the efficacy and cell based therapies for precision medicine.