(172) De novo generation of innate memory-like T cells occur early during human immune development

Introduction/Rationale: Infants rely heavily on innate immunity while adaptive memory develops. A subset of T cells, termed “virtual memory” or innate-like memory T cells, bridges innate and adaptive immunity, but their emergence in early human life is unclear. Infants receiving gene therapy for X-linked severe combined immunodeficiency (SCID-X1), whose immune systems reconstitute de novo, offer a unique model to study this process. We investigated whether innate-like memory CD8⁺ T cells arise during immune reconstitution and defined their epigenetic, transcriptional, and functional features.

Methods: Longitudinal blood samples from SCID-X1 infants post–gene therapy were analyzed.
Flow cytometry identified CD8⁺ subsets expressing NKG2A. TCR sequencing assessed clonal diversity, while DNA methylation and RNA profiling defined molecular signatures. Functional assays measured cytokine-induced, antigen-independent IFN-γ production after IL-12 and IL-18 stimulation.

Results: Early after gene therapy–induced immune reconstitution, infants’ peripheral blood showed a relative enrichment of innate-like memory CD8⁺ T cells marked by NKG2A expression. These NKG2A⁺ CD8 T cells displayed innate-associated transcriptional signatures and a TCR repertoire distinct from conventional naïve/memory subsets. DNA methylation profiling confirmed a subset-specific epigenetic signature, including open (poised) regions at effector genes, consistent with readiness for rapid response. Functionally, when stimulated ex vivo with IL-12 plus IL-18, NKG2A⁺ T cells produced IFN-γ in an antigen-independent fashion, indicative of innate‐like responsiveness. Together, these features distinguish them from conventional antigen-driven memory CD8 T cells.

Conclusion: Innate-like memory CD8⁺ T cells emerge early during immune reconstitution, primed for rapid, antigen-independent responses.