066 - Infant αβ CD8+ T cells are enriched for innate-like populations

Publication Number: 66.5358

Adam Geber, University of Rochester School of Medicine and Dentistry, Rochester, NY, United States; Darline Castro-Meléndez, University of Rochester School of Medicine and Dentistry, Rochester, NY, United States; Nathan Laniewski, University of Rochester School of Medicine and Dentistry, Rochester, NY, United States; David Topham, University of Rochester School of Medicine and Dentistry, Rochester, NY, United States; Heidie L. Huyck, University of Rochester School of Medicine and Dentistry, Rochester, NY, United States; Gloria S. Pryhuber, Golisano Children's Hospital at The University of Rochester Medical Center, Rochester, NY, United States; Kristin M. Scheible, University of Rochester, Rochester, NY, United States

Background: The infant immune system undergoes pre-and postnatal development that must rapidly and nonspecifically respond to signals of danger and tissue damage. There is evidence from animal models that fetal naïve T cells share characteristics with typical innate immune populations, which may enhance their reactivity outside of a well-controlled and antigen-specific response. Defining the functional capacities of T cell populations from early ontogeny is foundational to understanding mechanisms of perinatal inflammation and immunopathology.

Objective: We sought to test the hypothesis that naïve CD8+ T cells among premature and full-term infants overlap phenotypically with adult naïve CD8+ T cells but harbor functions that are permissive to TCR-independent reactivity. We further hypothesized that conventional αβ CD8+ T cells enriched for innate-like characteristics and that waned with age would identify a fetal-derived population.

Design/Methods: Mononuclear cells were isolated from premature (n=10) and full-term (n=10) infant cord blood (CBMC), and peripheral blood mononuclear cells (PBMCs) were isolated from healthy adult donors (n=10). Cells were stimulated in vitro with IL-12/IL-18 and PMA/ionomycin and were immunophenotyped using high-parameter flow cytometry and cluster-based profiling. Multimodal single cell profiling was performed to colocalize cell-specific identity, transcriptome, and TCR sequence. Clustering, trajectory inference, and regression analyses were performed to identify CD8+ T cell populations that were correlated with gestational age.

Results: Multiple naïve CD8+ T cell subpopulations were consistently detectable in cord blood and waned variably in adult donors. KLRG1+CD161+IL18R1+ cells were most abundant in premature subjects, responded to TCR-independent IL-12/IL-18 stimulation, and produced TNF and a gene expression program related to antiviral immunity. Innate cytokine (IL-8) producing cells were most abundant in full-term infants following PMA-Ionomycin treatment. CD8+ T cells with innate cytokine functions expressed TCR sequences that were widely shared among subjects (“public” clones).

Conclusion(s): Infants harbor specific CD8+ T cell populations with innate-like characteristics that vary by gestational age. These findings can clarify age-specific mechanisms of perinatal inflammation and identify cellular drivers of immunopathology in early life.

Infant CD8+ T cells are enriched for multiple naïve populations.
The relative frequency of CD45RA+CCR7+ clusters annotated as innate-like (CD161+KLRG1+) or IL-8+ was compared between premature, full-term, and adult subjects. The conventional naïve phenotype was defined as CD45RA+CD45RO-CCR7+ and lacked expression of CD56, KLRG1, CD161, TCRVα7.2, and TCRγδ as well as reactivity to the MR1:5-OP-RU tetramer. Left: cluster frequency relative to total CD8+ T cells (CD3+CD4-CD8a+). Subjects are ordered with increasing gestational age from left to right; adult subject ages ranged from 20-63y. Middle: faceted marker density plots for highlighted clusters. Right: ratios of innate-like or IL-8+ cells to conventional naïve cells stratified by cohort. Cohorts were compared using pairwise two-sample t-tests. Significance key: ns = p > 0.05, * = p ≤ 0.05, ** = p ≤ 0.01, *** = p ≤ 0.001.