Ventura Martinez, C. J.; Kempis Calanis, L. A.; Mijares Guevara, S.; Cedillo Banos, A.; Carreon Cortes, I. Y.; Vazquez Rodriguez, S.; Helguera Repetto, A. C.; Irles, C.; Spicuglia, S.; Rodriguez-Jorge, O.; Santana, A.

Premature birth and cesarean section are major perinatal factors influencing immune development and are associated with increased morbidity and inflammatory diseases. However, their impact on neonatal immunity remains incompletely defined. To determine how gestational age and mode of delivery shape early immune programming, we analyzed CD4 T cells, central regulators of adaptive responses, from preterm neonates and full-term neonates born by cesarean section or natural birth. We performed transcriptomic profiling (mRNA-seq) and functional assessment of T cell activation, proliferation, and cytokine production following stimulation. The mode of delivery exerted a dominant effect on the CD4 T cell transcriptome and function. CD4 T cells from full-term neonates delivered by natural birth exhibited an immune activation signature, produced higher levels of multiple cytokines, but showed reduced proliferative capacity. In contrast, prematurity induced modest changes in basal gene expression relative to full-term cesarean section neonates. CD4+ T cells from preterm neonates displayed enhanced proliferation and increased secretion of inflammatory cytokines IL-13, TNF, IL-6, and IL-17F upon stimulation, indicating heightened responsiveness. Collectively, our findings show that CD4 T cells from preterm neonates exhibit augmented inflammatory capacity, which becomes more regulated at term. The mode of delivery further refines this developmental trajectory: cesarean section is associated with a restrained functional profile, whereas natural birth is associated with an immune activation signature and increased responsiveness. These results provide evidence that neonatal CD4 T cell trajectories are established during fetal life and subsequently modulated at birth, underscoring the layered influence of perinatal factors on immune development.