Isolated neonatal T cells have a lower proliferative capacity and secrete lower amounts of IFN-gamma after polyclonal stimulation in vitro. In vivo, the ability of neonatal T cells to mount effective responses is likely influenced by the lower expression of B7 family molecules on antigen-presenting cells and the defective cytokine production by these cells. T cell responses induced by several routine vaccines are less polyfunctional, less proliferative and produce lower IFNgamma in infants compared to adults. The combination of lower capacity of T cells to proliferate and secrete IFN-gamma combined with the increased frequencies of G-MDSC during the first 6 months of life may impair the induction of protective pathogen-specific and vaccine- induced T cell immune responses in vivo. The age at which adult-like responses are achieved varies according to vaccine type, but is generally attained between the ages of 6 months to 1 year, which coincides with the age at which we observe G-MDSC levels to decrease. However, additional studies are required to determine whether this temporal association indicates a causal relationship between G-MDSC frequency and vaccine responsiveness in infants. Neonatal G-MDSC have strong T cell suppressive activity in vitro and their frequency in CB correlates with the proliferative capacity of CB T cells in response to polyclonal stimulation in vitro. Although the role these cells may play in vivo has not yet been defined, MDSC have been implicated in skewing T helper responses towards Th-2 phenotype, impairing NK responses, and inhibiting dendritic cell function, all of which are characteristics Motesanib described in the neonate��s immune dysfunction. In cancer ZK200775 hydrate models, G-MDSCs can be differentiated from immunosuppressive to immunogenic TNF-alpha secreting neutrophils after intra-tumoral injection of attenuated Salmonella vaccine, and therapeutic vaccination to cancer antigens is restored after in vivo depletion of MDSC. Furthermore, in cancer patients, MDSCs can be induced to differentiate and T cell function and vaccine responses have been restored by administration of either Vitamin A or Vitamin D3.