Novel Mouse Models Allow Selective Labelling and Depletion of Perinatal and Adult-derived Regulatory T Cells

Introduction/Rationale: Regulatory T cells (Tregs) that develop during the perinatal period (2-3 weeks after birth) are believed to be distinct from adult-derived Tregs. Previous approaches to selectively label perinatal versus adult derived Tregs have used Foxp3-GFP-Cre-ERT2 x R26YFP mice. This approach has two critical drawbacks: limited labeling of perinatal Tregs due to tamoxifen (TAM) toxicity, and failure to discriminate perinatal versus adult-derived Tregs later in life.

Methods: We developed two novel mouse models that overcome these limitations: Rag-Rox-cre-Rox x CAGS-DREERT2 x Foxp3-iDTR mice, in which developing Tregs express GFP until TAM is added, and Rag-Rox-STOP-Rox-Cre x CAGS-DREERT2 x Foxp3-iDTR mice, in which developing Tregs are GFP- until TAM administration. This allows us to selectively identify and delete Tregs that developed during the perinatal versus adult time frames.

Results: We used Rag-Rox-cre-Rox x CAGS-DREERT2 x Foxp3-iDTR mice to track the persistence of perinatal Tregs in tissues. At 15 weeks of age virtually all newly generated Tregs in the thymus were adult derived. In contrast, ~21% of splenic Tregs were perinatally derived. Higher percentages of Tregs in the lungs (49.8%), small intestine (34.2%), meninges (39.9%), skin (63.7%) and liver (25.7%) were perinatal Tregs. By examining perinatal Tregs in the blood at 11 and 18 weeks after birth we noted that the percentage of perinatal Tregs did decay with time, albeit quite slowly (3.5%/week). We are currently examining how the TCR repertoire and suppressive capacity of perinatal versus adult Tregs differ. Finally, by depleting perinatal Tregs with DT in older mice we can test their function at homeostasis and during inflammatory conditions such as EAE.

Conclusion: We developed two novel and complementary mouse models that can selectively label and deplete perinatal or adult derived Tregs. These models will allow us to determine the distribution, persistence, and function of perinatal Tregs throughout life.