Figure 3. mTECs select a substantial portion of the thymus-derived Treg repertoire.

(A) Analysis of individual Treg cell TCRs from C2TAkd chimeras. The top 15 Foxp3⁺ TCRs in the C2TAkd dataset are shown sorted by frequency, along with the corresponding frequency in the WT and MHC II def. BM datasets. (B) Change in Morisita-Horn index with removal of most common TCRs. Similarity between Foxp3⁺ TCR repertoires of C2TAkd versus WT (left) and MHC II def. BM APC versus WT (right) were assessed after removing the top 1, 2, or 3 highest frequency WT TCRs from the analysis. (C) In vivo validation of Treg cell TCRs dependent on mTEC antigen presentation. Three high frequency mTEC-dependent Treg TCRs were identified by sequencing, including G126, a common C2TAkd Treg TCR reduced in frequency in comparison with WT (Figure 3A). TCR-expressing Rag1^-/- thymocytes were injected into the thymi of WT or C2TAkd hosts and analyzed at ∼ 2.5 weeks for Foxp3 expression by flow cytometry by gating on CD45.1⁺ CD45.2″ Va2⁺ CD4SP cells. Data were pooled from at least two independent experiments with 2 replicates per experiment. See also Figure S3.