Because of these significant, albeit subtle, differences, we wondered whether individual Treg cells derived from TCR-Tg mice were intrinsically less competitive than WT Treg cells. For that reason, we generated mixed BM chimeras of WT and TCR-Tg mice and compared thymic and peripheral Treg-cell levels. When a 1:1 ratio of both donors was anti-PD-1 antibody used to reconstitute

lethally irradiated recipients, we found only a marginal contribution of TCR-Tg precursors to the generation of the thymic and peripheral Treg-cell pool (Fig. 3). This is consistent with the assumption that only a few T-cell precursors in TCR-Tg mice are able to rearrange proper endogenous TCR chains prior to positive selection by the transgenic TCR. However, in chimeras derived from 20 parts TCR-Tg to 1 part WT BM, approximately 15% of thymic Treg cells were from the TCR-Tg donor as defined by the congenic markers Thy.1.1 and Thy1.2 (Fig. 3). This frequency did not

decrease in the periphery, indicating that TCR-Tg donor-derived Treg cells showed similar fitness VX-809 in vivo to compete for peripheral Treg-cell niches once successfully developed in competition with WT Treg cells. We cannot rule out that the repertoire of TCR-Tg donor-derived Treg cells may be skewed in a competitive environment. However, we can conclude that rearrangement of endogenous TCR chains in OT-II TCR-Tg mice generates Treg cells that individually are as fit as Treg AZD9291 cells in WT mice. A recent study suggested that the Treg-cell repertoire varies by anatomical location 13. However, it was so far difficult to address the influence of TCR specificity on Treg-cell homing in adoptive transfer experiments because

recovery rates were not sufficient. Here, 9 wk after adoptive transfer, the distribution of WT Treg cells into TCR-Tg hosts showed a clear preference for pLN and spleen over mesenteric lymph nodes (mLNs) (Fig. 4A). Input Treg cells were pooled from spleens and all lymph nodes, comprising approximately 15–20% mLN-derived Treg cells. In contrast, one would likely need to perform a very high number of experiments in order to decide whether significant organ-specific homing might occur after transfer into WT mice because recovery rates were approximately 100-fold lower (Fig. 4B). It is possible that dissimilar expression of gut-associated lymphoid tissue (GALT) homing receptors of the donor Treg cells additionally influenced their migration in the host. When comparing Treg cells from spleen, pLN, and mLN of WT and OT-II TCR-Tg mice, we found that the frequency of double-positive cells for the GALT homing markers CCR9 37 and of the homing/activation marker CD103 38 was increased in mLNs compared with that in pLNs (Fig. 4C). However, we largely observed only minor differences in the expression of CCR9 and CD103 (Fig. 4C).