Abstract
Foxp3 reporter mice including DEREG (DEpletion of REGulatory T cells) mice have greatly helped in exploring the biology of Foxp3+ Tregs. DEREG mice express a DTR-eGFP fusion protein under the control of a bacterial artificial chromosome (BAC)-encoded Foxp3 promoter, allowing the viable isolation and inducible depletion of Foxp3+ Tregs. Adaptive Tregs differentiated in vitro to express Foxp3 (iTregs) are gaining high interest as potential therapeutics for inflammatory conditions such as autoimmunity, allergy and transplant rejection. However, selective isolation of Foxp3+ iTregs with a stable phenotype still remains to be a problem, especially in the human setting. While screening for culture conditions to generate stable CD4+Foxp3+ iTregs from DEREG mice, with maximum suppressive activity, we observed an unexpected dichotomy of eGFP and Foxp3 expression which is not seen in ex vivo isolated cells from DEREG mice. Further characterization of eGFP+Foxp3− cells revealed relatively lower CD25 expression and a lack of suppressive activity in vitro. Similarly, eGFP− cells isolated from the same cultures were not suppressive despite of a broad CD25 expression reflecting mere T cell activation. In contrast, eGFP+Foxp3+ iTregs exhibited potent suppressive activity comparable to that of natural eGFP+Foxp3+ Tregs, emphasizing the importance of isolating Foxp3 expressing iTregs. Interestingly, the use of plate-bound anti-CD3 and anti-CD28 or Flt3L-driven BMDC resulted in considerable resolution of the observed dichotomy. In summary, we defined culture conditions for efficient generation of eGFP+Foxp3+ iTregs by use of DEREG mice. Isolation of functional Foxp3+ iTregs using DEREG mice can also be achieved under sub-optimal conditions based on the magnitude of surface CD25 expression, in synergy with transgene encoded eGFP. Besides, the reported phenomenon may be of general interest for exploring Foxp3 gene regulation, given that Foxp3 and eGFP expression are driven from distinct Foxp3 loci and because this dichotomy preferentially occurs only under defined in vitro conditions.
Highlights
Foxp3 is an established marker for the identification of both natural and induced CD4+ regulatory T cells (Tregs) [1,2,3,4], yet it is inaccessible to reagents for their viable isolation or depletion
CD4+eGFP2 T cells sorted from DEREG mice to a high purity (Figure S1) were used to generate eGFP+Foxp3+ iTregs that could be isolated by FACS sorting on the basis of eGFP expression for their functional analysis
Populations in iTreg cultures supplemented with transforming growth factor-b (TGF-b, retinoic acid (RA), soluble anti-CD3 antibody and GM-CSF derived bone marrow dendritic cells (BMDC) (Figure 1A)
Summary
Foxp is an established marker for the identification of both natural and induced CD4+ regulatory T cells (Tregs) [1,2,3,4], yet it is inaccessible to reagents for their viable isolation or depletion. To overcome this limitation, DEREG mouse was generated which report Foxp promoter activity by the expression of a DTR-eGFP fusion protein from an ectopic bacterial artificial chromosome (BAC)-encoded Foxp locus [5]. Recent advances pertaining to ex vivo induction and expansion of
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