Targeting Treg Cells In Situ: Emerging Expansion Strategies for (CD4⁺CD25⁺) Regulatory T Cells

Model of IAC-induced suppression of HVG Tconv cells and facilitation of chimerism post-allogeneic hematopoietic stem cell transplantation (HSCT). Following conditioning, residual host Treg cells can be activated and expanded in situ by IL2/anti-L2 complex (IAC). A working hypothesis for the regulation of HVG and facilitation of engraftment is the subsequent engagement of host Treg cells and host Tconv cells at the donor APC interface. Inhibition of resistance against the donor graft might proceed via direct (Treg-Tconv) and/or indirect (Treg-donor APC) pathways. The effector molecules that mediate the regulation are unknown.

Potential strategies for manipulation of Treg cells following IAC or antigen- induced activation by targeting upregulated cell surface molecules. Treg cells can be activated and expanded following experimental treatment with IAC (IL2/anti-IL2 complex) or via responsiveness to auto (self), allogeneic (transplant), or conventional (pathogen) antigens. Following activation, upregulation of cell surface molecules including CD25 and TNFR family members may provide “targets” for additional manipulation of different Treg populations. 4-1BB (TNFRS9), Ox-40 (TNFRS4), and GITR (TNFRS18) reported to affect Treg function are shown, but other TNF family molecules as well as molecules yet to be identified could become potential targets for manipulation.