Role of Tregs in maintaining alloreactive Tconv hypofunction in transplantation tolerance 2291

Abstract Description Regulatory T cells (Tregs) are necessary for the induction of murine cardiac transplantation tolerance via costimulation blockade. Whether Tregs are necessary to maintain Tconv hypofunction long-term after tolerance has been achieved remains to be established. Our preliminary data indicate that complete, though transient, depletion of Tregs using diphtheria toxin (DT) in Foxp3-DTR mice at the maintenance phase of tolerance precipitated the rejection of previously tolerized cardiac allografts and resulted in the de novo production of graft-specific antibodies – potentially implying the reinvigoration of Tconvs which then provide help to B cells. Indeed, RNA-sequencing of graft-specific Tconvs following Treg depletion in tolerant mice demonstrated their transcriptional distinction from Tconvs in tolerant mice that retained Tregs. Conversely, graft-reactive Tconvs from tolerant mice infected with Listeria monocytogenes or having received a hydrodynamic injection of plasmids encoding the proinflammatory cytokines IFNb and IL-6 to break transplantation tolerance, were both transcriptionally similar to Tconvs from unmanipulated tolerant mice. Furthermore, allospecific Tconvs showed renewed cytokine production and proliferative capacity after Treg depletion. This indicates a unique state of potential reinvigoration and implicates Tregs in actively maintaining dysfunction of graft-specific Tconvs. Funding Sources Supported by the American Heart Association Pre-Doctoral Fellowship (https://doi.org/10.58275/AHA.24PRE1192022.pc.gr.190594) and the T32 Cardiovascular Sciences Training Grant (5-T32-HL-7381) Topic Categories Transplantation Immunology (TRAN)