Density dependent re-tuning of autoreactive T cells alleviates their pathogenicity in a lymphopenic environment

In experimental or clinical contexts of lymphopenia, mechanisms that normally maintain peripheral tolerance are weakened, resulting in auto-immunity or graft rejection. We now show that the exaggerated density of self-reactive T cells that can be maintained in such environments is a severe impediment to their complete tolerization. Reducing the frequency of T cells allowed the cell-intrinsic tolerance to progress further and eliminate residual immunopathology, even in lymphopenic hosts without the contribution of regulatory T cells. This stems from the effectively stronger stimulation of the autoreactive T cells, after density reduction, allowing them to tune down their TCR proximal signaling to a greater extent. In addition, this deeper state of tolerance was also accompanied by the modulation of transcriptional and epigenetic machinery in the T cell, which prevented the tolerance from being perturbed by pharmacological activators. These data suggest that, similar to the immunogenic activation of T cells, cell intrinsic tolerance is also a progressive process that can be stabilized at multiple intermediate stages by environmental factors. Adapting tolerance protocols to allow this progression to proceed further can therefore be a viable strategy to successfully tolerize T cells, especially in lymphopenic settings. Eight 2R arrays and five 1R arrays were labelled with Cy3. A standard reference RNA derived from pooled mouse T cells was labeled with Cy5.