IL21 and COVID-19: The positive effects of IL‐22 on thymus regeneration are limited to a damaged state, as IL‐22 treatment in healthy mice showed no increase in cellularity.[149] IL‐7 has shown to promote thymus repair and is critical for thymocyte development, as deletion of IL‐7 in TECs profoundly reduced the number of T cells.[150] Currently, IL‐7 is being used to improve lymphocyte levels in COVID‐19 patients.[151] Finally, IL‐21 can enhance hematopoietic reconstitution upon treatment, while IL‐21 has shown to enhance thymic function in mice.[152]