Simplified overview of hematopoietic or mesenchymal derived cells which have important effector and regulatory roles in transplant immunology – with potential candidates for tolerogenic cell therapy for clinical transplant tolerance highlighted (dotted boxes). BReg, regulatory B cell; DC, dendritic cell; Mreg, regulatory macrophage; NK, natural killer; TolDC, tolerogenic dendritic cell; Treg, regulatory T cell.