Improving T-cell reconstitution after allo-HSCT (adapted from Figure 5 in Toubert et al² ). Strategies intend to act on HSCs, lymphoid T-cell progenitors (proT), thymic differentiation (double negative stages DN2-4 to double positive [DP] and single positive [SP] thymocytes), and peripheral T-cell homeostasis (naive [T_N] and memory [T_M] T cells). Candidates for therapy are cytokines (IL-2, IL-7, IL-15), chemokines (SDF-1, S1P), growth factors (keratinocyte growth factor [KGF], FLT-3), and/or neuroendocrine hormones (growth hormone [GH]) acting on thymic epithelium, intratthymic proliferation, and/or peripheral homeostasis. Tools to follow immune reconstitution in peripheral blood samples are lymphocyte phenotyping by flow cytometry, T-cell repertoire diversity analysis, and T-cell receptor excision circles (TRECs) quantification. Professional illustration by Alice Y. Chen.