Heterogeneity of transplantable stem cells from Glimm et al¹⁵ and Guenechea et al.¹⁴Long-term and short-term SCID-repopulating cells (LT-SRC and ST-SRC, respectively) are detected in NOD/SCID mice and generate another class of short-term repopulating cell (STRC) that can only be assayed in the NK cell deficient β2-microglobulin knock-out/NOD-SCID mouse or in anti-NK treated NOD/SCID mice. The STRC can generate either myelo-lymphoid cells (STRC-ML) or are restricted to either lineage, STRC-M or STRC-L.