Different huPBMC engraftment patterns. The first experiment for engraftment of huPBMCs by intravenous transfer into irradiated RAG2^-/- γc^-/- mice was performed with 10 different donors. Engraftment occurred with 9 of 10 donors. After 2 to 4 weeks an increase in human CD45⁺ cells was observed (right Y-axis) and X-GVHD developed in the mice, characterized by a rapid and severe weight loss (left Y-axis). Two patterns of engraftment could be discerned: pattern I, “early” engraftment (5 donors); and pattern II, “late” engraftment (4 donors). Two groups are shown as representative examples. Symbols ▿, □, and ○ indicate 3 different mice. indicates death of the mouse; closed symbols, % human CD45⁺ cells; and open symbols, weight (as a percentage of the initial weight).