Experimentally observed and simulated engraftment kinetics in primary and secondary recipients. (A) The graphic illustrates experimentally observed engraftment kinetics, as determined in the peripheral blood (PB), generated by different, clonally derived transplants in primary hosts (different colors indicate different clones). At month 7, HSCs from these primary hosts were transplanted into secondary hosts. (B) Experimentally observed engraftment kinetics in the PB of secondary hosts. Corresponding colors were used to indicate the relationship of primary HSCs and its clonal progeny revealed in multiple secondary hosts. Data in panels A and B are taken from Muller-Sieburg et al.¹⁶  (C,D) Representative examples of simulated engraftment kinetics in primary (C) and secondary (D) host assuming no predetermined differences of individual clones. Identical color codes indicate identical clonal origin in primary and secondary recipients. Gray lines give more examples of primary kinetics to better illustrate the distribution. They are not shown in secondary hosts. (E,F) See panels C and D, but this time assuming small differences between individual HSCs with respect to parameter d. d has been randomly sampled from a normal distribution with mean 1.07 (reference value) and standard deviation 0.01. The particular d values for the given example realizations are 1.06052 (black), 1.06501 (red), 1.06624 (yellow), 1.06708 (green), and 1.07337 (blue). (G,H) See panels C and D but with large differences in parameter d. d has been randomly sampled from the 2 intervals [1.038, 1.049] and [1.091, 1.102], which relate to deviations of plus or minus 2% to 3% from the reference value 1.07. The particular d values for the given example realizations are 1.04705 (black), 1.04392 (red), 1.09377 (green), 1.02802 (blue), and 1.04761 (light blue). To facilitate the comparison with the experimental data, simulated engraftment levels are shown on a bimonthly scale, although they were actually simulated using a 1-hourly scale.