Table 1. Classification of morphologic characteristics of colonies generated from human fibroblasts using four retroviral vectors encoding Oct3/4, Sox2, Klf4, and c-Myc.

	number of nucleolus	nucleus to nucleolus ratio	cell size	cell density/mm2	nucleus to cytoplasm ratio	number of layer	number of colonies obtained (Experiment 1)	number of colonies obtained (Experiment 2)
Col A	2.35±0.51	3.30±0.48	87.69±11.04	2166.67±29.21	0.59±0.07	multilayer	16	22
Col B	1.46±0.59	2.95±0.41	113.20±13.40	1863.06±22.49	0.53±0.06	multilayer	55	49
Col C	1.34±0.55	2.50±0.50	69.82±9.29	3048.96±26.14	0.60±0.07	multilayer	95	102
Col D	1.33±0.47	3.17±0.50	52.09±7.69	5091.67±21.65	0.6±0.05	multilayer	6	8
Col E	1.24±0.48	2.52±0.43	45.72±7.14	3493.33±24.03	0.59±0.07	multilayer	10	8
Col F	1.27±0.49	2.42±0.23	58.34±5.92	5266.67±41.01	0.64±0.06	multilayer	8	12
Col G (iPS cell)	1.20±0.45	2.19±0.17	43.50±2.96	5933.33±20.82	0.87±0.04	single	2	2
human ES cell	1.20±0.45	2.20±0.17	43.70±3.61	6133.33±15.32	0.86±0.04	single

Each replicate represented 2×10⁵ transduced cells seeded onto a 60-mm dish containing feeder cells and cultured in Primate ES cell medium for thirty days.