Table 2.

Frequency of “negative” NOD/SCID mice 6–8 weeks after transplantation with varying numbers of freshly isolated or cultured CB cells

Type of cell	No. of experiments	Total No. of CB assessed	Cells/mouse	Proportion of negative mice
Light density	3	7	3  ×  106	2/10
			1  ×  106	2/8
			8  ×  105	0/6
			3  ×  105	3/8
			2  ×  105	1/6
			5  ×  104	3/4
CD34+CD38+	2	4	5  ×  104	0/5
			1.5  ×  104	5/6
			7,500	2/6
			3,000	5/5
			600	4/5
CD34+CD38−	7	16	4,400	1/2
			3,000	2/11
			2,000	5/5
			1,000	5/17
			500	5/12
			300	1/4
			200	10/14
			50	21/25
Cultured CD34+CD38−	6	14	4,400	0/3
			1,000	2/11
			500	3/5
			200	9/12
			100	3/3
			50	5/6
			40	3/7

Negative mice were defined as those that did not contain detectable levels of both human CD34⁻CD19⁺ (B-lymphoid) and CD34⁺ CFC (myeloid) cells. Pooled data from the number of experiments shown (2 to 3 CB samples pooled per experiment).