Table 1.

The biological and immunological effects of human factor IX (hFIX) production on hemophilia B mice

Treatment	FIX (ng/ml)	Clotting activity (%)	Tail clip challenge	Tolerance
Bu	105.7	1.25	+	+
	26.3	0.28	-	-
	15.7	0.12	-	-
	0	0.00	-	-
	69.0	0.78	+	+
Bu/ATS	600.7	7.33	+	+
	10.3	0.10	-	-
	89.5	1.00	+	+
	37.3	0.37	-	+
	373.7	4.63	+	+
Irradiation	603.4	8.57	+	+
	538.3	5.81	+	+
	687.2	8.52	+	+
	851.6	9.37	+	+
	290.8	3.49	+	+

Bu, Busulfan-treated group [Busulfan, intraperitoneal (i.p.) 2 × 20mg/kg, -72 and -48 hours before engraftment]. Bu/ATS, Busulfan and antithymocyte serum treated group (Busulfan, i.p. 2 × 20mg/kg, -72 and -48 hours; antithymocyte serum, i.p. 2 × 30mg/kg, -24 and 2-4 hours before engraftment). Irradiation, irradiation-treated group (recipient mice were irradiated with 10.5 cGy). FIX concentration was measured by enzyme-linked immunosorbent assay, clotting activity by activated partial thromboplastin test. Survival was monitored for 6 hours and overnight after tail clipping. Mice survived the challenge is marked (+). Immune tolerance was assessed by immunization of mice with Mononine and Titermax, followed by testing for FIX-specific antibodies in the plasma samples 5 weeks after immunization. Mice established immune tolerance are defined as the mice that have plasma anti-FIX antibody level <100ng/ml, and are marked (+).