BsAb-1 and BsAb-2 induce T-cell proliferation and accelerated GVHD in a mouse model engrafted with human PBMCs. (A) BALB/c mice (n=3 per group per time point) were administered 1 mg/kg BsAb-1 or BsAb-2 by tail-vein injection. Serum was collected at 6 time points over two weeks and tested together by ELISA for human IgG4 using rhIL-2Rγ as a capture antigen. Error bars show SD. Pharmacokinetic parameters were determined using Phoenix pharmacokinetic software. (B-D) Irradiated NSG mice (5 per treatment group) were engrafted with 20 million human PBMCs each. Animals were then treated with either vehicle only, rhIL-2 (daily), or BsAb-1 or BsAb-2 (twice weekly) until ≥ 20% body weight loss. (B) Relative body weight of treated mice after injection of PBMCs. Horizontal lines indicate mean, and error bars show SEM. p values were calculated using a two-way RM ANOVA test. (C and D) Percentage of engrafted CD8+ T-cells (C) and CD4+ T-cells (D) which showed at least one round of division by CSFE staining. Representative histograms shown in Fig. S3. p values were calculated using a one-way ANOVA. Horizontal lines indicate mean, and error bars show SEM (B) or SD (C and D). *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.