Comparative pharmacodynamics of keliximab and clenoliximab in transgenic mice bearing human CD4

Keliximab and clenoliximab are monkey/human chimeric CD4 monoclonal antibodies (mAbs) of the IgG1 and IgG4 isotypes, respectively. The pharmacokinetics (PK) and pharmacodynamics (PD) of these mAbs were evaluated in transgenic mice bearing human CD4 molecules on their T cells after a single i.v. administration at three dose levels (5-125 mg/kg). The PK of keliximab and clenoliximab were similar, dose-dependent, and adequately described by a two-compartment model with saturable elimination from both compartments. The enumeration of circulating CD4(+) T cells and density of CD4 on their surface were determined as the PD effects. An indirect response model was proposed to characterize the PD effects. With the increase in mAb dose, the maximum intensity (R(max)) of PD effects was increased, and the time to reach R(max) shifted to later times. At all three dose levels, keliximab caused a relatively rapid decline in the number of circulating CD4(+) T cells, which then recovered gradually. In contrast, clenoliximab at the lowest dose (5 mg/kg) did not produce a significant effect on CD4(+) T cell counts compared with the placebo group. At high doses, clenoliximab caused a significant decrease in the number of CD4(+) T cells. Keliximab appeared to be more potent and efficient in depleting CD4(+) T cells. Both mAbs produced similar down-modulation of CD4 at corresponding dose levels. The findings of this study are consistent with the results of a recent clinical trial that emphasize the importance of this transgenic mouse model for evaluating PK/PD to support clinical development of anti-human CD4 mAbs.