If a DLT is noted in a given cohort in Part I, the following dose escalation rules will be followed to ascertain the maximum administered dose (MAD). In the unlikely event that a DLT is seen in ≥ 2 patients at the starting dose used in Part I, the study may be resumed with a lower dose if there is adequate evidence of the desired pharmacodynamic effect, ie a reduction in B-cell count, at the starting dose.