An in vitro method for determining the dose of a PD-1 antagonist that is useful to treat a subject, comprising determining the proliferation of memory B cells in vitro in a first sample from the a subject administered a first dose of a PD-1 antagonist, wherein increased proliferation of memory B cells from the first sample as compared to a control indicates that the first dose of the PD-1 antagonist is of use treating the subject, and wherein an absence of a significant alteration in the proliferation of memory B cells as compared to the control indicates that the first dose of the PD-1 antagonist is not sufficient to treat the subject.
