Rituximab treatment elicits a lymphoma idiotype–specific IFN-γ T-cell response. Immature DCs from all 5 patients were generated, pulsed with autologous patient lymphoma-derived idiotype protein (Id), and matured overnight. Pulsed/matured DCs were then used to stimulate pre- or postrituximab treatment lymphocytes for 1 week (patients 1 and 5), or 2 weeks (patients 2-4) in Aim-V serum-free media with interleukin-2 (IL-2). The resultant week 1 or 2 effectors were then harvested, washed, and rested overnight in Aim-V media containing IL-2. Rested effectors were stimulated in IFN-γ ELISpot plates (in triplicate) with mature DCs alone or DCs pulsed and matured with either the patient's lymphoma-specific Id (DC-Id) or an irrelevant Id derived from a different patient (DC-Irr). The number of IFN-γ–secreting cells for each condition was then determined by standard ELISpot methods after incubation overnight. (A) The number of IFN-γ spots for patients 1 through 5, for both pre- or postrituximab effectors stimulated overnight by (□) DCs, (■) DC-Id, (■) DC-Irr are shown, as is the IVS repeat for patient 2 using the vaccine-specific Id for the IVS rather than the relapse Id. (B) The difference between the numbers of IFN-γ–secreting cells on stimulation with (□) DCs versus DC-Irr (■) DC-Id versus DCs (■) DC-Id versus DC-Irr was calculated for each of the pre- and postrituximab samples (eg, DC-Id − DC^Post), and then the difference between the pre- and postrituximab samples was calculated (eg, [DC-Id − DC]^Post − [DC-Id − DC]^Pre). A final difference that is greater in the postrituximab sample, compared with the prerituximab sample, is plotted as a positive number (more than zero), whereas a difference that is similar between the pre- and postrituximab samples is plotted around zero. The data are shown for each individual patient (symbols), as well as for the averages computed over all 5 patients for each condition (bars), with the corresponding P values from tests assessing the significance of each bar.