Long-Term Follow-Up of Patients Immunized with AN1792 Current Alzheimer Research, 2009, Vol. 6, No. 2 147 RESULTS Patients Of 372 patients treated in the phase 2a study (300 active; 72 placebo), a total of 264 (71.0%) patients/caregivers were contacted to determine interest in follow-up study participa- tion. One hundred and fifty-nine patients/caregivers agreed to participate in the follow-up study (30 placebo; 129 treated with AN1792 + QS-21). Of the original 59 subjects who were classified in the phase 2a study as antibody responders (anti-AN1792 titers 1:2,200 at any time after the first injec- tion), 25 (42.4%) agreed to participate in the follow-up study compared with 30/72 (41.7%) of the placebo-treated patients (Fig. 1). In addition, 104/241 (43.2%) of patients classified as low or non-responders from Study 201 were enrolled in this follow-up study; however, data gathered from these pa- tients and caregivers are beyond the objectives and scope of the present communication. Patient demographics and base- line characteristics were similar between antibody respond- ers and placebo-treated patients at the start of this follow-up study (Table 1). A substantial portion of patients and/or caregivers were not contacted for participation in this follow-up study. A number of patients not contacted were known to be dead or were lost to follow up. Similar numbers of patients/ caregiv- ers were not able to be contacted in both the antibody re- sponder group (n=19 [32.2%]) and the placebo group (n=22 [30.6%]) (Table 1). Of the live patients and their caregivers who were contacted to participate in this follow-up study, fewer antibody responders refused to participate (8/39, or 20.5%), compared with 15/48 (31.3%) of placebo-treated patients (Table 1). The majority of patients enrolled in this follow-up study were taking concomitant acetylcholinesterase inhibitors or memantine. The proportion of patients taking concomitant medications was similar between antibody responders and placebo-treated patients. Twenty-two of 30 (73.3%) placebo- treated patients were taking concomitant acetylcholinesterase inhibitors compared with 19/25 (76.0%) of antibody re- sponders. Fifteen of 30 (50.0%) placebo-treated patients were taking concomitant memantine, compared with 15/25 (60.0%) of antibody responders. Mean time of follow up, either from baseline or from the final study visit in the original Phase 2a study to final as- sessment in this analysis, was similar across treatment and response groups (Table 1). Immunologic Findings Of the 300 patients randomized to receive AN1792 in the phase 2a study, 59 (19.7%) were classified as antibody re- sponders (having total serum anti-AN1792 IgG titers 1:2,200 at any time after the first injection)—25 of these antibody responders agreed to participate in this follow-up study. Of these participating antibody responders, 19 submit- ted a blood sample for antibody testing. Seventeen of the 19 tested antibody responders (89.5%) had a low but persistent residual mean anti-AN1792 antibody titer, with a geometric mean of 1:331.5 compared with non-detectable levels in all 19 placebo-treated patients who submitted a blood sample (p<0.001). No detectable anti-AN1792 antibodies were found in patients not classified as antibody responders in the phase 2a study. Antibody responders retained low but persis- tent levels of anti-AN1792 antibodies after approximately 4.6 years despite receiving only 1 to 3 of the planned injec- tions in the original Phase 2a study. Changes in Functional, Dependence, and Global Meas- ures DAD Caregivers provided DAD ratings for 27/30 placebo- treated patients (90.0%) and 24/25 antibody responders Fig. (1). Disposition of patients classified as antibody responders and placebo-treated patients enrolled in Study 251. Patients were consid- ered antibody responders in Study 201 if they had a serum anti-AN1792 IgG (total) titer 1:2,200 at any time after injection 1.