Rituximab-Relapsing Patients with Non-Hodgkins Lymphoma Respond Even at Lower Doses of Humanized Anti-CD20 Antibody, IMMU-106 (hA20): Phase I/II Results.

Background: An open-label, multicenter, dose-escalation study in patients with recurrent NHL was initially undertaken to establish the safety, tolerance, PK, and immunogenicity (HAHA) of humanized anti-CD20 antibody, IMMU-106 (hA20), administered once-weekly for 4 weeks at different doses. Additional patients have now been entered to confirm the efficacy of 120 and 375 mg/m² dosing, and to determine the feasibility of using even lower hA20 doses.

Methods: A total of 55 patients (23 male, 32 female; 51 Caucasian; 40–84 years old) received hA20 at 120 (N=21), 200 (N=6), 375 (N=25) or 750 mg/m² (N=3). They had follicular (FL, N=37) or other (N=18) B-cell lymphomas, were predominantly stage III/IV (N=44) at study entry, and had received 1–7 prior treatments (median, 2), including 1 (N=34) or more (N=14) rituximab regimens (without progression within 6 months).

Results: Fifty-two patients completed all 4 infusions, 2 are currently being treated, and one patient with hives and chills after prior rituximab discontinued treatment after similar NCI CTC v.3 grade 1–2 reactions at 1st hA20 infusion. hA20 was generally well tolerated with a median infusion time at the lowest dose of 120 mg/m² of 2.2 h for 1st infusion and 1.2 h for subsequent infusions. Twenty-one patients had drug-related adverse events; these were all transient, mild-to-moderate (Grade 1–2) events, most occurring only at first infusion. No consistent pattern of abnormal laboratory changes occurred, and there was no evidence of immunogenicity in 29 patients now evaluated for HAHA. Mean antibody serum levels increased with dose and with repeated infusions, and limited post-treatment data indicate the serum clearance at 375 mg/m² dosing is similar to rituximab. Even at 120 mg/m², peripheral blood B-cell depletion occurred after the first infusion and persists after 4th infusion, with analysis continuing > 6 mo. Thirty-nine patients with at least 12 wks follow-up had one or more responses evaluated by Cheson criteria (Table), with all CR/CRu occurring in follicular lymphoma except for one patient with marginal zone lymphoma; 6 pts progressed by week 4. Of 18 pts with OR’s, 9 have continuing responses (median follow-up, 9 mos post-treatment), including 4 with long-lived responses (12–18 mos).

Conclusions: hA20 is well tolerated, with no evidence of significant toxicity or pattern of adverse events other than minor infusion reactions, even at short infusion times. All dose levels studied so far, including the lowest dose of 120 mg/m², resulted in B-cell depletion and objective responses (including CR/CRu), with no clear-cut evidence of dose response in efficacy. As such, further dose de-escalation is ongoing.