Ublituximab (TG-1101), a Novel Glycoengineered Anti-CD20 Monoclonal Antibody, in Combination with Ibrutinib Is Highly Active in Patients with Relapsed and/or Refractory Mantle Cell Lymphoma; Results of a Phase II Trial

Introduction: Ublituximab (UTX) is a novel, chimeric monoclonal antibody (mAb) which targets a unique epitope on the CD20 antigen and has been glycoengineered to enhance affinity for all variants of FcγRIIIa receptors, demonstrating greater ADCC than rituximab and ofatumumab.  In patients (pts) with rel/ref CLL, the combination of UTX with ibrutinib was well-tolerated and highly active demonstrating an 88% ORR (95% ORR in high-risk CLL) with responses attained rapidly (median time to iwCLL response of 8 weeks).  Ibrutinib has demonstrated single agent activity in Mantle Cell Lymphoma (MCL), achieving a 68% ORR (21% CR) in a single arm trial in relapsed or refractory patients (Wang et al, NEJM 2013).  Herein we report on the first combination of ibrutinib with a glycoengineered anti-CD20 mAb, UTX, in patients with Mantle Cell Lymphoma (MCL).

Methods: Eligible patients had rel/ref MCL with an ECOG PS < 3.  Prior ibrutinib treatment was permitted.  UTX (900 mg) was administered on Days 1, 8, and 15 in Cycle 1 followed by Day 1 of Cycles 2 - 6.  Ibrutinib was started on Day 1 and continued daily at 560 mg.  Following Cycle 6, patients came off study but could remain on ibrutinib.  Primary endpoints were safety and ORR with an emphasis on early activity with response assessments by CT scan scheduled prior to cycles 3 and 6 only (criteria per Cheson 2007).    

Results: 15 patients were enrolled:  13 M/2 F, median age 71 yr (range 55-80), ECOG 0/1: 9/6, median prior Tx = 3 (range 1-8), 53% with ≥ 2 prior anti-CD20 therapies, 40% prior bortezomib. Gr 3/4 AE’s occurring in at least 5% of patients and at least possibly related to UTX and/or ibrutinib included: neutropenia (13%), fatigue (7%), rash (7%) and atrial fibrillation (7%). Ibrutinib was dose reduced due to an AE in 1 patient (rash) and discontinued in 1 patient due to atrial fibrillation.  No UTX dose reductions occurred.  All 15 pts are evaluable for response with best response to treatment as follows:  87% (13/15) ORR with 33% (5/15) Complete Response.  Three of the CR’s occurred at week 8.  Of the two patients not achieving an objective response, one patient was stable at first scan and came off treatment prior to second efficacy assessment (ibrutinib related A-Fib) and one patient progressed at first assessment.  Responses generally improved from first to second assessment with median tumor reduction of 64% by week 8 and 82% by week 20.

Conclusions: Ublituximab, a glycoengineered anti-CD20 mAb, in combination with ibrutinib is both well-tolerated and highly active in pts with rel/ref MCL.  Response rate, depth of response, and time to response compare favorably to historical data with ibrutinib alone.  A randomized phase 3 trial with ibrutinib +/- ublituximab is currently ongoing in high-risk CLL pts and future studies using this combination in MCL are being evaluated.