Updated Results from a Phase II Study of the Fc Engineered CD19 Antibody MOR208 in Combination with Lenalidomide for Patients with Chronic Lymphocytic Leukemia (CLL) and Richter's Transformation or Ibrutinib for Patients with Ibrutinib-Resistant Clones

MOR208 is an Fc engineered CD19 monoclonal antibody with preliminary efficacy in CLL as a single agent (Woyach et al, Blood 2014). Compared to non-engineered antibodies, MOR208 has significantly enhanced antibody dependent cellular cytotoxicity (ADCC), which can be further augmented in vitro with the addition of lenalidomide. Given the potential synergy of these agents, acceptable individual safety profiles, and efficacy of each as a single agent, we chose to combine MOR208 and lenalidomide in patients (pts) with previously treated and previously untreated CLL and in pts who have undergone Richter's Transformation (RT). Because recent data show poor outcomes in pts who relapse after the Bruton's Tyrosine Kinase (BTK) inhibitor ibrutinib and the presence of mutations in BTK prior to relapse, we included a cohort of ibrutinib-treated pts with identified resistance mutations but no clinical relapse where MOR208 was added to ibrutinib.

This study is a single institution phase II trial of MOR208 in combination with lenalidomide or MOR208 in combination with ibrutinib with an initial safety run-in as part of each cohort. In combination with lenalidomide, MOR208 was given at a dose of 1 mg/kg on cycle 1 day 1, 9 mg/kg on days 2, 8, 15, and 22 of cycle 1, and day 1 of cycles 2-12. Lenalidomide was started at a dose of 2.5 mg daily on cycle 1 day 8 and given continuously. The dose of lenalidomide could be escalated up to 10 mg daily in pts without toxicity. After 12 cycles, lenalidomide could be continued indefinitely in responding pts. In combination with ibrutinib, ibrutinib was continued at a dose of 420 mg daily, and MOR208 was given at a dose of 1 mg/kg on cycle 1 day 1, 12 mg/kg on days 2, 8, 15, and 22 of cycle 1, then weekly during cycles 2 and 3, and every other week through cycle 12. Toxicity was assessed using the National Cancer Institute's Common Criteria for Adverse Events (AE) v4.0 for non-hematologic toxicity, and IWCLL 2008 guidelines for hematologic toxicity. For pts on MOR208 plus ibrutinib, variant allele frequency of mutant BTK was measured every 3 cycles.

In the previously untreated cohort, 11 pts have been enrolled, with a median age of 62 (range 44-75). 1 pt had both del(17p) and del(11q) on FISH. Grade 3/4 adverse events regardless of attribution have been uncommon and have included hypertension (3 pts), infusion reaction (2 pts), and fatigue, neutropenia, colitis, hyperglycemia, dyspnea, and sinusitis (1 pt each). After a protocol amendment augmenting steroid premedication, no further grade 3 infusion reactions were observed.

In the previously treated cohort, 11 pts have been enrolled, with a median age of 70 (range 62-75). 2 pts each had del(17p) and del(11q) on FISH, and 8 have Zap-70 methylated disease. Grade 3/4 toxicities regardless of attribution have included neutropenia (6), hyperglycemia (2), hypertension (2), and thrombocytopenia, fatigue, anemia, upper respiratory infection, catheter related infection, hypercalcemia, hypophosphatemia, infection, respiratory failure, and sepsis in 1 pt each.

In the RT cohort, 5 pts have been enrolled, with a median age of 60 (range 55-70). Four had previously treated CLL, and one was previously untreated. Three had del(17p) and 2 had del(11q) on FISH. Grade 3/4 toxicities included hyperglycemia (3) and hyponatremia, thrombocytopenia, and neutropenia in 1 pt each.

In the cohort of pts with molecular progression on ibrutinib, 7 pts have been enrolled, with a median age of 62 (range 45-77). Five have del(17p), 1 of whom also has del(11q). Grade 3/4 toxicities have included hypertension (2) and hyperglycemia and hyperuricemia in 1 pt each. Four pts have been on study for at least 3 cycles. One pt had an increase in BTK C481S variant allele frequency (VAF) from 66.3% to 78.8% while the others all have decreased (15.1% to 3.7%, 46.4% to 34.9%, and 67.2% to 18.1%). No pt has developed progressive disease.

In conclusion, this Phase II trial in progress demonstrates preliminary safety and activity of the combination of MOR208 and lenalidomide in pts with CLL. This combination also has the potential to positively modulate the immune system, and detailed correlative studies will evaluate T- and NK-cell function. MOR208 appears safe in combination with ibrutinib, and preliminary evidence of activity against CLL cells with BTK C481S has been observed. Trial accrual is ongoing and updated results will be presented at the meeting.