A Multicenter, Open-Label Feasibility Study of Daratumumab with Dose-Adjusted EPOCH in Newly Diagnosed Plasmablastic Lymphoma: AIDS Malignancy Consortium 105

Background: Plasmablastic lymphoma (PBL) is an aggressive large B-cell lymphoma commonly associated with HIV, immunosuppression, old age, and autoimmune disorders, but can be seen in immunocompetent patients. Intensive regimens, including EPOCH, have only a median overall survival between 9 to 15 months. Complete response rates are 40% to 65%. Patients with refractory or relapsed disease typically have a dismal prognosis. Little progress has been made in treating PBL without a single dedicated clinical trial to date.

PBL has morphologic and immunophenotypic characteristics overlapping high-grade B-cell lymphoma and multiple myeloma. It is CD20 negative and positive for plasma cell markers, including CD38, CD138, and MUM-1/IRF-4, with a proliferation index typically > 90%.

Daratumumab (DARA) is a human IgG1k anti-CD38 monoclonal antibody (mAb). CD38 is a transmembrane receptor with enzymatic activity highly expressed on the surface of plasma cells and plasmablasts. DARA induces directed cell killing of CD38 expressing cells including complement dependent cytotoxicity and antibody-dependent cell cytotoxicity (ADCC). DARA has significant activity as a single agent and part of combination therapy in myeloma. In non-Hodgkin lymphoma (NHL), DARA resulted in synergistic reduction of tumor growth when combined with rituximab and CHOP (R-CHOP) in follicular lymphoma systemic xenograft models and induced dose-dependent ADCC on mantle cell and follicular lymphoma cells lines in the presence of peripheral blood mononuclear cells in vitro (Pérez-Galán P, et al. Hematol Oncol. 2017). In addition, in vivo models using DLBCL (SU-DHL-6) cells injected in SCID mice showed superiority of DARA in combination with CHOP vs DARA alone (63% vs 55%, p <0.01). In a patient-derived DLBCL model with high CD38 expression, DARA with CHOP or R-CHOP showed tumor regression, and tumors did not regrow when treatment with DARA was stopped after 3 doses. (Doshi P, et al. Haematologica. 2014).

We designed an innovative approach to treat PBL using a combination of chemotherapy and directed immunotherapy with a mAb. We hypothesize that adding the potent CD38-directed mAb DARA to DA-EPOCH is safe and feasible and results in improved outcomes in PBL similar to the benefit seen with adding rituximab to a CHOP or EPOCH backbone in other DLBCL subtypes. This will be the first clinical trial dedicated to patients with PBL.

Study Design and Methods: This is a non-randomized, multicenter study conducted by the AIDS Malignancy Consortium. Both HIV negative and HIV positive PBL patients ≥ 18 years old with Stage II to IV PBL or Stage I with elevated LDH and/or bulky tumor, who have measurable disease and adequate organ function are eligible. HIV positive patients must have CD4 ≥ 100 cells/μL and be on concurrent combination antiretroviral therapy (cART) or agree to start cART. Key exclusion criteria include receiving ≥ 1 prior cycle of combination chemotherapy, hepatitis B seropositivity, and active CNS involvement. DARA will be given in conjunction with DA-EPOCH every 21 days for 6 cycles. DARA 16 mg/kg will be administered intravenously weekly for the first 3 cycles on days 1, 8, and 15, then on day 1 for cycles 4-6.

The primary aim is to determine the percentage of newly diagnosed PBL patients who complete ≥ 3 cycles of DARA with DA-EPOCH irrespective of HIV status. We expect that 85% of patients will complete ≥ 5 cycles of DA-EPOCH alone based on the CALGB 50303 study (Bartlett NL, et al. JCO. 2019). Allowing for a lower proportion completing with the addition of DARA, we hypothesize that > 75% of patients will complete ≥ 3 cycles of protocol treatment. An early stopping rule for completing <3 cycles will be employed. The planned enrollment is 15 patients.

Correlations with clinical outcomes will include immunohistochemistry on tumor specimens and peripheral blood to study EBV clearance and identify predictive biomarkers. We will study non-invasive monitoring by circulating tumor DNA using plasma DNA mutation panels and clonal immunoglobulin.