Cilag International, an affiliate of the Janssen Pharmaceutical Companies of Johnson & Johnson, will partner with argenx to develop its cancer-fighting antibody cusatuzumab (ARGX-110), through a collaboration that could generate more than $1.8 billion for argenx, the companies said today.

Cusatuzumab is now in development in a Phase I/II combination study with Vidaza® (azacytidine or AZA) for newly diagnosed, elderly patients with acute myeloid leukemia (AML) and high-risk myelodysplastic syndrome (MDS) who are unfit for chemotherapy (NCT03030612).

argenx is enrolling an initial 21 AML patients in the Phase II portion of the trial using the 10 mg/kg dose of cusatuzumab. Today, the company reported data from the Phase I portion of the trial, as of the October 15 cutoff date, during a workshop held today in conjunction with the 60th American Society of Hematology (ASH) Annual Meeting and Exposition, being held through tomorrow in San Diego.

In the Phase I dose escalation portion, argenx evaluated 12 newly diagnosed AML patients unfit for intensive chemotherapy. Patients received cusatuzumab in combination with Vidaza.

The new data showed an overall response rate (ORR) across the 12 patients of 92% (11/12 patients), including 10 patients (91%) with a complete remission with or without hematologic recovery (CR/CRi) and 1 (9%) partial remission (PR). Responses were seen in patients across age and risk category, including IDH2 and TP53 mutations, argenx said.

The median duration of patients on trial as of data cut-off was 8.1 months, ranging from 2 to 17.4 months, with 6 patients still on trial. Five patients (42%) achieved minimal residual disease (MRD) negativity as measured by flow cytometry and molecular genetics in the bone marrow, argenx added.

The company also cited translational data showing that cusatuzumab monotherapy and in combination with Vidaza significantly reduced leukemic stem cells in the bone marrow of AML patients.

“Cusatuzumab offers a novel mode of action targeting leukemic stem cells, which are a known driver of the relapse mechanism, and has shown a compelling response rate and tolerability profile to date,” argenx CEO Tim Van Hauwermeiren said in a statement. “Janssen is an ideal strategic partner for us to develop this differentiated investigational therapy given its extensive clinical, regulatory, and commercial expertise in oncology, and we believe that through this collaboration we are best positioned to reach the broadest number of patients as quickly as possible.”

Under an exclusive, global collaboration and license agreement, Janssen agreed to pay argenx $300 million upfront, while J&J’s venture capital subsidiary, Johnson & Johnson Innovation-JJDC, agreed to purchase $200 million (1,766,899) of newly issued shares representing 4.68% of argenx’s outstanding shares at €100.02 per share ($113.19).

Janssen also agreed to pay argenx potentially up to $1.3 billion tied to achieving development, regulatory, and sales milestones, in addition to tiered, double-digit royalties.

Janssen will oversee commercialization worldwide, while argenx retains the option to participate in commercialization efforts in the U.S., where the companies have agreed to share economics 50/50 on a royalty basis. Outside the U.S., Janssen will pay double-digit sales royalties to argenx, the companies said.

The licensing and collaboration deal is subject to customary closing conditions, including clearance under the Hart-Scott-Rodino Antitrust Improvements Act, and expected to close in the first quarter of 2019.