Xencor Reacquires CD20 x CD3 Bispecific T-Cell Engager

Xencor, Inc., a biopharmaceutical company based in Pasadena, California, announced on June 13, 2024, that it will regain exclusive global rights to plamotamab, a CD20 x CD3 bispecific T-cell engager. This decision follows the completion of Phase 1 clinical trials for plamotamab in treating hematologic cancers. Initially, in 2021, Xencor had entered into a collaboration and licensing agreement with Janssen Biotech, Inc., under which Janssen held rights to develop and commercialize plamotamab, along with other B-cell targeting bispecific antibodies designed to conditionally activate T cells via the CD28 co-stimulatory receptor. Xencor successfully completed patient enrollment for the Phase 1 study of plamotamab by the end of 2023.

Janssen has now decided to terminate its rights to plamotamab while retaining rights to other B-cell targeting CD28 bispecific antibodies, specifically JNJ-9401 (PSMA x CD28) and JNJ-1493 (CD20 x CD28). Bassil Dahiyat, President and CEO of Xencor, emphasized that plamotamab is poised for Phase 2 development and that the company will assess its potential to meet unmet medical needs. Dahiyat also underscored that Xencor's CD28 platform remains active in two ongoing collaborations with Janssen. These collaborations encompass JNJ-9401 and JNJ-1493, both of which entered clinical development in the fourth quarter of 2023 and target prostate cancer and B-cell malignancies respectively.

Under the existing collaboration agreements, Xencor and Janssen have conducted joint research to discover XmAb® bispecific antibodies targeting CD28 and other select targets. While Janssen holds exclusive global rights to develop and commercialize the products identified, it has progressed JNJ-9401 and JNJ-1493 into Phase 1 clinical trials. Xencor stands to benefit from development, regulatory, and sales-based milestone payments, alongside tiered royalties on net sales of approved products ranging from high-single to low-double digit percentages.

Upon achieving clinical proof-of-concept for each program, Xencor has the option to co-fund part of the development costs—20% for JNJ-9401 or 15% for JNJ-1493 and other B-cell targeting bispecifics. Additionally, Xencor can opt to perform up to 30% of detailing efforts in the United States. If these options are exercised, Xencor would be eligible for tiered royalties ranging from low-double digits to mid-teens percentages.

Plamotamab is an investigational bispecific antibody that leverages Xencor’s XmAb® technology. It contains domains that bind to CD20 and CD3, stimulating T cells to target and kill CD20-expressing cells effectively. Data from the Phase 1 study demonstrated that intravenously administered plamotamab was generally well tolerated and showed promising clinical activity in patients with B-cell malignancies.

Xencor is dedicated to developing engineered antibodies for treating cancer and other serious diseases. Over 20 candidates using the company's XmAb® technology are currently in clinical development, and three XmAb medicines are marketed through partnerships. Xencor's XmAb engineering technology facilitates small structural changes to proteins, leading to new therapeutic mechanisms.