J&J drops plamotamab bispecific, Xencor reclaims rights

Johnson & Johnson's Janssen unit has decided to relinquish its rights to the experimental drug plamotamab, a CD20xCD3 bispecific T-cell engager aimed at treating hematologic cancers. This decision hands full control of the drug back to its partner, Xencor. The termination dissolves part of a substantial deal valued at up to $1.2 billion, which was initially established in 2021. Under this deal, Janssen had paid $100 million upfront and invested $25 million in Xencor stock to secure exclusive global rights for plamotamab, intending to develop it either as a standalone treatment or in combination with other regimens.

Plamotamab was a pivotal part of the collaboration between Janssen and Xencor, focusing on developing innovative therapies for B-cell malignancies. The drug works by conditionally activating T-cells through the CD28 co-stimulatory receptor. By late 2023, Xencor had completed patient enrollment in a Phase I study of plamotamab, indicating it was ready to advance to Phase II testing. According to Xencor's CEO, Bassil Dahiyat, plamotamab is a Phase II-ready, subcutaneously administered, immune-cell targeted cytotoxic antibody. Dahiyat mentioned that the company would assess its potential to address unmet medical needs.

Despite relinquishing rights to plamotamab, Janssen continues its collaborative efforts with Xencor, centered on Xencor's CD28 bispecific antibody platform. This platform still supports two ongoing collaborations: JNJ-9401 for prostate cancer and JNJ-1493 for B-cell malignancies. Both candidates entered Phase I trials in late 2023.

Xencor retains the potential to benefit from additional development, regulatory, and sales milestones, along with net sales royalties ranging from high-single to low-double-digit percentages. If clinical proof-of-concept is demonstrated for any program, Xencor has the option to co-fund part of the development costs—specifically, 20% for JNJ-9401 and 15% for JNJ-1493 or other B-cell targeting bispecifics. Additionally, Xencor can carry out up to 30% of detailing efforts in the United States. Should Xencor opt-in, it stands to earn royalties in the low-double-digit to mid-teens percent range.

This latest development highlights the dynamic nature of pharmaceutical partnerships and the ongoing quest to bring new treatments to market. While the dissolution of Janssen's rights to plamotamab marks a significant shift, the continued collaboration on other projects underscores the commitment of both companies to advancing cancer therapies. The progress of Xencor's other candidates and the potential milestones and royalties indicate a sustained focus on innovation and development in the oncology sector.