- CX-801 is a dually masked, conditionally activated IFNα2b cytokine designed using the CytomX Probody® Therapeutic Platform -

- Phase 1 first-in-human study expected to start in first half of 2024 -

- Clinical trial will evaluate CX-801 as monotherapy and in combination with KEYTRUDA in patients with advanced metastatic solid tumors including melanoma, renal cell carcinoma and head and neck squamous cell carcinoma -

CytomX Therapeutics, a leader in the field of masked, conditionally activated biologics, today announced that it has entered into a clinical trial collaboration and supply agreement with Merck (known as MSD outside of the US and Canada) for CytomX’s first-in-human Phase 1 clinical trial assessing the clinical activity of CX-801, a dually-masked interferon-alpha2b cytokine in combination with Merck’s anti-PD-1 therapy KEYTRUDA® (pembrolizumab).

“Interferon-alpha-2b is a potent cytokine with demonstrated clinical activity against multiple cancer types, but its use has been limited by systemic toxicities. CX-801 is designed to overcome these limitations to unlock the full potential of interferon in activating the immune tumor microenvironment. With an improved therapeutic profile, our goal is to establish CX-801 as a cornerstone of immuno-oncology combination regimens, including in combination with checkpoint inhibitors such as Keytruda, for the treatment of a broad range of tumor types,” said Wayne Chu, M.D., chief medical officer of CytomX Therapeutics.

“CytomX is excited to be entering into this agreement with Merck to utilize Keytruda in combination with CX-801. The product design principles behind CX-801 integrate over a decade of continuous innovation and experience at CytomX in masking potent biologic therapies. The mechanistic combination of CX-801 and Keytruda is compelling and has potential to be a highly effective regimen to significantly improve the outcomes of patients with cancer,” said Sean McCarthy, D.Phil., chief executive officer and chairman of CytomX Therapeutics.