Bispecific PD-1xVEGF Data in NSCLC Raises Scale-Up Questions for Merck

Merck has disclosed early clinical data for its PD-1xVEGF bispecific antibody candidate, designated MK-series, in non-small cell lung cancer (NSCLC), yet the company has not committed publicly to phase 3 plans. For manufacturing and quality leaders tracking bispecific pipeline progression, the absence of a late-stage commitment signals that critical decisions around GMP scale-up, dual-target protein purification, and facility investment remain open. The timing is notable given that several large pharma competitors have already moved aggressively into bispecific development programs.

A Merck spokesperson indicated the company is focused on identifying where bispecific approaches "have the greatest benefit for patients" and noted that MK-series candidates are being evaluated in "various combination settings." The cautious posture stands in contrast to peers that have launched dedicated bispecific manufacturing platforms and committed capital to new or retrofitted production suites. For plant heads and process development teams, Merck's wait-and-see approach may reflect the genuine complexity of scaling bispecific antibody production, where heterodimer purity, chain-pairing fidelity, and downstream purification present challenges that monoclonal antibody facilities are not inherently designed to address.

Bispecific antibodies targeting both PD-1 and VEGF pathways require simultaneous expression and correct assembly of two distinct binding domains. From a process validation standpoint, ensuring consistent product quality at commercial scale demands tighter in-process controls and more sophisticated analytical methods than traditional mAb manufacturing. Facilities pursuing these molecules must evaluate whether existing stainless-steel or single-use bioreactor infrastructure can accommodate the additional chromatography steps and hold times needed to resolve product-related impurities, including homodimer and half-antibody species.

Merck's reticence on phase 3 timelines also carries implications for its broader oncology franchise. Keytruda, the company's blockbuster PD-1 inhibitor, remains the commercial backbone, and any bispecific successor would need to demonstrate not only clinical superiority or non-inferiority but also manufacturability at a scale and cost profile that supports global supply. Regulatory affairs teams should note that bispecific candidates face heightened CMC scrutiny from both FDA and EMA, particularly around comparability if process changes are introduced between clinical and commercial manufacturing.

Source: Pharmaceutical Industry News, published April 17, 2026. Merck spokesperson statements as reported by Fierce Biotech.