Sanofi’s $11.6bn Bioverativ purchase looks hit-and miss after phase 3 rare diseases drug runs into trouble

When Sanofi coughed up $11.6bn for rare diseases pharma Bioverativ in 2018, many commentators said the French firm had overpaid. It’s true that the deal has led to a rare disease blockbuster for Sanofi, but it remains to be seen whether the sales will recoup the investment in Bioverativ.

And the chances of success from other drugs in the Bioverativ pipeline just fell after the news about riliprubart, another hopeful that originates from the deal. Sanofi announced it has abandoned its Phase 3 MOBILIZE study of riliprubart in patients with the rare neurological condition chronic inflammatory demyelinating polyneuropathy (CIDP), after an interim analysis showed the C1s inhibitor class drug was ineffective.

Paris-based Sanofi is also reviewing other ongoing studies of riliprubart following the analysis by an independent data monitoring committee, including the VITALIZE phase 3 study in CIDP patients treated with intravenous immunoglobulin. The committee noted that there were no safety signals associated with the riliprubart.

Riliprubart works by selectively inhibiting activated C1s in the classical complement pathway of the innate immune system. C1s is a key serine protease protein that forms the catalytic core of the C1 complex, which initiates the classical pathway of the human complement system. Part of the innate immune response, it acts as a cascade trigger to identify and destroy pathogens.

The thinking is that by blocking C1s, riliprubart has the potential to inhibit key inflammatory mechanisms that drive demyelination and axonal damage in CIDP. In CIDP this pathway has become over-stimulated, leading to nerve damage and disease symptoms associated with CIDP.

Placebo-controlled MOBILIZE tested riliprubart in 140 patients refractory to standard of care, and according to information on Sanofi’s website, involved 134 sites worldwide

Bioverativ deal back in the spotlight

The failure of riliprubart comes after the R&D success story of Enjaymo (sutimlimab), another C1s inhibitor that originated from the Bioverativ acquisition.

It was a first-in-class approval for Sanofi in February 2022, as a classical complement inhibitor indicated to decrease the need for red blood cell transfusion due to hemolysis in adults with cold agglutinin disease (CAD). But Sanofi decided to sell Enjaymo to Recordati for $825 million and focus instead on another drug from the Bioverativ acquisition, Altuviiio (Efanesoctocog alfa) approved in 2023 by the FDA for haemophilia A, and developed in partnership with Sobi.

Altuviiio has already become Sanofi’s next blockbuster, with sales of around €325 million in Q1 2026. But there were doubts from the outset about the Bioverativ price tag amid suspicions that Sanofi was on the rebound after losing out to Pfizer in a bidding war to buy oncology biotech Medivation in 2016.

Despite the $14 billion price tag, the Medivation deal has been a huge success for Pfizer financially and strategically thanks to the success of PARP inhibitors Xtandi (enzalutamide) and Talzenna (talazoparib).

For now, the Bioverativ deal looks neither like a clear misstep nor an obvious bargain. Altuviiio has given Sanofi the blockbuster it needed in rare diseases, but the setback with riliprubart is a reminder that the rest of the pipeline still has to deliver if the company is to silence doubts over the $11.6bn price tag.

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