London-based biotech Cytospire Therapeutics has closed an oversubscribed £61 million ($83 million) Series A financing to push its pan-gamma delta T cell engager pipeline into human cancer trials. The round, announced on 5 May 2026, was led by 4BIO Capital and brought in a deep syndicate of new and existing biotech specialists.
Cytospire develops multispecific antibodies that direct the body's own immune system at solid and liquid tumours. Founded by Dr Natalie Mount, the company emerged from stealth in 2024 and is one of the most-watched UK immuno-oncology startups of the past two years.
Who led the Cytospire Series A?
4BIO Capital led the round and was joined by a notable group of new backers. Servier Ventures, the newly formed corporate venture arm of French pharmaceutical group Servier, made its first-ever investment as part of the round. Other new investors included Sound Bioventures, the British Business Bank, Criteria Bio Ventures, Modi Ventures, Medical Incubator Japan and Pathway Bioventures.
Founding investor Abingworth and LifeArc Ventures both followed on. Cytospire had previously raised around $19.8 million according to PitchBook, taking total funding to roughly $103 million after this round.
What will Cytospire spend the £61M on?
The proceeds will fund advancement of lead programme CYT X300 through IND-enabling preclinical studies and GMP manufacturing. A first-in-human clinical study is planned to evaluate CYT X300 as a treatment for EGFR-positive solid tumours, including colorectal, head and neck, and non-small cell lung cancers.
Most existing T cell engagers on the market activate CD3 T cells, an approach with known efficacy and safety limits. Cytospire's engagers instead activate gamma delta T cells, a population thought to be better suited for solid tumour penetration. The company is targeting all gamma delta T cell subtypes rather than a single one, which the team argues should produce broader anti-tumour responses across diverse patient populations.
What the CEO said
"We are excited to write the next chapter of Cytospire's story with this fantastic group of specialist investors," said Natalie Mount, Chief Executive Officer of Cytospire Therapeutics. "Immune cell engagers are an important type of cancer immunotherapy, but we know that there are significant limitations from both an efficacy and safety perspective with conventional CD3 T cell engagers."
Mount is on her fourth biotech start-up. She was previously CEO of Adaptate Biotherapeutics, acquired by Takeda in 2022, and Chief Scientific Officer at GammaDelta Therapeutics, also acquired by Takeda. In late 2025 she was named Woman Entrepreneur of the Year at the Cancer Research Horizons Innovation and Entrepreneurship Awards.
What this means for UK founders
Three things stand out for UK tech founders watching this round.
Deep-science biotech is still attracting major early-stage capital in the UK despite a tighter overall venture environment. The British Business Bank's participation alongside specialist life science funds signals continued public-private appetite for high-conviction therapeutic bets out of London.
Repeat founders with prior exits are commanding bigger rounds and more international syndicate participation. Mount's track record at Adaptate and GammaDelta gave Cytospire credibility to attract Servier Ventures' first deployment and Japanese investor Medical Incubator Japan.
Servier Ventures choosing London for its inaugural cheque is a useful signal too. Corporate venture funds tend to anchor in their home markets first. A French pharma group writing its first cheque into a UK biotech suggests Britain remains globally competitive on talent and science quality.
