Moderna has gained $125 million in preferred equity for its messenger RNA (mRNA) cancer vaccine partnership with Merck, following on from a series G finance round earlier this year which saw a gain of $500 million.

The programme has reportedly now raised more than $1.6 billion in equity and $1 billion in partnership payments.

The move marks an expansion of the vaccine programme, growing to include Moderna’s mRNA KRAS cancer vaccine mRNA-5671, which is to be examined in combination with immuno-oncology treatments.

KRAS mutations occur in up to 25% of lung cancers, 45% of colon tumours and 90% of pancreatic cancers. There are currently no effective treatments for these defects. mRNA-5671 is designed to target the KRAS mutations found in these conditions, and will reportedly only be tested in patients with these defects.

“While KRAS has long been a challenging target, we believe our mRNA platform offers a novel approach designed to generate and specifically present KRAS mutations to the immune system, potentially allowing the patient’s own immune system to attack and eradicate cancers that harbour these mutations,” Moderna CEO Stéphane Bancel said.

mRNA vaccines attempt to give cells a model which can be used to create specific proteins, enabling the immune system to recognise and attack corresponding markers on cancerous cells. mRNA can encode and express any type of protein, offering the chance to develop prophylactic and therapeutic vaccines that target a range of diseases, as well as protein replacement therapies.

The mRNA vaccines make use of specific mutations in patients’ individual tumours, and are designed to stimulate an immune response to destroy cancer cells. The vaccines are expected to be synergistic with checkpoint inhibitors, such as Keytruda.

The newly expanded deal will give Merck responsibility for clinical development and associated costs, while Moderna will be in charge of clinical supply.

Merck made an upfront contribution of $200 million when the collaboration was finalised in 2016. This sum was used to propel all R&D efforts through proof of concept, and to build a manufacturing facility in Boston. Following mRNA-5671’s proof of concept, Merck has the option to make a payment to Moderna of an undisclosed amount, after which the partners would share cost and profits.

The programme is looking at treatments for several types of cancer, and will include combinations with Merck’s Keytruda (pembrolizumab), which is FDA-approved for the treatment of unresectable or metastatic melanoma and metastatic non-small cell lung cancer (NSCLC) whose tumours express PD-L1.

The programme marks the fourth collaboration between Merck and Moderna. The two companies already have an existing partnership developing mRNA-based infectious disease vaccines and passive immunity treatments. Moderna is also in Phase I testing for its own pipeline of infectious disease vaccine candidates.