Juno Therapeutics, the Seattle biotechnology startup unveiled last month by leading cancer scientists here and in New York, has bumped its initial financing round to more than $145 million with new backing from Amazon.com founder Jeff Bezos and others.

The immunotherapy company on Monday said it has tacked about $25 million more onto last month’s already record-breaking $120 million start-up financing. The added investors include Bezos Expeditions, the Amazon chairman’s personal investment fund, and the venture capital firm Venrock.

Juno CEO Hans Bishop said in a recent interview that the company’s approach to bolstering patients’ cancer-fighting immune responses has attracted such big money because “the science is extraordinary and the potential is extraordinary.” But he cautioned, “There’s still a lot of work to do.”

Juno was formed in partnership with Fred Hutchinson Cancer Research Center, New York’s Memorial Sloan-Kettering Cancer Center, and Seattle Children’s Research Institute.

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