Precision immunology has emerged as one of the hottest fields in drugmaking over the past several years, spurred by new ways to make more potent drugs that don’t trigger as many side effects.

Large drugmakers and venture firms alike have shelled out billions of dollars for promising anti-inflammatory treatments. Johnson & Johnson and Roche both picked up autoimmune drugs in blockbuster deals, while Mirador Therapeutics launched in March with $400 million from investors to develop new autoimmune medicines.

On Thursday, Santa Ana Therapeutics became the latest such startup to emerge, making its debut with $168 million and a trio of programs that riff in new ways on existing ideas like targeting mast cells and stimulating the PD-1 pathway.

"We've been drugging lots of cytokines, trying to modify the biology, and it's worked," said Peter Emtage, Santa Ana's CEO. "But the opportunity really comes in when you can identify the culprit cell."

One of Santa Ana’s drugs, dubbed SAB01, is a so-called bispecific antibody. It is designed to mute the mast cells that drive allergic disease by blocking a protein called c-Kit. But the drug will only do so when it detects another target that’s found on those cells. Past attempts to treat such diseases by inhibiting c-Kit have failed due to side effects triggered by interfering with that protein on other cell types, Santa Ana said.

The company is developing SAB01 for chronic inducible urticaria, a common skin condition, and plans to enter the clinic in 2025.

A second candidate, a PD-1 agonist, is also due to enter Phase 1 trials for several inflammatory conditions next year. While checkpoint inhibitors that block PD-1 have proved powerful in treating cancer, SAB03 is meant to keep T cells from activating and preventing the immune system from going into overdrive. Other companies, such as MiroBio, which sold in 2022 to Gilead Sciences, have tried to do something similar.

“We almost think of Santa Ana as doing anger management for the immune system,” said Jerel Davis, a managing director at Versant.

Santa Ana is developing a third medicine that’s similar in concept to an antibody-drug conjugate, but designed to make glucocorticoid drugs safer.

Versant Ventures led Santa Ana’s $43 million Series A round, while GV was the major backer of its $125 Series B round. Other investors include TPG, a16z, Access Biotechnology and RTW.

Santa Ana’s name has similar origins to another Versant company, Chinook Therapeutics. While the latter took inspiration from the warm, western winds in the Pacific Northwest, Santa Ana’s is named after the desert and mountain winds of Southern California. (Santa Ana is based in Alameda, just a few miles across the bay from South San Francisco, however.)

Versant also recently backed SixPeaks Bio, an obesity drug startup molded as a “build-to-buy” biotech.

Versant debuts biotech working on ‘anger management for the immune system’

Santa Ana Therapeutics, a precision immunology startup, has raised $168 million to develop new autoimmune medicines. The company's lead drug, SAB01, is a bispecific antibody designed to mute mast cells that drive allergic disease. Santa Ana plans to enter the clinic with SAB01 in 2025 for chronic inducible urticaria. The company also has a PD-1 agonist, SAB03, in development for inflammatory conditions. Versant Ventures led Santa Ana’s $43 million Series A round, with GV as the major backer of its $125 Series B round.