Pfizer has agreed to pay iTeos Therapeutics €24 million ($30 million) up front for the exclusive rights to some preclinical candidates, also making an undisclosed equity investment in the company and promising untold milestone payments down the line.

Through the deal, Pfizer gets some early-stage drugs that target IDO1 and TDO2, cancer-expressed enzymes that break down tryptophan, which is integral to the immune system’s ability to recognize tumors. By blocking the enzymes, iTeos’ candidates can unblind the body’s defenses and help T cells better attack malignancies.