United Therapeutics (UTHR) is making a big bet on immune system regeneration. The company announced Thursday it has acquired privately held Thymmune Therapeutics for $140 million in cash, with the potential for up to $160 million more in milestone payments tied to clinical and regulatory goals through 2031.

Thymmune is a preclinical biotech working on regenerative thymic cell therapies. The thymus is the organ that trains T-cells, which are the immune system's soldiers. As we age, the thymus shrinks and becomes less effective, which is part of why older people are more vulnerable to infections and disease. Thymmune's approach is to use a proprietary process to convert human-induced pluripotent stem cells (iPSCs) into thymic cells. Once implanted, these cells can mature into multiple cell types that restore healthy T-cell function.

The lead candidate, THY-100, is being developed for congenital athymia, an ultra-rare condition where infants are born without a functioning thymus. Without it, they have virtually no immune system. Preclinical animal studies have shown that THY-100 can generate a neo-thymus inside the body that supports T-cell development. If that works in humans, the implications go far beyond this rare disease. The technology could eventually be used to improve transplant tolerance, treat autoimmune diseases, and even boost immune function in older adults with declining T-cell activity.

United Therapeutics had $1.28 billion in cash and equivalents as of March 31, so the $140 million upfront is a manageable outlay. The deal also includes earn-out payments that could add up to $160 million, but those are contingent on hitting clinical and regulatory milestones. In other words, Thymmune's former shareholders only get that extra money if the drugs actually work and get approved.

Investors seemed to like the news. UTHR shares were up 1.24% in premarket trading Thursday, sitting at $553.93.