New York’s IRX Therapeutics, a developer of drugs designed to stimulate the immune system against viruses and cancer, raised $12.5 million in a second convertible note offering. The investors were mostly private individuals, including Frank Loverro, managing director of the New York private-equity firm Kelso & Co., and other members of the firm, according to VentureWire (subscription required).

IRX has so far raised more than $35 million, including a prior $12.5 million convertible-note round. The company’s lead candidate, IRX-2, consists of a mix of cytokines, which are naturally occuring proteins that help regulate the immune system. The idea seems to be that administering these cytokines will provoke a more potent immune response against tumors. In a mid-stage human trial of the drug carried out at Mexico’s National Cancer Institute, two of 32 patients with head and neck cancer saw their tumors disappear, while 10 others saw them diminish by more than 50 percent.

It’s worth noting, though, that such uncontrolled studies are susceptible to many forms of bias and don’t come close to proving that the drug actually works. The company is now enrolling volunteers in a much larger mid-stage trial — also uncontrolled — at ten sites in the U.S.

The company’s release on the funding is here.