Mr. Maslow declined to say what happened with the company he was talking to. But four years later, no partner has come to light. BioMarin Pharmaceuticals, which specializes in rare diseases, tried to buy the rights last year but was turned down, according to the lawsuit. BioMarin would not comment.

Sloan Kettering has treated three or four patients, with treatments starting in late 2012. In one patient the need for transfusions was reduced by 50 percent, it reported.

Bluebird, by contrast, has reported on the treatments for seven patients with beta thalassemia and one with the more common sickle cell anemia, which can also potentially be treated with the same therapy. Some of the patients seemed to be freed of the need for transfusions.

Mr. Girondi argued that Bluebird treated less sick patients and used a harsher regimen, one he would not want his son to undergo. Bluebird’s chief executive, Nick Leschly, said that some of the patients treated by Bluebird were suffering from the most severe type of the disease.

Mr. Girondi says he is close to raising money to make more of the therapy and treat more patients. In its court filings, Sloan Kettering suggests it will not stop him, as long as he does not use the cancer center’s money, property or personnel. However, the fact that Errant Gene does not control the rights is a deterrent to potential partners and investors.

The cancer center seems to be trying to find a corporate partner itself, according to industry executives. Under the 2011 agreement, Errant Gene will be entitled to half of what Sloan Kettering earns from any licensing deal. So if his lawsuit prods the cancer center to make a deal, Mr. Girondi will profit.

Mr. Girondi said he had spent tens of millions of dollars, mostly his own, on his quest to cure his son since 1992, including $6 million for the gene therapy. He said he nearly faced bankruptcy in 2012 after some real estate investments soured. To save money, he sleeps in his lawyer’s office when he is in New York.

“I’m just a little guy trying to get my son cured,” he said. “I can’t sit by and watch the world go by and not do all I can to make sure what I believe is the better product pushes ahead.”