The company that helped create dollythe sheep said yesterday that it had cloned two lambs from genetically modified cells in a technique that could prove a major step in animal-to-human organ transplants. The company, PPL Therapeutics P.L.C., which is based in Edinburgh, inserted new DNA in a specific place in sheep cells, then fused the modified cells with sheep eggs from which the nucleus had been removed and produced two lambs, Cupid and Diana, with the genetic change.