TOKYO (AP) — The Japanese laboratory that retracted a paper reporting a potentially major breakthrough in stem cell research says that so far its researchers have not managed to replicate the results.

Scientists at the government-affiliated Riken Center for Developmental Biology said Wednesday they were still trying to match results reported in two papers published by the journal Nature. But they refused to say whether or not they expected to succeed in doing so.

The authors retracted the papers in July, admitting to extensive errors in the research, which had raised hopes for a discovery of a simple way to grow replacement tissue for various diseases.

Riken also announced plans an organizational overhaul to prevent any further problems, reducing by half the number of its researchers.