Pending further data, retroviral gene therapy trials for the so-called 'bubble boy' disease should remain on hold, says a US National Institutes of Health (NIH) committee. The Food and Drug Administration (FDA) is expected to make a decision about the trials based on the committee's recommendations and those of its own advisory group, which is scheduled to meet 28 February.

The NIH's Recombinant DNA Advisory Committee (RAC) met in December, and again on 10 February, to review the adverse events in a French gene therapy trial for X-linked severe combined immunodeficiency disease (SCID). The FDA placed the trial on hold after two study participants developed leukemia.

After reviewing the clinical and molecular data, RAC members concluded that the occurrence of leukemia in the trial was not a random event, and that both cases resulted from the introduction of a mutation at or near the LMO2 gene.

Because a majority of children in the trial “had major clinical improvement,” however, the committee continues to recommend gene transfer for patients who do not respond to stem-cell transplantation, or for whom no suitable stem cell donor can be identified.

It also concludes that there is not enough evidence to warrant suspending other trials with retroviral vectors, including those for non-X-linked SCID.