TO THE EDITOR:

We were interested to read the contribution of Dr. Ak and collaborators dealing with the chromosomal consequences induced by white blood cell labeling with ^99mTc-hexamethylpropyleneamine oxime (HMPAO) (1). The authors considered that their experimental conditions mimicked routine conditions. However, the final radioactive concentration they obtained was 325.6 MBq for 4.2–7 million mononuclear cells, that is, about 150-fold higher than the radioactive concentration on mononuclear cells we have under routine conditions (325 kBq per million mononuclear cells (2)). The authors said that they use “mixed leukocyte labeling,” whereas they have, in fact, labeled isolated mononuclear cells without reducing radioactive concentration in order to correct for the absence of granulocytes in their preparation. Mononuclear cells are only a fraction of white blood cells, less abundant than granulocytes, and their affinity for HMPAO is lower than granulocyte affinity (3).

In our opinion, it is therefore not surprising that the authors, having worked under such conditions, noted a high frequency of unstable chromosomal aberrations that led them to conclude that all the aberrant cells would be unable to clone after in vivo injection and would be eliminated.

In contrast to the observation made by Ak et al., we have previously shown that some lymphocytes, after being labeled under conditions mimicking routine nuclear medicine practice, had chromosomal aberrations and that a fraction of labeled cells was still able to clone in vitro.

We think that it is safer and therefore advisable to exclude lymphocytes before labeling in order to avoid the injection of damaged lymphocytes.