Molecular monitoring of tumor cell contamination in leukapheresis products from stage IV neuroblastoma patients before and after positive CD34 selection

Background Autologous peripheral blood stem cells (PBSCs) are frequently used to reconstitute hematopoiesis following administration of megatherapy in children with advanced stage IV neuroblastoma. Some centers prefer the use of autografts enriched for CD34+ progenitor cells because the positive selection procedure is believed to reduce indirectly tumor cell contamination. Procedure In this study, we monitored the efficiency of tumor cell purging following CD34 selection in PBSCs from seven patients with advanced neuroblastoma by using a highly sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Amplification of tissue-specific mRNA transcript of tyrosine hydroxylase gene with nested primers enabled the detection of residual neuroblastoma cells with a sensitivity of one malignantcell per 106 normals. Results Using this method, contaminating tumor cells were detected in seven of nine leukapheresis products of the patients. After positive immunoselection of CD34+ cells on Ceprate™ column, only one of nine enriched stem cell fraction still contained tumor cells detectable by RT-PCR. In six cases, PCR positive PBSCs became PCR negative after selection. Conclusions We conclude that tumor cell contamination may be frequently detected in PBSC harvests of stage IV neuroblastoma patients by sensitive molecular analysis. The load of contaminating malignant cells might be reduced following CD34 selection. Med. Pediatr. Oncol. 30:228–232, 1998. © 1998 Wiley-Liss,Inc.