The CD19+ B‐cell counts at peripheral blood stem cell mobilization determine different levels of tumour contamination and autograft purgability in low‐grade lymphoma

Summary. The tumour load of peripheral blood stem cell (PBSC) harvests and the outcome of ex vivo immunomagnetic B-cell purging was investigated in 19 patients with low-grade lymphoma. To quantify the tumour load, we combined fluorescence-activated cell sorting measurement of CD19+ B-cells and determination of the B-cell light chain ratio (LCR) with consensus complementarity-determining region III-polymerase chain reaction (CDRIII-PCR) and gene scan analysis. The number of tumour cells was calculated using B-cell extracts from the PBSCs. Two different patterns were distinguished. In eight patients (42%) with CD19+ B cells > 1% in the apheresis product, a high tumour load was found, characterized by a monoclonal LCR, positive PCR in seven out of eight cases, > 5 × 107 extracted lymphoma cells in six out of seven PCR-assessable cases, and the presence of residual lymphoma after purging in six of seven cases. In 11 patients (58%) with  5 × 107 extracted lymphoma cells in zero out of four PCR-assessable cases, and the presence of residual lymphoma after purging in zero out of four of these cases. The level of residual lymphoma following purging largely depended on the level of tumour contamination. CD19+ B-cells > 50/µl in the peripheral blood at mobilization predicted a high tumour load in the apheresis product.