Peripheral blood stem cell contamination in mantle cell non-Hodgkin lymphoma: the case for purging?

Intensification using peripheral blood stem cells collected after chemotherapy followed by growth factors is being increasingly investigated as an alternative to conventional chemotherapy for mantle cell non-Hodgkin lymphoma. We investigated 14 grades III-IV, t(11;14)-positive cases for contamination of PBSC collected after a polychemotherapy regimen followed by G-CSF. Patients were first treated with a polychemotherapy regimen. There were four CR, seven PR, two refractory and one early death. Seven patients have been transplanted, in whom PBSC were mobilized, using either cyclophosphamide/VP16 or Dexa-BEAM followed by G-CSF. For all patients, whether actually autografted or not, PB cells were tested at the time of regeneration on G-CSF after the first polychemotherapy or after the mobilizing regimen. PCR evaluation of contamination was performed first by a semi-quantitative approach, using serial dilutions of initial DNA, then confirmed using a limiting-dilution analysis. Two patients were not informative (one early death and one without an available molecular marker). PB cells collected at regeneration contained at least one log more lymphoma cells than steady-state blood or marrow, apart from in two cases. Moreover, where a mobilizing treatment diminished tumor burden in the patient, at the same time it increased PB contamination in most cases. We conclude that advanced mantle cell NHL appears to be largely resistant to significant in vivo purging by conventional chemotherapy. Where treatment brings benefits by reducing tumor load, it may at the same time negate it by mobilizing malignant cells into the collections used to intensify. Although the clonogenic potential of this massive infiltration is unknown (only gene marking studies could provide a definitive answer regarding the source of relapses), strategies aimed at reducing the level of contamination in the graft should be considered when designing future protocols.