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

Intensification using peripheral blood stem cells collected after chemother apy followed by growth factors is being increasingly investigated as an alt ernative to conventional chemotherapy for mantle cell non-Hodgkin lymphoma, We investigated 14 grades III-IV, t(11;14)-positive cases for contaminatio n of PBSC collected after a polychemotherapy regimen followed by G-CSF, Pat ients were first treated with a polychemotherapy regimen There were four CR , seven PR, two refractory and one early death. Seven patients have been tr ansplanted, in whom PBSC were mobilized, using either cyclophosphamide/VP16 or Dexa-BEAM followed by G-CSF, For all patients, whether actually autogra fted or not, PB cells were tested at the time of regeneration on G-CSF afte r the first polychemotherapy or after the mobilizing regimen. PCR evaluatio n of contamination was performed first by a semi-quantitative approach, usi ng serial dilutions of initial DNA, then confirmed using a limiting-dilutio n analysis. Two patients were not informative (one early death and one with out an available molecular marker). PB cells collected at regeneration cont ained at least one log more lymphoma cells than steady-state blood or marro w, apart from in two cases. Moreover, where a mobilizing treatment diminish ed tumor burden in the patient, at the same time it increased PB contaminat ion in most cases, We conclude that advanced mantle cell NHL appears to be largely resistant to significant in vivo purging by conventional chemothera py, Where treatment brings benefits by reducing tumor load, it may at the s ame time negate it by mobilizing malignant cells into the collections used to intensify. Although the clonogenic potential of this massive infiltratio n is unknown (only gene marking studies could provide a definitive answer r egarding the source of relapses), strategies aimed at reducing the level of contamination in the graft should be considered when designing future prot ocols.