Stem cell mobilisation in lymphoproliferative diseases.

A number of different regimens have evolved for the mobilisation of peripheral blood stem cells for autologous transplantation in patients with lymphoma or myeloma. A successful regimen could be defined as one which consistently resulted in the collection of an optimal number of CD34+ cells with a minimum number of apheresis procedures with minimal toxicity. Initial protocols, which used chemotherapy alone as a mobilising agent, have now been replaced by regimens involving the use of haematopoietic growth factors either alone or in combination with variable doses of cyclophosphamide. Although there is good evidence that high-dose cyclophosphamide (6-7 g/m2) is an effective mobilising agent it is associated with significant toxicity and many groups have now utilised lower doses of cyclophosphamide with reduced toxicity which have still proven to be effective in the majority of patients. More recently a number of 'second generation' combined salvage chemotherapy and mobilisation regimens have been reported for use in the lymphomas which have the advantage of avoiding a specific stem cell mobilisation step and at the same time appear more consistently effective at mobilising stem cells than cyclophosphamide and G-CSF. These regimens are associated with fewer 'poor-mobilisers' and indeed some patients who have failed previous mobilisation with cyclophosphamide and G-CSF have been successfully re-mobilised. It is clear that in both lymphoma and myeloma patients the success of PBSC mobilisation is affected by the amount and type of previous chemotherapy and radiotherapy and probably other pre-treatment factors as exemplified by variability seen in normal donors mobilised with G-CSF alone. In myeloma most groups have utilised cyclophosphamide in variable doses in combination with G-CSF or GM-CSF. However, recent randomised studies have confirmed that G-CSF alone is an effective and nontoxic alternative although it appears that the efficacy of G-CSF as a single agent is related to the dosage used with daily doses of 16 microg/kg/day or greater being most effective. Thus, disease-specific mobilisation strategies appear to be emerging and these will undoubtedly be modified further as more is understood concerning the biology of blood stem cell mobilisation.