Methodologies to estimate circulating hematopoietic progenitors for autologous transplantation in cancer patients

Optimal criteria for harvesting circulating hematopoietic progenitors (CHP) for autologous transplantation to support myeloablative cancer therapy are still uncertain mostly because the CFU-GM assay, the commonly used indirect indicator of the hematopoietic recovery of the graft, is poorly standardized and provides information evaluable only retrospectively. Based on the knowledge that CHP express CD34 and CD33 differentiation antigens and facilitated by the availability of a very efficient fluorescein-conjugated CD34 antibody (8G12), we developed a direct immunofluorescence flow cytometry assay with the aim of replacing the CFU-GM assay advantageously. Recently, in a comparative study, both assays were applied to 157 blood samples obtained daily throughout 20 different recoveries from pancytopenia induced by high-dose cyclophosphamide (7 g/m2) cancer therapy w/ or w/o rhGM-CSF. Results showed that: a) detectability of CD34+ CHP indicated an increase to greater than 500 CFU-GM/mL, a level clinically adequate for harvesting CHP; b) CD34+ cells correlated well with CFU-GM (R=0.89) and data fitted a linear regression line (y=388.3 + 64.0x; y=CFU-GM/mL and x=CD34+/uL); c) in a series of 8 patients treated with myeloablative chemoradiotherapy, early recovery of marrow functions was predicted more accurately by the number of transplanted blood CD34+/CD33+ cells than by nucleated cells, CFU-GM, CD34+/CD33-cells, or CD34-/CD33+ cells. As a guideline, provided platelets are greater than 70,000/uL, harvest of CHP by leukapheresis during recovery from chemotherapy induced pancytopenia should be started as soon as CD34+ cells appear in the circulation and continued until the threshold dose of 7.8x10(6) CD34+ cells/kg, equivalent to 50 x 10(4) CFU-GM/kg, is achieved.(ABSTRACT TRUNCATED AT 250 WORDS)