The most recent data show that 85 percent of patients undergoing an autologous transplant are able to successfully mobilize a sufficient number of stem cells for engraftment. But what about the remaining 15 percent? Three experts addressed the topic in Sunday’s session 5217-S-CT, “Strategies for Patients Who Fail to Mobilize.”

Patrick Stiff, MD, from Loyola University, began with a historical introduction to the problem, stating that standard approaches generally include the use of cytokines alone or cytokines with chemotherapy. He explained that the latter strategy appears to mobilize progenitor cells more effectively during the rebound phase, although chemotherapy brings its own set of risks to the situation.

Risk Factors, Options

Stiff described how certain autologous transplant populations are unable to yield a sufficient collection for transplantation with the initial mobilization procedure. This group may make up 30 percent of autologous patients. His approach to these “poor mobilizers” was to seek more optimal ways to manage them. Stiff reviewed the literature and shared the data with the audience. He then explored risk factors for poor mobilizers, including the effect of prior therapy in detail, in an attempt to identify these patients up front. However, he noted that 75 percent of those patients mobilize successfully.

Stiff then focused on the improved management of these patients. Options include a marrow harvest, remobilization and enhanced initial mobilization. Because marrow harvest has not improved platelet recovery, Stiff turned to the other approaches. The outcomes of these were discussed and included practical issues such as delay in time to transplant, development of genetic changes from the mobilization and costs.

Chemotherapy

Next, William Bensinger, MD, from Fred Hutchinson Cancer Center at the University of Washington reviewed the data for chemotherapeutic mobilization. Bensinger also examined patient characteristics in an attempt to predict mobilization response. Various chemotherapy regimens were reviewed in detail in an effort to determine the contribution of each. He concluded by listing potential approaches, including the incorporation of chemotherapy into the mobilization regimen and timing the mobilization with the induction or salvage chemotherapy regimen. Bensinger noted that cells collected early in the course of treatment appeared superior and radiation before collection was detrimental to success.

G-CSF Combinations

John Dipersio, MD, PhD, from Washington University School of Medicine, then walked the audience through an alternative perspective — using something other than chemotherapy, with granulocyte colony-stimulating factors (C-CSF) for mobilization. Without a standard approach for diseases such as non-Hodgkin’s lymphoma, Hodgkin’s disease and myeloma, the levels of circulating CD34+ cells vary widely with no correlation to mobilization efficiency. Rather, Dipersio showed the audience how CD34/µL from peripheral blood correlates well with collection yield. Results from a retrospective analysis were reviewed in detail. He asserted that chemotherapy does not effectively remove patient tumors in vivo and that while chemotherapy in combination with G-CSF might increase the numbers collected on day one of apheresis, the total after two or more days is not significantly different. Dispersio teased out duration of apheresis, yield and failure rates, along with other factors. The discussion then turned to the use of a new agent, AMD3100, and G-CSF. Mobilization effectiveness and engraftment kinetics were examined along with his center’s experience with this alternative remobilization strategy.

The session concluded with a lively discussion about other parameters that might have influenced the data, including apheresis operators, apheresis devices and kit selection. As stem cell transplantation increasingly becomes the standard treatment for certain diseases, novel approaches to these mobilization failures will become even more important.