Brief outline of study we intend to randomize 20 patients and treat them in a double-blinded manner for 1 year with G-CSF and 1 year with plerixafor using a crossover design to allow direct comparison of infection severity during treatment with both agents, at doses determined by the patient s individual neutrophil response. A schedule of events has been provided in Appendix A. Data will be analyzed as specified in the Statistics section (Section 14) after randomization. Tolerability and patient drug preference will also be assessed.