Based on the pre-clinical data the investigators hypothesize that G-CSF treatment in patients with multiple myeloma will generate a 'hostile' bone marrow microenvironment for myeloma cells, depriving them of key support signals and rendering them more sensitive to chemotherapy. The investigators therefore propose to do an initial pilot study 1) to explore the safety of the combination of G-CSF and bortezomib-, carfilzomib-, or IMID-based treatment regimens in patients with bortezomib-, carfilzomib-, or IMID-refractory myeloma and 2) to generate correlative data for a subsequent larger study looking at the combination.