Detection of residual murine LPC-1 myeloma cells from bone marrow cell mixture after purging by 4-hydroperoxycyclophosphamide

Mixtures of BALB/c bone marrow (5 x 10⁶) and LPC-1 myeloma (2 x 10⁶) cells have been purged in vitro with 100 μM 4-hydroperoxycyclophosphamide (4HC) for 30 min at 37°C. Elimination of tumor cells was assessed by monitoring newly synthesized tumor-specific IgG 2aκ in vitro and by reinjecting the cell subcutaneously into the hindlegs of mice. Drug-treated LPC-1 cells had no detectable tumor production and did not reproduce tumors. Untreated cells regrew as solid tumors and killed the host within 3-4 weeks. Bone marrow cell suspension purged of tumor cells were then used to reconstitute lethally pretreated mice injected 24 h earlier with 300 mg/kg cyclophosphamide (CY). Mice injected with CY alone died within 10 days. Those reconstituted with bone marrow cells or with purged bone marrow-tumor cell mixture lived longer than 7 months. Mice reconstituted with untreated bone marrow-tumor suspension grew tumors, had detectable tumor-specific IgG 2aκ in their serum, and died by day 44. These studies demonstrate that the success of myeloma cell purging can be determined by monitoring newly secreted tumor protein and that 4HC successfully eliminates malignant plasma cells in vitro without impairment of normal bone marrow stem cell functions.