[Combination of thalidomide and rituximab in suppressing myeloma cells in vitro]

The efficiency of rituximab (Mabthera) is related to CD20 expression density on cell membrane. It is not yet to be solved how to heighten expression level of CD20 on multiple myeloma (MM) cell membrane and to increase the efficacy of Mabthera to MM. This study was designed to observe whether thalidomide could promote the effect of Mabthera on suppressing myeloma cells in vitro and its possible mechanism.

Colony growth of 18 untreated and 20 relapsed or refractory MM patients' myeloma cells were observed in the methylcellulose semisolid medium adding thalidomide (10, 50, 75, 100, 150, 200, 300 micrograms/ml) or Mabthera (0.5, 1, 2, 4, 8, 12, 16 micrograms/ml) or thalidomide above 7 doses in combination with Mabthera of 16 micrograms/ml or Mabthera above 7 doses in combination with thalidomide of 75 micrograms/ml. Change of CD20 expression on the myeloma cells were measured by flow cytometer after and before myeloma cells were treated with thalidomide.

The inhibition of the colony formation of untreated MM patients' myeloma cells occurred in 1. use only of thalidomide at more than or equal to 75 micrograms/ml or use only of Mabthera at 16 micrograms/ml, 2. use of thalidomide at 75 micrograms/ml with or without Mabthera at 16 micrograms/ml, 3. use of thalidomide at more than or equal to 75 micrograms/ml with or without Mabthera at 16 micrograms/ml; The inhibition of the colony formation of relapsed or refractory MM patients' myeloma cells occurred in 1. use of thalidomide at 75 micrograms/ml with Mabthera at 16 micrograms/ml, 2. use of thalidomide at more than or equal to 100 micrograms/ml with or without Mabthera at 16 micrograms/ml; Thalidomide at more than 75 micrograms/ml enhanced the expression of CD20 antigen in untreated and relapsed or refractory MM patients' myeloma cells.

Thalidomide could enhance the inhibition of Mabthera on colony formation of MM patients' myeloma cells, which is related to that thalidomide enhances CD20 antigen expression of myeloma cells.