Objective   To investigate the effect of cimetidine on the clonal expansion of TCR Vβ subfamily of T cells in cord blood after the stimulation by K562 cells

in vitro

.    Methods   Cimetidine (1×10

-5

mol/L) or K562 cells (1×10

6

/ml) or both of them were respectively cultured with mononuclear cells (MNC) isolated from normal human cord blood for 2 weeks. After the induction

specific cytotoxicity of the proliferated T cells were detected with K562 cells as the target cells. The selective usages and clonal expansion of TCR Vβ subfa-mily of T cells were analyzed by RT-PCR and genescan technique.   

Results   After induction for 2 weeks

the 3 groups showed the increased cell proliferation

in which specific cytotoxicity of T cells induced by both cimetidine and K562 cells against K562 cells was enhanced significantly compared with the other 2 groups (

P

<

0.01). Differental selective usages of T cells TCR Vβ subfamily and TCR Vβ21 clonal proliferation were found significantly in every group.    Conclusion   Cimetidine enhances the specific cytotoxicity of T cells stimulated by chronic myelogenous leukemia L antigen.