为寻找克服Ｐ糖蛋白（Ｐｇｐ）介导肿瘤多药耐药的途径，选择环孢霉素Ａ（ＣｓＡ）作为耐药逆转剂，分别采用台盼蓝拒染法、ＭＴＴ法和免疫组化法分析ＣｓＡ对人白血病细胞株的毒性及逆转效果，观察ＣｓＡ及长春新碱（ＶＣＲ）对Ｋ５６２／ＶＣＲ生长的抑制作用及检测Ｋ５６２／ＶＣＲ细胞膜Ｐｇｐ的表达情况。结果显示，ＣｓＡ在非毒性剂量浓度４μｇ／ｍｌ以下能逆转细胞耐药，与ＶＣＲ合用能抑制Ｋ５６２／ＶＣＲ生长（Ｐ＜０．０１）；Ｋ５６２／ＶＣＲ细胞膜上Ｐｇｐ的高表达，经ＣｓＡ作用后其表达下降。这表明ＣｓＡ能逆转Ｋ５６２／ＶＣＲ耐药性，Ｋ５６２／ＶＣＲ耐药的产生与Ｐｇｐ的表达有关 In order to find a way to overcome P glycoprotein (Pgp)-mediated multidrug resistance of tumors, Cyclosporin A (CsA) was selected as the drug resistance reversal agent, using trypan blue dye exclusion method, MTT method and immunization respectively. The histochemical method was used to analyze the cytotoxicity and reversal effect of CsA on human leukemia cell lines. The inhibitory effects of CsA and vincristine (VCR) on the growth of K562/VCR and the expression of Pgp on K562/VCR cell membrane were observed. The results showed that CsA could reverse cell resistance at a non-toxic dose concentration of 4 μg/ml or less, and combined with VCR could inhibit the growth of K562/VCR (P<0.01); the high expression of Pgp on K562/VCR cell membrane was detected by CsA. After its effect, its expression decreased. This indicates that CsA can reverse the drug resistance of K562/VCR, and the production of K562/VCR resistance is related to the expression of Pgp.