Methods for preparing monomeric cytotoxic drug/carrier conjugates with a drug loading significantly higher than in previously reported procedures and with decreased aggregation and low conjugate fraction (LCF) are described. Cytotoxic drug derivative/ antibody conjugates, compositions comprising the conjugates and uses of the conjugates are also described. Monomeric calicheamicin derivative/anti-CD22 antibody conjugates, compositions comprising the conjugates and uses of the conjugates are also described.本發明係描述製備單體胞毒藥物/載體共軛物的方法,其具有比以先前報告之製程明顯更高的藥物裝載,並具有降低的聚集作用和低共軛部分(LCF)。亦描述胞毒藥物衍生物/抗體共軛物,包括該共軛物的組合物,以及該共軛物的用途。亦描述單體卡奇黴素衍生物/抗-CD22抗體共軛物,包括該共軛物之組合物,以及該共軛物之用途。