A method for detecting an immune response in a patient having undergone kidney transplantation, wherein the method comprises the following steps: a) a cell isolation step comprising: i. isolating epithelial cells from the urine of said patient, ii. providing a sample of whole blood obtained from said patient, iii. dividing said sample of whole blood into a first and a second portion of whole blood, b) a cell cultivation step comprising: i. cultivating said epithelial cells, yielding cultivated epithelial cells, ii. dividing said cultivated epithelial cells into a first and a second portion of cultivated epithelial cells, iii. contacting said first portion of cultivated epithelial cells with BK-Virus, yielding BKV-infected epithelial cells, c) a reactive T-cell determination step, comprising a direct reactive T-cell determination comprising: i. contacting said sample of whole blood of said patient with said BKV-infected epithelial cells, and ii. determining T-cells comprised within said sample of whole blood that are activated by said BKV-infected epithelial cells, yielding a BKV-reactive T-cell number; iii. contacting said second portion of whole blood with said second portion of cultivated epithelial cells and determining T-cells comprised within said second portion of whole blood that are activated by said cultivated epithelial cells, yielding an allograft reactive T-cell number; wherein the presence of BKV-reactive T-cells is indicative of an anti-BK-virus immune response and the presence of allograft reactive T-cells is indicative of an anti-graft immune response. a) a cell isolation step comprising: i. isolating epithelial cells from the urine of said patient, ii. providing a sample of whole blood obtained from said patient, iii. dividing said sample of whole blood into a first and a second portion of whole blood, i. isolating epithelial cells from the urine of said patient, ii. providing a sample of whole blood obtained from said patient, iii. dividing said sample of whole blood into a first and a second portion of whole blood, b) a cell cultivation step comprising: i. cultivating said epithelial cells, yielding cultivated epithelial cells, ii. dividing said cultivated epithelial cells into a first and a second portion of cultivated epithelial cells, iii. contacting said first portion of cultivated epithelial cells with BK-Virus, yielding BKV-infected epithelial cells, i. cultivating said epithelial cells, yielding cultivated epithelial cells, ii. dividing said cultivated epithelial cells into a first and a second portion of cultivated epithelial cells, iii. contacting said first portion of cultivated epithelial cells with BK-Virus, yielding BKV-infected epithelial cells, c) a reactive T-cell determination step, comprising a direct reactive T-cell determination comprising: i. contacting said sample of whole blood of said patient with said BKV-infected epithelial cells, and ii. determining T-cells comprised within said sample of whole blood that are activated by said BKV-infected epithelial cells, yielding a BKV-reactive T-cell number; iii. contacting said second portion of whole blood with said second portion of cultivated epithelial cells and determining T-cells comprised within said second portion of whole blood that are activated by said cultivated epithelial cells, yielding an allograft reactive T-cell number; wherein the presence of BKV-reactive T-cells is indicative of an anti-BK-virus immune response and the presence of allograft reactive T-cells is indicative of an anti-graft immune response. i. contacting said sample of whole blood of said patient with said BKV-infected epithelial cells, and ii. determining T-cells comprised within said sample of whole blood that are activated by said BKV-infected epithelial cells, yielding a BKV-reactive T-cell number; iii. contacting said second portion of whole blood with said second portion of cultivated epithelial cells and determining T-cells comprised within said second portion of whole blood that are activated by said cultivated epithelial cells, yielding an allograft reactive T-cell number;