A fusion protein for use in the treatment of HvG disease in a patient having received a transplant, for use in suppressing the host's immune response directed against the transplant. The fusion protein is adapted for use in suppressing the immune rejection of a transplant which contains or expresses HLA-A*02 or SLA-01*0401 in a recipient patient who is negative for HLA-A*02 or SLA-01*0401, i.e. the patient prior to transplantation does not express HLA-A*02 or SLA-01*0401. The fusion protein is a chimeric antigen receptor (CAR), which upon expression in regulatory T-cells (Treg) causes a specific suppressor activity of the regulatory T-cells in the presence of HLA-A*02 or SLA-01*0401.