Determination of mitogen response (G0/G1) and radiosensitivity (G2/GF) via bivariate flow cytometry. Circles: radiation resistant cases (controls); Triangles: radiosensitive cases (ataxia telangiectasia, AT). Squares: patient blood samples analyzed at different time points prior to (1) and after HSCT (2–7). BMT was performed in May 2002. Immunosuppression following BMT caused lack of mitogen response (time point 2).