A radioimmunoconjugate composed of basiliximab, a chimeric, mouse-human monoclonal antibody directed against the alpha subunit of interleukin-2 receptor (IL-2R alpha, CD25 or Tac antigen), and labeled with yttrium y 90, with potential antineoplastic activity. The basiliximab moiety of yttrium Y 90 basiliximab selectively binds to IL-2R alpha expressed on the surface of activated T-lymphocytes, thereby preventing IL-2 binding and blocking the IL-2-mediated activation of lymphocytes. The yttrium y 90 moiety selectively delivers a cytotoxic dose of beta radiation to lymphocytes that express the IL-2 receptor. This may prevent T cell-mediated activation of the immune system against a certain transplant and may prevent transplant rejection.