A client has just completed radiation and chemotherapy for head and neck cancer. Blood work shows that the client is severely anemic in addition to being severely deficient in platelets and white blood cells. The client is given massive intravenous doses of cephalosporin to treat an infection. The erythrocyte count continues to drop. Additional labs show erythroid hyperplasia in the blood smears and bone marrow biopsy. The client also has developed splenomegaly and jaundice. What is the most likely cause of the continued problem with the client's erythrocytes?