Immunex Corp.'s two recent clinical setbacks could leave it with a weak middle in its product pipeline. The company discontinued a Phase II/III trial of its Enbrel etanercept in patients with chronic heart failure and its Nuvance inhaled soluble interleukin-4 receptor missed its primary end point in two one-month Phase II trials in patients not using inhaled steroids (see BioCentury, March 26). With only two products besides