Studio has never been able to handle Alpha channels directly, with DS3 it meant using the Layer Image Editor (LIE) or build a custom shader with the ShaderMixer.

With DS4 you have the ShaderMixer for 3Delight but not with Iray, none of the MDL bricks give access to the Alpha channel, you have LIE as well, and an "Image Editor" built into the Surface tab that can force an Alpha to be used.