To Bold A Part Of The Cell Text

I am creating a sheet with the cell information coming from different cells. I want to bold and/or underline a part of the cell to add clarity.

For e.g.
Cell A1 = "Trans X" (Name of the transaction);
Cell B1 = "System Y" (System where the transaction exists)
Cell C1 = "Type Z" (Type of transaction)

I want to create a cell which has
Newsheet.Cell (x,y) =
"Name: Trans X
System: System Y
Type: Type Z"

I created the String by reading and concatenating the values, but I am not sure how to add the formatting to a part of the string.