ADO.NET :: Creating Dynamic Expressions For Lambda IQueryable Expressions?

I have a ListBox that contains userNames which is inputted by a user during run time. This number of items in the ListBox is dependent on the user's input. These userNames will then be used in a Lambda expression like this:

var vHandleResult = vHandleResult.Where(a => a.UserName.Contains("userName"));

This works fine when there is only 1 user in the ListBox but doesn't produce the correct results when there are multiple items in the listBox. I tried manually creating the expression which should be written as this:

var vHandleResult = vHandleResult.Where(a => a.UserName.Contains("userName1") || a.UserName.Contains("userName2") || a.UserName.Contains("userName3") || a.UserName.Contains("userName4"));

I tried forming the "a.UserName.Contains("userName") expression as a string which is dependent on the number of the items (using foreach) and then just plug in the resulting string in the expression but it seems that it doesnt accept string as an expression.