Editing Code: Selecting multiple items in a cell via data validation

The below code allows me to select multiple items in a cell and separates these items by a comma: However, it only allows me this option for data validation in column 3 ("C"). I am needing assistance on how to allow this code the same validation rule for, let's say columsn 3, 7, and 8? I've also attached the excel document to better illustrate what I would like to do.


Private Sub Worksheet_Change(ByVal Target As Range)
Dim rngDV As Range
Dim oldVal As String
Dim newVal As String
If Target.Count > 1 Then GoTo exitHandler

On Error Resume Next
Set rngDV = Cells.SpecialCells(xlCellTypeAllValidation)
On Error GoTo exitHandler

If rngDV Is Nothing Then GoTo exitHandler

If Intersect(Target, rngDV) Is Nothing Then
'do nothing
Else
Application.EnableEvents = False
newVal = Target.Value
Application.Undo
oldVal = Target.Value
Target.Value = newVal
If Target.Column = 3 Then
If oldVal = "" Then
'do nothing
Else
If newVal = "" Then
'do nothing
Else
Target.Value = oldVal _
& ", " & newVal
End If
End If
End If
End If

exitHandler:
Application.EnableEvents = True
End Sub