Change displayed text in XAML Combobox multi selection

I have the following code to allow users to select multiple items from a combobox. However when they click one item, it makes this the displayed text when combobox closes. Can I change the displayed text to something that isnt just the item selected. For example if the users select items A,B and D, I want the text part of the combobox to show "A, B, D"

<ComboBox ItemsSource="{Binding ListOfItems}">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <CheckBox IsChecked="{Binding IsChecked, Mode=TwoWay}" Width="20" />
                        <TextBlock Text="{Binding DisplayName}" Width="110" />
                    </StackPanel>
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>

Thanks