How to export with ManyToManyField

For the ManyToManyField, how to export it with a specified field?
For example:
Model: order, item, and order_to_item(many to many)
I'm going to use **make_response_from_query_sets** to generate the excel:
`excel.make_response_from_query_sets(
        orders, column_names=['id', 'items__content'], file_type='xls', file_name="Order List"`

But I get noting for the 'items__content' column.