How can i type new text and save in autocomplete cell in gridview in c#.net

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C#

Dear all
i have a windows based application with a gridview and autocomplete event. now i want to add new text in autocomplete list which is not present in current item collection.
I can edit text in gridview cell but can not persist changes after lost focus.
please help.

here is my code

private void Form1_Load(object sender, EventArgs e)
{
    DataGridViewComboBoxColumn combo1 = new DataGridViewComboBoxColumn();
    combo1.HeaderText = "Country";
    combo1.Items.Add("Antarctica");
    combo1.Items.Add("Australia");
    combo1.Items.Add("Belgium");
    combo1.Items.Add("Belarus");
    combo1.Items.Add("Canada");
    combo1.Items.Add("Candy");
    combo1.Items.Add("Finland");
    combo1.Items.Add("Albania");
    combo1.Items.Add("India");
    combo1.Items.Add("Barbados");
    dataGridView1.Columns.Add(combo1);
}

private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
    if (e.Control is DataGridViewComboBoxEditingControl)
    {
        ((ComboBox)e.Control).DropDownStyle = ComboBoxStyle.DropDown;
        ((ComboBox)e.Control).AutoCompleteSource = AutoCompleteSource.ListItems;
        ((ComboBox)e.Control).AutoCompleteMode = System.Windows.Forms.AutoCompleteMode.SuggestAppend;
    }
}