<DataTemplate x:Key ="UnderLineTemplate">
<TextBlock Text="{Binding}" TextDecorations="UnderLine"></TextBlock>
</DataTemplate>
CheckBoxCellType checkbox = new CheckBoxCellType();
checkbox.Content = "Custom TextFormat";
checkbox.ContentTemplate = this.Resources["UnderLineTemplate"] as DataTemplate;
gcSpreadGrid1[0, 0].CellType = checkbox;
Dim checkbox As New CheckBoxCellType()
checkbox.Content = "Custom TextFormat"
checkbox.ContentTemplate = TryCast(Me.Resources("UnderLineTemplate"), DataTemplate)
gcSpreadGrid1(0, 0).CellType = checkbox