You can add a Style to your window which targets DataCell. In your style, you can add the Setter for the ReadOnly property. You can also add Binding to style which would help things. You can add a converter in case you have certain criteria that your ReadOnly should follow. Here is a simple piece of XAML to get you started:
<Binding Path="Column5" />
Moreover, you can refer to a Blog post that Michel wrote last year which shows how to style cells based on other values. You can click on this link for a further explanation. Sample applications do come with the blog post just in case you want to see it in action.
Developer in Technical Support
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