Keep the backslashs in propertyregex

I'm trying to replace a directory path string in a XML file using ANT with the value stored in variable ${param_value}.

In my example ${param_value} contains c:\mypath\mydir

In order to replace as wished, I use propertyregex.

The issue is that the regex replace value is c:mypathmydir
I don't understand why "replace" removes all backslashes.

When I echo to check the value of my variable before regex, it looks like:

<echo message="param_value out=${param_value}"/>

This echo returns c:\mypath\mydir

${param_token} is xml token (output)

<propertyregex      property="param_temp"
                    input="${result}"
                    regexp="(&lt;${param_token})&gt;(.*|\\)*&lt;(/${param_token}&gt;)"
                    replace="\1&gt;${param_value}&lt;\3"
                    casesensitive="false" 
                    defaultvalue="NotFound"/>

Thank you for your help.