Swap first two letters of every word in string

I have a string:

Hello, How Are You.

I want this output:

eHllo, oHw rAe oYu.

It doesn't matter whether there are any special characters, I just want to reverse the first two letters in every word.

You can use preg_replace_callback like as

$str = "Hello, How Are You.";
echo preg_replace_callback("/([a-z]+)/i",function($m){
    return implode(array_map('strrev',str_split($m[0],2)));
},$str);

Output:

eHllo, oHw rAe oYu.

Demo