Excluding sub-categories from WP_Query

I have a dozen or so different category templates for the different sections of my site, and am trying to exclude a few categories from one of them.

Here’s my loop:

<?php $my_query = new WP_Query($query_string . "&cat=107,108,109,110&posts_per_page=16");
		while ($my_query->have_posts()) : $my_query->the_post();
		$wp_query->in_the_loop = true;
		if ( $post->ID == $do_not_duplicate ) continue;
		update_post_caches($posts);
		$do_not_duplicate = $post->ID; ?>

I’ve tried everything I could find/think of to either only include the four categories you see in the loop above (cat=107,108….) or exclude the others (cat=-112,-113…). Neither method seems to do anything, and I’m now thinking it’s because all the categories are sub-categories of a main one, 105 in my case.

Can you not exclude or only include sub-categories in a wp_query? Or is there another way to go about this?

Thanks guys.