"... Immunizing yourself from poison ivy in this way is not a far-fetched idea. Your doctor, at your request, will immunize you by injecting you with a series of poison ivy extract. ..."
After a little searching I found an article
at this web page that is almost like the one I read about the immunization from. The above quote is from the web page. There is a 'Publisher’s Notice' (disclaimer) and 'References' at the end of the page.
Edit: There is also a couple of treatments in the lower half of the article.
Excomantia
P.S. I've never done it myself, just read it.