It is really really rare, and as far i know pretty much exclusively young women have that, i don't think there is a recorded case of a men with this kind of allergy, but it is possible to treat it with an immunotherapy, so the women later is able to get in contact with semen and therefore is able to get pregnant the conventional way.
Obviously it is also possible just treating the symptoms with steroids, cortisone to be precisely, but an ongoing with cortisone in my opinion is not such a great idea,