This idea is inspired by Darko Savic's contribution and expanded based on the knowledge described here.
The first problem is definitely how to find the cells responsible for the allergies. If cells (B cells) can be found by the proposed trojan-horse system (it is important to make the procedure extremely safe for the patient), we could pull them down by antibodies mounted on silica beads. The suspension of cells could be filtered so that only these cells are extracted. These cells could then be eliminated.
As described in this contribution the second problem of eliminating cells is already partially solved. Since we would extract only the B cells expressing specific antigens, we could condition them with immunochemotherapy or simply not transplant them back into the patient. This idea is just a proposal that needs to be further examined.