Recombinant antibodies are increasingly used for efficient delivery of T cell epitopes to antigenpresenting cells (APCs), both for vaccination purposes and for immune modulation. We have previously shown that recombinant antibodies can accommodate single T cell epitopes inserted into loops between b-strands in constant (C) domains. Such recombinant antibodies have in addition been equipped with variable regions that target APCs for increased delivery of C region T cell epitopes. We here show

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... t loop 6 (loop FG) in C H 1 of human g3 can be exchanged with (i) long T cell epitopes up to 37 amino acids, (ii) epitopes with complex secondary structure such as gluten epitopes with a type II polyproline helical confirmation and (iii) two tandemly linked T cell epitopes. T cell responses increased with T cell epitope elongation, presumably due to a positive influence of flanking residues. Recombinant antibodies targeted to either CD14 on monocytes or HLA-DP on monocytes and dendritic cells gave similar results and were 2-4 logs more efficient at stimulating human T cells than were non-targeted controls. Thus, single loops in C regions of recombinant antibodies seem versatile and may be used for delivery of lengthy, complex and multiple T cell epitopes to human APCs.