Enhanced germinal center reaction by targeting vaccine antigen to major histocompatibility complex class II molecules

Vaccine proteins and model system. a Targeted vaccine proteins have a scFvαI-Ed targeting unit (specific for I-Ed) linked to the scFv315 antigen via a human CH3 dimerization domain. In non-targeted vaccine proteins, the scFvαI-Ed has been exchanged with a scFvαNIP specific for the hapten NIP. b Purified vaccine proteins analyzed by SDS-PAGE, either with or without β-mercaptoethanol. The displayed bands are from the same gel and were processed in parallel. c Targeted vaccine proteins bind to I-Ed MHCII molecules on APC, followed by processing and presentation. The scFv315 antigenic unit contains an idiotypic(Id)-peptide in the CDR3 loop of its Vλ2 region; this Id-peptide is presented on MHCII molecules (I-Ed) to Id-specific CD4+ T cells from TCR-transgenic mice. In addition, the pId315:I-Ed complex can be physically recognized by a T-cell receptor mimetic (TCRm) in a scFv format. d Model system for testing vaccine proteins in T–B-cell collaboration experiments. B cells from anti-Id BCR knock-in (anti-IdDKI) mice have V regions from an anti-Id mAb (Ab2-1.4) that binds to the antigen binding site of scFv315. Anti-Id B cells can therefore bind the vaccine protein in two ways: (i) the scFvαI-Ed part of targeted vaccine protein, or (ii) the scFv315 antigenic part common to targeted and non-targeted vaccine proteins. Presentation of the Id-peptide on I-Ed can be detected either by Id-specific CD4+ T cells from TCR-transgenic mice, or by TCRm. e Binding of purified vaccine proteins to spleen B cells (CD19+), macrophages (F4/80+ CD64+), DCs (Lin？CD11chi), and T cells (CD3+) from BALB/c mice, and to anti-Id B cells of anti-IdDKI mic