Alt: Pre-Clinical Models with Diverse Human Antibody Repertoires
The goal of this project is to continue efforts to develop pre-clinical models to advance HIV immunogen design. These models can be used in experiments to select candidate immunogens capable of activation and expansion of desired B cell lineages. To circumvent potential shortcomings of existing mouse vaccine models, the Alt lab developed a new type of mouse vaccine model for the potent VRC01 class of HIV-1 bnAbs, based on a strategy that allows the assembly of both the precursor human immunoglobulin heavy and light chain variable region exons for this class of bnAb to be developmentally assembled via V(D)J recombination and to dominate the B cell repertoire of the resultant mice. The team further introduced ectopic human TdT expression into this mouse model to increase the diversity of mouse Ig light chain variable regions and make them more human-like. In this "complete" VRC01-rearranging model, most individual B cells express one of a multitude of different variations of the potential VRC01 precursor, providing a much more human-like precursor VRC01 repertoire.
To address the caveats of the conventional knock-in mouse model, a strategy was designed to conditionally express bnAb intermediates in germinal center (GC) B cells in mice. The mouse model can be used to devise boost immunization conditions that can effectively expand and mature bnAb intermediates in GC reactions, move the bnAb intermediates into the memory compartment and, in the next round of immunization, recall the memory B cells (MBCs) back into GC reactions for additional rounds of maturation. With respect to the VRC01 intermediate antibody in the current GC conditional system, the objective is to find immunization conditions to mature the antibody further to overcome the hindrance of N276 glycan to broaden and potentiate its neutralization activities. The success of these studies hinges on the adoptive transfer system. If the GC conditional expression system and the boost immunization strategies prove effective, the techniques will be generally applicable to vaccine development for different bnAbs and pathogens.
Given the lack of physiologically relevant mouse models for bnAbs with long CDR H3s, this funding will support the generation of mouse models with diverse repertoires of long CDR H3s that are comparable to those in human bnAbs. The long CDR H3s will be further combined with human VH segments that are commonly utilized in bnAbs that target V2 apex and V3 glycan epitopes. These types of mouse models should provide diverse repertoires for V2 apex and V3 glycan bnAbs. In addition, the proposed mouse models will contain complex repertoires of mouse antibodies. Immunization of such mouse models can test the ability of an immunogen to select for rare bnAb precursors and mature them toward bnAbs.
The proposed models will facilitate the development of sequential immunization schemes. Given the complex and unprecedented nature of such immunization protocols, pre-clinical development in mouse models should greatly aid in narrowing down the most promising vaccination strategies for clinical trials. In conjunction with the VRC01 mouse model, these mouse models will support a multipronged approach for HIV-1 vaccine development.
The grant is led by Frederick W. Alt at the Boston Children’s Hospital.
1. Immunization studies of VRC01 mouse models with diverse humanized heavy chain and light chain repertoires.
2. Testing boost immunization strategies in a germinal center conditional expression mouse model.
3. Generating mouse models with diverse precursor repertoires for V2 apex and V3 glycan bnAbs.