Conditional antibody expression to avoid central B cell deletion in humanized HIV-1 vaccine mouse models

Abstract

HIV-1 vaccine development aims to elicit broadly neutralizing antibodies (bnAbs) against diverse viral strains. In some HIV-1–infected individuals, bnAbs evolved from precursor antibodies through affinity maturation. To induce bnAbs, a vaccine must mediate a similar antibody maturation process. One way to test a vaccine is to immunize mouse models that express human bnAb precursors and assess whether the vaccine can convert precursor antibodies into bnAbs. A major problem with such mouse models is that bnAb expression often hinders B cell development. Such developmental blocks may be attributed to the unusual properties of bnAb variable regions, such as poly-reactivity and long antigen-binding loops, which are usually under negative selection during primary B cell development. To address this problem, we devised a method to circumvent such B cell developmental blocks by expressing bnAbs conditionally in mature B cells. We validated this method by expressing the unmutated common ancestor (UCA) of the human VRC26 bnAb in transgenic mice. Constitutive expression of the VRC26UCA led to developmental arrest of B cell progenitors in bone marrow; poly-reactivity of the VRC26UCA and poor pairing of the VRC26UCA heavy chain with the mouse surrogate light chain may contribute to this phenotype. The conditional expression strategy bypassed the impediment to VRC26UCA B cell development, enabling the expression of VRC26UCA in mature B cells. This approach should be generally applicable for expressing other bnAbs that are under negative selection during B cell development.

Strategies for HIV-1 vaccines that induce broadly neutralizing antibodies

“…Mouse models are now being generated that mimic physiological conditions more closely, in which both V H and V L rearranging gene segments result in an immense diversity of humanized mouse BCR repertoires. Moreover, new models have been designed to circumvent B cell developmental blocks in the bone marrow by expressing bnAb precursors conditionally in mature B cells 237 .…”

In vivoaffinity maturation of murine B cells reprogrammed to express human antibodies

“…As mentioned, compared with these knock-in mice, B-cell engineering can be implemented more rapidly, accommodates variant libraries, and can be used in other species. In addition, unlike knock-in mice, the engineered B cells bypass central tolerance, perhaps enabling expression of antibodies that would be clonally deleted in transgenic mouse models 52–55 .…”

A Germline-Targeting Chimpanzee SIV Envelope Glycoprotein Elicits a New Class of V2-Apex Directed Cross-Neutralizing Antibodies

“…Moreover, the RUA of CH01, like that of PG9 or PG16, was inferred from very few lineage members and thus represents only an approximation of the unmutated common ancestor ( 35 , 69 ). Given these limitations, it seems clear that the germ line-targeting potential of the CAM13K Env and future derivatives will have to be confirmed in additional mouse models, such as long human CDR3 rearranging mice, as well as ultimately in outbred animals and humans ( 71 to 73 ).…”