Induction of HIV Neutralizing Antibody Lineages in Mice with Diverse Precursor Repertoires.

The design of immunogens that elicit broadly reactive neutralizing antibodies (bnAbs) has been a major obstacle to HIV-1 vaccine development. One approach to assess potential immunogens is to use mice expressing precursors of human bnAbs as vaccination models. The bnAbs of the VRC01-class derive from the IGHV1-2 immunoglobulin heavy chain and neutralize a wide spectrum of HIV-1 strains via targeting the CD4 binding site of the envelope glycoprotein gp120. We now describe a mouse vaccination model that allows a germline human IGHV1-2(∗)02 segment to undergo normal V(D)J recombination and, thereby, leads to the generation of peripheral B cells that express a highly diverse repertoire of VRC01-related receptors. When sequentially immunized with modified gp120 glycoproteins designed to engage VRC01 germline and intermediate antibodies, IGHV1-2(∗)02-rearranging mice, which also express a VRC01-antibody precursor light chain, can support the affinity maturation of VRC01 precursor antibodies into HIV-neutralizing antibody lineages.

An in vivo method for diversifying the functions of therapeutic antibodies.

V(D)J recombination generates mature B cells that express huge repertoires of primary antibodies as diverse immunoglobulin (Ig) heavy chain (IgH) and light chain (IgL) of their B cell antigen receptors (BCRs). Cognate antigen binding to BCR variable region domains activates B cells into the germinal center (GC) reaction in which somatic hypermutation (SHM) modifies primary variable region-encoding sequences, with subsequent selection for mutations that improve antigen-binding affinity, ultimately leading to antibody affinity maturation. Based on these principles, we developed a humanized mouse model approach to diversify an anti-PD1 therapeutic antibody and allow isolation of variants with novel properties. In this approach, component Ig gene segments of the anti-PD1 antibody underwent de novo V(D)J recombination to diversify the anti-PD1 antibody in the primary antibody repertoire in the mouse models. Immunization of these mouse models further modified the anti-PD1 antibodies through SHM. Known anti-PD1 antibodies block interaction of PD1 with its ligands to alleviate PD1-mediated T cell suppression, thereby boosting antitumor T cell responses. By diversifying one such anti-PD1 antibody, we derived many anti-PD1 antibodies, including anti-PD1 antibodies with the opposite activity of enhancing PD1/ligand interaction. Such antibodies theoretically might suppress deleterious T cell activities in autoimmune diseases. The approach we describe should be generally applicable for diversifying other therapeutic antibodies.

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

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.

Improving Delivery Behaviors During Exposure for Pediatric OCD: A Multiple Baseline Training Trial With Community Therapists.

This study tested whether a new training tool, the Exposure Guide (EG), improved in-session therapist behaviors (i.e., indicators of quality) that have been associated with youth outcomes in prior clinical trials of exposure therapy. Six therapists at a community mental health agency (CMHA) provided exposure therapy for 8 youth with obsessive-compulsive disorder (OCD). Using a nonconcurrent multiple baseline design with random assignment to baseline lengths of 6 to 16 weeks, therapists received gold-standard exposure therapy training with weekly consultation (baseline phase) followed by addition of EG training and feedback (intervention phase). The primary outcome was therapist behavior during in-session exposures, observed weekly using a validated coding system. Therapist behavior was evaluated in relation to a priori benchmarks derived from clinical trials. Additional outcomes included training feasibility/acceptability, therapist response to case vignettes and beliefs about exposure, and independent evaluator-rated clinical outcomes. Three therapists reached behavior benchmarks only during the EG (intervention) phase. Two therapists met benchmarks during the baseline phase; one of these subsequently moved away from benchmarks but met them again after starting the EG phase. Across all therapists, the percentage of weeks meeting benchmarks was significantly higher during the EG phase (86.4%) vs. the baseline phase (53.2%). Youth participants experienced significant improvement in OCD symptoms and global illness severity from pre- to posttreatment. Results provide initial evidence that adding the EG to gold-standard training can change in-session therapist behaviors in a CMHA setting.