High-affinity IgG antibodies develop naturally in Ig-knockout rats carrying germline human IgH/Igκ/Igλ loci bearing the rat CH region

Mice transgenic for human Ig loci are an invaluable resource for the production of human Abs. However, such mice often do not yield human mAbs as effectively as conventional mice yield mouse mAbs. Suboptimal efficacy in delivery of human Abs might reflect imperfect interaction between the human membrane IgH chains and the mouse cellular signaling machinery. To obviate this problem, in this study we generated a humanized rat strain (OmniRat) carrying a chimeric human/rat IgH locus (comprising 22 human V(H)s, all human D and J(H) segments in natural configuration linked to the rat C(H) locus) together with fully human IgL loci (12 Vκs linked to Jκ-Cκ and 16 Vλs linked to Jλ-Cλ). The endogenous Ig loci were silenced using designer zinc finger nucleases. Breeding to homozygosity resulted in a novel transgenic rat line exclusively producing chimeric Abs with human idiotypes. B cell recovery was indistinguishable from wild-type animals, and human V(D)J transcripts were highly diverse. Following immunization, the OmniRat strain performed as efficiently as did normal rats in yielding high-affinity serum IgG. mAbs, comprising fully human variable regions with subnanomolar Ag affinity and carrying extensive somatic mutations, are readily obtainable, similarly to conventional mAbs from normal rats.

A Targeted Protein Degradation Cell-Based Screening for Nanobodies Selective toward the Cellular RHOB GTP-Bound Conformation

The selective downregulation of activated intracellular proteins is a key challenge in cell biology. RHO small GTPases switch between a guanosine diphosphate (GDP)-bound and a guanosine triphosphate (GTP)-bound state that drives downstream signaling. At present, no tool is available to study endogenous RHO-GTPinduced conformational changes in live cells. Here, we established a cell-based screen to selectively degrade RHOB-GTP using F-box-intracellular single-domain antibody fusion. We identified one intracellular antibody (intrabody) that shows selective targeting of endogenous RHOB-GTP mediated by interactions between the CDR3 loop of the domain antibody and the GTP-binding pocket of RHOB. Our results suggest that, while RHOB is highly regulated at the expression level, only the GTP-bound pool, but not its global expression, mediates RHOB functions in genomic instability and in cell invasion. The F-box/intrabody-targeted protein degradation represents a unique approach to knock down the active form of small GTPases or other proteins with multiple cellular activities.

Increased CXCR3+ T Cells Impairs Recruitment of T-Helper Type 17 Cells via Interferon γ and Interleukin 18 in the Small Intestine Mucosa During Treated HIV-1 Infection

The restoration of CD4+ T cells, especially T-helper type 17 (Th17) cells, remains incomplete in the gut mucosa of most human immunodeficiency virus type 1 (HIV-1)–infected individuals despite sustained antiretroviral therapy (ART). Herein, we report an increase in the absolute number of CXCR3+ T cells in the duodenal mucosa during ART. The frequencies of Th1 and CXCR3+ CD8+ T cells were increased and negatively correlated with CCL20 and CCL25 expression in the mucosa. In ex vivo analyses, we showed that interferon γ, the main cytokine produced by Th1 and effector CD8+ T cells, downregulates the expression of CCL20 and CCL25 by small intestine enterocytes, while it increases the expression of CXCL9/10/11, the ligands of CXCR3. Interleukin 18, a pro-Th1 cytokine produced by enterocytes, also contributes to the downregulation of CCL20 expression and increases interferon γ production by Th1 cells. This could perpetuate an amplification loop for CXCR3-driven Th1 and effector CD8+ T cells recruitment to the gut, while impairing Th17 cells homing through the CCR6-CCL20 axis in treated HIV-1–infected individuals.

Effects of BCL-2 over-expression on B cells in transgenic rats and rat hybridomas

The rat is an important biomedical experimental model that benefited from the recent development of new transgenic and knockout techniques. With the goal to optimize rat mAb production and to analyze the impact of Bcl-2 on B-cell development, we generated bcl-2 transgenic rats. Transgenic rats showed Bcl-2 over-expression in B cells, increased B cell numbers in lymphoid organs, elevated production of immunoglobulins (Igs) and prolonged B-cell survival in vitro. Transgenic rats remained healthy, reproduced normally and did not develop autoimmunity. Fusions with bcl-2 transgenic splenocytes did not result in increased hybridoma generation. A comparison of on- and off-rates of 39 mAbs generated with bcl-2 transgenic and wild-type animals revealed no significant differences. Over-expression of Bcl-2 in hybridomas did not change cell proliferation but resulted in increased Ig production. Bcl-2 transgenic rats will be a useful tool for the generation of rat mAbs, the analysis of B cells in different pathophysiological models, such as autoimmunity, cancer or organ transplantation, and the study of rat B-cell biology.