Faulkes, S. | bioRxiv Science

bioRxiv2025

Reinke crystals are immunoreactive for purine-synthesizing metabolic enzymes

Reinke crystals are a defining histological feature of human adult Leydig cells, the testosterone producing cells of the testis. These structures are present in the cytoplasm and the nucleus and display quantitative alterations in a variety of physiological and pathological contexts. The functional significance and protein composition of Reinke crystals have remained elusive for over a century. Here, we demonstrate that Reinke crystals are intensely immunoreactive for inosine monophosphate dehydrogenase (IMPDH), and phosphoribosyl pyrophosphate synthetase (PRPS), two key rate-limiting enzymes in the de novo synthesis of purine nucleotides. IMPDH and PRPS are two of several metabolic enzymes that are capable of forming mesoscale filamentous aggregates as a mechanism to regulate enzyme activity. IMPDH is also able to form crystals in cellulo. Our observations link Reinke crystal formation to purine nucleotide metabolism in Leydig cells. We discuss how this novel finding may relate to the unique dependence of Leydig cells on guanyl-based purine nucleotides for testosterone synthesis. The results of this study may have important implications for understanding metabolic contributions to male reproductive disorders as well as offering a novel diagnostic and theranostic tool applicable to Leydig cell neoplasms.

pathology↗

bioRxiv2024

Broadly Reactive Anti-VHH Antibodies for Characterizing, Blocking, or Activating Nanobody-Based CAR-T Cells

Production of chimeric antigen receptor T cell (CAR-T) therapies is dependent on the use of antibody reagents to label, isolate, and/or expand T cell products. We sought to create antibody-based tools that directly target the variable domain of heavy-chain only antibodies (VHH or nanobody) used in some CAR molecules. Two murine antibodies were identified which bind to distinct epitopes in the conserved framework regions of llama-derived VHHs, and not to human VH domains. We produced a high-quality dual-clonal anti-VHH antibody product which reacts with over 98% of VHH proteins, regardless of their antigenic specificity. Anti-VHH binding did not disrupt VHH/antigen interaction, and thus could be used for secondary labeling to assess cellular or tissue reactivity of VHH molecules. Despite not interfering with antigen binding, anti-VHH antibodies potently inhibited VHH-CAR function, blocking CAR-T activation and cytolytic killing of target cells. When immobilized, anti-VHH antibodies could also be applied for activation and expansion of VHH CAR-T cells, inducing 730-fold mean expansion, >94% CAR purity, with retained CD8/CD4 heterogeneity. Functionally, anti-VHH antibody-expanded CAR-T cells maintained strong antigen specific activity without functional exhaustion. Overall, these data identify a useful new tool for understanding and manipulating VHH-based CAR-T cells. Funding SourceThis work was funded by the National Research Council Canada Disruptive Technology Solutions Cell and Gene Therapy challenge program, and BioCanRx Declaration of interestsThe anti-VHH antibodies reported here are the subject of a provisional patent application by the National Research Council of Canada

immunology↗