Latha Kallur Siddaramaiah

Summary: Accurate spectral unmixing is a critical step for flow cytometry data analysis and requires a single stain control for every fluorescent parameter used in an experiment. Currently, compensation particles are often used for making single stain controls when a target protein is of low abundance or a cell type is of low frequency. However, compensation particles introduce incongruencies in emission spectra compared to cells resulting in spectral unmixing or compensation errors. To enable the use of cells regardless of the abundance of target proteins or immune cell type, we generated a bispecific antibody that links a human anti-CD45 and mouse anti-IgG variable region. We refer to this new bispecific tool as CaptureBody (CB) and highlight the benefits of its final nanobody-based design. We provide all sequences and methods necessary for the in-house expression of a CaptureBody to disseminate their use for spectral flow cytometry experiments.

Background/Objectives: Despite progress in antiretroviral therapy, HIV remains a major global health challenge with over one million new infections annually. An effective vaccine is urgently needed. Germline-targeting immunogens show promise in initiating broadly neutralizing antibody (bNAb) precursors. This study developed a scalable, cGMP-compliant process to manufacture the HIV vaccine booster immunogen HxB2.WT.Core-C4b, a nanoparticle designed to direct bNAb precursor maturation after priming. Methods: A CHO cell platform was established through single-cell cloning from a high-producing stable pool. Upstream and downstream processes were optimized for scalability and yield. Three scales were tested 10 L, 40 L, and 400 L. Key parameters (pH, temperature, feeding, metabolite profiles) were systematically refined. Analytical characterization included glycosylation profiling, electron microscopy, and antigenicity testing. Viral clearance was evaluated per ICH Q5A guidelines. Results: Optimization ensured consistent yields above 130 mg/L, with titers up to 250 mg/L. The selected clone (4E22) demonstrated strong growth, viability, and reproducibility. Glycan occupancy at 18 N-linked sites, including bNAb epitopes (N276, N332), was stable across scales. Over 70% of self-assembling nanoparticle were fully assembled at the GMP level. Antigenicity and purity met cGMP release criteria. Viral clearance achieved >13-log reduction for enveloped and >7-log for non-enveloped viruses. Conclusions: This work establishes a robust, scalable platform for HIV nanoparticle immunogens. Consistent quality and yield across scales support clinical development of HxB2.WT.Core-C4b and provide a model for other glycosylated nanoparticle vaccines. The immunogen is being evaluated in clinical study HVTN 320 (NCT06796686), enabling early testing of next-generation vaccines designed to elicit broadly neutralizing antibodies.

Stabilized trimers preserving the native-like HIV envelope structure may be key components of a preventive HIV vaccine regimen to induce broadly neutralizing antibodies (bnAbs). We evaluated trimeric BG505 SOSIP.664 gp140 formulated with a novel TLR7/8 signaling adjuvant, 3M-052-AF/Alum, for safety, adjuvant dose-finding, and immunogenicity in a first-in-healthy adult (n = 17), randomized, and placebo-controlled trial (HVTN 137A). The vaccine regimen appeared safe. Robust, trimer-specific antibody, and B cell and CD4+ T cell responses emerged after vaccination. Five vaccinees developed serum autologous tier 2 nAbs (ID50 titer, 1:28-1:8647) after two to three doses targeting C3/V5 and/or V1/V2/V3 Env regions by electron microscopy and mutated pseudovirus-based neutralization analyses. Trimer-specific, B cell–derived monoclonal antibody activities confirmed these results and showed weak heterologous neutralization in the strongest responder. Our findings demonstrate the clinical utility of the 3M-052-AF/Alum adjuvant and support further improvements of trimer-based Env immunogens to focus responses on multiple broad nAb epitopes.