Biology subjects

Vykunta, V.

Publications and source records attributed to Vykunta, V..

3 recordsLinked to original sources

bioRxiv2023

Molecular basis for potent B cell responses to antigen displayed on particles of viral size

Although it has long been appreciated that multivalent antigens - and particularly viral epitope display - produce extremely rapid, robust, and T-independent humoral immune responses, the biochemical basis for such potency has been incompletely understood. Here we take advantage of a set of neutral liposomes of viral size that are engineered to display affinity mutants of the model antigen (Ag) hen egg lysozyme at precisely varied density. We show that particulate Ag display by liposomes induces highly potent B cell responses that are dose-and density-dependent but affinity-independent. Titrating dose of particulate, but not soluble, Ag reveals bimodal Erk phosphorylation and cytosolic calcium increases. Particulate Ag induces signal amplification downstream of the B cell receptor (BCR) by selectively evading LYN-dependent inhibitory pathways, but in vitro potency is independent of CD19. Importantly, Ag display on viral-sized particles signals independently of MYD88 and IRAK1/4, but activates NF-{kappa}B robustly in a manner that mimics T cell help. Together, such biased signaling by particulate Ag promotes MYC expression and reduces the threshold required for B cell proliferation relative to soluble Ag. These findings uncover a molecular basis for highly sensitive B cell response to viral Ag display and remarkable potency of virus-like particle vaccines that is not merely accounted for by avidity and BCR cross-linking, and is independent of the contribution of B cell nucleic acid-sensing machinery.

immunology↗

bioRxiv2021

Hybrid ssDNA repair templates enable high yield genome engineering in primary cells for disease modeling and cell therapy manufacturing

CRISPR-Cas9 offers unprecedented opportunities to modify genome sequences in primary human cells to study disease variants and reprogram cell functions for next-generation cellular therapies. CRISPR has several potential advantages over widely used retroviral vectors including: 1) site-specific transgene insertion via homology directed repair (HDR), and 2) reductions in the cost and complexity of genome modification. Despite rapid progress with ex vivo CRISPR genome engineering, many novel research and clinical applications would be enabled by methods to further improve knock-in efficiency and the absolute yield of live knock-in cells, especially with large HDR templates (HDRT). We recently reported that Cas9 target sequences (CTS) could be introduced into double-stranded DNA (dsDNA) HDRTs to improve knock-in, but yields and efficiencies were limited by toxicity at high HDRT concentrations. Here we developed a novel system that takes advantage of lower toxicity with single-stranded DNA (ssDNA). We designed hybrid ssDNA HDRTs that incorporate CTS sites and were able to boost knock-in percentages by >5-fold and live cell yields by >7-fold relative to dsDNA HDRTs with CTS. Knock-in efficiency and yield with ssCTS HDRTs were increased further with small molecule inhibitor combinations to improve HDR. We demonstrate application of these methods across a variety of target loci, knock-in constructs, and primary human cell types to reach ultra-high HDR efficiencies (>80-90%) which we use for pathogenic gene variant modeling and universal gene replacement strategies for IL2RA and CTLA4 mutations associated with mendelian immune disorders. Finally, we develop a GMP-compatible method for fully non-viral CAR-T cell manufacturing, demonstrating knock-in efficiencies of 46-62% and generating yields of >1.5 x 109 CAR+ T cells, well above current doses for adoptive cellular therapies. Taken together, we present a comprehensive non-viral approach to model disease associated mutations and re-write targeted genome sequences to program immune cell therapies at a scale compatible with future clinical application.

synthetic biology↗

bioRxiv2020

A negative feedback loop mediated by the NR4A family of nuclear hormone receptors restrains expansion of B cells that receive signal one in the absence of signal two

Ag stimulation (signal 1) triggers B cell activation and proliferation, and primes B cells to recruit, engage, and respond to T cell help (signal 2). However, failure to receive signal 2 within a defined window of time results in an abortive round of proliferation, followed by anergy or apoptosis. Although the molecular basis of T cell help has been extensively dissected, the mechanisms that restrain Ag-stimulated B cells, and enforce dependence upon co-stimulation, are incompletely understood. Nr4a1-3 encode a small family of orphan nuclear receptors that are rapidly induced by B cell receptor (BCR) stimulation, yet little is known about their function in humoral immune responses. Here we use germline and conditional loss-of-function mouse models to show that Nr4a1 and Nr4a3 play partially redundant roles to restrain both the survival and proliferation of B cells that receive signal 1 in the absence of co-stimulatory signals, and do so in part by repressing expression of BATF and consequently c-MYC. Correspondingly, Ab responses to TI-2 immunogens are enhanced in the absence of Nr4a1, but are unaltered in response to immunogens that incorporate co-stimulatory signals. Unexpectedly, we also identify a role for the NR4A family in restraining B cell access to T cell help by repressing expression of the T cell chemokines CCL3/4, as well as CD86 and ICAM1, and show that this is relevant under conditions of competition for limiting T cell help. Our studies collectively reveal a novel negative feedback loop mediated by the NR4A family that increases B cell dependence upon T cell help and restrains strongly Ag-activated B cell clones from monopolizing limiting amounts of T cell help. We speculate that this imposes B cell tolerance and dampens immunodominance to facilitate preservation of clonal diversity during an immune response.

immunology↗