Vaccine‐induced SARS‐CoV‐2 antibody responses are attenuated in solid organ transplant recipients (SOTRs) and breakthrough infections are more common. Additional SARS‐CoV‐2 vaccine doses increase anti‐spike IgG in some SOTRs, but it is uncertain whether neutralization of variants of concern (VOCs) is enhanced. We tested 47 SOTRs for clinical and research anti‐spike IgG, pseudoneutralization (ACE2 blocking), and live‐virus neutralization (nAb) against VOCs before and after a third SARS‐CoV‐2 vaccine dose (70% mRNA, 30% Ad26.COV2.S) with comparison to 15 healthy controls after two mRNA vaccine doses. We used correlation analysis to compare anti‐spike IgG assays and focused on thresholds associated with neutralization. A third SARS‐CoV‐2 vaccine dose increased median total anti‐spike (1.6‐fold), pseudoneutralization against VOCs (2.5‐fold vs. Delta), and neutralizing antibodies (1.4‐fold against Delta). However, neutralization activity was significantly lower than healthy controls (p < .001); 32% of SOTRs had zero detectable nAb against Delta after third vaccination compared to 100% for controls. Correlation with nAb was seen at anti‐spike IgG >4 Log10(AU/ml) on the Euroimmun ELISA and >4 Log10(AU/ml) on the MSD research assay. These findings highlight benefits of a third vaccine dose for some SOTRs and the need for alternative strategies to improve protection in a significant subset of this population.

Immunocompromised populations are at high risk for severe COVID-19. Vaccine-induced SARS-CoV-2 antibody responses are attenuated in solid organ transplant recipients (SOTRs), and breakthrough infections are more common. Additional SARS-CoV-2 vaccine doses may increase anti-spike antibody titers in some SOTRs, but whether this results in enhanced neutralizing capability, especially versus novel variants of concern (VOCs) that exhibit immune escape and higher infectivity (e.g., the Delta variant), is unclear. Here, we report that a third dose of a SARS-CoV-2 vaccine increases anti-SARS-CoV-2 spike and RBD IgG levels as well as plasma neutralizing capability versus VOCs, including Delta, in some SOTRs. However, anti-spike IgG and neutralizing capability remained significantly reduced compared to fully vaccinated healthy controls. These findings highlight the need for continued study of strategies to improve protection from COVID-19 in immunosuppressed populations as more SARS-CoV-2 VOCs emerge.

The lateral neural plate border (NPB), the neural part of the vertebrate neural border, is composed of central nervous system (CNS) progenitors and peripheral nervous system (PNS) progenitors. In invertebrates, PNS progenitors are also juxtaposed to the lateral boundary of the CNS. Whether there are conserved molecular mechanisms determining vertebrate and invertebrate lateral neural borders remains unclear. Using single-cell-resolution gene-expression profiling and genetic analysis, we present evidence that orthologs of the NPB specification module specify the invertebrate lateral neural border, which is composed of CNS and PNS progenitors. First, like in vertebrates, the conserved neuroectoderm lateral border specifier Msx/vab-15 specifies lateral neuroblasts in Caenorhabditis elegans. Second, orthologs of the vertebrate NPB specification module (Msx/vab-15, Pax3/7/pax-3, and Zic/ref-2) are significantly enriched in worm lateral neuroblasts. In addition, like in other bilaterians, the expression domain of Msx/vab-15 is more lateral than those of Pax3/7/pax-3 and Zic/ref-2 in C. elegans. Third, we show that Msx/vab-15 regulates the development of mechanosensory neurons derived from lateral neural progenitors in multiple invertebrate species, including C. elegans, Drosophila melanogaster, and Ciona intestinalis. We also identify a novel lateral neural border specifier, ZNF703/tlp-1, which functions synergistically with Msx/vab-15 in both C. elegans and Xenopus laevis. These data suggest a common origin of the molecular mechanism specifying lateral neural borders across bilaterians.C. elegans | neural plate border | neural border | Msx/vab-15 | ZNF703/tlp-1 T he vertebrate neural border is a transient embryonic domain located between the neural plate and nonneurogenic ectoderm from late gastrulation to early neurulation. The neural border is composed of the lateral neural plate border (NPB) and preplacode ectoderm (PPE) subdomains (1, 2). The NPB and PPE give rise to the neural crest and placode, respectively, both of which undergo epithelial-to-mesenchymal transition/delamination, migrate in prototypical paths, and give rise to the peripheral nervous system (PNS) and many other cell types (3, 4). However, the NPB and PPE also have many different features (5). For example, the PPE is confined to the anterior half of embryos and does not contribute to the central nervous system (CNS), whereas the NPB is the lateral border of the whole neural plate and consists not only of progenitors for the PNS but also those for the CNS in the dorsal neural tube. The juxtaposed localization of the CNS neuroectoderm and PNS progenitors also occurs in the trunk of invertebrate embryos such as nematodes, arthropods, annelids, and urochordates (6-9), reminiscent of vertebrate NPB. In Caenorhabditis elegans, lateral neuroblasts (P, Q, and V5 cells) are located between the embryonic CNS and skin from the birth of these cells (10). In addition, worm lateral neuroblasts possess several key cellular and developmental features of vertebra...