Infection- and vaccine-induced antibody binding and neutralization of the B.1.351 SARS-CoV-2 variant.

The emergence of SARS-CoV-2 variants with mutations in the spike protein is raising concerns about the efficacy of infection- or vaccine-induced antibodies. We compared antibody binding and live virus neutralization of sera from naturally infected and Moderna-vaccinated individuals against two SARS-CoV-2 variants: B.1 containing the spike mutation D614G and the emerging B.1.351 variant containing additional spike mutations and deletions. Sera from acutely infected and convalescent COVID-19 patients exhibited a 3-fold reduction in binding antibody titers to the B.1.351 variant receptor-binding domain of the spike protein and a 3.5-fold reduction in neutralizing antibody titers against SARS-CoV-2 B.1.351 variant compared to the B.1 variant. Similar results were seen with sera from Moderna-vaccinated individuals. Despite reduced antibody titers against the B.1.351 variant, sera from infected and vaccinated individuals containing polyclonal antibodies to the spike protein could still neutralize SARS-CoV-2 B.1.351, suggesting that protective humoral immunity may be retained against this variant.

Reduced binding and neutralization of infection- and vaccine-induced antibodies to the B.1.351 (South African) SARS-CoV-2 variant.

The emergence of SARS-CoV-2 variants with mutations in the spike protein is raising concerns about the efficacy of infection- or vaccine-induced antibodies to neutralize these variants. We compared antibody binding and live virus neutralization of sera from naturally infected and spike mRNA vaccinated individuals against a circulating SARS-CoV-2 B.1 variant and the emerging B.1.351 variant. In acutely-infected (5-19 days post-symptom onset), convalescent COVID-19 individuals (through 8 months post-symptom onset) and mRNA-1273 vaccinated individuals (day 14 post-second dose), we observed an average 4.3-fold reduction in antibody titers to the B.1.351-derived receptor binding domain of the spike protein and an average 3.5-fold reduction in neutralizing antibody titers to the SARS-CoV-2 B.1.351 variant as compared to the B.1 variant (spike D614G). However, most acute and convalescent sera from infected and all vaccinated individuals neutralize the SARS-CoV-2 B.1.351 variant, suggesting that protective immunity is retained against COVID-19.

Presurgical assessment of cognitive function in pediatric brain tumor patients: feasibility and initial findings.

BACKGROUND: Establishing a presurgical baseline of neurocognitive functioning for pediatric brain tumor patients is a high priority to identify level of functioning prior to medical interventions. However, few studies have obtained adequate samples of presurgery assessments. METHODS: This study examines the feasibility of completing tests to assess pre-surgical neurocognitive functioning in 59 identified pediatric brain tumor patients. RESULTS: Eighty-five percent of patients (n = 50) were referred by the neurosurgery team before surgery and 83% of patients (n = 49) enrolled in the study. A full battery, including both performance-based and parent-report measures of neurocognitive function, was completed for 54% (n = 32) of patients. Rates of completion for either parent-report or performance-based measures were 68% (n = 40) and 69% (n = 41), respectively. While the performance-based assessment fell within the average range (M = 95.4, SD = 14.7, 95% CI, 90.7-100.0), 32% of participants had scores one or more standard deviations below the mean, or twice the expected rate. Parent-reports indicated higher level of concern than the general population (M = 55.4, SD = 11.3, 95% CI, 51.8-59.0) and found that 35% fell one or more standard deviations above the mean, or more than twice the expected rate. CONCLUSIONS: Results suggest it is feasible to conduct pre-surgical assessments with a portion of pediatric brain tumor patients upon diagnosis and these results compare favorably with prior research. However, nearly half of identified patients did not receive a full test battery. Identifying barriers to enrollment and participation in research are discussed as well as recommendations for future research.

Borrelia burgdorferi RevA Significantly Affects Pathogenicity and Host Response in the Mouse Model of Lyme Disease.

The Lyme disease spirochete, Borrelia burgdorferi, expresses RevA and numerous outer surface lipoproteins during mammalian infection. As an adhesin that promotes bacterial interaction with fibronectin, RevA is poised to interact with the extracellular matrix of the host. To further define the role(s) of RevA during mammalian infection, we created a mutant that is unable to produce RevA. The mutant was still infectious to mice, although it was significantly less well able to infect cardiac tissues. Complementation of the mutant with a wild-type revA gene restored heart infectivity to wild-type levels. Additionally, revA mutants led to increased evidence of arthritis, with increased fibrotic collagen deposition in tibiotarsal joints. The mutants also induced increased levels of the chemokine CCL2, a monocyte chemoattractant, in serum, and this increase was abolished in the complemented strain. Therefore, while revA is not absolutely essential for infection, deletion of revA had distinct effects on dissemination, arthritis severity, and host response.

Borrelia burgdorferi harbors a transport system essential for purine salvage and mammalian infection.

Borrelia burgdorferi is the tick-borne bacterium that causes the multistage inflammatory disease Lyme disease. B. burgdorferi has a reduced genome and lacks the enzymes required for de novo synthesis of purines for synthesis of RNA and DNA. Therefore, this obligate pathogen is dependent upon the tick vector and mammalian host environments for salvage of purine bases for nucleic acid biosynthesis. This pathway is vital for B. burgdorferi survival throughout its infectious cycle, as key enzymes in the purine salvage pathway are essential for the ability of the spirochete to infect mice and critical for spirochete replication in the tick. The transport of preformed purines into the spirochete is the first step in the purine salvage pathway and may represent a novel therapeutic target and/or means to deliver antispirochete molecules to the pathogen. However, the transport systems critical for purine salvage by B. burgdorferi have yet to be identified. Herein, we demonstrate that the genes bbb22 and bbb23, present on B. burgdorferi's essential plasmid circular plasmid 26 (cp26), encode key purine transport proteins. BBB22 and/or BBB23 is essential for hypoxanthine transport and contributes to the transport of adenine and guanine. Furthermore, B. burgdorferi lacking bbb22-23 was noninfectious in mice up to a dose of 1 × 10(7) spirochetes. Together, our data establish that bbb22-23 encode purine permeases critical for B. burgdorferi mammalian infectivity, suggesting that this transport system may serve as a novel antimicrobial target for the treatment of Lyme disease.

GuaA and GuaB are essential for Borrelia burgdorferi survival in the tick-mouse infection cycle.

Pathogens lacking the enzymatic pathways for de novo purine biosynthesis are required to salvage purines and pyrimidines from the host environment for synthesis of DNA and RNA. Two key enzymes in purine salvage pathways are IMP dehydrogenase (GuaB) and GMP synthase (GuaA), encoded by the guaB and guaA genes, respectively. While these genes are typically found on the chromosome in most bacterial pathogens, the guaAB operon of Borrelia burgdorferi is present on plasmid cp26, which also harbors a number of genes critical for B. burgdorferi viability. Using molecular genetics and an experimental model of the tick-mouse infection cycle, we demonstrate that the enzymatic activities encoded by the guaAB operon are essential for B. burgdorferi mouse infectivity and provide a growth advantage to spirochetes in the tick. These data indicate that the GuaA and GuaB proteins are critical for the survival of B. burgdorferi in the infection cycle and highlight a potential difference in the requirements for purine salvage in the disparate mammalian and tick environments.

Genetic basis for retention of a critical virulence plasmid of Borrelia burgdorferi.

The genome of Borrelia burgdorferi is composed of one linear chromosome and approximately 20 linear and circular plasmids. Although some plasmids are required by B. burgdorferi in vivo, most plasmids are dispensable for growth in vitro. However, circular plasmid (cp) 26 is present in all natural isolates and has never been lost during in vitro growth. This plasmid carries ospC, which is critical for mammalian infection. We previously showed that cp26 encodes essential functions, including the telomere resolvase, ResT, and hence cannot be displaced. Here we identify two additional essential genes on cp26, bbb26 and bbb27, through a systematic attempt to inactivate each open reading frame (ORF). Furthermore, an incompatible plasmid carrying resT, bbb26 and bbb27 could displace cp26. Computational and experimental analyses suggested that both BBB26 and BBB27 are membrane-associated, periplasmic proteins. These data indicate that bbb26 and bbb27 encode essential but possibly redundant functions and that one or the other of these cp26 genes, in addition to resT, is required for bacterial viability. We conclude that the genetic linkage of critical physiological and virulence functions on cp26 is pertinent to its stable maintenance throughout the evolution of B. burgdorferi.

Differential telomere processing by Borrelia telomere resolvases in vitro but not in vivo.

Causative agents of Lyme disease and relapsing fever, including Borrelia burgdorferi and Borrelia hermsii, respectively, are unusual among bacteria in that they possess a segmented genome with linear DNA molecules terminated by hairpin ends, known as telomeres. During replication, these telomeres are processed by the essential telomere resolvase, ResT, in a unique biochemical reaction known as telomere resolution. In this study, we report the identification of the B. hermsii resT gene through cross-species hybridization. Sequence comparison of the B. hermsii protein with the B. burgdorferi orthologue revealed 67% identity, including all the regions currently known to be crucial for telomere resolution. In vitro studies, however, indicated that B. hermsii ResT was unable to process a replicated B. burgdorferi type 2 telomere substrate. In contrast, in vivo cross-species complementation in which the native resT gene of B. burgdorferi was replaced with B. hermsii resT had no discernible effect, even though B. burgdorferi strain B31 carries at least two type 2 telomere ends. The B. burgdorferi ResT protein was also able to process two telomere spacing mutants in vivo that were unresolvable in vitro. The unexpected differential telomere processing in vivo versus in vitro by the two telomere resolvases suggests the presence of one or more accessory factors in vivo that are normally involved in the reaction. Our current results are also expected to facilitate further studies into ResT structure and function, including possible interaction with other Borrelia proteins.

Borrelia burgdorferi OspC protein required exclusively in a crucial early stage of mammalian infection.

This study demonstrates a strict temporal requirement for a virulence determinant of the Lyme disease spirochete Borrelia burgdorferi during a unique point in its natural infection cycle, which alternates between ticks and small mammals. OspC is a major surface protein produced by B. burgdorferi when infected ticks feed but whose synthesis decreases after transmission to a mammalian host. We have previously shown that spirochetes lacking OspC are competent to replicate in and migrate to the salivary glands of the tick vector but do not infect mice. Here we assessed the timing of the requirement for OspC by using an ospC mutant complemented with an unstable copy of the ospC gene and show that B. burgdorferi's requirement for OspC is specific to the mammal and limited to a critical early stage of mammalian infection. By using this unique system, we found that most bacterial reisolates from mice persistently infected with the initially complemented ospC mutant strain no longer carried the wild-type copy of ospC. Such spirochetes were acquired by feeding ticks and migrated to the tick salivary glands during subsequent feeding. Despite normal behavior in ticks, these ospC mutant spirochetes did not infect naive mice. ospC mutant spirochetes from persistently infected mice also failed to infect naive mice by tissue transplantation. We conclude that OspC is indispensable for establishing infection by B. burgdorferi in mammals but is not required at any other point of the mouse-tick infection cycle.

The plasmids of Borrelia burgdorferi: essential genetic elements of a pathogen.

The spirochete Borrelia burgdorferi, the causative agent of Lyme disease, has an unusual genome comprised of a linear chromosome and the largest plasmid complement of any characterized bacterium. Certain plasmid-encoded elements are required for virulence and viability, both in vitro and in vivo. The genetic tools to manipulate B. burgdorferi are sufficiently developed for precise molecular genetic investigations. B. burgdorferi now represents a prime system with which to address basic questions of plasmid biology and plasmid contributions to bacterial virulence and disease pathogenesis.

The essential nature of the ubiquitous 26-kilobase circular replicon of Borrelia burgdorferi.

The genome of the type strain (B31) of Borrelia burgdorferi, the causative agent of Lyme disease, is composed of 12 linear and 9 circular plasmids and a linear chromosome. Plasmid content can vary among strains, but one 26-kb circular plasmid (cp26) is always present. The ubiquitous nature of cp26 suggests that it provides functions required for bacterial viability. We tested this hypothesis by attempting to selectively displace cp26 with an incompatible but replication-proficient vector, pBSV26. While pBSV26 transformants contained this incompatible vector, the vector coexisted with cp26, which is consistent with the hypothesis that cp26 carries essential genes. Several cp26 genes with ascribed or predicted functions may be essential. These include the BBB29 gene, which has sequence homology to a gene encoding a glucose-specific phosphotransferase system component, and the resT gene, which encodes a telomere resolvase involved in resolution of the replicated telomeres of the linear chromosome and plasmids. The BBB29 gene was successfully inactivated by allelic exchange, but attempted inactivation of resT resulted in merodiploid transformants, suggesting that resT is required for B. burgdorferi growth. To determine if resT is the only cp26 gene essential for growth, we introduced resT into B. burgdorferi on pBSV26. This did not result in displacement of cp26, suggesting that additional cp26 genes encode vital functions. We concluded that B. burgdorferi plasmid cp26 encodes functions critical for survival and thus shares some features with the chromosome.

Outer-surface protein C of the Lyme disease spirochete: a protein induced in ticks for infection of mammals.

Environmentally responsive synthesis of surface proteins represents a hallmark of the infectious cycle of the Lyme disease agent, Borrelia burgdorferi. Here we created and analyzed a B. burgdorferi mutant lacking outer-surface protein C (OspC), an abundant Osp that spirochetes normally synthesize in the tick vector during the blood meal and down-regulate after transmission to the mammal. We demonstrate that B. burgdorferi strictly requires OspC to infect mice but not to localize or migrate appropriately in the tick. The induction of a spirochetal virulence factor preceding the time and host in which it is required demonstrates a developmental sequence for transmission of this arthropod-borne pathogen.