A Summary of the Sixth International Workshop on Microbiome in HIV Pathogenesis, Prevention, and Treatment

In October of 2020, researchers from around the world met online for the sixth annual International Workshop on Microbiome in HIV Pathogenesis, Prevention, and Treatment. New research was presented on the roles of the microbiome on immune response and HIV transmission and pathogenesis and the potential for alterations in the microbiome to decrease transmission and affect comorbidities. This article presents a summary of the findings reported.

Connecting the Dots: Translating the Vaginal Microbiome Into a Drug

A Lactobacillus-dominated vaginal microbiota (VMB) has been associated with health and considered an important host defense mechanism against urogenital infections. Conversely, depletion of lactobacilli and increased microbial diversity, amplifies the risk of adverse gynecologic and obstetric outcomes. A common clinical condition that exemplifies dysbiosis is bacterial vaginosis (BV). BV is currently treated with antibiotics, but frequently recurs, due in part to persistent dysbiosis and failure of lactobacilli to repopulate the vagina. New treatment options are needed to address BV. The VMB is relatively simple and optimally dominated by one or several species of Lactobacillus. Lactobacillus crispatus is strongly associated with vaginal health and depleted in dysbiosis. Replenishing the dysbiotic VMB with protective L. crispatus CTV-05 is a promising approach to prevent recurrent infections and improve women's health. Here we discuss confirmation of this approach with the microbiome-based biologic drug, LACTIN-V (L. crispatus CTV-05), focusing on prevention of BV recurrence.

A Summary of the Fifth Annual Virology Education HIV Microbiome Workshop

In October of 2019, researchers and community members from around the world met at the NIH for the fifth annual International Workshop on Microbiome in HIV. New research was presented on the role of the microbiome on chronic inflammation and vaccine design, interactions of genetics, environment, sexual practice and HIV infection with the microbiome and the development and clinical trials of microbiome-based therapeutic approaches intended to decrease the probability of HIV acquisition/transmission or ameliorate sequelae of HIV. The keynote address by Dr. Jacques Ravel focused on his work on the vaginal microbiome and efforts to improve the analysis and resolution of microbiome data.

Novel Selective Inhibition of Lactobacillus iners by Lactobacillus-Derived Bacteriocins

Lactobacillus iners is often associated with vaginal dysbiosis and bacterial vaginosis (BV), which are risk factors for adverse gynecological and obstetric outcomes. To discover natural inhibitors of L. iners, cell-free culture supernatants (CFSs) from 77 vaginal human Lactobacillus strains and 1 human intestinal strain were screened for inhibitory activity. Three active strains were identified, and Lactobacillus paragasseri K7 (K7), a human intestinal strain, produced the most potent L. iners-inhibitory activity. The active material was purified from the K7 CFS and yielded three active peptides, identified as components of two different class IIb, two-peptide bacteriocins, gassericin K7A (GasK7A) and gassericin K7B (GasK7B). The peptides corresponded to the GasK7A α peptide and the GasK7B α and β peptides. While all three peptides exhibited individual activity against L. iners, GasK7B α was the most potent, with an MIC of 23 ng/ml (4 nM). When combined in equal amounts, the GasK7B α and β peptides showed synergistic inhibition, with an MIC of 2 ng/ml (each peptide at 0.4 nM). Among the four major vaginal Lactobacillus species, the K7 bacteriocins selectively inhibited L. iners All 21 strains of L. iners tested (100%) were inhibited by the K7 bacteriocins, whereas <20% of the vaginal Lactobacillus crispatus, L. jensenii, and L. gasseri strains were inhibited. The combination of the BV treatment metronidazole and K7 bacteriocins completely killed both L. iners and Gardnerella vaginalis in a coculture experiment to mimic BV conditions. In contrast, this treatment did not inhibit L. crispatus cultures.IMPORTANCELactobacillus iners is a prevalent species of the vaginal microbiome, but unlike other major vaginal Lactobacillus species, it is not considered protective against BV and can coexist with BV-associated bacteria. L. iners is generally the first Lactobacillus species to emerge following the treatment of BV with metronidazole, and mounting evidence suggests that it may contribute to the onset and maintenance of vaginal dysbiosis. The discovery of highly potent bacteriocins that selectively kill L. iners while sparing protective vaginal lactobacilli may provide novel pharmacological tools to better understand the roles of this enigmatic bacterium in vaginal ecology and potentially lead to new and improved therapies for dysbiosis-related conditions such as BV.

Stool antigen immunodetection for diagnosis of Giardia duodenalis infection in human subjects with HIV and cancer

Human infection with the protozoan parasite Giardia duodenalis is one the most common parasitic diseases worldwide. Higher incidence rates of giardiasis have been reported from human subjects with multiple debilitating chronic conditions, including hypogammaglobulinemia and common variable immunodeficiency (CVID). In the current study, stool specimens were collected from 199 individuals diagnosed with HIV or cancer and immunocompetent subjects. The sensitivity of microscopy-based detection on fresh stool preparations, trichrome staining and stool antigen immunodetection for the diagnosis of G. duodenalis were 36%, 45.5% and 100%, respectively when compared with a highly sensitive stool-based PCR method as the gold standard. Further multilocus molecular analyses using glutamate dehydrogenase (gdh) and triose phosphate isomerase (tpi) loci demonstrated that the AI genotype of G. duodenalis was the most prevalent, followed by the AII genotype and mixed (AI+B) infections. We concluded that stool antigen immunodetection-based immunoassays and stool-based PCR amplification had comparable sensitivity and specificity for the diagnosis of G. duodenalis infections in these populations. Stool antigen detection-based diagnostic modalities are rapid and accurate and may offer alternatives to conventional microscopy and PCR-based diagnostic methods for the diagnosis of G. duodenalis in human subjects living with HIV or cancer.

Expression of Human Immunodeficiency Virus Type 1 Neutralizing Antibody Fragments Using Human Vaginal Lactobacillus

Eradication of human immunodeficiency virus type 1 (HIV-1) by vaccination with epitopes that produce broadly neutralizing antibodies is the ultimate goal for HIV prevention. However, generating appropriate immune responses has proven difficult. Expression of broadly neutralizing antibodies by vaginal colonizing lactobacilli provides an approach to passively target these antibodies to the mucosa. We tested the feasibility of expressing single-chain and single-domain antibodies (dAbs) in Lactobacillus to be used as a topical microbicide/live biotherapeutic. Lactobacilli provide an excellent platform to express anti-HIV proteins. Broadly neutralizing antibodies have been identified against epitopes on the HIV-1 envelope and have been made into active antibody fragments. We tested single-chain variable fragment m9 and dAb-m36 and its derivative m36.4 as prototype antibodies. We cloned and expressed the antibody fragments m9, m36, and m36.4 in Lactobacillus jensenii-1153 and tested the expression levels and functionality. We made a recombinant L. jensenii 1153-1128 that expresses dAb-m36.4. All antibody fragments m9, m36, and m36.4 were expressed by lactobacilli. However, we noted the smaller m36/m36.4 were expressed to higher levels, ≥3 μg/ml. All L. jensenii-expressed antibody fragments bound to gp120/CD4 complex; Lactobacillus-produced m36.4 inhibited HIV-1_BaL in a neutralization assay. Using a TZM-bl assay, we characterized the breadth of neutralization of the m36.4. Delivery of dAbs by Lactobacillus could provide passive transfer of these antibodies to the mucosa and longevity at the site of HIV-1 transmission.

Robust vaginal colonization of macaques with a novel vaginally disintegrating tablet containing a live biotherapeutic product to prevent HIV infection in women

MucoCept is a biotherapeutic for prevention of HIV-1 infection in women and contains a human, vaginal Lactobacillus jensenii that has been genetically enhanced to express the HIV-1 entry inhibitor, modified cyanovirin-N (mCV-N). The objective of this study was to develop a solid vaginal dosage form that supports sustained vaginal colonization of the MucoCept Lactobacillus at levels previously shown, with freshly prepared cultures, to protect macaques from SHIV infection and to test this formulation in a macaque vaginal colonization model. Vaginally disintegrating tablets were prepared by lyophilizing the formulated bacteria in tablet-shaped molds, then packaging in foil pouches with desiccant. Disintegration time, potency and stability of the tablets were assessed. For colonization, non-synchronized macaques were dosed vaginally with either one tablet or five tablets delivered over five days. Vaginal samples were obtained at three, 14, and 21 days post-dosing and cultured to determine Lactobacillus colonization levels. To confirm identity of the MucoCept Lactobacillus strain, genomic DNA was extracted from samples on days 14 and 21 and a strain-specific PCR was performed. Supernatants from bacteria were tested for the presence of the mCV-N protein by Western blot. The tablets were easy to handle, disintegrated within two minutes, potent (5.7x10¹¹ CFU/g), and stable at 4°C and 25°C. Vaginal administration of the tablets to macaques resulted in colonization of the MucoCept Lactobacillus in 66% of macaques at 14 days post-dosing and 83% after 21 days. There was no significant difference in colonization levels for the one or five tablet dosing regimens (p=0.88 Day 14, p=0.99 Day 21). Strain-specific PCR confirmed the presence of the bacteria even in culture-negative macaques. Finally, the presence of mCV-N protein was confirmed by Western blot analysis using a specific anti-mCV-N antibody.

Protein-based HIV-1 microbicides

Although the development of a protective vaccine remains the most effective strategy for the global control of HIV/AIDS, another practical form of medical intervention would be a microbicide capable of preventing HIV-1 transmission at the mucosal level. A broad spectrum of antiviral molecules have demonstrated in vitro efficacy in proofof- principle studies, and a selected few have already been tested in pre-clinical and clinical microbicide trials. Nevertheless, major hurdles remain to be overcome and there is still much uncertainty about the choice of inhibitors, formulations and administration vehicles for obtaining a safe and effective microbicide. A special category of HIV-1 microbicides are those based on proteins or peptides that interfere with the earliest steps in the viral infectious cycle. Besides a high degree of target specificity and a limited, if any, systemic absorption, proteinbased microbicides offer the unique advantage of being suitable to in vivo expression by engineered bacteria or viral vectors, which might ensure prolonged protection without the need for planned, intercourse-coordinated application. In this respect, vaginal or rectal microbiota such as Lactobacillus spp. represent ideal expression systems as they would not only produce the inhibitor of choice at the mucosal surface, but also easily blend within the resident microflora and offer additional valuable homeostatic effects. In this article, we review the current state of the art on protein-based microbicides.

Demonstration of vaginal colonization with GusA-expressing Lactobacillus jensenii following oral delivery in rhesus macaques

The vaginal microbiome, which harbors beneficial Lactobacillus strains, is believed to be a major host defense mechanism for preventing infections of the urogenital tract. It has been suggested that the gastrointestinal tract serves as a reservoir for lactobacilli that colonize the vagina. Using rhesus macaques, we examined whether oral delivery of human vaginal Lactobacillus jensenii 1153-1646, a GusA-producing strain, would result in colonization of the rectum and the vagina. Lactobacilli were identified from the vagina tracts of three macaques on the basis of β-glucuronidase enzyme production, 16S rRNA gene sequence and DNA homology using a repetitive sequence-based polymerase chain reaction.

sCD4-17b bifunctional protein: extremely broad and potent neutralization of HIV-1 Env pseudotyped viruses from genetically diverse primary isolates

BACKGROUND

We previously described a potent recombinant HIV-1 neutralizing protein, sCD4-17b, composed of soluble CD4 attached via a flexible polypeptide linker to an SCFv of the 17b human monoclonal antibody directed against the highly conserved CD4-induced bridging sheet of gp120 involved in coreceptor binding. The sCD4 moiety of the bifunctional protein binds to gp120 on free virions, thereby enabling the 17b SCFv moiety to bind and block the gp120/coreceptor interaction required for entry. The previous studies using the MAGI-CCR5 assay system indicated that sCD4-17b (in concentrated cell culture medium, or partially purified) potently neutralized several genetically diverse HIIV-1 primary isolates; however, at the concentrations tested it was ineffective against several other strains despite the conservation of binding sites for both CD4 and 17b. To address this puzzle, we designed variants of sCD4-17b with different linker lengths, and tested the neutralizing activities of the immunoaffinity purified proteins over a broader concentration range against a large number of genetically diverse HIV-1 primary isolates, using the TZM-bl Env pseudotype assay system. We also examined the sCD4-17b sensitivities of isogenic viruses generated from different producer cell types.

RESULTS

We observed that immunoaffinity purified sCD4-17b effectively neutralized HIV-1 pseudotypes, including those from HIV-1 isolates previously found to be relatively insensitive in the MAGI-CCR5 assay. The potencies were equivalent for the original construct and a variant with a longer linker, as observed with both pseudotype particles and infectious virions; by contrast, a construct with a linker too short to enable simultaneous binding of the sCD4 and 17b SCFv moieties was much less effective. sCD4-17b displayed potent neutralizing activity against 100% of nearly 4 dozen HIV-1 primary isolates from diverse genetic subtypes (clades A, B, C, D, F, and circulating recombinant forms AE and AG). The neutralization breadth and potency were superior to what have been reported for the broadly neutralizing monoclonal antibodies IgG b12, 2G12, 2F5, and 4E10. The activity of sCD4-17b was found to be similar against isogenic virus particles from infectious molecular clones derived either directly from the transfected producer cell line or after a single passage through PBMCs; this contrasted with the monoclonal antibodies, which were less potent against the PMBC-passaged viruses.

CONCLUSIONS

The results highlight the extremely potent and broad neutralizing activity of sCD4-17b against genetically diverse HIV-1 primary isolates. The bifunctional protein has potential applications for antiviral approaches to combat HIV infection.

A Chinese rhesus macaque (Macaca mulatta) model for vaginal Lactobacillus colonization and live microbicide development

BACKGROUND

We sought to establish a nonhuman primate model of vaginal Lactobacillus colonization suitable for evaluating live microbial microbicide candidates.

METHODS

Vaginal and rectal microflora in Chinese rhesus macaques (Macaca mulatta) were analyzed, with cultivable bacteria identified by 16S rRNA gene sequencing. Live lactobacilli were intravaginally administered to evaluate bacterial colonization.

RESULTS

Chinese rhesus macaques harbored abundant vaginal Lactobacillus, with Lactobacillus johnsonii as the predominant species. Like humans, most examined macaques harbored only one vaginal Lactobacillus species. Vaginal and rectal Lactobacillus isolates from the same animal exhibited different genetic and biochemical profiles. Vaginal Lactobacillus was cleared by a vaginal suppository of azithromycin, and endogenous L. johnsonii was subsequently restored by intravaginal inoculation. Importantly, prolonged colonization of a human vaginal Lactobacillus jensenii was established in these animals.

CONCLUSIONS

The Chinese rhesus macaque harbors vaginal Lactobacillus and is a potentially useful model to support the pre-clinical evaluation of Lactobacillus-based topical microbicides.

Engineered vaginal lactobacillus strain for mucosal delivery of the human immunodeficiency virus inhibitor cyanovirin-N

Women are at significant risk of human immunodeficiency virus (HIV) infection, with the cervicovaginal mucosa serving as a major portal for virus entry. Female-initiated preventatives, including topical microbicides, are urgently needed to help curtail the HIV/AIDS pandemic. Here we report on the development of a novel, live microbicide that employs a natural vaginal strain of Lactobacillus jensenii engineered to deliver the potent HIV inhibitor cyanovirin-N (CV-N). To facilitate efficient expression of CV-N by this bacterium, the L. jensenii 1153 genome was sequenced, allowing identification of native regulatory elements and sites for the chromosomal integration of heterologous genes. A CV-N expression cassette was optimized and shown to produce high levels of structurally intact CV-N when expressed in L. jensenii. Lactobacillus-derived CV-N was capable of inhibiting CCR5-tropic HIV(BaL) infectivity in vitro with a 50% inhibitory concentration of 0.3 nM. The CV-N expression cassette was stably integrated as a single copy into the bacterial chromosome and resolved from extraneous plasmid DNA without adversely affecting the bacterial phenotype. This bacterial strain was capable of colonizing the vagina and producing full-length CV-N when administered intravaginally to mice during estrus phase. The CV-N-producing Lactobacillus was genetically stable when propagated in vitro and in vivo. This work represents a major step towards the development of an inexpensive yet durable protein-based microbicide to block the heterosexual transmission of HIV in women.

Inhibition of HIV infectivity by a natural human isolate of Lactobacillus jensenii engineered to express functional two-domain CD4

The predominant mode of HIV transmission worldwide is via heterosexual contact, with the cervico-vaginal mucosa being the main portal of entry in women. The cervico-vaginal mucosa is naturally colonized with commensal bacteria, primarily lactobacilli. To address the urgent need for female-controlled approaches to block the heterosexual transmission of HIV, we have engineered natural human vaginal isolates of Lactobacillus jensenii to secrete two-domain CD4 (2D CD4) proteins. The secreted 2D CD4 recognized a conformation-dependent anti-CD4 antibody and bound HIV type 1 (HIV-1) gp120, suggesting that the expressed proteins adopted a native conformation. Single-cycle infection assays using HIV-1HxB2 carrying a luciferase reporter gene demonstrated that Lactobacillus-derived 2D CD4 inhibited HIV-1 entry into target cells in a dose-dependent manner. Importantly, coincubation of the engineered bacteria with recombinant HIV-1HxB2 reporter virus led to a significant decrease in virus infectivity of HeLa cells expressing CD4-CXCR4-CCR5. Engineered lactobacilli also caused a modest, but statistically significant, decrease in infectivity of a primary isolate, HIV-1JR-FL. This represents an important first step toward the development of engineered commensal bacteria within the vaginal microflora to inhibit heterosexual transmission of HIV.

Integrin expression in oral hairy leukoplakia and normal tongue epithelium

OBJECTIVE

To describe the expression of integrins in the epithelium of oral hairy leukoplakia (HL) and compare to that of normal lateral tongue epithelium.

MATERIALS AND METHODS

Immunohistochemistry to identify integrins (alpha 2, alpha 3, alpha 5, alpha 6, alpha v, beta 1) was performed, using a standard biotin-streptavidin-peroxidase technique on five clinically and histologically confirmed frozen biopsy specimens of HL and five normal lateral tongue control tissues.

RESULTS

Expression of integrins alpha 2, alpha 3, alpha 6, alpha v, beta 1 was seen both in HL epithelium and in normal control tissue. alpha 5 expression was not seen in HL or in control tissue epithelium. alpha 2 and alpha 3 were expressed mainly in the basal and suprabasal layers; alpha 6 expression was most intense on the basal surface of the basal cells, alpha v was expressed in the basal and suprabasal layers with more expression seen in the higher differentiated cell layers than the other integrins. beta 1 expression was seen in the basal and suprabasal layers only. No apparent difference between HL and normal oral mucosa was noted in the staining pattern of the various integrins.

CONCLUSION

Integrins alpha 2, alpha 3, alpha 6, alpha v, beta 1 are expressed in HL and the expression pattern is not different from that of normal oral mucosa. alpha 5 is not expressed in HL or in normal oral epithelium.

Regulation of Epstein-Barr virus promoters in oral epithelial cells and lymphocytes

Hairy leukoplakia (HL) is a proliferative lesion of the tongue that supports abundant Epstein-Barr virus (EBV) replication. Previous work showed high-level expression of the EBV BMRF2 gene in HL. To characterize the regulation of BMRF2 expression in HL, we mapped the 5' ends of the BMRF1 and BMRF2 transcripts and showed that BMRF2 is expressed from a novel internal promoter within the BMRF1 coding region. Mechanisms of BMRF2 regulation were compared in oral epithelial cells and B lymphocytes, as were those of BMRF1 and BDLF3, early and late EBV transcripts, respectively, that are also known to be expressed in HL. Basal activity of the putative BMRF2 promoter was 10-fold higher in HSC-3 epithelial cells than in B lymphocytes. The BMRF2 and the BDLF3 promoters were responsive to induction by phorbol ester, but unlike the BMRF1 promoter, they were not responsive to BZLF1 transactivation. By mutational analysis, the major activity of the BMRF2 promoter mapped to a 50-bp region, which includes a TATA-like element and a GC box. The BMRF2 promoter may be regulated differentially from the BMRF1 promoter and more closely resembles that of BDLF3. This novel BMRF2 promoter likely belongs to a class of viral promoters that is more responsive to mechanisms known to induce epithelial cell differentiation, consistent with its high level of expression in HL.

Expression of Epstein-Barr virus BMRF-2 and BDLF-3 genes in hairy leukoplakia

The high level of Epstein-Barr virus (EBV) replication found in hairy leukoplakia (HL) provides a unique opportunity to study EBV expression in the oral epithelium. Screening of a cDNA library from an HL biopsy revealed expression of two genes not previously described in vivo: BMRF-2 and BDLF-3. Sequence analysis of the cDNAs demonstrated several nucleotide changes from the B95-8 sequence. In all six different HL strains studied, only one amino acid change was found in BMRF-2 relative to B95-8 and two amino acid changes were found in the BDLF-3 ORF. mRNA expression of both genes was localized to the lower prickle cell layer of the tongue epithelium. BMRF-2 protein expression was primarily detected in the cell nuclei of the upper prickle cell layer; immunoelectron microscopy revealed that BMRF-2 was associated with the nuclear chromatin. BDLF-3 protein expression was observed in the perinuclear space and cytoplasm of the prickle cells. BDLF-3 has recently been identified as a virion-associated protein, but the functions of BMRF-2 and BDLF-3 have not been elucidated.

Epstein-Barr virus BMRF-2 and BDLF-3 expression in hairy leukoplakia

Hairy leukoplakia (HL) is a lesion found on the side of the tongue of immunocompromised individuals, including those with human immunodeficiency virus (HIV) infection. The lesion has unique histopathologic features and is characterised by high-level Epstein-Barr virus (EBV) replication, multiple EBV strains, and extensive inter- and intra-strain recombination. Expression of EBV genes spanning the entire viral life cycle from latency-associated genes to late, replicative genes has been detected in the lesion. HL thus provides a unique opportunity to study EBV expression in oral epithelium, and to study expression of novel EBV genes. We therefore constructed a cDNA library from an HL biopsy and detected expression of two genes not previously described in vivo: BMRF-2 and BDLF-3. Sequence analysis of the cDNAs revealed few amino acid changes from the B95-8 sequence. Expression of both genes was localized to the lower prickle cell layer of the tongue epithelium. BMRF-2 protein expression was primarily detected in the cell nuclei of the upper prickle cell layer. BDLF-3 protein expression was observed in the peri-nuclear space and Golgi compartment. The function of these proteins is currently under investigation.

Apoptosis-associated markers in oral lichen planus

Hypothesizing that loss of basal cells in oral lichen planus is due to apoptosis, we evaluated LP specimens for apoptosis-regulating proteins [positive regulators Bcl-xS, Bax, Fas/Fas-ligand, p53, and negative regulators (anti-apoptotic) Bcl-2, Bcl-xL and compared results with reactions in normal mucosa and chronically inflamed gingiva. Also, sections were evaluated with an in situ TUNEL assay that identifies apoptotic DNA fragments. Basal keratinocytes in normal buccal mucosa, nonspecific gingivitis, and LP were negative for Bcl-2 protein, but melanocytes and lymphoid cells were positive. Keratinocyte staining for Bcl-x was negative to weak in normal buccal mucosa and gingivitis, and moderate in LP. Keratinocytes (especially upper prickle cells) in all tissues stained similarly for Bax at weak to moderate levels. Also, no differences in Fas and Fas-ligand staining were evident. Prominent p53-positive staining was seen in all LP biopsies (10-100% of basal keratinocytes) but not in normal buccal mucosa and gingivitis. Few basal keratinocytes in 5/10 LP cases exhibited a positive in situ signal for DNA fragment-associated apoptosis. That the Bcl-2 family of proteins and Fas/Fas-ligand were detected in normal and diseased tissues, and were occasionally expressed differently in oral LP, supports the notion that apoptosis is a potential mechanism of keratinocyte loss, especially in LP. The pattern of p53 staining in oral LP suggests over-expression of wild-type protein; a phenomenon that would arrest the cell cycle to allow repair of damaged DNA, or trigger apoptosis. While immunohistochemical evidence for apoptosis-associated basal keratinocyte death in LP was slight, it appeared that it may be p53 protein, and possibly Bcl-x associated.

Structure and function of the murine cytomegalovirus sgg1 gene: a determinant of viral growth in salivary gland acinar cells

The salivary gland has long been recognized as an important target organ for cytomegalovirus replication in the infected host. A viral gene, denoted sgg1, plays an important role for replication in the salivary gland even though it is dispensable for growth in other organs or in cultured cells. The nucleotide sequence of this gene and of cDNA clones representing two spliced transcripts (1.5 and 1.8 kb in size) has been determined. The more abundant 1.5-kb transcript contains a 312-amino-acid (aa) open reading frame (ORF) and encodes the corresponding 37-kDa protein (Sgg1) when expressed in transfected COS-7 cells. The 1.8-kb transcript initiates upstream of the 1.5-kb transcript and contains a 108-aa ORF in addition to the 312-aa ORF. This longer cDNA also encodes the 37-kDa protein Sgg1, although at lower abundance than the 1.5-kb cDNA. Sgg1 localizes to the cytoplasm of COS-7 cells, which is consistent with the predicted structural characteristics of the 312-aa ORF: a type 1 integral membrane protein. During viral infection, expression of both sgg1 transcripts is highest at early times (8 to 12 h) after infection; only the 1.5-kb transcript is present, at low levels, late in infection. A recombinant virus, RM868, carrying a lacZ-gpt insertion within sgg1, fails to express Sgg1 protein and exhibits reduced growth in the salivary gland. RM868 retains the capacity to disseminate in the infected mouse and to enter serous acinar cells, although it fails to replicate efficiently in this cell type. These results suggest that sgg1 is critical for high levels of viral replication in the salivary gland.

Cytomegalovirus determinant of replication in salivary glands

Murine cytomegalovirus carrying a deletion mutation disrupting the expression of a gene dispensable for growth in cultured cells was found to disseminate poorly in the mouse. The mutation resulted in a dramatic decrease in the expression of a 1.5-kb major and a 1.8-kb minor beta transcript from a region adjacent to the ie2 gene in the viral genome. Nucleotide sequence determination indicated that 323 bp, including a predicted polyadenylation signal, was deleted from this beta gene. In cultured cells, the plaque morphology and growth characteristics of the mutant were similar to those of parental or rescued wild-type viruses. Following intraperitoneal inoculation of BALB/c mice, growth of the mutant in the salivary gland was dramatically reduced 10,000-fold, while growth in the liver and spleen was not dramatically affected. The beta gene was thus denoted sgg1 (salivary gland growth gene 1). Neither intranasal infection nor direct inoculation into the salivary glands completely overcame the restriction of growth in this organ, suggesting that the sgg1 gene encoded a determinant of tissue tropism. To investigate the impact of the sgg1 mutation on virus dissemination via the blood, the virus titer in peripheral blood leukocytes was determined. No difference was found between the sgg1 mutant and rescued wild-type virus. Thus, murine cytomegalovirus sgg1 gene products appear to be involved in entry or replication of virus in salivary gland cells.

Septicemia and septic arthritis caused by Streptococcus pneumoniae in a cat: possible transmission from a child

Streptococcus pneumoniae serotype 23F was isolated from the blood and synovial fluid of an acutely ill, 15-year-old castrated male cat and from the nasopharynx of that regularly played with it, an infant child. Information presented supports the hypothesis that the infection was transmitted from child to cat.