Infectious cDNA clone of the RA27/3 vaccine strain of Rubella virus

Rubella virus (RUB), a small plus-strand RNA virus, is a significant human pathogen. The RA27/3 vaccine strain of RUB is one of the most successful live attenuated vaccines developed. In this article, we report the construction of an RA27/3 infectious clone, a complete cDNA copy of the RA27/3 genome that can be transcribed in vitro to generate infectious RNA molecules. Virus generated from such in vitro transcripts was phenotypically similar to RA27/3 virus. To investigate the attenuation of the RA27/3 strain, a series of chimeras was made by the insertion of different fragments of the RA27/3 genome into an infectious clone based on the Therien wild-type strain of RUB. Analysis of the resulting chimeric viruses revealed that the pattern of RA27/3 attenuation in cell culture is complex: attenuating elements in the RA27/3 genome were found in the 5' untranslated region (UTR), a region of the nonstructural proteins containing the protease motif and the capsid gene. Within the 5' UTR, the attenuation determinant was mapped to nt 7. Surprisingly, these analyses also revealed a potentiating mutation at nt 164 of the RA27/3 genome. Although this determinant was within the coding sequences of the nonstructural proteins, the encoded amino acid had no effect on cell culture phenotype and thus the determinant may operate at the level of RNA structure. In addition to investigation of the mechanisms of RA27/3 attenuation, the availability of the RA27/3 infectious clone offers the opportunity for strict genetic control over RUB vaccine manufacturing, for development of novel DNA-based vaccines against RUB, and for development of recombinant RUB vaccines that also target other diseases.

Mutations in the E1 hydrophobic domain of rubella virus impair virus infectivity but not virus assembly

Rubella virus (RV) virions contain three structural proteins, a capsid protein that interacts with viral genomic RNA to form a nucleocapsid and two membrane glycoproteins, E2 and E1. We found that substitution of either an aspartic acid residue at Gly93 (G93D) or a glycine residue at Pro104 (P104G) in the internal hydrophobic domain of E1 affected virus infectivity but not virus assembly. Viruses carrying G93D and P104G mutations had impaired infectivity, reduced 1,000-fold and 10-fold, respectively. A revertant was isolated from the G93D mutant. Sequencing analysis showed that the substituted aspartic acid residue in G93D mutant had reverted to the original glycine residue, suggesting the involvement of Gly93 in membrane fusion during viral entry.

[Ultrastructure of human L-68 diploid cells, infected with rubella virus]

A monolayer of human diploid cell culture L-68 (21st and 30th passages) was infected with a intermediate variant of rubella vaccine strain Orlov and studied for 8 days by light and electron microscopy. Virus reproduction was associated with slight cytopathic effect; virions were detected in low amounts inside vacuoles and cisterns of the lamellar complex, groups of virions were found in the cytoplasm in association with cytomembranes and outside cells. Cell cultures differed by the cytopathic effect of the virus on the monolayer: microfocuses were found in the 21st passage culture, while in the 30th passage culture the monolayer was diffusely damaged.

Effects of mutations in the rubella virus E1 glycoprotein on E1-E2 interaction and membrane fusion activity

Rubella virus (RV) virions contain two glycosylated membrane proteins, E1 and E2, that exist as a heterodimer and form the viral spike complexes on the virion surface. Formation of an E1-E2 heterodimer is required for transport of E1 out of the endoplasmic reticulum lumen to the Golgi apparatus and plasma membrane. To investigate the nature of the E1-E2 interaction, we have introduced mutations in the internal hydrophobic region (residues 81 to 109) of E1. Substitution of serine at Cys82 (mutant C82S) or deletion of this hydrophobic domain (mutant dt) of E1 resulted in a disruption of the E1 conformation that ultimately affected E1-E2 heterodimer formation and cell surface expression of both E1 and E2. Substitution of either aspartic acid at Gly93 (G93D) or glycine at Pro104 (P104G) was found to impair neither E1-E2 heterodimer formation nor the transport of E1 and E2 to the cell surface. Fusion of RV-infected cells is induced by a brief treatment at a pH below 6. 0. To test whether this internal hydrophobic domain is involved in the membrane fusion activity of RV, transformed BHK cell lines expressing either wild-type or mutant spike proteins were exposed to an acidic pH and polykaryon formation was measured. No fusion activity was observed in the C82S, dt, and G93D mutants; however, the wild type and the P104G mutant exhibited fusogenic activities, with greater than 60% and 20 to 40% of the cells being fused, respectively, at pH 4.8. These results suggest that it is likely that the region of E1 between amino acids 81 and 109 is involved in the membrane fusion activity of RV and that it may be important for the interaction of that protein with E2 to form the E1-E2 heterodimer.

Improvement of the specific infectivity of the rubella virus (RUB) infectious clone: determinants of cytopathogenicity induced by RUB map to the nonstructural proteins

A plasmid, Robo102, which contains a cDNA copy of the rubella virus (RUB) genomic RNA from which infectious transcripts can be synthesized in vitro, was recently developed (C. Y. Wang, G. Dominguez, and T. K. Frey, J. Virol. 68:3550-3557, 1994). To increase the specific infectivity of Robo102 transcripts (approximately 5 plaques/10 microg of transcripts), a modified reverse transcription-PCR method was used to amplify nearly 90% of the RUB genome in three fragments, which were then used to replace the corresponding fragments in Robo102. Replacement of a fragment covering nucleotides (nt) 5352 to 9759 of the RUB genome yielded a construct, Robo202, which produced highly infectious transcripts (10(4) plaques/microg), indicating the presence of an unrecognized deleterious mutation (or mutations) in this region of the Robo102 cDNA. Robo102 was based on the w-Therien strain of RUB, which forms opaque plaques in Vero cells, while the PCR replacement fragments were generated from a variant, f-Therien, which produces clear plaques in Vero cells. Although Robo202 contains over 4,000 nt from f-Therien, Robo202 virus produces opaque plaques. However, when the other two PCR fragments amplified from f-Therien (nt 1 to 1723 and nt 2800 to 5352) were introduced into Robo202, the resulting construct, Robo302, yielded transcripts that produced a virus that formed clear plaques. This indicates that the determinants of plaque morphology map to the regions of the genome covered by these two fragments, both of which are in the nonstructural open reading frame. Generation of Robo202/302 chimeras indicated that the most 5' terminal fragment (nt. 1 to 1723) had the greatest effect on plaque morphology. The plaque morphology was correlated with the ability of the viruses to kill infected cells. The only difference at the molecular level detected among the viruses was that the more cytopathic viruses produced more nonstructural proteins than did the less cytopathic viruses. This finding, as well as the mapping of the genetic determinants to the region of the genome encoding these proteins, indicates that the nonstructural proteins can mediate cell killing.

Retinal vasculitis caused by rubella

A patient with vasculitis apparently caused by rubella and diagnosed during her life-time is here presented. The girl showed optic neuritis and large vascular changes in the eye fundi (retinal vasculitis). High intrathecal antibody production against rubella but little or none against other viruses was found in the cerebrospinal fluid. This study suggests that immunoactivation after rubella vaccination may remain and lead to vascular changes.

Characterization of defective-interfering RNAs of rubella virus generated during serial undiluted passage

During serial undiluted passage of rubella virus (RUB) in Vero cells, two species of defective-interfering (DI) RNAs of approximately 7000 and 800 nucleotides (nts) in length were generated (Frey, T. K., and Hemphill, M. L., Virology 164, 22-29, 1988). In this study, these DI RNAs were characterized by molecular cloning, hybridization with probes of defined sequence, and primer extension. The 7000-nt DI RNA species were found to be authentic DI RNAs which contain a single 2500- to 2700-nt deletion in the structural protein open reading frame (ORF) region of the genome. The 800-nt RNAs were found to be subgenomic DI RNAs synthesized from the large DI RNA templates. Analysis of the extent of the deletions using a reverse-transcription-PCR protocol revealed that the 3' end of the deletions did not extend beyond the 3' terminal 244 nts of the genome. The 5' end of the deletions did not extend into the nonstructural protein ORF; however, DI RNAs in which the subgenomic start site was deleted were present. Following serial undiluted passage of seven independent stocks of RUB, this was the only pattern of DI RNAs generated. DI RNAs of 2000 to 3000 nt in length were the majority DI RNA species in a persistently infected line of Vero cells, showing that other types of RUB DI RNAs can be generated and selected. However, when supernatant from the persistently infected cells was passaged, the only DI RNAs present after two passages were 7000 nts in length, indicating that this species has a selective advantage over other types of DI RNAs during serial passage.

Construction of rubella virus genome-length cDNA clones and synthesis of infectious RNA transcripts

Plasmids containing a complete cDNA copy of the rubella virus (RUB) genomic RNA were constructed. Transfection into cell culture of genome-length RNA transcribed in vitro from one of these cDNA clones, Robo102, resulted in the production of virus which preserved the genetic and phenotypic characteristics of the parental virus from which the cDNA clone was derived. Prior to construction of the RUB genome-length cDNA clones, the 5'-terminal sequence of the RUB genomic RNA was determined to be 5'CAAUGG...3' following the cap structure. Analysis of the specific infectivity of RUB genomic RNA isolated from virions revealed that in Vero cells, the specific infectivity of RUB genomic RNA is roughly equivalent to that of Sindbis virus genomic RNA. In RUB virion RNA preparations, the subgenomic RNA was detected. It was demonstrated that subgenomic RNA was packaged into RUB virions; however, the presence of the subgenomic RNA was not essential for infectivity of the genomic RNA.

Characterization of rubella virus strain differences associated with attenuation

A comparison of the phenotypic properties of three rubella vaccines (HPV77/DE5, RA27/3 and Cendehill) and four wild-type (wt+) isolates (M33, Therien, Thomas and IB2) has been carried out. Differences in growth characteristics, plaque morphology and temperature sensitivity were identified. In addition differential reactivity of the strains to polyclonal and a monoclonal anti-E1 antibody were found in immunoperoxidase-staining reactions. The ability of the wt+ and vaccine strains to infect lymphoreticular cells and chondrocytes, also varied in that the RA27/3 and Cendehill strains were highly restricted in both these cell types while the wt+ strains and HPV77/DE5 vaccine grew to higher titer. This biological variation was associated with differences in E1 and E2 glycoproteins detected on immunoblots.

Induction of an organ-specific autoimmune disease, lymphocytic hypophysitis, in hamsters by recombinant rubella virus glycoprotein and prevention of disease by neonatal thymectomy

Glycosylated, membrane-associated E1 (58-kDa) and E2 (47- to 49-kDa) rubella virus proteins and unglycosylated nucleoprotein C (33 kDa), from separately expressed vaccinia virus recombinants, were injected into golden Syrian hamsters. Rubella virus E1 and E2 glycoproteins consistently induced an organ-specific autoimmune disease, autoimmune lymphocytic hypophysitis, which was evidenced by the induction of autoantibodies against pituitary cells and by lymphocytic infiltration of the pituitary. Neonatal thymectomy prevented the disease. In contrast, rubella virus nucleoprotein C did not induce either autoantibodies against pituitary cells or lymphocytic infiltration of the pituitary. This finding raises the possibility that virus-specific protein itself can induce an organ-specific autoimmune disease in certain circumstances.

Susceptibility of normal human joint tissue to viruses

A model system has been developed to investigate the comparative ability of different viruses to replicate and persist intraarticularly. The viruses chosen for study were rubella, mumps, Coxsackie B4, adenovirus and varicella zoster, a selection of viruses with different degrees of association with joint symptoms in clinical studies. Our results showed that these viruses demonstrated a range of abilities to infect and persist in human joint tissue cultured in vitro. The most arthritogenic viruses, rubella, and to a lesser extent mumps, replicated and penetrated deeply into the synovial membrane. In contrast, the other 3 viruses were much less arthrotropic, and may only induce arthritis by immunopathological mechanisms.

Rubella and mumps vaccines

As a fetal infection occurring during early pregnancy, rubella's potential for teratogenicity is unparalleled. In the postnatal period it is a relatively benign disease. Mumps, on the other hand, causes moderate morbidity and occasional mortality. Both infections cause considerable morbidity and disruption in the lives of young people gathered for group activities. Widespread use of safe and effective live attenuated vaccines has dramatically reduced the incidence of rubella, congenital rubella, and mumps in the United States. Nevertheless, significant numbers of young children, especially in areas of urban and rural immigration and poverty, fail to be immunized in a timely fashion; and some adolescents and young adults remain susceptible either because they escaped immunization in childhood or are primary vaccine failures. These individuals remain the source of individual cases and small outbreaks of rubella and mumps. For total eradication of these infections, we need to intensify vaccine efforts and to maintain surveillance efforts for mumps, rubella, and congenital rubella syndrome.

[Chronic rubella virus-induced infection of human continuous cells]

A stable chronically rubella virus-infected culture of HEp-2-BK cells existing for over 30 months has been obtained as a result of a single inoculation and further passages. This system is characterized by the lack of cell destruction and permanent production of infectious virus in titres of 2.5-6.3 lg PFU/ml. Synthesis of RNAs of the same classes as in the acute infection was demonstrated in the chronically infected cell culture (CICC) but virion RNA production was less marked. Only a portion of the cells in the population was found to carry the infectious virus. Virus-free cell clones were as susceptible to rubella virus as the control culture. The process of persistence proved to be resistant to virus-specific antibody as well as to the effect of higher (40 degree C) or lower (34 degree C) temperatures. Actinomycin D, 5-bromodeoxyuridine, and 5-iodo-2-deoxyuridine exerted no significant effect on virus reproduction in CICC which, combined with negative results of the experiments on transfection of the susceptible cultures with DNA preparations recovered from CICC, evidenced against the role of integration mechanisms in the establishment and maintenance of the HEp-2-BK system. A clear-cut interference with a heterologous virus was demonstrated in HEp-2-BK culture. The formation of the chronic form of infection in HEp-2-BK culture appears to be due to weak cytocidal properties of rubella virus and formation of endogenous interferon.

Oncocytic cardiomyopathy in an infant with oncocytosis in exocrine and endocrine glands

An 11 week old female infant with congenitally malformed eyes died from intractable cardiac arrhythmia. The heart showed extensive oncocytic transformation of myocytes, and this distinctive cardiomyopathy affected the conduction system. Oncocytes were found also in endocrine (pituitary, thyroid) and exocrine (submandibular, sublingual, minor salivary) glands. There is morphologic evidence that the lesions were caused early in gestation, possibly by a viral infection such as rubella.

[Teratogenic properties of freshly isolated strains of rubella virus in experiments on animals]

Teratogenic properties of rubella virus circulating in the Soviet Union were studied in animal experiments. After inoculation of the virus to white rats on the 5th day of pregnancy, an increased number of resorptions, a decrease in the number and weight of the embryos were observed. In some rats hydramnion was observed. The newborn rats of the infected mothers showed a higher lethality and some delay in weight gain as compared to the control animals, as well as hydrocephaly and microcephaly (2.2%). Persistence of rubella virus hemagglutination-inhibiting antibody in many infected rats and their progeny was established. The results indicate that the national s-rains of rubella virus affect the course of pregnancy and development of progeny in white rats.

Erythema infectiosum. An elementary school outbreak

An outbreak of erythema infectiosum (fifth disease) occurred in a North Carolina elementary school. Because rubella virus has been implicated as a possible cause of some cases of erythema infectiosum, we conducted an investigation to determine if the children were infected with rubella virus and to learn whether or not rubella virus vaccination prevents the disease. Throat swabs were obtained for viral isolation from 20 children with erythema infectiosum and from 25 healthy classmates; questionnaires were completed for 617 of the school's 817 students. One hundred fifty children (24%) reported having an acute exanthematous illness during the study period, and 45% of the ill children had one or more household contacts with a similar rash. No viruses were recovered from the children, and a history of rubella vaccination did not affect the risk of developing erythema infectiosum.