Attenuation of rubella virus by serial passage in primary rabbit kidney cell cultures. II. Experiments in animals

Analysis of the temperature sensitivity of Japanese rubella vaccine strain TO-336.vac and its effect on immunogenicity in the guinea pig

The marker of Japanese domestic rubella vaccines is their lack of immunogenicity in guinea pigs. This has long been thought to be related to the temperature sensitivity of the viruses, but supporting evidence has not been described. In this study, we generated infectious clones of TO-336.vac, a Japanese domestic vaccine, TO-336.GMK5, the parental virus of TO-336.vac, and their mutants, and determined the molecular bases of their temperature sensitivity and immunogenicity in guinea pigs. The results revealed that Ser(1159) in the non-structural protein-coding region was responsible for the temperature sensitivity of TO-336.vac dominantly, while the structural protein-coding region affected the temperature sensitivity subordinately. The findings further suggested that the temperature sensitivity of TO-336.vac affected the antibody induction in guinea pigs after subcutaneous inoculation.

Chapter 9 Infections caused by rubella, reoviridae, retro, Norwalk and ronaviruses

This chapter focuses on infections caused by rubella, reoviridae, retro, Norwalk and coronaviruses. High incidence of acute gastroenteritis caused by rotaviruses calls for prophylactic and therapeutic measures. Although no vaccine is presently available, it seems likely that vaccines will be developed in the next few years. There are also several rotavirus enzymes useful as targets for antiviral drugs. However, no antiviral drugs have shown therapeutic effects against rotavirus infections. The newly discovered human retrovirus (HTLV) has not yet been investigated in such detail as to predict the usefulness of vaccine or antiviral drugs. Several compounds are known to inhibit other retrovirus enzymes but the implication of this for chemotherapy of HTLV infection is unknown at present. The possibility and need for vaccination or chemotherapy against Norwalk virus and related agents is unclear. Very little work has been carried out to date with human coronaviruses, either from the point of view of vaccine development or specific antivirals. Both approaches may be usefully investigated in the future. Genetic cloning may be particularly useful for development of inactivated vaccines because the virus itself would be difficult to replicate and purify in large quantities for conventional vaccines.

Rubella vaccines: past, present and future

The association between rubella in pregnancy and congenital anomalies was first reported 50 years ago, by N. McAlister Gregg, an Australian ophthalmologist [1]. During the next 20 years his findings were confirmed by others (reviewed in [2]). However, the first reports of the isolation of rubella virus in cell cultures and development of tests for neutralizing antibodies were not published until 1962 [3, 4]. Subsequent studies conducted in the UK and North America during a pandemic of rubella in 1963–4, were therefore able to make a more accurate estimate of the risks of maternal rubella at different stages of pregnancy. It was estimated that about 30000 rubella-damaged babies were born in the USA alone in 1963–4 [5]. This emphasized the importance of developing a vaccine to prevent infection in pregnancy and thereby, the birth of babies with rubella-induced congenital defects.

Hybrids between rubella virus and a latent virus of baby hamster kidney cell line BHK21: characterization of rubella virus and type 2 hybrid virus genomes and determination of their physical homology

The biochemical nature of rubella virus and type 2 hybrid virus, which is a recombinant between rubella virus and a latent retrovirus of BHK21 cells, has been characterized. Type 2 hybrid virus carries DNA polymerase able to copy exogenous DNA. However, disrupted type 2 hybrid virions do not synthesize detectable amounts of DNA using the endogenous viral RNA or synthetic poly(rA)/oligo(dT) primed as a template. Thus, the type 2 hybrid virus DNA polymerase has no detectable reverse transcriptase activity. Rubella virus and type 2 hybrid virus RNA can serve as templates for avian myeloblastosis virus (AMV) reverse transcriptase, although they are inefficient. The addition of oligo(dT) to these viral RNA showed no significant stimulation of their template activity for AMV reverse transcriptase. The oligo(dT)-cellulose affinity column bound neither rubella virus nor type 2 hybrid virus RNA. This suggests that both RNA genomes have a very short poly(A) tail at their 3' end. Thus, complementary DNA (cDNA) synthesis by AMV reverse transcriptase using oligo(dT) primers showed no preferential reverse transcription from the genomic 3' terminus and produced only short cDNA fragments (about 200 nucleotides). We cross-hybridized these short cDNA fragments with their viral RNA, assuming that they are copies of random sites of the genome. These cDNA-RNA hybridization analyses of physical homology between type 2 hybrid virus and rubella virus genomes revealed that about 70% of the type 2 hybrid virus genome is derived from about an 85% portion of the rubella virus genome. These values indicate that the size of the type 2 hybrid virus genome is about 21% larger than that of the rubella virus genome. Co-sedimentation studies of these viral RNA by sucrose density gradient centrifugation confirmed that the molecular weight of type 2 hybrid virus RNA is 20% higher than that of rubella virus RNA. We propose a genomic structure of the type 2 hybrid virus taking into account both physical and biochemical data.

Inability of Japanese rubella vaccines to induce antibody response in rabbits is due to growth restriction at 39 degrees C

We have compared the kinetic growth patterns of To-336, MEQ11, KRT, and SK2 rubella vaccine strains licensed in Japan at 37 degrees and 39 degrees C with those of progenitor wild strains of rubella virus. The growth of vaccine strains was depressed at 39 degrees C to a level about 3 log10 lower than that at 37 degrees C. The difference in virus titer attained by wild strains at 37 degrees and 39 degrees C was less than tenfold. The growth potential at 39 degrees C paralleled the immunogenic marker of rubella virus, i.e. the capability of virus to induce antibody response upon subcutaneous injection in rabbits for all wild and vaccine strains examined, including one strain at an intermediate level of attenuation. Several clones were isolated from the progeny produced by a vaccine strain during the growth at 39 degrees C. Among them were partial revertants in immunogenic marker as well as in the growth potential at 39 degrees C. It was concluded that the immunogenic marker of rubella virus in rabbits represented its capability to replicate at the body temperature of the animal.

Rubella immunity testing by mixed hemadsorption

A mixed hemadsorption (MH) test for naturally acquired rubella immunity and immune responses after rubella vaccination has been compared with the hemagglutination-inhibition (HI) test, the immunodiffusion (ID) test, the neutralization test (NT), the hemolysis-in-gel (HIG) test and the indirect immunofluorescence (IF) test. The MH test was approximately equivalent to the HI test and the NT as to sensitivity for the early response to rubella vaccination, and all three tests are thought to measure protective antibodies, i.e. antibodies supposedly directed against envelope antigens, to about the same extent. The MH test for rubella antibodies is especially suited for laboratories in which this type of test is routinely used for other purposes, e.g. rabies, respiratory syncytial virus, herpes simplex, varicella and certain auto-antibodies. Where the method is already standard it may be preferable to the NT which, although of similar clinical value requires tedious standardization. Both tests may be necessary in cases where the HI test is equivocal or hampered by non-removable on-specific inhibitors.

Rubella-specific serum and nasopharygeal immunoglobulin responses following naturally acquired and vaccine-induced infection. Prolonged persistence of virus-specific IgM

Rubella-specific immunoglobulin responses in sera and nasopharyngeal secretions were compared in groups of adult females who had experienced naturally acquired rubella or infection induced by Cendehill, HPV77.DE-5, RA27/3 (subcutaneously and intranasally), and To-336 vaccines. Serum IgG and IgA and nasopharyngeal IgA responses after vaccination by RA27/3 intranasally most closely resembled those induced by naturally acquired infection. However, the other vaccines failed to induce a persistent local IgA response. Levels of local antibody induced by HPV77.DE-5 were especially poor. Virus-specific IgM was detected for prolonged periods. The highest levels and the most persistent response followed vaccination by HPV77.DE-5, four of five volunteers still having rubella-specific IgM at 1 year. Virus-specific IgM persisted for 6 months in seventeen of twenty-five (68%) and for a year in nine of twenty-four (38%) vaccinees. It was still present in four of nine (44%) naturally infected patients at a year.

New Japanese rubella vaccine: comparative trials

A total of 142 seronegative volunteers were given one of the following rubella vaccines: Cendehill, HPV77. DE-5, RA27/3, or a new Japanese vaccine, To-336. To-336 vaccine produced a slightly higher geometric mean antibody titre (G.M.T.) (65.7) than did the HPV77. DE-5 (63.1) or RA27/3 vaccine (61.9) but the G.M.T. induced by Cendehill vaccine was much lower (39.3).Reactions, particularly joint symptoms, occurred least commonly after vaccination with To-336 vaccine. Joint symptoms occurred within seven days of menstruation in 30 out of 37 (81%) vaccines (P <0.01); their incidence was not related to oral contraception.Though there is evidence to suggest that Japanese virus strains may be non-teratogenic further data on the incidence of congenitally acquired infection in Japan must be collected before this conclusion can be supported on epidemiological grounds.

Stability of the rabbit immunogenic marker of RA 27-3 rubella vaccine virus after human passage

Rabbits were inoculated intravenously with "wild" rubella virus, RA 27/3 rubella vaccine virus, or rubella virus isolated from recipients of RA 27/3 vaccine. Rabbits receiving "wild" virus developed rubella hemagglutination inhibition antibody, and those receiving vaccine virus did not. One of the five reisolates tested produced a low transient antibody response in two of the five rabbits inoculated with this strain. The study indicates that the rabbit immunogenic marker after intravenous injection can be used to determine if a rubella virus isolated from a patient is of "wild" or vaccine origin. There was no significant change in the reduced immunogenicity characteristics of the RA 27/3 vaccine virus after human passage.

Rubella vaccine trial in children

A study with RA 27/3 attenuated rubella virus vaccine (Plotkin strain) showed that this produced a significant antibody response in all of twenty-one vaccinated non-immune children without any appreciable marked clinical reactions. Serological examination of 53 non-immune and 29 immune siblings living in the same households failed to show any evidence of transmission of infection.

Markers of rubella virus strains in RK13 cell culture

When tested on RK(13) cell cultures, strains of rubella virus could be differentiated by their ability to form small or large plaques. Large plaques were produced by the HPV-77 and Cendehill strains, and also by a laboratory stock strain (West Point), after only 14 passages in RK(13) culture. Five wild-type rubella viruses, isolated and passaged only a few times in African green monkey kidney tissue culture, grew well in RK(13) cell culture, but they were sensitive to agar inhibitors and, therefore, formed small plaques. On the other hand, RA27/3, an attenuated strain grown in WI-38 human fibroblast cells, developed low titers in RK(13) cells and also produced small plaques. We concluded that the morphological differences between small-plaque and large-plaque viruses depended on their sensitivity to agar inhibitors and on the pH of the medium during plaque formation.

Clinical and laboratory studies with rubella vaccines in adults

Three live attenuated rubella vaccines were tested in adult volunteers. Clinical reactions were mild, but were more noticeable in vaccinated non-immune subjects than in control subjects. With the exception of two individuals, all of the remaining 54 subjects developed an immune response; the level of antibodies found was somewhat lower than that resulting from natural infection. Though virus could be isolated from some of the seronegative volunteers after vaccination, no evidence was found of transmission of infection.