Molecular cloning and complete nucleotide sequence of genomic RNA of the AIK-C strain of attenuated measles virus

Biosafety considerations for attenuated measles virus vectors used in virotherapy and vaccination

Attenuated measles virus (MV) is one of the most effective and safe vaccines available, making it attractive candidate vector to prevent infectious diseases. Attenuated MV have acquired the ability to use the complement regulator CD46 as a major receptor to mediate virus entry and intercellular fusion. Therefore, attenuated MV strains preferentially infect and destroy a wide variety of cancer cells making them also attractive oncolytic vectors. The use of recombinant MV vector has to comply with various regulatory requirements, particularly relating to the assessment of potential risks for human health and the environment. The present article highlights the main characteristics of MV and recombinant MV vectors used for vaccination and virotherapy and discusses these features from a biosafety point of view.

Recombinant measles AIK-C vaccine strain expressing heterologous virus antigens

Further attenuated measles vaccines were developed more than 50 years ago and have been used throughout the world. Recombinant measles vaccine candidates have been developed and express several heterologous virus protective antigens. Immunogenicity and protective actions were confirmed using experimental animals: transgenic mice, cotton rats, and primates. The recent development of measles vaccine-based vectored vaccine candidates has been reviewed and some information on recombinant measles vaccines expressing respiratory syncytial virus proteins has been shown and discussed.

Genetic characterization of measles vaccine strains

The complete genomic sequences of 9 measles vaccine strains were compared with the sequence of the Edmonston wild-type virus. AIK-C, Moraten, Rubeovax, Schwarz, and Zagreb are vaccine strains of the Edmonston lineage, whereas CAM-70, Changchun-47, Leningrad-4 and Shanghai-191 were derived from 4 different wild-type isolates. Nucleotide substitutions were found in the noncoding regions of the genomes as well as in all coding regions, leading to deduced amino acid substitutions in all 8 viral proteins. Although the precise mechanisms involved in the attenuation of individual measles vaccines remain to be elucidated, in vitro assays of viral protein functions and recombinant viruses with defined genetic modifications have been used to characterize the differences between vaccine and wild-type strains. Although almost every protein contributes to an attenuated phenotype, substitutions affecting host cell tropism, virus assembly, and the ability to inhibit cellular antiviral defense mechanisms play an especially important role in attenuation.

Development of a new neutralization test for measles virus

Sero-epidemiological studies are required to identify populations susceptible to measles. The hemagglutination inhibition (HI) test is no longer sensitive enough to confirm immunity to measles, and at present the particle agglutination (PA) test and enzyme-linked immunosorbent assay (EIA) are employed. The most reliable method is the neutralization test (NT), but it is time-consuming and requires experience. To simplify the NT, a recombinant measles AIK-C virus expressing green fluorescence protein (GFP-MVAIK) was constructed and used as a challenge virus. Plaques and cytopathic effects were visualized under ultraviolet light and detected easily, and measuring the intensity of the fluorescence enabled a reduction in the time-consuming steps. Neutralizing antibody titers of a complete inhibition neutralization test were equivalent to those of a 90% plaque reduction neutralization test. Comparison of four methods, HI, PA, EIA and the complete inhibition neutralization test, showed that only the results of EIA correlated well with those of the complete inhibition neutralization test, but sera with borderline levels by EIA were sometimes negative by the complete inhibition neutralization assay.

Protective immunity provided by HLA-A2 epitopes for fusion and hemagglutinin proteins of measles virus

Natural infection and vaccination with a live-attenuated measles virus (MV) induce CD8(+) T-cell-mediated immune responses that may play a central role in controlling MV infection. In this study, we show that newly identified human HLA-A2 epitopes from MV hemagglutinin (H) and fusion (F) proteins induced protective immunity in HLA-A2 transgenic mice challenged with recombinant vaccinia viruses expressing F or H protein. HLA-A2 epitopes were predicted and synthesized. Five and four peptides from H and F, respectively, bound to HLA-A2 molecules in a T2-binding assay, and four from H and two from F could induce peptide-specific CD8+ T cell responses in HLA-A2 transgenic mice. Further experiments proved that three peptides from H (H9-567, H10-250, and H10-516) and one from F protein (F9-57) were endogenously processed and presented on HLA-A2 molecules. All peptides tested in this study are common to 5 different strains of MV including Edmonston. In both A2K(b) and HHD-2 mice, the identified peptide epitopes induced protective immunity against recombinant vaccinia viruses expressing H or F. Because F and H proteins induce neutralizing antibodies, they are major components of new vaccine strategies, and therefore data from this study will contribute to the development of new vaccines against MV infection.

Passage in Vero cells alters the characteristics of measles AIK-C vaccine strain

Objective of this study is to evaluate the feasibility of measles vaccine production in Vero cell culture. We constructed the full-length cDNA, pIC-MVAIK-F278Leu (small plaque-type) and pIC-MVAIK-F278Phe (large plaque-type) from the AIK-C measles vaccine strain attenuated from the Edmonston wild-type. MVAIK-S/B2 was rescued from pIC-MVAIK-F278Leu after two passages in B95a cells and MVAIK-SL/B2V1 was obtained through large plaque cloning in Vero cells. MVAIK-SL/B2V8 was obtained after eight passages in Vero cells. It produced large plaques in Vero cells, grew well at 39 degrees C, and thus the characteristics of the AIK-C vaccine strain were lost. Thirteen amino acid changes were observed; one in the N, two in the P, one in the C, three in the F, one in the H, and five in the L protein regions. Twelve of these changes excluding one in the L gene were back mutated to the Edmonston strain. Change from Leu to Phe at position 278 of the F protein was an early event during adaptation to Vero cells and the P gene was back-mutated to the Edmonston wild-type. As for the control, MVAIK-L/B9 strain was obtained after passages in B95a cells from pIC-MVAIK-F278Phe (large plaque-type). It maintained the same temperature sensitivity as the AIK-C vaccine strain and only four amino acid changes, one in the N and three in the L protein region, were observed without any mutations in the P, C, M, F, and H genes. The passage of the measles vaccine AIK-C strain in Vero cells lost the characteristics of small plaque inducibility and temperature sensitivity (ts) phenotype.

The phosphoprotein of attenuated measles AIK-C vaccine strain contributes to its temperature-sensitive phenotype

Measles AIK-C vaccine strain exhibits temperature-sensitivity (ts). To identify the structural proteins, which contribute to the ts property of AIK-C virus, reverse genetics was used. MV-minigenome RNA was replicated at 32.5, 37, and 39 degrees C when the plasmids expressing N, P, and L proteins of the Edmonston strain (the parental strain of AIK-C) were used, whereas the minigenome RNA replicated only at 32.5 degrees C but did not at 37 degrees C and higher temperature when N, P, and L protein expression plasmids of the AIK-C strain were used. A series of minigenome experiments revealed that the amino acid substitution of leucine at position 439 of the P protein by proline (P439-Pro) contributes to the ts phenotype of AIK-C. Four recombinant viruses having various P genes were rescued from the modified AIK-C genome cDNA and ts-characteristics were compared in Vero cells by plaque formation assay. The results showed that the P439-Pro of AIK-C virus played a key role in the ts phenotype, but the other substitutions in the P gene might have an accessory function in the expression of the phenotype.

Measles virus genotyping by nucleotide-specific multiplex PCR

A simple genotyping method based on multiplex PCR has been developed to discriminate between all active measles virus (MV) clades and genotypes (A, B3.1, B3.2, C2, D2-D9, G2-G3, and H1-H2). The sequencing reaction was replaced by six multiplex PCRs: one to identify the clade and five to identify the respective genotype. Primers were sensitive to clade- and genotype-specific nucleotides and generated fragments of type-specific sizes that were analyzed by conventional agarose gel electrophoresis. On the basis of all published MV sequences, positive and negative predictive values of 99.2% and 98.6% were calculated. Variability in the primer binding sites, which could potentially reduce sensitivity, was very limited among published sequences. As new genotypes are described, additional specific primers can be included in the multiplex PCR with relative ease. Although sequencing remains the "gold standard," the present method should facilitate MV genotyping especially in developing countries and will therefore contribute to enhanced MV control and elimination strategies as recommended by the World Health Organization.

Limited diversity of measles field isolates after a national immunization day in Burkina Faso: progress from endemic to epidemic transmission?

Despite recent National Immunization Days in Burkina Faso, the rural province of Houët reported >400 measles cases in 2001 (82% not vaccinated). Phylogenetic analysis of 58 measles virus field isolates plus the first sequences from the Democratic Republic of the Congo and the Republic of Congo are reported. All viruses were genotype B3, which is common in the region. In Houët, there were two geographically confined genetic variants, suggesting two independent importation events. Strain diversity in Houët (1.5%) and the Congos was limited in comparison with Ibadan, Nigeria (4.6%), where measles is endemic. Strain variability, assessed by heteroduplex mobility assay, confirmed these findings. Despite large local pools of susceptible persons even after several rounds of vaccination, the limited strain diversity suggests that parts of rural Burkina Faso may be moving from an endemic to an epidemic transmission pattern of measles virus.

Co-circulation of two genotypes of measles virus and mutual change of the prevailing genotypes every few years in Osaka, Japan

Genotypes of 44 wild-type measles virus (MV) strains isolated in Osaka, Japan, during 1997-2001, were determined based on phylogenetic analyses of a 456-nt 3' terminal nucleoprotein gene sequence with the reference MV strains designated by the World Health Organization. The wild-type MV strains were classified into two genotypes, D3 and D5, recognized as indigenous in Japan. Six of 12 strains isolated in 1997 were classified into genotype D3 and the other 6 into D5. Eleven of 13 strains were D3, and 2 were D5 in 1998. There were no measles epidemics, and no strains were isolated in 1999. Nine of 10 strains were genotype D5, and only one was D3 in 2000, and 9 of 9 were D5 in 2001. These results indicate that the wild-type MV strains classified into genotypes D3 and D5 co-circulated without the complete change of the MV genotype in Osaka, except in 2001. Furthermore, the prevailing genotype was different between 1998 and 2000-2001. Together with a previous report about MV genotype in this area during 1993-1995, these results suggest that the mutual change of the prevailing wild-type MV genotypes between D3 and D5 occurs every few years in Osaka, Japan.

Rapid replacement of endemic measles virus genotypes

Although vaccination campaigns have significantly reduced the number of measles cases worldwide, endemic transmission of measles virus (MV) continues to occur in several continents, including Europe. To obtain current information on measles incidence and molecular data on circulating MVs in Germany, a nationwide measles sentinel was established. Phylogenetic analysis based on the variable part of the N gene from 80 MVs isolated between November 1999 and October 2001 revealed the presence of at least six distinct MV genotypes: B3, C2, D4, D6, G2 and a new variant of D7. Both the incidence and the pattern of MV genotypes differed markedly between the former East and West Germany. In the eastern part, few measles cases, mainly caused by genotypes originating from other countries (B3, D4, G2), were detected. In the western and southern parts, genotypes C2, D6 and D7 were associated with endemic transmission. Surprisingly, the indigenous genotypes predominant during the 1990s - C2 and D6 - disappeared simultaneously over the period of observation coinciding with the emergence and the wide spread of D7 viruses. While the incidence of measles remained constant, all MVs isolated in 2001 were assigned to D7. We note that the haemagglutinin (H) sequence of D7 viruses shows distinct exchanges of certain amino acids in the stem and propeller domain compared to C2, D6 and the MV vaccine strains used. This raises the possibility of a selective advantage of D7 viruses transmitted in the presence of H-specific antibodies.

Genetic characterization of wild-type measles viruses circulating in suburban Khartoum, 1997-2000

Measles remains endemic in many East African countries, where it is often associated with high morbidity and mortality. We collected clinical specimens from Sudanese measles patients between July 1997 and July 2000. Sequencing of the 3' 456 nucleotides of the nucleoprotein gene from 33 measles virus (MV) isolates and 8 RNA samples extracted from clinical specimens demonstrated the presence of a single endemic MV strain with little sequence variation over time (overall nucleotide divergence of 0 to 1.3%). This was confirmed by sequencing of the complete H gene of two isolates from 1997 and two from 2000, in which the overall divergence ranged between 0 and 0.5%. Comparison with MV reference strains demonstrated that the viruses belonged to clade B, genotype B3, and were most closely related to a set of viruses recently isolated in Nigeria. Our study demonstrates a remarkable genetic stability of an endemically circulating MV strain.

Detection of measles vaccine in the throat of a vaccinated child

Measles vaccine is widely used, most often in association with mumps and rubella vaccines. We report here the case of a child presenting with fever 8 days after vaccination with a measles-mumps-rubella vaccine. Measles virus was isolated in a throat swab taken 4 days after fever onset. This virus was then further genetically characterised as a vaccine-type virus. Fever occurring subsequent to measles vaccination is related to the replication of the live attenuated vaccine virus. In the case presented here, the vaccine virus was isolated in the throat, showing that subcutaneous injection of an attenuated measles strain can result in respiratory excretion of this virus.

Sequence analysis of measles virus strains collected during the pre- and early-vaccination era in Denmark reveals a considerable diversity of ancient strains

A total of 199 serum samples from patients with measles collected in Denmark, Greenland and the Faroe Islands from 1964 to 1983 were analysed by PCR. Measles virus (MV) RNA could be detected in 38 (19%) of the samples and a total of 18 strains were subjected to partial sequence analysis of the hemagglutinin gene. The strains exhibited a considerable genomic diversity, which is at odds with the assumption that one genome type prevailed among globally circulating MV strains prior to the advent of live-attenuated vaccines. Our data indicate that the similarity of the various vaccine strains is attributed to their having originated from the same primary isolate. Consequently, it is implied that a small number of clinical manifestations of MV worldwide from which strains similar to the vaccine strain were identified were vaccine related rather than being caused by members of a persistently circulating ancient genome type. The Danish pre- and early-vaccination era MV strains seem to change the evolutionary spectrum of genome types A, C2 and E into one coherent group, suggesting that the genome types of MV strains circulating in the world at present do not represent far ranging evolutionary lineages but merely members of an evolutionary continuum of pre-vaccination era MV strains which by chance or due to an improved capability survived the worldwide partial herd immunity accomplished through vaccination.

Genetic analysis of Asian measles virus strains--new endemic genotype in Nepal

In many parts of Asia measles virus (MV) continues to be endemic. However, little is known about the genetic characteristics of viruses circulating on this continent. This study reports the molecular epidemiological analysis based on the entire nucleocapsid (N) and hemagglutinin (H) genes of the first isolates from Nepal and Taiwan, as well as of recent MV strains from India, Indonesia, and China. Four isolates collected in various regions in Nepal during 1999 belonged to a new genotype, tentatively called D8. Another Nepalese isolate and one from India belonged to genotype D4. The diversity of the Nepalese strains indicated that measles continues to be endemic in this country. The isolate from Taiwan grouped with D3 viruses and one Chinese strain isolated in The Netherlands was assigned to the previously described clade H, known to be endemic in Mainland China. Molecular characterization emerges as an important tool for monitoring virus endemicity and vaccination efforts.

Leucine at position 278 of the AIK-C measles virus vaccine strain fusion protein is responsible for reduced syncytium formation

The live measles virus (MV) vaccine strain AIK-C was attenuated from the wild-type strain Edmonston by plaque purification at 33 degrees C. Strain AIK-C grew well at 33 degrees C with a mixture of small-and medium-sized plaques in Vero cells, but did not grow well at 40 degrees C. To investigate fusion inducibility, expression plasmids for the fusion (F) and haemagglutinin (H) protein regions of MV strains AIK-C (pAIK-F01 and pAIK-H) and Edmonston (pEdm-F and pEdm-H) were constructed. pEdm-F induced extensive cell fusion in B95a and Vero cells under the control of T7 RNA polymerase, whereas a sharp reduction in syncytium formation was observed when pAIK-F01 was used. Six amino acid differences were determined between pAIK-F01 and pEdm-F. Direct sequencing showed that the seed strain AIK-C contained either Leu or Phe at position 278 of the F protein. Experiments using recombinant F protein plasmids demonstrated that those with Leu at position 278 induced poor syncytium formation, while those with Phe at position 278 (Edmonston type) induced extensive cell fusion. Replacement of Phe with Leu at position 278 of pEdm-F reduced fusion-inducing capability. A full-length infectious clone of AIK-C with Leu at position 278 of the F protein was constructed. The rescued virus produced small plaques in Vero cells. However, the same rescued virus with Phe at position 278 produced large plaques. It was concluded that Leu at position 278 of the F protein of the MV vaccine strain AIK-C is responsible for the formation of small plaques.

Comparison of predicted amino acid sequences of measles virus strains in the Edmonston vaccine lineage

Protein-encoding nucleotide sequences of the N, P, M, F, H, and L genes were determined for a low-passage isolate of the Edmonston wild-type (wt) measles virus and five Edmonston-derived vaccine virus strains, including AIK-C, Moraten, Schwarz, Rubeovax, and Zagreb. Comparative analysis demonstrated a high degree of nucleotide sequence homology; vaccine viruses differed at most by 0. 3% from the Edmonston wt strain. Deduced amino acid sequences predicted substitutions in all viral polypetides. Eight amino acid coding changes were common to all vaccine viruses; an additional two were conserved in all vaccine strains except Zagreb. Comparisons made between vaccine strains indicated that commercial vaccine lots of Moraten and Schwarz had identical coding regions and were closely related to Rubeovax, while AIK-C and Zagreb diverged from the Edmonston wt along slightly different paths. These comparisons also revealed amino acid coding substitutions in Moraten and Schwarz that were absent from the closely related reactogenic Rubeovax strain. All of the vaccine viruses contained amino acid coding changes in the core components of the virus-encoded transcription and replication apparatus. This observation, combined with identification of noncoding region nucleotide changes in potential cis-acting sequences of the vaccine strains (C. L. Parks, R. A. Lerch, P. Walpita, H.-P. Wang, M. S. Sidhu, and S. A. Udem, J. Virol. 75:921-933, 2001), suggest that modulation of transcription and replication plays an important role in attenuation.

Genotypic and antigenic characterization of hemagglutinin proteins of African measles virus isolates

A comprehensive phylogenetic study based on the hemagglutinin (H) protein of all known African measles virus (MV) isolates is presented. The study includes 64 new H gene sequences from Ghana. Nigeria and South Africa as well as viruses from Zambia and The Gambia for which only incomplete sequencing data were available and that have previously not been genotyped. The results provide further support to the tentative assignment of the Nigerian and Ghanaian viruses to a new genotype B3 within clade B. A distinct geographic distribution pattern emerged with clade B viruses circulating exclusively in African countries north of the equator. All MV strains from southern Africa grouped in clades A and D with the majority of viruses belonging to genotype D4. The viruses considerably differed by their sensitivity to neutralization by monoclonal antibodies (mAb), but three selected antibodies were sufficient to distinguish between African MVs representing four different genotypes.

Identification of three lineages of wild measles virus by nucleotide sequence analysis of N, P, M, F, and L genes in Japan

The nucleotide sequences of nucleocapsid (N), phosphoprotein (P), matrix (M), fusion (F), and large protein (L) genes were partly determined for 19 wild strains of measles virus (MV) isolated over the past 10 years in Japan (nucleotide position N: 1301-1700, P: 1751-2190, M: 3571-4057, F: 6621-7210, L: 10381-11133) and also for a MV strain obtained from a patient with subacute sclerosing panencephalitis (SSPE) who had natural measles in 1980. The phylogenetic trees of these strains drawn for respective genes were very similar to each other and revealed that all the wild strains were classified chronologically into 3 subgroups, those isolated in 1984, 1984-1989, and 1990-1994. The SSPE strain was classified into the subgroup of 1984. Phylogenetic tree analyses including other strains in the world revealed that Japanese strains in 1984 were classified into a distinct lineage which might correlate with the European strains from late 1970s to mid 1980s. Japanese strains from 1984 to 1989 were almost identical to those of the United States isolated from 1989 to 1992, and Japanese strains in 1990s were related closely to some of the MV strains isolated in 1994 in the United States. Genetic recombination among the MV genes seemed not to have occurred.

A case of intractable epilepsy positive for the detection of measles virus genome in the cerebrospinal fluid and peripheral mononuclear cells using reverse transcriptase-polymerase chain reaction

We report a rare case of intractable frontal lobe epilepsy with mental deterioration, in which the measles virus gene was detected from the cerebrospinal fluid (CSF) and peripheral mononuclear cells (PBMC) obtained 9 years after the first epileptic episode using reverse transcriptase-polymerase chain reaction (RT-PCR). The patient had been immunized with an attenuated measles vaccine and had no history of clinically apparent acute measles infection. However the analysis of the sequence of the PCR product from CSF showed the circulating wild strain genotype at the time when the patient complained of his first epileptic episode.

Polymerase chain reaction detection of the hemagglutinin gene from an attenuated measles vaccine strain in the peripheral mononuclear cells of children with autoimmune hepatitis

We examined the measles H gene using reverse transcriptase-polymerase chain reaction in peripheral mononuclear cells obtained from 4 pediatric and 2 adult patients with autoimmune hepatitis and 12 healthy children who had been infected with measles or vaccinated with an attenuated measles vaccine in the past. All patients were positive for the presence of the gene. Only one healthy control, who had been vaccinated two weeks before the study, was positive, while the other 11 controls were negative for the presence of the gene. The restriction enzyme patterns of the products in the pediatric patients were different from those observed in adults. The sequences of amplified products from pediatric patients coincided with the vaccine strain, whereas those from adults were different from the vaccine strain. The sequence of those from one of two adult patients was similar to those of the isolates in 1990 and later. Our results demonstrated that children with autoimmune hepatitis can have persistence of the vaccine strain in vivo for many years after vaccination.

Detection of measles virus genome directly from clinical samples by reverse transcriptase-polymerase chain reaction and genetic variability

A simple and sensitive method for the detection of measles virus genome was developed, amplifying the regions encoding the nucleocapsid (N) protein and hemagglutinin (H) protein of measles virus by reverse transcriptase-polymerase chain reaction (RT-PCR). We examined a variety of measles patients: 28 patients with natural infection, 4 with measles encephalitis and 1 with subacute sclerosing panencephalitis (SSPE). In 28 patients with natural measles infection a single step PCR amplifying the N region resulted in a high detection rate for all plasma samples (28/28) within 3 days of the onset of rash and 80% (20/25) even on day 7 of the onset of rash and later. Within 3 days of the onset of rash, 24/25 (96.0%) of nasopharyngeal secretions (NPS) and 27/28 (96.4%) of peripheral blood mononuclear cells (PBMC) were positive for the N region PCR and the positivity rate of PCR decreased in NPS and PBMC after 7 days of the rash. In acute measles infection, measles genome was detected in all cell fractions, CD4, CD8, B cells, and monocytes/macrophages by the H gene nested PCR. Measles genome was also detected from cerebrospinal fluids (CSF) in patients with measles encephalitis, SSPE, and acute measles by the H gene nested PCR. PCR products of the N and H regions were sequenced and we confirmed the presence of measles genome. Based on the sequence data, chronological sequence differences were observed over the past 10 years. The sequences obtained from the SSPE patient were closely related to those of the wild viruses that were circulating at the time when the patient initially acquired measles. RT-PCR for NPS, PBMC, CSF, and plasma provides a useful method for the diagnosis of measles and molecular epidemiological study in addition to virus isolation.

Comparison of sequences of the H, F, and N coding genes of measles virus vaccine strains

Many live-attenuated vaccines for measles virus have been developed using either the prototype Edmonston strain or other locally isolated measles strains. The attenuation methods used to develop these vaccines have differed in the type(s) of cell line(s) used, number of passages, and temperatures of incubation. To assess the extent of genetic diversity within vaccine strains and to determine the extent to which the varied passage histories may have affected the viruses, we conducted sequence analyses of the fusion, hemagglutinin, nucleoprotein, and matrix genes of Edmonston-derived and non-Edmonston-derived strains. Despite the diverse geographic origins of the vaccine viruses and the different attenuation methods used, there was remarkable sequence similarity among all strains examined. The sequences of all of the vaccine strains were very similar to the sequences of a low-passage seed of the original Edmonston strain. The most divergent sequences were from two of the non-Edmonston-derived vaccines: CAM-70, a vaccine developed from a Japanese wild-type virus, and S-191, which was developed in China.