Immunogenomic profiles associated with response to neoadjuvant chemoradiotherapy in patients with rectal cancer

BACKGROUND

Accumulating evidence suggests that radiotherapy success has an immune-associated component. The immunogenomic profiles associated with responses to chemoradiotherapy (CRT) were assessed in patients with locally advanced rectal cancer in this study.

METHODS

CD8+ tumour-infiltrating lymphocyte (TIL) and stromal lymphocyte densities were assessed by immunohistochemistry using pretreatment biopsies from patients with advanced rectal cancer who had preoperative CRT. Whole-exome sequencing and gene expression microarray analysis were conducted to investigate the genomic properties associated with the response to CRT and CD8+ TIL density. Response to CRT was determined based on Dworak tumour regression grade (TRG); tumours with complete (TRG 4) or near-complete (TRG 3) regression were grouped as good responders, and those with TRG 1 as non-responders.

RESULTS

Immunohistochemical examinations (275 patients) showed that pre-CRT CD8+ TIL density was associated with better response to CRT and improved recurrence-free survival, whereas pre-CRT stromal CD8+ cell density was not associated with either response to CRT or recurrence-free survival. Whole-exome sequencing (74 patients) showed that the numbers of single-nucleotide variations (SNVs) and neoantigens predicted from SNVs were higher in good responders than in non-responders, and these correlated positively with CD8+ TIL density (r_S  = 0·315 and r_S  = 0·334 respectively). Gene expression microarray (90 patients) showed that CD8A expression correlated positively with the expression of programmed cell death 1 (PDCD1) (r_S  = 0·264) and lymphocyte-activation gene 3 (LAG3) (r_S  = 0·507).

CONCLUSION

Pre-CRT neoantigen-specific CD8+ T cell priming may be a key event in CRT responses where immune checkpoint molecules could be useful targets to enhance tumour regression.

Quantitative characterization of T-cell repertoire in allogeneic hematopoietic stem cell transplant recipients

Allogeneic hematopoietic stem cell transplantation (HSCT) is one of curative treatment options for patients with hematologic malignancies. Although GVHD mediated by the donor's T lymphocytes remains the most challenging toxicity of allo-HSCT, graft-versus-leukemia (GVL) effect targeting leukemic cells, has an important role in affecting the overall outcome of patients with AML. Here we comprehensively characterized the TCR repertoire in patients who underwent matched donor or haplo-cord HSCT using next-generation sequencing approach. Our study defines the functional kinetics of each TCRA and TCRB clone, and changes in T-cell diversity (with identification of CDR3 sequences) and the extent of clonal expansion of certain T-cells. Using this approach, our study demonstrates that higher percentage of cord-blood cells at 30 days after transplant was correlated with higher diversity of TCR repertoire, implicating the role of cord-chimerism in enhancing immune recovery. Importantly, we found that GVHD and relapse, exclusive of each other, were correlated with lower TCR repertoire diversity and expansion of certain T-cell clones. Our results highlight novel insights into the balance between GVHD and GVL effect, suggesting that higher diversity early after transplant possibly implies lower risks of both GVHD and relapse following the HSCT transplantation.

Kinetic Interpretation of the Importance of OATP1B3 and MRP2 in Docetaxel-Induced Hematopoietic Toxicity

Neutropenia is a lethal dose-limiting toxicity of docetaxel. Our previous report indicated that the prevalence of severe docetaxel-induced neutropenia is significantly associated with genetic polymorphisms in solute carrier organic anion transporter 1B3 (SLCO1B3) (encoding organic anion–transporting polypeptide 1B3 (OATP1B3)) and ATP-binding cassette subfamily C2 (ABCC2) (encoding multidrug-resistant–associated protein 2 (MRP2)). Therefore, we investigated their significance in docetaxel-induced neutropenia. In vitro experiments suggested their possible involvement in the hepatic uptake of docetaxel and its efflux from bone marrow cells. To further characterize a quantitative impact of OATP1B3 and MRP2 on neutropenia, we used an in silico simulation of the neutrophil count in docetaxel-treated subjects with functional changes in OATP1B3 and MRP2 in a pharmacokinetic/pharmacodynamic model. The clinically reported odds ratios for docetaxel-induced neutropenia risk were explained by the decreased function of OATP1B3 and MRP2 to 41 and 32%, respectively. These results suggest that reduced activities of OATP1B3 and MRP2 associated with systemic exposure and local accumulation in bone marrow cells, respectively, account for the docetaxel-induced neutropenia observed clinically.

Ethnic differences between Japanese and Caucasians in the expression levels of mRNAs for CYP3A4, CYP3A5 and CYP3A7: lack of co-regulation of the expression of CYP3A in Japanese livers

Using a newly developed real-time reverse transcriptase-polymerase chain reaction method, mRNAs were quantitated for CYP3A4, CYP3A5 and CYP3A7 in adult livers from 24 Japanese and 24 Caucasian subjects to elucidate the potential ethnic differences in the expression levels of human cytochrome P450 (CYP) 3As. The expression level of CYP3A4 mRNA in Japanese livers (n = 24) was approximately three times higher than that in Caucasian livers (n = 24, p < 0.001). The mean level of CYP3A5 mRNA was approximately twice higher in Japanese (n = 9) than in Caucasians (n = 5) heterozygous for the CYP3A5 *1 allele (p = 0.057). The CYP3A7 mRNA level was twice higher in Japanese (n = 24) than in Caucasians (n = 22) carrying the CYP3A7 *1A/ *1A genotype (p = 0.042). The level of CYP3A4 mRNA did not correlate with those of CYP3A5 (r = 0.044, n = 24) or CYP3A7 (r = 0.21, n = 24) mRNAs in Japanese livers in contrast to co-regulatory expression of CYP3A4, CYP3A5 and CYP3A7 in Caucasian livers. The results indicate that there are ethnic differences in the expression levels of adult liver CYP3A mRNAs between Japanese and Caucasians, and that the mechanism(s) regulating the hepatic CYP3A expression may be different between these ethnic groups.

Attenuation of a field Sendai virus isolate through egg-passages is associated with an impediment of viral genome replication in mouse respiratory cells

We investigated the mechanisms responsible for attenuation of mouse pathogenicity of Sendai virus (SeV) through passages in eggs. A highly virulent clone, E0, derived from the field SeV Hamamatsu strain, was successively passaged in hen's eggs. Analysis of the mouse lethal dose 50% (MLD50) of virus clones obtained from the viruses at egg-passages 1, 15, 30 and 50 demonstrated that attenuation of E0 by egg-passage occurred due to the gradual appearance of and replacement by virus variants possessing higher MLD50. Comparison of viral replication in the mouse lung and mouse pathogenicity with the representative SeV clones, E0, E15c12, E30c12 and E50c19, obtained from the respective egg-passages revealed that the low pathogenicity of the egg-passaged clones was due to poor multi-cycle viral replication in the lung. Furthermore, MLD50s of the SeV clones were found to be negatively correlated with the replication capability in primary mouse pulmonary epithelial (MPE) cells; the egg-passaged clones with more attenuated phenotypes showed lower replication capability in MPE cells. In the MPE cells infected with the SeV clones at m.o.i. 10, however, viral protein and mRNA syntheses of the egg-passaged clones were enhanced or comparable to those of the parental E0 clone at 1 day and 2 days post infection (p.i.) but decreased more rapidly thereafter. In contrast, viral genome synthesis of the egg-passaged clones in the cells at 2 days p.i. was several times lower than that of E0. These results strongly suggest that attenuation of a virulent field SeV strain by egg-passage occurs due to the appearance and selection of virus variants possessing poor propagation capacity in mouse respiratory epithelial cells, which is caused primarily by an impediment of viral genome replication.

Conserved and non-conserved regions in the Sendai virus genome: evolution of a gene possessing overlapping reading frames

We have sequenced the entire genome of a virulent field isolate of Sendai virus, the Hamamatsu strain, and compared the sequence with that of a distant related strain, the Z strain. Calculation of synonymous and non-synonymous (amino acid changing) nucleotide substitutions revealed regions where changes were permissive and non-permissive, and the experimentally determined functional region were found to be conserved, showing that important regions for function were conserved during evolution. In the cistron-overlapping regions in the P gene, one reading frame was conserved, whereas the other overlapping frame was flexible. The priority of one frame could be a strategy for evolution of an overlapping gene of RNA viruses. We found that the carboxyl two thirds of the C protein was conserved over the amino-terminal one third, possessing priority to the overlapping P polypeptide. This suggests that the carboxyl two thirds of the C protein have a functional importance. We also found a highly variable region between the L coding frame and the 5' trailer sequence. The relevance of these findings to actual viral replication should be clarified in the future.

Involvement of the zinc-binding capacity of Sendai virus V protein in viral pathogenesis

The V protein of Sendai virus (SeV) is nonessential to virus replication in cell culture but indispensable to viral pathogenicity in mice. The highly conserved cysteine-rich zinc finger-like domain in its carboxyl terminus is believed to be responsible for this viral pathogenicity. In the present study, we showed that the cysteine-rich domain of the SeV V protein could actually bind zinc by using glutathione-S-transferase fusion proteins. When the seven conserved cysteine residues at positions 337, 341, 353, 355, 358, 362, and 365 were replaced individually, the zinc-binding capacities of the mutant proteins were greatly impaired, ranging from 22 to 68% of that of the wild type. We then recovered two mutant SeVs from cDNA, which have V-C(341)S and V-C(365)R mutations and represent maximal and minimal zinc-binding capacities among the corresponding mutant fusion proteins, respectively. The mutant viruses showed viral protein synthesis and growth patterns similar to those of wild-type SeV in cultured cells. However, the mutant viruses were strongly attenuated in mice in a way similar to that of SeV V(DeltaC), which has a truncated V protein lacking the cysteine-rich domain, by exhibiting earlier viral clearance from the mouse lung and less virulence to mice. We therefore conclude that the zinc-binding capacity of the V protein is involved in viral pathogenesis.

Sendai virus gene start signals are not equivalent in reinitiation capacity: moderation at the fusion protein gene

In paramyxovirus transcription, viral RNA polymerase synthesizes each monocistronic mRNA by recognizing the gene start (S) and end (E) signals flanking each gene. These signal sequences are well conserved in the virus family; nevertheless, they do exhibit some variations even within a virus species. In Sendai virus (SeV) Z strain, the E signals are identical for all six genes but there are four (N, P/M/HN, F, and L) different S signals with one or two nucleotide variations. The significance of these variations for in vitro and in vivo replication has been unknown. We addressed this issue by SeV reverse genetics. The luciferase gene was placed between the N and P gene so that recombinant SeVs expressed luciferase under the control of each of the four different S signals. The S signal for the F gene was found to drive a lower level of transcription than that of the other three, which exhibited comparable reinitiation capacities. The polar attenuation of SeV transcription thus appeared to be not linear but biphasic. Then, a mutant SeV whose F gene S signal was replaced with that used for the P, M, and HN genes was created, and its replication capability was examined. The mutant produced a larger amount of F protein and downstream gene-encoded proteins and replicated faster than wild-type SeV in cultured cells and in embryonated eggs. Compared with the wild type, the mutant virus also replicated faster in mice and was more virulent, requiring a dose 20 times lower to kill 50% of mice. On the other hand, the unique F start sequence as well as the other start sequences are perfectly conserved in all SeV isolates sequenced to date, including highly virulent fresh isolates as well as egg-adapted strains, with a virulence several magnitudes lower than that of the fresh isolates. This moderation of transcription at the F gene may therefore be relevant to viral fitness in nature.

Double-layered membrane vesicles released from mammalian cells infected with Sendai virus expressing the matrix protein of vesicular stomatitis virus

The matrix (M) protein of vesicular stomatitis virus (VSV) was reported to form vesicles on the cell surface and subsequently to be released into the cultured medium when expressed from cDNA by virus vectors. To further investigate VSV M activity, we generated a recombinant Sendai virus (SeV) expressing the VSV M protein (SeV-M(VSV)). When cells were infected with SeV-M(VSV), VSV M was found abundantly in the culture medium. Electron microscopy demonstrated the budding of two-membraned vesicles (>/= 0.8 microm in diameter) from the infected cells. The outer membrane of the vesicle was derived from the plasma membrane and the inner one possibly derived from the membrane of an intracellular vesicle. Immuno-gold labeling showed that VSV M was exclusively located in a double-layered region. The released membranes were divided into three parts: the VSV M vesicles with SeV F and HN glycoproteins, SeV particles, and vesicles associated with the cytosolic components. The last abundantly contained phosphorylated SeV matrix (M) protein, which is not released in a usual SeV infection. Furthermore the VSV M protein expressed without using a virus vector was efficiently released into the culture medium. These results suggest that the VSV M protein has a budding activity per se and that SeV proteins are passively involved in the release of VSV M.

Role of primary constitutive phosphorylation of Sendai virus P and V proteins in viral replication and pathogenesis

Functional analysis of the primary constitutive phosphorylation of Sendai virus P and V proteins was performed using both in vitro and in vivo systems. Sendai virus minigenome transcription and replication in transfected cells were not significantly affected in the presence of primary phosphorylation deficient P protein (S249A, S249D, P250A) as measured by either the luciferase activity or the Northern blot analysis. Similarly, recombinant Sendai viruses lacking the primary phosphorylation in P grew to titers close to the wild-type virus in cell cultures and in the natural host of Sendai virus, the mouse. Mutant viruses showed no altered pathogenesis in mice lungs. Oligomerization of P by binding WT P or mutant P to GST-P (WT) Sepharose beads revealed that the primary phosphorylation was not crucial for P protein oligomerization. Similar to P protein primary phosphorylation, the V protein primary phosphorylation at serine249 was not essential for minigenome transcription and replication, as both WT and mutant V proteins were found equally inhibitory to the minigenome replication. These results show that the primary phosphorylation of P protein has no essential role in Sendai virus transcription, replication, and pathogenesis.

Accommodation of foreign genes into the Sendai virus genome: sizes of inserted genes and viral replication

Sendai virus (SeV) is an enveloped virus with a negative sense genome RNA of about 15.3 kb. We previously established a system to recover an infectious virus entirely from SeV cDNA and illustrated the feasibility of using SeV as a novel expression vector. Here, we have attempted to insert a series of foreign genes into SeV of different lengths to learn how far SeV can accommodate extra genes and how the length of inserted genes affects viral replication in cells cultured in vitro and in the natural host, mice. We show that a gene up to 3.2 kb can be inserted and efficiently expressed and that the replication speed as well as the final virus titers in cell culture are proportionally reduced as the inserted gene length increases. In vivo, such a size-dependent effect was not very clear but a remarkably attenuated replication and pathogenicity were generally seen. Our data further confirmed reinforcement of foreign gene expression in vitro from the V(-) version of SeV in which the accessory V gene had been knocked out. Based on these results, we discuss the utility of SeV vector in terms of both efficiency and safety.

Comparison of substrate specificities against the fusion glycoprotein of virulent Newcastle disease virus between a chick embryo fibroblast processing protease and mammalian subtilisin-like proteases

The fusion (F) protein precursor of virulent Newcastle disease virus (NDV) strains has two pairs of basic amino acids at the cleavage site, and its intracellular cleavage activation occurs in a variety of cells; therefore, the viruses cause systemic infections in poultry. To explore the protease responsible for the cleavage in the natural host, we examined detailed substrate specificity of the enzyme in chick embryo fibroblasts (CEF) using a panel of the F protein mutants at the cleavage site expressed by vaccinia virus vectors, and compared the specificity with those of mammalian subtilisin-like proteases such as furin, PC6 and PACE4 which are candidates for F protein processing enzymes. It was demonstrated in CEF cells that Arg residues at the -4, -2 and -1 positions upstream of the cleavage site were essential, and that at the -5 position was required for maximal cleavage. Phe at the +1 position was also important for efficient cleavage. On the other hand, furin and PC6 expressed by vaccinia virus vectors showed cleavage specificities against the F protein mutants consistent with that shown by the processing enzyme of CEF cells, but PACE4 hardly cleaved the F proteins including the wild type. These results indicate that the proteolytic processing enzymes of poultry for virulent NDV F proteins could be furin and/or PC6 but not PACE4. The significance of individual contribution of the three amino acids at the -5, -2 and +1 positions to cleavability was discussed in relation to the evolution of virulent and avirulent NDV strains.

Endogenous protease-dependent replication of human influenza viruses in two MDCK cell lines

Multi-cycle replication and plaque formation of influenza A and B viruses and cleavage activation of their hemagglutinin (HA) by an endogenous protease(s) were examined in two MDCK cell lines, MDCK(-) and MDCK(+). No exogenous trypsin was required for multi-cycle replication and plaque formation of all the influenza A viruses tested in the MDCK(+) cell, while those of the viruses in the MDCK(-) cell were completely trypsin-dependent. In both cell lines, on the other hand, influenza B viruses grew well in the absence of trypsin. The capability of multiple replication and plaque formation of the influenza viruses correlated with cleavage of the HA precursor (HA0) to HA1 and HA2, indicating that both cell lines express an HA activating endoprotease(s); that of the MDCK(+) cell activates the HA of influenza A and B viruses, and that of the MDCK(-) cell does only the HA of influenza B virus. Furthermore, the protease of the MDCK(+) cell was strongly suggested to be present on the cell surface and a serine protease. The MDCK(+) cell would be useful for isolation of influenza viruses from clinical specimens and for screening of protease inhibitors for anti-influenza virus drugs.

Sendai virus C proteins are categorically nonessential gene products but silencing their expression severely impairs viral replication and pathogenesis

BACKGROUND

The P/C mRNA of Sendai virus (SeV), a prototypic member of the family Paramyxoviridae in the Mononegavirales superfamily comprising a large number of nonsegmented negative strand RNA viruses, encodes a nested set of accessory proteins, C', C, Y1 and Y2, referred to collectively as C proteins, initiating, respectively, at ACG/81 and AUGs/114, 183, 201 in the +1 frame relative to the ORF of phospho (P) protein, the smaller subunit of RNA polymerase. Among them, C is the major species expressed in infected cells at a molar ratio which is several-fold higher than the other three. However, their function has remained an enigma. It has not even been established whether or not the C proteins are essential for viral replication. Many other viruses in Mononegavirales encode C-like proteins, but their roles also remain to be defined.

RESULTS

By taking advantage of a recently developed reverse genetics system to recover infectious SeV from cDNA, we created mutants in which C protein frames were variously silenced. C/C'(-) viruses which did not express C and C', but did express Y1 and Y2, were severely attenuated in replication in tissue culture cells of various species and tissues, as well as in embryonated chicken eggs. More notably, they were almost totally incapable of growing productively in--and hence nonpathogenic for mice--the natural host. Both gene expression and genome replication appeared to be impaired in C/C'(-) viruses. Additionally silencing the Y1 and Y2 expression was also possible, and a critically impaired but viable clone, the 4C(-) virus, was isolated which expressed none of the four C proteins.

CONCLUSION

SeV C proteins are categorically nonessential gene products, but greatly contribute to full replication capability in vitro and are indispensable for in vivo multiplication and pathogenesis. This study represents the first comprehensive functional assessment of the accessary C protein for Mononegavirales.

Importance of the cysteine-rich carboxyl-terminal half of V protein for Sendai virus pathogenesis

The Sendai virus V protein is a nonstructural trans-frame protein whose cysteine-rich C-terminal half is fused to the acidic N-terminal half of the P protein via mRNA editing. We recently created a mutant by disrupting the editing motif, which is devoid of mRNA editing and hence unable to produce the V protein, and demonstrated that this V(-) virus replicated normally or even faster with augmented gene expression and cytopathogenicity in cells in vitro, but was strongly attenuated in pathogenicity for mice (A. Kato, K. Kiyotani, Y. Sakai, T. Yoshida, and Y. Nagai, EMBO J. 16:578-587, 1997). Thus, although categorized as a nonessential protein, the V protein appeared to encode a luxury function required for the viral in vivo pathogenesis. Here, we created another version of a V-deficient mutant, VdeltaC, encoding only the N-terminal half but not the V-specific C-terminal half, by introducing a stop codon in the trans-V frame, and then we compared its in vitro and in vivo phenotypes with those of the V(-) and wild-type viruses. The VdeltaC virus was found to be similar to the wild-type virus in vitro with no augmented gene expression and cytopathogenicity, but in vivo, it resembled the V(-) virus, displaying a similarly attenuated phenotype. Thus, the pathogenicity determinant in the V protein was mapped to the C-terminal half. The N-terminal half was likely sufficient to confer normal (wild-type) in vitro phenotypes.

Phosphorylation of the Sendai virus M protein is not essential for virus replication either in vitro or in vivo

A large proportion of intracellular Sendai virus (SeV) M proteins is phosphorylated, but in mature virions the M protein is not phosphorylated or dephosphorylated. Phosphorylated M protein in cells is bound to the cytoskeletal components more firmly than unphosphorylated M protein. Thus it has been hypothesized that M protein phosphorylation plays an important role in the virus life cycle, especially in the step of maturation. Here, a transient expression-mutation experiment of the M gene demonstrated that a change of the Ser residue at the 70th position from the N-terminus to Ala (S70A) totally abolished M protein phosphorylation, strongly suggesting that this residue is phosphorylated. The mutated M gene was then placed in the corresponding region in the cDNA plasmid which generates a full-length antigenome SeV RNA, and a mutant SeV M-S70A was successfully recovered from the cDNA. This mutant virus was indeed defective in M protein phosphorylation but did not differ at all from the wild-type SeV recovered from the parental cDNA either in the replication kinetics and plaque morphology in cultured cells or in in vivo replication and pathogenicity for mice. We thus concluded that no phosphorylation of the M protein was required for SeV replication either in vitro or in vivo.

The paramyxovirus, Sendai virus, V protein encodes a luxury function required for viral pathogenesis

The Sendai virus (SeV) V protein is characterized by the unique cysteine-rich domain in its carboxy-terminal half which is fused to the amino-terminal half of the P protein, but its function has remained enigmatic. The V protein-directing mRNA is generated by a remarkable process known as mRNA editing involving the pseudotemplated addition of a single G residue at a specific septinucleotide locus in the P gene, whereas the unedited exact copy encodes the P protein. Here, we introduced two nucleotide changes in the septinucleotide motif (UUUUCCC to UUCUUCC) in a full-length SeV cDNA and were able to recover a virus from the cDNA, which was devoid of mRNA editing and hence unable to synthesize the V protein. Compared with the parental wild-type virus with regard to gene expression, replication and cytopathogenicity in various cell lines in vitro, the V(-) virus was found to be either potentiated or comparable but never attenuated. The V(-) virus, however, showed markedly attenuated in vivo replication capacity in and pathogenicity for mice. Thus, though categorized as a nonessential gene product, SeV V protein encodes a luxury function required for in vivo pathogenicity.

Protection of mice from respiratory Sendai virus infections by recombinant vaccinia viruses

Mechanisms of protection of mice from Sendai virus, which is exclusively pneumotropic and causes a typical respiratory disease, by immunization with recombinant vaccinia viruses (RVVs) were investigated. Although the RVV carrying a hemagglutinin-neuraminidase gene of Sendai virus (Vac-HN) propagated in the noses and lungs of mice by either intranasal (i.n.) or intraperitoneal (i.p.) inoculation, no vaccinia virus antigens were detected in the mucosal layer of upper and lower airways of the i.p.-inoculated mice. The mice immunized i.n. with Vac-HN or Vac-F (the RVV carrying a fusion protein gene of Sendai virus) demonstrated the strong resistance to Sendai virus challenge both in the lung and in the nose, whereas the i.p.-immunized mice showed almost no resistance in the nose but showed a partial resistance in the lung. Titration of Sendai virus-specific antibodies in the nasal wash (NW), bronchoalveolar lavage (BAL), and serum collected from the Vac-F-immunized mice showed that the NW from the i.n.-immunized mice contained immunoglobulin A (IgA) antibodies but no IgG and the BAL from the mice contained both IgA and IgG antibodies. On the other hand, neither IgA nor IgG antibodies were detected in the NW from the i.p.-immunized mice and only IgG antibodies were detected in the BAL, although both i.n.- and i.p.-immunized mice exhibited similar levels of serum IgG, IgA, and neutralizing antibodies. The resistance to Sendai virus in the noses of i.n.-immunized mice could be abrogated by the intranasal instillation of anti-mouse IgA but not of anti-IgG antiserum, while the resistance in the lung was not significantly abrogated by such treatments. These results demonstrate that IgA is a major mediator for the immunity against Sendai virus induced by the RVVs and IgG is a supplementary one, especially in the lung, and that the RVV should be intranasally inoculated to induce an efficient mucosal immunity even if it has a pantropic nature.

Correlation of proteolytic cleavage of F protein precursors in paramyxoviruses with expression of the fur, PACE4 and PC6 genes in mammalian cells

The fusion (F) protein precursor of virulent Newcastle disease virus (NDV) strains and human parainfluenza virus type 3 (HPIV3) has a multibasic amino acid sequence at the cleavage site, and intracellular cleavage activation occurs in a variety of cells. The host protease responsible for the cleavage has been proposed to be a subtilisin-like protease (subtilase) such as furin (the product of the fur gene). We found that the lymphocyte cell lines MOLT-4, Ramos and Daudi, in addition to NALM6, lacked the ability to fully cleave the F protein precursor of virulent NDV. In contrast, MT4 as well as the non-lymphocyte cell lines HeLa and Hep2 cleaved the F protein precursor efficiently. To investigate the role of subtilases in proteolytic processing, we examined the gene expression of candidate subtilases, furin, PACE4 and PC6 in these cleavage-competent and -incompetent cells. Considerable expression of the fur gene was observed in the cleavage-competent cells, but little or no expression was detected in the cleavage-incompetent cells. PACE4 and PC6 gene expression was observed in some of the cleavage-competent cells but not in the cleavage-incompetent cells. These results suggest that furin is the protease responsible for cleavage activation of the F protein of virulent NDV strains in cultured mammalian cells and the possibility is raised that PACE4 and PC6 also participate in processing in some of the cells. On the other hand, the HPIV3 F protein was cleaved efficiently in lymphocyte cells deficient in subtilases, suggesting that an unknown protease other than furin, PACE4 or PC6 may be involved in the processing.

Sendai virus pneumonia: evidence for the early recruitment of gamma delta T cells during the disease course

We previously reported that gamma delta T cells appeared and could play a protective role early in infections with intracellular bacteria such as Listeria monocytogenes, Mycobacterium bovis BCG, and Salmonella choleraesuis. To extend these findings to virus infection, we examined the developmental sequence of gamma delta T cells in bronchoalveolar lavage during the course of Sendai virus infection in C57BL/6 mice. To produce a natural but nonlethal infection course as far as possible, we used a sublethal dose of a wild-type virus which had not been subjected to serial passages in a chicken embryo, hence retaining full virulence for mice. Virus titers in lungs reached a peak on day 6 and then decreased to an undetectable level by day 10. This time course of virus reproduction was immediately and coincidentally followed by the developmental course of gamma delta T cells, in which the cell number peaked on day 7 and then decreased to a marginal level by day 10. On the other hand, the alpha beta T-cell number continued to increase until day 10 and remained at a high level thereafter. The early-appearing gamma delta T cells were CD4-, CD8-, IL-2R alpha- beta+, CD44+, Mel-14-, and LFA-1 alpha/beta+ in phenotype and used V gamma 1/2 and V gamma 4 and V delta 3, V delta 4, V delta 5, and V delta 6. The gamma delta T cells were responding to macrophages from infected mice when the cells were cultured in vitro. Furthermore, the expression of endogenous heat shock protein (hsp) was infection specific, and its level appeared to correlate with the gamma delta T-cell development. These results suggest that the early recruitment of gamma delta T cells, which proliferate in response to endogenous hsp+ cells, is also characteristic of this virus infection, although this view appears to be contradictory to earlier reports.

A field isolate of Sendai virus: its high virulence to mice and genetic divergence form prototype strains

A field isolate of Sendai virus, the Hamamatsu strain, was far more virulent in mice than the prototype Z strain. The Hamamatsu strain replicated more efficiently in the mouse lung than the Z strain, causing deteriorating lung lesions. Nucleotide sequence analysis of the HN, F and M genes revealed that the Hamamatsu strain was divergent from the prototype Z, Harris and Fushimi strains.

F0-containing noninfectious Sendai virus can initiate replication in mouse lungs but requires a relatively long incubation period

The replication of LLC-MK2-grown noninfectious Sendai virus, containing exclusively fusion (F) glycoprotein precursors, was examined in the mouse lung to study the accessibility of virus inoculated intranasally to the virus activator present in the lung. When mice were intranasally inoculated with various doses of the virus after in vitro activation with trypsin, the 50% mouse infectious dose (MID50) was determined to be 0.7 cell-infectious units (CIU) per mouse, indicating that one infectious unit of Sendai virus is enough to initiate replication in the mouse lung and that the present experimental system is highly sensitive. On the other hand, in mice inoculated with virus not treated with trypsin, virus replication in the lung was recognized even in mice inoculated with samples containing no infectious virus, and the MID50 was determined to be 67.5 CIU per mouse (here, CIU were assayed after in vitro trypsin treatment). When mice were infected with 20 MID50 of trypsin-treated infectious and untreated noninfectious viruses (an approximately 100-fold greater amount of noninfectious virus than of infectious virus was used), the noninfectious virus was found to require 2 more days of incubation than the infectious virus, and many of the F proteins synthesized in the lungs of mice infected with the F0-containing virus were present in the cleaved form. In addition, the infection of mice with noninfectious virus was strongly suppressed by aprotinin, a serine protease inhibitor. These results indicate that Sendai virus can initiate replication in the mouse lung even with the F0-containing noninfectious virus and strongly suggest that this infection process is mediated by cleavage activation of the F0 proteins of inoculated viruses by a serine protease(s) present in the lumen of the mouse respiratory tract but that activation of the noninfectious virus is an inefficient process.

Expression of the HN, F, NP and M proteins of Sendai virus by recombinant vaccinia viruses and their contribution to protective immunity against Sendai virus infections in mice

Recombinant vaccinia viruses (RVVs) expressing each of the haemagglutinin-neuraminidase (HN), fusion (F), nucleocapsid (NP) and matrix (M) proteins of Sendai virus were constructed to investigate their capacities to induce protective immunity against Sendai virus infections. The proteins expressed in cultured cells appeared to be authentic with respect to their antigenicity, electrophoretic mobility, surface expression of the HN and F proteins and, in the case of the HN protein, biological activities. Mice inoculated intranasally with these RVVs developed serum antibodies to the respective Sendai virus proteins, suggesting their in vivo expression. In mice immunized with RVV carrying either the HN or the F gene, growth of the challenging Sendai virus was almost completely suppressed in the lung, indicating their capacities to induce effective protective immunity against Sendai virus infections. In contrast, in mice immunized with RVV carrying the NP or M gene, the challenging virus propagated as well as in the control mice, but the virus titres were significantly lower at the late stage of infection than those in the control mice, suggesting that they can also induce protective immunity especially at the late stage of the challenge infection.

Distribution and substrate specificity of intracellular proteolytic processing enzyme(s) for paramyxovirus fusion glycoproteins

Intracellular proteolytic processing of fusion glycoprotein precursors (F0) of paramyxoviruses, i.e. a virulent strain of Newcastle disease virus (NDV), parainfluenza virus type 3 (PIV3) and simian virus 5 (SV5), was examined in NALM6 and BSC40 cells and compared with that in LLCMK2 cells to investigate the distribution of the virus-activating protease(s) among the cells and its substrate specificity. BSC40 cells lack a processing endoprotease of the neuropeptide precursor, pro-opiomelanocortin (POMC), which possesses multiple cleavage sites at pairs of basic residues, Lys-Arg and Arg-Arg, a motif similar to that found in the cleavage site of the F0 proteins. In NALM6 cells, only small amounts of the F0 protein of virulent NDV was cleaved whereas those of PIV3 and SV5 were efficiently cleaved. In BSC40 cells the F0 proteins of these three viruses were cleaved normally as well as in LLCMK2 cells. The processing inhibitors monensin, chloroquine and A23187 suppressed the F0 cleavage in the three cell types. These results indicate that both NALM6 and BSC40 cells possess virus-activating proteases similar to that of LLCMK2 cells, but suggest that the enzyme of NALM6 may be slightly different in its substrate specificity from those of BSC40 and LLCMK2. The results also suggest that the virus-activating proteases are different in their distribution and substrate specificity from the processing enzyme of POMC.

Detection of cytomegalovirus in urine samples by an enzyme-linked immunosorbent assay using a monoclonal antibody against the viral 150-kilodalton protein

McKeating et al. (J.A. McKeating, P.D. Griffiths, and J.E. Grundy, J. Gen. Virol. 68:785-792, 1987; J. A. McKeating, J. E. Grundy, Z. Varghese, and P. D. Griffiths, J. Med. Virol. 18:341-348, 1986; J. A. McKeating, S. Stagno, P. R. Stirk, and P. D. Griffiths, J. Med. Virol. 16:367-373, 1985) reported previously that beta 2 microglobulin inhibits the detection of human cytomegalovirus (CMV) in urine specimens by an enzyme-linked immunosorbent assay (ELISA) with a monoclonal antibody against the glycoprotein of CMV. They postulated that beta 2 microglobulin binds to the viral glycoproteins and masks the antigenic determinants. We developed here an ELISA method for the detection of CMV in urine by using a monoclonal antibody against the viral 150-kDa protein to capture the viral antigen. This assay detected CMV both in culture medium and in urine specifically at concentrations higher than 10(3) PFU/ml and quantitatively at concentrations higher than 10(4) PFU/ml. The sensitivity of the ELISA increased about 10-fold when peroxidase-labeled F(ab')2 from goat anti-human immunoglobulin G was used as a secondary detecting antibody in combination with concentration of the virus in urine samples by ultracentrifugation. The inhibition of ELISA by beta 2 microglobulin was not observed in this ELISA system. When 56 urine specimens from renal transplant recipients were examined for CMV antigens, the ELISA system had a sensitivity of 78% and a specificity of 97%. The positive and negative predictive values of the assay were 95 and 86%, respectively. Furthermore, CMV antigens in urine were quantitated by the assay during the course of typical CMV disease of renal transplant recipient. These results suggest strongly that the measurement of CMV antigens in urine by our rapid and quantitative ELISA system provides very useful data for the monitoring of CMV infections in renal transplant recipients and making decisions about therapy.

Identification of endoprotease activity in the trans Golgi membranes of rat liver cells that specifically processes in vitro the fusion glycoprotein precursor of virulent Newcastle disease virus

A ubiquitous host endoprotease(s) responsible for activation of the fusion glycoprotein precursor (F0) of virulent Newcastle disease virus (NDV) is an important determinant for its spreading and organ tropism in the host. To characterize the virus-activating protease (VAP), we isolated endoprotease activity from the trans Golgi membranes of rat liver cells by using F0-containing NDV particles grown in a lymphoid cell line NALM6 as substrate. The enzyme cleaved in vitro only the F0 protein of virulent NDV but not that of an avirulent strain, suggesting that it specifically recognizes pairs of basic residues at the cleavage site. Furthermore, the enzyme was found to be membrane-bound, calcium ion-dependent, and active over a broad pH range, from 6 to 8. The inhibitor spectrum of the protease together with the enzyme properties described above indicates that it is a KEX2-like enzyme. Experiments using monensin, A23187, and chloroquine indicate that the F0 cleavage of virulent NDV occurs normally in rat primary hepatocytes at or before the trans Golgi and is a calcium-dependent process. The correspondence between the characteristics of the cleavage in rat hepatocytes and those of the rat protease in vitro indicates that the endoprotease is a strong candidate for the VAP that determines the pantropic nature of virulent NDV.

Immediate protection of mice from lethal wild-type Sendai virus (HVJ) infections by a temperature-sensitive mutant, HVJpi, possessing homologous interfering capacity

Protection of mice from lethal Sendai virus (HVJ) infections by a temperature-sensitive mutant, HVJpi, which was isolated from a carrier culture, was studied. HVJpi had a strong interfering capacity with the replication of virulent wild-type virus in LLCMK2 cells. When a high dose of HVJpi (3.0 x 10(7) CIU) was inoculated intranasally into mice, the mice showed neither illness nor lung lesions but gained significant resistance against the challenge of virulent wild-type virus (18 LD50) immediately after inoculation. In contrast, the mice inoculated with a lower dose of HVJpi (8.2 x 10(5) CIU) did not show the immediate resistance but became immune several days after inoculation. Time courses of the virus replication in the lung revealed that the replication of wild-type virus was strongly suppressed to about 1/1000 by the simultaneous infection with a high dose of HVJpi, thus resulting in minimizing the lung lesions and survival of all the mice infected. Neither interferon nor natural killer cells appeared to play a major role in the immediate immune status by HVJpi, since no difference was observed in protection of mice simultaneously infected with wild-type virus and HVJpi in spite of pretreatment of the mice with anti-interferon and anti-asialo GM1 antibodies as compared with that of the untreated doubly infected mice. On the other hand, it was suggested by analysis of viral polypeptides synthesized in the lung of infected mice by Western blotting that the early stage of replication of wild-type virus in the lung was inhibited mainly by the interfering capacity of HVJpi. These results indicate that HVJpi is an unique virus mutant which is capable of protecting mice from lethal Sendai virus infections by its interfering capacity immediately after inoculation and then by the induction of virus-specific immune responses.

Endoproteolytic activation of Newcastle disease virus fusion proteins requires an intracellular acidic environment

Effects of weak bases, chloroquine and ammonium chloride, on the intracellular cleavage of the fusion protein precursor (F0) were examined in BHK cells infected with a virulent strain of Newcastle disease virus (NDV). Most of F0 molecules synthesized during a 15-min pulse period were chased out because of cleavage into F1 and F2 within a 60-min chase period in the absence of the weak bases. In contrast, significant amounts of the precursor were found to remain uncleaved when chloroquine or ammonium chloride was present. The uncleaved fusion proteins were incorporated into progeny virions as efficiently as cleaved ones, and about the half of fusion proteins were present as F0 in the virion released by the cells treated with 0.3 mM chloroquine. Taken together with the finding that the trans cisternae of Golgi apparatus and forming secretory vesicles have an acidic pH (K. G. W. Anderson and R. K. Pathak, Cell, 40, 685-643, 1985), the present results suggest that an acidic environment in these compartments is required for intracellular proteolytic activation of NDV fusion proteins.

Enzymological characteristics of avian influenza A virus neuraminidase

Neuraminidases of 18 strains of avian influenza A virus were examined by both colorimetric and fluorometric assays using fetuin and 4-methylumbelliferyl-N-Ac-alpha-D-neuraminide as substrates, respectively, to compare them with those of human influenza A and B viruses. The ratios of the neuraminidase activity of avian influenza virus measured by the colorimetric assay method to that measured by the fluorometric assay were distributed in the range of 2.4-20.3. The enzyme of avian influenza virus showed calcium-ion dependence in both assay methods. These results suggest that neuraminidase of avian influenza A virus is varies greatly from one strain to another in substrate specificity as compared with those of human influenza A and B viruses, and that some strains of avian influenza A virus have a neuraminidase with unique enzymological characteristics different from that of human influenza A virus as well as that of influenza B virus.

Enzymological heterogeneity of influenza B virus neuraminidase demonstrated by the fluorometric assay method

The neuraminidase activity of 26 strains of influenza B virus isolated from all over the world was investigated colorimetrically, using fetuin as a substrate, and fluorometrically, using 4-methylumbelliferyl(4-MU)-N-Ac-alpha-D-neuraminide as a substrate, with special reference to enzymological heterogeneity. The activity of influenza A viral neuraminidases and of a commercially available pure viral one was strongly inactivated by either ethylenediaminetetraacetic acid or glycoletherdiaminetetraacetic acid, when measured by the fluorometric assay method, whereas that of influenza B ones was not at all. However, the viral neuraminidases of both influenza A and B viruses were found to be calcium ion-dependent by the colorimetric assay method. A difference in the catalytic rate between the two assay methods was observed with influenza B viral neuraminidase to a much greater extent as compared with that of influenza A. A difference in substrate specificity of these enzymes was demonstrated to be due to a difference in the degree of competitive inhibition by N-acetylneuraminic acid. These findings strongly suggest that enzymological heterogeneity in influenza B viral neuraminidase may be attributed to delicate structural differences, between the enzymes of influenza A and B viruses demonstratable only by the fluorometric neuraminidase assay method using 4-MU-N-Ac-alpha-D-neuraminide as a substrate.

Purification and characterization of beta-glucuronidase inhibitor from Mycobacterium tuberculosis

Factors inhibitory to beta-glucuronidase were found in the culture filtrate and in a bacillary extract of Mycobacterium tuberculosis H37Rv grown for 6 weeks on Sauton medium. The inhibitors were purified by ammonium sulfate fractionation, treatment with n-butanol and streptomycin, and chromatography on DEAE-Sepharose CL-6B. Two inhibitors were obtained from the culture filtrate. The molecular weights were estimated to be 25,500 and 15,500 by gel filtration on a Sephadex G-75 column. Three inhibitors were purified from the bacillary extract, two of which were similar to those from the culture filtrate. The molecular weight of the third inhibitor was 21,000. However, the molecular weight of all the denatured inhibitors was 8,600 in the presence of sodium dodecyl sulfate. The inhibitors contained extremely high amounts of glutamic and aspartic acids and had a highly acidic isoelectric point of pH 2.5. The inhibitors acted noncompetitively against beta-glucuronidase of guinea pig origin at an optimal pH 4.5. beta-Glucuronidases from human peripheral leukocytes and beef liver were partially sensitive to the inhibitors; all the other enzymes tested for sensitivity were unaffected by the inhibitors.

A new heat-stable acid phosphatase test for mycobacteria

The heat-stable (70degrees C) acid phosphatase test performed by the method of Kind and King is a simple method for differentiating Mycobacterium kansasii, M. marinum, M. gastri, M. nonchromogenicum, and M. triviale from other slowly growing mycobacteria, and M. fortuitum from other rapidly growing acid-fast bacilli.