Title:  Hepatitus A virus vaccines

United States Patent:  6,680,060

Issued:  January 20, 2004

Inventors:  Funkhouser; Ann W. (Laurel, MD); Emerson; Suzanne U. (Rockville, MD); Purcell; Robert H. (Boyds, MD); D'Hondt; Eric (Ottenburg, BE)

Assignee:  The United States of America as represented by the Department of Health and (Washington, DC)

Appl. No.:  135988

Filed:  April 29, 2002

Abstract

A live hepatitis A virus adapted to growth in MRC-5 cells, which HAV is preferably characterized by suitable attenuation for effective vaccine administration to humans and animals without inactivation, methods for adapting HAV to growth in MRC-5, vaccine compositions and method of vaccinating humans against HAV infection.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a live hepatitis A virus adapted to growth in MRC-5 cells. This virus is preferably characterized by attenuation. The attenuated virus may be recombinant or chimeric. More preferably, the HAV is characterized by suitable attenuation for effective vaccine administration to primates or humans, without inactivation. The HAV may be characterized by containing one or more of sixteen specific nucleotides which differ from nucleotides in the same position in the genome of HAV HM-175, Pass 35.

In another aspect, the invention provides a vaccine useful for protecting humans or other primates against hepatitis A which vaccine contains at least one above-described HAV adapted to growth in MRC-5 cells. Preferably, the vaccine is effective in inducing a protective antibody response without adjuvant.

In still another aspect, the invention provides a method for protecting humans against hepatitis A virus infection which comprises administering to the human patient an effective amount of a vaccine composition of this invention.

In a further aspect, the invention provides a method for preparing a live HAV adapted to growth in MRC-5 cells by incorporating into a selected area of the genome of an HAV one or more of thirteen specific nucleotides. The HAV genome so modified is preferably HAV HM-175, Pass 35 [SEQ ID NO: 3] or a related cell culture-adapted mutant.

In another embodiment, the HAV may be constructed using another HAV cDNA clone and inserting appropriate nucleotides into its genome. According to this method an attenuated, MRC-5-adapted HAV is provided without requiring further passaging in MRC-5 or other primate cell lines.

In still another aspect, the invention provides polynucleotide sequences encoding the recombinant or chimeric HAVs described above. Preferably these sequences are cDNAs useful as master seeds for vaccine preparation.

Other aspects and advantages of the present invention are described further in the following detailed description of the preferred embodiments thereof.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides hepatitis A virus (HAV) adapted to growth in the human fibroblast-like cell line, MRC-5, a cell substrate suitable for commercial production and licensing of inactivated and live, attenuated hepatitis A vaccines. In addition to such adapted HAVs, the invention provides a method for adapting a selected HAV to growth in that human cell line and preparing an MRC-5-adapted, attenuated HAV without passaging in other primate cells. The HAV of this invention and the preparative method also preferably provides the HAV with sufficient attenuation to enable its efficacy as a vaccine for humans and animals.

Although the prior art discloses other candidate vaccine strains of hepatitis A virus which have been adapted to growth in human diploid fibroblasts, the genetic changes in the virus genome necessary and sufficient for such adaptation have not been characterized. Thus, these strains cannot be manipulated in vitro to assure a reproducible and fully-characterized vaccine product.

The present invention is based on the wild-type HAV, strain HM-175, which is described in detail in the above-cited and incorporated art [Cohen et al., J. Virol., 61:50-59 (1987); SEQ ID NOS: 1 and 2]. Briefly described, the wild type, infectious HAV HM-175 virus was previously adapted to growth in primary African green monkey kidney (AGMK) cells at 37^oC. After 26 passages in AGMK, the virus was cloned three times in AGMK cells by serial dilution, then passaged three more times to provide passage 32 (P-32). P-32 was found to be attenuated as described in R. A. Karron et al, J. Infec. Dis., 157:338-345 (1988).

The P-32 virus described above was passaged three more times in AGMK, and molecularly cloned. The virus that was cloned was called P-35 and the full-length clone was referred to as-pHAV/7 [SEQ ID NOS: 3 and 4]. pHAV/7 is an infectious-cDNA clone of the virus that can be maintained in a monoclonal state and amplified at will with diminished risk of spontaneous mutations. The resulting P-35 virus grew well in fetal rhesus monkey kidney (FRhK) cells and minimally in human fibroblastoid lung cells (MRC-5).

U.S. Pat. No. 4,894,228 and Cohen et al., Proc. Natl. Acad. Sci., USA, 84:2497-2501 (1987) provide the HAV nucleotide sequence of wild-type HAV strain HM-175 (SEQ ID NO: 1) and the nucleotide differences between HAV HM-175, Pass 35, clone pHAV/7 [SEQ ID NO: 3], and the wild-type sequence. Thus, these documents, incorporated by reference, provide the nucleotide sequence of pHAV/7, P-35 [SEQ ID NO: 3]. The nucleotide numbers used herein to which the mutations of this invention correspond (Tables I and VI below) are the nucleotide numbers assigned to positions of the wild-type sequence of FIG. 6 [SEQ ID NOS: 1 AND 2] from U.S. Pat. No. 4,894,228 containing the mutations for P-35. Note that the nucleotides which are deleted from wild-type virus to P-35 are assigned the nucleotide position of the wild-type sequence. Thus, for example, nucleotide position 131 represents a nucleotide that was deleted between wild-type and P-35.

The P-35 cDNA, i.e., HAV/HM-175/7, is on deposit at the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md. under Accession No. 67495, deposited Aug. 7, 1987. One of skill in the art can readily construct the nucleotide and amino acid sequences of P-35 by use of the above-cited art and its deposit. See, also, SEQ ID NOS: 3 and 4.

Yet another HAV virus was provided as follows. The P-32 AGMK cell-adapted and attenuated virus was manipulated to enable it to be adapted for growth in MRC-5 cells, so that it is available for large scale vaccine production. Passage 32 was double plaque cloned in MRC-5 to form Passage 37. A selected clone 25-4-21 of Passage 37 was passaged once in MRC-5. The resulting Passage 38 was passaged three times in MRC-5 cells, resulting in Passage 41, the master seed, designated 87J19. This master seed virus stock is also referred to as HAV 4380 or MRC5/9 (the latter term reflects its ability to grow in MRC5 cell, as well as the fact that it is 9 passages from P32). This virus is referred to throughout this disclosure by the name HAV 4380.

Live attenuated virus HAV 4380, was deposited on Apr. 4, 1990 at the Collection Nationale de Cultures de Microorganismes, Institut Pasteur, 25, rue du Docteur Roux, 75724, Paris CEDEX 15 under Accession No. 1936, which deposited HAV 4380 virus has a nucleic acid sequence shown in SEQ ID NO:5. This deposit was made under the Budapest Treaty on the International Recognition of the Deposit of Microorganisms and has not been publicly disseminated. HAV 4380 is a cell culture-adapted and attenuated strain of hepatitis A virus strain HM-175, adapted to growth in a human fibroblast cell line (MRC-5) suitable for vaccine development by incubation at a reduced temperature of 32-35^oC. Growth of the virus is determined by detection of viral antigen in a serological assay. The adapted virus is purified by plaque-purification, using an accepted method (radioimmunofocus assay).

As stated above, after a total of nine passages in MRC-5 cells at reduced temperature, the resultant virus was examined for its biological characteristics in cell culture and in two primate species that are considered to be surrogates for man, i.e., marmosets and chimpanzees. See, e.g., Example 1 below. The HAV 4380 virus was found to be temperature-sensitive (i.e., only grew at reduced temperatures) in MRC-5 cells but was still capable of growing at 37^oC. in primary African green monkey kidney cells. The virus was further attenuated in virulence, compared to the parent virus HM-175, P-32, when tested in chimpanzees and marmoset monkeys, in which species the virus replicated poorly or not at all. This reduced capacity for replication in primates was further confirmed in human volunteers, as described in Example 2.

A candidate inactivated hepatitis A vaccine was prepared from the HAV 4380 and demonstrated to be safe (i.e., it does not produce hepatitis or other serious adverse effects) and immunogenic in humans. It was also found to induce antibody production without adjuvant. HAV 4380, as it currently exists, grows well in a cell substrate suitable for commercial vaccine production. It also does not infect human beings when administered by the oral or intravenous route at doses of up to 10⁷ tissue culture infectious doses, even when not inactivated. HAV 4380 is suitable for use as a live HAV vaccine in humans. However, as indicated in Example 2, vaccine 4380 is believed to be somewhat over-attenuated, because it is not infectious, which characteristic reduces its efficiency when used as an attenuated vaccine.

In order to produce other vaccine candidates which are maximized for desirable levels of attenuation and good growth in MRC-5 cells, the inventors determined the genetic changes that occurred in the genome of the MRC-5-adapted HAV 4380 virus that altered its growth characteristics and made it more suitable for vaccine production than the related AGMK-adapted virus HM-175, Passage 35 [SEQ ID NO: 3]. The discovery of the following mutations in the nucleotide sequences in HAV 4380, when compared to HM-175 Pass 35 [SEQ ID NO: 3; Cohen et al, cited above; and U.S. Pat. No. 4,894,228], permit the manipulation of the HAV genome by genetic engineering techniques.

Thus, knowledge of the genomic differences between the AGMK-adapted passages of HM-175 and the more attenuated 4380 permit the construction of chimeric viruses having the improved growth characteristics, i.e., rapid and efficient growth in MRC-5 cell culture, but with a level of attenuation of virulence for primate species, including man, that will permit the virus to replicate efficiently without producing hepatitis or other untoward effects. This invention permits the design of a chimeric HAV that can achieve the optimum characteristics for a candidate live-attenuated hepatitis A vaccine. Such a virus will also permit the design of preferred inactivated vaccine candidates, if desired. The present invention identifies the mutations that are believed to have occurred during adaptation to growth of the HM-175 HAV, passage 32, strain in MRC-5 cells. One or a combination of these mutations are responsible for MRC-5 cell adaptation and overattenuation in HAV 4380.

The nucleotide sequence of the MRC-5 cell-adapted virus HAV 4380 was compared with that of the AGMK-adapted, HM-175 virus, passage 35, clone 7 [SEQ ID NO: 3]. Nucleotide consensus sequences were determined directly from polymerase chain reaction products.

The inventors have discovered that there are at least sixteen unique nucleotide differences between the Pass-35 HM-175/7 virus and the MRC-5-adapted virus 4380. Table I lists these sixteen mutations by nucleotide differences and resulting amino acid (AA) differences, if any, acquired by the MRC-5-adapted virus HAV 4380. Note that the partial sequence of LSH/S HAV of Fineschi et al., cited above, overlaps with only the mutation observed at position 5145.

In the Table, A represents adenine, G represents guanine, C represents cytosine, and T represents thymine; Leu represents leucine, Phe represents phenylalanine, Ile represents isoleucine, Val represents valine, Ser represents serine, Lys represents lysine, Asn represents asparagine, Thr represents threonine and Arg represents arginine. Note that the nucleotide positions in Table I correspond with the nucleotide positions of wt HM-175. This is true for all nucleotide positions referred to throughout this specification.

Note that two previously reported changes at nucleotide position 2864 from U to A in VP1, resulting in no amino acid change, and at nucleotide position 6216 from U to C in 3D, resulting in no amino acid change, are nucleotides that were actually present in a subset of HM175 wild-type cDNA clones made from virus before passage in cell culture. These changes occur due to microheterogeneity in some wild-type subpopulations of HM-175/7, as reported in Cohen, Proc. Natl. Acad. Sci., USA, 84:2497 (1987) and Cohen, J. Virol., 61:50 (1987), cited above. These nucleotides were present in the wt HM-175 sequence used to prepare HAV 4380.

The nucleotide changes at positions 2750, 3027 and 7255 were previously unreported. However, all of these nucleotide changes are contained in the HAV 4380 deposited virus.

A nucleotide change at nucleotide position 6383 from a C to a U in region 3D of the HAV genome, which would cause no change in amino acid sequence, has also been detected in some clones. This change is also believed to occur in some HAV strains due to microheterogeneity in the Virus 4380, since it was not present in a PCR consensus sequence, but was present in a subclone used to make a full length virus cDNA.

New HAV vaccine candidates are designed by introducing one or more of the nucleotides mentioned in Table 1 and discussed above into an HAV at a nucleotide position homologous to the nucleotide position in the genomic sequence of the wt HM-175 [SEQ ID NO:1 ] or the AGMK-adapted virus HM-175, Pass 35 [SEQ ID NO: 1]. These nucleotides identified in Table I may be introduced at analogous and/or homologous nucleotide positions to those of P-35 in the genomic sequences of other HAV strains and variants to produce a recombinant or chimeric HAV of this invention. By the phrase "analogous or homologous nucleotide position" is meant a nucleotide in an HAV other than HAV HM-175, Pass 35 which is present in the same viral region, e.g., 2C, 3D and the like, at a position in that region similar to that of the nucleotide of Table I. In other words, the nucleotide position may differ in position number due to deletions in other regions of the virus; but one of skill in the art can readily determine its functional similarity to the nucleotide position in HM-175 [SEQ ID NO: 1] or in HM-175, Pass 35 [SEQ ID NO: 3].

While such nucleotide positions may not have the identical nucleotide position numbers corresponding to the wild-type HM-175 [SEQ ID NO: 1], it is anticipated that these analogous and/or homologous positions can be readily identified to enable HAVs other than strain HM-175 derivatives to be modified to create novel HAVs according to this invention.

Similarly, the inventors are able to manipulate the genome of a progenitor or intermediate of HAV 4380 with resort to this knowledge and can thereby `reverse` certain mutations in 4380 to create new chimeric HAV viruses. One or more of these nucleotides, or varying combinations thereof, can be incorporated, by chimera formation or oligonucleotide-directed mutagenesis, into an HAV strain, most readily the cDNA clone HAV/HM-175/7, to produce new viable virus which has acquired the ability to grow in MRC-5 cells. Other EM-175 HAV derivatives are available from the American Type Culture Collection under ATCC designation numbers VR 2089, VR 2090, VR 2091, VR 2092, VR 2093, VR 2097, VR 2098, and VR 2099. These and other HAVs may be employed to derive desired HAVs of this invention. Since there are indications that the MRC-5-adapted virus 4380 may be over-attenuated for humans, it is important to be able to remove or introduce selected mutations into HM-175. The construction of nine exemplary chimeric viruses containing one or more such mutations is described in detail in Example 3 below.

The mutagenic and genetic engineering techniques employed to construct chimeric or recombinant HAVs which incorporate one or more of these mutations are conventional and known to those of skill in the art [see, for example, Sambrook et al., Molecular Cloning. A Laboratory Manual, 2d edition, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., (1989)]. Other conventional techniques, including polymerase chain reactions and chemical synthetic techniques may also be used to design HAVs of this invention. Similarly, it is anticipated that homologous mutations may be made using other HM-175 passages. It also may be possible to adapt similar changes to HAV strains other than HM-175 by introducing these nucleotides into homologous regions.

Chimeric and recombinant viruses of this invention may be designed by application of similar techniques and selecting one or more different combinations of the nucleotides (mutations) appearing in Tables I and VI. For example, data from growth analyses of the chimeric viruses of Example 3 demonstrate that one or more of the four MRC-5 specific mutations in the 5' non-coding region (mutations at nucleotide positions 591, 646, 669, and 687 of HM-175/7) and one or both of the MRC-5 specific mutations in the 2C region (mutations at nucleotide positions 4418 and 4643 of HM-175/7) are desirable for optimal growth of the virus in MRC-5 cells.

Additional viruses employing other combinations of these mutations were prepared by conventional cloning and PCR techniques. When acting together and in the presence of the 5' non-coding and 2C mutations of Table I, MCR-5- specific mutations in P3 and VP1/2AB in every instance increased growth efficiency in MRC-5 cells. Similarly it was noted that the mutations in the 5' non-coding region increased growth efficiency in every virus and in different background genotypes. Studies have shown that the 5' non-coding mutations can reduce biochemical evidence of hepatitis. Other mutations may also be involved.

Specific exemplary chimeric HAVs of this invention are characterized by the mutations in the genome of HAV HM-175/7 that appear in viruses designated #2 through #10 in Table VI of Example 3 below. However, other chimeric HAVs may be readily prepared by application of the same methods known to those of skill in the art.

HAVs of this invention may be characterized by the presence of one or more of these nucleotides of Tables I or VI in analogous genomic positions of HAV HM-175 derivatives or other HAV strains. HAVs of this invention may also be characterized by two or more such nucleotides, where one nucleotide in the HAV parent strain is a guanine (G) at position 5145 of pHAV/7 or the analogous position of another HAV strain.

It is further anticipated that additional mutations may appear in a few regions of HAV that have yet to be sequenced. The mutations appearing in Table I may be incorporated in any combination, and/or with other mutations yet to be identified to construct a number of chimeric or recombinant HAVs with desired characteristics for use as live HAV vaccines.

Additional chimeras and recombinant viruses constructed by oligonucleotide-directed mutagenesis may be designed and evaluated for assessment of the individual effects of the mutations and combinations thereof on viral growth in MRC-5 cells and on adaptation to growth in selected cell culture. The attenuation phenotype of these chimeric viruses may be evaluated in marmosets or chimpanzees by techniques such as described below in Example 1 for HAV 4380.

Also provided by this invention are the polynucleotide sequences encoding the HAVs of this invention. Such polynucleotide sequences are preferably cDNA sequences, which can form a master seed for the HAV vaccine. A cDNA sequence of this invention comprises a DNA sequence encoding a selected HAV genome characterized by the presence of one or more of the nucleotides identified as the thirteen mutations in Table I in any desired combination which imparts desired characteristics to the novel HAV. Such cDNAs may be obtained by conventional techniques known to those of skill in the art. See, e.g., Sambrook et al, cited above, and U.S. Pat. No. 4,894,228.

Thus, the present invention provides a live vaccine composition useful in protecting against HAV infection and a prophylactic method entailing administering to a primate, preferably a human, an effective amount of such a composition. This vaccine composition may contain one or more of the HAVs of the invention, including HAV 4380, as well as the chimeric and recombinant HAVs described herein. The vaccine composition may also contain mixtures of two or more of the HAVs, if desired.

A vaccinal composition may be formulated to contain a carrier or diluent and one or more of the HAVs of the invention. Suitable pharmaceutically acceptable carriers facilitate administration of the viruses but are physiologically inert and/or nonharmful. Carriers may be selected by one of skill in the art. Exemplary carriers include sterile saline, lactose, sucrose, calcium phosphate, gelatin, dextrin, agar, pectin, peanut oil, olive oil, sesame oil, and water. Additionally, the carrier or diluent may include a time delay material, such as glycerol monostearate or glycerol distearate alone or with a wax. In addition, slow release polymer formulations can be used.

Optionally, the vaccine composition may further contain preservatives, chemical stabilizers, other antigenic proteins, and conventional pharmaceutical ingredients. Suitable ingredients which may be used in a vaccinal composition in conjunction with the viruses include, for example, casamino acids, sucrose, gelatin, phenol red, N-Z amine, monopotassium diphosphate, lactose, lactalbumin hydrolysate, and dried milk. Typically, stabilizers, adjuvants, and preservatives are optimized to determine the best formulation for efficacy in the target human or animal. Suitable preservatives include chlorobutanol, potassium sorbate, sorbic acid, sulfur dioxide, propyl gallate, the parabens, ethyl vanillin, glycerin, phenol, parachlorophenol.

A vaccine composition of this invention is most preferably produced without an adjuvant. However, where necessary, one or more of the above described vaccine components may be admixed or adsorbed with a conventional adjuvant. The adjuvant is used as a non-specific irritant to attract leukocytes or enhance an immune response. Such adjuvants include, among others, mineral oil and water, aluminum hydroxide, Amphigen, Avridine, L121/squalene, D-lactide-polylactide/glycoside, pluronic plyois, muramyl dipeptide, killed Bordetella, saponins, and Quil A.

Alternatively, or in addition to the HAV of the invention, other agents useful in treating HAV infection, e.g., immunostimulatory agents, are expected to be useful in reducing and eliminating disease symptoms. The development of vaccine or therapeutic compositions containing these agents is within the skill of one of skill in the art in view of the teaching of this invention.

According to the method of the invention, a human or an animal may be vaccinated against HAV infection by administering an effective amount of a vaccine composition described above. An effective amount is defined as that amount of HAV vaccine capable of inducing protection in the vaccinee against HAV infection and/or against hepatitis. The vaccine may be administered by any suitable route. Such a composition may be administered parenterally, preferably intramuscularly or subcutaneously. However, it may also be formulated to be administered by any other suitable route, including orally.

Suitable effective amounts of the HAVs of this invention can be determined by one of skill in the art based upon the level of immune response desired. Such a composition may be administered once, and/or a booster may also be administered. However, suitable dosage adjustments may be made by the attending physician or veterinarian depending upon the age, sex, weight and general health of the human or animal patient.

Similarly, suitable doses of the vaccine composition of the invention can be readily determined by one of skill in the art. The dosage can be adjusted depending upon the human patient or the animal species being treated, i.e. its weight, age, and general health.

Claim 1 of 10 Claims

What is claimed is:

1. An isolated DNA molecule encoding a hepatitis A virus adapted to growth in MRC-5 cells, said molecule having a nucleotide sequence which corresponds to the cDNA sequence of HAV HM-175 Pass 35 (SEQ ID NO: 3) except for nucleotide positions 591 and 687 which have guanines as bases, nucleotide position 646 which has an adenine as a base and nucleotide position 669 which has a thymine as a base, and optionally at least one nucleotide selected from the group consisting of:

(a) T at position 2750;

(b) A at position 3027;

(c) A at position 3196;

(d) G at position 3934;

(e) I at position 4418;

(f) G at position 4563;

(g) T at position 4643;

(h) G at position 5145;

(i) T at position 5745;

(j) C at position 6908;

(k) T at position 7032;

(l) T at position 7255;

wherein the nucleotide numbers shown above are those assigned to positions of the wild-type HM-175 sequence.

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