Vaccine for Use in Protecting a Pig Against Porcine Endemic Diarrhea Virus

Abstract

The invention pertains to a vaccine for use in protecting a pig against an infection with porcine endemic diarrhea virus (PEDV), the vaccine comprising non-live PEDV antigen and a non-metabolizable oil containing adjuvant, wherein the total amount of oil in the vaccine is less than 50% v/v, by administration of a dose of the antigen corresponding to at least 3.0E6 TCID50 killed whole PEDV. The invention also pertains to a method of protecting a pig against an infection with porcine endemic diarrhea virus.

Claims

1. (canceled)

2. The method of claim 11, wherein the dose of the antigen corresponds to at least 1.5E7 TCID.sub.50 killed whole PEDV.

3. The method of claim 11, wherein the total amount of the oil is less than 40% v/v.

4. The method of claim 11, wherein the oil is emulsified in an hydrophilic solvent.

5. The method of claim 11, wherein the vaccine in addition to the non-metabolizable oil comprises vitamin E acetate.

6. The method of claim 11, wherein the antigen contains a polypeptide that corresponds to the C terminal two-third of the S1 domain of the spike protein of PEDV.

7. The method of claim 6, wherein the polypeptide corresponds to the S1 domain of the spike protein of PEDV.

8. The method of claim 7, wherein the polypeptide corresponds to the spike protein of PEDV.

9. The method of claim 11, wherein the antigen is killed whole PEDV.

10. The method of claim 11, wherein the vaccine is for administration to a sow to protect the off-spring of this sow against an infection with porcine endemic diarrhea virus (PEDV).

11. A method to protect a pig against an infection with porcine endemic diarrhea virus (PEDV) comprising administering to the pig a vaccine comprising non-live PEDV antigen and a non-metabolizable oil containing adjuvant, wherein the total amount of oil in the vaccine is less than 50% v/v, and the antigen is administered at a dose corresponding to at least 3.0E6 TCID.sub.50 killed whole PEDV.

12. A vaccine to protect a pig against an infection with porcine endemic diarrhea virus (PEDV) comprising non-live PEDV antigen and a non-metabolizable oil containing adjuvant, wherein the total amount of oil in the vaccine is less than 50% v/v, and the antigen is present in a concentration corresponding to at least 1.5E6 TCID.sub.50 killed whole PEDV per ml.

Description

EXAMPLES

Example 1 Virus Neutralization Assay

[0023] Sera were tested for the presence of neutralizing antibodies against PEDV using a virus neutralization (VN) assay on Vero cells. Briefly, serial two-fold dilutions of the test samples or reference sera were prepared in aMEM-TPB cell culture medium containing the antibiotics penicillin and streptomycin. Each dilution was mixed with an equal volume of 100 TCID.sub.50 of an infectious PEDV strain that expresses green fluorescent protein (GFP) upon infection of susceptible Vero cells. After a pre-incubation period of 1 hour at 37° C., virus/serum dilution mixtures were transferred to 96-well microtitre plates containing Vero-CCL81 cells. After incubation for 48 hours at 37° C., the extent of GFP fluorescence indicative for virus replication was determined by microscopy. The antibody titre was calculated as log 2 of the reciprocal of the highest serum dilution where no virus replication could be demonstrated. Obtained VN titres are presented as averages calculated from duplicate measurements.

[0024] This way, it was established that VN titres in wild-type PEDV infected pigs that survived the infection are at a level of 5.0 log 2 per ml or higher, with peak levels at 8.0 to 9.0 log 2.

Example 2 the Influence of the Type of Adjuvant

Study Design

[0025] Twenty piglets seronegative for PEDV were available for this trial. When the piglets were approximately five weeks old they were vaccinated via the intramuscular (IM) route, and boosted two weeks thereafter. All applications were given into the neck. The vaccines contained 1.5.Math.10.sup.7 TCID.sub.50 of 1 mM binary ethyleneimine (BEI) inactivated killed whole PEDV (cell culture adapted DR13) in 2 ml. Blood samples were collected right before the first vaccination, and one, two, three, four, and five weeks thereafter. Serum was collected from the blood samples and the virus neutralizing antibody titre was determined. Rectal temperatures were measured on the day of and one day after each vaccination.

[0026] The animals were divided over four groups of five animals each (see Table 1). The first group received the killed whole virus vaccine formulated in the commercially available adjuvant XSolve™ (available from MSD Animal Health, Boxmeer, The Netherlands), such that the final vaccine comprises 21% v/v of the non-metablizable oil Marcol™ 52 and 1.25% v/v of the metabolizable oil vitamin E acetate. The second group received the same antigen, formulated in the commercially available adjuvant Diluvac Forte™ (available from MSD Animal Health, Boxmeer, The Netherlands), such that the final vaccine comprises 7.5% v/v of the metabolizable oil vitamin E acetate. The third group received the same antigen formulated in the alum hydrogel containing vaccine ProSystem™ CE (available from Merck Animal Health, USA). The fourth group received the same antigen formulated in water without adjuvant.

TABLE-US-00001 TABLE 1 Overview of animal groups and their treatment Group # piglets PEDV antigen Dose Adjuvant 1 5 Killed whole virus 1.5E7 TCID.sub.50 XSolve 2 5 Killed whole virus 1.5E7 TCID.sub.50 Diluvac Forte 3 5 Killed whole virus 1.5E7 TCID.sub.50 ProSystem CE 4 5 Killed whole virus 1.5E7 TCID.sub.50 —

Results

Body Temperature

[0027] An overview of the mean body temperatures per group are shown in Table 2. It can be concluded that none of the vaccines caused a serious temperature elevation of more the 1° C., and that XSolve induced the largest temperature increase of the three adjuvants tested. The highest individual temperature increase observed in this group was 1.7° C.

TABLE-US-00002 TABLE 2 Mean rectal temperatures taken after the first or second vaccination. Temperature after 1.sup.st Temperature after 2.sup.nd vaccination vaccination t = t = t = t = Group Vaccine 0 h t = 4 h 24 h 0 h t = 4 h 24 h 1 XSolve 39.60 40.02 39.94 39.94 40.72 40.20 2 Diluvac Forte 39.90 40.14 39.68 40.03 40.60 39.94 3 ProSystem CE 39.54 40.16 39.76 39.89 40.18 39.84 4 No adjuvant 39.90 39.84 39.52 39.76 40.31 39.88

Virus Neutralization Assay

[0028] The calculated mean VN titres of each group are graphically presented in FIG. 1. It can be concluded that killed whole virus antigen is able to induce good VN titres. The contribution by the adjuvants is such that the adjuvant based on the non metabolizable oil gives the highest titres, followed by the adjuvant based on the metabolizable oil, thereafter followed by the adjuvant based on alum hydroxide gel.

Example 3 the Influence of the Type of Non-Live Antigen

Study Design

[0029] Sixty piglets seronegative for PEDV were available for this trial. When the piglets were approximately five weeks old they were immunized with 2 ml vaccine via the intramuscular (IM) route, and boosted three weeks thereafter. All applications were given into the neck. An overview of the experimental groups is given in Table 3. Blood samples were collected before the first vaccination, and two, three, four, five, and six weeks thereafter. Serum was collected from the blood samples and the virus neutralizing antibody titre was determined. Rectal temperatures were measured on the day of vaccination and 4 and 24 hours thereafter. After each vaccination all piglets were palpated at two, four, six, eight, ten, 12, and 14 days post vaccination on the site of administration.

TABLE-US-00003 TABLE 3 Overview of animal groups and their treatment Non live PEDV antigen Dose Group # piglets Name Type (in 2 ml) 1a 5 US S1 full-length S1of US strain 10 μg 1b 5 US S1-C C-domain of S1 of US strain 10 μg 2a 5 US S1-pFc full-length S1 of US strain + 10 μg Fc domain of porcine IgG 2b 5 US S1-Fc full-length S1 of US strain + 10 μg Fc domain of human IgG 3a 5 US S1-C-Fc C-domain of Spike of US 10 μg strain + Fc domain of human IgG 3b 5 US S1-N-Fc N-domain of Spike of US 10 μg strain + Fc domain of human IgG 4  10 DR13 KV 1 mM BEI inactivated 6.0 .Math.10.sup.5 caDR13-ESMN-ΔORF3 TCID.sub.50 5  10 DR13 KV 1 mM BEI inactivated 3.0 .Math. 10.sup.6 caDR13-ESMN-ΔORF3 TCID.sub.50 6  10 DR13 KV 1 mM BEI inactivated 1.5 .Math. 10.sup.7 caDR13-ESMN-ΔORF3 TCID.sub.50

Materials and Methods

Subunit Vaccines

[0030] The antigens present in the subunit vaccines used in this study were based on the S1 domain of the PEDV spike (5) protein. The S1 amino acid sequence was derived from a US isolate which is identical to the index strain USA/Colorado/2013. The full-length S1 domain as well as the N-terminal one-third or C-terminal two-third of the S1 domain were used. To facilitate protein purification and to improve immunogenicity, some S1 proteins were C-terminally tagged with an Fc fragment derived from either human or porcine immunoglobulins. All proteins were expressed in HEK293T cells, purified, and the protein content was determined. Briefly, the HEK293T cells were transfected with expression plasmids encoding the required polypeptide of PEDV (optionally with a mouse Fc tag). One day after transfection, cell culture fluid was replaced by fresh medium. Six days after transfection, the cell culture medium was collected and cleared by centrifugation. The polypeptide was subsequently purified by binding to protein-A sepharose beads. After allowing the polypeptide to bind to the beads, it was washed three times using PBS, and the polypeptide was eluted in 0.5M HAc pH 3. The pH was neutralized by using 3M Tris pH 8.8 (final pH 7.5). Finally, the polypeptide concentration was determined at OD.sub.280 using a nanodrop. The polypeptide was stored at −80° C.

[0031] An overview of the S1 proteins is given in FIG. 2. The subunit vaccines were formulated at 10 μg of S1 protein per 2 ml dose in XSolve.

Killed Virus Vaccines

[0032] The KV vaccines contained killed whole PEDV, inactivated with 1 mM BEI. The strain, cell culture adapted D13, shares 93.3% of its amino acids with USA/Colorado/2013. The KV antigens were formulated as a ready-to-use formulations in XSolve.

Virus Neutralization Assay

[0033] Sera were tested for the presence of neutralizing antibodies against PEDV using a virus neutralization (VN) assay on Vero cells. Briefly, serial two-fold dilutions of the test samples or reference sera were prepared in aMEM-TPB cell culture medium containing the antibiotics penicillin and streptomycin. Each dilution was mixed with an equal volume of 100 TCID.sub.50 of an infectious PEDV strain that expresses green fluorescent protein (GFP) upon infection of susceptible Vero cells. After a pre-incubation period of 1 hour at 37° C., virus/serum dilution mixtures were transferred to 96-well microtitre plates containing Vero-CCL81 cells. After incubation for 48 hours at 37° C., the extent of GFP fluorescence indicative for virus replication was determined by microscopy. The antibody titre was calculated as log 2 (per 50 μl) of the reciprocal of the highest serum dilution where no virus replication could be demonstrated. Obtained VN titres are presented as averages calculated from duplicate measurements.

[0034] Pooled sera were tested in an alternative VN test that allows the use of either strain DR13 or strain GD01. Since GD01 requires trypsin for infection, the method described above was modified as follows: After co-incubation of 1 hour at 37° C., the virus/serum mixtures were left on the Vero-CCL81 cells for 2 hours at 37° C. Then the mixtures were removed, the cells were washed twice with PBS, and the cells were incubated at 37° C. for 48 hours in the presence of aMEM-TPB plus 10 μg/ml trypsin for GD01 (or aMEM-TPB without trypsin in case strain DR13 was used in this procedure).

PEDV Antibody ELISA

[0035] Antibodies in sera against the S1 part of the PEDV spike protein derived from strain USA/Colorado/2013 were determined in an antibody ELISA. For this, plates were coated with 100 μl of PEDV S1 (0.25 μg/ml). Sera were diluted 1:900 in PBS0/1% BSA and added to the coated wells followed by incubation for 1 hour at 37° C. After two washes with PBS0/0.05% Tween-20, 100 μl of rabbit αSwine IgG HRPO conjugate diluted 1:10,000 in PBS0/1% BSA/0.5% tween20 was added to the wells, and plates were incubated for 1 hour at 37° C. After three washes with PBS0/0.05% Tween-20, 100 μl/well of TMB “super slow” substrate was added to each well followed by incubation at room temperature for 10 min (in the dark). Reactions were stopped by adding 100 μl of 25% sulfuric acid per well. The optical density (OD) at 450 nm was measured with an ELISA reader. Sera from naturally infected pigs were included as positive controls.

Results

Body Temperature

[0036] An overview of the mean body temperatures per group are shown in Table 4. It can be concluded that none of the vaccines caused a serious mean temperature elevation of more the 1 degrees Celsius. The largest temperature increase was seen at 4 hours post-vaccination, but in most cases the temperature returned to normal levels at 24 hours post-vaccination. The highest individual temperature increase (2.3° C.) was observed for one animal in Group 6, 4 h after the booster vaccination.

Local Reactions

[0037] Animals were palpated on the site of intramuscular vaccine application at 2, 4, 6, 8, 10, 12, and 14 days post-vaccination. From the length and width (in cm), the surface of the local reaction (i.e. swelling) was calculated. One animal in Group 2b displayed a very mild (<1 cm.sup.2) and transient (disappeared within a day) swelling directly after the booster vaccination. No local reactions were observed for all other 59 animals.

TABLE-US-00004 TABLE 4 Mean rectal temperatures taken after the first or second vaccination. Temperature after 1st Temperature after 2nd vaccination [° C.] vaccination [° C.] Group Vaccine t = 0 h t = 4 h t = 24 h t = 0 h t = 4 h t = 24 h 1a US S1 39.60 39.68 39.84 39.74 40.52 39.64 1b US S1-C 39.34 39.92 39.52 39.50 40.02 39.78 2a US S1-pFc 39.60 40.18 39.90 39.98 40.18 39.70 2b US S1-Fc 39.86 40.08 39.90 39.82 40.26 39.48 3a US S1-C-Fc 39.60 39.96 40.14 39.46 40.22 39.44 3b US S1-C-Fc 39.58 39.62 39.80 39.72 40.10 39.56 4 DR13 KV 6.0E5 39.28 40.04 39.55 39.84 40.49 39.57 5 DR13 KV 3.0E6 39.51 39.92 39.62 39.60 40.05 39.46 6 DR13 KV 1.5E7 39.25 39.94 39.77 39.84 39.81 39.61

Virus Neutralizing Antibodies

[0038] For the killed whole virus vaccines a virus neutralization assay was performed using the DR13 strain to be neutralized by the serum antibodies. The calculated mean VN titres of each group are presented in Table 5. From this table it can be concluded that DR13 KV antigen induced good VN titres in a clear dose responsive manner. It appears that a minimum dose corresponding to 3.0E6 TCID.sub.50 killed whole PEDV is necessary to induce VN titres above 5 log 2. The result of this example confirms the results of Example 2.

TABLE-US-00005 TABLE 5 PEDV neutralizing antibody titres (log.sub.2/50 μl). Group Vaccine t = 4 t = 5 t = 6 4 DR13 KV 6.0E5 2.8 3.9 3.3 5 DR13 KV 3.0E6 5.5 6.0 5.5 6 DR13 KV 1.5E7 8.6 8.8 8.1 Time (t) is indicated in weeks after the first vaccination.

[0039] For the subunit vaccines the alternative VN test was used. This is because the spike protein of the DR13-GFP strain used in the other VN test is about 93.3% identical to that of the US isolates from which the S1 subunits were derived and approximately 92.7% identical to spike of strain GD01. This sequence difference might explain why VN antibodies cannot be detected in the other test. Therefore, sera were pooled per group and the presence of serum neutralizing antibodies was determined in the alternative VN test that allows the use of either the DR13-GFP or GD01 strain. The results are summarized in Table 6.

TABLE-US-00006 TABLE 6 PEDV neutralizing antibody titres (log.sub.2/50 μl) in pooled sera. PEDV strain DR13-GFP PEDV strain GD01 Group Vaccine t = 4 t = 5 t = 6 t = 4 t = 5 t = 6 1a US S1 0.0 0.0 0.0 6.0 5.5 4.5 1b US S1-C 0.0 0.0 0.0 5.0 5.5 4.0 2a US S1-pFc 0.0 0.0 2.0 7.0 8.0 8.0 2b US S1-Fc 1.0 0.0 0.0 6.0 8.0 8.0 3a US S1-C-Fc 1.0 0.0 0.0 8.0 6.0 7.5 3b US S1-N-Fc 0.0 0.0 0.0 1.0 0.0 1.0 Time (t) is indicated in weeks after the first vaccination.

[0040] Indeed, the DR13 strain appears to be not suitable for detecting VN titres induced by the subunit vaccines. However, the DR13 neutralizing antibody titre in the pooled sera of the killed whole virus vaccines appeared to correspond well with the group averages of individually determined VN titres at 4, 5, and 6 weeks after the first vaccination (results no shown). This result demonstrates that (i) sera can be pooled to establish the VN titres per group, and (ii) the alternative VN assay for determining VN titres in pooled sera delivers similar results as the VN assay specifically developed for DR13-GFP. If the GD01 neutralizing antibody titre is determined, the picture for the S1 subunits (as shown in table 6, right hand side column) is as follows: With the exception of S1-N-Fc, they all induced a VN titre. The data show that (i) intact S1 or its C-terminal part are good antigens for triggering a VN antibody response, and (ii) a C-terminal extension with a Fc fragment improves the immune response.

[0041] Also, it is shown that 10 μg of the S1 subunits is able to induce a VN titer that at least the same as the level that can be obtained with a vaccine comprising per dose 3E06 TCID.sub.50 killed whole PED virus. Thus, 10 μg of the S1 subunit is a dose that corresponds to at least 3E06 TCID.sub.50 killed whole PED virus. To check this latter correspondence, a dose-response curve was made using the X-solve adjuvant and a dose range of 0.4 μg-2.0 μg-10 μg-50 μg of the S1 subunit. After IM vaccination (prime-boost scheme with interval of three weeks) the lower dosages led to maximum VN titres (log.sub.2/50 μl, 6 weeks post vaccination) of approximately only 1, whereas the 10 μg group had a VN titer of 6.5 and the 50 μg group had a VN titer of 7.0. This confirms that 10 μg of the S1 subunit is a dose that corresponds to at least 3E06 TCID.sub.50 killed whole PED virus (i.e. the established minimum dose able to induce a VN titre of at least 5).

Antibodies Against the S1 Subunit of Spike

[0042] An ELISA was performed on the pooled sera mentioned above for the last two time-points after vaccination. The ELISA data corresponded well with the VN titres (see Table 7).

TABLE-US-00007 TABLE 7 OD.sub.450 values of 1:900 diluted sera measured in the S1 ELISA. Group Vaccine t = 5 t = 6 1a US S1 3.026 3.366 1b US S1-C 2.88 3.075 2a US S1-pFc 3.087 3.298 2b US S1-Fc 2.848 2.697 3a US S1-C-Fc 2.952 2.994 3b US S1-N-Fc 0.305 0.326 Time (t) is indicated in weeks after the first vaccination.