WO2022090131A1

WO2022090131A1 - Recombinant african swine fever virus as live attenuated vaccine against african swine fever

Info

Publication number: WO2022090131A1
Application number: PCT/EP2021/079492
Authority: WO
Inventors: Yolanda Revilla Novella; Daniel PÉREZ NÚÑEZ
Original assignee: Consejo Superior De Investigaciones Científicas; Kansas State University Research Foundation
Priority date: 2020-10-26
Filing date: 2021-10-25
Publication date: 2022-05-05

Abstract

Use of recombinant African swine fever virus as a live attenuated vaccine against African swine fever. The present invention refers to a recombinant African Swine Fever Virus (ASFV) characterized by comprising a nucleic acid which consist of the SEQ ID NO: 1. Moreover, the present invention refers to a pharmaceutical composition, preferably a vaccine, comprising said recombinant ASF.

Description

RECOMBINANT AFRICAN SWINE FEVER VIRUS AS LIVE ATTENUATED VACCINE AGAINST AFRICAN SWINE FEVER

FIELD OF THE INVENTION

The present invention refers to the veterinary field. Particularly, the present invention refers to a recombinant African Swine Fever Virus (ASFV) strain characterized by comprising a nucleic acid sequence consisting of SEQ ID NO: 1. Particularly, SEQ ID NO: 1 includes a deletion of the gene O174L which codes for the DNA polymerase X protein, which has been introduced in the wildtype ASFV genome of SEQ ID NO: 2. Moreover, the present invention refers to a pharmaceutical composition, preferably a vaccine, comprising said recombinant ASFV strain, which can be used for the prophylactic treatment of African swine fever.

STATE OF THE ART

African swine fever, a fatal disease of pigs, has been around for decades. This disease originated in sub-Saharan Africa and then spread to other continents, with outbreaks surfacing in Russia, Brazil, and various parts of Europe and Asia in the 20^th and 21^st century where it still maintains a stronghold in swine populations. This disease is not only threatening the world’s largest pork industry, but also is a clear risk for the global supply of the blood thinner heparin, most of which is produced from Chinese pigs.

The complexity of ASFV is one of the reasons why it is so hard to tackle it. Its double-stranded DNA genome spans an impressive 190 kilobases and codes for almost 170 proteins, dwarfing many other viruses. ASFV infects and replicates in macrophages, but also induces cell death in uninfected B and T lymphocytes. Ultimately, ASFV kills pigs by causing hemorrhagic fever and destruction of lymphocytes in lymphoid tissues.

It has been previously shown that the classical and most obvious strategy of developing a vaccine for ASFV doesn’t work: killing or inactivating the virus and injecting it together with an adjuvant into healthy animals to prompt their immune system to generate antibodies that protect against future infections. This was attempted by different investigators, but it failed. The virus-specific antibodies which were produced just weren’t the right ones or not enough to ward off ASFV infection. Scientists have instead learned that one of the most effective ways to produce immunity against ASFV is to expose animals to a low virulent strain of the virus. Attenuated ASFV can be isolated from chronically infected animals: e.g., in wild boar populations across Europe many ASFV strains became attenuated and lost their ability to kill the host.

Regarding live attenuated vaccine candidates in general, the main concern is safety. Researchers realized this for ASFV attenuated viruses as early as the 1960s, when they tried to vaccinate large numbers of pigs in Portugal and Spain with a naturally attenuated strain of ASFV. Although the animals didn’t die, many of them developed a debilitating, chronic form of the disease.

In summary, African swine fever is a devastating disease which has caused the death of millions of pigs. To date, there is an unmet need of prophylactic treatments such as vaccines and therapeutics, which could help to protect pig populations around the world from this devastating disease.

The present invention is focused on solving this problem. Particularly, a specific recombinant ASFV strain is herein described which can be used as a novel live attenuated vaccine for the prophylactic treatment of African swine fever.

DESCRIPTION OF THE INVENTION

Brief description of the invention

A new recombinant ASFV has been generated by the inventors of the present invention. The recombinant ASFV of the invention is characterized by comprising a nucleic acid sequence consisting of the SEQ ID NO: 1. Particularly, SEQ IDNO: 1 includes a del eti on of the gene O174L (GenBank Accession CBW46763.1) which codes for DNA polymerase X protein, which is present in the wildtype genome of SEQ ID NO: 2

In this regard, the genome of the virulent parental ASFV strain (Arm/07) has been completely sequenced by the inventors of the present invention (SEQ ID NO: 2). Departing from the virulent parental strain Arm/07, the inventors of the present invention generated a new recombinant ASFV characterized by comprising a nucleic acid sequence consisting of the SEQ ID NO: 1, which includes in its genome a deletion of the gene O174L coding for DNA polymerase X protein. In other words, the new recombinant ASFV of the invention was preferably generated by deleting the gene O174L coding for DNA polymerase X protein from the parental strain Arm,/07 having SEQ ID NO: 2.

Examples 3 and 4 show relevant results regarding the safety and vaccine efficacy achieved by using the Arm-ADNA polymerase X-GFP strain of the invention.

So, the first embodiment of the present invention refers to a O174L-deleted recombinant ASFV strain designated Arm-ADNA polymerase X, characterized by comprising a nucleic acid sequence consisting of the SEQ ID NO: 1, which includes a deletion of the gene O174L which codes for DNA polymerase X protein.

In a preferred embodiment, the SEQ ID NO: 1 was characterized by using Illumina next generation sequencing technology as shown in the Examples.

The second embodiment of the present invention refers to the O174L-deleted recombinant ASFV strain of the invention for use in the prevention or prophylactic treatment of an infection caused by the virulent wild type form of ASFV. In other words, this embodiment is directed to the O174L- deleted recombinant ASFV strain of the invention for use in the prevention or prophylactic treatment of African Swine Fever. Alternatively, this embodiment also refers to a method for treating an infection caused by the virulent wild type form of ASFV (in other words, for treating African Swine Fever) which comprises the administration of a therapeutically effective dose/amount of the O174L-deleted recombinant ASFV strain of the invention, or a composition comprising thereof. The third embodiment of the present invention refers to a method for producing a pharmaceutical composition, preferably a vaccine, for the prevention or prophylactic treatment of an infection caused is by the virulent wild type form of the ASFV, which consists of the introduction of a deletion of the O174L gene coding for the DNA polymerase X protein in the wild type genome of the ASFV.

In a preferred embodiment, the method consists of introducing a deletion of the gene O174L which codes for DNA polymerase X protein in the wild type genome of the ASFV.

Consequently, the objective technical problem proposed in the present invention (i.e. the provision of a method or strategy for the prophylactic treatment of ASFV) is herein solved by providing a non-naturally occurring O174L-deleted recombinant ASFV strain, including a non-functional gene coding for DNA polymerase X protein wherein, preferably, such ASFV strain is a live attenuated ASFV.

In another aspect, the objective of the present invention is solved by providing a method for the generation of a non-functional ASFV O174L gene in a wild type ASFV genome, comprising the steps of: (a) introducing one or more full or partial deletions into the ASFV O174L gene and/or modifying one or more nucleotides controlling and/or encoding the corresponding ASFV O174L gene product and/or disrupting the ASFV O174L open reading frame (ORF), thereby rendering the ASFV O174L non-functional. In a preferred embodiment, the whole ORF is eliminated.

In yet another aspect, the objective of the present invention is solved by providing a non-naturally occurring O174L-deleted recombinant ASFV obtainable by a method as described above.

The fourth embodiment of the present invention refers to a pharmaceutical composition comprising of the O174L-deleted recombinant ASFV strain of the invention and, optionally, pharmaceutically acceptable vehicles and/or carriers. Thus, in a preferred embodiment, the objective of the present invention is solved by providing a composition (which can be an immunogenic composition or a vaccine) comprising a therapeutically effective amount of the O174L-deleted recombinant ASFV strain of the invention. This composition optionally comprises pharmaceutically acceptable vehicles and/or pharmaceutically acceptable carriers, preferably selected from the group comprising: solvents, dispersion media, adjuvants, stabilizing agents, diluents, preservatives, antibacterial and antifungal agents, isotonic agents, adsorption delaying agents.

In a preferred embodiment, the excipients recombinant ASFV strain of the invention or the pharmaceutical composition comprising thereof is administered to a mammal, preferably of the family Suidae, for instance pigs, more preferably domestic pigs (Sus scrofa domesticus) and wild pigs (Sus scrofa scrofa) in Europe, warthogs (Potamochoerus porcus), bushpigs (Potamochoerus larvatus) and giant forest hogs (Hylochoerus meinertzhageni) in Africa, as well as feral pigs in the Americas (which are probably partially derived from European wild boar).

In order to further increase the immunogenicity of the pharmaceutical composition which comprises the excipients recombinant ASFV strain of the invention, the composition may also comprise of one or more adjuvants.

The adjuvant may be purified by any of the techniques which are known in the prior art. The preferred purification technique is silica gel chromatography, in particular the "flash" (rapid) chromatographic technique. However, other chromatographic methods, including HPLC, may be used for purification of the adjuvant. Crystallization may also be used to purify the adjuvant. In some cases, no purification is required as a product of analytical purity is obtained directly from the synthesis.

The immunogenic compositions or the vaccine herein described are prepared by physically mixing the adjuvant with the excipients recombinant ASFV strain of the invention, under appropriate sterile conditions in accordance with known techniques to produce the adjuvanted composition

It is expected that an adjuvant can be added in an amount of about 100 pg to about 10 mg per dose, preferably in an amount of about 100 pg to about 10 mg per dose, more preferably in an amount of about 500 pg to about 5 mg per dose, even more preferably in an amount of about 750 pg to about 2.5 mg per dose, and most preferably in an amount of about 1 mg per dose. Alternatively, the adjuvant may be at a concentration of about 0.01% to 75%.

The immunogenic compositions or the vaccine herein described may be formulated using techniques similar to those used for other pharmaceutical compositions. Thus, the adjuvant and the O174L-deleted recombinant ASFV strain of the invention may be stored in lyophilized form and reconstituted in a physiologically acceptable vehicle to form a suspension prior to administration. Alternatively, the adjuvant and the O174L-deleted recombinant ASFV strain of the invention may be stored in the vehicle. Preferred vehicles are sterile solutions, in particular, sterile buffer solutions, such as phosphate buffered saline. The volume of a single dose of the pharmaceutical composition (immunogenic composition or vaccine) may vary but it will be generally within the ranges commonly employed in conventional vaccines. The volume of a single dose is preferably between about 0.1 ml and about 3 ml, preferably between about 0.2 ml and about 1.5 ml, more preferably between about 0.2 ml and about 0.5 ml. The formulations of the invention may comprise an effective immunizing amount of the composition and a physiologically acceptable vehicle.

The pharmaceutical composition, if desired, may also comprise minor amounts of wetting or emulsifying agents, or pH buffering agents. The pharmaceutical composition can be a liquid solution, suspension, emulsion, tablet, pill, capsule, sustained release formulation or powder. Oral formulation can include standard carriers such as pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate, etc.

The precise amount of the pharmaceutical composition to be employed in a formulation will depend on the route of administration and the nature of the subject (e.g. species, age, size, stage/level of disease), and should be decided according to the judgment of the practitioner and each mammal's circumstances according to standard clinical techniques. An effective immunizing amount is that amount sufficient to treat and/or prevent an African swine fever infection in a mammal. Effective doses may also be extrapolated from dose-response curves derived from animal model test systems and can vary from 0.001 mg/kg to 100 mg/kg. Toxicity and therapeutic efficacy of the pharmaceutical composition of the invention can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., for determining the LD50 (the dose lethal to 50% of the population) and the ED50 (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index and it can be expressed as the ratio LD50 /ED50. Compositions and/or immunogenic compositions and/or vaccines and/or one or more ASFV as described and/or defined herein which exhibit large therapeutic indices are preferred.

The pharmaceutical composition can be administered following different routes of administration, for example: intranasal, oral, intradermal and intramuscular. Administration in drinking water, most preferably in a single dose, is desirable. The skilled artisan will recognize that the pharmaceutical composition may also be administered in one, two or more doses, as well as, by other routes of administration. For example, such other routes include subcutaneously, intracutaneously, intravenously, intravascularly, intraarterially, intraperitoneally, intrathecally, intratracheally, intracardially, intralobally, intramedullarly, intrapulmonarily and intravaginally. Depending on the desired duration and effectiveness of the treatment, the compositions according to the invention may be administered once or several times, also intermittently, for instance daily for several days, weeks or months and in different dosages. In a preferred embodiment, the O174L- deleted recombinant ASFV strain of the invention is administered directly or as part of the composition (immunogenic composition or vaccine), in a dose ranging from 10 to 10⁸ plaque forming units (pfu), preferably 10, 10², 10³, 10⁴, IO⁵, 10⁶, 10⁷ or IO⁸ pfu. Preferably, the O174L- deleted recombinant ASFV strain of the invention is administered, directly or as part of the composition, in a single dose or in several doses. In a preferred embodiment, the recombinant ASFV of the invention is administered at a dose of 10² pfu per animal for 3 weeks.

Finally, it is important to note that the vaccine of the invention is designed to perform a DIVA test, to differentiate vaccinated animals from animals infected with natural attenuated strains. The recombinant virus of the invention comes from an Armenia 07 virus, which is the virulent parental circulating virus, in Europe and China. However, the recombinant virus of the invention, such as it is explained in the present invention, lacks the PolX gene, which makes it possible to differentiate vaccinated animals from animals infected with natural attenuated strains, since vaccinated animals will test negative in PCR test compared to animals infected with circulating viruses (both infected with Armenia 07 as infected with natural attenuated strains). Furthermore, the presence of the GFP marker (see Example 1.3) also makes it possible to differentiate animals vaccinated with our recombinant vaccine from all naturally infected animals, both with attenuated and virulent strains.

For the purpose of the present invention the following terms are defined:

• In the context of the present invention, the term “non-functional gene (preferably O174L) coding for DNA polymerase X protein" refers to a modified gene located in the genome of an ASFV, preferably a non-naturally occurring O174L-deleted recombinant ASFV strain, wherein the modification of the gene results in no gene product at all or in a biologically not functional gene product as compared to a non-modified functional gene. Including but without being limited to such a modification can be for instance a full or partial deletion of the gene and/or the modification of one or more nucleotides controlling and/or encoding the corresponding gene product and/or disruption of the open reading frame (ORF), for instance by inserting one or more nucleotides into that ORF, and/or any other currently known or conceivable method of inactivating or knocking-out functional expression of such gene. By means of such gene inactivation or knock-out, a live attenuated or subsequently inactivated ASFV strain can be generated.

• In the context of the present invention, the term “immunogenic composition" refers to a composition that can elicit a cellular and/or humoral immune response but does not necessarily confer full or partial immune protection against African swine fever in mammals. For the avoidance of doubt, however, such immunogenic composition may confer full or partial protection against African swine fever in mammals and this is also preferred. In contrast, a “vaccine" in the context of the present invention does confer full or partial, but at least partial immune protection against African swine fever in mammals.

• In the context of the present invention, the terms "protection against African swine fever", "protective immunity", "functional immunity" and similar phrases, means a response against African swine fever (virus) generated by administration of the O174L-deleted recombinant ASFV strain of the invention, that results in fewer deleterious effects than would be expected in a non-immunized mammal that has been exposed to African swine fever (virus). That is, the severity of the deleterious effects of the ASFV infection is lessened in a vaccinated mammal. Infection may be reduced, slowed, or possibly fully prevented, in a vaccinated mammal. Herein, where complete prevention of infection is meant, it is specifically stated. If complete prevention is not stated, then the term includes partial prevention.

• In the context of the present invention, the terms "reduction of the incidence and/or severity of clinical signs " or "reduction of clinical symptoms " mean, but are not limited to, reducing the number of ASFV-infected mammals in a group, reducing or eliminating the number of mammals exhibiting clinical signs of ASFV infection, or reducing the severity of any clinical signs that are present in one or more mammals, in comparison to wild-type ASFV infection. For example, it should refer to any reduction of pathogen load, pathogen shedding, reduction in pathogen transmission, or reduction of any clinical sign symptomatic of African swine fever. Preferably these clinical signs are reduced, by at least 10%, in subjects treated with the recombinant ASFV strain of the invention or with the composition, immunogenic composition or vaccine comprising thereof, in comparison to subjects not receiving the recombinant ASFV strain of the invention. More preferably, clinical signs are reduced in subjects treated with the recombinant ASFV strain of the invention by at least 20%, preferably by at least 30%, more preferably by at least 40%, and even more preferably by at least 50%.

• In the context of the present invention, the term "increased protection" means, but is not limited to, a statistically significant reduction of one or more clinical symptoms which are associated with infection by a wild-type ASFV, in a vaccinated group of mammals versus a non-vaccinated control group of mammals. The term "statistically significant reduction of clinical symptoms" means, but is not limited to, that the incidence of at least one clinical symptom in the vaccinated group of mammals is at least 10%, preferably 20%, more preferably 30%, even more preferably 50%, and even more preferably 70% lower than in the non-vaccinated control group after the challenge with the wild-type ASFV. • In the context of the present invention, the term "long-lasting protection" shall refer to improved efficacy that persists for at least 3 weeks, but more preferably at least 3 months, still more preferably at least 6 months. In the case of livestock, it is most preferred that the long-lasting protection shall persist until the average age at which animals are marketed for meat.

• In the context of the present invention, the term "immune response" or "immunological response" means, but is not limited to, the development of a cellular and/or antibody- mediated immune response to the recombinant ASFV strain of the invention, or the composition, immunogenic composition or vaccine comprising thereof. Usually, an immune or immunological response includes, but is not limited to, one or more of the following effects: the production or activation of antibodies, B cells, helper T cells, suppressor T cells, and/or cytotoxic T cells, directed specifically to an antigen or antigens included in the recombinant ASFV strain of the invention. Preferably, the host will display either a therapeutic or a protective immunological (memory) response, such that resistance to new infection will be enhanced and/or the clinical severity of the disease reduced. Such protection will be demonstrated by either a reduction in number of symptoms, severity of symptoms, or the lack of one or more of the symptoms associated with the infection of the wild-type ASFV, a delay in the of onset of viremia, reduced viral persistence, a reduction in the overall viral load and/or a reduction of viral excretion.

• In the context of the present invention, the term "a pharmaceutically acceptable or veterinary-acceptable carrier" includes any solvents, dispersion media, coatings, adjuvants, stabilizing agents, diluents, preservatives, antibacterial and antifungal agents, isotonic agents, adsorption delaying agents, and the like. In some preferred embodiments, and especially those that include lyophilized immunogenic compositions, stabilizing agents for use in the present invention include stabilizers for lyophilization or freeze-drying. In some embodiments, the immunogenic composition of the present invention contains an adjuvant. "Adjuvants" as used herein, can include aluminum hydroxide and aluminum phosphate, saponins e.g., Quil A, QS-21 (Cambridge Biotech Inc., Cambridge MA), GPI-0100 (Galenica Pharmaceuticals, Inc., Birmingham, AL), water-in-oil emulsion, oil-in-water emulsion, water-in-oil-in-water emulsion. The emulsion can be based in particular on light liquid paraffin oil (European Pharmacopeia type); isoprenoid oil such as squalane or squalene; oil resulting from the oligomerization of alkenes, in particular of isobutene or decene; esters of acids or of alcohols containing a linear alkyl group, more particularly plant oils, ethyl oleate, propylene glycol di-(caprylate/caprate), glyceryl tri- (caprylate/caprate) or propylene glycol di oleate; esters of branched fatty acids or alcohols, in particular isostearic acid esters. The oil is used in combination with emulsifiers to form the emulsion. The emulsifiers are preferably nonionic surfactants, in particular esters of sorbitan, of mannide (e.g. anhydromannitol oleate), of glycol, of polyglycerol, of propylene glycol and of oleic, isostearic, ricinoleic or hydroxystearic acid, which are optionally ethoxylated, and polyoxypropylene-polyoxyethylene copolymer blocks, in particular the Pluronic products, especially L 121. A further instance of an adjuvant is a compound chosen from the polymers of acrylic or methacrylic acid and the copolymers of maleic anhydride and alkenyl derivative. Advantageous adjuvant compounds are the polymers of acrylic or methacrylic acid which are cross-linked, especially with polyalkenyl ethers of sugars or polyalcohols. These compounds are known by the term carbomer (Phameuropa Vol. 8, No. 2, June 1996). Persons skilled in the art can also refer to U.S. Patent No. 2,909,462 which describes such acrylic polymers cross-linked with a polyhydroxylated compound having at least 3 hydroxyl groups, preferably not more than 8, the hydrogen atoms of at least three hydroxyls being replaced by unsaturated aliphatic radicals having at least 2 carbon atoms. The preferred radicals are those containing from 2 to 4 carbon atoms, e.g. vinyls, allyls and other ethylenically unsaturated groups. The unsaturated radicals may themselves contain other substituents, such as methyl. The products sold under the name Carbopol (BF Goodrich, Ohio, USA) are particularly appropriate. They are cross-linked with an allyl sucrose or with allyl pentaerythritol. Among then, there may be mentioned Carbopol 974P, 934P and 971P. Most preferred is the use of Cabopol 971P. Among the copolymers of maleic anhydride and alkenyl derivative, are the copolymers EMA (Monsanto), which are copolymers of maleic anhydride and ethylene. The dissolution of these polymers in water leads to an acid solution that will be neutralized, preferably to physiological pH, in order to give the adjuvant solution into which the immunogenic, immunological or vaccine composition itself will be incorporated. Further suitable adjuvants include, but are not limited to, the RIBI adjuvant system (Ribi Inc.), Block copolymer (CytRx, Atlanta GA), SAF-M (Chiron, Emeryville CA), monophosphoryl lipid A, Avridine lipid-amine adjuvant, heat-labile enterotoxin from E. coli (recombinant or otherwise), cholera toxin, IMS 1314 or muramyl dipeptide, or naturally occurring or recombinant cytokines or analogs thereof or stimulants of endogenous cytokine release, among many others.

• In the context of the present invention, the term "diluents " can include water, saline, dextrose, ethanol, glycerol, and the like. Isotonic agents can include sodium chloride, dextrose, mannitol, sorbitol, and lactose, among others. Stabilizers include albumin and alkali salts of ethylendiamintetracetic acid, among others. • In the context of the present invention, the term "attenuation" means reducing the virulence of a pathogen. In the present invention, an attenuated ASFV strain is one in which the virulence has been reduced so that it does not cause clinical signs of an African swine fever infection but is capable of inducing an immune response in the target mammal; this may also mean that the clinical signs are reduced in incidence or severity in animals infected with the attenuated ASFV strain in comparison with a "control group" of animals infected with non-attenuated, i.e. wild-type ASFV strain and not receiving the attenuated ASFV strain. In this context, the term "reduce/reduced" means a reduction of at least 10%, preferably 25%, even more preferably 50%, still more preferably 60%, even more preferably 70%, still more preferably 80%, even more preferably 90% and most preferably of 100% as compared to the control group as defined above. Thus, an attenuated ASFV strain is one that is suitable for incorporation into an immunogenic composition comprising the recombinant ASFV strain of the invention.

• In the context of the present invention, the term "effective dose" means, but is not limited to, an amount of antigen that elicits, or is able to elicit, an immune response that yields a reduction of clinical symptoms after infection with wild type ASFV in an animal to which the antigen is administered.

• In the context of the present invention, the term "effective amount" means, in the context of a composition, an amount of an immunogenic composition capable of inducing an immune response that reduces the incidence of or lessens the severity of infection or incident of disease in an animal. Particularly, an effective amount refers to plaque forming units (pfu) per dose. Alternatively, in the context of a therapy, the term "effective amount" refers to the amount of a therapy which is sufficient to reduce or ameliorate the severity or duration of African swine fever, or one or more symptoms thereof, prevent the advancement of such disease, cause the regression of such disease, prevent the recurrence, development, onset, or progression of one or more symptoms associated with such disease, or enhance or improve the prophylaxis or treatment of another therapy or therapeutic agent.

• In the context of the present invention "pfu " is defined as "plaque forming units", a standard value for the quantification of lytic viruses consisting of quantifying the lysis plaques provoked by the virus while infecting cell monolayers growing in semi-solid media. Under these conditions, each virus plaque is originated from one only parental virus particle. • The term "comprising" it is meant including, but not limited to, whatever follows the word "comprising". Thus, use of the term "comprising" indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

• By "consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of’. Thus, the phrase "consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present.

Description of the figures

Figure 1. Survival curve of piglets inoculated with Arm-ADNA polymerase X (Arm07delPolX) compared to Arm07wt controls. All 5 piglets inoculated intramuscularly with a dose of 10² PFU of Arm07delPolX survived the 14-day study trial. For comparison, the survival curve of 5 piglets challenged with wild type Arm07 virus at the same dose from a similar challenge study is provided. Figure 2. Daily temperatures of piglets inoculated with 10² PFU of Arm-ADNA polymerase X (Arm07delPolX). Daily rectal temperatures for individual pigs are illustrated as solid lines, and average daily temperatures as a dashed line. Average temperatures peaked on day 5 post inoculation above 105°F, but otherwise remained within a normal temperature range for the duration of the 14-day study. Piglets #55 and 57 had multiple temperature spikes above 105°F. Piglets #55 and 59 spiked with fevers above 106°F and 107°F which resolved within 24 or 48 hours.

Figure 3. ASFV DNA in blood of piglets inoculated with 10² PFU of Arm-ADNA polymerase X (Arm07delPolX) shows productive viral replication. Quantitative real-time PCR targeting ASFV p72 was used to determine viral copy number per ml blood collected on 1, 3, 5, 7, 10- and 14-days post inoculation (DPI) from piglets inoculated with 10² PFU Arm07delPolX. All pigs became viremic by 7 DPI based on ASFV DNA detected in blood, with ASFV DNA detected as early as 3 DPI in 1 piglet. Piglet #866 only had detectable ASFV DNA in blood at 7 DPI. ASFV copy numbers decreased in all pigs after 7 DPI until the end of the study at 14 DPI.

Figure 4. Survival curve of piglets post-vaccination with 10² PFU of Arm-ADNA polymerase X (Arm07delPolX). Five out of six piglets inoculated intramuscularly with a dose of 10² PFU of Arm07delPolX survived the 21 days post vaccination (DPV) prior to virulent ASFV challenge; one piglet died at 13 DPV. All six non-vaccinated control pigs survived the 21 days prior to virulent ASFV challenge.

Figure 5. Daily temperatures of piglets post-vaccination with 10² PFU of Arm-ADNA polymerase X (Arm07delPolX). Daily rectal temperatures for individual pigs are illustrated as solid lines, and average daily temperatures as a dashed line. Average temperatures peaked on day 5 post inoculation above 105°F, but otherwise remained within a normal temperature range for the duration of the 21 days post vaccination. Piglet #34 had a temperature above 105°F from day 2 to day 10 post vaccination and was euthanized on day 14 DPV. Piglets #33 and 37 had temperatures that peaked above 106°F later at 17 and 18 DPV.

Figure 6. ASFV DNA in blood of piglets post-vaccination with 10² PFU of Arm-ADNA polymerase X (Arm07delPolX) shows productive viral replication. Quantitative real-time PCR targeting ASFV p72 was used to determine viral copy number per ml blood collected on 1, 3, 5, 7, 10- and 14-days post vaccination (DPV) from piglets vaccinated with 10² PFU of Arm07delPolX. All pigs became viremic by 3 DPI based on ASFV DNA detected in blood, with peak ASFV DNA detected at 5 DPV for most pigs that subsequently gradually decreased. Piglet #34 had the highest level of ASFV DNA in blood of all the pigs which peaked at 10 DPV and was euthanized at 14 DPV; pig #35 had the lowest level of ASFV detected over the 21 DPV period.

Figure 7. Survival curves of Arm-ADNA polymerase X (Arm07delPolX) vaccinated and control piglets challenged with Arm07wt. At 21 days post vaccination, the 5 remaining vaccinated pigs and 6 non-vaccinated controls were challenged with 10^{2 2} HAU Arm07wt virus. Four of the five piglets vaccinated with 10² PFU of Arm07delPolX survived virulent ASFV challenge; one piglet was euthanized at 6 days post challenge (DPC). All six non-vaccinated control pigs died on 7 to 11 DPC.

Figure 8. Average daily temperatures of Arm-ADNA polymerase X (Arm07delPolX) vaccinated and control piglets challenged with Arm07wt. Average daily rectal temperatures for pigs vaccinated with 10² PFU of Arm07delPolX (blue line) and non-vaccinated controls (orange line) are shown with standard deviations. Average temperatures of non-vaccinated controls steadily increased from 5 to 10 days post challenge (DPC), while the average temperature of vaccinated pigs was maintained below 105°F for the duration of the 13 DPC.

Figure 9. ASFV DNA in the blood of Arm-ADNA polymerase X (Arm07delPolX) vaccinated piglets challenged with Arm07wt. Quantitative real-time PCR targeting ASFV p72 was used to determine viral copy number per ml blood collected on 0, 1, 3, 5, 7- and 11-days post challenge (DPC) from piglets vaccinated with 10² PFU of Arm07delPolX and challenged with 10^{2 2} HAU of Arm07wt virus. All 5 vaccinated pigs had detectable ASFV DNA in their blood prior to challenge at 21 days post vaccination/0 DPC; ASFV DNA levels in the 4 surviving pigs did not increase above this threshold for the remainder of the study. Piglet #36 had ASFV DNA levels that increased at 5 and 7 DPC, before it was euthanized.

Figure 10. ASFV DNA in the blood of piglets in the non-vaccinated control group challenged with Arm07wt. Quantitative real-time PCR targeting ASFV p72 was used to determine viral copy number per ml blood collected on 0, 1, 3, 5, 7- and 11-days post challenge (DPC) from nonvaccinated control piglets challenged with 10^{2 2} HAU of Arm07wt virus. ASFV DNA was detected in the blood of all pigs by 5 DPC, except for pig #541 (Analysis for animal #541 needs to be repeated, since animal died with acute ASF lesions as determined at necropsy).

Detailed description of the invention

Example 1. Materials and Methods.

Example 1.1. Design and generation of CRISPR-Cas9 vector for the deletion of the gene O174L (which codes for DNA polymerase X protein) from the virulent ASFV strain Armenia/07.

The CRISPR-Cas9 technique is based on using the cellular repair system to achieve more effectively the generation of recombinant viruses by the Homology Directed Repair (HDR) method. In particular, we adapted this technique to delete the O174L gene from the virulent ASFV strain Arm07 of SEQ ID NO: 2 (wild type Armenia/07) generating the recombinant virus of the invention designated ArmADNA polymerase X-GFP.

For that, two vector were used: (i) one derived from pSpCas9(BB)-2A-Puro (PX459), (containing the Cas9 nuclease of Streptococcus pyogenes and a gene conferring resistance to Puromycin), in which the Nuclear Localization Signal (NLS) has been deleted (pSpCas9(BB)ANLS-2A-Puro); and (ii) a pcDNA3.1 -derived vector containing the flanking sequences of the target gene (O174L), surrounding the fluorescent marker gene EGFP derived from the pEGFP-E3 vector (designed “donor vector”).

Into the pSpCas9(BB)ANLS-2A-Puro vector, we cloned specific gRNAs to disrupt the O174L gene, which codes for DNA polymerase X protein. For the design of the O174L-specific gRNAs we used Protospacer, based on the O174L sequence of the ASFV strain Georgia 2007/01 (FR682468.1). The designed gRNA sequences were as follow: SEQ ID NO: 3 (“gRNA_O174L- 0”) and SEQ ID NO: 4 (“gRNA_O174L-l”). Each of these gRNAs were cloned into the pSpCas9(BB)ANLS-2A-Puro vector, generating the vectors pSpCas9(BB)ANLS-2A- Puro O 174L-gRNA-0 and pSpCas9(BB)ANLS-2A-Puro_O174L-gRNA-l.

For the generation of the donor vector, we used a pcDNA3.1 vector as a backbone in which we first cloned the O174L gene (basepair 129,229-129,524 of the ASFV Georgia 2007/01 genome, FR682468.1) and its flanking regions (500pb upstream and 500pb downstream) (pFL-O174L), and then substituted the O174L gene by the EGFP gene derived from the pEGFP-E3 vector (pFL- AO174L-GFP). Finally, we substituted the CMV promoter of EGFP gene by a specific ASFV promoter (p72 promoter: basepair 105,530-105,570 of the ASFV Georgia 2007/01 genome, FR682468.1), generating the final donor vector pFL-AO174L-p72GFP.

For the first vector (pFL-O174L), we designed specific probes to clone the O174L and flanking regions by In-Fusion technology (Clontech), which were as follow: SEQ ID NO: 5 and SEQ ID NO: 6 for the amplification of O174L gene and its flanking regions, and SEQ ID NO: 7 and SEQ ID NO: 8 to linearize the pcDNA3.1 vector, and to eliminate the CMV-MCS-bGH region. PCR were performed using Phusion High-Fidelity PCR Master Mix with HF Buffer (ThermoScientific) and purified viral DNA from ASFV Armenia/07 strain.

Once the pFL-O174L vector was obtained, it was used as a scaffold for the generation of the next vector, pFL-AO174L-GFP. For that, we designed specific probes for the insertion of the EGFP gene into the pFL-O174L vector, eliminating the O174L gene, by In-Fusion technology. The probes were as follow: SEQ ID NO: 9 and SEQ ID NO: 10 to linearize the pFL-vector eliminating the O174L gene; and SEQ ID NO: 11 and SEQ ID NO: 12 to amplify the EGFP gene including CMV enhancer, CMV promoter and bGH, from the pEGFP-E3 vector. Next step, we substitute the CMV promoter by an ASFV promoter (p72 promoter, described in (Garcia-Escudero and Vinuela 2000)). Forthat, we designed the specific probes: SEQ ID NO: 13 and SEQ ID NO: 14 to amplify the p72 promoter; and SEQ ID NO: 15 and SEQ ID NO: 16 to linearize the pFL-AO174L- GFP vector eliminating the CMV promoter. The p72 promoter was generated by incubation of lOpl at lOOpM of each of the specific probes in H2O (final volume lOOpl) incubating 5 minutes at 95 °C and 30 minutes at 25 °C. This product was cloned into the pFL-AO174L-GFP by In-Fusion technology, generating the final donor vector, pFL-AO174L-p72GFP.

Example 1.2. Generation of recombinant virus Arm-AO174L-GFP by CRISPR-Cas9.

The recombinant virus was generated in COS-1 cells, from the American Type Culture Collection (ATCC), grown in Dulbecco modified Eagle medium (DMEM) supplemented with 2 mM 1- glutamine, 100 U/ml gentamicin, nonessential amino acids, and 5% fetal bovine serum. Cells were grown at 37°C in a 7% CO2 atmosphere saturated with water vapor.

COS-1 cells were co-transfected with specific pSpCas9(BB)ANLS-2A-Puro gRNAs together with the donor vector pFL-AO174L-p72GFP. In particular, for the generation of Arm-ADNA polymerase X-GFP virus, COS-1 cells were seeded in a 6-well plate at 90% confluence and individually wells were co-transfected with 2 pg of either pSpCas9(BB)ANLS-2A-Puro gRNA-0 and pFL-AO174L-GFP or pSpCas9(BB)ANLS-2A-Puro gRNA-1 and pFL-AO174L-GFP with FuGene HD (Promega). 24h post transfection, puromycin (Sigma) was added to the media of transfected and non-transfected control cells (Ipg/ml). After 24h, transfected cells were infected at two different MOI (1 and 0.1) with Armenia/07 ASFV strain. After lh30 of viral adsorption, puromycin was added (Ipg/ml) to the medium. At 5 days post infection (dpi), cell and medium was collected and conserved at -80°C, which we called first viral progeny. After several freeze / thaw cycles, supernatant was used to infect second round of transfected cells to generate the second viral progeny. These 2^nd round COS-1 cells were only transfected with pSpCas9(BB)ANLS-2A- Puro gRNAs (2pg/well) and selected with puromycin as explained above. After selection, cells transfected with pSpCas9(BB)ANLS-2A-Puro gRNA-0 were infected with first viral progeny obtained from cells co-transfected with pSpCas9(BB)ANLS-2A-Puro gRNA-1, and vice versa, in order to increase the percentage of recombinant viruses vs wild type viruses. At 5dpi, second viral progeny was collected and conserved at -80 °C.

Example 1.3. Isolation of recombinant viruses from wild-type viruses by plaque isolation.

Collected recombinant viruses (second progenies) are used to infect (non-transfected) COS-1 cells. After 1 hour and 30 minutes of viral adsorption, inoculum is removed and DMEM 2x with agar 1% is added. At 4-7 dpi viral plaques appear and are identified by optical microscopy. Recombinant Arm-ADNA polymerase X-GFP viruses are detected under fluorescent microscopy by green plaques (detected by GFP present in the recombinant viruses). Ones the recombinant plaque is identified, it is collected by sterile pipette tips in 40pl of DMEM and conserved at -80 °C. After three freeze / thaw cycles, the collected virus was used to infect new COS-1 cells using the same procedure explained above. This plaque isolation method was repeated at least three times in order to separate a recombinant virus from the wild type virus.

During the isolation procedure, the presence of wild type contaminant virus was checked by PCR. For that, lOpl ofthe isolated plaque is digested with proteinase K (Sigma) in ESmMMgCh, 50mM KC1, 0.45% Tween20, 0.45% NP40 and lOmM TrisHCl pH8.3 buffer, incubated 30 minutes at 45 °C and then 15 minutes at 95 °C to inactivate the proteinase K. The digested isolated plaque was used as a DNA template for PCR to detect the presence of recombinant or wild type parental virus. The primers used for the detection of recombinant and parental viruses by PCR are shown in Table 1

Table 1

If parental virus contamination was detected by PCR, additional rounds of plaque purification was performed in order to obtain pure recombinant viruses. If no parental virus contamination was detected by PCR, the recombinant virus was amplified by infecting six to eight P100 plates of COS-1 cells. After 3 dpi, total virus was collected and subjected to several freeze / thaw cycles. After centrifugation at 3000 rpm 5 minutes at RT, supernatant was collected and centrifuged at 7000 rpm O/N at 4 °C. The pellet was resuspended in fresh DMEM medium and a lOpl sample was collected in order to check for parental virus contamination by PCR, as explained above. If no contamination was detected, the recombinant virus was amplified for DNA extraction and next generation sequencing (NGS) analysis.

Example 1.4. Viral DNA extraction for NGS analysis.

Selected recombinant viruses were grown in 6-8 Pl 00 pre-confluent COS-1 cells. After 3-4 dpi, all cells and the supernatant were collected and centrifuged for5 minutes at 3000 rpm at RT. The supernatant was collected and centrifuged at 7000 rpm O/N at 4 °C. The pellet was resuspended in cold and filtrated lOmM Tris-HCl pH8.8. The pellet was treated with 0.25U/pl DNAsa I (Sigma), 0.25U/pl Nuclease S7 (Sigma) and 20 pg/ml RNAse A (Promega) in 800mM Tris-HCl pH7.5, 200mM NaCl, 20mM CaCh and 120mM MgCL during 2h at 37 °C, and further incubated with 12mM EDTA (Sigma) and 2mM EGTA (Sigma) 10 min at 75 °C. After that, the solution was treated with 200pg/ml proteinase K (Sigma) in 0.5% SDS for Ih at 45 °C. Next, viral DNA was precipitated by incubating 1:1 vol/vol of the sample with phenol:chloroform:isoamilic acid at 25:24:1. After centrifugation at 10,000 rpm for 3 minutes at RT, the aqueous fraction was transferred and further incubated with 0.1 volumes of 3M acetic acid pH5.2; 1 pl LPA (Sigma) and 2 volumes of cold 100% ethanol for Ih at -80 °C. Then, the sample was centrifuged at 13,000 rpm for 30 minutes at 4 °C and the supernatant discarded. The pellet was washed ones with cold 70% ethanol and air dried. Finally, the pellet was resuspended in lOmM Tris, pH8.8.

Example 1.5. Construction and sequencing of Illumina libraries.

A high-quality genomic DNA was submitted to MicrobesNG (Birmingham, UK). Illumina libraries were prepared with NEBNext Ultra DNA Library Prep Kit (New England Biolabs). The DNA sample was fragmented in a Covaris instrument and sequenced on an Illumina MiSeq device as paired-end (2 x 250 bp) reads. Example 1.6. Alignments of Illumina sequencing data.

Illumina reads from each sequenced sample were trimmed using Trimmomatic v0.36 (Bolger, Lohse et al. 2014) and quality-filtered (QF) with PrinSeq vl.2 (Schmieder and Edwards 2011). Only paired QF reads were considered for further analysis. These paired QF reads are as referred as Illumina QF reads in the text. Then, resulting paired reads were aligned against the reference sequence for each case, by using Bowtie 2 v2.3.4.1 (Langmead and Salzberg 2012) with default parameters.

Example 1.7. Genetic variants analysis.

Alignments of Illumina QF reads were used to identify mutations within the sequenced sample compared to Georgia 2007/1 strain (Accession: FR682468.1). SNPs and InDeis were obtained with SAMtools mpileup vl.9 (Li 2011) and VarScan v2.4.3 (Koboldt, Zhang et al. 2012), using standard settings with coverage > 20, minimum variant frequency > 10% and ignoring variants with >90% supported on one strand.

Example 2. Results.

Example 2.1. Generation of ASFV recombinant virus Arm-AO174-GFP by CRISPR-Cas9 technology.

ASFV recombinant viruses were generated by CRISPR-Cas9 technology in COS-1 cells, in order to generate a novel attenuated ASF virus for potential use as Live Attenuated Vaccines (LAVs). For that, specific vectors were transfected into COS-1 cells, which were then selected with puromycin and infected with wild-type virus in order to generate the recombinant virus, as detailed in the Material & Methods section.

We used the virulent ASFV strain Armenia 07 (Arm/07) of SEQ ID NO: 2, currently circulating in Europe, Russia and China (genotype II) as wild-type virus. We deleted the gene O174L, coding for DNA polymerase X protein that is involved into viral DNA repair system, and replaced this gene by EGFP, hence generating the recombinant virus Arm-ADNA Polymerase X-GFP. Viral DNA from Arm-ADNA polymerase X-GFP and Arm/07 wild-type was extracted and sequenced by NGS, as explained in the Materials & Methods section. Example 2.2. Sequence characterization of Arm/07 and the recombinant virus Arm-ADNA polymerase X-GFP.

Sequencing runs gave a broad range of paired reads per sample, which were mapped against each correspondent genome reference. Illumina reads from ASFV Armenia samples were aligned against the ASFV isolate Georgia 2007/1 reference sequence (accession no. FR682468). Estimated average coverage was calculated for each case based on the percentage of mapped reads and genome size.

In the Arm-ADNA polymerase X-GFP sample, up to 69.75% aligned against the reference genome reaching a mean coverage of 237x, as show in Table 2.

Table 2

Example 2.3. Genetic analysis of variability.

Genetic variability was analyzed by using sequencing data alignment from each sample. Numbers of single nucleotide polymorphisms (SNPs) and insertions/deletions (InDeis) were determined and characterized by their location in coding and non-coding regions, as well as by synonymous or nonsynonymous SNPs. Genetic variability analysis from ASFV Arm-ADNA polymerase X-GFP showed a very low number of mutations (Table 3), when aligned against the ASFV Georgia 2007/1 reference.

Table 3

Example 2.4. Sequencing analysis of the mutated locus and flanked regions.

ASFV Arm-ADNA polymerase X-GFP: As previously mentioned, the viral gene O174L was deleted by replacing it with a GFP cassette in the wild type ASFV isolate Armenia07. After a few rounds of amplification, plaque purification, and sequencing, the O174L locus was analyzed to confirm the correct substitution with the GFP cassette and the absence of wild type ORF O174L reads. We confirmed the correct substitution of the O174L gene by the GFP gene by aligning the ASFV Arm-ADNA polymerase X-GFP sequencing data against the wild-type ASFV genome, which was generated in silico for this purpose.

Example 3. Safety study with Arm-ADNA polymerase X (Arm07delPolX virus).

Example 3.1. Experimental design.

A total of 5 cross-bred piglets, 3-4 weeks of age and mixed sex were enrolled in the study (pig identification numbers: 55, 56, 57, 59, 866). Piglets were administered a 1 mL dose of 10² plaque forming units (PFU) of Arm07delPolX virus by intramuscular (IM) inoculation into the left side of the neck. Post inoculation, animals were observed for 14 days. Clinical symptoms and rectal temperatures were recorded daily. At the end of the observation period, at 14 days post inoculation (DPI), all animals were euthanized and necropsied. Blood for qPCR was collected at 0, 1, 3, 5, 7 and 10 DPI, and on day 14 at time of euthanasia prior to necropsy.

Example 3.2. Results.

All 5 piglets inoculated with a dose of 10² PFU of Arm07delPolX survived to the end of the observed period of 14 DPI, as compared to pigs inoculated with same dose of wildtype Arm07 which did not survive past 10 DPI (Figure 1). The average temperatures of piglets inoculated with Arm07delPolX remained below 105°F for the duration of the experiment, with the exception of day 5 post infection when the average temperature peaked at 105.5°F (Figure 2). Pig #55 had a temperature spike at above 105°F at 5 DPI, and above 107°F at 10 and 11 DPI. Pig #57 had a temperature spike above 105°F at 5, 9 and 13,14 DPI. Pig #59 had a temperature spike above 106°F at 5 DPI but maintained a normal temperature for the remainder of the study. Overall, fever temperatures of the piglets returned to a normal range within 24 to 48 hours.

Based on ASFV DNA in blood as determined by quantitative real-time PCR assay targeting the ASFV p72 gene, all pigs became viremic (Figure 3). ASFV DNA was detected in blood of three out of the five (3/5) pigs by 3 DPI, 4/5 pigs by 5 DPI, and in all pigs (5/5) by 7 DPI. ASFV DNA levels started to decline in all pigs by 10 DPI, with one pig (#866) falling to undetectable levels at 14 DPI. Peak viral DNA copy numbers ranged from 4 to above 7 LoglO per mL whole blood. These results indicate pigs were productively infected with the Arm07delPolX virus.

In conclusion, the results from this safety study indicate that the recombinant Arm07delPolX virus is highly attenuated compared to the wildtype Arm07, and 100% survival is observed when administered IM at a dose of 10² PFU per animal. Example 4. Vaccination with Arm-ADNA polymerase X (Arm07delPolX virus) and challenge with wild type Arm07(Arm07wt)

Example 4.1. Experimental design.

A total of 12 cross-bred piglets, 3-4 weeks of age, and of mixed sex were enrolled in the study. Piglets were divided into two groups as shown in the Table 4 below. Piglets in Group 1 were administered a 1 mL dose of 10² plaque forming units (PFU) of Arm07delPolX virus; and animals in Group 2 were held as unvaccinated controls for virulent ASFV challenge. Vaccination was intramuscular (IM) into the left side of the neck. At 21 days post vaccination (DPV), all animals were challenged with 1 mL dose of 10²² hemadsorption units (HAU) of virulent wild type Arm07 virus, administered IM into the left hind leg. Post challenge, animals were observed for 14 days and at the end of the observation period, all animals remaining in the study were necropsied. Clinical scores and rectal temperatures were recorded daily. Blood for qPCR was collected on days 0, 1, 3, 5, 10, 14 and 21 post vaccination and on days 0, 1, 3, 5, 7, and 10 post challenge (DPC) and prior to necropsy.

Example 4.2. Results.

Five out of six piglets inoculated intramuscularly with a dose of 10² PFU of Arm07delPolX survived the 21 days post vaccination (DPV) prior to virulent ASFV challenge; one piglet died at 13 DPV (Figure 4). All six non-vaccinated control pigs survived the observation period of 21 days prior to virulent ASFV challenge.

Average temperatures of Arm07delPolX vaccinated pigs peaked above 105°F at 5 DPV, but otherwise remained within a normal temperature range for the 21 DPV (Figure 5). Piglet #34 had a temperature above 105°F from day 2 to day 10 post vaccination and was euthanized on day 14 DPV. Piglets #33 and 37 had temperatures that peaked above 106°F at 17 and 18 DPV.

All vaccinated pigs became viremic by 3 DPI based on ASFV DNA detected in their blood, with peak ASFV DNA detected at 5 DPI for most pigs; the DNA load subsequently gradually decreased (Figure 6). Peak ASFV DNA levels ranged from over 4 to over 7 LoglO; Piglet #34 had the highest level of ASFV DNA in blood of all the pigs which peaked at 10 DPI, and #35 had the lowest level of ASFV detected over the 21 DPV observation period.

Overall, these results were consistent with our previous safety study (see Figures 1, 2 and 2), demonstrating that the recombinant Arm07delPolX virus efficiently replicates in vivo but is highly attenuated compared to the wild type Arm07 virus. At 21 DPV, the five remaining Arm07delPolX-vaccinated pigs and the 6 non-vaccinated controls were challenged IM with 10²²HAU Arm07wt virus. Four of the five vaccinated piglets survived virulent ASFV challenge; one piglet was euthanized at 6 days post challenge (DPC; Figure 7). All six non-vaccinated control pigs died on 7 to 11 DPC. Average daily temperatures of non-vaccinated controls steadily increased from 5 to 10 DPC, while the average temperature of vaccinated pigs was maintained below 105°F for the duration of the 13 DPC observation period (Figure 8).

All five Arm07delPolX vaccinated pigs had detectable ASFV DNA ranging from 3 to 7 Log 10 in their blood prior to challenge at 21 DP V/0 DPC; ASFV DNA levels in the four Arm07delPolX vaccinated and surviving pigs did not increase above this threshold for the remainder of the study (Figure 9). Piglet #36 had ASFV DNA levels that increased above an ASFV DNA load of 7 Log 10 at 5 and 7 DPC, before it was euthanized. In the non-vaccinated control group, ASFV DNA was detected in the blood of all pigs by 5 DPC, except for pig #541. The analysis for animal #541 needs to be repeated, since this animal died with acute ASF lesions as found at necropsy (Figure 10).

In conclusion, the results from this vaccine efficacy study shows 80% survival of Arm07delPolX- vaccinated pigs following highly virulent ASFV challenge.

Table 4. Groups and treatments assignment.

Claims

24 CLAIMS

1. A recombinant African Swine Fever Virus (ASFV) characterized by comprising a nucleic acid consisting of the SEQ ID NO: 1.

2. A recombinant African Swine Fever Virus (ASFV), according to claim 1, for use in the prevention or prophylactic treatment of an infection caused by the wild type form of the African Swine Fever Virus (ASFV).

3. A recombinant African Swine Fever Virus (ASFV) for use, according to claim 2, wherein the recombinant African Swine Fever Virus (ASGV) is administered at a dose of 10² plaque forming units (pfu) or similar per animal for 3 weeks.

4. Pharmaceutical composition comprising the recombinant African Swine Fever Virus (ASFV) of claim 1 and, preferably, pharmaceutically acceptable vehicles and/or carriers.

5. Pharmaceutical composition, according to claim 4, characterized in that it is a vaccine.