the vaccine of the present invention effectively protects cats against disease associated with fipv . furthermore , inoculated cats do not serve as carders of the disease . this protection , coupled with the fact that the vaccine is ostensibly virus - free , underscores obvious and highly significant advantages conveyed by the inventive vaccine . because the vaccine utilizes neither living nor dead virus , but rather a product of viral - infected cells ( i . e ., viral precursor immunogens ), it is not only extremely effective but essentially risk - free as well . the inventive fip vaccine can be combined with vaccines effective against other feline diseases without prejudicing its efficacy . other vaccines which may be combined with the instant vaccine include , for example , vaccines against feline leukemia virus ( felv ), feline sarcoma virus ( fesv ), feline panleukopenia virus ( fpv ), feline calicivirus ( fcv ), and feline herpesvirus i ( fhv - i ), which causes feline viral rhinotracheitis . the vital precursor immunogens derived from the persistently - infected cells are proteins or protein precursors ( i . e ., unassembled viral proteins ) associated with fip . with reference to the method of collecting the viral precursor immunogens , the first step requires the selection of a cell line capable of persistent infection with fipv , but for which fipv is noncytotoxic . further , it is desirable not to sacrifice the cell line for the sake of harvesting the viral precursor immunogens . thus , the cell line of choice should not only be capable of persistent infection with fip , but should also be amenable to the harvesting of vital precursor immunogens followed by recycle to the process for subsequent rounds of growth and harvesting . the presently preferred cell line of choice yielding the fip vaccine disclosed herein comprises crandall feline kidney ( crfk ) cells which have been persistently infected with fipv . the dahlberg strain of fipv ( atcc accession no . vr - 867 ) is used . the persistently infected cell line of the present invention has been assigned atcc accession no . crl11137 . the infected crfk cells first are placed in a serum - containing growth medium for culture . such serum - containing growth medium comprises a conventional serum - free growth medium having added thereto an appropriate quantity of animal serum , such as fetal bovine serum . appropriate serum - free media include mccoy &# 39 ; s 5a medium and rpmi 1640 medium ( gibco , grand island , n . y . ), and like conventional media . to such serum - free medium are added appropriate quantities of serum and antibiotics in conventional fashion . the cells are cultured in such medium , with additional serum optionally added from time to time , preferably until such cells have reached saturation density in the volume of medium used . conventional growth conditions are maintained as well known in the art . the next step of the process comprises transferring the cultured presistently - infected cells to a serum - free growth medium of composition desirably substantially the same as that used in the culturing step , except that no serum is used or added during this subsequent step . the cells placed in the serum - free medium apparently cease their normal growth cycle and virtually all vital production is arrested . as a result of the severe stress to which the cells are subjected in serum - free medium , an abundance of viral precursor immunogens ( and possibly additional cell matter ) are shed from the cells in substantial quantities . the supernatant , comprising serum - free medium containing viral precursor immunogens , then is separated from the persistently - infected cells by conventional separation techniques including , for example , centrifugation . the separated cell line can then be recycled to the culturing step of the process , with serum - containing growth medium . the fip viral precursor immunogens may be lyophilized or can be converted into a vaccine immediately . if lyophilization is the technique of choice , the viral precursor immunogen powder can be stored in such form or , if preferred , can be resuspended and stored at very low temperatures ( e . g ., - 67 . 8 ° to - 126 . 7 ° c .). in order to convert the fip viral precursor immunogens into a vaccine which is effective for the prevention of diseases caused by fipv , the fip vital precursor immunogen supernatant , preferably diluted to minimal effective amount , is blended with a pharmaceutically - acceptable adjuvant . the determination of fip vital precursor immunogens separated from the harvested infected cell lines can be conveniently determined by dot - blot analysis . thereafter , pharmaceutically - acceptable adjuvants are added in conventional amounts to the hp viral precursor immunogen serum - free medium . conventional adjuvants include , for example , complete or incomplete freund &# 39 ; s adjuvant , aluminum hydroxide , quil a , ema , dda , tdm - squalene , lecithin , alum , saponin , and such other adjuvants as are well known to those in the art , and also mixtures thereof . the vaccine , as prepared or in combination with other feline vaccines or inoculants , can be used to inoculate both domestic and wild felidae for the prevention of disease associated with fipv . viral precursor immunogen units per dosage are administered to these cats by conventional routes of administration , e . g ., parenteral inoculation , including subcutaneous and intramuscular vaccination , or oral administration . parenteral inoculation is the preferred route of administration . both kittens and adult cats can be vaccinated with the vaccine and thereby receive full protection from infection . the preferred minimum age of the kitten for inoculation , as with most other vaccines , is at about 8 weeks when the kitten has been weaned and maternal antibody has disappeared . a suggested time range for vaccination , thus , encompasses the period of 6 to 12 weeks of age . the following example illustrates the manner in which the present invention has been practiced , but should not be construed as limiting . all units herein are in the metric system unless otherwise expressly indicated , and all references cited herein are expressly incorporated by reference . crandall feline kidney ( crfk ) cell line was infected with feline infectious peritonitis virus ( atcc - vr - 867 ; dahlberg strain ) diluted 1 : 100 and incubated 1 hour at 37 ° c . the cells were incubated at 37 ° c . until cytopathic effect ( cpe ) was maximal . fresh growth medium ( gm ), comprising eagles minimum essential medium ( mem ) containing earles salts and supplemented with 10 % heat - inactivated fetal bovine serum , antibiotic mixture , and 2 mm glutamine , was added to the flask and incubated at 37 + c . the cultures were examined every three days and small islands of cell growth were observed . fresh gm was added until the cells reached confluency . cultures then were maintained by the addition of 0 . 025 % trypsin , to remove and dissociate cells from the flask into single cells , and passaged to other flasks . the cells also were grown on cover slips and examined for virus production by indirect immunofluorescent antibody ( iifa ) technique with fip monoclonal antibody as the primary reagent . cell lines were monitored each passage for virus production and were frozen for storage every five passages . 1 . cover slips were sterilized by steam sterilization in glass petri dishes . 2 . crfk - fip cells were added to cover slips in gm and incubated until confluent , usually 48 hours . 3 . medium was decanted and cells washed with dulbecco &# 39 ; s calcium - magnesium - free phosphate - buffered saline ( cmf - pbs ). 4 . the dishes were filled with - 20 ° c . acetone and fixed in the freezer for 10 minutes . the acetone was removed , and the cells were air - dried and either used immediately or stored &# 34 ; dry &# 34 ; at - 20 ° c . 5 . cover slips were flooded with fip monoclonal antibody , diluted 1 : 1000 , and incubated for 30 minutes at 37 ° c . in a humidified atmosphere . 6 . the cells were washed 3 times with cmf - pbs at 5 minutes per wash , dried , and secondary reagent was added . 7 . rabbit anti - mouse igg conjugated with fluorescein isothiocyanate ( fitc ) diluted 1 : 40 comprised the secondary reagent . 8 . the secondary reagent was incubated and washed as described in steps 5 and 6 . 9 . following the last wash , the cover slips were dipped in distilled water , air - dried , and mounted cell - side - down on a glass microscope slide in a 1 : 1 mixture of glycerin : cmf - pbs . 10 . the cells were examined with an ultraviolet epifluorescent microscope with appropriate exciter and barrier filters . for vaccine production , virus - tested cells were transferred to large plastic t - flasks ( 75 or 250 mm ) in gm and incubated at 37 ° c . until confluent . the medium was replaced with serum - free gm and incubated at 37 ° c . for 72 hours . samples were removed for testing at 24 and 48 hours . at 72 hours , the medium was collected and centrifuged to remove cellular debris . clarified supernatants were concentrated 10 × by dialysis with polyethylene glycol 1000 ( aquacide iii , calbiochem , la jolla , calif .) at 4 ° c . the 10 × concentrated supernatant was tested for fip antigens by dot - blot analysis and frozen at - 85 ° c . 2 . 20 microliter samples were pipetted onto strips of nitrocellulose paper ( pore size 45 micrometers ) and air - dried . the following samples were used : 3 . strips were incubated with 5 % bovine serum albumin ( bsa ) at 5 g / 80 ml pbs : 20 ml tween 20 ( sigma chemical , st . louis , mo .) for one hour at 37 ° c . 4 . strips were incubated in fip monoclonal antibody solution at 1 : 200 dilution for one hour at 37 ° c . 5 . strips were washed 3 times for 10 minutes per wash on an orbital platform in 5 % bsa - tween 20 wash . 6 . strips were incubated with secondary reagent , staphylococcus protein a conjugated to alkaline phosphatase , diluted 1 : 500 . strips were placed in bcip / nbt substrate comprising 1 ml bcip concentrate , 1 ml nbt concentrate , and 10 ml tris buffer ( kirke - gaard & amp ; perry labs , inc ., gaithersburg , md .) and the color was developed to desired intensity , usually between 5 and 10 minutes . 7 . the reaction was stopped by dipping the strips in distilled water . 9 . the strips were visualized for dark blue / black staining when compared to negative and positive controls . inactivation was accomplished by freshly preparing beta - propiolactone at a dilution of 1 : 100 in distilled deionized water and adding it to a virus suspension at a final concentration of 1 : 1200 , followed by incubation at 37 ° c . for 2 hours . the inactivated vaccine was tested for infectious virus by titrating inactivated sample on susceptible crfk cells . results were considered negative if no viral cytopathology was noted by daily observation of infected cells and appropriate controls . twelve spf cats were used for the immunization and protection studies , in accordance with the following protocol : group b : 4 cats , subcutaneous administration of vaccine ( 1 . 0 ml ) comprising 1 : 1 mixture of 10 × vaccine concentrate with septic isa50 adjuvant ( monatide , pads , france ); week 3 : pre - bleed cats for 1 . 0 ml serum and administer first vaccine dose ; summaries of the clinical course and histopathologic findings are set forth in the following tables : table 1______________________________________summary of clinical course survivalgroup cat # clinical signs dpc * ______________________________________a gu3 anorexia , fever , thin , weak 23 dpc . sub . 2 79a gf4 none , healthy alivea gj1 none , healthy alivea gu4 none , healthy aliveb ga2 none , healthy aliveb gb3 none , healthy aliveb gj2 [ anesthetic death ] xxxb gm1 none , healthy alivec gm2 anorexia 11 dpc . sub . 1 17c gn6 anorexia 18 dpc . sub . 1 36c gr5 anorexia 53c gp5 anorexia 8 dpc . sub . 1 ; recovered 13 dpc . sub . 1 ; alive did not receive 2nd challenge______________________________________ * dpc = days post challenge ( 1 and 2 ) table 2______________________________________summary of histopathologic findingscat # euthanized pathologic lesions______________________________________gm2 17 dpc . sub . 1 effusive peritonitis ; multifocal necrohistio - cytic inflammation of all visceral organs ; villous atrophy , ileum ; erythroid hypoplasia , myeloid hyperplasiagn6 36 dpc . sub . 1 effusive peritonitis , multifocal pyogranu - lomatous inflammation of all visceral or - gans , brain , and eye ; erythroid hypoplasia ; myeloid hyperplasiagr5 17 dpc . sub . 2 effusive peritonitis ; multifocal to coalescing pyogranulomatous inflammation of all vis - ceral organs , brain , and eye ; villous atro - phy , ileum ; transmural granulomatous ileitis ; erythroid hypoplasia ; myeloid hyperplasia______________________________________ animals were observed daily for clinical signs of fip . as the foregoing data reveal , after the first challenge , three of the four cats in the unvaccinated control group showed clinical signs of fip . these three cats were euthanized , all in moribund condition , two following the first challenge and the third following the second challenge . of the vaccinated cats , three of the four cats in group a and all of the cats in group b ( excepting cat gj2 , which succumbed to anesthesia ) remained healthy throughout the study . in the group c control cats , lesions typical of fip were found in a variety of organs . all three of the euthanized cats had effusive peritonitis and multifocal necrotizing to granulomatous lesions in liver , kidney , and lung . cat gm2 had a peracute histocytic response , while cats gn6 and gr5 evidenced mainly a pyogranulomatous response , more typical of spontaneous fip . in addition , pyogranulomatous lesions were present in the brains and eyes of the two cats with more prolonged disease , but were absent from the animal which had died acutely . the intestines of all three cats showed mild to severe dilatation of intestinal glands by necrotic debris , leukocytes and mucous , in both the small intestine and colon . in two cats , severe villous atrophy was evident in the ileum ; transmural granulomatous enteritis was present in the third cat . thus , inoculation of cats with hpv accurately recapitulates the pathologic features of severe spontaneous disease , with infected cats developing typical pyogranulomatous lesions . additionally , this fip strain induces intestinal lesions which are not dissimilar to coronaviral enteritides in other species , but which have not been associated with spontaneous fip . accordingly , the foregoing data demonstrate that the inventive vaccine provides protection against multiple exposures to a highly virulent fipv . in addition to being nearly 100 % effective , the inventive vaccine possesses significant advantages over traditional modified live vaccine approaches in that there is no risk of shedding infectious virus particles , there is no possibility of reversion to a virulent strain , and the vaccine can be readily mixed with other inactivated vaccines .
one aspect of the present invention comprises a vaccine for the prevention of disease caused by feline infectious peritonitis virus . such vaccine comprises fip viral precursor immunogens derived from in vitro produced cells persistently infected with fipv . preferred in the production of viral immunogens forming the vaccine of the present invention is the crandall feline kidney cell line . thus , a second aspect of the invention comprises fip - infected crandall feline kidney cell line , deposited at the american type culture collection , rockville , md , on sep . 23 , 1992 , and granted accession no . crl11137 . a third aspect of the invention relates to a method of producing fip viral precursor immunogens , which comprises culturing in vitro fip - persistent infected cells in a serum - containing growth medium , subsequently transferring and maintaining said cultured cells in a serum - free medium under conditions and for a time adequate to accumulate fip viral precursor immunogens shed from said cells , and then separating the cells from the supernatant containing the vital precursor immunogens . the supernatant containing the fip viral precursor immunogens is blended with a pharmaceutically - acceptable adjuvant in order to form the fip vaccine disclosed herein .