Genetic characterization of healthy and sebaceous adenitis affected Standard Poodles from the United States and the United Kingdom.

The degree of heterogeneity associated with geographic origin and sebaceous adenitis (SA) status in Standard Poodles from the United States (US) and the United Kingdom (UK) was assessed. Healthy and SA-affected Standard Poodles from the US and the UK shared a major mitochondrial DNA (mtDNA) haplotype and a single Y chromosome haplotype. However, minor mtDNA haplotypes and frequencies were somewhat different between US and UK dogs and were significantly less associated with SA than major haplotypes across both populations. The US and UK populations exhibited recent divergence from a common gene pool, based on allele frequencies of 24 highly polymorphic short tandem repeats and principle coordinates and cluster analyses of genotype frequencies. However, there was no differentiation between SA affected and unaffected dogs. Over 90% of US and UK Poodles shared a common dog leukocyte antigen (DLA) class II haplotype, but showed some differentiation in minor haplotype frequency. No difference was observed in haplotype heterozygosity between SA affected and unaffected dogs from the same country and no disease association for SA was found within the DLA region by a high density single nucleotide polymorphism (SNP) scan. Zygosity mapping in the DLA region of Poodles indicated much lower site-specific diversity than in an outbred population of street dogs from Bali, Indonesia, reflecting the degree that breed associated historical bottlenecks have reduced diversity in a polymorphic region of the genome. This study shows possible pitfalls in more extensive genome-wide association studies, such as case and control numbers, population stratification, the involvement of multiple genes, and/or the possibility that SA susceptibility is fixed or nearly fixed within the breed, which can reduce power to detect genetic associations.

The role of humoral antibody in the rejection of primary renal allografts in sheep.

Antibody which had cytotoxic and agglutinating activity against donor lymphocytes appeared in the blood stream of primary renal allograft recipients usually within 48 h of the graft being finally rejected. Appearance of the antibody See PDF for Structure in the blood was associated with severe alterations in vascular permeability and this led to increases in the numbers of red cells and in the protein content of the lymph coming from the allograft. It was possible to elute cytotoxic and agglutinating antibody from renal allograft tissue, showing that this type of antibody was bound to graft antigens during the rejection process. The transfusion of whole serum or serum globulins obtained from sheep that had previously rejected allografts led to the destruction of recently installed renal grafts and the histological changes produced in these grafts and the alterations in the composition of the lymph coming from them were similar to those seen in the terminal stages of primary rejection. These findings have led us to the conclusion that in the sheep, at least the terminal stage of primary renal allograft rejection is mediated by humoral antibody.

The role of the lymphatic system in the rejection of homografts: a study of lymph from renal transplants.

The rejection of renal homografts has been studied in sheep by transplanting kidneys into the neck and preserving the renal lymphatic drainage intact. Chronic fistulae were established in the transplanted renal lymphatics and lymph collected throughout the life of the graft. The changes that occurred in homografts during the process of rejection were reflected in changes in the lymph. Large numbers of basophilic, blast, lymphoid cells appeared in the lymph, and lymph production in the grafted kidney increased 20-50 fold. Over a period of about 10 days, up to 60 g wet weight of lymphoid cells and up to 10 liters of lymph were collected from the graft. Within 24 hr of grafting, the host cells present in the renal lymph had become sensitized to the graft and transformed into blast cells when cultivated in Millipore chambers in vitro. When the cells leaving the graft during the first 18-48 hr were injected into distant nonstimulated lymph nodes of the host sheep, they evoked significant cellular and antibody responses in the nodes. Within the graft, the main pathological changes were found in the vascular endothelium and many of the peritubular capillaries become plugged with emboli comprised of blast cells. There was extensive infiltration of the renal parenchyma with lymphoid cells and evidence of their transformation and proliferation within the renal blood capillaries. When all the lymph and cells leaving the homograft were diverted from the body, there was a greatly decreased reaction in the regional prescapular lymph node, and no reaction in lymph nodes distant from the graft. In these circumstances, the survival of the graft was not prolonged, and it was rejected without involvement of the lymph nodes of the host. Humoral antibody was produced in the lymph node regional to the homograft within 48-60 hr of grafting. Antibody was not detected in the blood or in the renal lymph until near to the time the graft was rejected. It was thought that this was due to the binding of antibody by the kidney graft tissue. We conclude that all the events which lead to the recognition and rejection of renal homografts can occur centrally within the graft itself.

Necrotizing meningoencephalitis of Pug dogs associates with dog leukocyte antigen class II and resembles acute variant forms of multiple sclerosis.

Necrotizing meningoencephalitis (NME) is a disorder of Pug Dogs that appears to have an immune etiology and high heritability based on population studies. The present study was undertaken to identify a genetic basis for the disease. A genome-wide association scan with single tandem repeat (STR) markers showed a single strong association near the dog leukocyte antigen (DLA) complex on CFA12. Fine resolution mapping with 27 STR markers on CFA12 further narrowed association to the region containing DLA-DRB1, -DQA1 and, -DQB1 genes. Sequencing confirmed that affected dogs were more likely to be homozygous for specific alleles at each locus and that these alleles were linked, forming a single high risk haplotype. The strong DLA class II association of NME in Pug Dogs resembles that of human multiple sclerosis (MS). Like MS, NME appears to have an autoimmune basis, involves genetic and nongenetic factors, has a relatively low incidence, is more frequent in females than males, and is associated with a vascularly orientated nonsuppurative inflammation. However, NME of Pug Dogs is more aggressive in disease course than classical human MS, appears to be relatively earlier in onset, and involves necrosis rather than demyelination as the central pathobiologic feature. Thus, Pug Dog encephalitis (PDE) shares clinical features with the less common acute variant forms of MS. Accordingly, NME of Pug Dogs may represent a naturally occurring canine model of certain idiopathic inflammatory disorders of the human central nervous system.

Isolation of a T-lymphotropic virus from domestic cats with an immunodeficiency-like syndrome.

A highly T-lymphotropic virus was isolated from cats in a cattery in which all the animals were seronegative for feline leukemia virus. A number of cats in one pen had died and several had an immunodeficiency-like syndrome. Only 1 of 18 normal cats in the cattery showed serologic evidence of infection with this new virus, whereas 10 of 25 cats with signs of ill health were seropositive for the virus. Tentatively designated feline T-lymphotropic lentivirus, this new feline retrovirus appears to be antigenically distinct from human immunodeficiency virus. There is no evidence for cat-to-human transmission of the agent. Kittens experimentally infected by way of blood or plasma from naturally infected animals developed generalized lymphadenopathy several weeks later, became transiently febrile and leukopenic, and continued to show a generalized lymphadenopathy 5 months after infection.

The nucleoside analog GS-441524 strongly inhibits feline infectious peritonitis (FIP) virus in tissue culture and experimental cat infection studies.

Feline infectious peritonitis (FIP) is a common and highly lethal coronavirus disease of domestic cats. Recent studies of diseases caused by several RNA viruses in people and other species indicate that antiviral therapy may be effective against FIP in cats. The small molecule nucleoside analog GS-441524 is a molecular precursor to a pharmacologically active nucleoside triphosphate molecule. These analogs act as an alternative substrate and RNA-chain terminator of viral RNA dependent RNA polymerase. We determined that GS-441524 was non-toxic in feline cells at concentrations as high as 100 uM and effectively inhibited FIPV replication in cultured CRFK cells and in naturally infected feline peritoneal macrophages at concentrations as low as 1 uM. We determined the pharmacokinetics of GS-441524 in cats in vivo and established a dosage that would sustain effective blood levels for 24 h. In an experimental FIPV infection of cats, GS-441524 treatment caused a rapid reversal of disease signs and return to normality with as little as two weeks of treatment in 10/10 cats and with no apparent toxicity.

Role of regional and distant lymph nodes in rejection of feline sarcoma virus-induced tumors in sheep.

The immune response of regional and distant lymph nodes was compared relative to rejection of feline sarcoma virus (FeSV)-induced tumors in sheep. Following injection of FeSV-transformed allogeneic or autochthonous fibroblasts into the lower leg, small tumors developed at the site of inoculation and subsequently regressed. Efferent lymph from the regional popliteal nodes and distant nodes in the same host was collected for periods up to 40 days after tumor cell inoculation. The cell response in the efferent lymph of the stimulated node was the same regardless of whether inoculum consisted of autochthonous or allogeneic FeSV-transformed sheep cells. There was a rapid rise in total lymphocytes leaving the regional node, beginning at 3 days and peaking at 6--8 days post inoculation. On days 6--8 post inoculation, lymphoblasts appeared in regional lymph ranging from 25 to 40% of the total cell output. The cell population in lymph from distant (nonstimulated) nodes, however, remained morphologically normal throughout the response. Lymphocytes cytotoxic to the injected FeSV-transformed cells appeared in efferent lymph from the regional node within 5 days post inoculation and in lymph from distant nonstimulated nodes several days later. Cytotoxic lymphocytic cells had no "killing" effect against the corresponding nontransformed cells if the inoculum was autochthonous in origin; however, they did have such an effect when corresponding nontransformed cells were allogeneic. The cytotoxicity of lymph cells varied according to the type of cells in the lymph. With the use of the growth inhibition assay, it was possible to demonstrate that lymph cell populations high in lymphoblasts "killed" all target cells in 24 hours, whereas populations of lymph cells comprised mainly of small lymphocytes took up to 2--3 days to "kill" the target cells. Complement-dependent antibody first appeared in lymph from the stimulated popliteal node at 8 days post inoculation and at 12 days post inoculation in blood sera and lymph from distant nodes.

Polymorphisms in ERAP1 and ERAP2 are shared by Caninae and segregate within and between random- and pure-breeds of dogs.

Specific polymorphisms in the endoplasmic reticulum amino peptidase genes ERAP1 and ERAP2, when present with certain MHC class receptor types, have been associated with increased risk for specific cancers, infectious diseases and autoimmune disorders in humans. This increased risk has been linked to distinct polymorphisms in both ERAPs and MHC class I receptors that affect the way cell-generated peptides are screened for antigenicity. The incidence of cancer, infectious disease and autoimmune disorders differ greatly among pure breeds of dogs as it does in humans and it is possible that this heightened susceptibility is also due to specific polymorphisms in ERAP1 and ERAP2. In order to determine if such polymorphisms exist, the ERAP1 and ERAP2 genes of 10 dogs of nine diverse breeds were sequenced and SNPs causing synonymous or non-synonymous amino acid changes, deletions or insertions were identified. Eight ERAP1 and 10 ERAP2 SNPs were used to create a Sequenom MassARRAY iPLEX based test panel which defined 24 ERAP1, 36 ERAP2 and 128 ERAP1/2 haplotypes. The prevalence of these haplotypes was then measured among dog, wolf, coyote, jackal and red fox populations. Some haplotypes were species specific, while others were shared across species, especially between dog, wolf, coyote and jackal. The prevalence of these haplotypes was then compared among various canid populations, and in particular between various populations of random- and pure-bred dogs. Human-directed positive selection has led to loss of ERAP diversity and segregation of certain haplotypes among various dog breeds. A phylogenetic tree generated from 45 of the most common ERAP1/2 haplotypes demonstrated three distinct clades, all of which were rooted with haplotypes either shared among species or specific to contemporary dogs, coyote and wolf.

Feline immunodeficiency syndrome--a comparison between feline T-lymphotropic lentivirus and feline leukemia virus.

A feline T-lymphotrophic lentvirus (FTLV) has recently been isolated from a domestic cat free of feline leukemia virus (FeLV). This virus is distinct from FeLV (an oncornavirus), although they share a common denominator, namely, the ability to cause immunosuppression and induce lymphadenopathy and anemia. Their differences can be revealed by examining the following: the metal requirement for reverse transcriptase activity, the antigenic comparison by Western blot analysis, the different susceptibilities of a variety of feline cells, and the morphology based on electron microscopy. In the serological survey of 1,612 cats surveyed in the USA, 232 (14.4%) were seropositive for antibodies to FTLV, which was lower than for the 42 Canadian cats surveyed of which 8 (19%) were seropositive. Of the 61 cats positive for FeLV, 15 (25%) were also positive for FTLV, giving the impression that coinfection between these two retroviruses plays an important role in the cliniocpathological signs of what was previously thought to be solely an FeLV syndrome.

Evaluation of in vivo and in vitro interactions of feline immunodeficiency virus and feline leukemia virus.

OBJECTIVE: To determine the potential mechanisms for disease potentiation where feline immunodeficiency virus (FIV) infection of persistently feline leukemia virus (FeLV)-infected cats results in more severe FIV disease and increased mortality than FIV infection of specific pathogen-free cats. DESIGN AND METHODS: To determine whether pseudotype formation resulting in expanded cell tropism may be an important mechanism, cellular targets and tissue distribution of FIV and FeLV were determined by in situ hybridization and/or immunohistochemistry. To determine whether FeLV can transactivate the FIV long terminal repeat (LTR) resulting in increased FIV expression, in vitro transient expression assays were performed. To examine whether persistent FeLV infection can cause the deletion of a suppressive T-lymphocyte population, peripheral blood mononuclear cell (PBMC) cultures from persistently FeLV-infected cats were infected with FIV and monitored for FIV antigen levels. RESULTS: Macrophages were the predominant target of FIV infection and were disseminated in a similar pattern in lymphoid and nonlymphoid tissues of both FIV-infected and FeLV/FIV-coinfected cats. FeLV-infected cells expressing FIV RNA were not present. Significant transactivation of the FIV LTR in FeLV-infected cells was not demonstrated. FIV antigen production was similar upon in vitro infection of PBMC from FeLV-infected and uninfected cats. CONCLUSIONS: Neither direct virus/virus interactions, such as FeLV/FIV pseudotype formation or transactivation of the FIV LTR in FeLV-infected cells, nor deletion of a regulatory cell subset from the blood of FeLV-infected cats, was found to be the mechanism of disease potentiation.

Two doses of PMPA protect newborn macaques against oral simian immunodeficiency virus infection.

BACKGROUND: Simple and affordable intervention strategies are needed to reduce the rate of HIV transmission from mother to infant in developing countries. Simian immunodeficiency virus (SIV) infection of newborn rhesus macaques is considered to be a useful model of human pediatric HIV infection. OBJECTIVE: To investigate whether short-term 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) administration can protect newborn rhesus macaques against perinatal SIV infection. DESIGN AND METHODS: Eight newborn macaques were inoculated orally with highly virulent SIVmac within the first 3 days of life. Four of these animals were untreated controls. The other four animals were given one dose of PMPA (30 mg/kg subcutaneously) 4 h before oral SIV inoculation, and were then given a second and final dose of PMPA 24 h later. RESULTS: All four untreated control animals were persistently SIV-positive within 2 weeks after virus inoculation. In contrast, no virus could be detected in the four animals that received two doses of PMPA; these animals were seronegative and healthy at 10 months. CONCLUSIONS: Two doses of PMPA prevented SIV infection of newborn macaques. Our data suggest that short-term administration of PMPA to HIV-infected pregnant women at the onset of labor and to their newborns after delivery may reduce the rate of intrapartum HIV transmission.

Protection against FIV challenge infection by genetic vaccination using minimalistic DNA constructs for FIV env gene and feline IL-12 expression.

OBJECTIVE: To evaluate the efficacy of a genetic vaccination protocol based on minimalistic, immunogenic defined gene expression (MIDGE) vectors coding for domains of the feline immunodeficiency virus (FIV) env gene and feline IL-12. METHODS: Three groups of four cats each were immunized three times within 6 weeks by the ballistic transfer of gold particles coated with MIDGE vectors. Group 1 received non-coated gold beads, groups 2 and 3 MIDGE vectors expressing FIV surface plus part of the transmembrane protein. In addition, group 3 received feline IL-12 DNA. All cats were challenged by intraperitoneal injection of 25 TCID50 of infectious FIV Z2. The following criteria were monitored: clinical signs, antibodies to transmembrane protein, antibodies to whole FIV, haematological parameters and kinetics of CD4 and CD8 cells, FIV proviral load (determined by quantitative polymerase chain reaction; PCR) and cytotoxic T lymphocyte (CTL) activity (in selected cats). RESULTS: None of the cats developed a detectable antibody response during immunizations. Four weeks after challenge exposure, all cats in group 1 (control) and group 2 (FIV surface-transmembrane protein) had seroconverted and showed a high proviral load until week 19 (end of experiment). In contrast, only one of four cats in group 3 (surface-transmembrane protein and IL-12) showed antibodies; it was provirus positive at reduced virus load. Short-lived CTL activity was found in two cats in group 3. CONCLUSION: Genetic vaccination using a MIDGE-based construct for the expression of the surface-transmembrane protein domain of FIV env and feline IL-12 DNA led to protection against homologous virus challenge in three out of four vaccinated cats.

Effects of incidental infections and immune activation on disease progression in experimentally feline immunodeficiency virus-infected cats.

Specific pathogen-free cats were experimentally infected with feline immunodeficiency virus (FIV) and subsequently exposed to common infectious pathogens and immune stimuli over a 3-year period. Cats with preexisting FIV infection showed signs of disease after exposure to Haemobartonella felis, Toxoplasma gondii, feline herpesvirus-1, and feline calicivirus similar to signs in non-FIV-infected cats, although they were more severe. No adverse effects of immunization with inactivated rabies virus vaccine and a synthetic polyproline immunogen were observed in either FIV-infected or non-FIV-infected cats, whereas the application of a diphtheria-tetanus-pertussis vaccine caused transient fever and lymphadenopathy in both groups of animals. Primary immune responses to pathogens or immunogens were usually delayed or diminished in FIV-infected compared with non-FIV-infected cats. Repeated infections and immune activation had no significant effects on the levels of FIV-specific antibodies or on the proportion of peripheral blood mononuclear cells (PBMCs) containing FIV proviral DNA. However, FIV-infected cats that were not exposed to immune stimuli had lower CD4+ T-lymphocyte numbers and lower CD4+/CD8+ T lymphocyte ratios at the end of the 3-year study than FIV-infected cats exposed to cofactors. The latter also had normal levels of interleukin-3 receptor (IL-2R) and major histocompatibility class II (MHC-II) antigen expression on PBMCs, while FIV-infected cats not exposed to cofactors had up-regulated IL-2R and down-regulated MHC-II antigen expression. It was concluded that repeated immune stimulation did not have a deleterious effect on the course of FIV-induced immunodeficiency.

Acquired immune dysfunction in cats with experimentally induced feline immunodeficiency virus infection: comparison of short-term and long-term infections.

Specific pathogen-free domestic cats with experimentally induced feline immunodeficiency virus (FIV) infections of short duration (less than or equal to 10 months) exhibited depressed total leukocyte and neutrophil numbers and a marginally decreased lymphocyte proliferative response to pokeweed mitogen (PWM), while cats with infections of more lengthy duration (greater than or equal to 25 months) exhibited normal leukocyte and neutrophil numbers but a dramatic loss of responsiveness to both PWM and concanavalin A (Con A). Cats with short-term infections exhibited a decrease in the percentage of CD4+ lymphocytes in peripheral blood and a corresponding depression of the CD4+:CD8+ ratio. Cats with long-term infections exhibited a similar but more profound perturbation of the CD4+ lymphocyte subset that also included a decrease in the absolute number of CD4+ cells. The decreased responsiveness to Con A and PWM in cats infected long term paralleled the decline in CD4+ cell counts, and the duration of infection was directly correlated with the decrease in the percentage of CD4+ cells. These data provide evidence supporting the hypothesis that FIV is the cause of an immune dysfunction in cats, with distinct similarities to that produced by human immunodeficiency virus (HIV) in people.

Monoclonal antibodies to three epitopic regions of feline leukemia virus p27 and their use in enzyme-linked immunosorbent assay of p27.

Three different monoclonal antibodies were developed against the major core protein (p27) of feline leukemia virus (FeLV). Each antibody was directed against a different epitope of the species-specific portion of FeLV-p27. The 3 antibodies reacted with 5 different isolates of FeLV but not with 7 other retroviruses (MuLV (Rauscher), MuLV (AKR), MPMV, MMTV, SMRV, BAEV, RD 114). These monoclonal antibodies could readily be adapted to an enzyme-linked immunosorbent assay (ELISA) for the specific measurement of FeLV-p27. When compared in an ELISA with conventional reagents, the battery of monoclonal antibodies proved to be as sensitive as conventional polyclonal antibodies.

The response of the lymphoid system to renal allografts in sheep.

The immunological events which occur in lymph nodes situation regional to renal allografts have been studied by collecting lymph from these nodes and monitoring the changes in its cellular and humoral antibody content. Simultaneously, reactions occurring in the renal allograft and in lymph nodes distant to the graft were also monitored in the lymph from these organs throughout thelife of the graft. Large basophilic lymphoid cells appeared first in lymph from the renal allograft at around 48 hr postgrafting, whereas these cells did not appear in the lymph from the regional node until 80-100 hr after the graft was installed. Lymphoid blast cells were not seen inany significant numbers in lumph from nodes situated at a distance from the graft. The first detectable antibody was produced by the regional lymph node between 110 and 175 hr postgrafting, andin other undetermined sites within the next 80 hr. Antibody was not synthesized in any detectable amounts by the graft or by lymph nodes situated at a distance from the graft. The antibody which was present in the lymph from the regional node was produced primarily by fixed cells which remained in the node, and very little antibody was produced by the lymphoid cells which migrated from the node in efferent lymph. The cells in the lymph from the renal allograft produced only small amounts of immunoglobulin. Cells present in lymph from the renal allograft and in lymph from the regional lymph node actively synthesized and secreted significant amounts of nonimmunoglobulin proteins which were separated on Sephadex G-200 columns into peaks which coincided with 19S, 7S, and 4S proteins. The identities and biological activities of these proteins have not yet been determined.

Pathologic studies of acute rejection of mismatched feline musculocutaneous flaps. Effect of cyclosporine and prednisolone.

The gracilis musculocutaneous flap was developed as an allograft model to study acute rejection and immunosuppression in the cat. Twelve adult cats received a MLC incompatible flap. Six of the cats received cyclosporine oral solution and prednisolone (0.5 mg/kg/24 hr) for 100 days and six cats were not treated. Trough whole-blood levels of cyclosporine in the treatment group were maintained at approximately 750 ng/ml for 70 days, then 500 ng/ml for the remaining 30 days. Three flaps failed due to technical problems; 5 flaps were studied in the treatment group and 4 in the untreated group. All 5 flaps in the treatment group survived the 100 day treatment period and were rejected 30 +/- 26 days following cessation of treatment. Prior to discontinuation of treatment, with the exception of one cat, inflammatory changes associated with rejection were not observed in biopsy specimen. The flaps in the untreated group survived 13 +/- 1.5 days. Histopathologic examination of the flaps revealed little difference in the appearance of acute rejection and rejection after cessation of therapy. The most prominent lesion was a vasculitis with extensive perivascular lymphohistocytic inflammation. The lymphoid infiltrates consisted predominantly of T cells of both major classes (CD4 and CD8). Full-thickness epidermal necrosis and subsequent bacterial invasion followed vascular compromise.

Cyclosporine pharmacokinetics in cats following topical ocular administration.

Topical ocular administration of two forms of cyclosporine were studied in the cat. Both forms were able to produce measurable whole-blood levels capable of suppressing in vitro lymphocyte stimulation. The kinetics of cyclosporine following administration of either oral solution or cyclosporine in olive oil were variable, with peak concentrations ranging from 450 to 1033 ng/ml and 288 to 648 ng/ml, respectively. Absorption lag time ranged from 0 to 1.34 hr for oral solution, and 0.27 to 1.2 hr for cyclosporine in olive oil. The half-life of elimination ranged from 2.41 to 10.04 hr, and 3.09 to 15.75 hr, respectively. When compared with the commercially available oral solution, cyclosporine dissolved in olive oil was better tolerated during administration. Topical ocular administration of cyclosporine in cats offers a possible alternative method of treatment for individuals intolerant of oral administration. Topical ocular administration might also replace the need for intravenous administration of cyclosporine during perioperative periods or during periods of vomiting and nausea associated with rejection or other illnesses. Due to individual variation in absorption and elimination of topically applied cyclosporine, dosages in each cat must be determined by monitoring blood, plasma, or serum levels.

The demonstration of antibody specificity by a new technique. The gel electrophoresis-derived enzyme-linked immunosorbent assay (GEDELISA) and its application to antibodies specific for feline leukemia virus.

By combining the high resolution of sodium dodecylsulfate polyacrylamide gel electrophoresis with the sensitivity of enzyme-linked immunosorbent assay (ELISA) antibodies specific for different feline leukemia virus components are characterized. Based on the same principle, Concanavalin A binding sites of FeLV components are also detected.

Feline leukemia virus envelope protein expression encoded by a recombinant vaccinia virus: apparent lack of immunogenicity in vaccinated animals.

We have constructed a recombinant vaccinia virus encoding the expression of the feline leukemia virus (FeLV) envelope gene of the Gardner-Arnstein strain of FeLV subgroup B. Human cells infected with the recombinant virus (vFeLVenv) express and process the FeLV envelope protein similarly to cells infected with authentic FeLV. The mature gp 70 protein is transported to and accumulates on the surface of vFeLVenv-infected cells. Vaccinia virus replication and FeLV gp70 accumulation was also observed in cells of feline and murine origin, albeit at levels somewhat reduced from those in human cells. Toward the goal of developing a recombinant vaccinia virus as a live vaccine for feline leukemia disease in cats, immunogenicity studies were performed in cats and mice. These experiments yielded surprising results: although animals mounted a typical virus-neutralizing antibody response to the vaccinia virus vector, we were unable to detect antibodies against FeLV gp70 in any of the vaccinated animals. A subsequent 'booster' immunization with killed FeLV was unable to elicit evidence of immunologic 'priming' by the recombinant virus. We are presently unable to explain the apparent lack of immunogenicity. These results may point to complexities involved in the development of vaccines to protect against retrovirus infection.