Comparing the preclinical risk profile of inhalable candidate and potential candidate modified risk tobacco products: A bridging use case

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Heated tobacco products tested for reduced exposure and reduced risk properties.

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Bridging opportunities for nonclinical results from two heated tobacco products.

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Similarly reduced impact on apical and molecular endpoints relative to cigarettes.

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Evidence evaluated along a “causal chain of events leading to disease” (CELSD).

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Representative assays along CELSD could support nonclinical substantial equivalence.

Cigarette smoking causes major preventable diseases, morbidity, and mortality worldwide. Smoking cessation and prevention of smoking initiation are the preferred means for reducing these risks. Less harmful tobacco products, termed modified-risk tobacco products (MRTP), are being developed as a potential alternative for current adult smokers who would otherwise continue smoking. According to a regulatory framework issued by the US Food and Drug Administration, a manufacturer must provide comprehensive scientific evidence that the product significantly reduces harm and the risk of tobacco-related diseases, in order to obtain marketing authorization for a new MRTP. For new tobacco products similar to an already approved predicate product, the FDA has foreseen a simplified procedure for assessing “substantial equivalence”. In this article, we present a use case that bridges the nonclinical evidence from previous studies demonstrating the relatively reduced harm potential of two heat-not-burn products based on different tobacco heating principles. The nonclinical evidence was collected along a “causal chain of events leading to disease” (CELSD) to systematically follow the consequences of reduced exposure to toxicants (relative to cigarette smoke) through increasing levels of biological complexity up to disease manifestation in animal models of human disease. This approach leverages the principles of systems biology and toxicology as a basis for further extrapolation to human studies. The experimental results demonstrate a similarly reduced impact of both products on apical and molecular endpoints, no novel effects not seen with cigarette smoke exposure, and an effect of switching from cigarettes to either MRTP that is comparable to that of complete smoking cessation. Ideally, a subset of representative assays from the presented sequence along the CELSD could be sufficient for predicting similarity or substantial equivalence in the nonclinical impact of novel products; this would require further validation, for which the present use case could serve as a starting point.

A framework for in vitro systems toxicology assessment of e-liquids

Various electronic nicotine delivery systems (ENDS), of which electronic cigarettes (e-cigs) are the most recognized prototype, have been quickly gaining ground on conventional cigarettes because they are perceived as less harmful. Research assessing the potential effects of ENDS exposure in humans is currently limited and inconclusive. New products are emerging with numerous variations in designs and performance parameters within and across brands. Acknowledging these challenges, we present here a proposed framework for an in vitro systems toxicology assessment of e-liquids and their aerosols, intended to complement the battery of assays for standard toxicity assessments. The proposed framework utilizes high-throughput toxicity assessments of e-liquids and their aerosols, in which the device-to-device variability is minimized, and a systems-level investigation of the cellular mechanisms of toxicity is an integral part. An analytical chemistry investigation is also included as a part of the framework to provide accurate and reliable chemistry data solidifying the toxicological assessment. In its simplest form, the framework comprises of three main layers: (1) high-throughput toxicity screening of e-liquids using primary human cell culture systems; (2) toxicity-related mechanistic assessment of selected e-liquids, and (3) toxicity-related mechanistic assessment of their aerosols using organotypic air-liquid interface airway culture systems. A systems toxicology assessment approach is leveraged to enable in-depth analyses of the toxicity-related cellular mechanisms of e-liquids and their aerosols. We present example use cases to demonstrate the suitability of the framework for a robust in vitro assessment of e-liquids and their aerosols.

Ribonucleotides: conditionally essential nutrients shown to enhance immune function and reduce diarrheal disease in infants

It remains a goal of pediatric nutrition to provide optimal nourishment for infants who are not fed human milk. Investigators have attempted to emulate the composition and functionality of human milk, the gold standard for infant nutrition. These efforts began with the analysis of milk components and continued with assessments of biological effects that culminated in clinical studies in infants. This chapter summarizes the path that researchers followed to study ribonucleotides and their role in infant nutrition. Based on analytical methods for the quantification of ribonucleotides in human milk, investigators assessed their potential impact on the immune systems of infants and looked for concomitant mechanistic explanations. These inquiries evolved into clinical trials in which ribonucleotide-supplemented formula performance was compared with that of non-supplemented formulas and with human milk. This chapter intends to summarize an area of pediatric nutrition that has yielded both enlightening evidence and seemingly contradictory data.

Longitudinal study of intracellular T cell cytokine production in infants compared to adults

Intracellular cytokine production in lymphocytes obtained longitudinally from 325 healthy infants aged 2-12 months was compared with adult lymphocytes using four-colour flow cytometry. Peripheral blood samples (180 microlitres) were stimulated with phorbol 12-myristate 13-acetate, ionomycin and brefeldin A to induce production and intracellular accumulation of cytokines. The method was validated by assessing reproducibility, repeatibility, ruggedness (i.e. fresh versus day-old blood samples), precision, linearity and sensitivity. Among infants, the number and percentage of T lymphocytes (helper/inducer T cell subsets and cytotoxic/suppressor T cell subsets) producing IFN-gamma (type 1) and IL4 (type 2) increased over the first year of life but remained significantly lower than levels found in adults. In both infants and adults more CD4- T cells than CD4+ T cells were induced to make IFN-gamma. Infant Th1/Th2 ratios revealed modest Th1-skewed (predominant) profiles compared to adults, which were 5-10 times higher. Infant Tc1/Tc2 ratios revealed Tc1-skewed responses which were equal to adult ratios by age 12 months. At 12 months infant Th2 responses were closer to adult levels than were Th1 cells. Intracellular cytokine detection by flow cytometry is a rapid, sensitive, rugged and precise method to characterize immune status changes over time.

Modulation of the immune system by human milk and infant formula containing nucleotides

OBJECTIVE

To determine whether human milk and nucleotides added to infant formula at levels present in human milk enhance development of the immune system during infancy.

METHODS

A 12-month, controlled, randomized and blinded, multisite feeding trial was conducted on two infant formulas: iron-fortified, milk-based control formula (Control) or the same formula fortified with nucleotides (Nucleotide). The level (72 mg/L) and ratio of individual nucleotides selected were patterned after those available in human milk. A third group fed human milk exclusively for 2 months and then human milk or Similac with iron until 12 months of age also was studied. Response to immunizations was chosen to assess development of the immune system. Infants followed the immunization schedule recommended by the American Academy of Pediatrics in 1991.

OUTCOME VARIABLES

Antibody responses were determined at 6, 7, and 12 months of age to Haemophilus influenzae type b polysaccharide (Hib), to diphtheria and tetanus toxoids, and to oral polio virus (OPV) immunizations.

RESULTS

Of 370 full-term, healthy infants enrolled, 311 completed the study (107 Control, 101 Nucleotide, 103 human milk/Similac with iron). Intake, tolerance, and growth of infants were similar in all three groups. Compared with the Control group 1 month after the third immunization (7 months of age), the Nucleotide group had a significantly higher Hib antibody concentration (geometric mean concentrations of 7.24 vs 4.05 micrograms/mL, respectively), and a significantly higher diphtheria antibody concentration (geometric mean of 1.77 vs 1.38 U/mL). The significantly higher Hib antibody response in the Nucleotide group persisted at 12 months. The antibody responses to tetanus and OPV were not enhanced by nucleotide fortification. There also was an effect of breastfeeding on immune response. Infants who breastfed had significantly higher neutralizing antibody titers to polio virus than either formula-fed group (1:346 vs 1:169 and 1:192 in the Control and Nucleotide groups, respectively) at 6 months of age.

CONCLUSION

Infant formula fortified with nucleotides enhanced H influenzae type b and diphtheria humoral antibody responses. Feeding human milk enhanced antibody responses to OPV. Dietary factors play a role in the antibody response of infants to immunization.

Prevention of human rotavirus-induced diarrhea in gnotobiotic piglets using bovine antibody

The efficacy of passively administered bovine antibody for preventing human rotavirus (HRV)-induced diarrhea was investigated using a gnotobiotic pig model. Cows were immunized with inactivated HRV serotypes 1 (Wa) and 2 (S2) and simian rotavirus serotype 3 (SA11), and immune colostrum and milk were collected. Antibody concentrates derived from these materials were fed to germ-free piglets that were subsequently inoculated with HRV Wa. Both viral shedding and diarrhea were effectively reduced or eliminated in a dose-dependent manner as a result of HRV immune antibody feeding. A quantitative virus-neutralizing (VN) antibody method permitted assessment of the functional antibody dose required to achieve a 50% reduction of disease (PD50). PD50 dose levels of 15.8 and 19.5 x 10(6) VN antibody units were determined for inhibition of diarrhea and viral shedding, respectively. Studies reported here provide new information on the quantitative relationship between protective antibody dose and diarrheal disease response.

Bis(bioreductive) alkylating agents: synthesis and biological activity in a nude mouse human carcinoma model

Chemical investigations leading to the construction of bis(bioreductive) alkylating agents having both conformationally restricted and mobile spacer regions are described. Two targets having the conformationally mobile ethylene spacer group, namely, 2,2'-ethylenebis[6-(hydroxymethyl)-p-benzoquinone] diacetate (3b) and 2,2'-ethylenebis[6-(bromomethyl)-p-benzoquinone] (3c), were studied in vivo and in vitro using an established epithelial/Burkitt lymphoma hybrid cell line (D98/HR1) previously shown to induce carcinomas in nude mice. Inactivity of both test compounds in vitro, the relative resistance of these cells to test drugs in vitro, and the selective antitumor properties of the bis(bromomethyl) analogue in vivo lead to the proposal that this compound undergoes bioreduction to an alkylating species in the hypoxic core of the tumor, thereby exerting its action.

Induction of retinal degeneration in cats by methylnitrosourea and ketamine hydrochloride

Persistent mydriasis seen in cats used in an oncology study apparently was not related to neoplasia. Ophthalmoscopically, the cats had severely atrophic retinas and clinically observable visual impairment. These findings were confirmed by electroretinographic and histologic examination. Cats with these retinal lesions had received combinations of methylnitrosourea, ketamine hydrochloride, and feline leukemia virus. Retinopathy was not seen in ketamine-anesthetized cats receiving feline leukemia virus. To test the nature of this phenomenon, four cats were given both drugs and three received methylnitrosourea alone. The four cats developed severe generalized retinal degeneration by day 5, whereas the three cats given methylnitrosourea alone had normal retinas. Histologic changes in the affected cats were extensive loss of rods and cones, and of the outer nuclear layer. The electroretinographic responses to white light were depressed or extinguished. Retinal degeneration, therefore, appeared to be dependent upon administration of both methylnitrosourea and ketamine hydrochloride.

Infection of feline embryo adherent cells with feline leukemia virus: feline oncornavirus-associated cell membrane antigen expression and morphologic transformation

Feline embryo adherent cells were infected with the Richard or Kawakami-Theilen strains of feline leukemia virus (FeLV) and examined for feline oncornavirus-associated cell membrane antigen (FOCMA), viral group-specific antigen (gsa) production, and in vitro evidence of transformation. As early as 10 days after infection, when more than half of the infected cells were gsa positive, FOCMA was detected on 5-10 percent of the cells. Transitory morphologic alterations (epithelioid appearance and rounding) were first noted in most cultures around 20-30 days post infection. At this time, approximately 50% of the cells in infected cultures expressed FOCMA. Morphologic characteristics of transformed fibroblastic cells (rounded shape, disordered alignment, and low adhesion to substratum), as well as enhanced agglutinability by plant lectins and ability to grow in agar, were demonstrated in one of four FeLV-infected, FOCMA-positive cultures. Findings showed that FOCMA may be expressed in FeLV-infected monolayer cells independent of transformation as assessed by in vitro criteria.

The effects of methylnitrosourea on the immune system and hematopoietic system of adult specific pathogen free cats

The effects of a single non-carcinogenic dose of 15 mg/kg methylnitrosourea (MNU) on the immune and hematopoietic systems of adult specific-pathogen-free (SPF) cats were determined. The cell-mediated-immune (CMI) system was markedly suppressed, as evidenced by: (i) Prolonged cutaneous allograft retention time (41-84 days); (ii) Decreased lymphocyte blast transformation response to mitogens (2% of pretreatment response to pokeweed mitogen or concanavalin A) and antigen (12% of untreated control cat response to keyhole limpet hemocyanin); (iii) Reduced number of absolute erythrocyte-rosetting T-cells in the peripheral blood. This immunosuppression lasted at least 3 months, the duration of the experiment. Suppression of the hematopoietic system was also noted as evidenced by: (i) Peripheral lymphopenia lasting 3 months and neutropenia lasting 3 weeks; (ii) Bone marrow hypocellularity lasting 3 weeks; (iii) Hypoplasia of neutrophilic precursors lasting 3 weeks and erythroid precursors lasting 4 days. It was concluded that a single non-carcinogenic dose of MNU induces a prolonged suppression of the CMI system and a brief suppression of hematopoiesis in adult SPF cats. The immunosuppression may in part be responsible for the previously observed increased susceptibility to feline leukemia virus infection and disease of adult SPF cats treated with MNU.

Enhancement of feline leukemia virus-induced leukemogenesis in cats exposed to methylnitrosourea

The effect of methylnitrosourea (MNU), a potent resorptive carcinogen, was evaluated for its influence on the susceptibility of adult cats to infection and induction of oncornavirus disease by feline leukemia virus (FeLV). Young adult cats at an age previously demonstrated to be highly resistant to FeLV, were injected intravenously with moderately toxic doses (15-20 mg/kg) of MNU alone or with infections FeLV (Rickard strain). Following exposure to virus and chemical, cats were monitored for antibody to the feline oncornavirus-associated cell membrane antigen (FOCMA), viremia by direct infectivity and the presence of gsa in peripheral blood leukocytes, and for toxic effects of MNU by hemogram analyses on peripheral blood. Of 8 cats injected with MNU + FeLV, 6 developed persistent viremia, 5 of which became debilitated from thymic lymphoma. Only 1 of 6 non-MNU-treated and infected cats of the same age became transiently viremic. FOCMA antibody development was markedly depressed in MNU + FeLV inoculated cats compared with cats inoculated with FeLV alone. Results show that MNU was apparently responsible for the obliteration of age-related susceptibility in cats to FeLV infection and induction of FeLV-related disease, and suggest that in nature exposure to toxic chemical carcinogens may act as factors which determine susceptibility to feline oncornaviruses in the cat.

Immunosuppressive properties of a virion polypeptide, a 15,000-dalton protein, from feline leukemia virus

The 15,000-molecular-weight polypeptide (p15) of feline leukemia virus (FeLV) was shown to impair normal lymphocyte function in vitro and to abrogate immunity to feline oncornavirus disease in vivo. FeLVp15 suppressed concanavalin A-induced blast transformation of normal feline lymphocytes by 68%, while other virion proteins had no effect. p15 suppression was not due to toxicity, nor was p15 a competitive inhibitor of concanavalin A binding. Capping of receptors for concanavalin A on normal feline lymphocytes also was inhibited by either inactivated FeLV or FeLV p15. Groups of cats were immunized with either killed feline oncornavirus-associated cell membrane antigen bearing tumor cells or tumor cells plus FeLV p15. After challenge with feline sarcoma virus, three of four p15-treated cats developed progressive fatal fibrosarcoma as compared to one of five non-p15-treated cats. The cats receiving p15 also had lower cytotoxic antibody titers against feline oncornavirus-associated cell membrane antigen (mean peak titer, 1:6) than did the non-p15 group (1:74). These data support the hypothesis that the immunosuppression in cats infected with FeLV is mediated by FeLV p15.

Modifications of the immunofluorescence assay for feline leukemia virus group-specific antigens

Observations and minor modifications are presented concerning the immunofluorescence assay for feline leukemia virus (FeLV) group-specific antigens (GSA) in blood cells of cats. Data are given regarding absorption of goat FeLV GSA antiserum in vivo in cats, absorption of the antiserum in vitro with feline blood cells, and the comparative efficacy of various chemical fixatives in preservation of FeLV GSA for immunofluorescent staining. The best results were obtained with in vitro absorption of antiserum and methanol fixation of FeLV GSA in blood smears.

Increased susceptibility to feline leukemia virus infection in cats exposed to methylnitrosourea

Exposure of adult specific-pathogen-free cats to methylnitrosourea resulted in increased susceptibility to infection by feline leukemia virus. A greater proportion of cats exposed to methylnitrosourea and feline leukemia virus (69%) became persistently viremic than those exposed to feline leukemia virus alone (17%). Segmented neutrophils were reduced by 90 to 99% within 3 days following exposure to methylnitrosourea, (15 to 20 mg/kg) whereas the effects on lymphocytes and erythrocytes, although less obvious, were also detected.

Detection and evaluation of feline oncornavirus-induced cell surface antigen(s) shed from cells in vitro

A method for preparation of soluble feline oncornavirus-induced cell surface antigens was described. This technique relied upon the natural release of antigen(s) from FL-74 feline lymphoblastoid cells during their maintenance at 37 degrees in serum-deficient medium. When concentrated and clarified spent medium from 4-day cultures was tested for its antigen content by inhibition of humoral cytotoxicity, it was found that this natural production of soluble antigen provided more feline oncornavirus-associated cell membrane antigen per cell than did a solubilization procedure in which papain was used. The shed antigen preparation was immunogenic in cats, eliciting humoral antibody that was reactive with the surface of FL-74 Cells and feline sarcoma virus-transformed nonproducer mink cells but was not reactive with feline leukemia virus in a virus neutralization assay.

Relationship between feline leukemia virus antigen expression and viral infectivity in blood, bone marrow, and saliva of cats

Correlation was greater than 90% between feline leukemia virus (FeLV), group-specific antigen (GSA) in leukocytes, and viral infectivity (VI) in serum or plasma from 132 cats infected with either the Rickard strain of FeLV, the Snyder-Theilen strain of feline sarcoma virus, or field strains of FeLV. Detection of GSA in blood cells was at least as sensitive as detection of VI in serum. In 45% of FeLV GSA-positive cats inoculated with FeLV-Rickard strain, VI was detected in saliva. No saliva samples from GSA-negative cats had VI. Sequential bone marrow biopsies from 34 cats inoculated with Snyder-Theilen feline sarcoma virus indicated that the correlation between FeLV GSA in bone marrow cells and blood cells was virtually 100%. FeLV GSA appeared in bone marrow leukocyte precursors 1 week before its appearance in peripheral blood leukocytes in 50% of the cats. The FeLV GSA-positive state was transient (3 to 6 weeks) in 34% of the Snyder-Theilen feline sarcoma virus-inoculated cats.

Abrogation of resistance to feline oncornavirus disease by immunization with killed feline leukemia virus

Four-week-old specific-pathogen-free cats were immunized with a combined vaccine composed of killed feline leukemia virus and killed feline oncornavirus-associated cell membrane antigen-containing tumor cells. Immunization induced feline oncornavirus-associated cell membrane antigen antibody titers ranging from 1:32 to 1:256 but did not elicit detectable virus-neutralizing antibody titers. Kittens immunized with tumor cells alone developed higher feline oncornavirus-associated cell membrane antigen antibody titers (ranging from 1:512 to 1:2048) than those given the combined vaccine. All kittens were challenged with virulent Dynder-Theilen feline sarcoma virus at 12 weeks of age. Seventy-five % of the kittens vaccinated with combined vaccine and 67% of unvaccinated control kittens developed progressive fibrosarcomas after challenge. By contrast, none of the kittens vaccinated with killed tumor cells alone developed progressive fibrosarcomas after challenge. The combined vaccine did not, however, inhibit the induction of feline leukemia virus viremia.

Passive immunity to feline leukemia: evaluation of immunity from dams naturally infected and experimentally vaccinated

Antibodies against feline leukemia virus (FeLV) and the feline oncornavirus-associated cell membrane antigen (FOCMA) were transferred from pregnant cats to their suckling kittens. All of these kittens were protected against infection and oncogenesis by virulent FeLV when challenged at 2 weeks of age. Suckling kittens acquired 25 to 100% of maternal virus-neutralizing and FOCMA titers by 3 days of age, and titers underwent linear decay to undetectable levels by 2 to 3 months of age. FOCMA antibody in dams and kittens was identified as immunoglobulin G (IgG) by use of goat anti-human IgG serum, which cross-reacts with feline IgG in the indirect membrane immunofluorescence test for FOCMA antibody. In an attempt to induce protective maternal antibody by vaccination, 10 pregnant cats were immunized by three to five weekly intramuscular injections with purified FeLV inactivated by ultraviolet irradiation. After the course of immunization, neither virus-neutralizing nor FOCMA antibody was detectable in the dams or in 19 kittens born to these cats. When these kittens were challenged with FeLV at 2 weeks of age, 18 of 19 developed persistent viremia and FeLV-related disease.

Preparation of cell-free feline oncornavirus-associated cell membrane antigen

Cell-free feline oncornavirus-associated cell membrane antigen (FOCMA) was prepared from a feline lymphoblastoid cell line of tumor origin (FL-74). Membrane fractions, separated on sucrose density gradients, and papain-solubilized products were found to contain FOCMA as determined by their capacity to inhibit reference cytotoxic cat antisera.

Horizontal transmission of feline leukemia virus under experimental conditions

Thirty-seven specific-pathogen-free (SPF) cats ranging from newborn to 1 year were inoculated with the Rickard strain of feline leukemia virus (FeLV). Each inoculated cat shared a cage with a control SPF cat for 40 weeks post inoculation. After 4-5 weeks, 20 of the inoculated cats became group-specific antigen (gsa)-positive; the other 17 remained gsa-negative but developed virus neutralizing and feline oncornavirus cell membrane-associated antigen antibody titers. Seventeen of the control cats in contact with the gsa-positive cats developed evidence of FeLV infection 4-18 weeks after virema was detected in their inoculated cage mates. Of the control cats in contact with inoculated cats that remained gsa-negative, none developed evidence of FeLV infection. Data indicated that the gsa-positive state in cats inoculated with FeLV correlated with the capacity for horizontal transmission of the virus.

Immunization against feline oncarnavirus disease using a killed tumor cell vaccine

Specific pathogen-free cats were immunized with an inactivated feline oncornavirus tumor cell vaccine. Immunized cats produced high antibody titers to the feline oncornavirus-associated cell membrane antigen and were protected from oncogenic feline sarcoma virus challenge. However, immunization did not produce virus-neutralizing antibody nor did it prevent viremia.

Feline leukemia virus infection: age-related variation in response of cats to experimental infection

Sixty-seven specific-pathogen-free cats of various ages (newborn, 2 wk, 1 mo, 2 mo, 4 mo, and 1 yr) were inoculated ip with either the Rickard (R) or the Kawakami-Theilen (KT) strain of feline leukemia virus (FeLV). Susceptibility to FeLV was judged by induction of a) FeLV group-specific antigens (gsa) in leukocytes, b) FeLV-related disease, c) antibody to feline oncornavirus-associated cell membrane antigen (FOCMA), and d) virus-neutralizing (VN) antibody. Susceptibility to FeLV-decreased with age. Persistent viremia and FeLV-related disease developed in 100% of cats inoculated as newborns, in 85% of cats inoculated at 2 weeks to 2 months of age, and in 15% of cats inoculated at 4 months or 1 year of age. Cats susceptible to FeLV leukemogenesis became persistently FeLV gsa-positive (viremic) at 4 weeks post inoculation and thereafter and produced little or no FOCMA or VN antibody. Cats that resisted leukemogenesis by FeLV all developed persistent FOCMA and VN titers and never became FeLV gsa-positive. The disease in inoculated cats was influenced by virus strain; FeLV-R induced predominantly thymic lymphosarcoma, whereas FeLV-KT caused fatal nonregenerative anemia without concurrent neoplasia.

Influence of glucocorticoid, estrogen, and androgen hormones on transformation of human cells in vitro by feline sarcoma virus

Infection of human foreskin cells (D-550) by the Snyder-Theilen strain of feline sarcoma virus produced small but countable foci and demonstrated "single-hit" dose-response kinetics. Significant quantitative and qualitative enhancement of focus formation was observed when the glucocorticoid hormones, dexamethasone, hydrocortisone, cortisol acetate, and prednisolone were added to cell cultures (1.0 mug/ml) 24 hr postinfection. However, aldosterone, while inducing qualitatively larger foci, did not bring about a quantitative enhancement in total foci number. By contrast, 17beta-estradiol, progesterone, cortisone acetate, methyltestosterone, and estrone elicited little or no effect on focus induction by Snyder-Theilen feline sarcoma virus. Evidence is suggestive of a posttranscriptional effect possibly modulating viral genome expression resulting in an increased efficiency of viral transformation, and an increased proliferation of transformed cells.

Feline oncornavirus-associated cell membrane antigen. VI. Cytotoxic antibody in cats exposed to feline leukemia virus

Feline leukemia virus (FeLV)-infected specific pathogen-free (SPF) cats, normal uninfected SPF cats, and healthy cats from leukemic households were tested for antibody reactive to the feline oncornavirus-associated cell membrane antigen (FOCMA)-containing target cell line FL-74 by microcytotoxicity and indirect membrane immunofluorescence. Of the infected SPF animals, 81% showed concordant reactivity for the two tests. In contrast, only 55% of the healthy cats known to be naturally exposed to FeLV for long periods showed such concordance. FOCMA antibody could not be detected in normal SPF cats by either indirect membrane immunofluorescence or microcytotoxicity. Most cats in the FeLV-infected SPF group developed antibody detectable by both procedures by the fifth week post inoculation. Antibody detectable by membrane immunofluorescence persisted in a high percentage (75-90%) of the animals throughout the observation period of 19 weeks; after 9 weeks, fewer cats had antibody that was also detectable by microcytotoxicity.

Inactivation of tumor cell-associated feline oncornavirus for preparation of an infectious virus-free tumor cell immunogen

Ultraviolet (UV) and thermal methods of inactivating the oncogenic potential of C-type particle-producing feline oncornavirus-induced tumor cells were developed. The techniques were evaluated by several parameters for their use in preparation of cellular immunogens. The UV inactivation dose required to reduce the number of focus-forming units per ml by 1 log10 for FL-74 lymphoblastoid cell-associated feline leukemia virus was 44,000 ergs/sq mm, and the thermal inactivation dose required to reduce the number of focus-forming units per ml by 1 log10 at 45 degrees was 16 min. Inactivation of greater than 6 log10 of virus per ml associated with 4 x 10(8) cells required a UV dose of 270,000 ergs/sq mm, 100 min at 45 degrees or 3 min at 56 degrees. All three treatments concomitantly destroyed the replicating potential of FL-74 cells as shown by their inability to propagate under normal growth conditions and to incorporate [3H]thymidine into nuclear DNA. UV inactivation and thermal inactivation at 45 degrees allowed the best retention of feline oncornavirus-associated cell membrane antigen. A 50% loss in antigenic activity was observed as a result of 56 degrees treatment, but this method was the only one that did not destroy the surface structural integrity of FL-74 cells.

Experimental oncornavirus vaccines in the cat

An experimental approach to the immunoprophylatic control of feline oncornavirus-mediated diseases has included induction of antivirus immunity and antibodies to the feline oncornavirus-associated membrane (tumor) antigens. A suitable model for exploring the effectiveness of killed oncornavirus vaccines in the cat has been provided by the use of feline sarcoma virus. Immunization of seven pregnant queens over a 6-week period with ultraviolet light-inactivated Gardner-Arnstein feline sarcoma virus resulted in significant protection among 12 kittens challenged with a tumor-forming Dose 90 at 7 days of age. This immunity was not present in kittens challenged at 35 days of age. Among 12 kittens born of queens immunized during pregnancy with ultraviolet light-inactivated Kawakami-Theilen feline leukemia virus and challenged with the same live virus at 4 days of age, significant protection was noted, ranging from prolongation of survival time to complete protection in 3 kittens. In general, the higher the antibody titer in the mother, the more effective the protection afforded the kittens. Immunization of 43 kittens during their first 5 weeks of life with the same vaccines used in adult cats did not immunize sufficiently to protect against feline sarcoma virus challenge at 5 weeks of age. Neutralizing antibody responses in these kittens were significantly lower than in pregnant queens. That kittens of this age are immunologically responsive was established, since complete protection of 9 kittens to feline sarcoma virus was obtained by immunization with a crude tumor extract inactivated with 5 to 7 megarads of gamma-irradiation. All these kittens developed feline oncornavirus-associated membrane antibodies while 3 developed demonstrable levels of virus-neutralizing antibodies. The results of these studies are believed indicative that killed virus vaccines and tumor vaccines can be effective immunoprophylatic measures in the control of RNA tumor virus oncogenesis in the cat. Developments in this model system should be relevant to any consideration given similar vaccines in humans.

Influence of culture conditions of growth of FL-74 cells and feline oncornavirus cell membrane associated antigen production

The FL-74 cell, a feline lymphoblastoid cell line derived from a tumor induced by leukemia virus, grows equally well in static suspension culture (plastic T-flask or silicone treated glass bottles) or in spinner culture. No growth was observed in unsiliconized glass bottles. Although feline leukemia virus production was nearly the same in FL-74 grown in each of the above types of vessel, the expression of the feline oncornavirus membrane associated antigen (FOCMA), as determined by membrane immunofluorescence, was more intense and more complete on cells grown in static suspension. Moreover, higher fluorescent antibody titer endpoints were observed with cells from static suspension cultures than with cells from spinner cultures, FL-74 cells grown in spinner culture, when subjected to partial synchrony by cold block or by deprivation of essential amino acids (arginine and/or isoleucine) for 12 hr, achieved a membrane fluorescent pattern for FOCMA similar to cells grown in static suspension. It is proposed that the expression of FOCMA on the cell membrane surface is cell-cycle dependent, and that the rate at which a cell passes through the cell cycle determines the pattern and intensity of the fluorescence of the cell membrane.

Feline oncornavirus-associated cell membrane antigen. V. Humoral immune response to virus and cell membrane antigens in cats inoculated with Gardner-Arnstein feline sarcoma virus

Tumor growth responses in 5- to 6-week-old kittens inoculated with the Gardner-Arnstein strain of feline sarcoma virus exhibited three distinct pattern: 1) complete tumor regression or no detectable tumor growth in approximately one-third of 43 inoculated kittens, 2) rapid tumor progression which led to debilitation and death within 16.2 +/- 4.2 weeks following infection in an additional one-third, and 3) slow tumor growth or temporary regressions in the remaining third. The feline oncornavirus-associated cell membrane antigen (FOCMA) antibody response was closely correlated with tumor progression; rapid progressors had the lowest antibody titers, whereas those in the "no tumor or permanent regression" categories had the highest titers. These results agreed with those previously observed with another virus strain, the Snyder-Theilen feline sarcoma virus. Cats in the intermediate categories of tumor growth also had intermediate levels of FOCMA antibody. The presence of virus-neutralizing (VN) activity was not always correlated with anti-FOCMA activity. Animals in the rapid-progressor category, compared to the regressors or slow progressors, were more likely to have detectable VN antibody during early periods. Conversely, animals in the regressor group or group with no tumors were more likely to show an early rise in detectable anti-FOCMA activity than animals in either of the progressor groups.

Determination of subgroup-specific feline oncornavirus-neutralizing antibody

A microneutralization assay was developed for antibody-to-subgroup-specific feline oncornaviruses. This study combines the economic advantage of a microtiter system and the quantitative focus reduction method which permits contruction of multiplicity curves for determination of virus-neutralizing titers. A twofold increase in Synder-Theilen feline sarcoma virus (ST-FeSV) on feline embryo cells decreased by approximately twofold the titer of reference goat serum prepared against Kawakami-Theilen feline leukemia virus. Similar dose effects with FeLV serotype virus preparations were not observed. An assay system utilizing FeLV serotypes on sarcoma-positive leukemia-negative cells demonstrated slightly greater sensitivity than one employing ST-FeSV on FE cells. Differential antibody responses to the three subgroup-specific feline oncornaviruses (A, B ,and C) were observed in reference goat sera. This test demonstrated good reproducibility as well as sensitivity and constitutes a significant improvement over end point dilution assay systems.

Transformation potentials of the noninfectious (defective) component in pools of adenoviruses type 12 and simian adenovirus 7

Pools of adenovirus 12 and simian adenovirus 7 were separated into four or five fractions by density gradient centrifugation in cesium chloride. Each fraction was analyzed for total in vitro infectivity units, total transformation activity, and for total virus particle (VP) content. Two major subpopulations were separated with mean densities of 1.30 +/- 0.02 and 1.34 +/- 0.02 g/ml, respectively. Virions in the 1.34 g/ml range were highly infectious (10(2) to 10(3) VP per infectivity unit) in contrast to virions at 1.30 g/ml density (10(4) to 10(5) VP per infectivity units). Transformation capacity was evenly distributed throughout fractions of both viruses, indicating that genetically incomplete or defective virus particles were not deficient in their ability to induce transformation. The average VP per transformation unit for adenovirus 12 (2.85 x 10(6)) and for simian adenovirus 7 (4.00 x 10(6)) did not vary significantly from fraction to fraction. These values were obtained with optimal input multiplicities of 16 to 64 VP per cell. At higher multiplicities the apparent increase in VP per transformation unit was attributable to the viral cytocidal effect on hamster cells. These studies revealed that quantitation of in vitro transformation based on VP multiplicities was more reliable than on the basis of infectious units. These estimates were independent of method of virus production, extraction, and purification.