Antibody-mediated enhancement of hormone activity

Non-human primates in the PKPD evaluation of biologics: Needs and options to reduce, refine, and replace. A BioSafe White Paper

Monoclonal antibodies (mAbs) deliver great benefits to patients with chronic and/or severe diseases thanks to their strong specificity to the therapeutic target. As a result of this specificity, non-human primates (NHP) are often the only preclinical species in which therapeutic antibodies cross-react with the target. Here, we highlight the value and limitations that NHP studies bring to the design of safe and efficient early clinical trials. Indeed, data generated in NHPs are integrated with in vitro information to predict the concentration/effect relationship in human, and therefore the doses to be tested in first-in-human trials. The similarities and differences in the systems defining the pharmacokinetics and pharmacodynamics (PKPD) of mAbs in NHP and human define the nature and the potential of the preclinical investigations performed in NHPs. Examples have been collated where the use of NHP was either pivotal to the design of the first-in-human trial or, inversely, led to the termination of a project prior to clinical development. The potential impact of immunogenicity on the results generated in NHPs is discussed. Strategies to optimize the use of NHPs for PKPD purposes include the addition of PD endpoints in safety assessment studies and the potential re-use of NHPs after non-terminal studies or cassette dosing several therapeutic agents of interest. Efforts are also made to reduce the use of NHPs in the industry through the use of in vitro systems, alternative in vivo models, and in silico approaches. In the case of prediction of ocular PK, the body of evidence gathered over the last two decades renders the use of NHPs obsolete. Expert perspectives, advantages, and pitfalls with these alternative approaches are shared in this review.

Immunogenicity of biologically-derived therapeutics: assessment and interpretation of nonclinical safety studies

An evaluation of potential antibody formation to biologic therapeutics during the course of nonclinical safety studies and its impact on the toxicity profile is expected under current regulatory guidance and is accepted standard practice. However, approaches for incorporating this information in the interpretation of nonclinical safety studies are not clearly established. Described here are the immunological basis of anti-drug antibody formation to biopharmaceuticals (immunogenicity) in laboratory animals, and approaches for generating and interpreting immunogenicity data from nonclinical safety studies of biotechnology-derived therapeutics to support their progression to clinical evaluation. We subscribe that immunogenicity testing strategies should be adapted to the specific needs of each therapeutic development program, and data generated from such analyses should be integrated with available clinical and anatomic pathology, pharmacokinetic, and pharmacodynamic data to properly interpret nonclinical studies.

Antibodies as molecular mimics of biomolecules: roles in understanding physiological functions and mechanisms

Physiologists have routinely used understanding of the immune system to generate antibodies against regulatory molecules, growth factors, plasma membrane receptors, and other mammalian molecules in the development of analytical tools and assays. In taking this notion further, antibodies have been used in vivo to modulate physiological systems and to improve our understanding of their molecular interactions. To develop antibodies with physiological activity (efficacy), physiologists have worked with immunologists in developing interdisciplinary insights, requiring basic knowledge of immune system function in designing strategies to generate antibodies that interact with endogenous molecules of physiological interest, in vivo. Antibodies in different physiological systems have been shown to enhance or inhibit endogenous molecular functions. Two approaches have been used: passive and active immunization. Antibodies in these contexts have provided tools to develop further insights into molecular physiological mechanisms. Perhaps surprisingly, enhancing antibodies have been developed against a diverse set of target molecules including several members of the growth hormone/insulin-like growth factor-I axes and those of the beta(2)-adrenoceptor axis. Antibodies that inhibit the actions of somatostatin have also been developed. A further novel approach has been the development of antibodies that interact with adipose cells in vivo. These have the potential to be used in therapeutic antiobesity approaches. Antibodies with efficacy in vivo have provided new insights into molecular physiological mechanisms, enhancing our understanding of these complex processes.

Positive effects of testosterone and immunochallenge on energy allocation to reproductive organs

A number of studies have suggested the incompatibility of simultaneous increases in immune and reproductive functions. Other research has indicated that immune responses may be modulated depending on the relative benefits of increased survival and prospects for current and future reproduction. We tested the hypothesis that energy allocation to reproductive and other organ systems is not affected by testosterone level and energy expenditure on immune functions. Adult male white-footed mice (Peromyscus leucopus) with or without elevated testosterone levels and with or without immunochallenges were tested. Testosterone treatment was associated with reduced humoral immune response indicating immunosuppressive effects, reduced masses of gastrointestinal organs, reduced corticosterone level, increased kidney and seminal vesicle masses, and increased hematocrit. Immunochallenge was associated with increased resting metabolic rate and testes and seminal vesicle masses. Reproductive organ masses were greatest in immunochallenged mice with exogenous testosterone. Simultaneous increases in energy allocation to immune and reproductive structures may be an adaptive response that would enhance survival and current prospects for reproduction.

Monoclonal Antibodies Inducing Conformational Changes on the Antigen Molecule

Monoclonal antibodies (MoAbs) are extensively used as biological tools because of their invariable specificity. However, the interpretation of results can be misled by the behaviour of MoAb displaying allosteric effects, i.e. long-range conformational changes on the antigen (Ag). It has been shown that some MoAbs are able to modify the spatial structure of the corresponding protein Ag, affecting in this way its biological activity as well as its binding to a second MoAb. Thus, a researcher using a MoAb as a tool to investigate some features of an antigenic molecule must be aware of the possible positive or negative allosteric properties of the antibody.

Serum IgG levels to bovine insulin in type I diabetes mellitus

OBJECTIVES

This study was undertaken to determine humoral immune response to bovine insulin in Iranian children with type 1 diabetes mellitus.

METHODS

Serum samples were taken from 93 children aged 4-17 years with type I diabetes mellitus from two centers in Iran (the Iranian Association of Diabetes in Tehran and Center for Diabetes Research in Hamedan), 17 apparently healthy siblings of the diabetic patients (related controls), 28 apparently healthy age- and sex- matched controls (unrelated controls), 14 patients aged 11-15 years with auto-immune thyroiditis, and 45 patients with type II diabetes (aged 44-68 years). Samples were then examined for specific IgG to bovine insulin by enzyme-linked immunosorbent assay (ELISA). A questionnaire on medical history, duration of exclusive and non-exclusive breast feeding and daily intake of dairy products was completed before bleeding.

RESULTS

Duration of exclusive and non-exclusive breast-feeding showed no significant difference between patients with type I diabetes, related and unrelated controls and thyroid patients. Diabetic children, however, had significantly higher serum levels of anti-bovine insulin IgG than did unrelated and related healthy controls and patients with type II diabetes (P< 0.01). There was no significant difference between healthy siblings of diabetic children and unrelated controls. In type I diabetic patients and their healthy siblings, serum levels of IgG to bovine insulin were inversely correlated with the duration of non-exclusive breast feeding (rs= -0.37, P= 0.016 and rs= -0.53, P= 0.049, respectively). There was no correlation between serum levels of IgG to bovine insulin with daily intake of dairy products. Bovine insulin cross-reacted with human insulin as judged by ELISA inhibition assay.

CONCLUSION

The emergence of anti-insulin antibodies in Iranian patients with type I DM, which is associated with the duration of breast-feeding is less likely to be due to early exposure of infants with the proteins found in cow's milk. One speculation could be that the production of antibodies to insulin in type I diabetes may just be a physiologic response (probably to increase the half-life of the circulating insulin). The importance of anti-insulin antibodies in type I diabetes mellitus needs further studies.

Actions of monoclonal antibodies on the activity of human growth hormone (GH) in an in vitro bioassay

An in vitro bioassay for GH was established, based on the response of the 3T3-F442A mouse preadipocyte cell line, together with a parallel receptor-binding assay using the same cells. The effects of monoclonal antibodies on the biological activity of human GH in vitro were then explored. Antibodies that did not bind GH had no effect on the bioassay or on receptor binding. Antibodies EB1 and EB2, which strongly enhance growth-promoting actions in vivo, inhibited the actions of human GH in the in vitro bioassay, and blocked binding of human GH to receptors. Antibody NA71, which weakly enhances growth promotion by human GH in vivo, enhanced biological activity in vitro but did not affect receptor binding. Thus, enhancement of the biological activity of human GH has been shown in this in vitro system, but the effect does not correlate completely with the established enhancement effects in vivo. Of the various mechanisms that have been proposed to explain the enhancement effect these results support the 'restriction hypothesis'--the idea that monoclonal antibodies may enhance GH action in vivo by preventing binding of GH to receptors/binding sites that are not involved in growth promotion.

Immunological manipulation of body composition

Hormonal growth promoters (e.g., growth hormone [GH], beta-adrenergic agonists, steroids), which improve growth rate and/or lean:fat ratios in the carcass, have received considerable adverse publicity and are either banned or have no licence for their use in the EC. This has led to the development of a number of techniques, involving the use of antibodies, aimed at regulating metabolic processes involved in determining growth and body composition. A different approach to the problem of excess fat deposition involves the use of antibodies directed against the plasma membranes of adipocytes in order to elicit their destruction and thereby limit the capacity for fat storage. This technique has been demonstrated in rats, sheep and pigs in both passive and active immunisation techniques. This promising approach is, however, limited by the lack of a commercially suitable vaccine. The identification of individual membrane proteins that are antigenic has been achieved and this affords the prospect of producing recombinant DNA-derived vaccines. Whether these new approaches will be perceived as acceptable to the general public remains a serious concern and a potential limitation to their development as many would-be sponsors withdraw their support for research in these areas.

Structure and function of bovine growth hormone. Bovine growth hormone as an experimental model for studies of protein-protein interactions

Growth hormone (GH) is a polipeptide that controls the differentiation, growth and metabolism of many cell types, and is secreted from the hypophysis of all vertebrate species tested so far. Despite the overlapping evolutionary, structural, immunological and biological properties, it is well-known that GHs from distinct mammalian species have significant species-specific characteristics. The main purpose of this review is to highlight bovine GH (bGH) structural features related to its species-specific properties. Novel interest in bGH is also aroused by the advent of biotechnological methods for production of recombinant proteins. In fact recombinant bGH will have a great importance in veterinary medicine research and as a 'high tech' drug that needs to be monitored in zootechnical productions.

Immunological effect of a synthetic growth hormone peptide on the growth performance in swine

A mouse monoclonal antibody (mAb), designated PS-7.6, was previously shown to enhance the activity of porcine growth hormone (pGH) in promoting the growth of hypophysectomized (hypox) rats. Epitope mapping studies indicated that the region recognized by PS-7.6 resided within an amino acid sequence 54-95 of pGH. A peptide corresponding to this sequence was synthesized and found to induce swine antibodies capable of augmenting pGH activity in hypox rats. On the basis of these previous observations, an attempt was made in this study to determine whether or not the peptide pGH(54-95) could be used as a vaccine to elicit antibodies functionally similar to PS-7.6 mAb, thus potentiating the efficacy of endogenous GH in swine. Young pigs (15-20 kg) were immunized with pGH(54-95) that had been conjugated with ovalbumin (OVA) and boosted twice at 4-week intervals. Control animals were similarly immunized with OVA. The weight gains and feed consumption of these animals were closely monitored throughout the trials. A number of carcass parameters were also examined when these animals reached 110-120 kg, at which time they were killed. Results indicated that immunization with peptide significantly accelerated the daily weight gain during the growing phase of growth. However, this effect disappeared during the finishing phase of growth. The failure to prolong the initial growth effect by the peptide immunization apparently correlated with the kinetics of antibody production, because antibodies immunoreactive to the peptide and pGH were detected in these animals after immunization but gradually diminished. This idea was supported by the fact that antibodies obtained from pigs 5 and 9 weeks after the initial immunization potentiated the activity of pGH in hypox rats, whereas antibodies harvested at week 16 did not. Furthermore, carcass evaluation was performed at time of killing and showed that the leaf fat and loin eye muscle were also significantly improved by peptide immunization. Taken together, the present findings suggest that pGH(54-95) peptide can be employed as a potential growth-promoting vaccine to improve the performance of swine.

Facilitation of the growth promoting effect of growth hormone (GH) by an antibody to methionyl-GH

Despite the development of antibodies to methionyl growth hormone in a child with hypopituitarism, the patient grew at a rapid rate on low doses of somatotropin. Serum immunoglobulins from this patient stimulated the growth of Nb2 lymphoma cells in vitro in samples obtained within 48 hours after the last dose of growth hormone, while samples obtained several weeks after an injection of methionyl growth hormone did not. Immunoglobulins from normal subjects or from hyposomatotropic patients being treated with methionyl growth hormone who had not developed antibodies did not stimulate Nb2 lymphoma cell growth. We suggest that the antibodies to methionyl growth hormone in this child served as a reservoir for exogenous growth hormone or facilitated the interaction of growth hormone with the prolactin receptor on the Nb2 lymphoma cell.

A humanized anti-tumor necrosis factor-alpha monoclonal antibody that acts as a partial, competitive antagonist of the template antibody

We have constructed several humanized versions of a monoclonal antibody (MAb78) against human tumor necrosis factor-alpha (huTNF-alpha) retaining the complementarity-determining regions (CDR) of the original mouse MAb with or without a variable number of original framework region (FR) residues. All versions, except one, showed a loss of binding affinity and neutralizing potency of at least 10-fold compared to the original mouse MAb or its chimeric equivalent. In some cases, however, the decrease in neutralizing potency was significantly greater than the decrease in binding affinity. Two humanized versions showing the greatest dissociation between these two parameters were studied for their capacity to inhibit the neutralizing activity of chimeric or murine MAb78 when used at concentrations that bound but only partially neutralized huTNF-alpha. One humanized version (MAb78D) was indeed able to do so, whereas the other (MAb78C) was not found to exert any inhibitory activity at all concentrations tested. The antagonistic effect of MAb78D was concentration dependent and could be overcome by increasing the concentrations of chimeric or murine MAb78. Two different models of MAb78-huTNF-alpha interaction that may help explain the antagonist activity of humanized MAb78D are discussed.

Selective enhancement of the tumour necrotic activity of TNF alpha with monoclonal antibody

The binding and biological activity of human TNF alpha on endothelial and tumour cells has been studied in the presence of monoclonal antibodies (MAbs). In particular, one monoclonal antibody to TNF alpha (MAb 32) has been identified which failed to inhibit binding and cytotoxicity of TNF alpha on WEHI-164 tumour cells but which was a potent inhibitor of TNF alpha-induced endothelial cell procoagulant activity on bovine aortic endothelial cells. The ability of MAb 32 to inhibit selectively the actions of TNF alpha on endothelial cells but not on tumour cells suggests a mechanism for enhancement of the anti-tumour action of TNF alpha in vivo when in complex with this antibody. Treatment of tumour bearing mice (WEHI-164 and Meth A fibrosarcoma) with TNF alpha-MAb 32 complex resulted in a 5- to 10-fold enhancement in the potency of the cytokine in comparison to free TNF alpha. Complexes between this cytokine and other MAbs generally resulted in either no effect or inhibition of TNF alpha activity in vivo and in vitro. Neither intact MAb 32 nor FAb' fragments of MAb 32 showed any tumour regressive activity in the absence of TNF alpha. The FAb' fragments were equipotent to the bivalent form of the antibody in enhancing TNF alpha activity. These data provide evidence that it is possible to segregate the individual biological activities of TNF alpha with concomitant enhancement of the tumour regressive activity of the cytokine in vivo.

Antigenic structure of human tumour necrosis factor: recognition of distinct regions of TNF alpha by different tumour cell receptors

TNF alpha is a cytokine which causes cytolysis of tumour cell lines in vitro as well as haemorrhagic necrosis of many transplanted tumours in vivo. In association with these activities, the cytokine manifests a high degree of toxicity in vivo. The in vitro and in vivo effects of a panel of 13 monoclonal antibodies against human TNF alpha have been investigated. Of these MAbs, eight neutralized TNF alpha activity in the WEHI-164 cytotoxicity assay as well as in the binding of TNF alpha to receptors on these cells. The effects of this group of antibodies on TNF alpha-induced regression of WEHI tumours in vivo correlated with their in vitro neutralizing activities. One MAb which inhibited cytotoxicity, receptor interaction and tumour regression in the WEHI model (MAb 37) failed to inhibit TNF alpha-receptor binding and tumour regression in Meth A models. This observation indicates that different classes of receptor specificity may exist on different tumour cells. Together the antibodies define six non-overlapping epitopic domains on TNF alpha and within these regions there are at least nine overlapping epitopes. Inhibitory MAbs, when co-injected into tumour-bearing mice with radiolabelled TNF alpha, resulted in the diversion of TNF alpha away from both tumour and lung, which correspond to the sites of highest TNF alpha uptake in control MAb-TNF alpha treated mice. In contrast, uptake of TNF alpha by the liver was increased and overall, biodistribution studies showed that very little TNF alpha reached the target tumour but was rapidly and widely dispersed throughout the body. Preliminary studies with these MAbs show that segregation of TNF alpha activities and receptor binding may be possible.

Somatotropin antibody formation in cows treated with a recombinant bovine somatotropin over two lactations

Blood plasma from cows treated with somidobove, a form of recombinant bovine somatotropin, was assayed for development of antibodies against the protein. Forty-three Holstein cows, selected from an animal safety study, were monitored. Cows were divided into four groups and treated with placebo, 960, 2880, or 4800 mg somidobove per dose at 28-d intervals during two successive lactation periods. Blood plasma was collected at intervals prior to and during the lactations, and levels of IgG antibody reactive with somidobove were determined in an enzyme-linked immunosorbent assay. Virtually all of the cows treated with somidobove developed low levels (less than 40 micrograms/ml) of antibody against somidobove. One or two cows from each group responded with some-what higher levels, ranging from 40 to 200 micrograms/ml. Responses generally increased during the first 3 mo of treatment, then decreased, and remained constant with continued treatment. There was no sign of a memory response within or among the lactation periods, and no adverse health effects or decreases in lactational performance were associated with antibody production.