Cross-reactivity studies human tissue

This chapter will discuss various experimental approaches used to select the relevant species for conduct of toxicology studies for biopharmaceuticals, as well as highlight advances made in scientific approaches and technologies to facilitate this process. Methods discussed include the traditional immunohisto-chemistry and tissue cross-reactivity studies, flow cytometry, protein sequencing, and functional in vitro assays, as well as newer approaches such as utilization of microarray databases for genomic mRNA expression data and use of transcript profiling studies as an adjunct to functional assays, to understand similarity in pharmacological responsiveness between animals and humans. 

An example of results from a tissue cross-reactivity study comparing binding of a monoclonal antibody therapeutic to human, cynomolgus monkey, and mouse tissues is shown in Table 9.2. A cell line that did not express the target was used as negative control tissue the same cell line transfected with the... 

Biological Relevance of Human Tissue Cross-Reactivity Studies 233... 

Human Tissues According to the Points-to-Consider and other regulatory documents, tissues from at least three unrelated human donors should be evaluated in a tissue cross-reactivity study in order to screen for individual variation. In a 3-donor, 37-tissue cross-reactivity study, up to 111 different donors could theoretically be represented. To the extent possible, both males and females should be equally represented. 

Tissue banks are the most common source of human tissues. While surgical biopsy accessions are preferred, they are limited in availability and often unavailable for many tissues (e.g., brain and other vital organs). Therefore the majority of tissue samples used in cross-reactivity studies are those acquired at autopsy. For autopsy accessions all efforts must be made to minimize the time interval between death and tissue collection. Information provided with specimens generally includes age, gender, and usually race and some clinical history and/or cause of death. As suggested in the Points-to-Consider document, the tissues used in a standard tissue cross-reactivity study are acquired from adults (>18 years of age). Pediatric tissues are often very difficult to obtain and are usually not used in a standard tissue cross-reactivity study unless there is a clear pediatric indication for the test article. 

BIOLOGICAL RELEVANCE OF HUMAN TISSUE CROSS-REACTIVITY STUDIES 233... 

Tissue cross-reactivity studies, although burdensome, provide a rational in vitro assay to determine the range and intensity of distribution of potential epitopes reactive with a monoclonal antibody test article prior to its administration to humans. In addition, cross-reactivity studies provide a useful tool to identify animal species for safety assessment. The cross-reactivity profiles of different species can be compared to the profiles obtained in human tissues. The predictive value of the assay lies in incorporating the characteristics of the monoclonal antibody (isotype, subtype, and other molecular modifications) with the biological activity of the molecule itself, and the potential in vivo distribution of it. 

Tissue cross-reactivity (TCR) studies Tissue cross-reactivity studies with human tissues (or cells if applicable) are conducted prior to Phase 1 to search for cross-reactions with the intended target and/or nontarget tissue. In special cases of bispecific antibodies, each parent antibody is evaluated individually in addition to testing the bispecific product. Human cells or tissues are surveyed immunocyto-chemically or immunohistochemically with appropriate controls. Animal species are also surveyed to determine relevant species for toxicology studies. 

In a typical tissue cross-reactivity study (see Appendix J, cryosections of normal human (3 unrelated donors) and/or animal (2 unrelated donors) tissues are stained... 

Tissue cross-reactivity studies are required by FDA for monoclonal antibody products to determine if the product binds to target and/or nontarget tissues. They are also performed for nonmonoclonal biopharmaceuticals if warranted. For example, ARANESP was tested in a human tissue panel ex vivo to determine if it bound to nontarget tissues or cross-reacted with related cytokine receptors. These studies are also used to explore known or potential clinical adverse safety events (i.e., mechanism of toxicity). For example, one patient in a Raptiva study developed unilateral hearing loss. This finding was further evaluated by cross-reactivity studies with human optic chiasm, acoustic nerve, and inner ear tissues. 

Tissue cross-reactivity studies comparing human and animal tissues... 

For monoclonal antibodies, the immunological properties of the antibody should be described in detail, including its antigenic specificity, complement binding, and any unintentional reactivity and/or cytotoxicity towards human tissues distinct from the intended target. Such cross-reactivity studies should be carried out by appropriate immunohistochemical procedures using a range of human tissues. 

Pulmonary Assessment in ICH S7A Safety Pharmacology Studies for Human the Conscious Rat Pharmaceuticals Tissue Cross-Reactivity (TCR) 2-4 4-8 25,000 5,000... 

Fertility and early embryonic development rats Developmental rats, rabbits Prenatal and postnatal development rats Genetic toxicology in vitro bacterial and CFIO cell assays, mouse micronucleus assay Carcinogenicity proliferation in vitro and in vivo Tissue cross-reactivity human tissues Other safety studies in a variety of species Single dose none... 

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