Biopharmaceuticals immune response

In-vitro models can provide preliminary insights into some pharmacodynamic aspects. For example, cultured Caco 2 cell lines (derived from a human colorectal carcinoma) may be used to simulate intestinal absorption behaviour, while cultured hepatic cell lines are available for metabolic studies. However, a comprehensive understanding of the pharmacokinetic effects vfill require the use of in-vivo animal studies, where the drug levels in various tissues can be measured after different dosages and time intervals. Radioactively labelled drugs (carbon-14) may be used to facilitate detection. Animal model studies of human biopharmaceutical products may be compromised by immune responses that would not be expected when actually treating human subjects. 

The duration of such toxicity tests varies. In the USA, the FDA usually recommends a period of up to 2 years, whereas in Europe the recommended duration is usually much shorter. Chronic toxicity studies of biopharmaceuticals can also be complicated by their likely stimulation of an immune response in the recipient animals. In the context of new chemical entities (NCEs, i.e. low molecular weight traditional chemicals), not only can the drug itself exhibit a toxic effect, but so potentially can drug breakdown products. As proteins are degraded to amino acids, any potentially toxicity associated with protein-based drugs is typically associated with the protein itself and not degradation products. 

The duration of such toxicity tests varies. In the USA, the FDA usually recommends a period of up to 2 years, while in Europe the recommended duration is usually much shorter. Chronic toxicity studies of biopharmaceuticals can also be complicated by their likely stimulation of an immune response in the recipient animals. 

Assay performance criteria for biopharmaceuticals are often highly variable therefore strict statistical criteria that attempt to rigorously establish traditional in vivo bioequivalence may not always be appropriate. In some cases an assessment of rate and extent of absorption as indicated by the maximum concentration (Cmax), time of maximum concentration (Tmax) and area under the curve (AUC) may be needed. In other cases complicating factors related to binding proteins, endogenous concentration, and unusual concentration-time profiles may need to be considered [15]. In cases where complications may arise from immune response to heterologous proteins, cross-over designs are inappropriate. 

Immunogenicity is an important issue to consider for biopharmaceuticals as it can limit toxicity testing. An immune response to the biopharmaceutical is expected because the test agents are human proteins administered to animals, and the response can limit the duration of the toxicity studies. Antibodies to a test agent can neutralize its activity and thus reduce exposure. In addition antidrug antibodies can potentially cause toxicity such as deposition of immune complexes in the kidney. This issue is discussed further in Chapter 10. 

Four-week toxicology studies in rodent and nonrodent The four-week studies are designed for subchronic exposure of rodents and nonrodents to the test article. These studies also look at reversibility of any toxicity observed. Many times these are the pivotal studies used to support the first in human dosing. Toxicokinetic assessments are generally included in repeat-dose toxicity studies. When testing biopharmaceuticals, studies also include assessment and characterization of immune response (immunogenicity). 

As the biotechnology industry comes of age, and protein-based therapeutics become a practical reahty, the importance of protein-stabilizing technologies comes increasingly to the fore. The therapeutic efficacy of many of these biopharmaceuticals is impeded by the hosts natural immune defense system [23]. When a host encounters a foreign protein in its circulation, the hosts immune system initiates an immune response, which results in the production of protein-inactivating antibodies that dear the protein from the circulation. When the immune system develops an abihty to inactivate the protein, the therapy becomes ineffective. Hence, to counteract... 

A direct prediction of immunogenicity potential in humans (the incidence and/or severity) based on animal studies using a therapeutic dosing regimen with a biopharmaceutical (not designed to invoke a strong immune response) is very challenging. However, there is the need for a more reliable way to... 

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