Immune function studies assay

If the weight-of-evidence review indicates that additional immunotoxicity studies are needed, there are a number of assays which can be used. It is recommended that an immune function study be conducted, such as a T-cell dependent antibody response (TDAR). If specific cell types are affected in STS not involving cells participating in a TDAR, assays that measure... 

A major difficulty with any of these assays is their lack of sensitivity to demonstrate mild to moderate changes in immune function. These assays are typically used for the diagnosis of primary or acquired immune deficiency when one given arm of the immune response is thought to be profoundly affected. Otherwise, there is a wide physiological range in response in these assays so that defects caused by treatment or exposure to unintended immunosuppressive drugs are likely to be missed or overlooked. In fact, the same situation is found in preclinical immunotoxicity studies. 

The best human data available on immune response involve small numbers of subjects and lack of adequate controls. Additional studies on immune function parameters in both children and adults are needed to verify or refute the lack of immunotoxicify seen in humans to date. These studies should include a well defined set of immunologic assays in order to facilitate comparisons between studies. 

Migration of cells in response to stimuli is responsible for several physiological functions mostly in the case of inflammatory responses and immune functions. The transwell chemotaxis assay is useful to study mechanisms of migration during chemotaxis. The main purpose of this assay is to determine if a molecule of interest exhibits chemotactic activity. Molecules that... 

Generally accepted 28 consecutive daily doses in rodents. Adaptations of immunotoxicity assays have been described using non-rodent species. The species, strain, dose, duration, and route of administration used in immune function assays should be consistent, where possible, with the non-clinical toxicology study in which an adverse immune effect was observed. 

There have been no reports that physical and mental development or renal function are altered. In one study, there were changes in T lymphocyte development in seven children born to mothers who had taken azathioprine or ciclosporin, but immune function assays were normal (203). Thus, development of the fetal immune system is not affected by ciclosporin (204). 

An important immune function to evaluate in the context of immuno-deficiency, and one that represents a form of nonspecific immunity/host resistance, is the function of natural killer (NK) cells. NK cells are lymphocytes distinct from either B-cells or T-cells, which contribute to immunocompetence by mediating major histocompatibility complex-independent cytotoxicity (Lotzova 1993). For the purposes of these studies, a combined measurement of both basal and augmented NK cell function was used. In this assay, murine splenoc5des were exposed for 24 hours to various concentrations of drugs in the presence or absence of an optimum concentration of recombinant IL-2 (Thomas et al. 1993). The cells were then washed and cocultured for 4 hours with radiolabeled YAC-1 tumor cells (a murine NK-sensitive cell line). Tumor cell lysis was quantitated as described above for the CTL procedure. 

Other animal studies indicate that repeated inhalation exposure to formaldehyde at high concentrations, between 10 and 15 ppm, did not produce significant effects in several assays of immune function including resistance to intravenous or subcutaneous injection of neoplastic cells in mice (Dean et al. 

Effects on immune function, as indicated by altered responses in humoral and cell-mediated immunity assays and host resistance tests, were also induced by intermediate-duration oral exposure to commercial mixtures. Studies in nonprimate species showed reduced antibody responses to tetanus toxoid in guinea pigs exposed to Clopen A-60 (4 mg/kg/day for 3-5 weeks), keyhole limpet hemocyanin in rats exposed to Aroclor 1254 (4.3 mg/kg/day for 10 weeks), and SRBC in mice exposed to Aroclor 1242 (22 mg/kg/day... 

The subcommittee reviewed several recentimmunotoxicity studies ofJP-8 that used immune-function assays (see Table 6-1). However, the methods for those studies largely have not been standardized through interlaboratory com-... 

Figure 3.3.1-2 Application of the TDAR assay in immunotoxicity assessment. When evaluating unintended immunosuppression, the TDAR assay may be conducted when evidence of immunotoxicity is seen in repeated-dose toxicity studies. In these instances, the assay should be conducted prior to Phase 3 or earlier, depending on factors such as the severity of the findings and the intended patient population. The TDAR assay also could be used early in the drug development process to screen for immunotoxicity potential. This approach may be useful particularly to help de-risk unintended off-target immunomodulation or when a novel target/mechanisms may alter immune function.

Since assays to measure cell-mediated immunity are not as well established and not as quantitative as those used to measure other immune end points, inclusion of the DTH test within a battery of other immune function assays or studies would be beneficial in determining the relative risk of immuno-toxicity. A weight-of-evidence approach should be used when evaluating DTH responses to determine the biological and/or toxicological relevance for observed changes. The following points should be considered ... 

Preclinical studies have shown that impaired immune function determined using a variety of assays, e.g., the plaque-forming cell (PFC) assay, lymphocyte proliferation, delayed-type hypersensitivity, and NK cell activity, is associated with decreased resistance toward experimental infections (Luster et al., 1994). When a drug candidate has been shown to impair immune function in animal studies, the question arises whether similarly negative effects can also be seen in treated human subjects. 

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