IMMUNOTOXICITY STUDIES FOR HUMAN PHARMACEUTICALS S8

1. INTRODUCTION
   1. Objectives of the Guideline

This guideline’s goals are to: (1) offer suggestions for nonclinical testing methods to find substances that may be immunotoxic; and (2) offer guidance on a weight-of-evidence method for immunotoxicity testing.For the purposes of this guideline, immunotoxicity is defined as unintended immunosuppression or augmentation. Autoimmunity and drug-induced hypersensitivity are not included.

1. Background

Evaluation of potential adverse effects of human pharmaceuticals on the immune system should be integrated into standard drug development. Immune toxicity includes suppression, which reduces host resistance to infections or tumors, and enhancement, which may worsen autoimmune diseases. Drug-related proteins can evoke anti-drug responses, leading to hypersensitivity reactions upon re-exposure. While past research has focused on immunosuppression and contact sensitization, standardized testing for respiratory or systemic allergenicity and drug-specific autoimmunity is not currently mandated. Furthermore, no regional differences exist in skin sensitization testing approaches.

Two different groups can be linked to immunosuppression or enhancement:

1. Drugs that are meant to alter immune function for therapeutic reasons (such as preventing organ transplant rejection), in which case adverse immunosuppression may be seen as excessive pharmacodynamics; 
2. Immunotoxicity is caused by drugs that are not meant to impact immune function, such as when immune cells undergo necrosis or apoptosis or interact with cellular receptors that are shared by both target tissues and non-target immune system cells.

Anti-proliferative agents for cancer treatment can unintentionally cause immunosuppression, with adverse findings in nonclinical studies often predicting human immunotoxicity effectively. Specific assays for immunotoxicity may lack value in drug risk assessment due to the rapid division of target tissues like bone marrow-derived immune progenitor cells, allowing for reliable evaluation in non-clinical studies. Conversely, for compounds not aimed at immune suppression, it can be challenging to differentiate between exaggerated pharmacodynamics and undesired effects, as seen with some anti-inflammatory drugs that may influence innate immune functions without impacting the adaptive immune response.

1.3 Scope of the Guideline

This guideline is focused on providing recommendations on nonclinical testing for immunotoxicity induced by human pharmaceuticals. It is restricted to unintended immunosuppression and immunoenhancement, excluding allergenicity or drug specific autoimmunity.

This guideline pertains to new pharmaceuticals for human use and to marketed drugs seeking different indications or variations that may raise immunotoxicity concerns. It also applies to drugs showing clinical signs of immunotoxicity during trials or post-approval. However, it excludes biotechnology-derived products covered by the ICH S6 Guideline and other biologicals.

Existing guidance on sensitization and hypersensitivity remains unaffected by this document, which does not aim to provide specific instructions for conducting immunotoxicity studies. General methodology guidance can be found in the Appendix.

1.4 Overview

The general principles that apply to this guideline are:

1) All new human pharmaceuticals should be evaluated for the potential to produce immunotoxicity;

2) Methods include standard toxicity studies (STS) and additional immunotoxicity studies conducted as appropriate. Whether additional immunotoxicity studies are appropriate should be determined by a weight of evidence review of factor(s) in section 2.1. The description of the guideline below will follow the recommended decision process in immunotoxicity evaluation as shown in the flow diagram (Figure 1). More detailed descriptions of the testing methods are in the Appendix.

2. GUIDELINE

2.1 Factors to Consider in the Evaluation of Potential Immunotoxicity

The following factors can be taken into account that could lead to further immunotoxicity studies: (1) STS results; (2) the drug’s pharmacological characteristics; (3) the target patient population; (4) structural similarities to known immunomodulators; (5) the drug’s disposition; and (6) clinical data.

Standard toxicity tests are used as the first screen for possible immunotoxicity. It is important to take into account data from both rodent and non-rodent investigations, ranging from early short-term to longer-term repeat-dose studies. The Appendix contains more information about the factors that need to be assessed and how histopathological results should be reported.  

2.1.1 Standard Toxicity Studies

It is important to look for indications of immunotoxic potential in STS data. The following are indicators that need to be considered:

1. Hematological changes such as leukocytopenia/leukocytosis, granulocytopenia/granulocytosis, or lymphopenia/lymphocytosis;
2. Alterations in immune system organ weights and/or histology (e.g., changes in thymus, spleen, lymph nodes, and/or bone marrow);
3. Changes in serum globulins that occur without a plausible explanation, such as effects on the liver or kidney, can be an indication that there are changes in serum immunoglobulins;
4.  Increased incidence of infections;
5. Increased occurrence of tumors can be viewed as a sign of immunosuppression in the absence of other plausible causes such as genotoxicity, hormonal effects, or liver enzyme induction.

Immunosuppression or increased immune system activation may be indicated by changes in these parameters. Immune parameters often show decreased values in immunosuppression and increased levels in immunoenhancement. These connections are not absolute, though, and they may occasionally be reversed.

The evaluation of immunotoxicity should incorporate the following elements, just like the evaluation of risk with toxicities in other organ systems:

• Statistical and biological significance of the changes;
• Severity of the effects;
• Dose/exposure relationship;
• Safety factor above the expected clinical dose;
• Treatment duration;
• Number of species and endpoints affected;
• Changes that may occur secondarily to other factors (e.g., stress, see the Appendix, section 1.4, see reference at the end, for complete ICguideline S8);
• Possible cellular targets and/or mechanism of action;
• Doses which produce these changes in relation to doses which produce other toxicities; and
• Reversibility of effect(s).

2.1.2 Pharmacological Properties

If a test compound may influence immune function, particularly anti-inflammatory drugs, further immunotoxicity testing is advised. Data from nonclinical pharmacology studies can help determine the necessity of additional immunotoxicity studies using a weight of evidence approach.

2.1.3 Intended Patient Population

If the majority of the patient population for whom the drug is intended is immunocompromised due to a disease state or concurrent therapy, further immunotoxicity studies may be necessary.

2.1.4 Structural Similarity

For further immunotoxicity testing, substances that share structural similarities with substances known to have immunosuppressive qualities should be taken into account.

2.1.5 Disposition of the Drug

If the compound and/or its metabolites are retained at high concentrations in cells of the immune system, additional immunotoxicity testing should be considered.

2.1.6 Signs Observed in Clinical Trials or Clinical Use

Clinical findings suggestive of immunotoxicity in patients exposed to the drug could call for additional nonclinical immunotoxicity testing.

2.1.7 Weight of Evidence Review

A weight of evidence review should assess information from all outlined factors to identify any cause for concern. A significant finding in one area may lead to more immunotoxicity studies. Similarly, findings from multiple insufficient factors could also prompt additional studies. If such studies are not conducted, the sponsor must justify their decision.

APPENDIX

Methods to Evaluate Immunotoxicity

The parameters that should be assessed in routine toxicity investigations for indications of immunotoxicity are listed in the following table. Documents from professional toxicological pathology societies provide more detailed descriptions of these characteristics (apart from haematology and clinical chemistry) as well as techniques for collecting samples and assessing tissue sections.

Parameter	Specific Component
Hematology	Total and absolute differential leukocyte counts
Clinical Chemistry	Globulin levels¹ and A/G ratios
Gross pathology	Lymphoid organs / tissues
Organ weights	Thymus, spleen (optional: lymph nodes)
Histology	Thymus, spleen, draining lymph node and at least one additional lymph node, bone marrow², Peyer’s patch³, BALT⁴, NALT⁴

1 Unexplained alterations in globulin levels could call for measurement of immunoglobulins.
2 Unexplained alterations in peripheral blood cell lines or histopathologic findings might suggest that cytologic evaluation of the bone marrow would be appropriate.
3 Oral administration only.
4 For inhalation or nasal route only. BALT: bronchus-associated lymphoid tissues.
NALT: nasal-associated lymphoid tissues

Reference:                                                                                   

https://database.ich.org/sites/default/files/S8_Guideline_0.pdf

                                                                                                                   Dr Subramanian S Iyer