ANIMAL MODELS

HIV Cure Research Training Curriculum The HIV CURE training curriculum is a collaborative project aimed at making HIV cure research science accessible to the community and the HIV research field.

Session Goals• Understand purpose of animal models in

HIV cure research

• Identify two major types of animal models• As well as their benefits and disadvantages

• Know mechanisms to be tested in animal models for cure research

Why we use animal models• Researchers can investigate disease models thoroughly to

assess risks and benefit

• Models can be evaluated using methods that may not be possible in humans

• Work in animals may impose a level of harm that would be unethical in humans

• Offer reliable and reproducible experimental systems for research

• Able to control timing, dose and route of infection

What is an animal model?• Living but non-human

• Has features similar to the system being studied or has a feature that is advantageous for research

• Have become an essential component of translational research for HIV/AIDS• No two humans are alike, so model should address a

specific problem to be evaluated

Timeline to drug development

Lab research for proof of

concept

Animal model

Phase 1

Phase 1I

PhaseIII

Preclinical research Clinical testing Roll out

NDP filing Accepted

and approved applicatio

n

Product launch.

Post marketsurveillance.

Animal models in HIV• Average rate of successful transition from

animal models to clinical research is low

• Two major categories of animal models used in HIV research are:

1. Humanized mice2. Non-human primates

Isolate human hematopoietic stem cells (HSC)a. Blood cells that give rise to other blood cellsb. Located in bone marrow

Humanized mice: overview

Engraft immunodeficient mouse with human HSC to develop humanized mouse

• Mouse model that shares similar features with human immune system

Immunodeficient mouse

Humanized mouse

HSC

Humanized mice: overview

• Alternatively, can also have immunocompetent mice expressing human genes by transgenesis

• Advantages of engraftment model is that the lympocytes developed in mice from hHSCs undergo selection and are then tolerant to the mouse host

Humanized mice: overview

• Relatively inexpensive & simple• Cheaper to acquire than other models

• Small size• Lower maintenance costs• Lower requirements for storage/space

• Able to genetically mutate because it is a small model

• Can generate multiple cohorts of mice from multiple human donors

Humanized mice: benefits

Humanized mice: challenges• Unlike other small animal models, can not

breed humanized mice

• Can’t create large cohorts from a single human donor

• Lack normal lymphoid structure and function

Non-human primates: overview• Physiologically and immunologically similar to

humans• Provides advantage over other models

• There are many models based on the macaque species• Rhesus, pigtail, cynomolgus, etc.

• SIV is not pathogenic in it’s host but NHP models are available with particular challenge viruses that allow for pathogenic SIV infection of macaque

Non-human primates: benefits• The infection pathway of SIV is closely

related to HIV in humans

• Non-human primates share physiological similarities with humans. Such as:• Gastrointestinal tracts – important in evaluating

reservoir• Reproductive system

Non-human primates: challenges• Very costly to develop and maintain long term

• Natural resistance to non-nucleoside reverse transcriptase inhibitors

• Genetic variation between animals• Can make work difficult in terms of controlling for variables• MHC expression can vary

• Can’t infect with HIV but alternatives produce many important, key elements of HIV infection

• Can infect with SIV or SHIV• Not identical to HIV but very close in function

• NHP models used for HIV cure research are underdeveloped compared with those used in HIV transmission studies

• Use of NHPs banned in some countries due to ethical concerns

Animal models and cure research• No consensus on how animal models should be used for cure research

• But in animal models, can monitor HIV replication• Monitor viral load levels• CD4+ T cell depletion• Immune activation

• Also, thorough characterization of persistent reservoirs (active and persistent)

• Using consistent and invasive sampling of reservoirs

• Assess effects of therapeutic interventions• Particularly advantageous for ATI

• Models can also be used to assess the source of viral rebound after treatment interruption

Animal models and cure research

Animal models can be particularly useful in evaluating HIV cure mechanisms in the following areas:• Viral expression activators• Immune cell exhaustion• Can be challenged with HIV multiple times

• Measure/quantify the response

• Measuring the HIV reservoir - in the brain especially

Conclusions• Animal models have contributed greatly to HIV

research generally

• Models are being optimized for use in HIV cure research• Many useful applications and avenues to explore in viral

eradication

• Animal models provide many benefits but also pose challenges• Even within a category of animal model, each sub-type is

characterized by it’s own unique set of challenges