DOG ANTIBODY LIBRARY FOR PHAGE DISPLAY

The use of dog antibodies
in research and therapy

In the past decade, the use of immunotherapies in veterinary medicine has been gaining ground over conventional treatments. But one of the major challenges still hindering their widespread use is the limited availability of canine-specific reagents, vital to better understand dogs’ immune systems. Additionally, there are still significant gaps in knowledge concerning the genotype and phenotype of tumors in dogs and corresponding disease biomarkers. Although these limitations hamper the efforts of immunotherapy development for dogs, they also create an unprecedented opportunity for progress.

The lack of native antibodies was the main driving force behind the generation of our new premium dog antibody library – LiAb-SFDog^TM. Being the first of its kind on the market, it offers an avenue for quickly generating antibodies for veterinary research and therapy. But what is known about the use of monoclonal antibodies to treat animals?

The proof that canine cancer was responsive to immunotherapy was provided in the 1960s with the first successful bone marrow transplant between littermates. Since then, the use of immunotherapy in dogs was shown to successfully tackle conditions such as sarcoma, lymphoma, mammary cancer, arthritis, dermatitis, and parvovirus infections, among others.

Immunotherapy for dogs: are monoclonal
antibodies used to treat animals?

Antibodies are a hallmark of human medicine. In comparison, the development of new dog immunotherapeutics has lagged considerably. Currently, only a few therapies are commercially available in the USA and Canada:

• Tactress®, an anti-canine CD52 monoclonal antibody (Tamtuvetmab), USDA-approved in 2014
• Blontress®, an anti-canine CD20 monoclonal antibody (Blontuvetmab), USDA-approved in 2015
• Cytopoint®, an anti-canine IL31 monoclonal antibody (Lokivetmab), USDA-approved in 2016

In comparison to their human equivalents, these antibodies have shown limited effectiveness. One reason for this limitation may stem from the fact that these therapeutics have been developed by a process of caninization.

As the name indicates, this process is similar to antibody humanization. However, our limited knowledge regarding dog immunology has made caninization significantly more risky, expensive, and time-consuming than the humanization process. Moreover, disease targets may differ significantly between dogs and humans, making the process of target selection and antigen design suboptimal when it comes to the treatment of canine diseases.

Despite the current challenges, interesting breakthroughs were achieved in recent years in the development of efficient antibody treatments for dogs:

• Canine lymphoma monoclonal antibody treatment: lymphoma is the most common type of hematological cancer found in dogs. Good responses have been obtained using multi-agent chemotherapy. However, survival rates remain low (<20%). One study recently reported promising results when a chimeric (canine-rat) anti-canine CD20 monoclonal antibody showed significant B cell depletion in in vivo experiments. Comparative studies with the currently approved Blontress® are still necessary to understand how both treatments perform over time.
• Canine arthritis monoclonal antibody treatment: arthritis is a slowly progressing degenerative joint disease, primarily affecting the hip, stifle, and elbow joints in dogs. In time, arthritis leads to chronic panic and loss of joint function. Several studies are currently underway attempting to develop efficient species-specific anti-NGF (nerve growth factor) monoclonal antibodies to reduce pain and slow the progress of the disease in dogs.
• Canine atopic dermatitis monoclonal antibody treatment: dermatitis is an allergic inflammation of the skin, often tied to environmental factors such as house dust mites and pollen. The only monoclonal antibody treatment currently available for veterinary medicine is Cytopoint®. The treatment consists of an anti-canine IL31 antibody (Lokivetmab), a caninized chimeric antibody. Studies show that this treatment is efficient at reducing itchy skin and inflammation.
• Canine parvovirus monoclonal antibody treatment: canine parvovirus is a devastating and deadly enteric infection currently on the rise across the globe. Although it can be prevented by vaccination, there are currently no approved treatments for this condition. The only known treatment under active development is KIND-030, a chimeric monoclonal antibody targeting canine parvovirus (CPV). It was shown to significantly increase survival rates in infected dogs but more studies are necessary to determine its effectiveness.

The generation of monoclonal antibodies targeting high-incidence diseases is expected to alleviate the burden imposed on the veterinary healthcare system. All available monoclonal antibody treatments for dogs are early generations (chimeric or caninized) with most of the biopharmaceuticals generated by caninization of xenogeneic antibodies (mouse, rat, etc.).

The promising results obtained with these antibodies suggest that the use of native dog antibodies would significantly boost the development of new, highly efficient, and cost-effective immunotherapies.

The relevance of dogs as cancer animal models

In parallel to the development of immunotherapies for dogs, many researchers are actively investigating the relevance and feasibility of using dogs as cancer animal models.

The dominant models of human disease at the preclinical stage are mouse models. Despite the wealth of knowledge generated by these models, they are prone to important limitations. For instance, due to their small size, it is challenging to study the importance of dose and dosage regimen in these models. Additionally, mice disease phenotypes often differ significantly from their human counterparts, making it harder to extrapolate results to the clinic.

In contrast, the use of dogs as disease models has been invaluable to increase our knowledge on pathogenesis and treatment efficacy. Dogs and humans share over 58% of diseases caused by mutations in the same genes. Moreover, a plethora of arguments makes they suited for preclinical studies including

• The canine immune system is more similar to humans than the mouse’s immune system. Like humans, dogs of a certain age have a very immunologically experienced system caused by repeated exposure to antigens and multiple immunizations.
• Dogs also share the same environment as their human companions. For this reason, they are exposed to many of the same allergens, food antigens, and environmental chemicals. Therefore, dogs’ immune response is more analogous to humans.
• Dogs develop spontaneous tumors (not implanted or induced as occurs in mouse models), which means that, like humans, they are exposed to tumor-associated antigens for long periods and thus react to immunotherapy differently than rodents.
• Due to their large size (often comparable to that of a human child), drugs administrated to dogs based on their weight or body surface area are much more likely to result in an accurate drug activity and toxicity profile. In contrast, mice are frequently treated with much higher doses, often toxic to humans, making them ill-suited to estimate dose-response relationships.
• Also due to their large size, access to blood and tissue samples is more straightforward in dogs in comparison to rodents. This facilitated access allows closer monitoring of the progression of the immune response to different treatments and dosage regimens.

Research shows that rodent models will continue to be essential for early proof-of-concept studies, particularly when it comes to their use as cancer models. However, these models have proven to be insufficient when estimating the ultimate effectiveness of new immunotherapies in humans (dosage and regimen-wise).

Dogs are large animals, sharing much with their human owners such as their immune response, disease markers, and exposure to the same or similar antigens. One particular area of research where the use of dogs as cancer models may bring great value is in the study of checkpoint molecule targeted immunotherapies. The use of checkpoint inhibitors in dogs both as monotherapies or combined therapeutic approaches (e.g., in combination with chemotherapy), would improve our knowledge regarding the effectiveness of these treatments, particularly against solid tumors where much research remains to be done.