The future of canine cancer treatment

Combining ACTs with more traditional treatment modalities is being actively researched as avenues to improve response rates

Roscoe the Great Dane was one of 14 dogs to take part in a recently published pilot study evaluating VACT therapy in canine osteosarcoma. Photo courtesy ELIAS Animal Health
Roscoe the Great Dane was one of 14 dogs to take part in a recently published pilot study evaluating VACT therapy in canine osteosarcoma.
Photo courtesy ELIAS Animal Health

The use of immunotherapies to treat cancers has become increasingly widespread in human medicine, with some of these promising therapeutics producing remarkable outcomes. Further, many of these immunotherapeutics are becoming increasingly available to the veterinary practitioner, providing them with new options to treat oncology patients.

While there are a variety of immunotherapy approaches (e.g. vaccines, checkpoint inhibitors), they share the therapeutic objective of attempting to stimulate an anti-cancer immune response from the host, specifically targeting and eliminating cancer cells. Cancer cells have specific antigens that make them identifiable to the immune system.

Gene mutations caused by genetic instability during carcinogenesis can cause mutations, which can generate proteins not found in normal cells.1 These proteins can activate the immune system and lead its attack on cancer cells. These aberrant antigens, which can be recognized by immune cells, are referred to as “neoantigens.”2 These neoantigens can be presented on the cell surface and subsequently recognized by T cells.2-4

Nevertheless, cancer cells can and do evade detection from the immune system through a variety of methods, including presenting as “self” to immune cells via checkpoint proteins; microenvironment immunosuppression via cytokine signaling; and inducing tolerance in T cells by engaging the T cell receptor in the absence of co-stimulation.5,6 The numerous and diverse defenses cancer cells use to protect themselves are some of the challenges immunotherapies must overcome to generate their desired effects. 


Among the better known immunotherapeutics are the adoptive T cell therapies (ACTs), such as chimeric antigen receptor T cell therapy (CAR-T) and tumor infiltrative lymphocyte therapy (TIL). In CAR-T, host T cells are ex vivo genetically modified to target a specific cancer antigen(s); whereas in TIL, naturally occurring T cells that have already infiltrated patients’ tumors are harvested.7

In both cases, the T cells are ex vivo activated and expanded (i.e. proliferated and made active versus the antigen), then reinfused into the patient. While they differ in initial approach, the goal of ACT treatments is to stimulate the host immune system to specifically target and ultimately eliminate cancer cells.

Here we look at a vaccine primed form of adoptive T cell therapy (VACT), which is currently under development for the treatment of canine osteosarcoma and, potentially, other types of canine cancers. Instead of genetically manipulating T cells or harvesting these cells directly from tumor tissue, VACT uses autologous attenuated cancer cell vaccines manufactured from surgically removed host cancer tissue.

These autologous vaccines are used to condition host T cells to the cancer antigens. The vaccine-primed mononuclear cells are later harvested, and ex vivo expanded and activated prior to reinfusion into the patient. Using vaccines made from autologous tissue also affords the possibility the T cells potentially becoming familiarized with multiple cancer antigens.

In action

Clinical trials in humans evaluating VACT therapy for the treatment of renal cell carcinoma and malignant glioma have been conducted with promising results. VACT for the treatment of glioma in humans has been evaluated in Phase II clinical trials and recently received fast track designation from the U.S. Food and Drug Administration (FDA).8

In a recently published pilot study evaluating VACT therapy in canine osteosarcoma, dogs (n=14) with appendicular osteosarcoma underwent amputation surgery of the affected limb to reduce the disease burden and to harvest source tumor tissue for the production of vaccines.9 Three autologous attenuated-cancer cell/adjuvant vaccines were administered once-weekly intradermally.

Approximately two weeks after the final vaccination, the dogs underwent mononuclear cell apheresis to harvest some of the now vaccine-primed T cells. Once harvested, the T cells were ex vivo activated, expanded, and then sent back to the clinician for intravenous infusion approximately one week later. A day after infusion, a series of low-dose (20,000 IU/Kg), subcutaneous interleukin-2 shots were given every other day (five total). Interleukin-2 is added to the protocol to help continue further T cell proliferation in vivo.

Dogs in the study tolerated the VACT procedures well, with most adverse events reported as mild to moderate (veterinary cooperative oncology group [VCOG] graded 1 or 2). The most common reported adverse events after the T cell infusion were vomiting and gastrointestinal disturbances.

Adoptive T cell therapies, such as VACT, can also potentially trigger cytokine release syndrome (CRS) when the activated T cells are infused into the patient; however, these can be managed. CRS is an acute systemic immune response that can be triggered by the excessive production of pro-inflammatory cytokines generated by the infused activated T-cells. CRS can present with mild- to life-threatening signs, which can include fever, lethargy, dyspnea, and hypotension.

In this canine study, pre-medicants maropitant (1 mg/kg, SC) and diphenhydramine (2 mg/kg, IM) were administered to help mitigate potential nausea or inflammatory events. Clinicians need to be observant post-infusion for early signs of CRS in their patients and intervene, if necessary, to slow its progression.

In this canine study, CRS was not observed in dogs receiving the premedicants. In human studies, high dose dexamethasone (0.25 mg/kg, IV) has been used to relieve and resolve the symptoms of CRS.10 Glucocorticoid use was an option in canine study if needed, but no dogs required steroid intervention. Glucocorticoids would seem contraindicated for an immunotherapy and their chronic use will impair efficacy; however, short-term steroid use (e.g. one or two treatments) to manage CRS is acceptable and has also been used in human CRS patients successfully.11

Outcomes, challenges, and future

Outcomes from this pilot VACT study in osteosarcoma resulted in five dogs surviving at least two years after their treatment (36 percent of treated dogs). Three of these dogs survived more than two years and were reported as cancer-free since receiving treatment. One dog had its osteosarcoma in remission for two years before the malignancy returned and no further treatments were pursued.

Finally, in one exceptional case involving a six-year-old Great Dane, there occurred spontaneous remission of a large 1.2-in. subcutaneous osteosarcoma lesion that appeared several months after T cell infusion. A CT scan of the dog was conducted approximately two months after the metastasis was reported finding no evidence of any malignancy. This Great Dane recently passed away at nine years of age due to difficulty ambulating; however, its cancer had remained in remission until that point. None of the five long-term survivors received any additional cancer therapy post-infusion.

As noted above, it can be challenging for these therapies to breach the many defensive obstacles within the tumor microenvironment. Further, as see in the canine study, only a fraction of patients will respond to therapy. Despite the modest response rate for the patients responding, the effects were pronounced with long-lasting remission.

Combining ACTs with more traditional treatment modalities, such as chemotherapies and radiotherapies, are being actively researched as avenues to improve response rates and outcomes.12,13 The hypothesis being these traditional therapies will not only kill cancer cells, but also disrupt the cancer microenvironment—which then permits greater T cell penetration in affected tissues along with greater interaction with cancer cells. Similarly, combining ACTs with other immunotherapeutics, such as checkpoint inhibitors and oncolytic viruses, has also resulted in improved response rates and promising early results.14

A larger clinical trial evaluating VACT therapy in osteosarcoma-bearing dogs is ongoing with results expected in late 2022. As VACT uses autologous cancer cell vaccines, it has the potential to be of use in any cancer type where source tumor material can be obtained. This has been the case in humans (renal cell carcinoma, glioma). Pilot studies evaluating VACT in other canine cancers, such as oral malignant melanoma, are also currently underway with evaluation in other cancer indications planned.

Noe Reyes, DVM, is the chief medical officer at ELIAS Animal Health, which is developing its VACT therapy (ECI) for the treatment of canine osteosarcoma and other canine cancers.


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