IMMUNE THERAPY OF CANINE CANCER: AN UPDATE ON CURRENT CLINICAL TRIALS IN CANINE
LYMPHOMA AND OSTEOSARCOMA AT THE UNIVERSITY OF PENNSYLVANIA
Nicola Mason, BVetMed, PhD (Immunology), DACVIM
Assistant Professor of Medicine
Penn Vet, Ryan Hospital
315 Hill Pavilion, 380 South University Avenue
Philadelphia, PA 19104
VACCINE TARGETING HER2/NEU FOR THE PREVENTION OF METASTATIC OSTEOSARCOMA
Osteosarcoma (OSA) is a common, highly aggressive mesenchymal tumor that affects approximately 8000 dogs
per year in the USA and accounts for approximately 85% of all canine bone tumors. It most frequently affects the
long bones of adult large and giant breed dogs including Rottweilers, Labradors, Greyhounds, Newfoundlands,
Great Danes and Irish Wolfhounds. Although osteosarcoma is a locally invasive tumor it is also highly metastatic
and it is estimated that 90-95% of dogs have microscopic pulmonary metastases at the time of diagnosis. Current
therapy for canine osteosarcoma consists of limb amputation followed by systemic chemotherapy. However
despite therapy 60% of patients die within one year of diagnosis from pulmonary metastatic disease and less
frequently metastases to the bone and local lymph nodes.
The Human Epidermal Growth Factor Receptor-2, (Her2/neu) is one of four membrane bound receptor tyrosine
kinases belonging to the erbB family. Her2/neu forms heterodimers with the other family members and
engagement of the EGFRs with epidermal growth factors promotes cellular proliferation, survival, angiogenesis
and cellular migration and invasion. Over-expression of Her2/neu occurs commonly in human cancers including
breast, ovarian, stomach, colon, pancreas and prostate and is a bone fide target for immunotherapy in these
cancers. Furthermore, over-expression of Her2/neu in these cancer types is associated with a more aggressive
tumor phenotype.
Her2/neu is also over-expressed in 40-50% of human OSA and 40% of canine OSA. In human patients, overexpression
of Her2/neu in OSA has been associated with a more aggressive phenotype and increased risk of
metastasis. One small study in dogs has suggested that over-expression of Her2/neu in OSA correlates with
reduced overall survival, but larger studies are needed to confirm these findings. Taken together the literature suggests that Her2/neu may serve as a clinically relevant target for the prevention and treatment of metastatic
OSA.
In collaboration with the developmental stage biotechnology company Advaxis, we are currently performing a
high profile phase I clinical trial to evaluate the safety and therapeutic efficacy of a recombinant L. moncytogenes
expressing huHer-2/neu vaccine as adjuvant therapy in dogs with osteosarcoma. The purpose of this study is to
identify the maximum tolerate dose (MTD) of modified L. moncytogenes and whether this can safely elicit Her-
2/neu specific T cell immune responses and anti-tumor immunity in dogs with appendicular osteosarcoma (OSA).
The secondary outcome measures include event free survival and overall survival.
Dogs with a histological diagnosis of appendicular osteosarcoma that over-express Her2/neu (determined by
immunohistochemistry), an ECOG performance score of <1, no other systemic diseases, no evidence of pulmonary
metastases, intact immune function (as determined by neutrophil oxidative burst assays and lymphocyte
proliferation assays), no evidence of cardiac dysfunction or penicillin hypersensitivity and a life expectancy of >2
months are eligible for enrollment. All eligible patients must have undergone standard of care for OSA that
includes amputation of the affected limb and follow up chemotherapy consisting of 4 doses of carboplatin.
Patients received three vaccinations given three weeks apart. Dogs are re-staged three weeks following the third
vaccine and then every 2 months thereafter. Peripheral blood mononuclear cells are collected at baseline, prior to
each vaccination and then every 2 months thereafter to evaluate the effects of the vaccine on her2/neu specific T
cell responses.
To date, 8 dogs have been enrolled to the study and 6 have been vaccinated at the University of Pennsylvania.
Two enrolled dogs did not qualify for vaccination due to the presence of subclinical cardiac dysfunction (1) and
poor immune function (2). Three dogs were treated with the lowest dose of vaccine. All three dogs tolerated the
vaccine well with no significant adverse effects noted either at the time of vaccination or in long term follow up
(up to 6 months to date). Given the safety of the vaccine at this dose, the dose has been escalated and 3 dogs
have been vaccinated with the higher dose. At this dose, one dog developed a moderate and self-limiting fever
and flu-like symptoms (myalgia, arthralgia, lethargy). These side effects are encouragingly consistent with immune
activation. The other 2 dogs showed no significant adverse effects of the higher dose of vaccine. One of the 6
dogs (low dose recipient) developed pulmonary metastases and was euthanized 247 days post diagnosis. All other
dogs remain metastases free at this time. Three more dogs have been screened and found to be positive for
Her2/neu expression in their tumors. If eligible, these patients will be vaccinated at an escalated dose. Immune
analysis of vaccine efficacy will be evaluated for each dog at the end of the study.
The data so far indicates that the vaccine is safe and has minimal immediate and long-term side effects. It is too
early to determine whether the vaccine prolongs overall survival in this pilot group of dogs, but as the data
matures evidence of its therapeutic efficacy may be seen. This study represents a very exciting new approach to
the treatment of a disease in which the abysmal prognosis has remained unchanged for several decades. We
expect that within the next year we will have preliminary data that will determine the merit of this approach for
delaying or preventing metastatic disease. If we confirm safety and demonstrate efficacy in this group of dogs a
phase II clinical trial in a larger group of dogs will be initiated in the Fall of 2013.
RE-DIRECTED T CELL THERAPY FOR TARGETING CANCER
Adoptive immunotherapy (AI) using autologous, re-directed T cells to recognize and kill
tumor cells represents a powerful strategy to target primary, metastatic and relapsing
neoplastic disease. In this approach, the patient’s own T cells are genetically modified to
express a cell surface immunoglobulin fragment (scFv) that is specific for a known tumor
antigen. The antibody fragment is genetically linked to intracellular signaling molecules
within the T cell such that engagement of the antibody with tumor antigen leads to T cell
activation, proliferation and cytotoxic effector function (Fig. 3). Large numbers of the
patient’s T cells can be genetically modified ex vivo and infused into the patient. Preconditioning
regimes that act to lymphodeplete the patient prior to adoptive transfer aid in
ensuring appropriate T cell engraftment and long-term persistence of modified T cells. This
approach has shown to be highly effective in the treatment of human patients with Chronic
Lymphocyte Leukemia (CLL) however, it has not yet been applied in veterinary medicine.
We have now generated the appropriate viral vectors for use in canine T cells and are exploring a variety of ways
to optimally transduce canine T cells using lentiviral and retroviral vectors. Once this has been achieved we will
demonstrate proof of principle in in vitro experiments prior to initiating a phase I clinical trial to evaluate the
safety and efficacy of this approach. Our first efforts utilizing this cutting edge therapy will be in patients with
relapsed, refractory B cell lymphoma. We will enroll 10 dogs with confirmed relapsed, refractory B cell lymphoma.
Enrollment criteria will include 1) confirmed diagnosis of relapsed or refractory B cell lymphoma, 2) confirmation
of systemic health, based on complete blood counts and serum chemistry profile and 3) ECOG performance status
of <1 at enrollment. Dogs will be excluded from the trial if they are <20kg; T cell or null-cell phenotype, have
evidence of systemic disease, and/or have been treated with chemotherapy within the last 3 weeks prior to blood
draw for T cell procurement and genetic modification. Dogs will be staged prior to T cell infusion using standard
oncological criteria. T cells will be genetically modified and tumor-specific T cells will be expanded ex vivo in the
laboratory. Five days prior to adoptive transfer, dogs will receive a non-myeloablative preconditioning
chemotherapy regime to provide a niche for transferred T cells to expand. Genetically re-directed T cells will be
administered intravenously and their persistence will be measured in peripheral blood samples. Hematological
and biochemical parameters will also be assessed. Clinical responses will be characterized using standard
oncologic criteria and survival data will be analyzed using Kaplan-Meier survival analysis.
In summary, the increasing success of both active and passive immunotherapies in the treatment of human
cancers indicates that similar success may be achieved with these approaches in canine cancer patients. However,
immunotherapy in veterinary medicine is in its infancy and much work needs to be done through phased and
carefully controlled clinical trials to demonstrate the safety of these approaches and their therapeutic efficacy. In
this way one may predict that within the next decade immunotherapy will become commonplace in the treatment
of canine cancers.
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