Approaches to cancer therapy using biological response modifiers

Cancer Immunotherapy

The enhanced understanding of immunology experienced over the last 5 decades afforded through the tools of molecular biology has recently translated into cancer immunotherapy becoming one of the most exciting and rapidly expanding fields. Human cancer immunotherapy is now recognized as one of the pillars of treatment alongside surgery, radiation, and chemotherapy. The field of veterinary cancer immunotherapy has also rapidly advanced in the last decade with a handful of commercially available products and a plethora of investigational cancer immunotherapies, which will hopefully expand our veterinary oncology treatment toolkit over time.

Cancer Immunotherapies

The enhanced understanding of immunology experienced over the last 4 decades afforded through the tools of molecular biology has recently translated into cancer immunotherapy becoming one of the most exciting and rapidly expanding fields. Human cancer immunotherapy is now recognized as one of the pillars of treatment alongside surgery, radiation, and chemotherapy. The field of veterinary cancer immunotherapy has also rapidly advanced in the last decade with a handful of commercially available products and a plethora of investigational cancer immunotherapies that will hopefully expand the veterinary oncology treatment toolkit over time.

Cancer immunotherapy in veterinary medicine: Current options and new developments

Excitement in the field of tumor immunotherapy is being driven by several remarkable breakthroughs in recent years. This review will cover recent advances in cancer immunotherapy, including the use of T cell checkpoint inhibitors, engineered T cells, cancer vaccines, and anti-B cell and T cell antibodies. Inhibition of T cell checkpoint molecules such as PD-1 and CTLA-4 using monoclonal antibodies has achieved notable success against advanced tumors in humans, including melanoma, renal cell carcinoma, and non-small cell lung cancer. Therapy with engineered T cells has also demonstrated remarkable tumor control and regression in human trials. Autologous cancer vaccines have recently demonstrated impressive prolongation of disease-free intervals and survival times in dogs with lymphoma. In addition, caninized monoclonal antibodies targeting CD20 and CD52 just recently received either full (CD20) or conditional (CD52) licensing by the United States Department of Agriculture for clinical use in the treatment of canine B-cell and T-cell lymphomas, respectively. Thus, immunotherapy for cancer is rapidly moving to the forefront of cancer treatment options in veterinary medicine as well as human medicine.

Immunotherapy in veterinary oncology

Tumor immunology and immunotherapy is one of the most exciting and rapidly expanding fields. The immune system is divided into 2 primary components: the innate immune response and the highly specific, but more slowly developing, adaptive or acquired immune response. Immune responses are separated by whether they are induced by exposure to a foreign antigen (active response) or transferred through serum or lymphocytes from an immunized individual (passive response). The ideal cancer immunotherapy agent should discriminate between cancer and normal cells (specificity), be potent enough to kill small or large numbers of tumor cells (sensitivity), and prevent recurrence of a tumor (durability).

Cancer immunotherapy

The immune system is generally divided into 2 primary components: the innate immune response, and the highly specific but more slowly developing adaptive or acquired immune response. Immune responses can be further separated by whether they are induced by exposure to a foreign antigen (an "active" response) or whether they are transferred through serum or lymphocytes from an immunized individual (a "passive" response). The ideal cancer immunotherapy agent should be able to discriminate between cancer and normal cells (ie, specificity), be potent enough to kill small or large numbers of tumor cells (ie, sensitivity), and lastly be able to prevent recurrence of the tumor (ie, durability). Tumor immunology and immunotherapy is one of the most exciting and rapidly expanding fields at present.

Anticancer vaccines

With the tools of molecular biology and a greater understanding of mechanisms to harness the immune system, effective tumor immunotherapy is becoming a reality. This new class of therapeutics offers a more targeted, and therefore precise, approach to the treatment of cancer. The recent conditional licensure of a xenogeneic DNA vaccine for advanced canine malignant melanoma strongly suggests that immunotherapy can play an extremely important role alongside the classic cancer treatment triad components of surgery, radiation therapy, and chemotherapy.

Therapeutic immunostimulating effects of plant mitogens exemplified by the L4 isolectin of PHA

A sizable body of evidence has accumulated showing that the characteristics of certain plant mitogens should endow them with valuable immunomodulating effects. Immune stimulation would be the fundamental function operating through the broad consequences of nonspecific T cell activation following binding with their CD3 or CD2 molecules. Based on in vitro evidences that PHA, operating through the LDCC pathway, might kill any tumor target if it remains present in adequate concentration, the administration of mitogens for cancer therapy would be rational, and the same mechanism should also justify these agents for treatment of certain infections. Being nonerythroagglutinating, although leukoagglutinating in higher concentrations, PHA-L4 serves as a suitable model for immunostimulating activities of the mitogens that can be applied directly or as in vitro activators of adoptive leukocytes. The PHA skin test can be utilized to gauge the serum levels of inhibitory glycoproteins that become elevated in a number of the disorders treatable by the mitogen, thus facilitating necessary dosage modifications. While PHA is the only mitogenic lectin that has been tested clinically, Con A and PWM are the two most widely studied among the alternatives, with others also available and many undoubtedly awaiting discovery. The development of practical methods for producing industrial quantities of nonagglutinating mitogens in pure form should be the goal, and accomplishing the latter might also answer certain hypersensitivity concerns.

Propionibacterium acnes immunotherapy in chronic recurrent canine pyoderma. An adjunct to antibiotic therapy

In a randomized, double-blind, placebo-controlled study, dogs with chronic recurrent pyoderma were treated with antibiotics plus intravenous injections of either Propionibacterium acnes or placebo. Responses (an increase, decrease, or clearing of lesions) were measured and evaluated statistically. Eighty percent (12 of 15) of the dogs treated with antibiotics and P acnes compared with 38% (five of 13) of the dogs treated with antibiotics and placebo responded with significant improvement or complete remission of lesions at the end of the 12-week treatment schedule (P less than 0.05).

Whole-body hyperthermia. Rationale and potential use for cancer treatment

Whole-body hyperthermia is the controlled elevation of systemic temperature for therapeutic purposes. Historically, this treatment has been used for symptomatic control of many diseases. Recently, the potential therapeutic benefit of whole-body hyperthermia in the management of neoplastic disease has been investigated vigorously. The rationale for improved tumor control is based on heat-induced enhancement of the antineoplastic effects of radiation and chemotherapy. Although the complex biologic interaction of heat and radiation has been studied for many years, chemotherapy combined with hyperthermia has been studied less thoroughly. Despite a lack of adequate long-term laboratory and clinical investigation, use of whole-body hyperthermia with chemotherapy and radiotherapy is a logical and potentially powerful therapeutic strategy for neoplasia. Relevant issues regarding the application of whole-body hyperthermia with more traditional modes of therapy are being studied in preliminary clinical trials involving dogs and humans. Identification of optimal timing and sequencing of adjunctive therapy, proper cytotoxic drug application, methods to further minimize toxicity, and heat-sensitive tumor types will lead to expanded clinical use of whole-body hyperthermia. The historical development, clinical rationale, and application of whole-body hyperthermia for the control of disseminated or refractory neoplasia in humans and dogs is reviewed.

Biological response modifiers in the management of viral infection

The rapid evolution of immunopharmacology as a recognized scientific discipline dedicated to unraveling complex interrelationships between immunologic responsiveness and disease states in general supports the importance of the potential role biological response modifiers have in clinical medicine. To administer a drug, or combination of drugs, that safely, effectively, and favorably alter the course of infection, cancer, autoimmune disease, and allergy is within grasp. Although the greatest emphasis on therapeutic application of BRMs is placed on cancer, many of these immunomodulating agents have well-documented effects on the course of infectious disease. By either restoring immune responses or by enhancing the response of a normal immune system, it is conceivable that BRM therapy will someday be used routinely as adjunct therapy in the management of viral infections in companion animals.