Research Grants Awarded
Multivalent VRP-Based Immunotherapy for Breast Cancer
Tumor Cell Biology III
We have elicited significant anti-tumor activity including the ability to cure a substantial proportion of animals with pre-existing tumor and generate sufficient immunologic pressure to result in outgrowth of tumors with down regulated target antigen expression in a very stringent model system. We have employed the recently developed Venezuelan Equine Encephalitis virus-derived replicon vector (VRP) system, which has selective and restricted DC tropism in an antigen-specific anti-tumor immunotherapy targeting a single tumor associated antigen (TAA), rat neu. The observation of tumor escape variants strongly supports the development and evaluation of immunotherapies targeting more than one TAA. Our team has shown that BORIS, a recently described cancer testes antigen, is aberrantly expressed in nearly 100% of breast carcinomas, is a bone fide immunogenic TAA, and is expressed in our mammary tumor. Thus, we have identified a second attractive non-mutated, "self", target antigen for initial evaluation of VRP-based multivalent anti-tumor immunotherapy. These studies have the following Central Hypothesis: targeting multiple TAAs can enhance VRP-based immunotherapy efficacy and this will decrease the outgrowth of escape variants with down regulated TAA expression, that will be tested by pursuing the following Specific Aims: 1. Define optimal dose for VRP-BORIS in the setting of tumor challenge protection 2. Characterize the activity of VRP-BORIS immunotherapy in treating pre-existing tumor 3. Evaluate immunotherapy with VRP-rNeu, VRP-BORIS, and the combination at established optimal doses in treating pre-existing tumor 4. Assess humoral and cellular antigen-specific immune responses for individual antigens in animals immunized with the combination of VRPs (VRP-rNeu, VRP-BORIS). We will employ our established rat mammary tumor model throughout these experiments. We will use classical tumor challenge protection experiments before proceeding to the more stringent and clinically relevant tumor treatment experiments. These proposed experiments will permit evaluation of potential antigen competition as has been reported for some peptide-based immunotherapy. We will also characterize the elicited immune response using in vitro immunological assays including proliferation, cytokine release, and cytolytic assays. These proposed studies will permit us to 1) define the added benefit to our base VRP immunotherapy of targeting of two "self" TAAs, i.e. as a proof of concept for multivalent VRP-based immunotherapy for breast cancer, 2) extend the range of models in which anti-BORIS immune responses have been elicited, and if successful 3) increase the activity and efficacy of the VRP-based immunotherapeutic strategy and decreased the outgrowth of antigen loss variants, and 4) accelerate the preclinical development of a potent and promising antigen-specific anti-tumor immunotherapy strategy for the treatment of breast cancer patient.
Despite recent advances in breast cancer treatment, most patients will experience a recurrence of their disease. This occurs because of hidden micrometastatic tumor cells. The immune system is particularly well suited to seek out and destroy these occult tumor cells. However, we now recognize that tumors have subtle differences from patient's own "self" tissues, which the immune system does not respond to (autoimmune diseases if it does), and other factors lead to barriers to anti-tumor immune surveillance. In order to overcome these barriers many have tried to use the most potent immune stimulating cell, the Dendritic Cell (DC), in immunotherapy. Anti-tumor immunotherapy or cancer vaccines are methods to elicit anti-tumor immunity by making the immune system see pieces of tumors called tumor associated antigens (TAAs). We have developed a novel anti-tumor immunotherapy that takes advantage of a vaccine vector, delivery system, which specifically goes into DCs inside the body and a designed target antigen derived from a non-mutated over-expressed "self" TAA (the rat equivalent to human HER2/neu). The advantage of this vector is that it works inside the body getting TAAs into DCs and allowing them to work as they are supposed to, in contrast to efforts at "loading" DCs outside the body and giving them back. This immunotherapy has shown remarkable promise in the ability to cure 20% - 40% of animals with pre-existing tumor, a situation analogous to humans. However, some tumors initially respond to our immunotherapy and then progress, leading to animal death. We have shown that these escaping tumors decrease the expression of the targeted TAA. We know tumors can change rapidly if given a chance. So, just as some serious bacteria become resistant to single antibiotics or tumors need more than one chemotherapy drug to shrink, targeting more than one TAA may broaden the immune response and increase in immunotherapy effectiveness leading to fewer escaping tumors and higher cure rates. Some peptide vaccines have shown competition between TAAs, but this is not a universal observation. It is not known if such competition will occur with our vector system that goes directly to DCs. We have identified a particularly attractive second TAA, the molecule BORIS, which is a molecule expressed in nearly 100% of human breast tumors, but not normal tissues except the male testes. Our team has shown this molecule to be immunogenic and expressed in the tumor in our model system. Thus, we will formally test whether an immunotherapy targeting these two TAAs will be more active than either TAA alone. These studies will accelerate the development of a particularly promising and readily translatable anti-tumor immunotherapy by evaluations in stringent animal models of ?self? TAAs. If our novel vector and immunotherapy shows that targeting these two TAAs is more effective, then this strategy can be rapidly and directly translated into the clinical arena.