Venezuelan Equine Encephalitis Replicon Immunization Overcomes Intrinsic Tolerance and Elicits Effective Anti-tumor Immunity to the ‘Self’ tumor-associated antigen, neu in a Rat Mammary Tumor Model

Abstract

SummaryMany tumor-associated antigens (TAAs) represent 'self' antigens and as such, are subject to the constraints of immunologic tolerance. There are significant barriers to eliciting anti-tumor immune responses of sufficient magnitude. We have taken advantage of a Venezuelan equine encephalitis-derived alphavirus replicon vector system with documented in vivo tropism for immune system dendritic cells. We have overcome the intrinsic tolerance to the 'self' TAA rat neu and elicited an effective anti-tumor immune response using this alphavirus replicon vector system and a designed target antigen in a rigorous rat mammary tumor model. We have demonstrated the capacity to generate 50% protection in tumor challenge experiments (p = 0.004) and we have confirmed the establishment of immunologic memory by both second tumor challenge and Winn Assay (p = 0.009). Minor antibody responses were identified and supported the establishment of T helper type 1 (Th1) anti-tumor immune responses by isotype. Animals surviving in excess of 300 days with established effective anti-tumor immunity showed no signs of autoimmune phenomena. Together these experiments support the establishment of T lymphocyte dependent, Th1-biased anti-tumor immune responses to a non-mutated 'self' TAA in an aggressive tumor model. Importantly, this tumor model is subject to the constraints of immunologic tolerance present in animals with normal developmental, temporal, and anatomical expression of a non-mutated TAA. These data support the continued development and potential clinical application of this alphaviral replicon vector system and the use of appropriately designed target antigen sequences for anti-tumor immunotherapy.

An alphavirus vector overcomes the presence of neutralizing antibodies and elevated numbers of Tregs to induce immune responses in humans with advanced cancer

“…Other advantages of VRP are their tropism for, and maturation of (5), DCs, which could result in enhanced T cell activation. A number of preclinical studies have reported that VRP induce potent immunity despite the presence of neutralizing antibodies (4)(5)(6)(7)(8)(9)(10)(11)(12).…”

Comparison of Two Cancer Vaccines Targeting Tyrosinase: Plasmid DNA and Recombinant Alphavirus Replicon Particles

“…This class of virus is particularly attractive because the double-stranded RNA created during viral replication stimulates the innate immune response through interaction with TLR3 (23). Moreover, the efficacy of VRP vaccines based on VEEV has been attributed to the expression of heterologous proteins at high levels, to targeting expression to dendritic cells, and to the ability to induce both humoral and cellular immune responses against the product of the gene carried by the vector (24,26).…”

HER2/neu: an increasingly important therapeutic target. Part 1: basic biology & therapeutic armamentarium

“…The high degree of homology with other receptor tyrosine kinases, including other members of the HER family, and the expression of HER2/neu in normal tissues, pose significant challenges that need to be addressed, including overcoming the anticipated immunological tolerance while maintaining specificity of the elicited immune response. Much of the preclinical work was performed in HER2/neu transgenic mouse models due, in part, to the fact that a murine homolog was not confirmed until the early 2000s [14][15][16], although other models were also employed (dog, guinea pig, rat, primate) [209][210][211][212][213][214]. The majority of these have focused on the extracellular domain of HER2/neu due, in large part to the high degree of homology of the intracellular kinase domain with other receptor tyrosine kinases both in and outside of the HER family [209,[215][216][217][218][219], although some strategies have included elements from the intracellular domain [213][214][215].…”

“…Dendritic cells (DCs) are the most potent antigen presenting and immune-stimulating cells within the immune system, thus, DC-based immunotherapeutic strategies directed against HER2/neu have been investigated, including DCs loaded with various fragments or peptides from the HER2/neu sequence [234][235][236][237] (NCT00266110 and NCT00923143) and transduced DCs [213,[237][238][239][240][241][242][243] including adenoviral transduced autologous DCs expressing the extra cellular and transmembrane domains of HER2/neu (NCT01730118). A preparation analogous to Sipuleucel-T (the first FDAapproved cellular based-immunotherapy) [244] is being developed, Lapuleucel-T, consisting of a HER2/neu truncated fusion with granulocyte macrophage colonystimulating factor that is used to generate an autologous mixture of antigen-presenting cells targeting the HER2/neu component [245].…”

“…Viral vector vaccine strategies using adenovirus vectors [257][258][259][260], alphavirus vectors [212,213,261], vaccinia virus vectors (NCT00485277 and NCT01152398), vesicular stomatitis virus [262] and polyoma virus systems [263,264] have all been used to elicit anti-HER2/neu immune responses. The intracellular bacteria Listeria monocytogenes has also been adapted as an immunotherapeutic vector system and studied in strategies to elicit anti-HER2/neu immune responses [215,265].…”