Some summarized thoughts on Oncosec's IL-12 TAVO program, IL-12 in general and Oncosec's electroporation platform.
Electroporation using empty vectors - that's correct, not encoding anything - results in the release of tumor-associated antigens in the tumor microenvironment (TME). These antigens get picked up by antigen presenting cells, e.g., dendritic cells, which then present to naive t cells to initiate priming. Sometimes this priming occurs locally in the TME, in the spleen, and in tumor draining lymph nodes. Mature antigen-loaded dendritic cells release interleukin 12. This might account for some of the transient immune responses observed in preclinical models using empty vectors. IL-12 concentrations are simply too low to contribute to much of a significant adaptive immune response when electroporating an empty vector, but the point is that electroporation by itself triggers the release of antigens in the TME.
The production of IL-12 that is encoded on Oncosec's plasmid constructs produces a protracted release of the cytokine in the TME. When the IL-12 is adequately expressed intratumorally, it appears to trigger the activation and expansion of natural killer (NK) cells. This activation results in the production of CCL5, FLT3 ligand, interferon gamma and additional chemokines. CCL5 attracts dendritic cells, thus improving tumor antigen presentation locally. Through cross talk - observations have been made elsewhere that show clustering of NK cells and dendritic cells - more IL-12 is released in the immediate proximity of NK cells, thus leading to more CCL5, interferon gamma, FLT3 ligand, and chemokines. It's essentially a positive feedback loop. The release of FLT3 ligand, a well known growth factor for dendritic cells, results in the expansion of antigen presentation machinery.
As IL-12 helps to activate and expand the NK cell population, after some time passes and IL-12 is at lower concentrations, a portion of these cells start upregulating PD-1 on their surface. At the point from which they exhibit an exhausted phenotype, an intratumoral administration of anti-PD-1 or its ligand would help to rescue the innate cells along with their release of CCL5, interferon gamma, FLT3 ligand, etc. It's possible that Oncosec has already thought of this if you look at the collaboration between them and Avacta to develop intratumorally delivered encoded affimers, specifically anti-PD-L1.
In the context of IL-12, more T cells take on an effector phenotype and their exhaustion, despite being challenged, is delayed. In addition, perhaps through the expression of BLIMP-1 and T-bet following IL-12 exposure, CD8 T cells lose their propensity to upregulate PD-1. These activated effector T cells relocate throughout the body to "kill" tumor cells containing matching antigens. This is essentially the abscopal effect that we observe where untreated lesions are reduced or eliminated over time. Some of these cells become exhausted due to chronic antigen stimulation whereas others become memory effector cells. Assuming adequate levels of IL-12 are expressed intratumorally and in the context of naive T cells, we should be observing sustained responses in untreated lesions. This might negate the need for systemic delivery of an anti-PD-1 agent like pembrolizumab or nivolumab due to the sustained low level of PD-1 surface expression on effector T cells. I think the key would be to maximize and sustain IL-12 delivery in the context of naive T cells to ensure expression of BLIMP-1 and T-bet. This would likely lead to low levels of PD-1 surface expression on CD8 T cells (owing to the knockout of NFATC1) in untreated TMEs. We have observed these effector T cells in both the spleen and untreated tumors of mice as well as humans now. Sufficient intratumoral levels of IL-12, again, contribute to NK cell activation and expansion, consequently leading to improvements in antigen presentation, vis-a-vis FLT3 ligand expression originating from NK cells. If there is an adequate level of dendritic cell-derived IL-12 expression in lymphatic tissue - remember, FLT3 ligand expands dendritic cell populations which then mobilize to lymphatic tissue - you should observe improvements in T-bet and BLIMP-1 expression, fewer exhausted CD8 T cells and higher percentages of effector T cells in the periphery.
T-regs, which constitutively express CTLA-4, appear to hijack CD80 and CD86 on antigen presenting cells. This results in handicapped co-stimulation with CD28 on T cells. As a result, effector cells cannot proliferate. To overcome this obstacle, one solution could be to simply expand dendritic cells through intratumoral delivery of encoded FLT3 ligand on multigene plasmid constructs. This would essentially improve the ratio of dendritic cells to T-regs without requiring a CTLA-4 antibody. The dendritic cells would numerically overwhelm CTLA-4.
A p2a-linked multigene plasmid construct containing encoded IL-12 and FLT3 ligand, when electroporated intratumorally in low voltage conditions, could be a nail in the coffin for many solid tumor cancers including those that are advanced. The electroporation procedure by itself potentially exposes ALL tumor antigens. This provides the key ingredients for in-situ vaccination and adaptive long term immunity. The approach wouldn't require adaptive T cell transfer/expansion ex vivo, nor would it require biopsies or personalized/engineered vaccines that could be cost prohibitive, dangerous, slow to manufacture and ineffective against all tumor antigens. Oncosec's electroporated IL-12 TAVO approach is a single off-the-shelf product, the most personalized medicine I can imagine for solid tumors. The p2a-linked plasmid construct in low voltage conditions might even eliminate or reduce the need for systemic administration of checkpoint inhibitors, specifically anti-PD-1 if it results in sustained low levels of PD-1 expression on effector cells in the periphery.
