EVOLVE is focused on the development of dendritic cells (DCs) that are transduced with extracellular vesicle-internalizing receptors (EVIRs). These chimeric receptors promote (i) the uptake of tumor-derived EVs by the engineered DCs, and (ii) the presentation of tumor-associated antigens to T cells.
We have published a first study describing the EVIR platform in 2018. This work was initiated before the beginning of the project, but during the course of EVOLVE we undertook studies of the mechanism of antigen presentation by EVIR-engineered DCs (DC-EVIR), as described in Aim 1. We obtained exciting results indicating that the EVIR captures tumor-derived EVs and promotes “cross-dressing” of DCs with pre-formed MHC-peptide tumor antigens. This unusual mode of antigen presentation by DCs has been found recently to play important roles in anti-tumor immunity.
As planned in Aim 1, we have also designed new EVIRs with engineered signaling domains. After a laborious process of design, screening and validation, we have selected a new EVIR that induces the activation of transduced DCs in an EV-dependent manner, i.e. only upon binding of the EVIR to tumor-derived EVs. The new EVIR induces expression of co-stimulatory molecules on the DC, and may thus help to overcome some of the inherent limitations of early-generation EVIRs lacking intracellular signaling domains, such as antigen-induced tolerance. We have tested the new EVIR for DC vaccination of mice with melanoma and obtained proof that its activity is superior to that of the parental EVIR. Furthermore, we have engineered the DCs to express a cytokine payload (IL-2, IL-12, and/or FLT3L). DCs engineered to express the EVIR and/or a cytokine payload have been studied extensively in the context of preclinical trials in various tumor models, as described in Aim 2 below.
As planned in Aim 2, we have performed preclinical trials in mouse models of cancer. Although not originally planned, we have made efforts to obtain more efficient DCs. We developed protocols that generate a new population of mouse DC progenitors (DCPs) that efficiently produce cDC1 and cDC2 (i.e. professional DCs) in tumor-bearing mice. Murine DCPs were obtained by culturing bone marrow cells in a cocktail of cytokines enabling (i) expansion of hematopoietic progenitors and (ii) commitment to the cDC lineage. We first demonstrated that traditional monocyte-derived DCs (moDCs) could not contribute to the cDC pool of either naïve or tumor-bearing mice; conversely, transfer of DCPs enabled the engraftment of substantial amounts of cDC1 in both lymphoid organs and tumors. We then found that DCPs transduced to express IL-12 and FLT3L (and, in some experiments, the EVIR as third transgene) boosted anti-tumor immunity in various mouse tumor models. Overall, our results in mouse models of melanoma, liver cancer, lung cancer, and glioblastoma, demonstrated that engineered DCPs robustly activate anti-tumor immunity and clearly outperform traditional vaccination with antigen-loaded moDCs.
As planned in Aim 4, we have developed engineered human DCs. We have shown that human DC-EVIR efficiently and specifically uptake human melanoma EVs and activate T cells toward unrelated melanoma antigens. Furthermore, we could generate engineered human DCPs from CD34+ progenitor cells. The successful generation of engineered human DCPs will facilitate translation of the pre-clinical studies described in Aim 2 to the clinic.
