Programmable bacteria induce durable tumor regression and systemic antitumor immunity

Abstract

SUMMARY PARAGRAPH Synthetic biology is driving a new era of medicine through the genetic programming of living cells 1 , 2 . This transformative approach allows for the creation of engineered systems that intelligently sense and respond to diverse environments, ultimately adding specificity and efficacy that extends beyond the capabilities of molecular-based therapeutics 3 – 6 . One particular focus area has been the engineering of bacteria as therapeutic delivery systems to selectively release therapeutic payloads in vivo 7 – 11 . Here, we engineered a non-pathogenic E. coli to specifically lyse within the tumor microenvironment and release an encoded nanobody antagonist of CD47 (CD47nb) 12 , an anti-phagocytic receptor commonly overexpressed in several human cancers 13 , 14 . We show that delivery of CD47nb by tumor-colonizing bacteria increases activation of tumor-infiltrating T cells, stimulates rapid tumor regression, prevents metastasis, and leads to long-term survival in a syngeneic tumor model. Moreover, we report that local injection of CD47nb bacteria stimulates systemic tumor antigen–specific immune responses that reduce the growth of untreated tumors – providing, to the best of our knowledge, the first demonstration of an abscopal effect induced by an engineered bacterial immunotherapy. Thus, engineered bacteria may be used for safe and local delivery of immunotherapeutic payloads leading to systemic antitumor immunity.

Macrophages show higher levels of engulfment after disruption of cis interactions between CD47 and the checkpoint receptor SIRPα

“…1Ai) (Advani et al, 2018;Andrechak et al, 2019). Expression of anti-CD47 from bacteria within a mouse tumor might activate macrophages via bacterial pathways (Chowdhury et al, 2019), but the same anti-CD47 is also likely to disrupt CD47-SIRPα cis interactions on tumor-associated macrophages and thereby drive hyper-phagocytosis. SIRPα blockade should lead to similarly high activation and hyper-phagocytosis, which is interesting to consider in light of anti-tumor efficacy with systemically injected anti-SIRPα blocked macrophages (Alvey et al, 2017).…”

“…1A). B16 cells were studied to generalize species effects and because they are widely used in preclinical immunotherapy, including CD47-SIRPα blockade (Ingram et al, 2017;Chowdhury et al, 2019;Mandal et al, 2019). CRISPR/Cas9-mediated knockout (KO) of CD47 or SIRPα was performed in B16 cells, alongside a line with a non-targeting guide RNA for control, and all B16 cells were equally opsonized with anti-Tyrp1 (Figs S1B and S4A) before being added to mouse bone- marrow derived macrophages (BMDMφs).…”

“…When a macrophage engages a 'self' cell, a phagocytic synapse forms in which trans binding of SIRPα to CD47 leads to local accumulation of SIRPα and phosphatase-mediated signaling that opposes engulfment ('eating') of 'self' cells including tumor cells (Fig. 1Ai,upper) (Oldenborg et al, 2000;Tsai and Discher, 2008;Weiskopf et al, 2013;Chowdhury et al, 2019). Phagocytosisactivating interactions occur in parallel, with the clearest pathway involving Fc-receptors (FcRs) that bind and organize IgG-type antibodies on a target cell (Lopes et al, 2017;Bakalar et al, 2018).…”

Radiolabelled Bacterial Metallophores as Targeted PET Imaging Contrast Agents for Accurate Identification of Bacteria and Outer Membrane Vesiclesin vivo

“…We have also validated how 64 Cu-YbT can potentially be used to advance bacterial therapies using engineered bacteria. Advances in genetic engineering have enabled us to explore the potential of using bacteria, particularly for cancer therapy in the last two decades 31,[48][49][50][51] . One of the most notable initial studies tested genetically engineered Salmonella for its anticancer activity in mouse models of subcutaneously implanted B16F10 melanoma tumors 51 .…”

The Role of Circulating Tumor Cells in the Metastatic Cascade: Biology, Technical Challenges, and Clinical Relevance

“…This effect could be avoided by producing anti-CD47 nanobodies that lack the Fc-mediated adverse effector function [204,206]. Also, engineered bacteria containing a synchronized lysis circuit (eSLC) to locally release a CD47 antagonist can be used to specifically deliver the agent at the tumor site, to induce a systemic anti-tumor immune response and lyse tumor cells in response to diverse tumor microenvironment stimuli [207].…”