Listeria-based cancer vaccines that segregate immunogenicity from toxicity

Abstract

The facultative intracellular bacterium Listeria monocytogenes is being developed as a cancer vaccine platform because of its ability to induce potent innate and adaptive immunity. For successful clinical application, it is essential to develop a Listeria platform strain that is safe yet retains the potency of vaccines based on wild-type bacteria. Here, we report the development of a recombinant live-attenuated vaccine platform strain that retains the potency of the fully virulent pathogen, combined with a >1,000-fold reduction in toxicity, as compared with wild-type Listeria. By selectively deleting two virulence factors, ActA (⌬actA) and Internalin B (⌬inlB), the immunopotency of Listeria was maintained and its toxicity was diminished in vivo, largely by blocking the direct internalin B-mediated infection of nonphagocytic cells, such as hepatocytes, and the indirect ActA-mediated infection by cellto-cell spread from adjacent phagocytic cells. In contrast, infection of phagocytic cells was not affected, leaving intact the ability of Listeria to stimulate innate immunity and to induce antigenspecific cellular responses. Listeria ⌬actA͞⌬inlB-based vaccines were rapidly cleared from mice after immunization and induced potent and durable effector and memory T-cell responses with no measurable liver toxicity. Therapeutic vaccination of BALB͞c mice bearing murine CT26 colon tumor lung metastases or palpable s.c. tumors (>100 mm 3 ) with recombinant Listeria ⌬actA͞⌬inlB expressing an endogenous tumor antigen resulted in breaking of self-tolerance and long-term survival. We propose that recombinant Listeria ⌬actA͞⌬inlB expressing human tumor-associated antigens represents an attractive therapeutic strategy for further development and testing in human clinical trials.C ancer immunotherapy represents a promising treatment strategy that has produced some tantalizing clinical responses for a variety of malignant diseases. Although promising, there continues to be a strong need for a practical immunization strategy that can be routinely adopted to specific malignancies and that consistently yields durable and robust therapeutic antitumor responses.Progress in molecular and cellular immunology, combined with increasing understanding of pathogen physiology and hostpathogen interaction has facilitated the design and use of attenuated bacteria as conventional vaccine vectors. However, the practical utility of live attenuated vaccines relies on achieving a proper balance between the virulence͞toxicity and immunogenicity of the vaccine. The potency of a pathogen to elicit adaptive immunity is related in part to its ability to stimulate significant innate immunity through recognition of microbial pathogen-associated molecular patterns by Toll-like receptors. Microbial encounter with professional antigen-presenting cells (APC), such as dendritic cells, results in activation and maturation (1) as well as secretion of high levels of T helper-1-type cytokines (2). This interaction initiates adaptive immune responses and therefore link...

Induction of Protective Immunity to Listeria monocytogenes in Neonates

“…We now show that neonatal mice survived a high dose of ⌬actA-Lm infection without any sign of disease, and cleared the inoculum similar to adult mice. Although ⌬actA-Lm derivatives have been shown to be safe in adult mice (10,11), ours is the first demonstration of their safety in neonatal mice.…”

“…Recombinant Lm has great potential as a vaccine vehicle (10,11,25). Importantly for neonatal vaccination, recombinant attenuated strains of Lm induce Ag-specific immunity even in the presence of preexisting immunity (10), an issue of importance for vaccines where preexisting maternal immunity might interfere with the vaccine response in the newborn or infant.…”

“…Furthermore, Lm possesses biologically strong Th1 adjuvant characteristics, making it an attractive vehicle for vaccinations (10,11). Recombinant attenuated strains of Lm induce specific immunity, even in the presence of preexisting immunity to the Lm vehicle (10), making Lm an ideal candidate vector for neonatal vaccination in the face of preexisting maternal immunity.…”

Live attenuated Listeria monocytogenes expressing HIV Gag: Immunogenicity in rhesus monkeys

“…As Lm can cause serious infections in neonates, pregnant women and immunocompromised hosts, different attenuation strategies have been considered: a) to delete the Lm actA gene (either alone or with the plcB or inlB genes) so that both intracellular movement and cell-tocell spreading of bacteria is stopped but immunogenicity is maintained [27,29,30]; b) to delete the uvrA and uvrB genes, which encode nucleotide excision repair genes [31]; and c) to delete essential genes in the D-alanine (D-ala) synthesis pathway. We have chosen the latter approach to develop a highly attenuated vaccine vector, called Lmdd.…”

Listeria monocytogenesinduces host DNA damage and delays the host cell cycle to promote infection

“…43 Importantly, attenuated Lm strains have been used as a delivery system in anticancer therapies 44 and considered serious candidates for anticancer vaccines. 45,46 Our data are particularly important in this context, as we show that Lm causes DNA damage in diverse host cells, possibly contributing to genomic instability. Additionally, Lm infection is potentiated in environments where host DNA is already injured.…”