A major limitation associated with systemic administration of cationic lipid:plasmid DNA (pDNA) complexes is the vector toxicity at the doses necessary to produce therapeutically relevant levels of transgene expression. Systematic evaluation of these toxicities has revealed that mice injected intravenously with cationic lipid:pDNA complexes develop significant, dose-dependent hematologic and serologic changes typified by profound leukopenia, thrombocytopenia, and elevated levels of serum transaminases indicative of hepatocellular necrosis. Vector administration also induced a potent inflammatory response characterized by complement activation and the induction of the cytokines IFN-gamma, TNF-alpha, IL-6, and IL-12. These toxicities were found to be transient, resolving with different kinetics to pretreatment levels by 14 days posttreatment. The toxic syndrome observed was independent of the cationic lipid:pDNA ratio, the cationic lipid species, and the level of transgene expression attained. Mechanistic studies determined that neither the complement cascade nor TNF-alpha were key mediators in the development of these characteristic toxicities. Administration of equivalent doses of the individual vector components revealed that cationic liposomes or pDNA alone did not generate the toxic responses observed with cationic lipid:pDNA complexes. Only moderate leukopenia was associated with administration of cationic liposomes or pDNA alone, while only mild thrombocytopenia was noted in pDNA-treated animals. These results establish a panel of objective parameters that can be used to quantify the acute toxicities resulting from systemic administration of cationic lipid:pDNA complexes, which in turn provides a means to compare the therapeutic indices of these vectors.

We previously reported that treatment of intraperitoneal tumors with complexes of cationic lipid and noncoding plasmid DNA leads to the development of a specific, cytotoxic T-cell response correlating with the rejection of established tumor cells as well as subsequent tumor re-challenge. Here, focusing on an intraperitoneal AB12 mesothelioma model, we show that the anticancer effects of the lipid:DNA complex are associated with DNA containing immunostimulatory CpG motifs. Complexes prepared with cationic lipid and bacterial plasmid DNA, Escherichia coli genomic DNA fragments, or synthetic immunostimulatory CpG oligodeoxynucleotides provided a substantial survival benefit, whereas eukaryotic DNA and methylated bacterial DNA had little or no therapeutic activity. Alternative inflammatory stimuli such as thioglycolate, poly(I:C), and incomplete or complete Freund's adjuvant failed to reproduce the antitumor activity obtained with the lipid:DNA complex. The innate immune response triggered by lipid:DNA complexes led to the development of a systemic immune response against tumor cells that allowed animals to reject tumors not only at the intraperitoneal treatment site, but also at a distal subcutaneous site. These data demonstrate that immunostimulatory DNA complexed with cationic lipid is a potent inducer of innate and adaptive immune responses against tumor cells and represents a potentially useful tool in the immunotherapy of cancers for which tumor-associated antigens have not been identified.

Maximizing operational efficiency while maintaining appropriate animal housing conditions is a continuous focus of research animal care programs. Our institution’s longstanding approach to cage-change management included scheduled cage changes every 2 wk, with spot changes if cages met established visual criteria during the intervening period. This 2-wk plus spot changing (2WS) practice for mice housed in IVC was problematic during the COVID-19 pandemic when the need arose to minimize workload to reduce on-site staffing out of concern for employee health and possible absenteeism. With the approval of the IACUC, a spot-change–only (SCO) process was adopted, with the requirement to evaluate microenvironmental parameters under both practices to confirm acceptable equivalence. These parameters (humidity, temperature, and ammonia) were evaluated in a controlled study that found no significant difference between the 2 groups. Ammonia levels did not exceed 10 ppm in any group throughout the study. To assess operational differences between these 2 approaches, we collected cage-change data and employee feedback from facilities operating under these schemes. The SCO method required fewer cage changes than did the 2WS method (10.3% per day with 2WS and 8.4% per day with SCO). Despite this benefit, through a Plan–Do–Check–Act process that has been regularly employed at our institution, employee feedback identified important operational challenges associated with the SCO practice. The SCO approach was thus refined into a scheduled spot change (SSC) practice that builds on the SCO model by incorporating a scheduled focused cage evaluation period. Based on subsequent feedback, the SSC was found to retain the efficiency benefits afforded by the SCO model and simultaneously alleviated staff and operational concerns. This result underscores the importance of integrating staff feedback with a performance standard-based approach when assessing cage-change management.