Mechanisms of tumor-induced immunosuppression: evidence for contact-dependent T cell suppression by monocytes.

BACKGROUND: The progressive growth of tumors in mice is accompanied by down-regulation of specific T cell responses. The factors involved in this suppression are not completely understood. Here, we have developed a model to examine the role of host immune effector cells in the inhibition of T cell function. In this model, progressive growth of a colon carcinoma line, CT26, is accompanied by loss of T cell response to alloantigens in both cytolytic and proliferation assays. MATERIALS AND METHODS: The CT26 tumor was inoculated into BALB/c syngeneic mice. Tumor growth, cytolytic T cell responses, lymphocyte proliferation, and flow cytometric analysis was performed in tumor-bearing animals 7 or 28 days after tumor inoculation. RESULTS: Spleen cells from tumor-bearing mice were found to suppress the proliferative response of spleen cells from normal mice to alloantigens. Examination of the spleen cell population by FACS analysis revealed an increase in the percentage of monocytes as defined by expression of CD11b, the Mac-1 antigen. Removal of the Mac-1-positive cells from the tumor-bearing hosts spleen relieved suppression of the tumor-bearing mouse spleen cell proliferative response to alloantigens, and addition of the Mac-1-positive enriched cells suppressed proliferation of normal T cells in response to alloantigens. Cell contact was required for this inhibition. CONCLUSIONS: Tumor induction of suppressive monocytes plays an important role in the general immunosuppression noted in animals bearing CT26 tumors. Identification of the mechanisms responsible for this effect and reversal of tumor-induced macrophage suppression may facilitate efforts to develop effective immunotherapy for malignancy.

Safety and short-term toxicity of a novel cationic lipid formulation for human gene therapy.

Among the potential nonviral vectors for human gene therapy are DNA-liposome complexes. In a recent clinical study, this delivery system has been utilized. In this report, a novel cationic lipid, dimyristyloxypropyl-3-dimethyl-hydroxyethyl ammonium (DMRIE), has been substituted into the DNA-liposome complex with dioleoyl phosphatidylethanolamine (DOPE), which both improves transfection efficiencies and allows increased doses of DNA to be delivered in vivo. The safety and toxicity of this DNA-liposome complex has been evaluated in two species, mice and pigs. The efficacy of DMRIE/DOPE in inducing an antitumor response in mice after transfer of a foreign MHC has been confirmed. No abnormalities were detected after administration of up to 1,000-fold higher concentrations of DNA and lipid than could be tolerated in vivo previously. Examination of serum biochemical enzymes, pathologic examination of tissue, and analysis of cardiac function in mice and pigs revealed no toxicities related to this treatment. This improved cationic lipid formulation is well-tolerated in vivo and could therefore allow higher dose administration and potentially greater efficiency of gene transfer for gene therapy.

Radioimmunoassay data processing with a small programmable calculator.

We have developed three programs for data processing for radioimmunoassays RIA implemented on a small, inexpensive, programmable calculator (Texas Instrument Co., Model 59): 1) The first program performs a weighted logit-log regression for analysis of the RIA standard curve, and provides several descriptive statistics: slope, intercept, ED50 (and their corresponding standard errors), residual variance, and correlation coefficient. This program also provides: dose interpolation for unknowns; an estimate of the precision (percent coefficient of variation) for each result; corrections for variable sample volumes or recoveries; and the mean and standard error of the mean for samples analyzed in replicate. 2) The second program uses the "four parameter logistic model" to describe the dose responses curve and perform dose interpolation. This is the equivalent to the use of the logit-log method, with provision for adjustment for the position of the 0% and 100% response. As such, it is more flexible and versatile than the logit-log method. 3) A third program is used for routine Within-Lab Quality Control: it calculates within-assay and between-assay precision, utilizing an analysis of variance (ANOVA) with a components of variance estimation. These programs incorporate the most important features of programs previously developed in this laboratory for an IBM 370 or a DECsystem-10 computer, and demonstrate the availability of adequate statistical analyses to laboratories without access to large centralized computer facilities.