Kinetics study on markers of the immune system by gene expression profiling of an in vivo heated tumor

Purpose: To analyze effects of hyperthermia on immune cells within tumors. Materials and methods: Subcutaneously implanted rat gliomas were treated with water-bath hyperthermia for one hour at day zero (HT) (intratumoral temperature of 43C), low-dose metronomic cyclophosphamide (CTX) 35 mg/kg three times a week for two weeks, both HT and CTX (CTX-HT0), or saline. Tumors harvested at day 1, 7, 14 and 21 were analyzed for changes in gene expression by microarrays, focusing on genes expressed in immune cells. Microarray analyses and real-time RT-PCR were previously performed on tumors harvested day zero at 0, 45, 90 and 180 minutes after end of treatment. Gene expression kinetics of selected genes were analyzed in all tumors by quantitative real-time RT-PCR (qPCR) to validate the results of the microarrays. Results: Previous microarray analyses have indicated a suppression of gene expression in immune cells within tumors by hyperthermia the first three hours after treatment. qPCR analyses of CD14, CD36, Klrd1 (CD94), Tlr2 and Lrp1 confirmed these results. Global mRNA screen revealed no hyperthermia-induced changes in gene expression of immune cells at day 1, 7, 14 and 21. qPCR analyses of CD14, CD36, Klrd1 (CD94), Tlr2 and Lrp1 confirmed the results of the microarrays, i.e. none of these were differentially expressed after the first day, with the exception of Lrp1 which displayed elevated mRNA levels. Conclusion: The suppression in gene expression of a range of immune cells within tumors treated with hyperthermia at 43C is a transient phenomenon.