Immature myeloid cells derived from mouse placentas and malignant tumors demonstrate similar proangiogenic transcriptional signatures

Objective: To determine whether CD11b⁺Gr1⁺ immature myeloid cells (IMCs), initially identified to infiltrate tumors and support angiogenesis and recently identified also in mouse and human placentas, are similar in that they share common gene expression. Design: Animal experiment. Setting: Reproductive immunology laboratory. Animal(s): All 6- to 8-week-old C57Bl/6 female mice. Main Outcome Measure(s): We analyzed gene expression of IMCs isolated from placentas of pregnant mice (n = 3) and Lewis lung carcinoma tumors (n = 3), using flow cytometry. Expression patterns were compared to primary muscle cells (n = 4), using Affymetrix microarrays. Quantitative polymerase chain reaction (PCR) was used to validate microarray data. Similarity of gene expression was evaluated with the mass-distance algorithm. Result(s): The IMCs that infiltrate mouse placentas share ∼500 expressed genes with tumor IMCs (set a). This gene set is enriched with proangiogenic and inflammatory genes. Unique gene expression sets for tumor IMCs (set b) and placenta IMCs (set c) were also detected. Conclusion(s): The IMCs derived from placentas and tumors express common molecular signatures, suggesting similar origins and functions. This observation lends further support to the notion that the placenta uses a similar angiogenic machinery as tumors for survival and growth. Unique gene-sets, differentially expressed in tumor versus placenta-derived IMCs, may be required for specific IMC-hosting tissue interactions.