Pregnancy promotes melanoma metastasis through enhanced lymphangiogenesis.

The relationships of pregnancy and melanoma have been debatable. Our aim was to assess the influence of gestation on the course of melanoma in a classic murine model of tumor progression and in women. B16 mouse melanoma cells were injected in nonpregnant or pregnant mice on day 5 of gestation. Animals were evaluated for tumor progression, metastases, and survival. Tumor sections were analyzed for lymphatic and blood vessel number and relative surface and expression of angiogenic growth factors. Finally, primary melanomas from pregnant and nonpregnant women, matched for age and tumor thickness, were also considered. Tumor growth, metastasis, and mortality were increased in B16-injected pregnant mice. Tumors displayed an increase in intratumoral lymphangiogenesis during gestation. This increased lymphatic angiogenesis was not observed in normal skin during gestation, showing its specificity to the tumor. An analysis of melanoma from pregnant and matched nonpregnant women showed a similar increase in lymphatic vessels. Tumors from pregnant mice had increased expression of vascular endothelial growth factor A at the RNA and protein levels. The increased vascular endothelial growth factor A production by melanoma cells could be reproduced in culture using pregnant mouse serum. In conclusion, pregnancy results in increased lymphangiogenesis and subsequent metastasis. Caution should be applied in the management of patients with advanced-stage melanoma during gestation.

Fetal microchimeric cells participate in tumour angiogenesis in melanomas occurring during pregnancy.

Melanoma is a major malignancy in younger individuals that accounts for 8% of all neoplasias associated with gestation. During pregnancy, a small number of fetal cells enter the maternal circulation. These cells persist and then migrate to various maternal tissues where they may engraft and differentiate, particularly if there is organ damage, adopting the phenotype of the host organ. To understand the relationship between melanoma and pregnancy, we analyzed these tumors in both humans and mice. Fetal cells were detected in 63% of human primary melanomas versus 12% in nevi during pregnancy (P = 0.034) and in 57% of B16 melanomas in pregnant mice but never in normal skin (P = 0.000022). More than 50% of these fetal cells expressed the CD34, CD31, or von Willebrand factor endothelial cell markers. In addition, the Lyve-1 lymphatic antigen was expressed by more than 30% of fetal cells in mice. In conclusion, we show that melanomas during pregnancy frequently harbor fetal cells that have an endothelial phenotype. Further studies are needed to assess whether the fetal contribution to lymphangiogenesis may alter the prognosis of the maternal tumor.

Early phase of maternal skin carcinogenesis recruits long-term engrafted fetal cells.

During pregnancy, fetal cells enter the maternal circulation. These may be mesenchymal stem cells, haematopoietic or endothelial progenitors, which may persist for decades and be recruited to damaged maternal tissues. Recently, fetal cells were also identified in tumour tissues such as cervical cancer and breast carcinomas. However, the timing of malignant tumour infiltration was not demonstrated. In this study, we used two step carcinogenesis to assess the presence of fetal cells in early phases of skin tumour formation in previously pregnant mice. Wild-type female C57/BL6 mice were bred to transgenic mice for EGFP. After delivery, skin papillomas were induced by two-step carcinogenesis. The tumours were dissected 9 months after gestation. Fetal cells were identified in 75% of cutaneous papillomas (9/12 tumours), but never in normal skin from the same mice. Fetal cells expressed von-Willebrand factor, and less frequently CD45 or cytokeratin but did not express the tumoral epidermal keratins. Our study shows that long-term engrafted fetal cells home to early stage skin tumours where they participate in formation of the stroma.

Feto-maternal cell trafficking: a transfer of pregnancy associated progenitor cells.

The embryonic and fetal development in the maternal uterine environment implies that different population of fetal progenitors must be in close contact to the maternal tissues. Accordingly, fetal mesenchymal and hematopoietic stem and progenitor cells have been described in the placenta and the fetal blood. Seeding in the maternal circulation, fetal progenitor cells can be detected in the circulation of pregnant women during most pregnancies. Decades after delivery, fetal CD34+ or mesenchymal stem cells are still detectable in maternal circulation or bone marrow. Recent studies point to the possibility for fetal progenitor cells persisting after pregnancy to home to maternal injured tissue and to adopt various phenotypes. Fetal cells in various maternal tissues can express epithelial, hepatocytic, hematopoietic, renal, cardiomyocytic, glial, or neuronal markers in human as well as mouse models. This apparent multipotency has been attributed to a fetal population of stem/progenitor cells acquired by the mother during pregnancy, named the pregnancy-associated progenitor cells. We will discuss the possible origins of this cell population and review the most recent data suggesting that these fetal microchimeric cells may participate in maternal tissue regeneration processes.

Pregnancy allows the transfer and differentiation of fetal lymphoid progenitors into functional T and B cells in mothers.

T lymphocytes of fetal origin found in maternal circulation after gestation have been reported as a possible cause for autoimmune diseases. During gestation, mothers acquire CD34+CD38+ cells of fetal origin that persist decades. In this study, we asked whether fetal T and B cells could develop from these progenitors in the maternal thymus and bone marrow during and after gestation. RAG-/--deficient female mice (Ly5.2) were mated to congenic wild-type Ly5.1 mice (RAG+/+). Fetal double-positive T cells (CD4+CD8+) with characteristic TCR and IL-7R expression patterns could be recovered in maternal thymus during the resulting pregnancies. We made similar observations in the thymus of immunocompetent mothers. Such phenomenon was observed overall in 12 of 68 tested mice compared with 0 of 51 controls (p=0.001). T cells could also be found in maternal spleen and produced IFN-gamma in the presence of an allogenic or an Ag-specific stimulus. Similarly, CD19+IgM+ fetal B cells as well as plasma Igs could be found in maternal RAG-/- bone marrow and spleen after similar matings. Our results suggest that during gestation mothers acquire fetal lymphoid progenitors that develop into functional T cells. This fetal cell microchimerism may have a direct impact on maternal health.

Maternal neoangiogenesis during pregnancy partly derives from fetal endothelial progenitor cells.

Fetal progenitor cells enter the maternal circulation during pregnancy and can persist for decades. We aimed to determine the role of these cells in tissue inflammation during pregnancy. WT female mice were mated to males transgenic for the EGFP (ubiquitous) or the luciferase gene controlled by the VEGF receptor 2 (VEGFR2; V-Luc) promoter. A contact hypersensitivity reaction was triggered during such pregnancies. Fetal cells were tracked by using real-time quantitative amplification of the transgene (real-time PCR), Y chromosome in situ hybridization (FISH), immunofluorescence or in vivo bioluminescence imaging. Real-time PCR disclosed fetal cells in the inflamed areas in all tested mice (17/17) with higher frequency and numbers in the inflamed compared with the control areas (P = 0.01). Double labeling demonstrated CD31+ EGFP+ fetal cells organized as blood vessels. In WT pregnant mice bearing V-Luc fetuses, a specific luciferase activity signal could be detected at the hypersensitivity site only, demonstrating the elective presence of VEGFR2-expressing fetal cells. In conclusion, using various techniques, we found the presence of fetal endothelial cells lining blood vessels in maternal sites of inflammation. These results imply that fetal endothelial progenitor cells are acquired by the mother and participate in maternal angiogenesis during pregnancy.