You are presented with a paragraph from a COVID-19 literature. Classify the topics of this piece of text by choosing from the following categories:

- Epidemic Forecasting: The content relates to predictions about the spread of COVID-19.
- Treatment: The paragraph discusses therapeutic methods or medication for COVID-19.
- Prevention: The content covers measures to prevent the spread of COVID-19.
- Mechanism: The paragraph explains the biological mechanisms of the virus.
- Case Report: The content is a report of a COVID-19 case.
- Transmission: The paragraph discusses how COVID-19 is transmitted.
- Diagnosis: The content is about diagnosing COVID-19 in individuals.

Your classification should be provided as an element within a JSON array. The array should be formatted with topics enclosed in double quotes and separated by commas, following the JSON format, for example: ["Topic1", "Topic2", ...]. Include all applicable topics within the array. Your output should be a valid JSON array, and no additional text should be included in your response.

Article:

BACKGROUND: SARS-CoV-2 infection in term placenta is relatively rare. However, growing evidence suggests that susceptibility of the human placenta to infection may vary by gestational age and pathogen. For several viral infections, susceptibility appears to be greatest during early gestation. Infections of the peri-implantation placenta that result in pre-clinical pregnancy loss would typically go undetected. Little is known about the effects of SARS-CoV-2 on the peri-implantation human placenta since this time in pregnancy can only be modeled in vitro. METHODS: We used a human embryonic stem cell-derived model of peri-implantation placental development to assess patterns of ACE2 and TMPRSS2 transcription and protein expression in primitive trophoblast. These molecules are involved in SARS-CoV-2 cell entry and infection. We then infected the same trophoblast cell model with a clinical isolate of SARS-CoV-2, and documented infection dynamics. RESULTS: ACE2 and TMPRSS2 were transcribed and translated in stem-cell derived trophoblast, with preferential expression in syncytialized cells. These same syncytialized cells supported replicative and persistent infection by SARS-CoV-2, while non-syncytialized trophoblast cells in the same cultures did not. CONCLUSIONS: Co-expression of ACE2 and TMPRSS2 in early human embryonic stem cell-derived trophoblast and the robust and replicative infection limited to syncytiotrophoblast equivalents support the hypothesis that increased viral susceptibility may be a defining characteristic of primitive trophoblast. Potential implications of these findings for early pregnancy loss deserve further investigation.
["Mechanism", "Treatment"]