First: Stephen Alan Marglin is an economics professor at Harvard who self identifies as a Marxist. He's only one of many. (Link below). You're welcome. Always glad to help.
https://en.wikipedia.org/wiki/Stephen_Marglin
Second. Even if no professors in Harvard did identify as Marxists - That would be completely irrelevant and what's known in logic as an argument from silence fallacy. How a person self identifies and what their positions imply are entirely separate issues.
Third: Marxism is not solely a political system. Marxism is a philosophical, social, political, and economic ideology and movement whose ultimate goal is the establishment of a communist society, which is a socioeconomic order structured upon the ideas of common ownership of the means of production.