this from the 1974 Watchtower is still current teaching as far as I know:
In what way are they “virgins”? The Bible explains. Concerning the 144,000, who are seen standing with the Lamb of God on the spiritual Mount Zion, it says: “These are the ones that did not defile themselves with women [like the religious harlot Babylon the Great, and her daughters]; in fact, they are virgins. These are the ones that keep following the Lamb no matter where he goes.” (Rev. 14:4; 17:3-5) After becoming spirit-begotten ones, having hope of reigning with Christ in the heavens, they do not commit spiritual “adultery” with this world. Consequently, these Christians do not defile themselves with the religious and political system of this world. They do not meddle or interfere in any way with politics or the operations of human governments.—2 Tim. 2:3, 4.