Midfielder Lee, 20, has put pen to paper on a one-year deal after making seven senior appearances for the O's.
Meanwhile, 18-year-old winger Semedo has penned a two-year contract after impressing in the youth team.
Orient start the new season at home to Barnet on August 8.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Forest Green RoversForest Green | 15 | 9 | 4 | 2 | 27 | 13 | 14 | 31 |
| 2 | Port Vale | 16 | 8 | 5 | 3 | 28 | 16 | 12 | 29 |
| 3 | Exeter CityExeter | 16 | 7 | 8 | 1 | 27 | 16 | 11 | 29 |
| 4 | Northampton TownNorthampton | 16 | 8 | 3 | 5 | 21 | 13 | 8 | 27 |
| 5 | Harrogate TownHarrogate | 16 | 7 | 5 | 4 | 30 | 21 | 9 | 26 |
| 6 | Newport CountyNewport | 16 | 7 | 5 | 4 | 27 | 19 | 8 | 26 |
| 7 | Swindon TownSwindon | 15 | 7 | 5 | 3 | 22 | 15 | 7 | 26 |
| 8 | Sutton UnitedSutton | 16 | 8 | 2 | 6 | 24 | 18 | 6 | 26 |
| 9 | Leyton Orient | 16 | 5 | 9 | 2 | 27 | 14 | 13 | 24 |
| 10 | Hartlepool UnitedHartlepool | 16 | 7 | 2 | 7 | 18 | 22 | -4 | 23 |
| 11 | Bradford CityBradford | 16 | 5 | 7 | 4 | 22 | 19 | 3 | 22 |
| 12 | Tranmere RoversTranmere | 16 | 6 | 4 | 6 | 11 | 11 | 0 | 22 |
| 13 | Rochdale | 16 | 5 | 6 | 5 | 21 | 21 | 0 | 21 |
| 14 | Bristol Rovers | 16 | 6 | 3 | 7 | 19 | 24 | -5 | 21 |
| 15 | Walsall | 16 | 5 | 5 | 6 | 20 | 22 | -2 | 20 |
| 16 | Barrow | 16 | 4 | 7 | 5 | 20 | 20 | 0 | 19 |
| 17 | Salford City | 16 | 4 | 5 | 7 | 17 | 18 | -1 | 17 |
| 18 | Mansfield TownMansfield | 16 | 4 | 5 | 7 | 16 | 21 | -5 | 17 |
| 19 | Colchester UnitedColchester | 15 | 4 | 5 | 6 | 12 | 19 | -7 | 17 |
| 20 | Crawley TownCrawley | 15 | 5 | 2 | 8 | 17 | 25 | -8 | 17 |
| 21 | Stevenage | 16 | 3 | 5 | 8 | 12 | 28 | -16 | 14 |
| 22 | Carlisle UnitedCarlisle | 16 | 2 | 7 | 7 | 11 | 24 | -13 | 13 |
| 23 | Oldham AthleticOldham | 16 | 3 | 3 | 10 | 12 | 24 | -12 | 12 |
| 24 | Scunthorpe UnitedScunthorpe | 16 | 2 | 6 | 8 | 12 | 30 | -18 | 12 |
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