A method for the in vitro production of a cell population P′ from a cell population P, the production requiring the presence of at least one factor which is expressed by feeder cells, wherein a) feeder cells proliferate at a temperature T1, b) proliferated feeder cells are contacted with the cell population P, c) the cell mixture obtained at step (b) is cultivated at a temperature T2 which is chosen such that the cell population P proliferates and the feeder cells do not proliferate, the at least one factor being expressed by the feeder cells, and d) the cell population P′ so produced is recovered. Advantageously, the production consists in an expansion, the feeder cells are insect feeder cells and the cell population P to be expanded is a T lymphocyte population, preferably a Trl lymphocyte population.