A method of expanding TCRalpha deficient T-cells by expressing pTalpha or functional variants thereof into said cells, thereby restoring a functional CD3 complex. This method is particularly useful to enhance the efficiency of immunotherapy using primary T-cells from donors. This method involves the use of pTalpha or functional variants thereof and polynucleotides encoding such polypeptides to expand TCRalpha deficient T-cells. Such engineered cells can be obtained by using specific rare-cutting endonuclease, preferably TALE-nucleases. The use of Chimeric Antigen Receptor (CAR), especially multi-chain CAR, in such engineered cells to target malignant or infected cells. The invention opens the way to standard and affordable adoptive immunotherapy strategies for treating cancer and viral infections.