The invention relates to a mutated env gene which codes for a mutated envelope glycoprotein of virus HIV-1. In relation to the env gene of a reference or primary infection primary isolate, said gene presents at least two mutations at the glycosylation sites which are preserved from one primary isolate to another. Each mutation consists in the replacement of an AAC or AAT codon which codes for an asparagine with a CAG or CAA codon which codes for a glutamine, the two mutations at least being selected from the following: (a) at least two mutations in the part of the env gene that codes for region C3 of the env protein; (b) at least one mutation in the part that codes for region C3 and at least one mutation in the part that codes for region V3; (c) at least one mutation in the part that codes for region C2 and at least one mutation in the part that codes for region V3 chosen from the glycosylation sites at codons 862-864 and 970-972; (d) at least one mutation in the part that codes for region C2 selected from the glycosylation sites at codons 667-669, 679-681, 700-702,763-765, 844-846 and at least one mutation in the part that codes for region V3. Alternatively, the mutated env gene consists of any one of the following sequences: SEQ ID NO: 8, SEQ ID NO: 9 or SEQ ID NO: 10, or the complementary sequences thereof. The invention also relates to the mutated Env glycoprotein and the use of the gene and the glycoprotein in a pharmaceutical composition in order to produce antibodies and to evaluate a therapeutic agent.