Nucleic acid vectors for immunization

1. A nucleic acid vector encoding a dimeric protein comprising a first fusion protein and a second fusion protein,

wherein the first fusion protein comprises:

(i) CTLA-4 or the V-like domain thereof,

(ii) a leucine zipper domain, and

(iii) a viral antigen;

and wherein the second fusion protein comprises:

(i) CTLA-4 or the V-like domain thereof,

(ii) a leucine zipper domain, and

(iii) optionally an antigen.

2. A nucleic acid vector encoding a fusion protein comprising:

(i) CTLA-4 or the V-like domain thereof,

(ii) a leucine zipper domain, and

(iii) a viral antigen.

3. The nucleic acid vector according to claim 1 wherein an additional sequence selected from the group consisting of a nucleotide sequence encoding a secretory sequence, a nucleotide sequence encoding a leader sequence, and a nucleotide sequence encoding a retention sequence is fused to the nucleotide sequences encoding the first fusion protein or the second fusion protein.

4. A composition comprising two nucleic acid vectors according to claim 2 , said vectors encoding a dimeric protein comprising a first fusion protein and a second fusion protein, wherein the first fusion protein comprises:

(i) CTLA-4 or the V-like domain thereof,

(ii) a leucine zipper domain, and

(iii) a viral antigen;

and wherein the second fusion protein comprises

(i) CTLA-4 or the V-like domain thereof,

(ii) a leucine zipper domain, and

(iii) optionally an antigen.

5. An isolated host cell comprising a nucleic acid vector according to claim 1 .

6. A composition comprising the nucleic acid vector according to claim 1 or claim 2 and a suitable pharmaceutical carrier.

7. An isolated host cell comprising two nucleic acid vectors according to claim 1 , each of said vectors encoding a dimeric protein comprising a first fusion protein and a second fusion protein, wherein the first fusion protein comprises:

(i) CTLA-4 or the V-like domain thereof,

(ii) a leucine zipper domain, and

(iii) a viral antigen;

and wherein the second fusion protein comprises

(i) CTLA-4 or the V-like domain thereof,

(ii) a leucine zipper domain, and

(iii) optionally an antigen.

8. The composition according to claim 4 , further comprising a suitable pharmaceutical carrier.

9. The nucleic acid vector according to claim 2 , wherein an additional sequence selected from the group consisting of a nucleotide sequence encoding a secretory sequence, a nucleotide sequence encoding a leader sequence, and a nucleotide sequence encoding a retention sequence is fused to the nucleotide sequence encoding the fusion protein.

10. The nucleic acid vector according to claim 3 or 9 , wherein said additional sequence is selected from the group consisting of a nucleotide sequence encoding the human tissue-type plasminogen activator signal/pro sequence, a nucleotide sequence encoding the ER retention sequence KDEL (SEQ ID NO:22) and a nucleotide sequence encoding the GPI anchor signal.

11. The nucleic acid vector according to claim 1 , wherein the first fusion protein or the second fusion protein comprises a GCN4 leucine zipper domain.

12. The nucleic acid vector according to claim 1 , wherein the second fusion protein comprises a viral antigen.

13. The nucleic acid vector according to claim 2 , wherein the fusion protein comprises a GCN4 leucine zipper domain.

14. The nucleic acid vector according to claim 4 , wherein the first fusion protein or the second fusion protein comprises a GCN4 leucine zipper domain.

15. The nucleic acid vector according to claim 4 , wherein the second fusion protein comprises a viral antigen.

16. The nucleic acid vector according to claim 7 , wherein the first fusion protein or the second fusion protein comprises a GCN4 leucine zipper domain.

17. The nucleic acid vector according to claim 7 , wherein the second fusion protein comprises a viral antigen.