7th Conference - Abstract 434

In Vivo T Cell Priming in Rhesus Macaques by Reinjected Immature and Mature Dendritic Cells Bearing Soluble or Recombinant Viral Vector-Encoded Antigens

R. IGNATIUS*¹, M. LEWIS³, W. I. COX³, S. FRANKEL^4,5, J. MASCOLA^4,6, L. VILLAMIDE¹, E. MEHLHOP¹, R. M. STEINMAN¹, and M. POPE¹. ¹The Rockefeller Univ., New York, NY; ²Henry M. Jackson Fndn., Rockville, MD; ³Virogenetics Corp., Rensselaer Technology Park, Troy, NY; ⁴Walter Reed Army Inst. of Res., Rockville, MD; ⁵Armed Forces Inst. of Pathology, Washington, DC; and ⁶Naval Med. Res. Inst., Bethesda, MD

As the most potent antigen presenting cells, dendritic cells (DCs) are being studied for their capacity to elicit immunity to immunodeficiency viruses. One approach to utilize DCs to induce antigen-specific immunity, involves generating large numbers of DCs from blood, loading them with different forms of antigen, and re-injecting them into the donor. Using SIV and rhesus macaques as a non-human primate model, we are able to address [i] which form of antigen, [ii] what DC subset(s), and [iii] which route of injection will elicit the best responses in vivo.
Using fluorescently labeled cells, we found that both immature and mature DCs migrate predominantly to the T cell areas of the draining lymph nodes following s.c. injection. When either DC subset was pulsed with soluble tetanus toxoid, prior to re-injection, antigen-specific T cell activation was observed. We then looked at DCs infected with SIV-recombinant canarypox vectors (ALVAC-SIV). Immature and mature DCs could be infected with ALVAC-SIV in vitro, the former being more susceptible. SIV-specific T cell responses were detected in animals re-injected with ALVAC-SIV-infected immature or mature DCs. However, animals that received ALVAC-SIV-infected mature DCs exhibited more rapid, stronger, and longer lasting T cell immunity.
This work provides the first evidence that immature and mature DCs can efficiently be loaded with different forms of antigen, i.e. soluble protein or recombinant ALVAC, and that the s.c. re-injection of these cells leads to antigen-specific T cell priming in vivo. DC-mediated immunization can now be compared to antigens delivered with other adjuvants.

Key Words: ALVAC, dendritic cells, Immunity