Replication-Defective Canarypox (ALVAC) Vectors Effectively Activate Anti–Human Immunodeficiency Virus-1 Cytotoxic T Lymphocytes Present in Infected Patients: Implications for Antigen-Specific Immunotherapy

G. Ferrari, C. Berend, J. Ottinger, R. Dodge, J. Bartlett, J. Toso, D. Moody, J. Tartaglia, William I. Cox, E. Paoletti and K.J. Weinhold


In the attempt to develop immunotherapeutic strategies for acquired immunodeficiency syndrome capable of activating effector cells in an antigen-specific manner while maintaining the broadest possible T-cell repertoire, we evaluated two canarypox (ALVAC)-based vectors for their capacity to induce ex vivo activation/expansion of human immunodeficiency virus (HIV)-specific CD8+ cytotoxic lymphocyte precursors (CTLp) obtained from HIV-1–infected donors. These two vectors, vCP205 encoding HIV-1 gp120 + TM (28 amino acid transmembrane anchor sequence) in addition to Gag/protease and vCP300 encoding gp120 + Gag/protease as well as Nef and Pol CTL determinants, are pancytotropic but replication incompetent in mammalian cells. Bulk peripheral blood mononuclear cells (PBMCs) or enriched CD8+ T cells were stimulated for 10 days with autologous ALVAC-infected PBMCs in the presence of different cytokine combinations (interleukin-2 [IL-2], IL-4, IL-7, and IL-12). Activation by ALVAC constructs was highly antigen-specific, because vCP205 elicited only Env and Gag CTL, whereas vCP300 elicited broader reactivities against Env, Gag, Pol, and Nef determinants. The ALVAC activation of CTLp was IL-2 dependent and enhanced by the addition of IL-7, whereas IL-4 and IL-12 failed to augment cytotoxic reactivities elicited by these constructs. The expansion of enriched CD8+ T cells after activation with vCP300 was higher in patients with CD4 counts greater than 400 cells/μL. Two rounds of in vitro stimulation (IVS) with vCP300 resulted in nearly an eightfold expansion of CD8+ lymphocytes over a 25-day period. After the second IVS, an average 3.2-fold increase among the different antigen-specific CTL frequencies was achieved. These studies clearly show that HIV-recombinant ALVAC vectors represent powerful polyvalent antigenic stimuli for activation and expansion of the CD8 lymphocyte response that occurs as a result of HIV infection.

  • Submitted July 13, 1996.
  • Accepted May 27, 1997.
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