Modulation of antigen-specific humoral responses in rhesus macaques by using cytokine cDNAs as DNA vaccine adjuvants

Abstract

An important limitation of DNA immunization in nonhuman primates is the difficulty in generating high levels of antigen-specific antibody responses; strategies to enhance the level of immune responses to DNA immunization may be important in the further development of this vaccine strategy for humans. We approached this issue by testing the ability of molecular adjuvants to enhance the levels of immune responses generated by multicomponent DNA vaccines in rhesus macaques. Rhesus macaques were coimmunized intramuscularly with expression plasmids bearing genes encoding Th1 (interleukin 2 [IL-2] and gamma interferon)- or Th2 (IL-4)-type cytokines and DNA vaccine constructs encoding human immunodeficiency virus Env and Rev and simian immunodeficiency virus Gag and Pol proteins. We observed that the cytokine gene adjuvants (especially IL-2 and IL-4) significantly enhanced antigen-specific humoral immune responses in the rhesus macaque model. These results support the assumption that antigen-specific responses can be engineered to a higher and presumably more desirable level in rhesus macaques by genetic adjuvants.

FIG. 1

Modulation of antibody responses in rhesus macaques. Five groups of two rhesus macaques were immunized with 200 μg of each DNA vaccine construct at weeks 0, 6, and 12 and boosted with 500 μg of each DNA at week 28. Serum samples were collected from the immunized macaques at weeks 0, 18, and 36. Binding reactivities to recombinant HIV-1 gp120 envelope and SIV p27 Gag proteins (ImmunoDiagnostics, Inc., Bedford, Mass.) were determined by enzyme-linked immunosorbent assay as previously described (1). Specific binding (absorbance at 450 nm) was calculated by subtracting A₄₅₀ values from serum samples bound to bovine serum albumin (control) from A₄₅₀ values from serum samples bound to gp120, that is, the A₄₅₀s of experimental wells minus the A₄₅₀s of control wells. The endpoint antibody titers for immunized rhesus macaques were determined as previously described (1).