In animal models administration of immunostimulatory DNA sequences preferentially elicits T_H1-dominated (type 1-dominated) immunity and can inhibit developing or ongoing T_H2 (type 2) responses.

Our objective was to investigate this phenomenon in humans.

In a randomized, third party-blinded, placebo-controlled, proof-of-concept study conducted entirely in the winter in 19 adults with ragweed allergy, we administered 6 subcutaneous injections of purified Amb a 1 linked to the 22-base-long immunostimulatory phosphorothioate oligodeoxyribonucleotide 1018 (Amb a 1–immunostimulatory DNA sequence conjugate [AIC]). Before the course of AIC or placebo injections and 2 and 16 weeks afterward, we measured recall responses to ragweed, streptokinase, and PHA in short-term primary culture of fresh PBMCs after restimulation with antigen. We quantified regulatory cytokine and chemokine responses characteristic of T_H2 immunity (IL-5, IL-13, CCL17 [TARC], and CCL22 [MDC]), and T_H1 immunity (IFN-γ, CXCL9 [Mig], and CXCL10 [IP-10]), as well as IL-10, a cytokine sometimes linked to regulatory T-cell populations.

We demonstrated for the first time that human systemic in vivo ragweed-specific T_H2 responses were selectively redirected toward T_H1 responses, with significant increases in IFN-γ, CXCL9, and CXCL10 and significant decreases in IL-5, CCL17, and CCL22 found at 2 and 16 weeks after the sixth injection. Cytokine and chemokine responses to the unrelated bacterial antigen streptokinase and the global capacity to mount immune responses on polyclonal activation with PHA did not change. No clinically significant systemic or local allergic reactions were associated with AIC or placebo injections.

AIC, injected in concentrations that were approximately 40-fold lower than those used in most murine studies published to date, led to a prolonged shift from T_H2 immunity toward T_H1 immunity and appeared to be safe. This novel approach has the potential for immune redirection in human immediate hypersensitivity diseases.