Mutual Helper Effect in Copulsing of Dendritic Cells With 2 Antigens

Abstract

To develop an efficient dendritic cell (DC)-based immunotherapy protocol, we examined whether simultaneous pulsing of DCs with a given antigen and a third-party antigen could enhance their antigen presentation capacity. Purified splenic DCs of Balb/c mice were pulsed separately with immunoglobulin G, ovalbumin, conalbumin, P15 peptide of Mycobacterium tuberculosis, and prostate-specific antigen or double combinations of the aforementioned antigens. In some settings, DCs pulsed with 1 antigen were mixed equally with those pulsed with another antigen. Antigen-pulsed DCs were injected into the footpad of syngeneic mice and proliferation of whole, CD4 and CD8 depleted lymph node cells was measured after restimulation with cognate antigen. Antigen-specific production of interferon-gamma (IFNgamma) was tested in culture supernatants. Frequency of responding lymph node cells was determined by IFNgamma enzyme-linked immunosorbent spot assay. Our results showed that copulsing of DCs with 2 unrelated antigens increased the capacity of DCs to induce antigen-specific T-cell proliferation against both antigens up to 16-fold. Injection of 2 populations of DCs each pulsed with a different antigen, increased proliferation of primed T cells significantly as well. Both CD4 and CD8 depleted populations showed vigorous proliferative response in copulsing system. In addition, copulsing of DCs with 2 antigens resulted in higher frequency of antigen-specific responding cells and significantly more IFNgamma production. Our results clearly showed that unrelated peptides and proteins could be used to enhance efficacy of DC-based vaccines and in this system, each antigen served to help the other one, a condition that we termed as "mutual helper effect."

Improved Efficacy of a Dendritic Cell-Based Vaccine against a Murine Model of Colon Cancer: The Helper Protein Effect

“…Accordingly, in an immunotherapeutic study, it was indicated that utilization of a Th0- or Th2-inducing helper Ag, would in fact serve the needs of tumor cells, rather than prevent tumor growth [ 13 ]. In the current study, we did not determine the type of T cell–mediated responses; however, as mentioned earlier, in our previous study we observed that OVA-pulsing of DCs would shift T-cell responses towards Th1 [ 12 ]. In this regard, Eriksson et al [ 23 ], in two DC-based studies, reported that conjugation of the helper Ag to the target Ag could lead to more pronounced antitumor responses as compared to simply mixing the Ags [ 24 ].…”

“…In particular, numerous studies have attempted to fully exploit the potential of potent ex vivo –generated antitumor DCs in order to elicit efficient T-cell responses [ 21 ]. In our previous study, we showed that the presence of a helper Ag next to the target Ag during pulsing of DCs could enhance the proliferation rate of CD8 T cells specific to both the helper and target Ags, a phenomenon we termed “mutual helper effect” [ 12 ]. In this study, elucidate the in vivo effectiveness of this approach against tumor, we vaccinated a murine model of colon cancer with DCs pulsed with the combination of a helper Ag (OVA) and a tumor Ag (AH1).…”

“…According to the results, splenic cells of mice vaccinated with DC-Pep-OVA showed the highest proliferation rate, which further verified the helper role that OVA could play in enhancement of AH1-specific immune responses. In our previous in vitro study, we showed that injection of DCs loaded with OVA (helper Ag) plus the target Ag could elicit secretion of high levels of interferon γ together with robust proliferative responses of CD8 T cells specific to both Ags [ 12 ]. Eriksson et al [ 22 ], using DCs pre-loaded ex vivo with cholera toxin (CT)–conjugated tumor Ag, accomplished induction of efficient CTL-mediated antitumor responses both in vitro and in vivo .…”

“…Mice injected with spleen-derived naive DCs (DC-alone group) or with PBS alone (tumor group) served as control. To determine whether the observed responses were specific to the tumor-derived peptide (AH1), we included another control group: DCs pulsed with OVA plus P15, as an irrelevant peptide derived from Micobacterium tuberculosis [ 12 ]. Overall, animals were divided into five groups according to the type of injection they received ( Table 1 ).…”

“…Our laboratory demonstrated that coupling of a helper Ag with the target tumor Ag increased the efficiency and stability of Ag presentation by DCs and elicited more robust immunogenic responses against both the target tumor Ag and the helper Ag [ 12 ]. This phenomenon, which we called a “mutual helper effect,” generates better Ag-specific immune responses against both Ags.…”