Specific peptide-mediated immunity against established melanoma tumors with dendritic cells requires IL-2 and fetal calf serum-free cell culture

Abstract

Melanoma, despite its aggressive growth characteristics, is an antigenic tumor expressing several characterized neo‐ and differentiation antigens. Dendritic cells (DC) when pulsed with definedpeptides have been shown to effectively induce melanoma‐specific T cell responses in humans and mice. These protect animals from challenge with melanoma, but so far have failed to induce significant tumor regressions. To study the efficacy of DC‐based anti‐tumor vaccinations, we set up a therapeutic model using C57BL/6J mice with established pulmonary and subcutaneous metastases induced by the B16‐melanoma cell line B78‐D14. Mice were vaccinated twice with 20,000 antigen‐presenting cells, either bone marrow‐derived DC or epidermal Langerhans cells (LC), which were loaded with the tyrosinase‐related protein 2 (TRP2) peptide. Generally, DC cultured with fetal calf serum (FCS) induced a dominant unspecific response. This was not seen using LC cultured without serum; however, vaccination with TRP2‐loaded FCS‐free LC alone failed to influence the growth of established B16 tumors. A reproducible reduction of tumor size and weight was only obtained if LC vaccinations with TRP2 were followedby a 5‐day treatment of mice with 200,000 IU IL‐2 intraperitoneally twice/daily. Omitting the TRP2 peptide abolished the efficacy of this combined treatment, demonstrating the crucial role of priming a melanoma‐specific T cell response. Microcytotoxic assays performed with spleen‐derived T cells and melanoma as well as congenic fibroblast lines as targets confirmed the TRP2‐dependent specificity of LC‐induced immune responses. Thus, despite the fact that tumor‐specific T cells were primed, an additional IL‐2‐dependent stimulus was needed to translate this immune response into a therapeutic effect against established tumors.

NK Cells Are Required for Dendritic Cell–Based Immunotherapy at the Time of Tumor Challenge

“…In contrast, some studies have demonstrated that immunization with syngenic DC alone (in the absence of tumor Ag) can induce NK cell-dependent antitumor responses against melanoma, colon, or lung carcinoma (17,20,23). We have previously noted that immunization with syngenic DC in the absence of tumor Ag can induce antimelanoma immunity in the prophylactic setting, but only if FCS Ags are present in both the DC and the melanoma culture medium (37,39). Unless rigorous attempts are made to exclude FCS from all steps of either DC (37) or melanoma (39) culture, anti-FCS responses could be mistaken for the action of the innate immune response, including NK cell activation.…”

“…For the in vitro cytokine release assays, splenocytes were cultured at 2 3 10 6 /ml in the presence or absence of S. salivarius K12 in 96-well round-bottom plates (Nunc, Auckland, New Zealand) for 18 h. Soluble IFN-g was measured by ELISA (BD Biosciences). In vitro cytotoxicity of lymph node or splenic NK cells against the B16-OVA melanoma line was tested by plating 250 target B16-OVA cells in 10 ml R10 in triplicate in Terasaki wells (37). Effector NK cells, isolated from lymph node or spleen using the untouched NK cell Isolation Kit II (Miltenyi Biotec, Pharmaco, Auckland, New Zealand), were overlaid in 5 ml R10 at a 100:1 E:T ratio.…”

Comparison of recombinant adenovirus and synthetic peptide for DC-based melanoma vaccination

“…The limited efficacy of cultured DC pulsed with the TRP2 aa180-188 peptide epitope may be enhanced by coadministration of immunostimulatory cytokines such as IL-2 12,36 or by multiple injections of peptide-pulsed DC. 11 As an alternative strategy, Wang et al 13 attached the TRP2 aa180-188 peptide to the protein transduction domain of HIV TAT, which leads to prolonged antigen presentation by DC.…”

SPAS-1 (stimulator of prostatic adenocarcinoma-specific T cells)/SH3GLB2: A prostate tumor antigen identified by CTLA-4 blockade

“…3B). Despite the well documented nonspecific protective effect conferred by vaccination with BM-DC alone (17)(18)(19)(20), targeting the response to SPAS-1 (SNC9-H 8 ) led to a significantly greater delay in tumor growth rate compared with vaccination with SL8-pulsed BM-DC (P Ͻ 0.05) (Fig. 3A), confirming that SNC9-H 8 was indeed a target of the anti-TRAMP tumor T cell response in vivo.…”