Phase I study utilizing a novel antigen-presenting cell-targeted vaccine with Toll-like receptor stimulation to induce immunity to self-antigens in cancer patients

Abstract

Purpose: The use of tumor-derived proteins as cancer vaccines is complicated by tolerance to these self-antigens. Tolerance may be broken by immunization with activated, autologous, ex vivo generated and antigen-loaded, antigen-presenting cells (APC); however, targeting tumor antigen directly to APC in vivo would be a less complicated strategy. We wished to test whether targeted delivery of an otherwise poorly immunogenic, soluble antigen to APC through their mannose receptors (MR) would induce clinically relevant immunity.

Experimental design: Two phase I studies were conducted with CDX-1307, a vaccine composed of human chorionic gonadotropin beta-chain (hCG-β) fused to an MR-specific monoclonal antibody, administered either locally (intradermally) or systemically (intravenously) in patients with advanced epithelial malignancies. An initial dose escalation of single-agent CDX-1307 was followed by additional cohorts of CDX-1307 combined with granulocyte-macrophage colony-stimulating factor (GM-CSF) and the Toll-like receptor (TLR) 3 agonist polyinosinic-polycytidylic acid (poly-ICLC) and TLR7/8 agonist resiquimod to activate the APC.

Results: CDX-1307 induced consistent humoral and T-cell responses to hCG-β when coadministered with TLR agonists. Greater immune responses and clinical benefit, including the longest duration of stable disease, were observed with immunization combined with local TLR agonists. Immune responses were induced equally efficiently in patients with elevated and nonelevated levels of serum hCG-β. Antibodies within the serum of vaccinated participants had tumor suppressive function in vitro. Toxicity consisted chiefly of mild injection site reactions.

Conclusions: APC targeting and activation induce adaptive immunity against poorly immunogenic self-antigens which has implications for enhancing the efficacy of cancer immunotherapy.

Figures

Figure 1. CDX-1307 Vaccine Regimen

When required for a particular cohort, adjuvants were administered as pictured. All cohorts allowed retreatment in the event of stable disease.

Figure 2. Accumulation of hCG-β in dermal APCs of a patient treated with 1 mg of CDX-1307

Skin biopsy samples were obtained near the injection site 48 hours after i.d. injection of CDX-1307 for analysis of hCG-β. Samples were stained with anti-hCG-β or control rabbit IgG (A, B). Sequential sections were stained for MR using B11-FITC or isotype-FITC control, and then detected using a rabbit anti-FITC probe (C, D). The black scale bar = 50 μm.

Figure 3. Induction of hCG-β-specific antibodies by intradermal (ID) CDX-1307

(A) Anti-hCG-β antibody responses were measured by ELISA as described in Materials and Methods. Initial Cohorts with CDX-1307 alone did not have antibody responses above baseline. Values shown are the maximum titer achieved in each patients and the line represents the geometric mean reciprocal titer for patients in that cohort. P values are shown for analysis of the combination cohorts against GM-CSF alone or GM-CSF + resiquimod. There was no significant difference between the combination TLR cohorts and the cohort with GM-CSF and Poly ICLC. (B) Data from flow population analysis of SCaBER bladder cancer cells subjected to 72 hour incubation with serum from patient sample 5028 at 1:50 dilution under standard cell culture conditions with and without addition of 1 mg/ml hCG β. All non-viable cell populations (propidium iodide positive) are indicated after incubation with pre and post CDX 1307 (following 3 doses).

Figure 3. Induction of hCG-β-specific antibodies by intradermal (ID) CDX-1307

(A) Anti-hCG-β antibody responses were measured by ELISA as described in Materials and Methods. Initial Cohorts with CDX-1307 alone did not have antibody responses above baseline. Values shown are the maximum titer achieved in each patients and the line represents the geometric mean reciprocal titer for patients in that cohort. P values are shown for analysis of the combination cohorts against GM-CSF alone or GM-CSF + resiquimod. There was no significant difference between the combination TLR cohorts and the cohort with GM-CSF and Poly ICLC. (B) Data from flow population analysis of SCaBER bladder cancer cells subjected to 72 hour incubation with serum from patient sample 5028 at 1:50 dilution under standard cell culture conditions with and without addition of 1 mg/ml hCG β. All non-viable cell populations (propidium iodide positive) are indicated after incubation with pre and post CDX 1307 (following 3 doses).

Figure 4. Induction of hCG-β-specific T cell responses by ELISPOT in patients treated with intradermal (ID) CDX-1307 in combination with adjuvants

Interferon-gamma ELISpot was used to measure T cells responding to hCG-β overlapping peptides after restimulation in vitro as described in Materials and Methods. Initial Cohorts with CDX-1307 alone did not have T cell responses above baseline and are not depicted. Values shown are the maximum T cell response achieved in each patients and the line represents the mean for patients in that cohort.