Abstract CT251: Immunological and histopathological tumor responses to a novel neoadjuvant peptide vaccine targeting HSP70 and GPC3 antigens in patients with resectable HCC

Background: Even with curative resection, the recurrence rate of HCC remains high, and effective adjuvant therapies are not currently available. Our previous Phase I study with novel therapeutic peptides and immune adjuvants demonstrated safety, antigen-specific CTL induction in PBMC, and a sign of efficacy (ASCO 2017 Abstract # 3086). We thus started a Phase I study of the same vaccination therapy as a perioperative immunotherapy setting in patients with resectable HCC (jRCTs061180058). Methods: Two mg each of HLA-A*24:02, 02:01, or 02:06-restricted HSP70- and GPC3-derived peptides, in combination with hLAG-3Ig (1.0 mg) + poly-IC:LC (1.4 mg) were injected intradermally at four sites of the inguinal and axillary regions every week for 6 weeks before surgery. Patients subsequently received 10 injections of adjuvant immunotherapy over 4 months. Surgical specimens and PBMCs were analyzed by mass cytometry (CyTOF), using 66 antibodies to monitor T-cell exhaustion, T-cell activation, and effector Treg induction. Tumor specimens were also subjected to HE staining and immunohistochemical staining for CD3, CD8, PD1, HSP70, and GPC3. Results: Nine patients were treated with preoperative vaccination, and resected surgical specimens and PBMC were examined. Pathohistological analysis revealed three response types: “hot cellular immunity”, “intermediate fumoral immunity”, and “cold response”. In three patients, massive infiltration of CD8+ and PD1+ T cells accompanied necrotic and fibrous regions, in which the targeted tumor antigens HSP70 and GPC3 were highly expressed, representing “hot cellular immunity”. Regarding “intermediate”, three patients showed necrotic regions with infiltrating macrophages. HSP70 and/or GPC3 were also highly expressed, but little infiltration of lymphocytes was evident. In the remaining three patients, “cold response” manifested as tumor comprising a pseudo-glandular pattern with no infiltration of T cells or macrophages. Two of these three patients showed no expression of targeted tumor antigens. CyTOF analysis of the tumors also revealed the percentages of CD3+ cells among live cells and of PD1+ cells among CD8+ cells were extremely low in cold response. However, this trend was not observed in PBMCs, suggesting the critical importance of TIL analysis. Conclusions: This novel therapeutic peptide and immune adjuvant combination induced sustained immune cell infiltration into tumor microenvironments, especially in those presenting target tum