AFP-specific CD4+ Helper T-cell Responses in Healthy Donors and HCC Patients

Abstract

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, and is often diagnosed at an advanced stage. We have investigated α-fetoprotein (AFP) as a tumor-associated antigen for HCC. We identified major histocompatibility complex class I-restricted peptide epitopes derived from AFP and studied CD8+ T-cell responses in vivo and in vitro in ongoing immunotherapy studies. Helper T cells are of critical importance in shaping the immune response; therefore, we investigated the frequency and function of AFP-specific CD4+ T cells in the general population and among HCC patients. CD4+ T-cell responses were assessed by direct ex vivo multicytokine enzyme-linked immunospot assay and by measurement of cytokine levels using a multicytokine assay. Our analysis indicates that healthy donors have very low frequencies of AFP-specific CD4+ T-cell responses, which are of TH1 type, detectable ex vivo. In contrast, these T cells were either reduced or eliminated in HCC patients at advanced stages of disease. To better activate these cells, we compared the stimulatory capacity of both AFP protein-fed and AdVhAFP-engineered dendritic cells (DC). Healthy donors have CD4+ T-cell responses, which were activated in response to AFP protein-fed DC whereas HCC patients do not demonstrate significant responses to AFP protein. AdVhAFP-transduced DC were capable of activating higher frequency TH1 CD4+ responses to AFP in both healthy donors and AFP-positive HCC patients. Importantly, CD4+ T-cell cytokine expression profiles were skewed towards interleukin-2 and interferon-γ production when activated by adenovirally engineered DC, which has therapeutic implications for vaccination efforts.