Effect of apoptosis-associated speck-like protein containing a caspase recruitment domain on vaccine efficacy: Overcoming the effects of its deficiency with aluminum hydroxide adjuvant

Host factors such as nutritional status and immune cell state are important for vaccine efficacy. Inflammasome activation may be important for triggering vaccine-induced humoral and cell-mediated immune responses. Formulations with alum as a typical adjuvant to overcome the effects of host factors have recently been shown to induce inflammasome activation, which augments vaccine efficacy. Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is one of the main components of inflammasomes, but it is not clear whether ASC affects the vaccine-induced immune response. Herein, we used two types of vaccines: inactivated influenza vaccine not formulated with alum, and HPV vaccine formulated with alum. We gave the vaccines to ASC knockout (ASC^−/−) mice to investigate the role of ASC in vaccine efficacy. Influenza vaccine-immunized ASC^−/− mice did not show antibody titers in week 2 after the first vaccination. After boosting, the antibody titer in ASC^−/− mice was about half that in wild type (WT) mice. Furthermore, a cytotoxic T-lymphocyte response against influenza vaccine was not induced in ASC^−/− mice. Therefore, vaccinated ASC^−/− mice did not show effective protection against viral challenge. ASC^−/− mice immunized with alum-formulated HPV vaccine showed similar antibody titers and T-cell proliferation compared with immunized WT mice. However, the HPV vaccine without alum induced up to threefold lower titers of HPV-specific antibody titers in ASC^−/− mice compared with those in WT mice. These findings suggest that alum in vaccine can overcome the ASC-deficient condition.