Single Dose of a Polyanhydride Particle-Based Vaccine Generates Potent Antigen-Specific Antitumor Immune Responses

Many factors affect vaccine efficacy. One of the most salient is the frequency and intervals of vaccine administration. In this study, we assessed the vaccine administration modality for a recently reported polyanhydride-based vaccine formulation, shown to generate antitumor activity. Polyanhydride particles encapsulating ovalbumin (OVA) were prepared using a double-emulsion technique and subcutaneously delivered to mice either as a single-dose or as prime-boost vaccine regimens in which two different time intervals between prime and boost were assessed (7 or 21 days). This was followed by measurement of cellular and humoral immune responses, and subsequent challenge of the mice with a lethal dose of E.G7-OVA cells to evaluate tumor protection. Interestingly, a single dose of the polyanhydride particle-based formulation induced sustained OVA-specific cellular immune responses just as effectively as the prime-boost regimens. In addition, mice receiving single-dose vaccine had similar levels of protection against tumor challenge compared with mice administered prime-boosts. In contrast, measurements of OVA-specific IgG antibody titers indicated that a booster dose was required to stimulate strong humoral immune responses, since it was observed that mice administered a prime-boost vaccine had significantly higher OVA-specific IgG₁ serum titers than mice administered a single dose. These findings indicate that the requirement for a booster dose using these particles appears unnecessary for the generation of effective cellular immunity.