Kinetic and Phenotypic Analysis of CD8 ⁺ T Cell Responses after Priming with Alphavirus Replicons and Homologous or Heterologous Booster Immunizations

Abstract

Alphavirus replicons are potent inducers of CD8؉ T cell responses and thus constitute an attractive vaccine vector platform for developing novel vaccines. However, the kinetics and memory phenotype of CD8 ؉ T cell responses induced by alphavirus replicons are not well characterized. Furthermore, little is known how priming with alphavirus replicons affects booster immune responses induced by other vaccine modalities. We demonstrate here that a single immunization with an alphavirus replicon, administered as viral particles or naked DNA, induced an antigen-specific CD8 ؉ T cell response that had a sharp peak, followed by a rapid contraction. Administering a homologous boost before contraction had occurred did not further increase the response. In contrast, boosting after contraction when CD8؉ IMPORTANCEAlphavirus replicons are promising vaccine candidates against a number of diseases and are by themselves developed as vaccines against, for example, Chikungunya virus infection. Replicons are also considered to be used for priming, followed by booster immunization using different vaccine modalities. In order to rationally design prime-boost immunization schedules with these vectors, characterization of the magnitude and phenotype of CD8 ؉ T cell responses induced by alphavirus replicons is needed. Here, we demonstrate how factors such as timing and dose affect the phenotypes of memory T cell populations induced by immunization with alphavirus replicons. These findings are important for designing future clinical trials with alphaviruses, since they can be used to tailor vaccination regimens in order to induce a CD8 ؉ T cell response that is optimal for control and/or clearance of a specific pathogen.

Attenuated and vectored vaccines protect nonhuman primates against Chikungunya virus

“…We recently developed a number of CHIKV vaccine candidates based on the La Reunion (LR-CHIKV) strain of East Central South African (ECSA) genotype. These were able to induce protective immunity against CHIKV infection in mice (8)(9)(10)(11). Here, we have evaluated the safety, immunogenicity, and efficacy of 3 of those candidates in nonhuman primates.…”

Potent therapeutic efficacy of an alphavirus replicon DNA vaccine expressing human papilloma virus E6 and E7 antigens

“…We previously demonstrated that weekly injection of replicon vaccines (before contraction of the CD8 + T cell response), results in lower memory responses. 18,25 Hence we could speculate that the frequent injections as well as the high dose could synergistically weaken the immune response. Immunization with 3.2 µg of pVAX resulted in the same tumor growth pattern as for non-vaccinated mice.…”

“…18 Moreover, dosages higher than 10 μg results in lower antigen-specific responses. 18,25 For this reason, we also evaluated the anti-tumor effect of DREP at doses lower than 10 μg. Using the same schedule after tumor inoculation, we immunized mice with 0.2 and 0.05 μg of DREP.…”

“…In a previous study, we have demonstrated that boosting at a short interval of 1 week with replicon SFV significantly decreased cellular immunity. 25 It may be that injection of a short interval further decreases the strength of the immune response, yet this affects memory rather than acute responses. This decrease is not likely a result of vector-specific immune responses as we previous demonstrated in a study using an homologous prime-boost immunization with rSFV.…”

“…39 It was observed that increasing the dose of replicon particles favored T effector memory (Tem) development and inhibited T central memory (Tcm) formation. 25 This may have implications within the context of tumor immunity as Tcm cells possess recall proliferation capacity that are required for effective anti-tumor control. 40,41 It has also been previously observed that homologous SFV replicon immunization results in better tumor control over homologous adenovirus immunization or heterologous immunization due to a favored central memory T cell response.…”