Application of Chimeric Feline Foamy Virus-Based Retroviral Vectors for the Induction of Antiviral Immunity in Cats

Abstract

In order to define the potential and applicability of replication-competent foamy virus-based vaccine vectors, recombinant feline foamy virus (FFV) vectors encoding defined segments of the feline calicivirus (FCV) capsid protein E domain were constructed. In cell cultures, these FFV-FCV vectors efficiently transduced and expressed a hybrid fusion protein consisting of the essential FFV Bet protein and the attached FCV E domains. The stability of the vectors in vitro was inversely correlated to the size of the heterologous insert. The deletion of a part of the FFV U3 sequence in these FFV-FCV vectors did not interfere with replication and titer in cell cultures but increased the genetic stability of the hybrid vectors. Selected chimeric vectors were injected into immunocompetent cats and persisted in the transduced host concomitant with a strong and specific humoral immune response against vector components. In a substantial number of cats, antibodies directed against the FCV E domain were induced by the FFV-FCV vectors, but no FCV-neutralizing activities were detectable in vitro. When the vaccinated cats were challenged with a high-titer FCV dose, sterile immunity was not induced by any of the hybrid FFV-FCV vectors. However, the FFV-FCV vector with a truncated U3 region of the long terminal repeat promoter significantly reduced the duration of FCV shedding after challenge and suppressed the appearance of FCV-specific ulcers. Possible mechanisms contributing to the partial protection will be discussed.The great success of applied virology during the last century has been mainly due to the development and application of efficient and safe antiviral vaccines. These prevent virus-mediated disease or spread of the infectious agent and have even resulted in the eradication of poxvirus (reviewed in reference 7). These achievements are on one hand based on the injection of defined virus-derived proteins, as in the case of the hepatitis B virus vaccine or inactivated viruses, which are both capable of inducing a stable and broadly reactive humoral immunity. Alternatively, attenuated, apathogenic virus variants and/or related viruses inducing a stable cross-protection are used. Modified live virus vaccines have the great advantage of mimicking the natural route and mode of virus replication, inducing not only a humoral, mainly immunoglobulin G (IgG)-mediated immunity, but also stimulating the cell-mediated and/or mucosal arm of the adaptive immune response (7). Although these strategies have been efficient in controlling various viruses pathogenic to humans and livestock animals, vaccines against some virus infections are presently either not available or display only a limited degree of protection (23).Over the last several years, novel vaccination strategies have been developed based on recombinant, chimeric viruses used to deliver and efficiently express heterologous vaccine antigens in the recipient (28). These novel strategies include not only prophylactic preexposure vaccination but also therapeutic postexposure im...

Construction and characterization of efficient, stable and safe replication-deficient foamy virus vectors

“…For instance, we recently showed that replication-competent vectors that are directly related to the replicationdeficient ubi-lacZ vectors are efficient at expressing a heterologous vaccine antigen without any side effects. 6 In order to use the current vectors in animal experiments, we employed the constitutively active human ubi C promoter for transgene expression as this promoter displays long-term activity in several cell types from men and a broad range of animals. 37 In addition, mapping of vector integration sites in the authentic animal model will become possible considering the success of the cat genome sequencing project.…”

“…18,19 Additionally, replication-competent FFV-based vaccine vectors induce a partially protective immunity against a highly pathogenic challenge virus in cats. 6 In one of our previous studies, we have demonstrated that FFV self-inactivating (SIN) vectors rapidly give rise to replication-competent revertants (RCRs) indicating that additional genetic deletions are required to generate safe vectors. 4 In a following study, we determined that the essential cis-acting sequences required for FFV-based vectors are located upstream and around the gag start codon and inside pol.…”

“…2 Novel retroviral vectors based on primate-and nonprimate foamy viruses (FV) which constitute the Spumavirinae subfamily of the retroviruses have currently been established and intensively examined by us and others. [3][4][5][6][7][8][9][10][11][12][13] For instance, FV vectors based on the human/primate FV allow efficient, stable and long-term transduction of human haematopoietic cells without detectable side effects. 11,12 FVs are considered to be apathogenic in their natural animal hosts and after zoonotic transmission into humans.…”

Kinetics and characteristics of replication-competent revertants derived from self-inactivating foamy virus vectors

“…Recently, we demonstrated applicability, efficiency, and safety of replication-competent feline FV (FFV) vectors for the transfer of vaccine antigens into cats. 19 More important for medical application, replication-deficient FV-based vectors carrying substantial deletions in structural and regulatory genes have been shown to be especially suited for the long-term transduction of human haematopoietic stem cells. [20][21][22] However, the proposed transduction of haematopoietic stem cells or other long-lived cells demands that RCRs are not generated in the patient.…”

“…This deletion is compatible with vector replication in vitro and in cats. 19,27 Each of two independent clones of the novel SIN vectors pCF-SIN (#2 and #8) and pCF-Bet-Gfp-SIN (#6 and #8) was characterized in detail.…”