Immunogenicity and protective efficacy of recombinant human T-cell leukemia/lymphoma virus type 1 NYVAC and naked DNA vaccine candidates in squirrel monkeys (Saimiri sciureus)

We assessed the immunogenicities and efficacies of two highly attenuated va ccinia virus-derived NYVAC vaccine candidates encoding the human T-cell leu kemia/lymphoma virus type 1 (HTLV-1) ear gene or both the env and gag genes in prime-boost pilot regimens in combination with naked DNA expressing the HTLV-1 envelope. Three inoculations of NYVAC HTLV-1 env at 0, 1, and 3 mon ths followed by a single inoculation of DNA env at 9 months protected again st intravenous challenge with HTLV-1-infected cells in one of three immuniz ed squirrel monkeys. Furthermore, humoral and cell-mediated immune response s against HTLV-1 Env could be detected in this protected animal. However, p riming the animal with a single dose of env DNA, followed by immunization w ith the NYVAC HTLV-1 gag and env vaccine at 6, 7, and 8 months, protected a ll three animals against challenge with HTLV-1-infected cells. With this pr otocol, antibodies against HTLV-1 Fm and cell-mediated responses against En v and Gag could also be detected in the protected animals. Although the rel ative superiority of a DNA prime-NYVAC boost regimen over addition of the G ag component as an immunogen cannot be assessed directly, our findings neve rtheless show that an HTLV-1 vaccine approach is feasible and deserves furt her study.