OA04-02. Strong HIV-specific CD4 and CD8 T-lymphocyte proliferation in HIV-1 DNA prime/modified vaccinia virus Ankara (MVA) heterologous boost vaccinees

Background

We determined HIV-1-vaccine-induced lymphoproliferative responses in vaccinees immunized with a multigene, multiclade HIV-1 plasmid DNA vaccine boosted with heterologous HIV-1 recombinant MVA in a phase I HIV safety and immunogenicity study (HIVIS01/02).

Methods

Healthy volunteers were immunized intradermally or intramuscularly (with or without adjuvant GM-CSF protein) with DNA expressing HIV-1 gag, env, rev and rt at months 0, 1 and 3 using a Biojector and were boosted at nine months with an MVA expressing heterologous inserts of HIV-1 gag, env and pol genes. Lymphoproliferative responses to AT-2 inactivated HIV-1 antigen were tested by a 3H-thymidine uptake assay and a flow-cytometric assay of specific cell-mediated immune-response in activated whole blood (FASCIA-WB) two weeks after HIV-1 MVA boost (n = 38). A FASCIA using peripheral blood mononuclear cells (FASCIA-PBMC) was also employed during the later part of the study (n = 14).

Results

Thirty-five of 38 (92%) vaccinees were reactive by the 3H-thymidine-uptake assay (SI > 8). Thirty-two of 38 (84%) vaccinees were reactive by the CD3+CD4+ T-cell FASCIA-WB (% stimulation > 1.2), seven (18%) also exhibited CD8+ (CD3+ CD4-) T-cell responses. Of the 14 vaccinees analyzed using all three assays, ten (71%) and eleven (79%) demonstrated CD4+ T-cell responses in FASCIA-WB and FASCIA-PBMC, respectively. CD8+ T-cell reactivity was observed in 3 of 14 (21%) and 7 of 14 (50%) using the FASCIA-WB and FASCIA-PBMC, respectively. There was strong correlation between the proliferative responses measured by the 3H-thymidine uptake assay and the CD4+ T-cell FASCIA-WB (r = 0.68; p < 0.01).

Conclusion

HIV-1 specific T-lymphocyte proliferative responses were detected in a high proportion (37/38) of volunteers following HIV-1 DNA/MVA immunization. The FASCIA revealed both CD4+ and CD8+ T-cell proliferation in response to HIV-1 antigen stimulation. A standardized FASCIA-PBMC, which allows simultaneous phenotyping may be an option to the conventional 3H-thymidine uptake assay for assessment of vaccine-induced T-cell proliferation, especially in isotope-restricted settings.