Protection of Macaques against Intrarectal Infection by a Combination Immunization Regimen with Recombinant Simian Immunodeficiency Virus SIVmne gp160 Vaccines

SIV-specific antibody responses in immunized and control macaques after challenge. Dilutions of macaque sera collected at the indicated times were incubated with disrupted, gradient-purified SIVmne virion proteins immobilized on microtiter plates. Endpoint titers were defined as the reciprocal of the highest dilution that gave an optical absorbance value at least threefold higher than the average values obtained with SIV-negative macaque sera. Panels (a) and (b), immunized and control animals challenged with SIVmne E11S; panels (c) and (d), immunized and control animals challenged with uncloned SIVmne. Arrows indicate the time of challenge.

Immunoblot analysis of SIV-specific antibody responses in macaques challenged with SIVmne clone E11S (A) or uncloned SIVmne (B). Macaque plasma (diluted 100-fold) was reacted with SDS-PAGE-separated proteins from disrupted, sucrose gradient-purified SIVmne clone E11S as described earlier (5). At various times after SIV challenge, antibodies were detected in infected animals to envelope surface (gp120) and transmembrane (gp32) proteins; to the Gag proteins p28, p16, and p6; and to the Vpx protein p14. Antibodies to gp120 and gp32 were evident in all immunized macaques on the day of challenge (week 0). A weak antibody that cross-reacts with p28 was also present in one control animal at week 0 (animal 92169 [panel A]). This has occasionally been observed in naive M. fascicularis. The source of this cross-reactive antibody is unknown.

In situ hybridization analysis of lymph nodes from macaques challenged intrarectally with uncloned SIVmne. Peripheral lymph node samples from control (a to f) and immunized (g to i) animals were collected on day 14 (a to c) or day 26 or 27 (d to i) after challenge. Samples were examined with SIV-specific digoxigenin-labeled riboprobes as described in Materials and Methods. Panels: a and b, macaque 93191; c, macaque 93080; d, macaque 93204; e, macaque 93205; f, macaque 93206; g, macaque 90099; h, macaque 90108; and i, macaque 91074. Magnifications in panels a to i are, respectively, ×25, ×25, ×31.2, ×10, ×15, ×31.2, ×31.2, ×12.5, and ×12.5. The sample in panel a was hybridized with a “sense” probe as a control. All other samples shown were hybridized with “anti-sense” probes.

SIV-specific antibody responses in immunized macaques. Sera collected on the day of challenge were analyzed for neutralizing activities against the homologous challenge virus (E11S or uncloned SIVmne). Neutralizing titers are expressed as the reciprocal serum dilutions that resulted in >50% cytopathicity of E11S or uncloned SIVmne infection in CEMx174 cells (a and c). Serum reactivity with disrupted SIVmne E11S virion proteins was analyzed by ELISA, and the results are expressed as endpoint titers (b and d). Top panels (a and b), animals challenged with SIVmne E11S; bottom panels (c and d), animals challenged with uncloned SIVmne. Solid symbols denote persistently infected animals; open symbols show the protected animals. The shaded areas denote the 95% confidence interval for the mean titer of the protected animals. The upper and lower dotted lines represent, respectively, the titers of positive and negative control serum samples in each assay.

Analysis of env V1 sequences recovered from the PBMC of macaques infected intrarectally with uncloned SIVmne. (A) Percentages of E11S-like (solid area) and variant-like (stippled area) V1 sequences in each of the six intrarectally infected control macaques are represented in individual pie charts. For comparison, the composition of the uncloned challenge virus and the results of a similar analysis (31) of intravenously infected animals are included. Analyses of PBMC were done on samples collected 2 weeks after infection. (B) Change of V1 genotype in the PBMC of animals 93204 and 93205 during the acute phase of infection. Percentages of E11S-like (solid bar) and variant-like (stippled bar) V1 sequences are as indicated.