Complement-mediated virus infectivity neutralisation by HLA antibodies is associated with sterilising immunity to SIV challenge in the macaque model for HIV/AIDS

Abstract

Sterilising immunity is a desired outcome for vaccination against human immunodeficiency virus (HIV) and has been observed in the macaque model using inactivated simian immunodeficiency virus (SIV). This protection was attributed to antibodies specific for cell proteins including human leucocyte antigens (HLA) class I and II incorporated into virions during vaccine and challenge virus preparation. We show here, using HLA bead arrays, that vaccinated macaques protected from virus challenge had higher serum antibody reactivity compared with non-protected animals. Moreover, reactivity was shown to be directed against HLA framework determinants. Previous studies failed to correlate serum antibody mediated virus neutralisation with protection and were confounded by cytotoxic effects. Using a virus entry assay based on TZM-bl cells we now report that, in the presence of complement, serum antibody titres that neutralise virus infectivity were higher in protected animals. We propose that complement-augmented virus neutralisation is a key factor in inducing sterilising immunity and may be difficult to achieve with HIV/SIV Env-based vaccines. Understanding how to overcome the apparent block of inactivated SIV vaccines to elicit anti-envelope protein antibodies that effectively engage the complement system could enable novel anti-HIV antibody vaccines that induce potent, virolytic serological response to be developed.

Figure 1. Association between anti-HLA reactivity following vaccination with formalin-inactivated SIV and outcome of challenge.

Virus infection status was determined by PCR for SIVgag proviral DNA and virus isolation (VI) from PBMC of macaques challenged with SIVmac₂₅₁32H (a) following vaccination with inactivated SIV with either 3×500 µg doses (group A) or 4×100 µg doses (group B). Bar charts show the associated median fluorescence intensity (y axis) of serum samples for each macaque tested against HLA class I (red bars) and class II (green bars) bead sets (x axis). Background binding of pre-vaccination sera is shown as light red and light green for HLA class I and class II respectively. * indicates not tested, probe number refers HLA allele-specific bead sets.

Figure 2. Association between anti-HLA reactivity following vaccination with fixed-inactivated SIV infected and uninfected C8166 cells and outcome of challenge.

Virus infection status was determined by PCR for SIVgag proviral DNA and virus isolation (VI) from PBMC of macaques challenged with SIVmac₂₅₁32H (a) following vaccination with 2 doses of SIV infected C8166 cells (group C) or with uninfected C8166 cells (group D). Bar charts show the associated median fluorescence intensity (y axis) of serum samples for each macaque tested against HLA class I (red bars) and class II (green bars) bead sets (x axis). Background binding of pre-vaccination sera is shown as light red and light green for HLA class I and class II respectively. * indicates not tested, probe number refers HLA allele-specific bead sets.

Figure 3. Association between anti-HLA reactivity following vaccination with uninfected C8166 cells using different adjuvants and outcome of challenge.

Virus infection status was determined by PCR for SIVgag proviral DNA and virus isolation (VI) from PBMC of macaques challenged with SIVmac₂₅₁32H (a) following vaccination with 4 doses of uninfected C8166 cells with Quil A adjuvant (group E) or with GMDP adjuvant (group F) (a) following vaccination with 2 doses of SIV infected C8166 cells (group C) or with uninfected C8166 cells (group D). Bar charts show the associated median fluorescence intensity (y axis) of serum samples for each macaque tested against HLA class I (red bars) and class II (green bars) bead sets (x axis). Background binding of pre-vaccination sera is shown as light red and light green for HLA class I and class II respectively. * indicates not tested, probe number refers HLA allele-specific bead sets.

Figure 4. Virus infectivity neutralising activity following vaccination with inactivated SIV.

Neutralising antibody activity against SHIV_W61D propagated on human C8166 cells in sera from macaques immunised with SIV-containing vaccines in the absence (left panel) or presence (right panel) of complement. Pre-immune sera (black line) are means of all animals with standard deviations. Group A immunised with 500 µg of inactivated SIV (red lines); group B immunised with 100 µg of inactivated SIV (blue lines) group C immunised with SIV-infected C8166 cells (green lines). Dashed lines indicate unprotected animals.

Figure 5. Virus infectivity neutralising activity following vaccination with uninfected cells.

Neutralising antibody activity against SHIV_W61D propagated on human C8166 cells in sera from macaques immunised with uninfected C8166 cell vaccines in the absence (left panel) or presence (right panel) of complement. Pre-immune sera (black line) are means of all animals with standard deviations. Group D (pink lines); group E (purple lines) group F (pale brown lines). Dashed lines indicate unprotected animals.

Figure 6. Infectivity neutralising activity against virus unrelated to vaccine.

Neutralising antibody activity against SIVsmE660 propagated on human C8166 cells in sera from macaques immunised with uninfected C8166 cell vaccines (group E) in the absence (left panel) or presence (right panel) of complement. Pre-immune sera (black line) shows means of all animals with standard deviations. Dashed lines indicate unprotected animal.

Figure 7. Infectivity neutralising activity against virus propagated on discordant cell substrate.

Neutralising antibody activity against SHIV_W61D propagated on either human C8166 cells (solid lines) or macaque HSC-F cells (dotted lines) in sera from macaques immunised with SIV-infected (J69; green lines) or uninfected C8166 cell (J73; purple lines) vaccines.