Enhanced in vitro transcytosis of simian immunodeficiency virus mediated by vaccine-induced antibody predicts transmitted/founder strain number after rectal challenge

Abstract

Background: The time to acquisition of simian immunodeficiency virus (SIV) infection following low-dose repeated rectal challenge correlated inversely with the number of transmitted/founder strains among macaques vaccinated with ALVAC-SIV/gp120 or gp120 alone. We determined if the ability of postvaccination, prechallenge sera to enhance SIVmac251 transcytosis across epithelial cells was associated with transmitted/founder strain number.

Methods: Transcytosis was carried out by exposing sera and SIVmac251 to the apical surface of human endometrial carcinoma (HEC-1A) cells at pH 6.0 and 12 hours later quantifying virus in fluid bathing the basolateral cell surface (maintained at pH 7.4). These conditions allow Fc neonatal receptor (FcRn)-dependent shuttling of virus across cells.

Results: There was a strong correlation between the amount of virus transcytosed and number of transmitted variants (R = 0.86, P < .0001). We also found that 4 animals who remained uninfected after repeated rectal challenges had lower serum transcytosis activity than did 19 animals who subsequently became infected (P = .003). Using immunohistochemistry, we demonstrated FcRn on columnar epithelial cells facing the lumen of the macaque rectum.

Conclusions: Vaccine-induced antibody capable of enhancing transcytosis in vitro via FcRn may play a role in determining transmitted/founder strain number and infection outcomes following in vivo challenge.

Keywords: Fc neonatal receptor; SIV; antibody; transcytosis; vaccine.

Figure 1.

Transcytosis of SIVmac251 mediated by prechallenge sera at pH 6.0 correlates with the number of transmitted SIVmac251 variants. Prechallenge sera (1:100 dilution) from animals in both vaccine groups (A), from ALVAC-SIV/gp120-vaccinated animals (B) or from gp120-vaccinated animals (C) that subsequently became infected were incubated with SIVmac251 and applied to the apical surface of HEC-1A cells at pH 6.0. Twelve hours later, the amount of transcytosed virus was determined by RT-PCR in the subnatant fluid (pH 7.4). Data are reported as the fold-increase in transcytosis compared to preimmune serum and are median values from 8 independent experiments. D, Enhanced transcytosis of SIVmac251 occurs with IgG and is pH dependent. SIVmac251 and 100 µg/mL of IgG from an SIV-infected rhesus macaque were added to the apical surface of HEC-1A cells at the indicated pH. Twelve hours later, SIVmac251 in the subnatant fluid (pH 7.4) was quantified by RT-PCR. Data are reported as the fold-increase in transcytosis compared to no antibody controls. Bars represent averages of 2 experiments (± standard error). Abbreviations: IgG, immunoglobulin G; RT-PCR, reverse-transcription polymerase chain reaction; SIV, simian immunodeficiency virus.

Figure 2.

Transcytosis of infectious SIVmac251 mediated by prechallenge sera at pH 6.0 correlates with the number of transmitted variants. Serum (1:100) and SIVmac251 were applied to the apical surface of HEC-1A cells at pH 6.0, and 12 hours later, the amount of transcytosed virus was determined by adding the subnatant fluid (pH 7.4) to TZM-bl cells. Data are reported as the fold-increase in infectivity compared to preimmune serum and are median values from 3 independent experiments.

Figure 3.

Transcytosis of SIVmac251 mediated by prechallenge sera at pH 6.0 correlates inversely with the number of rectal challenges required for infection. Prechallenge sera (1:100 dilution) from animals in both vaccine groups were incubated with SIVmac251 and applied to the apical surface of HEC-1A cells at pH 6.0. Twelve hours later, the amount of transcytosed virus was determined in the subnatant fluid (pH 7.4) by RT-PCR (A) or by infecting TZM-bl cells (B). Data are reported as the fold-increase in transcytosis or infectivity compared to preimmune serum and are median values from 8 (A) or 3 (B) independent experiments. For plotting purposes, animals uninfected after 5 challenges were assigned the value 6 as their number of challenges. Abbreviation: RT-PCR, reverse-transcription polymerase chain reaction.

Figure 4.

Prechallenge sera from uninfected animals mediate less transcytosis of SIVmac251 than prechallenge sera of animals who subsequently became infected. Virus and sera were applied to the apical surface of HEC-1A cells at pH 6.0, and subnatant fluid (pH7.4) was sampled 12 hours later by RT-PCR. Data are reported as the fold-increase in transcytosis compared to preimmune serum and are median values from 8 independent experiments. Abbreviation: RT-PCR, reverse-transcription polymerase chain reaction.

Figure 5.

FcRn is expressed by epithelial cells on the surface of the rectal mucosa of rhesus macaques. Tissue obtained by biopsy was stained with anti-FcRn rabbit serum (A, low magnification or B, high magnification) or with normal rabbit serum (C). Note that FcRn staining is limited to the surface epithelial cells (inset, arrows) and to mononuclear cells (presumptive macrophages and endothelial cells) in the lamina propria of the rectum. DAB label (brown) and hematoxylin nuclear stain were used. Scale bars denote the degree of magnification. Abbreviation: FcRn, Fc neonatal receptor.