P34.08
Background: We previously identified an individual (CAP88), from the CAPRISA 002 cohort, with potent strain-specific neutralization. This response mapped to the C3 region of gp120 and was detected at 11 weeks post-infection (wpi) and then later waned co-incident with viral escape. A monoclonal antibody (CAP88-CH06) was isolated at 34 wpi which utilized the IGHV4-39*01, D3-3*01 and J4*02 genes, had 5.9% divergence from germline, and CDRH3 length of 17 amino acids. This study examined the evolution of the CAP88-CH06 heavy chain immunoglobulin genes over 121 weeks, starting from 11 weeks of infection.
Methods: RNA and DNA were extracted from PBMCs from donor CAP88 at four time-points (11, 17, 38 and 121 wpi). The heavy chain VDJ regions of IGHV4-39 gene were PCR amplified and sequenced by Illumina MiSeq. The resulting sequences were blasted against a database of germline IGHV and IGHJ sequences from IMGT and compared to the CAP88-CH06 sequence.
Results: We detected ∼3,500 sequences that were highly related to CAP88-CH06. The majority (75%) of these were from RNA at 11 wpi (1,051 sequences, 39%), 17 wpi (1,625, 61%) and 1 sequence each in 38 wpi and 121 wpi. This corresponded to the antibody response which first appeared at 11 wpi, peaked at 26 wpi and by 54 weeks had declined. Most of the DNA sequences were from 11 wpi (n=761) followed by 38 wpi (n=113) and fewer than 10 from 17 wpi and 121 wpi. The 38 wpi DNA sequences were closely related to the 11 wpi sequences of both RNA and DNA.
Conclusions: We have identified clonally related antibody sequences from 4 different time-points from CAP88 in both RNA and DNA. The frequency of sequences in RNA corresponded with plasma neutralizing antibody titres. DNA-derived sequences from later time-points clustered in phylogenetic trees with RNA-derived sequences from earlier time-points, suggesting that they were from the memory B cell compartment.
