Differences in neutralization susceptibility between clade C HIV viruses from breastmilk versus contemporaneous circulating viruses from sexually acquired infections

HIV viruses that establish infection possess phenotypic and genotypic characteristics that have been selected for and that differ across transmission routes, including their susceptibility to broadly neutralizing antibodies (bnAbs). While sexually transmitted viruses have been well characterized, studies of vertically transmitted viruses are sparse and from cohorts that are often small in size and more than a decade old. To investigate whether viruses transmitted vertically during lactation possess distinct neutralization profiles compared to viruses transmitted sexually, we compared the neutralization sensitivity of 25 clade C breastmilk viruses to that of 99 contemporaneous clade C viruses from sera of adults with sexual acquisition against three bnAbs in clinical development. Three out of 7 breastmilk donors (43%) had one or more viruses resistant to 2 or more bnAbs, compared to 8 out of 99 (8%) contemporaneous adult viruses (p=0.02). Breastmilk viruses were more resistant to PGT121 and VRC07.523 (median IC80 >50 compared to 1.16 for PGT121, and 12.75 vs. 0.38 for VRC07.523; p=0.013 and <0.001 respectively), and more breastmilk viruses than adult viruses were resistant to VRC07.523 (94% vs. 43%, p=0.001). Interestingly, the breastmilk viruses most resistant to VRC07.523 had on average one or more glycans in V3 compared to adult transmitted viruses (median 3 vs. 2 glycosylation sites, including flanking position 295; p=0.009), and the number of V3 glycans was negatively correlated with VRC07.523 sensitivity (p=0.007). These findings highlight potential differences in bnAb susceptibility of vertically transmitted viruses and emphasize the need to increase sequencing efforts and screening of infant viruses to better inform the efficacy of candidate bnAbs to prevent vertical transmission of HIV.