Background
Many viruses evade innate immune surveillance by expressing high levels of sialoglycans (sialic acid-enriched glycans) that bind to Siglecs—glyco-immune checkpoint molecules on immune cells, primarily those of myeloid origin, such as monocytes and neutrophils. This interaction suppresses the cytotoxic activity of these immune cells. HIV infection increases sialoglycan expression on the surface of CD4+ T cells; however, whether this increase facilitates the binding of HIV-infected cells to specific Siglecs on myeloid cells, thereby aiding in evasion from myeloid cell surveillance, remains unclear.
Methods
Primary CD4+ T cells were infected with HIV strains (HIVTYBE or HIVDH12), with or without T cell activation. The expression of various Siglec ligands was analyzed using recombinant Siglec-3, -7, -9, and -10 chimeras. HIV-mediated alterations in glycosylation-associated gene expression were assessed via RNA-sequencing. The HIV-specific antibody 10-1074, conjugated with sialidase (Sia), was employed to disrupt the sialic acid-Siglec interaction specifically on HIV-infected cells. Monocyte- and neutrophil-mediated cytotoxicity against HIV-infected cell lines and autologous primary CD4+ T cells was measured using luciferase assays and p24 staining in the presence of either 10-1074 or 10-1074-Sia.
Results
HIV-infected CD4+ T cells exhibited increased expression of Siglec-3, -7, and -9 ligands, but not Siglec-10 ligands, regardless of activation status. This increase was abolished by the glycosylation inhibitor BADG (Fig. 1A; p<0.0001). Transcriptomic analysis showed that HIV infection induced the expression of several glycan-related genes involved in sialoglycan production, including GALNT6 (FDR<0.01), NANP (sialic acid biosynthesis; p<0.05), and ST8SIA4 (sialyltransferase; p<0.05). In vitro, removal of sialic acid from HIV-infected cell lines using 10-1074-Sia significantly increased the cytotoxic activity of monocytes and neutrophils by 6-fold and 19-fold, respectively (p<0.02). Ex vivo, 10-1074-Sia significantly enhanced monocyte cytotoxicity against autologous primary HIV-infected CD4+ T cells compared to 10-1074 (q=0.004) (Fig. 1B).
Conclusions
We have identified a novel, targetable glyco-immune mechanism through which HIV-infected cells may evade myeloid cell-mediated cytotoxicity by upregulating the expression of specific Siglec ligands. Targeting this interaction presents a promising opportunity for developing innovative immunotherapeutic strategies to eliminate HIV-infected cells.