Normal and malignant lymphocyte migration: Glycosyltransferases and integrins in lymphocyte homing and CXCR4 inhibition of multiple myeloma

Naive lymphocyte trafficking to peripheral lymph nodes (PLNs) requires the interaction between L-selectin expressed on lymphocytes and L-selectin ligands expressed in post-capillary high endothelial venules (HEVs) in PLNs. These L-selectin ligands are collectively referred to as peripheral node addressin (PNAd), and are highly sulfated, sialylated and fucosylated O-glycan decorated sialomucins. Here, we examined mice deficient in enzymes responsible for carbohydrate modification of L-selectin ligands. Specifically we studied core1extension beta1,3-N-acetylglucosaminyltransferase (C1GlcNAcT), core2-GlcNAcT-1 (C2GlcNAcT-1), N-acetylglucosaminyl-6-sulfotransferase-1 (GlcNAc6ST-1) and HEC-GlcNAc6ST deficient mice. In knockout mice, T and B cell trafficking was compromised compared to wild-type (WT) mice, however, B cell trafficking was more impaired than T cell. Using intravital microscopy (IVM) we observed that in C1GlcNAcT-/- and C2GlcNAcT-1 -/- mice, B cell, but not T cell rolling fraction was impaired. In contrast, in GlcNAc6ST-1 and HEC-GlcNAc6ST deficient mice, there was little change in the rolling fraction of either T or B cells. In all four knockout mice, we observed a significant decrease in the ability of T and B cells to arrest in PLN HEVs, which resulted from an increased velocity of rolling cells, as rolling velocity is a critical determinant of lymphocyte arrest in HEVs. A mechanism for the difference in T and B cell trafficking in knockout mice was identified in the 50% lower expression of L-selectin on B cells compared to T cells. The MECA-79 antigen was completely absent in C1GlcNAcT-/- mice, while in GlcNAc6ST-1 -/- mice, MECA-79 was only lost on the abluminal HEV surface and in HEC-GlcNAc6ST-/- mice MECA-79 could not be detected on the luminal HEV surface, but was still expressed abluminally. We further demonstrated that immobilized chemokine activation of LFA-1 on lymphocytes rolling in PLN HEVs occurs rapidly with no gradual deceleration of the rolling cell. In addition to the contribution of chemokine receptor signaling, we discovered that the sphingosine-1-phosphate-1 receptor (SIP 1) is also responsible for mediating rolling lymphocyte arrest in HEVs.; In a separate study we demonstrated that inhibition of CXCR4 signaling could prevent development of multiple myeloma (MM) in mice. Although blockade of CXCR4 did not impair MM cell trafficking to the bone marrow (BM), the survival and/or retention of cells in the BM was severely impaired. This inhibition increased the survival of mice injected with MM cells, suggesting that CXCR4 inhibition may be a useful therapy for human MM.