P-selectin glycoprotein ligand-1 as a potential target for humoral immunotherapy of multiple myeloma.

Monoclonal antibodies (mAbs), successfully adopted in the treatment of several haematological malignancies, have proved almost ineffective in multiple myeloma (MM), because of the lack of an appropriate antigen for targeting and killing MM cells. Here, we demonstrate that PSGL1, the major ligand of P-Selectin, a marker of plasmacytic differentiation expressed at high levels on normal and neoplastic plasma cells, may represent a novel target for mAb-mediated MM immunotherapy. The primary effectors of mAb-induced cell-death, complement-mediated lysis (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC), were investigated using U266B1 and LP1 cell-lines as models. Along with immunological mechanisms, the induction of apoptosis by PSGL1 cross-linking was assessed. The anti-PSGL1 murine mAb KPL1 induced death of MM cells in a dose- and time-dependent fashion and mediated a significant amount of ADCC. KPL1 alone mediated C1q deposition on target cells but proved unable to induce CDC due to inhibition of the lytic activity of complement by membrane complement regulators (mCRP) expressed on the cell surface. Consistently, CDC was induced by KPL1 upon mCRP blockage. Our results suggest a role for PSGL1 in MM humoral immunotherapy and support further in vivo studies assessing the effects of anti-PSGL1 mAbs on MM growth and interaction with the bone marrow microenvironment.

Isolation and characterization of two cDNA clones coding for isoforms of the Parietaria judaica major allergen Par j 1.0101.

Two cDNA clones named P9* and P1* of 794 and 631 bp, respectively, were isolated from a lambda ZAP cDNA expression library using Parietaria judaica (Pj) pollen-specific IgE antibodies from a pool of sera (n = 23) of patients allergic to Pj. Sequence analysis showed open reading frames of 176 and 138 amino acids. Both clones contain a putative signal peptide giving two mature processed proteins named Par j 1.0102 of 14,726 D and Par j 1.0201 of 10,677 D. These proteins represent isoallergenic forms of the major Pj allergen Par j 1.0101 (clone P5) previously reported. The Par j 1.0102 shared 98% amino acid sequence homology with the P5, while the Par j 1.0201 shared 89% homology. Since P1, P5 and P9 clones were expressed in Escherichia coli, and since the three allergenic proteins shared a very high degree of sequence identity and comparable binding to the Pj-specific IgE, we decided to analyze in more detail the immunological properties of only one allergen, the recombinant Par j 1.0101. The allergenic activity determined by the histamine release assay ranged between 9 and 56%, depending on the allergic patient analyzed, while it blocked approximately 40% of all the Pj-specific IgE antibodies, as detected after ELISA and cross-absorption analysis.