Keulen, Virginia P. Van

Summary A patient with Waldenstrom’s macroglobulinaemia expresses a high titre IgM antibody in serum that binds both mouse and human dendritic cells (DC) in a B7-DC (PD-L2)-dependent manner. We have reported previously that purified antibody from patient serum activates immature and mature DC in vitro, enhancing the ability of these professional antigen-presenting cells to activate naive T cells, take up antigen, resist a cytokine-depleted environment and secrete immunomodulatory cytokines, such as interkeukin (IL)-6 and tumour necrosis factor (TNF)-α. Systemic treatment of experimental animals with this antibody induces potent anti-melanoma immunity and modulates protectively the recall response against antigen challenge through the airway in an experimental model of inflammatory airway disease. Here we describe a monoclonal IgM antibody derived from this serum immunoglobulin that recapitulates each of these earlier observations, providing direct evidence that M protein from the Waldenstrom’s patient mediates these potent immunomodulatory effects. Furthermore, cell lines expressing this recombinant form of the human antibody provide the basis for developing this reagent for clinical application.

Abstract A naturally occurring human antibody potentiates dendritic cell function on cross-linking B7-DC (PD-L2), supporting robust T-cell responses in vitro. Moreover, treatment of dendritic cells with B7-DC cross-linking antibody resulted in secretion of interleukin-12, suggesting a TH1 polarization of this response. Here we show an in vivo immunotherapeutic effect of this B7-DC cross-linking antibody using a poorly immunogenic B16 melanoma tumor model. Treatment of mice systemically with antibody at the time of tumor cell engraftment prevented tumor growth in a CD4 and CD8 T-cell-dependent manner. The protective effect of B7-DC cross-linking antibody treatment was independent of endogenous antibody responses. Tumor-specific CTL precursors could be isolated from lymph nodes draining the tumor site in animals treated with B7-DC cross-linking antibody, but not from those treated with isotype control antibodies. The elicited antitumor responses in vivo were specific and long-lasting. More strikingly, treatment of mice with B7-DC cross-linking antibody after the tumors were established in the lungs resulted in protection in a CD8-, perforin-, and granzyme B-dependent fashion. Depletion of natural killer cells did not block the effects of treatment with B7-DC cross-linking antibody. Together, these findings demonstrate that cross-linking B7-DC with the human IgM antibody sHIgM12 can induce a protective immune response against a weakly antigenic experimental tumor and therefore has potential as a novel immunotherapeutic approach for treating cancer.

ABSTRACT Certain human sera from patients with monoclonal gammopathies contain factors that induce myelin repair in animals with demyelinating disease. We hypothesize that antibodies functionally distinguish the serum of one patient from another. However, pooled normal polyclonal human IgM antibodies also induce remyelination. Definitive proof that specific antibodies are the biologically active components of serum is missing because unquestionably pure preparations of antibody molecules cannot be generated by fractionation. To demonstrate definitively that antibody is the biologically active component of patient serum, recombinant antibody was generated for evaluation in bioassays. The induction of remyelination in vivo requires milligram quantities of antibody. Consequently, an expression system was engineered to express high‐titer, recombinant human IgM antibodies in vitro. A resulting recombinant antibody (rHIgM22) was evaluated for its ability to induce remyelination in the Theiler's virus mouse model of chronic‐progressive demyelinating disease. We demonstrate that a single recombinant monoclonal antibody recapitulates the key characteristics of patient serum, including binding specificity, the induction of calcium signals in oligodendrocytes in vitro, and the induction of myelin repair within demyelinated plaques in vivo. The rHIgM22 antibody provides a new venue for the analysis of mechanisms governing remyelination and may prove useful in the treatment of demyelinating diseases.