Multiple myeloma (MM) cells inhibit certain T-cell functions. We examined the expression of B7-H1 (PD-L1), a B7-related protein that inhibits T-cell responses, in CD138- IntroductionIn addition to the cytogenic and molecular abnormalities reportedly associated with malignant transformation of plasma cells, interactions between multiple myeloma (MM) cells and the bone marrow microenvironment are crucial for plasma cell survival and proliferation. [1][2][3] Several factors that mediate MM cell cross-talk with mesenchymalderived cells, such as vascular endothelial growth factor, an angiogenic factor, have been previously described; however, there is growing evidence that MM cells also interact with immune cells. Plasma cells interact with T cells via the RANK/RANK-L system. 4 A recent study demonstrated that the survival and growth of malignant plasma cells was supported by bone marrow dendritic cells via RANK/RANK-L and BAFF-APRIL. 5 There is also evidence that malignant plasma cells can be targeted for an immune response. Several tumor antigens are expressed by plasma cells isolated from MM and monoclonal gammopathy of undetermined significance (MGUS) patients, and allogenic bone marrow transplantation can induce a graft-versus-myeloma effect. [6][7][8] However, MM is also associated with immune dysfunction. Defects in T-cell responses to mitogenic and TCR-mediated stimulation have been reported. [9][10][11] Interestingly, regulatory T cell (T reg cell) populations are significantly modified in both MGUS and MM patients, suggesting that immune dysfunction is an early event in the malignant transformation process of plasma cells. 12,13 However, the factors produced by plasma cells that create these immune defects are poorly defined.A possible candidate responsible for such T-cell inhibitory mechanisms in MM plasma cells is B7-H1. B7-H1 (also known as PD-L1 or CD274) is a B7 family member and is the ligand for PD-1 (programmed death-1), a member of the CD28 family. 14 B7-H1 is broadly distributed in various tissues and cell types and is often expressed after exposure to inflammatory cytokines, especially IFN-␥. B7-H1 interacts with PD-1 and another as yet unknown receptor on T cells and can inhibit T cell activation and cytotoxic T lymphocytes (CTL)-mediated lysis. [15][16][17][18] B7-H1 can also increase T-cell activation. [19][20][21] Marked expression of B7-H1 has been reported for various human carcinomas and in mouse models expression of B7-H1 enhances tumor growth and allows dormant tumor cells to escape from CTLs. 16,[22][23][24][25][26][27][28][29] Blocking B7-H1 enhances the effects of cancer vaccines. [30][31][32][33][34] Toll-like receptor (TLR) stimulation can also induce B7-H1 expression in mouse tumor cells. 35 Thus, B7-H1 overexpression appears as a possible mechanism for tumors to avoid the host's immune response.Little is known regarding the expression of B7-H1 in B-lineage lymphocytes. We show here that B7-H1 is expressed by malignant plasma cells from most MM patients but not from MGUS patients. ...

The balance between immune effector cells and immunosuppressive cells and how this regulates the tumor microenvironment has been well described. A significant contribution of immune regulatory cells, including regulatory T cells, to tumor progression has been widely reported. An emerging body of evidence has recently recognized a role for B cells in modulating the immune response to tumors and lymphoid malignancies. Regulatory B cells (Bregs) are a newly designated subset of B cells that have been shown to play a pivotal role in regulating immune responses involved in inflammation, autoimmunity and, more recently, cancer. Bregs can suppress diverse cell subtypes, including T cells, through the secretion of anti-inflammatory mediators, such as IL-10, and can facilitate the conversion of T cells to regulatory T cells, thus attenuating anti-tumor immune responses. Similar B-cell subpopulations have been reported to be recruited to the tumor but to acquire their immunosuppressive properties within the tumor bed and thereby attenuate anti-tumor immune responses. However, despite a pivotal role for Bregs in promoting inflammation and carcinogenesis, the phenotypic diversity of the cell surface markers that are unique to Bregs remains unclear in mice and humans. In this review, we summarize the characteristics of Bregs and review our current knowledge of Bregs and their inhibition of anti-tumor immune responses in murine tumor models and cancer patients.

Key Points T cells genetically targeted to the tumor-promoting antigen CD44v6 are effective against AML and MM. CD44v6-targeted T cells do not recognize hematopoietic stem cells and keratinocytes but cause reversible monocytopenia.

In tumor dormancy, tumor cells persist in the host over a long period of time but do not grow. We investigated in the DA1-3b mouse model of acute myeloid leukemia how leukemic cells could persist for months in spite of an effective antileukemic immune response. Mice were immunized with irradiated interleukin 12 (IL12)-or CD154-transduced DA1-3b cells, challenged with wild-type DA1-3b cells, and randomly killed during 1-year follow-up. Quantification of residual disease 1 year after challenge showed that persistent leukemic cells represented less than 0.02% of spleen cells in most animals. These residual cells were still able to kill naive hosts, even when isolated after 1 year of persistence. Persistent leukemic cells were more resistant to specific cytotoxic Tcell (CTL)-mediated killing and had en-

SummaryUmbilical cord blood transplant (UCBT) is associated with impaired early immune reconstitution. This might be explained by a lower T‐cell dose infused, the naivety of cord blood T‐cells and the use of in vivo T‐cell depletion. We studied the pattern of early immune reconstitution and the clinical outcome of children undergoing unrelated UCBT when in vivo T‐cell depletion was omitted. Thirty children affected by malignancies (46%) or immunodeficiencies (54%) underwent an unrelated UCBT. Prospective assessment of immune reconstitution and clinical outcome was performed. We observed an unprecedented CD4+ T‐cell reconstitution, with a median cell count at 30 and 60 d post UCBT of 0·3 × 109/l and 0·56 × 109/l, respectively. Early T‐cell expansion was thymic‐independent, with a rapid shift from naïve to central memory phenotype and early regulatory T‐cell recovery. Viral infections were frequent (63%) but resolved rapidly in most cases and virus‐specific T‐lymphocytes were detected within 2 months post‐UCBT. Acute graft‐versus‐host disease (GvHD) was frequent (grade II = 34%, grade III–IV = 16%) but steroid responsive, and the incidence of chronic GvHD was low (14%). The omission of in vivo T‐cell depletion promotes a unique thymic‐independent CD4+ T‐cell reconstitution after unrelated UCBT in children. We postulate that this relates to the specific immunological and ontological qualities of fetal‐derived lymphocytes.

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Improper activation of the immune system contributes to a variety of clinical conditions, including autoimmune and allergic diseases as well as solid organ and bone marrow transplantation. One approach to counteract this activation is through adoptive therapy with regulatory T cells (Tregs). Efforts to manufacture these cells have led to good maunfacturing practice-compliant protocols, and Treg products are entering early clinical trials. Here, we report the stance of the European Union Cooperation in Science and Technology Action BM1305, "Action to Focus and Accelerate Cell-based Tolerance-inducing Therapies-A FACTT," which identifies hurdles hindering Treg clinical applications in Europe and provides possible solutions.

Natural killer (NK) cells are lymphocytes of the innate immune system able to kill different targets such as cancer cells and virally infected cells without prior activation making then attractive candidates for cancer immunotherapy. Umbilical cord blood (UCB) has become a source of hematopoietic stem cells for transplantation but as we gain a better understanding of the characteristics of each immune cell that UCB contains, we will also be able to develop new cell therapies for cancer. In this review, we present what is currently known of the phenotype and functions of UCB NK cells and how these cells could be used in the future for cancer immunotherapy.