MIP-1alpha and MIP-1beta differentially mediate mucosal and systemic adaptive immunity

Macrophage inflammatory protein-1alpha (MIP-1alpha) and MIP-1beta are distinct but highly homologous CC chemokines produced by a variety of host cells in response to various external stimuli and share affinity for CCR5. To better elucidate the role of these CC chemokines in adaptive immunity, we have characterized the affects of MIP-1alpha and MIP-1beta on cellular and humoral immune responses. MIP-1alpha stimulated strong antigen (Ag)-specific serum immunoglobulin G (IgG) and IgM responses, while MIP-1beta promoted lower IgG and IgM but higher serum IgA and IgE antibody (Ab) responses. MIP-1alpha elevated Ag-specific IgG1 and IgG2b followed by IgG2a and IgG3 subclass responses, while MIP-1beta only stimulated IgG1 and IgG2b subclasses. Correspondingly, MIP-1beta produced higher titers of Ag-specific mucosal secretory IgA Ab levels when compared with MIP-1alpha. Splenic T cells from MIP-1alpha- or MIP-1beta-treated mice displayed higher Ag-specific Th1 (interferon-gamma [IFN-gamma]) as well as selective Th2 (interleukin-5 [IL-5] and IL-6) cytokine responses than did T cells from control groups. Interestingly, mucosally derived T cells from MIP-1beta-treated mice displayed higher levels of IL-4 and IL-6 compared with MIP-1alpha-treated mice. However, MIP-1alpha effectively enhanced Ag-specific cell-mediated immune responses. In correlation with their selective effects on humoral and cellular immune responses, these chemokines also differentially attract CD4(+) versus CD8(+) T cells and modulate CD40, CD80, and CD86 expressed by B220(+) cells as well as CD28, 4-1BB, and gp39 expression by CD4(+) and CD8(+) T cells in a dose-dependent fashion. Taken together, these studies suggest that these CC chemokines differentially enhance mucosal and serum humoral as well as cellular immune responses.     

High-affinity memory B cells induced by conjugate vaccines against weak tumor antigens are vulnerable to nonconjugated antigen

Induction of antibody-mediated immunity against hematologic malignancies requires CD4(+) T-cell help, but weak tumor antigens generally fail to induce adequate T-cell responses, or to overcome tolerance. Conjugate vaccines can harness alternative help to activate responses, but memory B cells may then be exposed to leaking tumor-derived antigen without CD4(+) T-cell support. We showed previously using lymphoma-derived idiotypic antigen that exposure to "helpless" antigen silences the majority of memory IgG(+) B cells. Transfer experiments now indicate that silencing is permanent. In marked contrast to IgG, most coexisting IgM(+) memory B cells exposed to "helpless" antigen survive. Confirmation in a hapten (NP) model allowed measurement of affinity, revealing this, rather than isotype, as the determinant of survival. IgM(+) B cells had Ig variable region gene usage similar to IgG but with fewer somatic mutations. Survival of memory B cells appears variably controlled by affinity for antigen, allowing a minority of low affinity IgG(+), but most IgM(+), memory B cells to escape deletion in the absence of T-cell help. The latter remain, but the majority fail to undergo isotype switch. These findings could apply to other tumor antigens and are relevant for vaccination strategies aimed to induce long-term antibody.     

Requirement for CD1d expression by B cells to stimulate NKT cell-enhanced antibody production

Activation of natural killer-like T (NKT) cells with the CD1d ligand alpha-galactosylceramide enhances T-dependent humoral immune responses against coadministered T-dependent Ag. At present, there is little information on the mechanisms involved other than a dependence on CD1d expression by antigen-presenting cells and/or development of the NKT subset. We therefore tested the hypothesis that direct presentation of alpha-GC by B cells was required for NKT-enhanced Ab responses against T-dependent Ag. We reconstituted B cell-deficient microMT mice with B cells from C57Bl/6 donors or CD1d(-/-) donors before immunization with NP-KLH alone or NP-KLH mixed with alpha-GC. We made the surprising observation that B-cell expression of CD1d is absolutely required for the NKT-enhanced Ab response. Our data show that the mechanism by which NKT cells enhance humoral immune responses involves interaction with CD1d-expressing B cells.     

Impaired IgA class switching in APRIL-deficient mice

The tumor necrosis factor (TNF) family member APRIL binds to the receptors BCMA on B cells and TACI on B and T cells. To investigate the role of APRIL in immunity, we generated APRIL-deficient mice. APRIL(-/-) mice have normal T and B lymphocyte development, normal T and B cell proliferation in vitro, but increased numbers of CD44(hi)CD62L(lo) CD4(+) effector/memory T cells and increased IgG responses to T-dependent antigens. Serum IgA levels were significantly decreased, and serum IgA antibody responses to mucosal immunization with TD antigens and to type 1 T-independent antigens were impaired in APRIL(-/-) mice. APRIL by itself induced IgA as well as IgG1 isotype switching in CD40-deficient IgM(+)IgD(+) sorted B cells. These results suggest that APRIL down-regulates T cell-dependent antibody responses and promotes IgA class switching.     

Mechanisms of broad cross-protection provided by influenza virus infection and their application to vaccines

Mice recovered from influenza A virus infection have been shown to be cross-protected against challenge infection with either drift viruses within a subtype (subtype-specific immunity) or different subtype viruses (heterosubtypic immunity). The mechanisms of broad-spectrum of cross-protection could be explained as follows. (i) Pre-existing S-IgA and IgG antibodies (Abs) induced by infection are involved in the elimination of challenge viruses by forming virus-Ig complexes shortly after re-infection. Due to their polymeric nature, the S-IgA Abs, existing more abundant on the mucosa than are IgG Abs, are strongly cross-reactive with challenge viruses, whereas the IgG Abs are weakly cross-reactive with challenge viruses, due to their monomeric nature. The specificity of Abs is directed mainly at hemagglutinin and neuraminidase. (ii) CD8+ memory T cells induced by infection are involved in the elimination of challenge viruses by the accelerated killing of host cells infected with different subtype viruses from day 3 onwards after re-infection. The specificity of memory T cells is directed against viral internal proteins. (iii) The accelerated IgA and IgG Ab responses, produced by B memory cells after a challenge, are also involved in cross-protection from day 4 onwards after re-infection. (iv) In the epithelial cells of infected mice, dimeric IgA that is trafficked through the epithelial cells can contribute to the prevention of viral assembly by binding to newly synthesized viral proteins. Natural infection is well known to be superior to parenteral inactivated vaccines in inducing the broad-spectrum cross-protection. To improve the efficacy of current inactivated vaccines, many trials have been conducted to mimic natural infection, including intranasal or epidermal administration of inactivated vaccine with or without an adjuvant; such studies are still ongoing. In the near future, some of these trials may provide new, safer and more effective broad-spectrum vaccines than those currently available.     

Impaired T- and B-cell development in Tcl1-deficient mice

TCL1, the overexpression of which may result in T-cell leukemia, is normally expressed in early embryonic tissues, the ovary, and lymphoid lineage cells. Our analysis of mouse B-lineage cells indicates that Tcl1 expression is initiated in pro-B cells and persists in splenic marginal zone and follicular B cells. T-lineage Tcl1 expression begins in thymocyte progenitors, continues in CD4(+)CD8(+) thymocytes, and is extinguished in mature T cells. In Tcl1-deficient mice, we found B lymphopoiesis to be compromised at the pre-B cell stage and T-cell lymphopoiesis to be impaired at the CD4(+)CD8(+) thymocyte stage. A corresponding increase was observed in thymocyte susceptibility to anti-CD3epsilon-induced apoptosis. Reduced numbers of splenic follicular and germinal center B cells were accompanied by impaired production of immunoglobulin G1 (IgG1) and IgG2b antibodies in response to a T-dependent antigen. The marginal zone B cells and T-cell-independent antibody responses were also diminished in Tcl1(-/-) mice. This analysis indicates a significant role for Tcl1, a coactivator of Akt signaling, in normal T- and B-cell development and function.     

Dendritic cell based genetic immunization stimulates potent tumor protection dependent on CD8 CTL cells in the absence of autoimmunity

Although antibodies (Abs) produced by B cells can treat cancer in certain models, T cells have been accountable for the major effector to control cancer. Immune recognition toward tyrosinase-related protein-1 (TRP-1), a melanoma associated antigen up-regulated on the surface of B16F10 melanomas, generally leads to tumor protection mediated by Abs. In this study, immunization with dendritic cells ex vivo transduced with adenovirus encoding TRP-1 stimulates immune activation and potent tumor protection mediated by CD8 T cells in the absence of autoimmune consequence. Transfer of CD8 T cells from immunized mice also leads to tumor protection. The immune activation and CD8 T cell mediated tumor protection rely on the CD4 T cell help. Thus DC based genetic immunization targeting TRP-1, an antigen usually causes Ab predominant immune recognition, is capable of stimulating potent tumor protection dependent on CD8 T cells in the absence of autoimmunity.     

Expression and function of inducible costimulator on peripheral blood T cells in patients with systemic lupus erythematosus

OBJECTIVE: To investigate the role of inducible costimulator (ICOS) in the pathogenesis of SLE, we assessed its expression on peripheral blood CD4 and CD8 T cells and functional roles in patients with systemic lupus erythematosus (SLE). METHODS: Expression of ICOS on peripheral blood CD4 and CD8 T cells and ICOS ligand (ICOSL) on peripheral blood CD19 B cells from patients with SLE, patients with rheumatoid arthritis (RA) and healthy volunteers were determined by two-colour flow cytometry. The functional costimulatory effects of ICOS on peripheral blood mononuclear cells (PBMC) were assessed by T-cell proliferative responses, cytokines, anti-double-stranded DNA (anti-dsDNA) antibody and total IgG production. RESULTS: Peripheral blood CD4 and CD8 T cells expressing ICOS were significantly increased in patients with SLE compared with patients with RA and healthy subjects. Peripheral blood CD19 B cells expressing ICOSL in SLE were markedly reduced compared with RA. Proliferative responses of anti-CD3/ICOS costimulation were significantly higher than those of anti-CD3/hamster IgG (HIgG) in healthy subjects, but not in patients with SLE. Anti-CD3/ICOS-stimulated SLE PBMC secreted similar levels of IL-10 and IFN-gamma but a significantly lower level of IL-2 than healthy PBMC. Anti-CD3/ICOS-mediated costimulation significantly enhanced the production of anti-dsDNA antibodies and total IgG in patients with SLE. CONCLUSION: Hyperexpression of ICOS on peripheral blood CD4 and CD8 T cells from patients with SLE contributed to the dysregulated T-cell proliferation, T-cell activation and pathogenic autoantibody production, which showed that the abnormality of ICOS costimulation may play an immunopathological role(s) in the pathogenesis of SLE.     

Oxidative/reductive conjugation of mannan to antigen selects for T1 or T2 immune responses.

The induction of CD8+ cytotoxic T lymphocytes (CTLs) is desirable for immunization against many diseases, and recombinant-synthetic peptide antigens are now favored agents to use. However, a major problem is how to induce CTLs, which requires a T1-type response to such synthetic antigens. We report that T1-type (generating high CTL, low antibody) or T2-type (the reciprocal) responses can be induced by conjugation of the antigen to the carbohydrate polymer mannan: T1 responses are selected by using oxidizing conditions; T2 responses are selected by using reducing conditions for the conjugation. Using human MUC1 as a model antigen in mice, immunization with oxidized mannan-MUC1 fusion protein (ox-M-FP) led to complete tumor protection (challenge up to 5 x 10(7) MUC1+ tumor cells), CTLs, and a high CTL precursor (CTLp) frequency (1/6900), whereas immunization with reduced mannan-MUC1 FP (red-M-FP) led to poor protection after challenge with only 10(6) MUC1+ tumor cells, no CTLs, and a low CTLp frequency (1/87,800). Ox-M-FP selects for a T1 response (mediated here by CD8+ cells) with high interferon gamma (IFN-gamma) secretion, no interleukin 4 (IL-4), and a predominant IgG2a antibody response; red-M-FP selects for a T2-type response with IL-4 production and a high predominant IgG1 antibody response but no IFN-gamma.     

Inducible costimulator is required for type 2 antibody isotype switching but not T helper cell type 2 responses in chronic nematode infection

Inducible costimulator (ICOS) has been suggested to perform an important role in T helper cell type 2 (Th2) responses, germinal center formation, and isotype switching. The role of ICOS in chronic Th2 responses was studied in a nematode model with the filarial parasite, Brugia malayi. Contrary to expectations, we did not observe a significant defect in IL-4-producing Th2 cells in ICOS-/- mice or in eosinophil recruitment. We also found that ICOS was not required for the differentiation of alternatively activated macrophages (AAMPhi) that express Ym1 and Fizz1. Although the production of IgE was slightly reduced in ICOS-/- mice, this was not as significant as in CD28-/- mice. In contrast to live infection, the primary response of ICOS-/- mice immunized with soluble B. malayi antigen and complete Freund's adjuvant resulted in significantly fewer IL-4-producing cells in the lymph nodes. As previously reported, we observed a defect in antibody isotype switching toward the IgG1 isotype in ICOS-/- mice during live infection. Interestingly, there was a significant enhancement of parasite-specific IgG3 isotype antibodies. CD28-/- and MHC class II-/- mice also had enhanced parasite-specific IgG3 isotype antibodies. Our results suggest that ICOS is not required to maintain a chronic cellular Th2 response. The primary role of ICOS in a chronic helminth infection could be to drive antibodies toward type 2 isotypes. T-independent antibody response to the parasite could be enhanced in the absence of costimulation and T cell help.     

T-cell responses to versican in ankylosing spondylitis

The objective of our study was to undertake a systematic analysis of the T-cell response to the proteoglycan versican G1-globular domain (VG1) in ankylosing spondylitis (AS) as immunity to VG1 in mice can induce a pathology closely resembling AS. Peripheral blood lymphocytes from 36 AS patients and 33 healthy controls were incubated with recombinant human VG1 in culture for 6 h. T-cell responses were assessed by FACS analyses using mAb against surface expression of the activation marker CD69 and against the intracellular cytokines interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha. T cells activated by exposure to versican were determined by assessing the percentage of CD4+ or CD8+ T cells that were CD69/cytokine double-positive cells as compared to isotype control staining. In the AS patients, exposure to VG1 resulted in increased expression by CD4+ T cells of IFN-gamma in 55.6% of patients and of TNF-alpha in 52.8% of patients. In the controls, only 36.4% of subjects demonstrated an IFN-gamma response and 36.4% demonstrated a TNF-alpha response (P value 0.148, 0.227, respectively). With respect to CD8+ T-cell responses, versican stimulation enhanced IFN-gamma expression in 44.4% of AS patients and 39.4% of controls, and enhanced TNF-alpha response in 50.0% of AS patients and 39.4% of controls (P value 0.620, 0.327, respectively). Although, there was no statistically significant difference in the magnitude of the IFN-γ or TNF secretion by CD4+ T cells and CD8+ T cells between AS and controls, our results demonstrate an enhanced T-cell response to VG1 in AS.     

Immunization with two recombinant Bacillus Calmette-Guérin vaccines that combine the expression of multiple tandem repeats of mucin-1 and colony stimulating-factor suppress breast tumor growth in mice

Purpose  

Mucin-1 (MUC1) is a breast tumor-associated antigen. However, clinical trials with MUC1 showed that, with respect to its expression levels, MUC1 is a relatively poor immunogen in human beings. Evidence showed that MUC1-specific immunodominant B and T cell epitopes are derived from the variable-number tandem repeat (VNTR) region. Therefore, immunotherapy that targets multiple VNTRs may induce anti-MUC1 immune responses. GM-CSF has been shown to increase the percentage and activity of antigen-presenting cells. In this study, we constructed two recombinant Bacillus Calmette-Guérin (BCG) vaccines that combine the expression of multiple tandem repeats of MUC1 and CSF. The effect of two novel breast cancer vaccines (rBCG-MVNTR4-CSF and rBCG-MVNTR8-CSF) on the growth of breast tumor on hu-PBL-SCID mice was evaluated.     

Impaired peripheral blood T-follicular helper cell function in HIV-infected nonresponders to the 2009 H1N1/09 vaccine

The generation of Ab-secreting plasma cells depends critically on CD4 T-follicular helper (TFH) cells during the germinal center reaction. Germinal center TFH cells share functional properties with circulating CXCR5(+) CD4 T cells, referred to herein as peripheral TFH (pTFH) cells. Because deficient Ab production and CD4 T-cell loss are recognized features of HIV infection, in the present study, we investigated pTFH cells in 25 HIV-infected patients on antiretroviral therapy. pTFH frequency was equivalent in patients and healthy controls (HCs), and these cells displayed a central memory phenotype. Sixteen patients and 8 HCs in this group were given a single dose of H1N1/09 influenza vaccine during the 2009 H1N1 influenza outbreak. In the vaccine responders (n = 8) and HCs, pTFH cells underwent expansion with increased IL-21 and CXCL13 secretion in H1N1-stimulated PBMC culture supernatants at week 4 (T2). These changes were not seen in vaccine nonresponders (n = 8). In coculture experiments, sorted pTFH cells supported HIN1-stimulated IgG production by autologous B cells only in vaccine responders. At T2, frequencies of pTFH were correlated with memory B cells, serum H1N1 Ab titers, and Ag-induced IL-21 secretion. Characterization of pTFH cells may provide additional insight into cellular determinants of vaccine-induced Ab response, which may have relevance for vaccine design.     

High levels of antibodies to the CD4 binding domain of human immunodeficiency virus type 1 glycoprotein 120 are associated with faster disease progression

Human monoclonal antibodies (Abs) to the CD4 binding domain of human immunodeficiency virus (HIV) type 1 glycoprotein (gp) 120 (gp120(CD4bd)) inhibit gp120 presentation to gp120-specific T helper (Th) cells. Since Th responses are critical to control HIV, anti-gp120(CD4bd) Abs could be involved in HIV pathogenesis. Therefore, anti-gp120(CD4bd) Ab levels were compared in serum samples from matched pairs of HIV-positive rapid progressors (RPs) and slow progressors (SPs). Many RPs had higher levels of anti-gp120(CD4bd) Abs than their corresponding SPs. However, Ab levels to whole gp120 and to its C5 domain were similar. Hence, the higher levels of anti-gp120(CD4bd) Abs detected in the serum of RPs do not reflect generalized increases in Ab levels to whole gp120. Moreover, anti-gp120(CD4bd) Ab levels correlated with the amount of inhibition of gp120-specific Th proliferation in the presence of respective serum immunoglobulin G. These findings document a novel mechanism of HIV pathogenesis mediated by anti-gp120(CD4bd) Abs exhibiting suppressive activity on gp120 presentation.     

The persistent elimination of B cells responding to blood group A carbohydrates by synthetic group A carbohydrates and B-1 cell differentiation blockade: novel concept in preventing antibody-mediated rejection in ABO-incompatible transplantation

We demonstrated a novel strategy for specific and persistent inhibition of antibody (Ab) production against blood group A or B carbohydrate determinants necessary for successful ABO-incompatible transplantation. Similar to human blood group O or B individuals, mice have naturally occurring Abs against human blood group A carbohydrates in their sera. B cells with receptors for A carbohydrates in mice belonging to the CD5(+)CD11b(+)B-1a subset have phenotypic properties similar to those of human B cells. These cells could be temporarily eliminated by injecting synthetic A carbohydrates (GalNAcalpha1-3, Fucalpha1-2Gal) conjugated to bovine serum albumin (A-BSA) and anti-BSA Abs. In mice that received the injection of A-BSA/anti-BSA Abs, the serum levels of anti-A IgM were reduced, but immunization with human A erythrocytes resulted in increased serum levels of anti-A Abs. When combined with cyclosporin A (CsA) treatment, which blocks B-1a cell differentiation, and treatment with A-BSA/anti-BSA Abs, the serum levels of anti-A Abs were persistently undetectable in the mice even after the immunization. B cells with receptors for A carbohydrates were markedly reduced in these mice. These results are consistent with the hypotheses that treatment with A-BSA/anti-BSA Abs temporarily depletes B cells responding to A determinants, and CsA treatment prevents the replenishment of these cells.     

Different costimulation signals used by CD4(+) and CD8(+) cells that independently initiate rejection of allogenic hepatocytes in mice

The current study evaluated the role of CD40/CD40 ligand (CD40L) and CD28/B7 costimulation signals during alloimmune responses independently mediated by CD4(+) or CD8(+) T cells. Allogeneic hepatocytes were transplanted into CD8 or CD4 knock out (KO) mice under cover of costimulatory blockade. Rejection of FVB/N (H-2(q)) hepatocytes occurred by day 10 posttransplant in untreated CD8 or CD4 KO (H-2(b)) mice. Treatment of CD8 or CD4 KO mice with anti-CD40L monoclonal antibody (mAb; MR1) resulted in significant prolongation of hepatocyte survival indicating that CD40/CD40L interactions were critical in both CD4(+) and CD8(+) T-cell initiated hepatocyte rejection. Anti-CD40L mAb also prolonged hepatocyte survival in B-cell KO (H-2(b)) mice, indicating that the efficacy of CD40/CD40L blockade in preventing hepatocyte rejection was B-cell (and antibody) independent. In contrast, treatment with CTLA4 fusion protein (CTLA4Ig), prolonged hepatocyte survival in CD8 KO but not CD4 KO mice, showing that CD28/B7 interactions were important in CD4(+) but not CD8(+) T-cell initiated hepatocyte rejection. Under selected circumstances, such as in CD40 KO mice, both CD4(+) and CD8(+) T cells mediate hepatocyte rejection in the absence of CD40/CD40L costimulation and without a significant contribution from CD28/B7 costimulation signals. These results highlight the disparate roles of CD40/CD40L and CD28/B7 costimulation signals in CD4(+) versus CD8(+) T-cell mediated immune responses to allogeneic hepatocytes. The CD4(+) T-cell independent, CD40L-sensitive, CD28/B7-independent pathway of CD8(+) T-cell activation in response to transplantation antigens is novel.     

Inverse association between IgG-anti-kappa and antierythrocyte autoantibodies in patients with cold agglutination

It has been known for a long time that IgG-anti-F(ab')(2) antibodies (Abs) are able to suppress the B-cell response. We showed that natural IgG-anti-F(ab')(2) autoantibodies appear in the serum of patients with cold agglutination. If the anti-F(ab')2 Ab suppresses cold agglutinin (CA)-producing B cells, one would expect an inverse correlation between the titers of these two Abs. Our study confirmed this correlation. Subsequent experiments showed that some anti-F(ab')(2) Abs bind to the hinge region of IgG. It was difficult to explain how this Ab suppresses CA-producing B cells, which are of IgM isotype. Here we show that patients with cold agglutination have an IgG-anti-kappa light chain autoantibody in their serum. This is another member of the anti-F(ab')(2) Ab group. Because the vast majority of CAs are IgM-kappa Abs, the anti-kappa Ab might suppress CA-producing B cells. If this is the case, there should be an inverse association between the titer of anti-kappa Ab and CA. In a group of 302 patients, we found that high titers of the anti-kappa Ab correlate with low titers of CA and vice versa (P =.009). Interestingly, this association is found only in patients whose disease is caused by noninfectious agents, including mainly B-cell proliferations (P =.0058). Our data show that the inverse correlation is not confined to a particular CA autoantibody specificity. The results are discussed in the light of recent findings showing that anti-IgM Abs may either inactivate or kill tumoral B cells by apoptosis.     

The CD19 signal transduction molecule is a response regulator of B-lymphocyte differentiation.

The phenotypes of CD19-deficient (CD19-/-) mice, and human CD19-transgenic (hCD19TG) mice that overexpress CD19 indicate that CD19 is a response regulator of B-lymphocyte surface receptor signaling. To further characterize the function of CD19 during B-cell differentiation, humoral immune responses to a T-cell-independent type 1 [trinitrophenyl-lipopolysaccharide (TNP-LPS)], a T-cell-independent type 2 [dinitrophenyl (DNP)-Ficoll], and a T-cell-dependent [DNP-keyhole limpet hemocyanin (KLH)] antigen were assessed in CD19-/- and hCD19TG mice. B cells from CD19-/- mice differentiated and underwent immunoglobulin isotype switching in vitro in response to mitogens and cytokines. In vivo, CD19-/- mice generated humoral responses to TNP-LPS and DNP-KLH that were dramatically lower than those of wild-type littermates. Surprisingly, the humoral response to DNP-Ficoll was significantly greater in CD19-/- mice. In contrast, hCD19TG mice were hyperresponsive to TNP-LPS and DNP-KLH immunization but were hyporesponsive to DNP-Ficoll. These results demonstrate that CD19 is not required for B-cell differentiation and isotype switching but serves as a response regulator which modulates B-cell differentiation. Since humoral responses to both T-cell-dependent and T-cell-independent antigens were similarly affected by alterations in CD19 expression, these differences are most likely to result from intrinsic changes in B-cell function rather than from the selective disruption of B-cell interactions with T cells.     

Anti-CD19 inhibits the growth of human B-cell tumor lines in vitro and of Daudi cells in SCID mice by inducing cell cycle arrest

In this report, we extend our previous findings that IgG or F(ab')2 fragments of HD37 anti-CD19 antibody (Ab) in combination with the immunotoxin (IT), RFB4-anti-CD22-deglycosylated ricin A chain (dgA) (but neither reagent alone), prolonged the survival of SCID mice with disseminated human Daudi lymphoma (SCID/Daudi mice) to 1 year at which time they still remained tumor-free. We explored the mechanisms by which the HD37 Ab exerts antitumor activity in vivo by studying its activity in vitro. We found that it has antiproliferative activity (IC50 = 5.2 - 9.8 x 10(-7) mol/L) on three CD19+ Burkitt's lymphoma cell lines (Daudi, Raji, and Namalwa) but not on a weakly CD19-positive (CD19lo) pre-B cell tumor (Nalm-6). The inhibitory effect was manifested by cell cycle arrest, but not apoptosis. Results using three additional anti-CD19 Abs, suggest that the affinity of the antibody and possibly the epitope which it recognizes may effect its capacity to transmit a signal that induces cell cycle arrest. Hence, therapeutically useful Abs may exert anti-tumor activity by a variety of mechanisms, each of which should be evaluated before undertaking clinical trials in humans.