B cell reductive therapy with rituximab in the treatment of rheumatoid arthritis

The approach to treating autoimmune disorders is currently undergoing a significant change in focus. As therapies are developed that are more precise in targeting the pathogenesis for these diseases, patients experience significantly fewer side effects. At the same time, as more precise therapies are discovered, the etiologies of these diseases become further elucidated. It is now widely accepted that B-lymphocytes play a significant role in the pathogenesis of various autoimmune diseases, the extent of which continues to be the focus of ongoing research. Rheumatoid arthritis is one such disease process that has been the focus of various B-lymphocyte-directed therapeutic trials. In this paper we review the current research available on rituximab as treatment for rheumatoid arthritis. This review details results from four main studies, as well as others, which used rituximab in at least one of the arms in treatment of rheumatoid arthritis. The results are promising and will likely lead to longer term studies as well as a potential focus on B cell subsets.

Development and characterization of CD22-targeted pegylated-liposomal doxorubicin (IL-PLD)

Non-Hodgkin’s lymphoma (NHL) is the sixth most common cause of cancer deaths in the U.S. Most NHLs initially respond well to chemotherapy, but relapse is common and treatment is often limited due to the toxicity of chemotherapeutic agents. Pegylated-liposomal doxorubicin (PLD, Ben Venue Laboratories, Inc), a produces less myelotoxicity than non-liposomal (NL) doxorubicin. To further enhance efficacy and NHL targeting and to decrease toxicity, we conjugated an anti-CD22 monoclonal antibody (HB22.7) to the surface of PLD, thereby creating CD22-targeted immunoliposomal PLD (IL-PLD). HB22.7 was successfully conjugated to PLD and the resulting IL-PLD exhibits specific binding to CD22-expressing cells as assessed by immunofluorescence staining. IL-PLD exhibits more cytotoxicity than PLD in CD22 positive cell lines but does not increase killing of CD22 negative cells. The IC₅₀ of IL-PLD is 3.1 to 5.4 times lower than that of PLD in CD22+ cell lines while the IC₅₀ of IL-PLD is equal to that of PLD in CD22- cells. Furthermore, IL-PLD remained bound to the CD22+ cells after washing and continued to exert cytotoxic effects, while PLD and NL- doxorubicin could easily be washed from these cells.

Lenalidomide oral monotherapy produces a high response rate in patients with relapsed or refractory mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive non-Hodgkin lymphoma with a poor prognosis following first relapse. We present a subgroup analysis of an open-label phase II trial investigating the efficacy and safety of lenalidomide in patients with relapsed or refractory MCL. Oral lenalidomide 25 mg was self-administered once daily on days 1-21 every 28 d for up to 52 weeks, according to tolerability or until disease progression. The primary endpoint was overall response rate (ORR) and secondary endpoints were duration of response, progression-free survival (PFS) and safety. Among 15 patients with MCL with a median disease duration of 5.1 years and a median of four prior treatments, the ORR was 53%. Three patients (20%) had a complete response and 5 (33%) had a partial response. The median duration of response was 13.7 months and median PFS was 5.6 months. Four of five patients who relapsed after transplantation and two of five patients who previously received bortezomib responded to lenalidomide. The most common grade 4 adverse event was thrombocytopenia (13%) and the most common grade 3 adverse events were neutropenia (40%), leucopenia (27%) and thrombocytopenia (20%). In conclusion, oral lenalidomide monotherapy is well tolerated and active in relapsed or refractory MCL.

Imaging and pharmacokinetics of (64)Cu-DOTA-HB22.7 administered by intravenous, intraperitoneal, or subcutaneous injection to mice bearing non-Hodgkin's lymphoma xenografts

PURPOSE

The aim of the study is to compare the tumor-specific targeting, pharmacokinetics, and biodistribution of (64)Cu-DOTA-HB22.7 when administered to xenograft-bearing mice intravenously (IV), intraperitoneally (IP), and subcutaneously (SQ).

PROCEDURES

Mice bearing human non-Hodgkin's lymphoma (NHL) xenografts were injected IV, IP, or SQ with (64)Cu-DOTA-HB22.7. Xenograft targeting was evaluated by micro positron emission tomography (microPET) and confirmed by organ biodistribution studies. Blood measurements of (64)Cu were performed to determine the pharmacokinetics and clearance of (64)Cu-DOTA-HB22.7.

RESULTS

(64)Cu-DOTA-HB22.7 demonstrated equivalent tumor targeting within 24-48 h, regardless of the route of administration. Organ biodistribution confirmed tumor-specific targeting. Blood pharmacokinetics demonstrated that (64)Cu-DOTA-HB22.7 accessed the bloodstream after IP and SQ administration to a similar degree as IV administration, albeit at a slower rate.

CONCLUSIONS

These findings establish (64)Cu-DOTA-HB22.7 as a potential radioimmunotherapeutic and/or NHL-specific imaging agent. These findings provide evidence that IP and SQ administration can achieve results equivalent to IV administration and may lead to more efficient, reproducible treatment plans for antibody-based therapeutics.

Lenalidomide monotherapy in relapsed or refractory aggressive non-Hodgkin's lymphoma

PURPOSE

The major cause of death in aggressive lymphoma is relapse or nonresponse to initial therapy. Lenalidomide has activity in a variety of hematologic malignancies, including non-Hodgkin's lymphoma (NHL). We report the results of a phase II, single-arm, multicenter trial evaluating the safety and efficacy of lenalidomide oral monotherapy in patients with relapsed or refractory aggressive NHL.

PATIENTS AND METHODS

Patients were treated with oral lenalidomide 25 mg once daily on days 1 to 21, every 28 days, for 52 weeks, until disease progression or intolerance. The primary end point was response; secondary end points included duration of response, progression-free survival (PFS), and safety.

RESULTS

Forty-nine patients with a median age of 65 years received lenalidomide in this study. The most common histology was diffuse large B-cell lymphoma (53%), and patients had received a median of four prior treatment regimens for NHL. An objective response rate of 35% was observed in 49 treated patients, including a 12% rate of complete response/unconfirmed complete response. Responses were observed in each aggressive histologic subtype tested (diffuse large B-cell, follicular center grade 3, mantle cell, and transformed lymphomas). Of patients with stable disease or partial response at first assessment, 25% improved with continued treatment. Estimated median duration of response was 6.2 months, and median PFS was 4.0 months. The most common grade 4 adverse events were neutropenia (8.2%) and thrombocytopenia (8.2%); the most common grade 3 adverse events were neutropenia (24.5%), leukopenia (14.3%), and thrombocytopenia (12.2%).

CONCLUSION

Oral lenalidomide monotherapy is active in relapsed or refractory aggressive NHL, with manageable side effects.

Multiple myeloma: epidemiology and therapeutic options

Myeloma remains an incurable disease, but its management has significantly improved with the introduction of novel treatment agents. Variations in both disease manifestation and patient response to treatment have personalized approaches to care.

High-dose radioimmunotherapy combined with fixed, low-dose paclitaxel in metastatic prostate and breast cancer by using a MUC-1 monoclonal antibody, m170, linked to indium-111/yttrium-90 via a cathepsin cleavable linker with cyclosporine to prevent human anti-mouse antibody

PURPOSE

Although radioimmunotherapy alone is effective in lymphoma, its application to solid tumors will likely require a combined modality approach. In these phase I studies, paclitaxel was combined with radioimmunotherapy in patients with metastatic hormone-refractory prostate cancer or advanced breast cancer.

EXPERIMENTAL DESIGN

Patients were imaged with indium-111 (111In)-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-peptide-m170. One week later, yttrium-90 (90Y)-m170 was infused (12 mCi/m2 for prostate cancer and 22 mCi/m2 for breast cancer). Initial cohorts received radioimmunotherapy alone. Subsequent cohorts received radioimmunotherapy followed 48 hours later by paclitaxel (75 mg/m2). Cyclosporine was given to prevent development of human anti-mouse antibody.

RESULTS

Bone and soft tissue metastases were targeted by 111In-m170 in 15 of the 16 patients imaged. Three prostate cancer patients treated with radioimmunotherapy alone had no grade 3 or 4 toxicity. With radioimmunotherapy and paclitaxel, two of three prostate cancer patients developed transient grade 4 neutropenia. Four breast cancer patients treated with radioimmunotherapy alone had grade 3 or 4 myelosuppression. With radioimmunotherapy and paclitaxel, both breast cancer patients developed grade 4 neutropenia. Three breast cancer patients required infusion of previously harvested peripheral blood stem cells because of neutropenic fever or bleeding. One patient in this trial developed human anti-mouse antibody in contrast to 12 of 17 patients in a prior trial using m170-radioimmunotherapy without cyclosporine.

CONCLUSIONS

111In/90Y-m170 targets prostate and breast cancer and can be combined with paclitaxel with toxicity limited to marrow suppression at the dose levels above. The maximum tolerated dose of radioimmunotherapy and fixed-dose paclitaxel with peripheral blood stem cell support has not been reached. Cyclosporine is effective in preventing human anti-mouse antibody, suggesting the feasibility of multidose, "fractionated" therapy that could enhance clinical response.

Safety and efficacy of rituximab in patients with rheumatoid arthritis refractory to disease modifying antirheumatic drugs and anti-tumor necrosis factor-alpha treatment

OBJECTIVE

To determine the safety and efficacy of rituximab treatment in patients with active seropositive rheumatoid arthritis (RA) who had experienced an inadequate response to treatment with anti-tumor necrosis factor-alpha agents and/or traditional disease modifying antirheumatic drugs.

METHODS

Rituximab was administered to 17 patients as weekly infusions for 4 consecutive weeks. Patients continued their baseline therapy and were followed for 28 weeks.

RESULTS

All patients were evaluable for safety, and 13 for efficacy. Profound B cell depletion occurred by 12 weeks and was sustained at 24 weeks, whereas T cell, complement, and immunoglobulin levels remained within normal ranges. Rituximab was well tolerated, with no infusion related reactions and only mild/moderate adverse events. American College of Rheumatology 20% response (ACR20) was achieved in 55% of patients by Week 5, 75% by Week 8, 50% at Week 16, and 67% at Week 28. Corresponding ACR50 and ACR70 responses were achieved in 36% and 18%, 25% and 17%, 42% and 25%, and 33% and 17% of patients at Weeks 5, 8, 16, and 28, respectively. There were significant improvements over baseline in tender and swollen joint counts (p < 0.0001), physician's global assessment of disease activity (p = 0.0001), and patient assessed pain (p = 0.0005) and disability (p = 0.0386). Erythrocyte sedimentation rate (p = 0.0361) and rheumatoid factor titers (p < 0.0001) also decreased significantly.

CONCLUSION

These results support the hypothesis that B cells play an important role in RA pathophysiology, and suggest that rituximab is effective and well tolerated, with a rapid onset of clinical benefit, in patients with refractory, seropositive active RA.

Increased cyclooxygenase-2 (COX-2): a potential role in the pathogenesis of lymphoma

B cell lymphomas are a diverse group of clinicopathologic diseases with an increasing incidence. As with other malignancies, the accumulation of genetic abnormalities are required for malignant transformation of human lymphocytes. Cyclooxygenase-2 (COX-2) is a key biosynthetic enzyme in prostaglandin synthesis and has been implicated in the pathogenesis of numerous malignancies including colon, breast, and lung cancer. There is little data on the potential role of COX-2 in lymphoma pathogenesis. In this study, several B lymphoma cell lines and primary B cells obtained from normal volunteer controls were examined for COX-2 protein expression. Immunoblot analysis demonstrated between an approximately 2.2-4.3-fold increase in COX-2 protein expression relative to primary B cells in all lymphoma cell lines examined. Increased COX-2 phosphorylation was found in the BJAB, BL41, and Raji cells whereas the levels in Daudi, Namalwa, and Ramos did not differ from that of primary B cells. Treatment with 25-100 microM celecoxib (CEL) resulted in decreased proliferation as measured by [3H]thymidine in all cell lines examined, and the effect was dose-dependent, and not significantly enhanced by chlorambucil (CHL). The effect of COX-2 inhibition on apoptosis in lymphoma cells was examined and revealed apoptotic induction of greater than 85% in all cell lines examined at 50 microM celecoxib. The pro-apoptotic effect was dose-dependent, and was not significantly enhanced by chlorambucil. Examination of apoptosis-related proteins by immunoblot analysis revealed levels of BCL-2, BCL-X(L), and Bax to be unaffected by celecoxib. In contrast, levels of Akt, MCL-1, and phosphorylated SAP-kinase were all decreased after incubation with 50 microM celecoxib. These findings suggest that increased COX-2 expression and activity, contributes to the pathogenesis of B cell lymphomas and point to a possible role for COX-2 inhibition in their treatment.

Applications of one-bead one-compound combinatorial libraries and chemical microarrays in signal transduction research

The "one-bead-one-compound" (OBOC) combinatorial library method synthesizes millions of random compounds such that each bead displays only one compound. Bead libraries are screened, and positive beads are isolated for structure analysis. Peptide substrates and inhibitors of protein kinases, and peptide ligands for cell surface receptors have been identified using this method. A novel encoding strategy for OBOC libraries has been developed to identify peptidomimetic and small-molecule ligands that specifically interact with cellular proteins. These ligands will be tested for their effects on cell signaling and used to construct chemical microarrays for further characterization of ligand-protein interactions.

Anti-CD22 ligand-blocking antibody HB22.7 has independent lymphomacidal properties and augments the efficacy of 90Y-DOTA-peptide-Lym-1 in lymphoma xenografts

CD22 is a membrane glycophosphoprotein found on nearly all healthy B-lymphocytes and most B-cell lymphomas. Recent in vitro studies have identified several anti-CD22 monoclonal antibodies (mAbs) that block the interaction of CD22 with its ligand. One of these mAbs, HB22.7, has been shown to effectively induce apoptosis in several B-cell lymphoma cell lines. Lymphoma xenograft studies with Raji-xenograft mice were used to assess the toxicity and efficacy of HB22.7 alone and with combined modality immunotherapy (CMIT) with yttrium (90)Y-DOTA-peptide-Lym-1 radioimmunotherapy (RIT). The effect of the sequence of these agents on the combined treatment was assessed by administering HB22.7 24 hours before, simultaneously with, or 24 hours after RIT. Within the groups treated with RIT alone or with RIT and HB22.7 (CMIT), the reduction in tumor volume was the greatest when HB22.7 was administered simultaneously with and 24 hours after RIT, and in the RIT treatment groups, this translated into the greatest overall response and survival, respectively. Overall survival rates at the end of the 84-day CMIT trial were 67% and 50% in the groups treated with HB22.7 simultaneously and 24 hours after RIT, respectively. This compared favorably with the untreated and the RIT alone groups, which had survival rates of 38% and 43% at the end of the trial. Surprisingly, when compared with untreated controls and all other treatment groups, the greatest cure and overall survival rates were observed in the group treated with HB22.7 alone, with 47% cured and 76% surviving at the end of the 84-day trial. RIT clearance was not affected by treatment with HB22.7. When compared with RIT alone, there was no significant additional hematologic (white blood cell, red blood cell, or platelet count) toxicity when HB22.7 was added to RIT. Nonhematologic toxicity (assessed as change in body weight) was also unchanged when HB22.7 was added to RIT. Thus the anti-CD22 ligand-blocking antibody HB22.7 has independent lymphomacidal properties and augments the efficacy of (90)Y-DOTA-peptide-Lym-1 in lymphoma xenografts without significant toxicity.

B lymphocytes contribute to autoimmune disease pathogenesis: current trends and clinical implications

Abnormal B lymphocytes influence the pathogenesis of many autoimmune diseases, in addition to serving as the origin of pathogenic autoantibodies. Although aberrant B cell function and autoimmunity have complex polygenic origins, recent studies in mouse models of autoimmune diseases have revealed overlapping defects in signal transduction pathways that alter B cell survival or activation, and lead to an autoimmune phenotype. Discovery of these important signaling pathways in mice has lead to an intense search for B cell abnormalities that correlate with autoimmune diseases in humans. This search has identified potential targets for therapeutic intervention that are the focus of planned and ongoing human clinical trials. This promises an arsenal of highly targeted, less toxic therapies focused on restoring normal B cell function that will eliminate pathogenic autoantibodies and replace the current use of immunosuppressive drugs.

Phosphorylation abnormalities: NZB mice exhibit a B-cell signalling defect

NZB mice demonstrate common and consistent abnormalities in B-cell activation and signalling. One of the hallmark characteristics of lupus disease is the prevalent hypergammaglobulinaemia, composed primarily of anti-nuclear antibodies. In addition to the hyperproliferation seen in mice exhibiting disease, the B cells also demonstrate a marked degree of hyperactivity in response to B-cell receptor occupancy. This points to an intrinsic defect in the signalling pathways regulating the response to an activation event. Correspondingly, B cells of NZB mice exhibit a significant lack of phosphatase activity, both at baseline and in response to stimulation. This is directly reflected by a higher level of phosphorylation of tyrosine residues. Individually, SAPK and SHIP-1, both players in the B-cell receptor signalling cascade, are also found to be abnormally phosphorylated in the NZB mouse.

Acetaminophen and diphenhydramine as premedication for platelet transfusions: a prospective randomized double-blind placebo-controlled trial

Non-hemolytic transfusion reactions (NHTR) occur in up to 30% of patients receiving platelet transfusions. Premedication with acetaminophen and diphenhydramine is a common strategy to prevent NHTR, but its efficacy has not been studied. In this prospective trial, transfusions in patients receiving pre-storage leukocyte-reduced single-donor apheresis platelets (SDP) were randomized to premedication with either acetaminophen 650 mg PO and diphenhydramine 25 mg IV, or placebo. Fifty-one patients received 98 transfusions. Thirteen patients had 15 NHTR: 15.4% (8/52) in the treatment arm and 15.2% (7/46) in the placebo arm. Premedication prior to transfusion of pre-storage leukocyte reduced SDP does not significantly lower the incidence of NHTR as compared to placebo.

Radioimmunotherapy: potential as a therapeutic strategy in non-Hodgkin's lymphoma

Lymphomas are the fifth most common malignancy in the United States and are increasing in incidence. Despite being among the most responsive malignancies to radiation and chemotherapy, the majority of patients relapse or have progressive disease. Monoclonal antibodies (MAbs) directed at cell-specific surface antigens have been useful in the diagnosis of lymphomas and, more recently, the therapeutic mouse-human chimeric MAb rituximab has demonstrated effectiveness in B cell lymphomas. Conjugating MAbs to radionuclides is a strategy for improving the efficacy of MAb lymphoma therapy by delivering radiation in close proximity to the tumour (radioimmunotherapy or RIT). In addition, the low dose rate of the delivered radiation may exert a greater antitumour activity than an equivalent dose of conventional external beam radiation. The antigenic targets for MAb therapy have included CD20, CD22, HLA-DR, and B cell idiotype. Radionuclides that have been used include iodine-131, yttrium-90, and copper-67; there are relative merits and disadvantages to each source of radiation. Clinical studies to date have focused on relapsed and refractory patients with both indolent and aggressive lymphomas, although more recent studies have included previously untreated patients with indolent lymphoma. Radioimmunoconjugate has been delivered as either single or multiple doses. Response rates have varied widely, dependent on the patient population and the response criteria. Of note, complete responses can be achieved in this typically refractory patient group. Toxicities have generally consisted of mild infusion-related nausea, fever, chills, and asthenia. Neutropenia and thrombocytopenia are the dose-limiting toxicities and have prompted the incorporation of autologous stem cell support as a means of achieving dose escalation. To date, RIT has been delivered to highly selected patients in relatively few centres with requisite equipment and specialised personnel. In addition to these requirements, cost is likely to be a barrier to widespread use. The combination of RIT with chemotherapy at conventional or high dose, or with biological agents is a fertile area for investigation. The potential of RIT in the treatment for lymphomas will be defined only by well designed comparative prospective clinical studies.

Prognostic factors and response to fludarabine therapy in patients with Waldenström macroglobulinemia: results of United States intergroup trial (Southwest Oncology Group S9003)

Current information on Waldenström macroglobulinemia (WM) is based on retrospective or single-institution studies of patients requiring therapy. Between 1992 and 1998, 231 patients with WM were enrolled in a prospective observational multicenter clinical trial. Of these, 182 patients with symptomatic or progressive disease were treated with 4 to 8 cycles of therapy with a purine nucleoside analogue, fludarabine (FAMP; 30 mg/m(2) of body-surface area daily for 5 days every 28 days). A serum beta2-microglobulin (beta2M) level below 3 mg/L and a hemoglobin level of at least 120 g/L (12 g/dL) at presentation predicted a lower likelihood of requiring therapy. The overall rate of response to FAMP therapy was 36% (95% confidence interval, 29%-44%), with 2% complete remissions. Patients who were 70 years old or older had a substantially lower likelihood of response (odds ratio, 0.34; P =.004) than younger patients. On multivariate analysis, a serum beta2M level of 3 mg/L or higher, hemoglobin level below 120 g/L, and serum IgM level below 40 g/L [4 g/dL] were significant adverse prognostic factors for survival. We developed a simple staging system for WM by using these variables and identified 4 distinct subsets of patients with estimated 5-year overall survival rates of 87%, 64%, 53%, and 22%, and 5-year progression-free survival rates of 83%, 55%, 33%, and 12%. Prognosis in WM is highly variable and serum beta2M was the dominant predictor of a need for therapy and of survival. FAMP has activity against WM. Our staging system may provide guidance for a risk-based approach to the treatment of WM.

CD22 cross-linking generates B-cell antigen receptor-independent signals that activate the JNK/SAPK signaling cascade

CD22 is a B-cell-specific adhesion molecule that modulates BCR-mediated signal transduction. Ligation of human CD22 with monoclonal antibodies (MoAbs) that block the ligand binding site triggers rapid tyrosine phosphorylation of CD22 and primary B-cell proliferation. Because extracellular signal-regulated kinases (ERKs) couple upstream signaling pathways to gene activation and are activated by B-cell antigen receptor (BCR) signaling, we examined whether CD22 ligation also activated ERKs and/or modified BCR-induced ERK activation. Ligation of CD22 on either primary B cells or B-cell lines failed to significantly activate the mitogen activated protein kinase (MAPK) ERK-2, but did activate the stress-activated protein kinases (SAPKs; c-jun NH2-terminal kinases or JNKs). In contrast, BCR ligation resulted in ERK-2 activation without significant SAPK activation. Concurrent ligation of CD22 and BCR enhanced BCR-mediated ERK-2 activation without appreciably modulating CD22-induced SAPK activation. Consistent with its induction of SAPK activity, there was a marked increase in nuclear extracts of activator protein-1 (AP-1) and c-jun levels within 2 hours of exposure of primary B cells to the CD22 MoAb. Despite their differences in ERK activation, both CD22 and BCR ligation triggered several Burkitt lymphoma cell lines to undergo apoptosis, and the 2 stimuli together induced greater cell death than either signal alone. The pro-apoptotic effects were CD22-blocking MoAb-specific and dose-dependent. Examination of expression levels of Bcl-2 protoncogene family members (Bcl-2, Bcl-x(L), Mcl-1, and Bax) showed a downregulation of Bcl-x(L) and Mcl-1 after CD22 ligation. This study provides a plausible mechanism to explain how CD22 and BCR signaling can costimulate B-cell proliferation and induce apoptosis in Burkitt lymphoma cell lines.

GCKR links the Bcr-Abl oncogene and Ras to the stress-activated protein kinase pathway

The Bcr-Abl oncogene, found in Philadelphia chromosome-positive myelogenous leukemia (CML), activates Ras and triggers the stress-activated protein kinase (SAPK or Jun NH2-terminal kinase [JNK]) pathway. Interruption of Ras or SAPK activation dramatically reduces Bcr-Abl-mediated transformation. Here, we report that Bcr-Abl through a Ras-dependent pathway signals the serine/threonine protein kinase GCKR (Germinal Center Kinase Related) leading to SAPK activation. Either an oncogenic form of Ras or Bcr-Abl enhances GCKR catalytic activity and its activation of SAPK, whereas inhibition of GCKR impairs Bcr-Abl-induced SAPK activation. Bcr-Abl mutants that are impaired for GCKR activation are also unable to activate SAPK. Consistent with GCKR being a functional target in CML, GCKR is constitutively active in CML cell lines and found in association with Bcr-Abl. Our results indicate that GCKR is a downstream target of Bcr-Abl and strongly implicate GCKR as a mediator of Bcr-Abl in its transformation of cells.

CD22 negatively and positively regulates signal transduction through the B lymphocyte antigen receptor

The CD22 cell-surface adhesion molecule is capable of modulating B lymphocyte antigen receptor (BCR)-mediated signals, as well as the generation of BCR-independent signals. Within the cytoplasmic domain of CD22 are motifs that are structurally homologous to known activation and inhibitory motifs. These motifs demonstrate physiologic significance via associations with known effector proteins that likely mediate their corresponding inhibitory and activation roles. Furthermore, the targeted deletion of CD22 in mice results in phenotypic changes and alterations in BCR-mediated signal transduction that are consistent with both positive and negative roles for CD22 in B cell development and activation.

Tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) in B-lymphocyte function

Two cytokines important in the regulation of B-cell function are tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). They act at different steps in B-cell differentiation and can be produced by the B cells themselves upon appropriate stimulation. Crosslinking of surface Ig and signaling through CD22 or CD40 lead to increased secretion of both cytokines. Neutralization of TNF-alpha or IL-6 biologic activity in B-cell cultures results in a significant reduction in B-cell proliferation and Ig secretion. Increased production of these cytokines is found in several diseases associated with aberrant B-cell function. This review will focus on the role of TNF-alpha and IL-6 in normal and pathophysiological conditions of B-cell function.

Bcl-x rather than Bcl-2 mediates CD40-dependent centrocyte survival in the germinal center

Both rapid B-cell proliferation and programmed cell death (PCD) occur during the differentiation and selection of B cells within the germinal center. To help elucidate the role of Bcl-x in B-cell antigen selection and PCD within the germinal center, we examined its expression in defined B-cell populations and by immunochemistry of tonsil tissue. Purified B-cell fractions enriched for centrocytes express high amounts of Bcl-x and relatively low amounts of Bcl-2, whereas fractions enriched for centroblasts lack significant levels of both proteins. Consistent with this observation, immunocytochemistry localized Bcl-x within cells scattered throughout the germinal center. Stimulation of tonsil B cells with either CD40 or Staphylococcus aureus Cowan increase bcl-x mRNA and protein levels. Treatment of a cell line with a germinal center phenotype (RAMOS) or the tonsillar B-cell centroblast fraction with CD40 rapidly increased Bcl-x levels and partially rescued B cells from PCD. These data suggest that Bcl-x rather than Bcl-2 may rescue centrocytes during selection in the germinal center.

Involvement of p72syk kinase, p53/56lyn kinase and phosphatidyl inositol-3 kinase in signal transduction via the human B lymphocyte antigen CD22

CD22 is a B lymphocyte-specific membrane protein that functions as an adhesion molecule via its interactions with a subset of alpha 2-6-linked sialic acid-containing glycoproteins. Engagement of CD22 with a monoclonal antibody (HB22.23) that blocks the binding of CD22 to its ligands results in rapid CD22 tyrosine phosphorylation and in increased association of CD22 with p53/56lyn kinase, p85 phosphatidyl inositol-3 kinase, and p72syk kinase. Synthetic peptides that span various regions of the intracellular portion of CD22 were used to map potential kinase binding sites. All three kinases associated with a tyrosine-phosphorylated peptide that spans tyrosine amino acid residues 822 and 842, implicating this as an important region in mediating CD22 signal transduction. In addition, purified p56lyn directly bound to the same peptide. Engagement of CD22 with HB22.23 was sufficient to stimulate normal B cell proliferation. This study further substantiates the importance of CD22 as a B lymphocyte signaling molecule and begins to unravel the mechanisms by which CD22 cross-linking can alter B cell function.

A novel human homeobox gene distantly related to proboscipedia is expressed in lymphoid and pancreatic tissues

A novel human homeobox gene, HB9, was isolated from a cDNA library prepared from in vitro stimulated human tonsil B lymphocytes and from a human genomic library. The HB9 gene is composed of 3 exons spread over 6 kilobases of DNA. An open reading frame of 1206 nucleotides is in frame with a diverged homeodomain. The predicted HB9 protein has a molecular mass of 41 kilodaltons and is enriched for alanine, glycine, and leucine. The HB9 homeodomain is most similar to that of the Drosophila melanogaster homeobox gene proboscipedia. Northern blot analysis of poly(A) RNA purified from the human B cell line RPMI 8226 and from activated T cells revealed a major mRNA transcript of 2.2 kilobases. Similar analysis of poly(A) RNA from a variety of adult tissues demonstrated HB9 transcripts in pancreas, small intestine, and colon. Reverse transcriptase-polymerase chain reaction was used to examine HB9 RNA transcripts in hematopoietic cell lines. HB9 RNA transcripts were most prevalent in several human B cell lines and K562 cells. In addition, transcripts were detected in RNA prepared from tonsil B cells and in situ hybridization studies localized them in the germinal center region of adult tonsil. These findings suggest the involvement of HB9 in regulating gene transcription in lymphoid and pancreatic tissues.

Increased expression of the glucose-regulated gene encoding the Mr 78,000 glucose-regulated protein in chemically and radiation-transformed C3H 10T1/2 mouse embryo cells

Expression of the gene coding for the Mr 78,000 glucose-regulated protein (GRP78) was examined in nontransformed and chemically and radiation-transformed C3H 10T1/2 Cl 8 mouse embryo cells. When cells were grown in complete medium with 10% fetal bovine serum, GRP78 mRNA was increased 4- to 9-fold in 3-methylcholanthrene (MCA; Clones 15 and 16)-, bleomycin (Bleo 1)-, and ultraviolet light (UV-C3)-transformed cell lines compared to nontransformed 10T1/2 clone 8 cells (Cl 8) at similar cell number and growth phase. Increased steady-state levels of GRP78 protein in MCA Cl 15 compared to Cl 8 cells were confirmed by 2-dimensional gel electrophoresis. Under these conditions transformed MCA Cl 15 exhibited increased GRP78 RNA within 24 h after addition of fresh glucose-containing medium, whereas nontransformed Cl 8 cells did not increase expression of this gene even after 5 days of culture in conditioned medium. Incubation of Cl 8 and MCA Cl 15 in glucose-free medium for 16 h caused a 3- and 15-fold induction of GRP78 RNA, respectively. In addition, chemically transformed cells were highly sensitive to glucose deprivation and responded by rounding up and detaching from the substratum. Cl 8 cells exhibited no such sensitivity to glucose deprivation. These results extend earlier reports on virally transformed cells to include chemically and radiation-transformed cells and expand earlier reports to include mRNA expression and 2-dimensional gel electrophoresis of GRP78 protein.