T cell-dependent survival of CD20+ and CD20- plasma cells in human secondary lymphoid tissue

The signals mediating human plasma cell survival in vivo, particularly within secondary lymphoid tissue, are unclear. Human tonsils grafted into immunodeficient mice were therefore used to delineate the mechanisms promoting the survival of plasma cells. Tonsillar plasma cells were maintained within the grafts and the majority were nonproliferating, indicating a long-lived phenotype. A significant depletion of graft plasma cells was observed after anti-CD20 treatment, consistent with the expression of CD20 by most of the cells. Moreover, anti-CD52 treatment caused the complete loss of all graft lymphocytes, including plasma cells. Unexpectedly, anti-CD3, but not anti-CD154, treatment caused the complete loss of plasma cells, indicating an essential role for T cells, but not CD40-CD154 interactions in plasma cell survival. The in vitro coculture of purified tonsillar plasma cells and T cells revealed a T-cell survival signal requiring cell contact. Furthermore, immunofluorescence studies detected a close association between human plasma cells and T cells in vivo. These data reveal that human tonsil contains long-lived plasma cells, the majority of which express CD20 and can be deleted with anti-CD20 therapy. In addition, an important role for contact-dependent interactions with T cells in human plasma cell survival within secondary lymphoid tissue was identified.     

Re-occurrence of the CD20 molecule expression subsequent to CD20-negative relapse in diffuse large B-cell lymphoma

We report the first case of diffuse large B-cell lymphoma (DLBCL) of the stomach displaying CD20-negative relapse after rituximab-containing treatment and the re-appearance of CD20 expression at the second failure. The loss of CD20 expression in B-cell lymphomas relapsing after rituximab is a well-known phenomenon, but its actual impact in DLBCL is difficult to estimate. This paradigmatic case suggests that CD20-expression reappearance after purging of CD20-positive clones with rituximab might be an underestimated occurrence in B-cell lymphomas. Accordingly, every relapse, whenever possible, should be histologically assessed with diagnostic and immunophenotyping purposes.     

Aberrant CD20 expression in angioimmunoblastic T-cell lymphoma

We report on a 60-year-old man, having angioimmunoblastic T-cell lymphoma (AITL) with aberrant expression of CD20. The initial biopsy specimen showed features of AITL with the typical CD3(+)CD20(-) immunophenotype. As the disease progressed, biopsy specimens of the recurrent lesions showed unusual results for AITL with the CD20(+) immunophenotype in both flow cytometry and immunohistochemistry analysis. Double immunostaining confirmed that the lymphoma cells were simultaneously positive for CD3 and CD20. The disease became resistant to combined chemotherapies and the patient died 3 years after the initial diagnosis. Autopsy revealed a composite of AITL and EBV-positive diffuse large B-cell lymphoma. Although it is unknown whether the instability of the CD20 antigen expression is correlated with the behaviour of AITL, the administration of rituximab should be considered as an alternative therapeutic option in such cases.     

CD20 and CD40 mediated mitogenic responses in B-lineage acute lymphoblastic leukaemia

Activation of CD20, a cross-membrane ion channel, induces cell cycle progression from G₀ to G₁ in B lymphocytes. Subsequent activation of CD40, a membrane receptor of the nerve growth factor receptor superfamily, transits the B cells to the S phase. CD40 may also act synergistically in combination with IL-4 (B lymphocytes) or IL-3/IL-7 (B-cell precursors). We investigated the proliferative responses of B-lineage acute lymphoblastic leukaemia (ALL) cells to CD20/CD40 activation. In 18/56 ALL cases, CD20 activation resulted in significant increases in DNA synthesis. Similar, although more moderate, effects were seen of activation of CD40 in 10/44 cases. Responses to CD20 or CD40 activation were independent of co-stimulation with IL-3, IL-4 or IL-7, and various cocktails of the different growth stimuli did not act synergistically.     

CD20-negative pyothorax-associated B cell lymphoma

We describe an 86-year-old male who developed CD20-negative pyothorax-associated B cell lymphoma 64 years after he had suffered from tuberculous pleuritis. Therapy with 8 courses of THP-COP at 2-week intervals was followed by involved-field radiotherapy of 30 Gy. Uncertain complete remission was achieved. Thereafter, local recurrence of pyothorax-associated lymphoma (PAL) at the primary site was seen. The patient received salvage radiotherapy of 50 Gy. The patient died of pneumonia during a second uncertain complete remission. The progression-free survival and overall survival of this patient were 10 and 15 months, respectively. When compared with the median survival of 9 months reported in the literature, the adverse effect of CD20 negativity on prognosis may not apply to PAL patients with an occasional aberrant phenotype.     

CD20-positive T-cell chronic lymphocytic leukaemia

Although CD20 is considered to be a representative marker for B lymphocytes, the antigen is weakly expressed on a small subset of normal T lymphocytes. A 60-year-old man developed pancytopenia and hepatosplenomegaly due to clonal proliferation of atypical lymphocytes that were weakly positive for CD20. The leukaemic cells were also positive for T-cell antigens such as CD2, CD3, CD5, CD7, CD8 and T-cell receptor (TCR) Vβ8 and for activation antigens such as CD38 and HLA-DR, but were negative for CD19, CD21, CD22, CD25. Southern blot analysis revealed rearrangement of the TCR-β gene and a germline configuration of the immunoglobulin heavy chain gene. This is the first report of a case of clonal expansion of CD20dim Tlymphocytes     

CD20-positive adult T-cell leukemia.

A 67-year-old woman was admitted to our hospital because of lymphadenopathy and lymphocytosis. Monoclonal integration of HTLV-I provirus DNA was detected, and a diagnosis of adult T-cell leukemia (ATL) was made. Flow cytometry revealed that the ATL cells expressed CD20 as well as T-cell-associated antigens, and expression of CD20 mRNA was also demonstrated. A novel T-cell subpopulation expressing CD20 molecules has recently been identified. This is the first report of CD20-positive ATL, suggesting that HTLV-I can infect and transform CD20-positive T cells.     

Circulating CD20 and CD52 in patients with non-Hodgkin's lymphoma or Hodgkin's disease

The cell surface proteins CD20 and CD52 differ significantly in their structures and are expressed on the majority of B cells. Both circulating CD20 (cCD20) and circulating CD52 (cCD52) have been recently documented in patients with chronic lymphocytic leukaemia. A retrospective study to establish whether cCD20 and/or cCD52 were detectable in patients with lymphoma, and the clinical associations of these soluble antigens if detected, was conducted. cCD20 and cCD52 levels were analysed in a cohort of 65 patients with non-Hodgkin's lymphoma (NHL) and 37 with Hodgkin's disease (HD). Patients with NHL had elevated pretherapy levels of cCD20 and cCD52 compared with normal individuals. Patients with HD had significantly lower than normal pretherapy levels of both cCD20 and cCD52. cCD20 levels were marginally elevated post-therapy in NHL patients while in patients with HD, cCD20 levels remained significantly lower than normal after therapy. Serum cCD52 levels became significantly lower than normal post-therapy in NHL patients, and remained significantly lower than normal in HD patients. No predictive effects were found for pretherapy or post-therapy levels of cCD52 on survival for either cohort of patients. Post-therapy cCD20 levels independently highly correlated with survival in patients with NHL. Prospective evaluation will be required to establish if cCD20 and cCD52 may be used as biomarkers in the diagnosis, prognostic categorization, and monitoring of the clinical course in patients with lymphoma. The clinical significance of circulating antigen in patients receiving monoclonal antibody therapy directed against CD20 and/or CD52 warrants study.     

New insights in Type I and II CD20 antibody mechanisms‐of‐action with a panel of novel CD20 antibodies

Based on their mechanisms‐of‐action, CD20 monoclonal antibodies (mAbs) are grouped into Type I [complement‐dependent cytotoxicity (CDC) and antibody‐dependent cell‐mediated cytotoxicity (ADCC)] and Type II [programmed cell death (PCD) and ADCC] mAbs. We generated 17 new hybridomas producing CD20 mAbs of different isotypes and determined unique heavy and light chain sequence pairs for 13 of them. We studied their epitope binding, binding kinetics and structural properties and investigated their predictive value for effector functions, i.e. PCD, CDC and ADCC. Peptide mapping and CD20 mutant screens revealed that 10 out of these 11 new mAbs have an overlapping epitope with the prototypic Type I mAb rituximab, albeit that distinct amino acids of the CD20 molecule contributed differently. Binding kinetics did not correlate with the striking differences in CDC activity among the mIgG2c mAbs. Interestingly, chimerization of mAb m1 resulted in a mAb displaying both Type I and II characteristics. PCD induction was lost upon introduction of a mutation in the framework of the heavy chain affecting the elbow angle, supporting that structural changes within this region can affect functional activities of CD20 mAbs. Together, these new CD20 mAbs provide further insights in the properties dictating the functional efficacy of CD20 mAbs.     

Loss of CD20 expression in relapsed lymphomas after rituximab therapy

The response rate at relapse to rituximab in prior responders B-cell non-Hodgkin's lymphoma (NHL) patients is below 50%. Loss of CD20 expression after rituximab therapy may explain this secondary resistance. However, the frequency of CD20 negative relapses cannot be assessed since most patients that relapsed after rituximab therapy have not been re-biopsied. Here, we present two patients with CD20 positive low grade B-cell NHL that lost the cell surface and cytoplasmic expression at relapse after rituximab therapy. Our findings suggest that confirmation of CD20 expression on the malignant B cells is required whenever rituximab therapy is considered.     

Expression of CD20 in B Cell Precursor Acute Lymphoblastic Leukemia

CD20 is a B cell differentiation antigen with variable expression in B cell precursor acute lymphoblastic leukemia (BCP-ALL). The significance of CD20 expression has been evaluated in BCP-ALL with conflicting results. There is paucity of data regarding CD 20 expression in BCP-ALL in Indian patients. We retrospectively analyzed 100 patients of BCP-ALL for CD20 expression. CD20 positivity was defined as expression of CD20 to be more than or equal to 20 % in the blast population. 62 % patients expressed CD20 while 38 % patients were negative for CD20. The positivity ranged from negative to dim (35.5 % patients), moderately bright (19.3 % patients) to bright (45.2 % patients). Additional prospective studies are needed to determine the optimal use of rituximab in treatment of CD20-positive BCP-ALL.     

Expression of CD20 on acute lymphoblastic leukemia cells in children

CD20 determinant expressed on B precursors is associated with regulation of proliferation, apoptosis and maturation of these cells. The acute lymphoblastic leukemia "common" type (cALL) based on expression of CD20 is subdivided in type I and II. However, the clinical significance of CD20 expression on cALL and significance of cALL type I and II discernment are not fully elucidated. The association of CD20 expression with the expression of multidrug resistance molecule (MDR), CD34, atypical immunophenotypes of leukemia cells and response to induction therapy were determined in the group of 147 patients with acute lymphoblastic leukemia (ALL) B progenitor type (ALL-proB -14 patients) and common type (cALL-133 patients). The expression of CD20 on leukemia cells was studied routinely at diagnosis before the therapy. This expression was noted on leukemia cells of 6 ALL-proB patients (42.8%) and 66 cALL patients (49.6%). The expression of CD20 showed no association with the expression of CD34, CD22 and MDR. The reverse association was observed between CD20 expression and the presence of co-expression of myeloid (CD13, CD33, CD65, CD15) and T lymphoid determinants (CD2, CD5, CD7) on leukemia cells. The effect of induction therapy analyzed as time of blast cells cytoreduction in peripheral blood and time of reaching the complete remission showed the slower clearance of peripheral blood from blast cells associated with expression of CD20. There was no association of CD20 expression with the time of reaching the hematological remission. The above results suggested a "protective" role of CD20 against co-expression of other determinants (myeloid and lymphoid) and no association with the results of induction therapy.