CD22 ligation inhibits downstream B cell receptor signaling and Ca(2+) flux upon activation.

OBJECTIVE: CD22 is a surface molecule exclusively expressed on B cells that regulates adhesion and B cell receptor (BCR) signaling as an inhibitory coreceptor of the BCR. Central downstream signaling molecules that are activated upon BCR engagement include spleen tyrosine kinase (Syk) and, subsequently, phospholipase Cγ2 (PLCγ2), which results in calcium (Ca(2+)) mobilization. The humanized anti-CD22 monoclonal antibody epratuzumab is currently being tested in clinical trials. This study was undertaken to determine the potential mechanism by which this drug regulates B cell activation. METHODS: Purified B cells were preincubated with epratuzumab, and the colocalization of CD22 and CD79α, without BCR engagement, was assessed by confocal microscopy. The phosphorylation of Syk (Y348, Y352) and PLCγ2 (Y759) as well as the Ca(2+) flux in the cells were analyzed by flow cytometry upon stimulation of the BCR and/or Toll-like receptor 9 (TLR-9). The influence of CD22 ligation on BCR signaling was assessed by pretreating the cells with epratuzumab or F(ab')(2) fragment of epratuzumab, in comparison with control cells (medium alone or isotype-matched IgG1). RESULTS: Epratuzumab induced colocalization of CD22 and components of the BCR independent of BCR engagement, and also reduced intracellular Ca(2+) mobilization and diminished the phosphorylation of Syk and PLCγ2 after BCR stimulation in vitro. Inhibition of kinase phosphorylation was demonstrated in both CD27- and CD27+ B cells, and this appeared to be independent of Fc receptor signaling. Preactivation of the cells via the stimulation of TLR-9 did not circumvent the inhibitory effect of epratuzumab on BCR signaling. CONCLUSION: These findings are consistent with the concept of targeting CD22 to raise the threshold of BCR activation, which could offer therapeutic benefit in patients with autoimmune diseases.

[Photodynamic therapy of bladder cancer. A new option]. / Die photodynamische Therapie des Harnblasenkarzinoms. Eine neue Option.

BACKGROUND: Bladder cancer (BCa) is the third most common tumor in Germany. Currently, resection therapy for superficial BCa (Ta, CIS) includes photodynamic diagnostics (PDD) using HEXVIX® for improved assessment of tumor spread. Trials using these photosensitizers for photodynamic therapy (PDT) showed only limited success. Especially low tissue penetration due to short-wave excitation was a limiting factor. METHODS: This study which was funded by the German Research Foundation (DFG) examined the feasibility of the novel photosensitizer tetrahydroporphyrin-tetratosylate (THPTS) for PDT in a rat bladder cancer model. RESULTS: As THPTS is very effectively excitable at a near infrared wavelength of 760 nm it is within the so-called phototherapeutic window and allows tissue penetration of up to 15 mm. Thus THPTS can also be used for PDT of larger, solid tumors as was previously demonstrated for other tumor entities. Therefore, effective treatment of even muscle-invasive bladder cancer (≥T2) may become an option using THPTS. In this current study the effectiveness and safety of THPTS-PDT was examined in an orthotopic bladder cancer rat model.