Expression of wild-type p53 and Bcl-2 family genes oscillates with recurrent remission and relapse in an unusual case of low-grade lymphoma.

Downregulation of apoptosis has been proposed as a mechanism of clonal expansion in low-grade B cell neoplasms. We have previously described an unusual case of CD5+ B cell lymphoma characterized by cycles of leukemic phase alternating with spontaneous remission. In the present study, we examined the involvement of apoptosis-related proteins in the progression of this cyclic lymphoma ex vivo. During the leukemic phases, the clonal cells were activated blasts expressing elevated levels of wild-type (wt) p53, Bcl-2, Bcl-x(L), and Bax, while Bak expression increased during the decline of lymphocytosis. Bax heterodimerized with Bcl-2 but not with Bcl-x(L). The anti-apoptotic Bcl-2/Bax heterodimers peaked during early leukemic phases and declined during regression. The elevation in Bcl-2, Bcl-x(L) and Bax expression during early leukemic phases seems to result from cell activation since a similar increase was induced by activating the remission phase leukemic cells in culture. The data suggest that wt p53, Bcl-x(L), and Bcl-2/Bax heterodimers support the accumulation of activated leukemic cells during the leukemic phases, while Bax and Bak may be involved in their decline during regression.

Neoplastic cell activation and proliferative response to CD40-ligand characterize recurrent leukemic bouts in an unusual case of low grade lymphoma.

Spontaneous fluctuations in activity of low-grade B cell lymphomas are common but not understood. An explanation may be offered by studying an atypical SLL/CLL case characterized by recurrent cycles of leukemic phase alternating with spontaneous remission (1). During remissions, residual IgMkappa+ leukemic cells exhibited resting phenotype, low proliferative response to CD4O-ligand and delayed apoptosis. In contrast, the acute phase counterparts were phenotypically activated, underwent rapid apoptosis in culture and proliferated extensively in response to membrane-anchored CD40-ligand. Transient bursts of serum TNFalpha and IL-10 preceded the acute phases, which were characterized by the co-existence of CD40-ligand+ T lymphocytes and lymphoma cells in the bone marrow. Based on ex-vivo and in-vitro data, we suggest that changes in the lymphoma milieu affect the neoplastic cell activation status, rate of proliferation in response to activated T cells and rate of apoptosis. These responses may underlie both the induction and spontaneous regression of the acute phases in this unique lymphoma. Our findings raise the possibility that part of this mechanism may have evolved during transformation of indolent common CLL to its more aggressive form.

A photodynamic pathway to apoptosis and necrosis induced by dimethyl tetrahydroxyhelianthrone and hypericin in leukaemic cells: possible relevance to photodynamic therapy.

The mechanism of cell death induction by dimethyl tetrahydroxyhelianthrone (DTHe), a new second-generation photodynamic sensitizer, is analysed in human leukaemic cell lines in comparison with the structurally related hypericin. DTHe has a broad range of light spectrum absorption that enables effective utilization of polychromatic light. Photosensitization of HL-60 cells with low doses of DTHe (0.65 microM DTHe and 7.2 J cm(-2) light energy) induced rapid apoptosis of > or =90% of the cells. At doses > or =2 microM, dying cells assumed morphological necrosis with perinucleolar condensation of chromatin in HL-60 and K-562 cell lines. Although nuclear fragmentation that is characteristic to apoptosis was prevented, DNA digestion to oligonucleosomes proceeded unhindered. Such incomplete apoptosis was more prevalent with the related analogue hypericin throughout most doses of photosensitization. Despite hypericin being a stronger photosensitizer, DTHe exhibited advantageous phototoxic properties to tumour cells, initiating apoptosis at concentrations about threefold lower than hypericin. Photosensitization of the cells induced dissociation of the nuclear envelope, releasing lamins into the cytosol. DTHe also differed from hypericin in effects exerted on the nuclear lamina, causing release of an 86-kDa lamin protein into the cytosol that was unique to DTHe. Within the nucleus, nuclear envelope lamin B underwent covalent polymerization, which did not affect apoptotic nuclear fragmentation at low doses of DTHe. At higher doses, polymerization may have been extensive enough to prevent nuclear collapse. Hut-78, CD4+ cells were resistant to the photodynamically activated apoptotic pathway. Beyond the tolerated levels of photodynamic damage, these cells died exclusively via necrosis. Hut-78 cells overexpress Bcl-X(L) as well as a truncated Bcl-X(L)tr isoform that could contribute to the observed resistance to apoptosis.